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United States Environmental Protection Agency Environmental Criteria and Assessment Office Research Triangle Park, NC 27711 EPA-600/8-83/028cF June 1986 Research and Development Air Quality Criteria for Lead FINAL DRAFT Volume III of IV E P A -6 0 0 /8 -8 3 /0 2 8 c F A ir Quality Criteria fo r Lead; Volume ill of IV DU P05 0452424 EPA-600/8-83/028cF June 1986 Air Quality Criteria for Lead Volume III of IV U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Research and Development Office of Health and Environmental Assessment Environmental Criteria and Assessment Office Research Triangle Park, NC 27711 TEH 0411827 DUP050452425 DISCLAIMER This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial, products does not constitute endorsement or recommendation. ! 1 :) I :I t TEH 0411828 j DUP050452426 ABSTRACT The document evaluates and assesses scientific information on the health and welfare effects associated with exposure to various concentrations of lead in ambient air. The literature through 1985 has been reviewed thoroughly for information relevant to air quality criteria, although the document is not intended as a complete and detailed review of all literature pertaining to lead. An attempt has been made to identify the major discrepancies in our current knowledge and understanding of the effects of these pollutants. Although this document is principally concerned with the health and welfare effects of lead, other scientific data are presented and evaluated in order to provide a better understanding of this pollutant in the environment. To this end, the document includes chapters that discuss the chemistry and physics of the pollutant; analytical techniques; sources, and types of emissions; environmental concentrations and . exposure levels; atmospheric chemistry and dispersion modeling; effects on vegetation; and respiratory, physiological, toxicological, clinical, and epidemiological aspects of human exposure. i ii TEH 0411829 DUP050452427 CONTENTS Ms VOLUME I Chapter 1. Executive Summary and Conclusions .......................................................................... VOLUME II Chapter 2. Chapter 3. Chapter 4. Chapter 5. Chapter 6. Chapter 7. Chapter 8. Introduction .................................................................................................................. Chemical and Physical Properties ................ Sampling and Analytical Methods for Environmental Lead ............................... Sources and Emissions ................................................................................................. Transport and Transformation...................................... ........................... ................ Environmental Concentrations and Potential Pathways toHumanExposure .. Effects of Lead on Ecosystems ................................................................................. VOLUME III Chapter 9. Chapter 10. Chapter 11. Quantitative Evaluation of Lead and Biochemical Indices of Lead Exposure in Physiological Media ............................................................................ Metabolism of Lead..................................... Assessment of Lead Exposures and Absorption in Human Populations............. Volume IV Chapter 12. Biological Effects of Lead Exposure ..................................................................... Chapter 13. Evaluation of Human Health Risk Associated with Exposure toLead and Its Compounds ...................................................................................................... 1-1 2-1 3-1 4-1 5-1 6-1 7-1 8-1 9-1 10-1 11-1 12-1 13-1 $ $I < > ft ` * iv TEH 0411830 DUP050452428 TABLE OF CONTENTS 9. QUANTITATIVE EVALUATION OF LEAD AND BIOCHEMICAL INDICES OF LEAD EXPOSURE IN PHYSIOLOGICAL MEDIA ............................................................................................................... 9.1 INTRODUCTION ......................................................................................................................... 9.2 DETERMINATIONSOF LEAD IN BIOLOGICAL MEDIA................................................................. 9.2.1 Sampling and Sample Handling Procedures for Lead in Biological Media .............................................................................................. 9.2.1.1 Blood Sampling ...................................................................................... 9.2.1.2 Urine Sampling ...................................................................................... 9.2.1.3 Hair Sampling ........................................................................................ 9.2.1.4 Mineralized Tissue ................................................................................ 9.2.1.5 Sample Handling in the Laboratory ................................................. 9.2.2 Methods of Lead Analysis .................................................................................. 9.2.2.1 Lead Analysis in Whole Blood .......................................................... 9.2.2.2 Lead in Plasma ..................... 9.2.2.3 Lead in Teeth....................................... 9.2.2.4 Lead in Hair........................................................................................ 9.2.2.5 Lead in Urine ........................................................................................ 9.2.2.6 Lead in OtherTissues ......................................................................... 9.2.3 Quality Assurance Procedures in Lead Analysis ........................................... 9.3 DETERMINATION OF ERYTHROCYTE PORPHYRIN (FREE ERYTHROCYTE PROTOPORPHYRIN, ZINC PROTOPORPHYRIN) ...... .................................................................... 9.3.1 Methods of Erythrocyte Porphyrin Analysis ................................................... 9.3.2 Interlaboratory Testing of Accuracy and Precision in EP Measurement........................................................................................................ 9.4 MEASUREMENT OF URINARY COPROPORPHYRIN .................................................... 9.5 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID DEHYDRASE ACTIVITY .............................. 9.6 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID INURINE AND OTHER MEDIA .................... 9.7 MEASUREMENT OF PYRIMIDINE-5'-NUCLEOTIDASE ACTIVITY ............................................... 9.8 MEASUREMENT OF PLASMA 1,25-DIHYDROXYVITAMIN D ...................................................... 9.9 SUMMARY................................................................................................................................... 9.9.1 Determinations of Lead in Biological Media ................................................. 9.9.2 Determination of Erythrocyte Porphyrin (Free Erythrocyte Protoporphyrin, Zinc Protoporphyrin) ........................................................ 9.9.3 Measurement of Urinary Coproporphyrin ........................................................... 9.9.4 Measurement of Delta-Aminolevulinic Acid DehydraseActivity .................. 9.9.5 Measurement of Delta-Aminolevulinic Acid in Urine andOther Media ... 9.9.6 Measurement of Pyrimidine-5'-Nucleotidase Activity .............................. 9.9.7 Measurement of Plasma 1,25-Dihydroxyvitamin D ........................................... 9.10 REFERENCES............................................................................................................................. 10. METABOLISM OF LEAD ....................................................................................................................... 10.1 INTRODUCTION............................... ........................................................................................ 10.2 LEAD ABSORPTION IN HUMANS AND ANIMALS ........................................................................ 10.2.1 Respiratory Absorption of Lead ...................................................................... 10.2.1.1 Human Studies .................................................................................... 10.2.1.2 Animal Studies .................................................................................. 10.2.2 Gastrointestinal Absorption of Lead ............................................................. 10.2.2.1 Human Studies ............................................... .................................... 10.2.2.2 Animal Studies ....................... 10.2.3 Percutaneous Absorption of Lead .................................................................... 10.2.4 Transplacental Transfer of Lead .................................................................... v Page 9-1 9-1 9-2 9-2 9-3 9-4 9-4 9-5 9-5 9-6 9-7 9-11 9-12 9-13 9-14 9-15 9-16 9-20 9-20 9-23 9-25 9-25 9-27 9-29 9-30 9-31 9-32 9-35 9-36 9-36 9-37 9-38 9-38 9-39 10-1 10-1 10-1 10-1 10-2 10-6 10-6 10-6 10-10 10-13 10-14 TEH 0411831 DUP050452429 TABLE OF CONTENTS (continued). 10.3 DISTRIBUTION OF LEAD IN HUMANS AND ANIMALS ............................................................... 10.3.1 Lead in Blood ........................................................................................................ 10.3.2 Lead Levels in Tissues ...................................................................................... 10.3.2.1 Soft Tissues ...................................................................................... 10.3.2.2 Mineralizing Tissue ........................................................................ 10.3.3 Chelatable Lead .................................................................................................... 10.3.4 Mathematical Descriptions of Physiological Lead Kinetics .................... 10.3.5 Animal Studies ...................................................................................................... 10.4 LEAD EXCRETION AND RETENTION IN HUMANS AND ANIMALS............................................... 10.4.1 Human Studies ........................................................................................................ 10.4.2 Animal Studies ........................... 10.5 INTERACTIONS OF LEAD WITH ESSENTIAL METALS AND OTHER FACTORS ........................... 10.5.1 Human Studies ............................................................ 10.5.2 Animal Studies ..................... 10.5.2.1 Interactions of Lead with Calcium......................................... ... 10.5.2.2 Interactions of Lead with Iron ................................................... 10.5.2.3 Lead Interactions with Phosphate ............................................... 10.5.2.4 Interactions of Lead with Vitamin D ......................................... 10.5.2.5 Interactions of Lead with Lipids ................................. ............. 10.5.2.6 Lead Interaction with Protein ..................................................... 10.5.2.7 Interactions of Lead with Milk Components .............................. 10.5.2.8 Lead Interactions with Zinc and Copper ................................... 10.6 INTERRELATIONSHIPS'OF LEAD EXPOSURE, EXPOSURE INDICATORS, AND TISSUE LEAD BURDENS................................................................................... 10.6.1 Temporal Characteristics of Internal Indicators of Lead Exposure .................................... 10.6.2 Biological Aspects of External Exposure/Internal Indicator Relationships .................................................................................... 10.6.3 Internal Indicator/Tissue Lead Relationships ........................................... 10.7 METABOLISM OF LEAD ALKYLS ................................................................................................ 10.7.1 Absorption of Lead Alkyls in Humans and Animals ..................................... 10.7.1.1 Gastrointestinal Absorption....................... 10.7.1.2 Percutaneous Absorption of Lead Alkyls .................................... 10.7.2 Biotransformation and Tissue Distribution of Lead Alkyls .................... 10.7.3 Excretion of Lead Alkyls .................................................................................. 10.8 SUMMARY ................................................................................................................................... 10.8.1 Lead Absorption in Humans and Animals ...................................................... 10.8.1.1 Respiratory Absorption of Lead ................................................... 10.8.1.2 Gastrointestinal Absorption of Lead .......................................... 10.8.1.3 Percutaneous Absorption of Lead ................................................. 10.8.1.4 Transplacental Transfer of Lead ................................................. 10.8.2 Distribution of Lead in Humans and Animals ............................................... 10.8.2.1 Lead in Blood.................................................................................... 10.8.2.2 Lead Levels in Tissues ................................................................... 10.8.2.2.1 Soft Tissues ............................................................... 10.8.2.2.2 Mineralizing Tissue ................................................. 10.8.2.2.3 Chelatable Lead ................................... 10.8.2.2.4 Animal Studies ........................................................... 10.8.3 Lead Excretion and Retention in Humans and Animals ................................ 10.8.3.1 Human Studies ................................................................................... Page 10-14 10-15 10-19 10-20 10-23 10-24 10-26 10-31 10-32 10-32 10-38 10-41 10-41 10-44 10-44 10-48 10-48 10-49 10-49 10-50 10-50 10-50 10-51 10-52 10-53 10-54 10-57 10-57 10-57 10-58 10-58 10-59 10-60 10-60 10-60 10-61 10-62 10-62 10-62 10-62 10-53 10-63. 10-64 10-65 10-65 10-66 10-66 . 1 DUP050452430 TABLE OF CONTENTS (continued). 10.8.3.2 Animal Studies .......... 10.8.4 Interactions of Lead with Essential Metals and Other Factors ............ 10.8.4.1 Human Studies .................................................................................... 10.8.4.2 Animal Studies ........................................................ 10.8.5 Interrelationships of Lead Exposure with Exposure Indicators and Tissue LeadBurdens .................................................................................. . 10.8.5.1 Temporal Characteristics of Internal Indicators of Lead Exposure...... .......................................................................... 10.8.5.2 Biological Aspects of External Exposure/Internal Indicator Relationships .........................................................,... 10.8.5.3 Internal Indicator/Tissue Lead Relationships ........................ 10.8.6 Metabolism of Lead Alkyls ................................................................................ 10.8.6.1 Absorption of Lead Alkyls in Humans andAnimals .................... 10.8.6.2 Biotransformation and Tissue Distribution of Lead Alkyls ........................................................................................ 10.8.6.3 Excretion of Lead Alkyls ............. 10.9 REFERENCES............................................................................................................................. 11. ASSESSMENT OF LEAD EXPOSURES AND ABSORPTION IN HUMAN POPULATIONS .............................. 11.1 INTRODUCTION......................................................................................................................... 11.2 METHODOLOGICALCONSIDERATIONS .......................................................................................... 11.2.1 Analytical Problems .............................................................. ............................. 11.2.2 Statistical Approaches ...................................................................................... 11.2.3 Confounding of Relevant Variables ........................... .................................... 11.3 LEAD IN HUMAN POPULATIONS ............................................................................................... 11.3.1 Introduction .......................................................................... ........ ..................... 11.3.2 Ancient and Remote Populations ...................................................................... 11.3.2.1 Ancient Populations .................................................. 11.3.2.2 Remote Populations .......................................................................... 11.3.3 Levels of Lead and Demographic Covariates in U.S. and Other Populations ............................................................................................................ 11.3.3.1 The NHANES II Study................................................ 11.3.3.2 The Childhood Blood Lead Screening Programs .......................... 11.3.3.3 Levels of Lead and Demographic CovariatesWorldwide ............ 11.3.4 Distributional Aspects of Population Blood Lead Levels ........................ 11.3.5 Time Trends in Blood Lead Levels Since 1970 ............................................. 11.3.5.1 Time Trends in NHANES II Study Data ....................................... 11.3.5.2 Time Trends in the Childhood Lead Poisoning Screening Programs .............................................................................................. 11.3.5.3 Newark .................................................................................................. 11.3.5.4 Boston .................................................................................................. 11.3.5.5 Lead Studies in the United Kingdom ........................................... 11.3.5.6 Other Studies .................................................... 11.3.6 Gasoline Lead as an Important Determinant of Trends in Blood Lead Levels ............................................................................................................ 11.3.6.1 NHANES II Study Data ...................................................................... 11.3.6.2 Isotope Studies ................................................................................ 11.3.6.2.1 Italy................................................................... 11.3.6.2.2 United States ............................................................. 11.3.6.3 Studies of Childhood Blood Lead Poisoning Control Programs ..................... 11.3.6.4 Frankfurt, West Germany ................................................................. vi i Page 10-67 10-67 10-67 10-67 10-68 10-69 10-69 10-69 10-70 10-70 10-71 10-71 10-72 11-1 11-1 11-4 11-4 11-5 11-6 11-8 11-8 11-8 11-10 11-13 11-14 11-14 11-20 11-24 11-24 11-31 11-31 11-34 11-37 11-37 11-40 11-41 11-42 11-42 11-45 11-45 11-52 11-55 11-60 TEH 0411833 DUP050452431 TABLE OF CONTENTS (continued). 11.4 STUDIES RELATING EXTERNAL DOSE TO INTERNAL EXPOSURE ............................................. 11.4.1 Air Studies ............................................................................................................ 11.4.1.1 The Griffin et al. Study............................................................... 11.4.1.2 The Rabinowitz et al. Study ......................................................... 11.4.1.3 The Chamberlain et al. Study....................................................... 11.4.1.4 The Kehoe Study ................................................................................ 11.4.1.5 The Azar et al. Study..................................................................... 11.4.1.6 Silver Valley/Kellogg, Idaho Study ........................................... 11.4.1.7 Omaha, Nebraska Studies ................................................................. 11.4.1.8 Roels et al. Studies ....................................................................... 11.4.1.9 Other Studies Relating Blood Lead Levels to Air Exposure...................................................................................... 11.4.1.10 Summary of Blood Lead versus Inhaled Air LeadRelations .. 11.4.2 Dietary Lead Exposures Including Water ....................................................... 11.4.2.1 Lead Ingestion from Typical Diets ............................................. 11.4.2.1.1 Ryu Study on Infants and Toddlers ...................... 11.4.2.1.2 Rabinowitz Infant Study ......................................... 11.4.2.1.3 Rabinowitz Adult Study ........................................... 11.4.2.1.4 Hubermont Study ........................................................ 11.4.2.1.5 Sherlock Studies ....................................................... 11.4.2.1.6 Central Directorate on Environmental Pollution Study ......................................................... 11.4.2.1.7 Pocock Study ............................... .............................. 11.4.2.1.8 Thomas Study ............................................................... 11.4.2.1.9 Elwood Study ....................... ....................................... 11.4.2.2 Lead Ingestion from Experimental DietarySupplements .......... 11.4.2.2.1 Kehoe Study ................................................................. 11.4.2.2.2 Stuik Study................ ............................................... 11.4.2.2.3 Cools Study ................................................................. 11.4.2.2.4 Schlegel Study ........................................................... 11.4.2.2.5 Chamberlain Study ..................................................... 11.4.2.3 Inadvertent Lead Ingestion From Lead Plumbing ..................... 11.4.2.3.1 Early Studies ............................................................. 11.4.2.3.2 Moore Studies ............................................................. 11.4.2.3.3 Thomas Study ............................................................... 11.4.2.3.4 Worth Study ................................................................. 11.4.2.4 Summary of Dietary Lead Exposures, IncludingWater .............. 11.4.3 Studies Relating Lead in Soil and Dust to Blood Lead ........................... 11.4.3.1 Omaha, Nebraska Studies ......................... ...................................... 11.4.3.2 Stark Study ........................................................................................ 11.4.3.3 The Silver Valley/Kellogg Idaho Study..................................... 11.4.3.4 Blood Lead Levels of Dutch City Children ........................... .. 11.4.3.5 Charney Study .................................................................................... 11.4.3.6 Charleston Studies .......................................................................... 11.4.3.7 Barltrop Studies .............................................................................. 11.4.3.8 The British Columbia Studies ....................................................... 11.4.3.9 The Baltimore Charney Study: A Controlled Trial of Household Dust Lead Reduction................................... .. 11.4. 3.10 Gallacher Study ..................................................................... . 11.4.3.11 Other Studies of Soil and Dusts ................................................. 11.4.3.12 Summary of Soil and Dust Lead..................................................... 11.4.4 Paint Lead Exposures .......................................................................................... VI 11 Page 11-63 11-66 11-67 11-71 11-74 11-76 11-78 11-81 11-89 11-91 11-94 11-99 11-106 11-108 11-108 11-110 11-111 11-111 11-111 11-114 11-115 11-119 11-119 11-119 11-119 11-120 11-122 11-122 11-122 11-122 11-122 11-124 11-126 11-127 11-127 11-134 11-134 11"1^ 1 11-143 ^7*1 t TIic i TEH 0411834 DUP050452432 TABLE OF CONTENTS (continued). Page 11.5 SPECIFIC SOURCE STUDIES ....................................................................................................... 11-161 11.5.1 Primary Smelter Populations ................................................................................ 11-161 11.5.1.1 El Paso, Texas ....................................................................................... 11-161 11.5.1.2 CDC-EPA Study ......................................................................................... 11-163 11.5.1.3 Meza Valley, Yugoslavia ..................................................................... 11-163 11.5.1.4 Kosovo Province, Yugoslavia ............................................................. 11-165 11.5.1.5 The Cavalleri Study ............................................................................. 11-165 11.5.1.6 Hartwell Study ....................................................................................... 11-166 11.5.2' Battery Plants......................................................................................................... 11-166 11.5.3 Secondary Smelters ................................................................................................ 11-166 11.5.4 Secondary Exposure ofChildren ........................................................................... 11-170 11.5.5 Miscellaneous Studies ..................................................................................... 11-177 11.5.5.1 Studies Using Indirect Measures of Air Exposure .................. 11-177 11.5.5.1.1 Studies in the United States ................................ 11-177 11.5.5.1.2 BritishStudies ............................................................... 11-179 11.5.5.2 Miscellaneous Sources of Lead ..................................................... 11-181 11.6 SUMMARY AND CONCLUSIONS ........................................................................................................ 11-183 11.7 REFERENCES ................................................................................. APPENDIX 11A................................................................................................................................... 11A-1 APPENDIX 11B........................................................................................................................... .... 11B-1 APPENDIX 11C ................................................................................................................................... 11C-1 ix TEH 0411835 DUP050452433 LIST OF FIGURES Fipure 10-1 Effect of particle size on lead deposition rate in the lung............................. 10-2 The curvilinear relationship of serum lead to blood lead.................................. . 10-3 Schematic model of lead metabolism in infant baboons, with compartmental transfer coefficients ............................................................ .......................................... 10-4 A compartmental model for lead biokinetics with multiple pools for blood lead....................................................................................................................................... 10-5 Fitting of nonlinear blood lead model to data of DeSilva (1981). Broken line incorporates an intercept term of 0.25; solid line does not incorporate intercept term............................................................................................. 10- 6 Renal clearance (ratio of urinary lead to blood lead) from (A) King et a!., 1979; (B) Williams et al., 1969; (C) Gross, 1981; (D) DeVoto and Spinazzola, 1973; (E) Azar et al., 1975; (G) Chamberlain et al., 1978 ........ 11- 1 Pathways of lead from the environment to and within man...................................... 11-2 Estimated lead concentrations in bones (pg/g) from 5500 years before present (BP) to the present time ................................................................................ 11-3 Geometric mean blood lead levels by race and age for younger children in the NHANES II study. EPA calculations from data furnished by the National Center for Health Statistics ........................................................................................ 11-4 Geometric mean blood lead values by race and age for younger children in the New York City screening program (1970-1976) ................................................... . 11-5 Unweighted geometric mean blood lead level for male and female nonsmoking teachers (gg/dl) for several countries .................................................................... 11-6 Histograms of blood lead levels with fitted lognormal curves for the NHANES II study. All subgroups are white non-SMSA residents with family incomes over $6000/year .................................................................................................. 11-7 Average blood lead levels of U.S. population aged 6 months-74 years, United States February 1976-February 1980, based on dates of examination of NHANES II examinees with blood lead determinations ....................................... . 11-8 Reduction in mean blood lead levels, according to race, sex, and age. Data on sex and age are for whites ............................................................................ 11-9 Time-dependence of blood lead levels for blacks, aged 25 to 36 months, in New York City and Chicago .............................................................................................. 11-10 Modeled umbilical cord blood lead levels by date of sample collection for infants in Boston ............................................................................................................ 11-11 Parallel decreases in blood lead values observed in the NHANES II study and amounts of lead used in gasoline during 1976-1980 ....................................... 11-12 Change in 206Pb/207Pb ratios in petrol, airborne particulate and blood from 1974 to 1984 ............................................................................................................. 11-13 Estimated direct and indirect contributions of lead in gasoline to blood lead in Italian men based on EPA analysis of ILE data (Table 11-16) ............ 11-14 Geometric mean blood lead levels of New York City children (aged 25-36 months) by ethnic group, and ambient air lead concentration versus quarterly sampling period, 1970-1976 ........................................................................ 11-15 Geometric mean blood lead levels of New York City children (aged 25-36. months) by ethnic group, and estimated amount of lead present in gasoline sold in New York, New Jersey and Connecticut versus quarterly sampling period, 1970-1976 .................................................................................. ........................... 11-16 Geometric mean blood levels for blacks and Hispanics in the 25- to 36-month age group and rooftop quarterly averages for ambient city-wide lead levels .......................... ................................................... .......................... '............... Page 10-4 10-18 10-28 10-29 10-30 10-35 11-3 11-12 11-19 11-23 11-25 11-28 11-32 11-33 11-35 11-38 11-43 11-47 11-51 11-58 11-59 11-63 . 1 \p DUP050452434 LIST OF FIGURES (continued). Figure Page 11-17 11-18 11-19 11-20 11-21 11-22 11-23 11-24 11-25 11-26 11-27 11-28 11-29 11-30 11-31 11-32 11-33 11B-1 11C-1 11C-2 11C-3 11C-4 11C-5 Time dependence of blood lead and gas lead for blacks, aged 25 to 36 months, in New York................................................................................................................ Data plots for individual subjects as a function of time for Kehoe subjects, as presented by Gross (1979) .......................................................................... Blood lead versus air lead relationships derived from Kehoe inhalation studies: Linear relationship holds for low exposures, quadratic for high exposures. 95 percent confidence bands are also shown ........................................... Monthly ambient air lead concentrations in Kellogg, Idaho, 1971 through 1975 .............................................................................................................................. Fitted equations to the Kellogg Idaho/Silver Valley, adjusted blood lead data ............................................................................................................................................. Blood lead concentrations versus weekly lead intake for bottle-fed infants ....................................................................................................................................... Mean blood lead for men grouped by first draw water concentration ...................... Averageblood lead levels, Phase I ................................................................................... Averageblood lead levels, Phase II ................................................................................. Lead in blood (mean values and range) in volunteers. In the lower curve the average daily lead dose of the exposed group is shown ..................................... Cube root regression of blood lead on first flush water lead. This shows mean S.D. of blood lead for pregnant women grouped in 7 intervals of first flush water lead ........................................................................................................ Relation of blood lead (adult female) to first flush water lead in combined estates. (Numbers are coincidental points; 9 = 9 or more.) Curve a, present data; curve b, data of Moore et al. (1979) ................................................... Cumulative distribution of lead levels in dwelling units ....................................... Correlations of children's blood lead levels with fractions of surfaces within a dwelling having lead concentrations i2 mg/cm2 .......................................... Arithmetic mean air lead levels by traffic volume, Dallas, 1976 .......................... Blood lead concentration and traffic density by sex and age, Dallas, 1976 ............................................................................................................................................. Geometric mean blood lead levels by race and age for younger children in the NHANES II study, and the Kellogg/Silver Valley and New York Childhood Screening Studies ................. Residual sum of squares for nonlinear regression models for Azar data (N=149) ............................................................................................................................. . Individual values of blood Pb-206/207 ratio for subjects follow-up in Turin (12 subjects) ...................................................................... .................................................... Individual values of blood Pb-206/207 ratio for subjects follow-up in Costagneto (4 subjects) ....................................................................................................... Individual values of blood Pb-206/207 ratio for subjects follow-up in Duento and Fiano (6 subjects) ................................................................................................. Individual values of blood Pb-206/207 ratio for subjects follow-up in Nole and Santeno (9 subjects) ...................................................................................................... Individual values of blood Pb-206/207 ratio for subjects follow-up in Viu (4 subjects) ................................................. ................................................................... 11-62 11-77 11-79 11-83 11-88 11-116 11-118 11-121 11-121 11-123 11-125 11-128 11-155 11-157 11-178 11-180 11-184 11B-2 11C-2 11C-3 11C-3 11C-4 11C-4 xi TEH 0411837 DUP050452435 LIST OF TABLES Table 10-1 10-2 10-3 10-4 11-1 11-2 11-3 11-4 11-5 11-6 11-7 11-8 11-9 11-10 11-11 11-12 11-13 11-14 11-15 11-16 11-17 11-18 11-19 11-20 11-21 11-22 Deposition of lead in the human respiratory tract ............................................... Distribution of lead in brain regions of humans and animals ........................... Daily lead excretion and retention data for adults and infants ...................... Effect of nutritional factors on lead uptake in animals ................................... Summary of Representative Studies of Past Exposures to Lead ............................ NHANES II blood lead levels of persons 6 months-74 years, with weighted arithmetic mean, standard error of the mean, weighted geometric mean, median, and percent distribution, by race and age. United States, 1976-80 ................................................................................................................................. NHANESII blood lead levels of males 6 months-74 years, with weighted arithmetic mean, standard error of the mean, weighted geometric mean, median, and percent distribution, by race and age. United States, 1976-80 ................................................................................................................................. NHANES II blood lead levels of females 6 months-74 years, with weighted arithmetic mean, standard error of the mean, weighted geometric mean, median, and percent distribution, by race and age, United States, 1976-80 ................................................................................................................................. Weighted geometric mean blood lead levels from NHANES II survey by degree of urbanization of place of residence in the U.S. by age and race, United States 1976-80 ................................. ................................................ Annual geometric mean blood lead levels from the New York blood lead screening studies of Billick et al. (1979). Annual geometric means are calculated from quarterly geometric means estimated by the method of Hasselblad et al. (1980) ............................. .................................................................. Summary of unweighted blood lead levels in whites not living in an SMSA, with family income greater than $6,000......................................................... Summary of fits to NHANES II blood lead levels of whites not living in an SMSA, with income greater than $6,000, for five different two-parameter distributions ...................................................................... Estimated mean square errors resulting from analysis of variance on various subpopulations of the NHANES II data using unweighted data .............. Characteristics of childhood lead poisoning screening data .............................. Distribution of blood lead levels for 13- to 48-month-old blacks by season and year for New York screening data ............... ..................................... Comparison of median blood lead levels (pg/dl) in several countries from studies of Goldwater and Hoover (1967) and Friberg and Vahter (1983) .......... Pearson correlation coefficients between the average blood lead levels for six-month periods and the total lead used in gasoline production per six months, according to race, sex, and age .................................................................. Estimated contribution of leaded gasoline to blood lead by inhalation and non-inhalation pathways .................................................................................................. Assumed air lead concentrations for model ............................................................... Regression model for blood lead attributable to gasoline ................................. Rate of change of 206Pb/204Pb and 206Pb/207Pb in air and blood, and percentage of airborne lead in blood of subjects 1, 3, 5, 6 and 9 ................ Calculated blood lead uptake from air lead using Manton isotope study ........ Respired and other inputs of airborne Pb to blood for some Dallas residents in 1975 ............................................................................................................... ................ Mean air lead concentrations during the various blood sampling periods at the measurement sites described in the text (pg/m3) ........................................... Griffin et al. (1975) experiment inhalation slope estimates ........................... Griffin et al. (1975) experiment mean residence time in blood ....................... xii Page 10-3 10-21 10-34 10-45 11-11 11-16 11-17 11-18 11-21 11-22 11-26 11-27 11-30 11-36 11-36 11-42 11-44 11-49 11-50 11-51 11-54 11-54 11-56 11-63 11-70 11-70 TEH 041183 -- DUP050452436 LIST OF TABLES (continued). Table 11-23 11-24 11-25 11-26 11-27 11-28 11-29 11-30 11-31 11-32 11-33 11-34 11-35 11-36 11-37 11-38 11-39 11-40 11-41 11-42 11-43 11-44 11-45 11-46 11-47 11-48 11-49 Air lead concentrations (pg/m3) for two subjects in theRabinowitz studies ... Estimates of inhalation slope, p, for Rabinowitz studies ........................................ Linear slope for blood lead versus air lead at low air lead exposures in Kehoe's subjects ..................................................................................................................... Geometric mean air and blood lead levels (gg/100 g) for five cityoccupation groups (data calculated by EPA) .................................................................. Geometric mean blood lead levels by area compared with estimated air lead levels for 1- to 9-year-old children living near Idaho smelter ............................ Geometric mean blood lead levels by age and area for subjects living near the Idaho smelter................................................................................................................... Age-specific regression coefficients for the analysis of log (blood lead) levels in the Idaho smelter study .................................................................................... Estimated coefficients and standard errors for the Idahosmelter study ............. Air, dustfall and blood lead concentrations in Omaha, NE,study, 1970-1977 ... Mean airborne and blood lead levels recorded during five distinct surveys (1974 to 1978) for study populations of 11-year old children living less than 1 km or 2.5 km from a lead smelter, or living in a rural or urban area .. Geometric mean air lead and adjusted blood lead levels for 11 communities in study of Tepper and Levin (1975) as reported by Hasselblad and Nelson (1975) ........................................................................................................................... Mean air and blood lead values for five zones in Tokyo study........................ Blood lead-air lead slopes for several population studies as calculated by Snee ....................................................................................................................................... Characteristics of studies on the relationship between air lead and blood lead in children..................................................................................................................... A selection of recent analyses on occupational 8-hour exposures to high air lead levels .............................................................. Cross-sectional observational study with measured individual air lead exposure ..................................................................................................................................... Cross-sectional observational studies on children with estimated air exposures .......................................... Longitudinal experimental studies with measured individual air lead exposures ........................................................ Household consumption of canned foods, pounds per week ... ....................................... Blood lead levels and lead intake values for infants in the study of Ryu et al............................. Influence of level of lead in water on blood lead level in blood and placenta ...................................................... Distributions of observed blood lead values in Ayr .................................................. Blood lead and kettle water lead concentrations for adult women living in Ayr ........................................................................................... Relationship of blood lead and water lead in 910 men aged 40-59 from 24 British towns ..................................................................................................................... Dose-response analysis for blood lead levels in the Kehoe study as analyzed by Gross (1981) ...................................................................................................... Blood lead levels of 771 persons in relation to lead content of drinking water, Boston, MA ..................... Studies relating blood lead levels (pg/dl) to dietary intakes (pg/day) ........... Page 11-72 11-73 11-78 11-80 11-84 11-84 11-85 11-87 11-90 11-93 11-96 11-96 11-98 11-100 11-101 11-102 11-103 11-104 11-109 11-110 11-112 11-113 11*113 11-117 11-120 11-129 11-130 I i xiii TEH 0411839 DUP050452437 LIST OF TABLES (continued). Table 11-50 11-51 11-52 11-53 11-54 11-55 11-56 11-57 11-58 11-59 11-60 11-61 11-62 11-63 11-64 11-65 11-66 11-67 11-68 11-69 11-70 11-71 11-72 11-73 11-74 Studies involving blood lead levels (pg/dl) and experimental dietary intakes ....................................................................................................................................... Studies relating blood lead levels (pg/dl) to first-flush water lead (pg/1) .. Studies relating blood lead levels (pg/dl) to running water lead (pg/1) .......... Coefficients and standard errors for Omaha study model ........................................... Multiple regression models for blood lead of children in New Haven, Connecticut, September 1974 - February 1977 ................................................................ Air Lead Levels in the Rotterdam Area ............................................................................ Blood lead levels in pg/100 ml for children who participated in blood survey and environmental survey ........................................................................................ School variables (arithmetic means) for measured lead concentrations ................ Results of lead measurements reported by Brunekreef et al. (1983) ...................... Coefficients and standard errors from model of Charleston study .......................... Mean blood and soil lead concentrations in English study ....................................... Lead concentration of surface soil and children's blood by residential area of trail, British Columbia ........................................................................................ Analysis of relationship between soil lead and blood lead in children .............. Estimates of the contribution of soil lead to blood lead ....................................... Estimates of the contribution of housedust to blood lead in children ................ Results of screening and housing inspection in childhood lead poisoning control project by fiscal year .......................................................................................... Mean blood lead levels in selected Yugoslavian populations, by estimated weekly time-weighted air lead exposure .......................................................................... Levels of lead recorded in Hartwell et al. (1983) study ......................................... Spearman correlations of lead in air, water, dust, soil, and paint with lead levels in blood: by site and age groups, 1978-1979 ....................................... Environmental parameters and methods: Arnhem lead study, 1978 ............................ Geometric mean blood lead levels for children based on reported occupation of father, history of pica, and distance of residence from smelter (micrograms per deciliter) ........................................................................ Sources of lead ....................................................................................................................... Summary of blood lead pooled geometric standard deviations and estimated analytic errors ....................................................................................................................... Estimated contribution of leaded gasoline to blood lead by inhalation and non-inhalation pathways ................................................................................................ Summary of blood inhalation slopes, (p) pg/dl per pg/m3 ......................................... Page 11-131 11-132 11-133 11-135 :. -:rt xiv AAS Ach ACTH ADCC ADP/Q ratio AIDS AIHA All ALA ALA-D ALA-S ALA-U APDC APHA ASTM ASV ATP B-celIs Ba BAL BAP BSA BUN BW C.V. CaBP CaEDTA CaNa9EDTA CBD * Cd CDC CEC CEH CFR CMP CNS CO COHb CPB CP-U cBat1 D.F. DA 6-ALA DCMU DPP DNA DTH EEC EEG EMC LIST OF ABBREVIATIONS Atomic absorption spectrometry Acetylcholine Adrenocorticotrophic hormone Antibody-dependent cell-mediated cytotoxicity Adenosine diphosphate/oxygen ratio Acquired immune deficiency syndrome American Industrial Hygiene Association Angiotensin II Aminolevulinic acid Aminolevulinic acid dehydrase Aminolevulinic acid synthetase Aminolevulinic acid in urine Ammoniurn pyrrolidine-dithiocarbamate American Public Health Association Amercian Society for Testing and Materials Anodic stripping voltammetry Adenosine triphosphate Bone marrow-derived lymphocytes Barium British anti-Lewisite (AKA dimercaprol) benzo(a)pyrene Bovine serum albumin Blood serum urea nitrogen Body weight Coefficient of variation Calcium binding protein Calcium ethylenediaminetetraacetate Calcium sodium ethylenediaminetetraacetate Central business district Cadmium Centers for Disease Control Cation exchange capacity Center for Environmental Health reference method Cytidine monophosphate Central nervous system Carbon monoxide Carboxyhemoglobin Competitive protein binding Urinary coproporphyrin plasma clearance of p-aminohippuric acid Copper Degrees of freedom Dopamine delta-aminolevulinic acid [3-(3,4-dichlorophenyl)-l,1-dimethyl urea Differential pulse polarography Deoxyribonucleic acid Delayed-type hypersensitivity European Economic Community Electroencephalogram Encephalomyocarditis XV TEH 0411841 DUP050452439 EP EPA FA FDA Fe FEP FY G.M. G-6-PD GABA GALT GC GFR GI HA HANES I Hb Hg hi-vol HPLC i .m. i.p. i. v. IAA IARC ICD ICP IDMS IF ILE IRPC K LDH-X LLLDHC55c 00 LIPO In LPS LRT mRNA ME MEPP MES MeV MLC MMD MMAD Mn MND MSV MTD LIST OF ABBREVIATIONS (continued). Erythrocyte protoporphyrin U.S. Environmental Protection Agency Fulvic acid Food and Drug Administration Iron Free erythrocyte protoporphyrin Fiscal year Grand mean Glucose-6-phosphate dehydrogenase Gamma-aminobutyric acid Gut-associated lymphoid tissue Gas chromatography Glomerular filtration rate Gastrointestinal Humic acid Health Assessment and Nutrition Evaluation Survey Hemoglobin Mercury High-volume air sampler High-performance liquid chromatography Intramuscular (method of injection) Intraperitoneally (method of injection) Intravenously (method of injection) Indol-3-ylacetic acid International Agency for Research on Cancer International classification of diseases Inductively coupled plasma emission spectroscopy Isotope dilution mass spectrometry Interferon Isotopic Lead Experiment (Italy) International Radiological Protection Commission Potassium Lactate dehydrogenase isoenzyme x Lethyl concentration (50 percent) Lethal dose (50 percent) Luteinizing hormone Laboratory Improvement Program Office Natural logarithm Lipopolysaccharide Long range transport Messenger ribonucleic acid Mercaptoethanol Miniature end-plate potential Maximal electroshock seizure Mega-electron volts Mixed lymphocyte culture Mass median diameter Mass median aerodynamic diameter Manganese Motor neuron disease Moloney sarcoma virus Maximum tolerated dose xv i M ii n N/A NA NAAQS NAD NADB NAMS NAS NASN NBS NE NFAN NFR-82 NHANES II Ni NTA OSHA P P PAH Pb PBA Pb(Ac),, PbB c PbBrCl PBG PFC pH PHA PHZ PIXE PMN PND PNS P. 0. ppm PRA PRS PWM Py5N RBC RBF RCR redox RES RLV RNA S-HT SA-7 S.C. scm S.D. LIST OF ABBREVIATIONS (continued). Number of subjects or observations Not Available Not Applicable National ambient air quality standards Nicotinamide Adenine Dinucleotide National Aerometric Data Bank National Air Monitoring Station National Academy of Sciences National Air Surveillance Network National Bureau of Standards Norepinephrine National Filter Analysis Network Nutrition Foundation Report of 1982 National Health Assessment and Nutritional Evaluation Survey II Nickel Nitrilotriacetonitrile Occupational Safety and Health Administration Phosphorus Significance symbol Para-aminohippuric acid Lead Air lead Lead acetate concentration of lead in blood Lead (II) bromochloride Porphobilinogen Plaque-forming cells Measure of acidity Phytohemagglutinin Polyacry1 amide-hydrous-zirconia Proton-induced X-ray emissions Polymorphonuclear leukocytes Post-natal day Peripheral nervous system Per os (orally) Parts per million Plasma renin activity Plasma renin substrate Pokeweed mitogen Pyrimide-51-nucleotidase Red blood cell; erythrocyte Renal blood flow Respiratory control ratios/rates Oxidation-reduction potential Reticuloendothelial system Rauscher leukemia virus Ribonucleic acid Serotonin Simian adenovirus Subcutaneously (method of injection) Standard cubic meter Standard deviation xvii TEH 04118-43 DUP050452441 SDS S.E.M. SES SGOT slg SLAMS SMR Sr SRBC SRMs STEL SW voltage T-cells t-tests TBL TEA TEL TIBC TML TMLC TSH TSP U.K. UMP USPHS VA V. v Ir WHO XRF r In ZPP dl ft g g/gai g/ha*mo km/hr 1 /mi n mg/ km pg/m3 mm pm pmol ng/cmz nm LIST OF ABBREVIATIONS (continued). Sodium dodecyl sulfate Standard error of the mean Socioeconomic status Serum glutamic oxaloacetic transaminase Surface immunoglobulin State and local air monitoring stations Standardized mortality ratio Strontium Sheep red blood cells Standard reference materials Short-term exposure limit Slow-wave voltage Thymus-derived lymphocytes Tests of significance Tri-n-butyl lead Tetraethyl-ammonium Tetraethyllead Total iron binding capacity Tetramethyllead Tetramethyllead chloride Thyroid-stimulating hormone Total suspended particulate United Kingdom Uridine monophosphate U.S. Public Health Service Veterans Administration Deposition velocity Visual evoked response World Health Organization X-Ray fluorescence Chi squared Zinc Erythrocyte zinc protoporphyrin MEASUREMENT ABBREVIATIONS deciliter feet gram gram/gallon gram/hectare-month kilometer/hour liter/minute milligram/ki1ometer microgram/cubic meter mi 11imeter micrometer micromole nanograms/square centimeter nanometer xviii TEH 041 DUP050452442 LIST OF ABBREVIATIONS (continued). t nM nanomole sec second t tons * xix TEH 0411845 DUP050452443 GLOSSARY VOLUME III aerosol - a suspension of liquid or solid particles in a gas BAL (British Anti-Lewisite) - a chelating agent often used in the treatment of metal toxicity biliary clearance - an excretion route involving movement of an agent through bile into the GI tract Brownian diffusion - the random movement of microscopic particles "chelatable" or systemically active zinc - fraction of body's zinc store available or accessible to removal by a zinc-binding agent chi-square goodness-of-fit tests - made to determine how well the observed data fit a specified model, these tests usually are approximately distributed as a chi-square variable first-order kinetics - a kinetic process whose rate is proportional to the concentration of the species undergoing change geochronometry - determination of the age of geological materials hematocrit - the percentage of the volume of a blood sample occupied by cells intraperitoneal - within the body cavity likelihood function - a relative measure of the fit of observed data to a specified model. In some special cases it is equivalent to the sum of squares function used in least squares analysis. mass median aerodynamic diameter (MMAD) - the aerodynamic diameter (in pm) at which half the mass of particles in an aerosol is associated with values below and half above multiple regression analysis - the fitting of a single dependent variable to a linear combination of independent variables using least squares analysis plumburesis - lead excreted in urine R2 - this statistic, often called the multiple R squared, measures the proportion of total variation explained. A value near 1 means that nearly all of the variation is explained, whereas a value near zero means that almost none of the variation is explained. xx TEH 0411846; DUP050452444 AUTHORS, CONTRIBUTORS, AND REVIEWERS Chapter 9: Quantitative Evaluation of Lead and Biochemical Indices of Lead Exposure in Physiological Media Principal Author Dr. Paul Mushak Department of Pathology School of Medicine University of North Carolina Chapel Hill, NC 27514 The following persons reviewed this chapter at EPA's request. The evaluations and conclusions contained herein, however, are not necessarily those of the reviewers. Dr. Carol Angle Department of Pediatrics University of Nebraska College of Medicine Omaha, NE 68105 Dr. A. C. Chamberlain Environmental and Medical Sciences Division Atomic Energy Research Establishment Harwell 0X11 England Dr. Lee Annest Division of Health Examin. Statistics National Center for Health Statistics 3700 East-West Highway Hyattsville, MD 20782 Dr. Neil Chernoff Division of Developmental Biology MD-67 U.S. Environmental Protection Agency Research Triangle Park, NC 27711 Dr. Donald Barltrop Department of Child Health Westminister Children's Hospital London SW1P 2NS England Dr. Julian Chisolm Baltimore City Hospital 4940 Eastern Avenue Baltimore, MD 21224 Dr. Irv Billick Gas Research Institute 8600 West Bryn Mawr Avenue Chicago, IL 60631 Mr. Jerry Cole International Lead-Zinc Research Organization 292 Madison Avenue New York, NY 10017 Dr. Joe Boone Clinical Chemistry and Toxicology Section Centers for Disease Control Atlanta, GA 30333 Dr. Robert Bornschein University of Cincinnati Kettering Laboratory Cincinnati, OH 45267 Dr. Max Costa Department of Pharmacology University of Texas Medical School Houston, TX 77025 Dr. Anita Curran Commissioner of Health Westchester County White Plains, NY 10607 xx i TEH 0411847 DUP050452445 Dr. Jack Dean Immunobiology Program and Immunotoxicology/Cel1 Biology program CUT P.0. Box 12137 Research Triangle Park, NC 27709 Dr. H. T. Delves Chemical Pathology and Human Metabolism Southampton General Hospital Southampton S09 4XY England Dr. Fred deSerres Assoc. Director for Genetics NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Robert Dixon Laboratory of Reproductive and Developmental Toxicology NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Claire Ernhart Department of Psychiatry Cleveland Metropolitan General Hospital Cleveland, OH 44109 Dr. Sergio Fachetti Section Head - Isotope Analysis Chemistry Division Joint Research Center 121020 Ispra Varese, Italy Dr. Virgil Ferm Department of Anatomy and Cytology Dartmouth Medical School Hanover, NH 03755 Dr. Alf Fischbein Environmental Sciences Laboratory Mt. Sinai School of Medicine New York, NY 10029 Dr. Jack Fowle Reproductive Effects Assessment Group U.S. Environmental Protection Agency RD-689 Washington, DC 20460 xx ii Dr. Bruce Fowler Laboratory of Pharmacology NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Warren Galke Department of Biostatistics and Epidemiology School of Allied Health East Carolina University Greenville, NC 27834 Mr. Eric Goldstein Natural Resources Defense Council, Inc. 122 E. 42nd Street New York, NY 10168 Dr. Harvey Gonick 1033 Gayley Avenue Suite 116 Los Angeles, CA 90024 Dr. Robert Goyer Deputy Director NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Stanley Gross Hazard Evaluation Division Toxicology Branch U.S. Environmental Protection Agency Washington, DC 20460 Dr. Paul Hammond University of Cincinnati Kettering Laboratory Cincinnati, OH 45267 Dr. Ronald D. Hood Department of Biology The University of Alabama University, AL 35486 Dr. V. Houk Centers for Disease Control 1600 Clifton Road, NE Atlanta, GA 30333 rTEH 0411848 f DUP050452446 Dr. Loren D. Koller School of Veterinary Medicine University of Idaho Moscow, ID 83843 Dr. Kristal Kostial Institute for Medical Research and Occupational Health Yu-4100 Zagreb Yugoslavia Dr. Lawrence Kupper Department of Biostatistics UNC School of Public Health Chapel Hill, NC 27514 Dr. Phillip Landrigan Division of Surveillance, Hazard Evaluation and Field Studies Taft Laboratories - NIOSH Cincinnati, OH 45226 Dr. David Lawrence Microbiology and Immunology Dept. Albany Medical College of Union University Albany, NY 12208 Dr. Jane Lin-Fu Office of Maternal and Child Health Department of Health and Human Services Rockville, MD 20857 Dr. Don Lynam Air Conservation Ethyl Corporation 451 Florida Boulevard Baton Rouge, LA 70801 Dr. Kathryn Mahaffey Division of Nutrition Food and Drug Administration 1090 Tusculum Avenue Cincinnati, OH 45226 Dr. Ed McCabe Department of Pediatrics University of Wisconsin Madison, WI 53706 Dr. Chuck Nauman Exposure Assessment Group U.S. Environmental Protection Agency Washington, DC 20460 Dr. Herbert L. Needleman Department of Psychiatry Children's Hospital of Pittsburgh Pittsburgh, PA 15213 Dr. H. Mitchell Perry V.A. Medical Center St. Louis, M0 63131 Dr. Jack Pierrard E.l. duPont de Nemours and Company, Inc. Petroleum Laboratory Wilmington, DE 19898 Dr. Sergio Piomelli Columbia University Medical School Division of Pediatric Hematology and Oncology New York, NY 10032 Dr. Magnus Piscator Department of Environmental Hygiene The Karolinska Institute 104 01 Stockholm Sweden Dr. Robert Putnam International Lead-Zinc Research Organization 292 Madison Avenue New York, NY 10017 Dr. Michael Rabinowitz Children's Hospital Medical Center 300 Longwood Avenue Boston, MA 02115 j ! xxi i i TEH 0411849 DUP050452447 Dr. Harry RoeIs Unite de Toxicologie Industrielle et Medicale Universite de Louvain Brussels, Belgium Dr. John Rosen Division of Pediatric Metabolism Albert Einstein College, of Medicine Montefiore Hospital and Medical Center 111 East 210 Street Bronx, NY 10467 Dr. Michael Rutter Department of Psychology Institute of Psychiatry DeCrespigny Park London SE5 8AL England Dr. Stephen R. Schroeder Division for Disorders of Development and Learning Biological Sciences Research Center University of North Carolina Chapel Hill, NC 27514 Dr. Anna-Maria Seppalainen Institutes of Occupational Health Tyoterveyslaitos Haartmaninkatu 1 00290 Helsinki 29 Finland Or. Ellen Silbergeld Environmental Defense Fund 1525 18th Street, NW Washington, DC 20036 Dr Ron Snee E.I. duPont Nemours and Company, Inc. Engineering Department L3167 Wilmington, DE 19898 Dr. Gary Ter Haar Toxicology and Industrial Hygiene Ethyl Corporation 451 Florida Boulevard Baton Rouge, LA 70801 Dr. Ian von Lindern Department of Chemical Engineering University of Idaho Moscow, Idaho 83843 Dr. Richard P. Wedeen V.A. Medical Center Tremont Avenue East Orange, MJ 07019 tip -sU xxiv " i.iir i i TEH 0411*5 . DUP050452448 Chapter 10: Metabolism of Lead Principal Author Dr. Paul Mushak Department of Pathology School of Medicine University of North Carolina Chapel Hill, NC 27514 Contributing Author Dr. Alan Marcus Department of Mathematics Washington State University Pullman, WA 99164-2930 The following persons reviewed this chapter at EPA's request. The evaluations and conclusions contained herein, however, are not necessarily those of the reviewers. Dr. Carol Angle Department of Pediatrics University of Nebraska College of Medicine Omaha, NE 68105 Dr. Robert Bornschein University of Cincinnati Kettering Laboratory Cincinnati, OH 45267 Dr. Lee Annest Division of Health Examin. Statistics National Center for Health Statistics 3700 East-West Highway Hyattsville, MD 20782 Dr. A. C. Chamberlain Environmental and Medical Sciences Division Atomic Energy Research Establishment Harwell 0X11 England Dr. Donald Barltrop Department of Child Health Westminister Children's Hospital London SW1P 2NS England Dr. Irv Billick Gas Research Institute 8600 West Bryn Mawr Avenue Chicago, IL 60631 Dr. Joe Boone Clinical Chemistry and Toxicology Section Centers for Disease Control At!anta, GA 30333 Dr. Neil Chernoff Division of Developmental Biology MD-67 U.S. Environmental Protection Agency Research Triangle Park, NC 27711 Dr. Julian Chisolm Baltimore City Hospital 4940 Eastern Avenue Baltimore, MD 21224 Mr. Jerry Cole International Lead-Zinc Research Organization 292 Madison Avenue New York, NY 10017 xxv TEH 0411851 DUP050452449 Dr. Max Costa Department of Pharmacology University of Texas Medical School Houston, TX 77025 Dr. Anita Curran Commissioner of Health Westchester County White Plains, NY 10607 Dr. Jack Dean Immunobiology Program and Immunotoxicology/Cell Biology program CUT P.0. Box 12137 Research Triangle Park, NC 27709 Dr. H.T. Delves Chemical Pathology and Human Metabolism Southampton General Hospital Southampton S09 4XY England Dr. Fred deSerres Assoc. Director for Genetics NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Robert Dixon Laboratory of Reproductive and Developmental Toxicology NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Claire Ernhart Department of Psychiatry Cleveland Metropolitan General Hospital Cleveland, OH 44109 Dr. Sergio Fachetti Section Head - Isotope Analysis Chemistry Division Joint Research Center 121020 Ispra Varese, Italy Dr. Virgil Ferm Department of Anatomy and Cytology Dartmouth Medical School Hanover, NH 03755 xxvi Dr. Alf Fischbein Environmental Sciences Laboratory Mt. Sinai School of Medicine New York, NY 10029 Dr. Jack Fowle Reproductive Effects Assessment Group U.S. Environmental Protection Agency RD-689 Washington, DC 20460 Dr. Bruce Fowler Laboratory of Pharmacology NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Warren Galke Department of Biostatistics and Epidemiology School of Allied Health East Carolina University Greenville, NC 27834 Mr. Eric Goldstein Natural Resources Defense Council, Inc. 122 E. 42nd Street New York, NY 10168 Dr. Harvey Gonick 1033 Gayley Avenue Suite 116 Los Angeles, CA 90024 Dr. Robert Goyer Deputy Director NIEHS P.0. Box 12233 Research Triangle Park, NC 27709 Dr. Stanley Gross Hazard Evaluation Division Toxicology Branch U.S. Environmental Protection Agency Washington, DC 20460 Dr. Paul Hammond University of Cincinnati Kettering Laboratory Cincinnati, OH 45267 DUP050452450 Dr. Ronald D. Hood Department of Biology The University of Alabama University, AL 35486 Dr. V. Houk Centers for Disease Control 1600 Clifton Road, NE Atlanta, GA 30333 Dr. Loren D. Koller School of Veterinary Medicine University of Idaho Moscow, ID 83843 Dr. Krista! Kostial Institute for Medical Research and Occupational Health Yu-4100 Zagreb Yugoslavia Dr. Lawrence Kupper Department of Biostatistics UNC School of Public Health Chapel Hill, NC 27514 Dr. Phillip Landrigan Division of Surveillance, Hazard Evaluation and Field Studies Taft Laboratories - NIOSH Cincinnati, OH 45226 Dr. David Lawrence Microbiology and Immunology Dept. Albany Medical College of Union University Albany, NY 12208 Dr. Jane Lin-Fu Office of Maternal and Child Health Department of Health and Human Services Rockville, MD 20857 Dr. Don Lynam Air Conservation Ethyl Corporation 451 Florida Boulevard Baton Rouge, LA 70801 Dr. Kathryn Mahaffey Division of Nutrition Food and Drug Administration 1090 Tusculum Avenue Cincinnati, OH 45226 xxv ii Dr. Ed McCabe Department of Pediatrics University of Wisconsin Madison, WI 53706 Dr. Chuck Nauman Exposure Assessment Group U. S. Environmental Protection Agency Washington, DC 20460 Dr. Herbert L. Neddleman Department of Psychiatry Children's Hospital of Pittsburgh Pittsburgh, PA 15213 Dr. H. Mitchell Perry V. A, Medical Center St. Louis, M0 63131 Dr. Jack Pierrard E.I. duPont de Nemours and Company, Inc. Petroleum Laboratory Wilmington, DE 19898 Dr. Sergio Piomelli Columbia University Medical School Division of Pediatric Hematology and Oncology New York, NY 10032 Dr. Magnus Piscator Department of Environmental Hygiene The Karolinska Institute 104 01 Stockholm Sweden Dr. Robert Putnam International Lead-Zinc Research Organization 292 Madison Avenue New York, NY 10017 Dr. Harry Roels Unite de Toxicologie Industrielle et Medicale Universite de Louvain Brussels, Belgium Dr. John Rosen Division of Pediatric Metabolism Albert Einstein College of Medicine Montefiore Hospital and Medical Center 111 East 210 Street Bronx, NY 10467 TEH 0411853 DUP05G452451 Dr. Michael Rutter Department of Psychology Institute of Psychiatry DeCrespigny Park London SE5 8AL England Dr. Stephen R. Schroeder Division for Disorders of Development and Learning Biological Sciences Research Center University of North Carolina Chapel Hill, NC 27514 Dr. Anna-Maria Seppalainen Institutes of Occupational Health Tyoterveyslaitos Haartmaninkatu 1 00290 Helsinki 29 Finland Dr. Ellen Silbergeld Environmental Defense Fund 1525 18th Street, NW Washington, DC 20036 Dr. Ron Snee E.I. duPont Nemours and Company, Inc. Engineering Department L3167 Wilmington, DE 19898 Dr. Gary Ter Haar Toxicology and Industrial Hygiene Ethyl Corporation 451 Florida Boulevard Baton Rouge, LA 70801 Dr. Ian von Lindern Department of Chemical Engineering University of Idaho Moscow, ID 83843 Dr. Richard P. Wedeen V.A. Medical Center Tremont Avenue East Orange, NJ 07019 i 1is 1H!; xxvm TEH 04118^4 DUP050452452 Chapter 11: Assessment of Lead Exposures and Absorption in Human Populations Principal Authors Dr. Warren Galke Department of Biostatistics and Epidemiology School of Allied Health East Carolina University Greenville, NC 27834 Dr. Vic Hasselblad Biometry Division MD-55 U.S. Environmental Protection Agency Research Triangle Park, NC 27711 Dr. Alan Marcus Department of Mathematics Washington State University Pullman, WA 99164-2930 Contributing Author: Dr. Dennis Kotchmar Environmental Criteria and Assessment Office MD-52 U.S. Environmental Protection Agency Research Triangle Park, NC 27711 The following persons reviewed this chapter at EPA's request. The evaluations and conclusions contained herein, however, are not necessarily those of the reviewers. Dr. Carol Angle Department of Pediatrics University of Nebraska College of Medicine Omaha, NE 68105 Dr. Joe Boone Clinical Chemistry and Toxicology Section Centers for Disease Control Atlanta, GA 30333 Dr. Lee Annest Division of Health Examin. Statistics National Center for Health Statistics 3700 East-West Highway Hyattsville, MD 20782 Dr. Robert Bornschein University of Cincinnati Kettering Laboratory Cincinnati, OH 45267 Dr. Donald Barltrop Department of Child Health Westminister Children's Hospital London SW1P 2NS England Dr. A. C. Chamberlain Environmental and Medical Sciences Division Atomic Energy Research Establishment Harwell 0X11 England Dr. Irv Billick Gas Research Institute 8600 West Bryn Mawr Avenue Chicago, IL 60631 Dr. Neil Chernoff Division of Developmental Biology MD-67 U.S. Environmental Protection Agnecy Research Triangle Park, NC 27711 xx ix TEH 0411855 DUPQ50452453 Dr. Julian Chisolm Baltimore City Hospital 4940 Eastern Avenue Baltimore, MD 21224 Dr. Virgil Farm Department of Anatomy and Cytology Dartmouth Medical School Hanover, NH 03755 Mr. Jerry Cole International Lead-Zinc Research Organization 292 Madison Avenue New York, NY 10017 Dr. Max Costa Department of Pharmacology University of Texas Medical School Houston, TX 77025 Dr. Anita Curran Commissioner of Health Westchester County White Plains, NY 10607 Dr. Jack Dean Immunobiology Program and Immunotoxicology/Cell Biology Program CUT P.0. Box 12137 Research Triangle Park, NC 27709 Dr. Fred deSerres Assoc. Director for Genetics NIEHS P.O. Box 12233 Research Triangle Park, NC 27709 Dr. Robert Dixon Laboratory of Reproductive and Developmental Toxicology NIEHS P.O. Box 12233 Research Triangle Park, NC 27709 Dr. Alf Fischbein Environmental Sciences Laboratory Mt. Sinai School of Medicine New York, NY 10029 Dr. Jack Fowle Reproductive Effects Assessment Group U.S. Environmental Protection Agency RD-689 Washington, DC 20460 Dr. Bruce Fowler Laboratory of Pharmocology NIEHS P.O. Box 12233 Research Triangle Park, NC 27709 Mr. Eric Goldstein Natural Resources Defense Council, Inc. School of Allied Health 122 E. 42nd Street New York, NY 10168 Dr. Harvey Gonick 1033 Gayley Avenue Suite 116 Los Angeles, CA 90024 Dr. Robert Goyer Deputy Director NIEHS P.O. Box 12233 Research Triangle Park, NC 27709 Dr. Claire Ernhart Department of Psychiatry Cleveland Metropolitan General Hospital Cleveland, OH 44109 Dr. Sergio Fachetti Section Head - Isotope Analysis Chemistry Division Joint Research Center 121020 Ispra Varese, Italy Dr. Stanley Gross Hazard Evaluation Division Toxicology Branch U.S. Environmental Protection Agency Washington, DC 20460 Dr. Paul Hammond University of Cincinnati Kettering Laboratory 3223 Eden Avenue Cincinnati, OH 45267 xxx TEH 0411856 DUP050452454 Dr. Ronald D. Hood Department of Biology The University of Alabama University, AL 35486 Dr. V. Houk Centers for Disease Control 1600 Clifton Road, NE Atlanta, GA 30333 Dr. Loren Koller School of Veterinary Medicine University of Idaho Moscow, ID 83843 Dr. Kristal Kostial Institute for Medical Research and Occupational Health Yu-4100 Zagreb Yugoslavia Dr. Lawrence Kupper Department of Biostatistics UNC School of Public Health Chapel Hill, NC 27514 Dr. Phillip Landrigan Division of Surveillance, Hazard Evaluation and Field Studies Taft Laboratories - NIQSH Cincinnati, OH 45226 Dr. David Lawrence Microbiology and Immunology Dept. Albany Medical College of Union University Albany, NY 12208 Dr. Jane Lin-Fu Office of Maternal and Child Health Department of Health and Human Services Rockville, MD 20857 Dr. Don Lynam Air Conservation Ethyl Corporation 451 Florida Boulevard Baton Rouge, LA 70801 Dr. Kathryn Mahaffey Division of Nutrition Food and Drug Administration 1090 Tusculum Avenue Cincinnati, OH 45226 Dr. Ed McCabe Department of Pediatrics University of Wisconsin Madison, WI 53706 Dr. Paul Mushak Department of Pathology UNC School of Medicine Chapel Hill, NC 27514 Dr. Chuck Nauman Exposure Assessment Group U.S. Environmental Protection Agency Washington, DC 20460 Dr. Herbert L. Needleman Children's Hospital of Pittsburgh Pittsburgh, PA 15213 Dr. H. Mitchell Perry V.A. Medical Center St. Louis, M0 63131 Dr. Charles G. Pfieffer Engineering Department Engineering Services Division E I. duPont, Incorporated Wilmington, DE 19898 Dr. Jack Pierrard E.I. duPont de Nemours and Company, Inc. Petroleum Laboratory Wilmington, DE 19898 Dr. Sergio Piomelli Columbia University Medical School Division of Pediatric Hematology and Oncology New York, NY 10032 XXXI ______ TEH 0411857 DUP050452455 .............: .'......... ............ Dr. Magnus Piscator Department of Environmental Hygiene The Karolinska Institute 104 01 Stockholm Sweden Dr. Robert Putnam International Lead-Zinc Research Organization 292 Madison Avenue New York, NY 10017 Dr. Michael Rabinowitz Children's Hospital Medical Center 300 Longwood Avenue Boston, MA 02115 Dr. Harry Roels Unite de Toxicologie Industrielle et Medicale Universite de Louvain Brussels, Belgium Dr. John Rosen Division of Pediatric Metabolism Albert Einstein College of Medicine Montefiore Hospital and Medical Center 111 East 210 Street Bronx, NY 10467 Dr. Stephen R. Schroeder Division for Disorders of Development and Learning Biological Sciences Research Center University of North Carolina Chapel Hill, NC 27514 Dr. Anna-Maria Seppalainen Institutes of Occupational Health Tyoterveyslaitos Haartmaninkatu 1 00290 Helsinki 29 Finland Dr. Ellen Silbergeld Environmental Defense Fund 1525 18th Street, NW Washington, DC 20036 Dr. Ron Snee E.I. duPont Nemours and Company, Inc. Engineering Department L3267 Wilmington, DE 19898 Dr. Gary Ter Haar Toxicology and Industrial Hygiene Ethyl Corporation 451 Florida Boulevard Baton Rouge, LA 70801 Dr. Ian von Lindern Department of Chemical Engineering University of Idaho Moscow, ID 83843 Dr. Richard P. Weeden V.A. Medical Center Tremont Avenue East Orange, NJ 07019 m ajMiai issr^ I xxx i i TEH 041V DUP050452456 9. QUANTITATIVE EVALUATION OF LEAD AND BIOCHEMICAL INDICES OF LEAD EXPOSURE IN PHYSIOLOGICAL MEDIA 9.1 INTRODUCTION To understand the effects of an agent on an organism and, in particular, to formulate statements of dose-effect relationships, one must be able to assess quantitatively the organ ism's degree of exposure to the substance. In the case of lead. Internal biologically based measures provide a more accurate indication of exposure than do external measures such as am bient air concentrations. Internal measures may be either direct--e.g., the level of lead in a biological medium such as blood, calcified tissue, etc.--or indirect--e.g., the level of some biochemical parameter or "indicator" closely associated with internal lead exposure. This chapter examines the merits and weaknesses of various measurement methods as they are currently used to assess lead exposure. Quantitative analysis involves a number of discrete steps, all of which are important contributors to the quality of the final result: (1) sample collection and transmission to the laboratory; (2) laboratory manipulation of samples, physically and chemically, before ana lysis by instruments; (3) instrumental analysis and quantitative measurement; and (4) esta blishment of relevant criteria for accuracy and precision, namely, internal and external qua lity assurance checks. Each of these steps is discussed in this chapter in relation to the measurement of lead exposure. Clearly, the definition of "satisfactory analytical method" for lead has changed over the years, paralleling (1) the evolution of more sophisticated instrumentation and procedures, (2) a greater awareness of such factors as background contamination and loss of the element from samples, and (3) development of new statistical methods to analyze data. For example, current methods of lead analysis, such as anodic stripping voltammetry, background-corrected atomic absorption spectrometry, and particularly isotope-dilution mass spectrometry, are more sensi tive and specific than the older classical approaches. Increasing use of the newer methods would tend to result in lower lead values being reported for a given sample. Whether this trend in analytical Improvement can be isolated from other variables such as temporal changes in exposure is another matter. Because lead is ubiquitously distributed as a contaminant, the constraints (i.e., ultra clean, ultra-trace analysis) placed upon a laboratory attempting analysis of geochemical sam ples of pristine origin, or of extremely low lead levels in biological samples such as plasma, are quite severe (Patterson, 1980). Very few laboratories can credibly claim such capability. 9-1 TEH 0411859 DUP050452457 gljagSJSKgaRfeiH.xHf'-- Ideally, similar standards of quality should be adhered to across the rest of the analytical spectrum. With many clinical, epidemiological, and experimental studies, however, these standards may be unrealistic given the practical limitations and objectives of the studies. Laboratory performance is but one part of the quality equation; the problems of sampling are equally important but less subject to tight control. The necessity of rapidly obtaining a blood sample in cases of suspected lead poisoning, or of collecting hundreds or thousands of blood samples in urban populations, limits the number of sampling safeguards that can be rea listically achieved. Sampling in this context will always be accompanied by a certain amount of analytical "suspicion." Furthermore, a certain amount of biological lead analysis data is employed for comparative purposes, as in experimental studies concerned with the relative In crease in tissue burden of lead associated with increases in doses or severity of effects. In addition, any major compromise of an analytical protocol may be statistically discernible. Thus, analysis of biological media for lead must be done under protocols that minimize the risk of Inaccuracy. Specific accuracy and precision characteristics of a method in a parti cular report should be noted to permit some judgment on the part of the reader about the in fluence of methodology on the reported results. The choice of measurement method and medium for analysis is dictated both by the type of information desired and by technical or logistical considerations. As noted elsewhere in this document, whole blood lead reflects recent or continuing exposure, whereas lead in mineralized tissue, such as deciduous teeth, reflects an exposure period of months and years. While urine lead values are not particularly good correlates of lead exposure under steady-state condi tions in populations at large, such measurements may be of considerable clinical value. In ac quiring blood samples, the choice of venipuncture or finger puncture will be governed by such factors as cost and feasibility, contamination risk, and the biological quality of the sample. The use of biological indicators that strongly correlate with lead burden may be more desira ble, since they provide evidence of actual response and, together with blood lead data, pro vide a less risky diagnostic tool for assessing lead exposure. 9.2 DETERMINATIONS OF LEAD IN BIOLOGICAL MEDIA 9.2.1 Sampling and Sample Handling Procedures for Lead in Biological Media Lead analysis in biological media requires careful sample collection and handling for two reasons: (1) lead occurs at trace levels in most indicators of subject exposure, even under conditions of high lead exposure; and (2) such samples must be obtained against a backdrop of " ftjL, K$g>L 9-2 TEH 0411860 ^ DUP050452458 pervasive contamination, the full extent of which may still be unrecognized by many laborato ries. The reports of Speecke et al. (1976), Patterson and Settle (1976), Murphy (1976), Berman (1976), and Settle and Patterson (1980) review detailed aspects of the problems of sampling and subsequent sample handling in the laboratory. These reports indicate that the normal pre cautions taken during sampling (detailed below for clinical and epidemiological studies) should not be considered absolute, but rather as what is practical and feasible. They further indicate that the inherent sensitivity or accuracy of a given method or instrument may be less of a determining factor in the overall analysis than the quality of sample collection and handling. 9.2.1.1 Blood Sampling. Samples for blood lead determination may be collected by venipunc ture (venous blood) or fingertip puncture (capillary blood). Collection of capillary versus venous blood is usually decided by a number of factors, including the feasibility of obtaining samples during the screening of many subjects and the difficulty of securing subject com pliance, particularly in the case of children and their parents. Furthermore, capillary blood may be collected as discrete quantities in small-volume capillary tubes or as spots on filter paper disks. With capillary tubes, obtaining good mixing with anticoagulant to avoid clotting is important, as is the problem of lead contamination of the tube. The use of filter paper requires the selection of paper with uniform composition, low lead content, and uniform blood dispersal characteristics. Whether venous or capillary blood is collected, much care must be exercised in cleaning the site before puncture as well as in selecting lead-free receiving containers. Cooke et al. (1974) employed vigorous scrubbing with a low-lead soap solution and rinsing with deionized water, while Marcus et al. (1975) carried out preliminary cleaning with an ethanolic citric acid solution followed by rinsing with 70-percent ethanol. Vigor in cleaning the puncture site is probably as important as the choice of any particular cleaning agent. Marcus et al. (1977) have noted that in one procedure for puncture site preparation, where the site is covered with wet paper towels, contamination will occur if the paper towels are made from re cycled paper. Recycled paper retains a significant amount of lead. In theory, capillary and venous blood lead levels should be virtually identical. However, the literature indicates that some differences, which mainly reflect sampling problems, do arise in the case of capillary blood. A given amount of contaminant has a greater Impact on a lOO-pl fingerstick sample than on a 5-ml sample of venous blood. Finger-coating techniques may reduce some of the contamination (Mitchell et al., 1974). An additional problem is the presence of lead in the anticoagulants used to coat capillary tubes. Also, lower values of capillary versus venous blood lead may reflect "dilution" of the sample by extracellular fluid 9-3 TEH 0411861 DUP050452459 Mm from excessive compression of the puncture site. When Joselow and Bogden (1972) compared a method using finger puncture and spotting onto filter paper with a procedure using venous blood and Bessel's procedure (1968) for flame atomic absorption spectrometry (see Section n 9.2.2.1), they obtained a correlation coefficient of r = 0.9 (range, 20-46 pg/dl). Similarly, lilllll Cooke et al. (1974) found an r value of 0.8 (no range given), while Mitchell et al. (1974) ob iiP^ tained a value of 0.92 (10-92 pg/dl). Mahaffey et al. (1979) found that capillary blood' levels in a comparison test were approximately 20 percent higher than corresponding venous' blood levels in the same subjects, presumably reflecting sample contamination. Similar eleva tions have been described by DeSilva and Donnan (1980). Carter (1978) has found that blood samples with lower hemoglobin levels may spread onto filter paper differently from normal hemoglobin samples, requiring correction in quantification to obtain reliable values. This BlBi |H[ HN complication should be kept in mind when considering children, who are frequently prone te h iron-deficiency anemia. The relative freedom of the blood container from interior surface lead and the presence of lead in the anticoagulant to be added to the blood are important considerations in venous sampling. For studies focusing on "normal" ranges, such tubes may add some lead to blood and still meet certification requirements. The "low-lead" heparinized blood tubes commercially available (blue stopper Vacutainer, Becton-Dickinson) were found to contribute less than 0.2 pg/dl to whole blood samples (Rabinowitz and Needleman, 1982). Nackowski et al. (1977) sur veyed a large variety of commercially available blood tubes for lead and other metal contami nation. Lead uptake by blood over time from the various tubes was minimal with the "low-lead" Vacutainer tubes and with all but four of the other tube types. In the large survey of Mahaffey et al. (1979), 5-ml Monoject (Sherwood) or 7-ml lavender-top Vacutainer (Becton- Dickinson) tubes were satisfactory. However, when more precision is needed, tubes are best recleaned in the laboratory and lead-free anticoagulant added (although this would be less convenient for sampling efficiency than the commercial tubes). In addition, blank levels for 5*1 1 every batch of samples should be verified. 9.2.1.2 Urine Sampling. Urine samples require collection using lead-free containers and caps, as well as the addition of a low-lead bactericide if samples are to be stored. While not always feasible, 24-hr samples should be obtained because they level out any effect of vari ation In excretion over time. If spot sampling is done, lead levels should be expressed per unit creatinine, or corrected for a constant specific gravity, if greater than 1.010. 9.2.1.3 Hair Sampling. The usefulness of hair lead analysis depends on the manner of samp jjj|ling. Hair samples should be removed from subjects by a consistent method, either by a pre pap determined length measured from the skin or by using the entire hair. Hair should be placed 1811 98in air-tight containers for shipment or storage. For segmental analysis, the entire bai'", length is required. 1.1 9-4 TEH 041167 DUP050452460 9.2.1.4 Mineralized Tissue. An important consideration in deciduous tooth collection is con sistency in the type of teeth collected from various subjects. Fosse and Justesen (1978) re ported no difference in lead content between molars and incisors, and Chatman and Wilson (1975) reported comparable whole tooth levels for cuspids, incisors, and molars. On the other hand, Mackie et al. (1977) and Lockeretz (1975) noted levels varying with tooth type, with a statistically significant difference (Mackie et al., 1977) between second molars (lowest levels) and incisors (highest levels). That the former two studies found rather low overall lead levels across groups, while Mackie et al. (1977) reported higher values, suggests that dentition differences in lead content may be magnified at relatively higher levels of ex posure. Delves et al. (1982), comparing pairs of central incisors or pairs of central and lateral incisors from the same child, found that lead content may even vary within a specific type of tooth. These data suggest the desirability of acquiring two teeth per subject to get an average lead value. Teeth containing fillings or extensive decay are best eliminated from analysis. Mackie et al. (1977) discarded decayed teeth if the extent of decay exceeded approximately 30 per cent. 9.2.1.5 Sample Handling in the Laboratory. The effect of storage on lead content is a poten tial problem with blood samples. During storage, dilute aqueous solutions of lead surrender a sizable portion of the lead content to the container surface, whether glass or plastic, unless the sample is acidified (Issaq and Zielinski, 1974; Unger and Green, 1977). Whether there is a comparable effect, or comparable extent of such an effect, with blood is not clear. Unger and Green (1977) claim that lead loss from blood to containers parallels that seen with aque ous solutions, but their data do not support this assertion. Moore and Meredith (1977) used isotopic lead spiking (203Pb) with and without carrier in various containers at differing tem peratures to monitor lead stability in blood over time. The only material loss occurred with soda glass at room temperature after 16 days. Nackowski et al. (1977) found that "low-lead" blood tubes, while quite satisfactory in terms of sample contamination, began to show transfer of lead to the container wall after 4 days. Meranger et al. (1981) studied movement of lead, spiked to various levels, to containers of various composition as a function of temperature and time. In all cases, reported lead loss to containers was significant. However, problems exist with the above reports. Spiked samples probably are not Incorporated into the same bio chemical environment as lead inserted iji vivo. Also, Nackowski et al. (1977) did not indicate whether the blood samples were kept frozen or refrigerated between testing intervals. Mitchell et al. (1972) found that the effect of blood storage depends on the method of analy sis, with lower recoveries of lead from aged blood using the Hesse! (1968) method. 9-5 TEH 0411863 DUP050452461 Lerner (1975) collected blood samples (35 originally) from a single subject into leadfree tubes and, after freezing, forwarded them in blind fashion to a certified testing labor atory over a period of 9 months. Four samples were lost, and one was rejected as grossly con taminated (4 standard deviations from mean). Of the remaining 30 samples, the mean was 18.3 pg/dl with a standard deviation (S.O.) of 3.9. The analytical method had a precision of 3.5 pg/dl (S.D. = 1) at normal levels of lead, suggesting that the overall stability of the sam ples' lead content was good. Boone et al. (1979) reported that samples frozen for periods of less than 1 year showed no effect of storage, while Piscator (1982) noted no change in low levels (<10 pg/dl) when samples were stored at -20C for 6 months. Based on the above data, blood samples to be stored for any period of time should be frozen rather than refrigerated, with care taken to prevent breaking the tube during freezing. Teeth and hair samples, when stored in containers to minimize contamination, are indefinitely stable. The actual site of analysis should be as free from lead as possible. Given the limited availability of an "ultra-clean" facility such as that described by Patterson and Settle (1976), the next desirable level of laboratory is the "Class 100" facility, in which fewer than 100 airborne particles are greater than 0.5 pm in diameter. These facilities employ highefficiency particulate air filtering and laminar air flow (with movement away from sample handling areas). Totally inert surfaces in the working area and an antechamber for removing contaminated clothes, appliance cleaning, etc., are other necessary features. All plastic and glass ware coming into contact with samples should be cleaned rigorously and stored away from dust contact, and materials such as ashing vessels should permit minimal lead leaching. In this regard. Teflon or quartz ware is preferable to other plastics or borosilicate glass (Patterson and Settle, 1976). Reagents, particularly for chemical degradation of biological samples, should be both certified and periodically tested for quality. Several commercial grades of reagents are available, although precise work may require doubly purified materials from the National Bureau of Standards (NBS). These reagents should be stored with a minimum of surface contami nation around the top of the containers. For a more detailed discussion of appropriate laboratory practices, the reader may con sult LaFleur (1976). 9.2.2 Methods of Lead Analysis Detailed technical discussion of the array of instruments available to measure lead in blood and other media is outside the scope of this chapter (see Chapter 4). This discussion is structured more appropriately to those aspects of methodology dealing with relative sensi tivity, specificity, accuracy, and precision. While acceptance of international standardized # 9-6 TEH 041186* DUP050452462 (SI) units for expressing lead levels in various media is increasing, units familiar to clini cians and epidemiologists will be used here. (To convert pg Pb/dl blood to SI units [grades/ liter], multiply by 0.048.) Many reports over the years have purported to offer satisfactory analysis of lead in bio logical media, but in fact have shown rather meager adherence to criteria for accuracy and precision or have shown a lack of demonstrable utility across a wide spectrum of analytical applications. Therefore, discussion in this section is confined to ''definitive" and reference methods for lead analysis, except for a brief treatment of the traditional but now widely sup planted colorimetric method. Using the definition of Cali and Reed (1976), a definitive method is one in which all major or significant parameters are related by solid evidence to the absolute mass of the ele ment with a high degree of confidence. A reference method, by contrast, is one of demonstra ted accuracy, validated by a definitive method, and arrived at by consensus through perfor mance testing by a number of different laboratories. In the case of lead in biological media, the definitive method is isotope-dilution mass spectrometry (IDMS). IDMS is so accurate be cause all manipulations are on a weight basis involving simple procedures. The measurements entail only ratios and not the absolute determinations of the isotopes involved, which greatly reduces Instrumental corrections or errors. No interferences occur from sample matrix or other elements, and the method does not depend on recovery. Reproducible results to a pre cision of one part in 104 or 105 are routine with specially designed instruments. In terms of reference methods for lead In biological media, such a label is commonly attached to atomic absorption spectrometry (AAS) in its various instrumentation/ methodology configurations and to the electrochemical technique, anodic stripping voltammetry (ASV). These have been termed reference methods Insofar as their precision and accuracy can be veri fied or calibrated against IDMS. Other methods that are recognized for general trace-metal analysis are not fully applica ble to biological lead or have inherent shortcomings. X-ray fluorescence analysis lacks the requisite sensitivity for media with low lead content, and the associated sample preparation may present a high contamination risk. A notable exception may be X-ray fluorescence analysis of teeth or bone i_n situ as discussed below. Neutron-activation analysis is the method of choice with many elements, but it is not technically feasible for lead analysis because of the absence of long-lived isotopes. 9.2.2.1 Lead Analysis in Whole Blood. The first generally accepted technique for quantifying lead in whole blood and other biological media was a colorimetric method that involved spectrophotometric measurement based on the binding of lead to a chromogenic agent to yield a chromophoric complex. The complexing agent has typically been dithizone, 1,5-diphenylthiocarbazone, yielding a lead complex that is spectrally measured at 510 nm. 9-7 TEH 0411865 DUP050452463 Two variations of the spectrophotometric technique used when measuring low levels of lead ! have been the procedures of the U.S. Public Health Service (USPHS) (National Academy of Sciences, 1972) and of the American Public Health Association (APHA) (1955). In both, venous blood or urine is wet ashed using concentrated nitric acid of low lead content followed by ad justment of the ash with hydroxyl amine and sodium citrate to a pH of 9-10. Cyanide ion if* added and the solution extracted with dithizone in chloroform. Back extraction removes thf lead into dilute nitric acid; the acid layer is treated with ammonia, then cyanide, and re'' extracted with dithizone in chloroform. The extracts are read in a spectrophotometer at 51Q nra. Bismuth interference is handled (APHA variation) by removal with dithizone at pH 3.4. According to Lerner (1975), the analytical precision in the "normal" range is about 3.5 pg/dl (S.D. = 1), using 5 ml of sample. The most accurate and precise method for lead measurement in blood is IDMS. As typified by the report of Mach!an et al. (1976), whole blood samples are accurately weighed, and | weighed aliquot of 206Pb-enriched isotope solution is added. After sample decomposition with ' ultra-pure nitric and perchloric acids, samples are evaporated, residues are taken up in di-r lute lead-free hydrochloric acid (HC1), and lead is isolated using anion-exchange columns. ' Column eluates are evaporated with the above acids, and lead is deposited onto high-purity platinum wire from dilute perchloric acid. The 206Pb/2O8Pb ratio is then determined by ther mal ionization mass spectrometry. Samples without added isotope and reagent blanks are also carried through the procedure. In terms of precision, the 95-percent confidence level for l-1 lead samples overall is within 0.15 percent. Because of the expense incurred by the require- l! ments for operator expertise, the amount of time involved, and the high standard of laboratory cleanliness, IDMS is mainly of practical value in the development of standard reference ma terials and for the verification of other analytical methods. tr; - AAS is widely used for lead measurements in whole blood, with sample analysis involving analysis of venous blood with chemical degradation, analysis of liquid samples with or without degradation, and samples applied to filter paper. It is thus the most flexible for samples already collected or subject to manipulation. By means of flame or electrothermal excitation, ionic lead in a matrix is first vaporized and then converted to the atomic state, followed by resonance absorption from either a hollow cathode or electrodeless discharge lamp generating lead absorption lines at 217.0 and 283.3 nm. After monochrometer separation and photomulti plier enhancement of the differential signal, lead content is measured electronically. The earliest methods of AAS analysis involved the aspiration of ashed blood samples into a flame, usually subsequent to extraction into an organic solvent, to enhance sensitivity by preconcentration. Some methods did not involve digestion steps prior to solvent extraction m m 9-8 (Kopito et al., 1974). Of these various flame AAS methods, Hessel's (1968) technique con tinues to be used with some frequency. Currently, lead measurement in blood by AAS employs several different methods that permit greater sensitivity, precision, and economy of sample and time. The flame method of Delves (1970), called the "Delves cup" procedure, usually involves delivery of discrete small samples (S100 pi) of unmodified whole blood to nickel cups, with subsequent drying and peroxide decom position of organic content before positioning in the flame. The.marked enhancement of sen sitivity over conventional flame aspiration results from immediate, total consumption of the sample and generation of a localized population of atoms. In addition to discrete blood vol umes, blood-containing filter paper disks have been used (Joselow and Bogden, 1972; Cernik and Sayers, 1971; Piomelli et al., 1980). Among the several modifications of the Delves method are that of Ediger and Coleman (1972), in which dried blood samples in the cups are pre ignited to destroy organic matter by placement near the flame in a precise, repeatable manner, and the variation of Barthel et al. (1973), in which blood samples are mixed with dilute nitric acid in the cups followed by drying in an oven at 200C and charring at 450C on a hot plate. A number of laboratories eschew even these modifications and follow dispensing and drying with direct placement of the cup into the flame (e.g., Mitchell et al., 1974). The Delves cup procedure may require correction for background spectral interference. This cor rection is usually achieved using instrumentation equipped at a nonresonance absorption line. While the 217.0-nm line of lead is less subject to such interference, precise work is best done with correction. This method as applied to whole blood lead appears to have an oper ational sensitivity down to 1.0 pg Pb/dl, or somewhat below when competently employed, and a relative precision of approximately 5 percent in the range of levels encountered In the United States. AAS methods using electrothermal (furnace) excitation in lieu of a flame can be approxi mately tenfold more sensitive than the Delves procedure. A number of reports describing whole blood lead analysis have appeared in the literature (Lawrence, 1982, 1983). Because of in creased sensitivity, the "flameless" AAS technique permits the use of small blood volumes (1-5 pi) with samples undergoing drying and dry ashing in situ. Physicochemical and spectral interferences are inherently severe with this approach, requiring careful background cor rection. In one flameless AAS configuration, background correction exploits the Zeeman ef fect, where correction is made at the specific absorption line of the element and not over a band-pass region, as is the case with the deuterium arc. While control of background inter ference up to 1.5 molecular absorbance is claimed with the Zeeman system (Koizumi and Yasuda, 1976), employing charring before atomization is technically preferable. Hinderberger et al. (1981) used dilute ammonium phosphate solution to minimize chemical interference in their fur nace AAS method. 9-9 TEH 0411867. DUP050452465 Precision can be a problem in the flameless technique unless careful attention is paid to the problem of sample diffusibility over and into the graphite matrix of the receiving recep tacle (tube, cup, or rod). With the use of diluted samples and larger applied volumes, the relative precision of this method can approach that of the Delves technique (Delves, 1977). In addition to the various AAS methods noted above, electrochemical techniques have been applied to blood lead analysis. Electrochemical methods, in theory, differ from AAS methods in that the latter are ''concentration" methods regardless of sample volumes available, while electrochemical analysis involves bulk consumption of sample and hence would have infinite sensitivity, given an infinite sample volume. This intrinsic property is of little practical advantage given usual limits of sample volume, instrumentation design, and blanks. The most widely used electrochemical method for lead measurement in whole blood and other biological media is ASV, which is also probably the most sensitive because it involves an elec trochemical preconcentration (deposition) step in the analysis (Matson and Roe, 1966; Matson et al., 1971). In this method, samples such as whole blood (50-100 pi) are preferably, but not commonly, wet ashed and reconstituted in dilute acid or made electro-available with metal exchange reagents. Using freshly prepared composite electrodes of mercury film deposited on carbon, lead is plated out from the solution for a specific amount of time and at a selected negative voltage. The plated lead is then reoxidized in the course of anodic sweeping, gene rating a current peak that may be recorded on a chart or displayed on commercial instruments as units of concentration (pg/dl). One alternative to the time and space demands of wet ashing blood samples is the use of metal exchange reagents that displace lead from binding sites in blood by competitive binding (Morrell and Giridhar, 1976; Lee and Meranger, 1980). In one commercial preparation, this re agent consists of a solution of calcium, chromium, and mercuric ions. Use of the metal ex change reagent adds a chemical step that must be carefully controlled for full recovery of lead from the sample. The working detection limit of ASV for blood is comparable to that of the AAS flameless methods, while the relative precision is best with prior sample degradation, approximately 5 percent. The precision is less when the blood samples are run directly with the ion exchange reagents (Morrell and Giridhar, 1976), particularly at the low end of "normal" blood lead values. While AAS methods require attention to various spectral interferences to achieve satisfactory performance, electrochemical methods such as ASV require consideration of such factors as the effects of co-reducible metals and agents that complex lead and alter its re duction-oxidation (redox) potential properties. Chelants used In therapy, particularly peni cillamine, may interfere, as does blood copper, which may be elevated in pregnancy and during such disease states as leukemia, lymphoma, and hyperthyroidism (Berman, 1981). Slli i' 9-10 TEH 0411868 DUP050452466 if*'- Correction of whole blood lead values for hematocrit, although carried out in the past, is probably not appropriate and not commonly done at present. While the erythrocyte is the carrier for virtually all lead in blood, the saturation capacity of the red blood cell (RBC) for lead is so high that it can still carry lead even at highly toxic levels (Kochen and Greener, 1973). Kochen and Greener (1973) also showed that acute or chronic dosing at a given lead level in rats with a wide range of hematocrits (Induced by bleeding) gave similar blood lead values. Rosen et al. (1974), based on studies of hematocrit, plasma, and whole blood lead in children, noted hematocrit correction was not necessary, a view supported by Chisolm (1974). 9.2.2.2 Lead in Plasma. While virtually all of the lead present in whole blood is bound to the erythrocyte (Robinson et al., 1958; Kochen and Greener, 1973), lead in plasma is trans ported to affected tissues. Therefore, every precaution must be taken to use nonhemolyzed blood samples for plasma isolation. The very low levels of lead in plasma require that more attention be paid to "ultra-clean" methods. Rosen et al. (1974) used flameless AAS and microliter samples of plasma to measure plasma lead, with background correction for the smoke signal generated for the unmodified sample. Cavalleri et al. (1978) used a combination of solvent extraction of modified plasma with pre concentrating and flameless AAS. These authors noted that the method used by Rosen et al. (1974) permitted less precision and accuracy than did their technique, because a significantly smaller amount of lead was delivered to the furnace accessory. DeSilva (1981), using a technique similar to that of Cavalleri et al. (1978), but col lecting samples in heparinized tubes, claimed that the use of ethylenediaminetetraacetic acid (EDTA) as anticoagulant disturbs the cell-plasma distribution of lead enough to yield errone ous data. Much more care was given in this procedure to background contamination. In both cases, increasing levels of plasma lead were measured with increasing whole blood lead, sug gesting an equilibrium ratio that contradicts the data of Rosen et al. (1974). They found a fixed level of 2-3 pg/dl plasma over a wide range of blood lead values. However, the actual levels of lead in plasma in the DeSilva (1981) study were much lower than those reported by I Cavalleri et al. (1978). Using IDMS and sample collection/manipulation in an "ultra-clean" facility, Everson and l Patterson (1980) measured the plasma lead levels in two subjects, a control and a lead-exposed worker. The control had a plasma lead level of 0.002 pg/dl, several orders of magnitude lower than that seen with studies using less precise analytical approaches. The lead-exposed worker had a plasma level of 0.2 pg/dl. Several other reports in the literature using IDMS noted somewhat higher values of plasma lead (Manton and Cook, 1979; Rabinowitz et al., 1974), which Everson and Patterson (1980) have ascribed to problems of laboratory contamination. 9-11 TEH 0411869 DUP050452467 Using tracer lead to minimize the impact of contamination results in a value of 0.15 pg/d (Rabinowitz et al., 1974). With appropriate plasma lead methodology, reported lead levels are extremely low, the de gree varying with the methods used to measure such concentrations. While the data of Everso and Patterson (1980) were obtained from only two subjects, it seems unlikely that using mol-e subjects would result in a plasma lead range extending upward to the levels seen with ordin methodology in ordinary laboratory surroundings. The above considerations are important when'^ discussing appropriate methodology for plasma analysis, and the Everson and Patterson (1980) report indicates that some doubt surrounds results obtained with conventional methods, though not the primary focus of their study, the values obtained by Everson and Patterson (1980) for whole blood lead, unlike the data for plasma, are within the ranges for unexposed (11 pg/dl) and exposed (80 pg/dl) subjects generally reported with other methods. This agree ment would suggest that, for the most part, reported values do actually reflect jin vivo blooj lead levels rather than sampling problems or inaccurate methods. -`4 V* 9.2.2.3 Lead in Teeth. When analyzing shed deciduous or extracted permanent teeth, some in- vestigators have used the whole tooth after surface cleaning to remove contaminating lead:4gS|| (e.g., Moore et al., 1978; Fosse and Justesen, 1978; Mackie et al., 1977), while others havmeasured lead in dentine (e.g., Shapiro et al., 1973; Needleman et al., 1979; Al-Naimi et al., 'V'L' 1980). Several reports (Grandjean et al., 1979; Shapiro et al., 1973) have also described the O.* analysis of circumpulpal dentine, that portion of the tooth found to have the highest relative * fraction of lead. Needleman et al. (1979) separated dentine by embedding the tooth in wax, 11118 is$rfollowed by thin central sagittal sectioning. The dentine was then isolated from the sawed ,V . sections by careful chiseling. n Determining mineral and organic composition of teeth and their components requires the use of thorough chemical decomposition techniques, including wet ashing and dry ashing steps and sample pulverizing or grinding. In the procedure of Steenhout and Pourtois (1981), teeth ffiL are dry ashed at 450C, powdered, and dry ashed again. The powder is then dissolved in nitric tt! acid. Fosse and Justesen (1978) reduced tooth samples to a coarse powder by crushing In a vise, followed by acid dissolution. Oehme and Lund (1978) crushed samples to a fine powder in an agate mortar and dissolved the samples in nitric acid. Mackie et al. (1977) and Moort et al. (1978) dissolved samples directly in concentrated acids. Chatman and Wilson (1975) and Needleman et al. (1974) carried out wet ashing with nitric acid followed by dry ashing 450C. Oehme and Lund (1978) found that acid wet ashing of tooth samples yielded better re sults if carried out in a heated Teflon bomb at 200C. " ,'s. With regard to methods of measuring lead in teeth, AAS and ASV have been employed nost`:...3. often. With the AAS methods, the high mineral content of teeth tends to argue for isolating'n ,*V\ 1. M ,m9-12 1PPSB TEH 0411870 A DUP050452468 lead from this matrix before analysis. In the methods of Needleman et al. (1974) and Chatman and Wilson (1975), ashed residues in nitric acid were treated with ammonium nitrate and ammo nium hydroxide to a pH of 2.8, followed by dilution and extraction with a methyl isobutyl ketone solution of ammonium pyrrolidinecarbodithioate. Analysis was by flame AAS, using the 217.0-nm lead-absorption line. A similar procedure was employed by Fosse and Justesen (1978). ASV has been successfully used in tooth lead measurement (Shapiro et al., 1973; Needleman et al., 1979; Oehme and Lund, 1978). As typified by the method of Shapiro et al. (1973), sam ples of dentine were dissolved in a small volume of low-lead concentrated perchloric acid and diluted (5.0 ml) with lead-free sodium acetate solution. With deoxygenation, samples were analyzed in a commercial ASV unit, using a plating time of 10 min at a plating potential of -1.05 V. Anodic sweeping was at a rate of 60 mV/sec with a variable current of 100-500 pA. Since lead content of teeth is higher than in most samples of biological media, the relative precision of analysis with appropriate accommodation of the matrix effect, such as the use of matrix-matched standards, in the better studies indicates a value of approximately 5-7 per cent. In an analysis of lead levels in permanent teeth of Swedish subjects, Moller et al. (1982) used particle-induced X-ray emission (PIXE). While this method permits analysis with minimal contamination risk, it measures only coronal dentine, which is relatively less re vealing about cumulative exposure than secondary or circumpulpal dentine. All of the above methods involve shed or extracted teeth and consequently provide a ret rospective determination of lead exposure. In Bloch et al.'s (1976) procedure, tooth lead is measured in situ using an X-ray fluorescence technique. A collimated beam of radiation from 57Co was allowed to irradiate the upper central Incisor teeth of the subject. Using a rela tively safe 100-sec Irradiation time and measurement of Kat and Ka2 lead lines via a germanium diode and a pulse-height analyzer for signal processing, lead levels of 15 ppm or higher could be measured. Multiple measurement by this method would be very useful in prospective studies because it would show the "ongoing" rate of Increase in body lead burden. Furthermore, when combined with serial blood sampling, it would provide data for blood lead-tooth lead relation ships. 9.2.2.4 Lead in Hair. Hair constitutes a noninvasive sampling source with virtually no prob lems with sample stability on extended storage. However, the advantages of accessibility and stability are offset by the problem of assessing external contamination of the hair surface by atmospheric fallout, hand dirt, lead in hair preparations, etc. Thus, such samples are prob ably of less value overall than those from other media. The various methods that have been employed for removal of external lead have been re viewed (Chatt et al., 1980; Gibson, 1980; Chattopadhyay et al. , 1977). Cleaning techniques obviously should be vigorous enough to remove surface lead but not so vigorous as to remove 9-13 TEH 0411871 DUP050452469 the endogenous fraction. To date, no published cleaning procedure has been proven reliable enough to permit acceptance of reported levels of lead in hair. Such a demonstration would! have to use lead isotopic studies with both surface and endogenous isotopic lead removal moni tored as a function of a particular cleaning technique. 9.2.2.5 Lead in Urine. Analysis of lead in urine is complicated by its relatively low con centrations (lower than in blood in many cases) as well as by the complex mixture of mineral elements present. Lead levels are higher, of course, in cases where lead mobilization '& '*18 therapy with chelants is in progress, but in these cases samples must be analyzed to account ....... , --. - -' ..... % for lead bound to chelants such as EDTA. Such analysis requires either sample ashing or the use of standards containing the chelant. Although analytical methods have been published for the direct analysis of lead in urine, samples are probably best wet ashed before analysis, using the usual mixtures of nitric plus sulfuric and/or perchloric acids. Both AAS and ASV methods have been applied to urine lead analyses, the former employing either direct analysis of ashed residues or a preliminary chelation-extraction step. With flame AAS, ashed urine samples must invariably be extracted with a chelant such as ammonium pyrrolidinecarbodithioate in methylisobutylketone to achieve reasonably satisfactory results. Furthermore, direct analysis creates mechanical problems with burner operation, due to the^ 'f>,33 high mineral content of urine, and results in considerable maintenance problems with equip- ment. The procedure of Lauwerys et al. (1975) is typical of flame AAS methods with prelimin ary lead separation. Because of the relatively greater sensitivity of graphite furnace (flameless) AAS, this variation of the method has been applied to urine analysis. In scat tered reports of such analyses, adequate performancefor direct sample analysis seems to require steps to minimize matrix interference. A typical example of one of the better direct analysis methods is that of Hodges and Skelding (1981). Urine samples were mixed with iodine solution and heated, then diluted with a special reagent containing ammonium molybdate, phos phoric acid, and ascorbic acid. Small aliquots (5 pi) were delivered to the furnace accessory i f of an AAS unit containing a graphite tube pretreated with ammonium molybdate. The relative standard deviation of the method is reported to be about 6 percent. In the method of Legotte et al. (1980), such tube treatment and sample modifications were not employed and the average precision figure was 13 percent. su;.. Compared with various AAS methods, ASV has been less frequently employed for urine lead *y K&r!* analysis. From a survey of available electrochemical methods in general, such techniques applied to urine appear to require further development. Frankeandde Zeeuw (1977) used d.ilferential-pulse ASV as a screening tool for lead and other elements in urine. Jagner et a . Ml iMscrfemni (1979) described analysis of urine lead using potentiometric stripping. In their procedure the J, , _ element was preconcentrated at a thin-film mercury electrode as in conventional ASV, but , . . 9-14 TEH 0411;&r. DUP050452470 deoxygenated samples were reoxidized with either oxygen or mercuric ions after the circuitry was disconnected. As noted in Section 9.1.1.2, if collection of 24-hr samples is not possible, spot sam pling of lead in urine can be conducted, and results should be expressed per unit creatinine. 9.2.2.6 Lead in Other Tissues. Bone samples of experimental animal or human autopsy origin require preliminary cleaning procedures for removal of muscle and connective tissue, with care being taken to minimize sample contamination. As is the case with teeth, samples must be chemically decomposed before analysis. Satisfactory instrumental methods for bone lead analy sis comprise a much smaller literature than is the case for other media. Wittmers et al. (1981) have described the measurement of lead in dry ashed (450C) bone samples using flameless AAS. Ashed samples were weighed and dissolved in dilute nitric acid containing lanthanum ion, the latter being used to suppress interference from bone elements. Small volumes (20 pi) and high calcium content required that atomization be done at 2400C to avoid condensation of calcium within the furnace. Quantification was by. the method of addi tions. Relative precision was 6-8 percent at relatively high lead content (60 pg/g ash) and 10-12 percent at levels of 14 pg/g ash or less. Ahlgren et al. (1980) described the application of X-ray fluorescence analysis to i_n vivo lead measurement in the human skeleton, using tibia and phalanges. In this technique, irra diation is carried out with a dual 57Co gamma ray source. The generated Kffl and lead lines are detected with a lithium-drifted germanium detector. The detection limit is 20 ppm. Soft organs differ from other biological media in the extent of anatomic heterogeneity as well as lead distribution, e.g., brain versus kidney. Hence, sample analysis involves either discrete regional sampling or the homogenizing of an organ. The efficiency of the latter can vary considerably, depending on the density of the homogenate, the efficiency of rupture of the formed elements, and other factors. Glass-on-glass homogenizing should be avoided because lead is liberated from the glass matrix with abrasion. AAS, in its flame or flameless variations, is the method of choice in many studies. In the procedure of Slavin et al. (1975), tissues were wet ashed and the residues taken up in di lute acid and analyzed with the furnace accessory of an AAS unit. A large number of reports representing slight variations of this basic technique have appeared over the years (Lawrence, 1982, 1983). Flame procedures, being less sensitive than the graphite furnace method, require more sample than may be available or are restricted to measurement in tissues where levels are relatively high, e.g., kidney. In the method of Farris et al. (1978), samples of brain, liver, lung, or spleen (as discrete segments) were lyophilized and then solubilized at room temperature with nitric acid. Following neutralization, lead was extracted into methyliso- butylketone with ammonium pyrrolidinecarbodithioate and aspirated into the flame of an AAS unit. The reported relative precision was 8 percent. 9-15 TEH 0411873 DUP050452471 9.2.3 Quality Assurance Procedures In Lead Analysis Regardless of technical differences among the different methodologies for lead analysis, one can define the quality of such techniques as being of certain categories: (1) poor accu racy and poor precision; (2) poor accuracy and good precision; or (3) good accuracy and good precision. In terms of available Information, the major focus in assessing quality has been on blood lead determinations. According to Boutwell (1976), the use of quality control testing for lead measurement rests on four assumptions: (1) that the validity of the specific procedure for lead in some matrix has been established; (2) that the stability of the factors making up the method has been both established and manageable; (3) that the validity of the calibration process and the calibrators with respect to the media being analyzed has been established; and (4) that surro gate quality control materials of reliably determined analyte content can be provided. These assumptions, when translated into practice, revolve around steps employed within the labora tory, using a battery of "internal checks" and a further reliance on "external checks" such as a formal, well-organized, multi-laboratory proficiency testing program. Analytical quality protocols can be further divided into start-up and routine procedures, the former entailing the establishment of detection limits, "within-run" and "between-run" precision, and recovery of analyte. When a new method is adopted for some specific analytical advantage, the procedure is usually tested inside or outside the laboratory for comparative performance. For example, Hicks et al. (1973) and Kubasik et al. (1972) reported that flame less techniques for measuring lead in whole blood had a satisfactory correlation with results using conventional flame procedures. Matson et al. (1971) noted a good agreement between ASV and both AAS and dithizone colorimetric techniques. The problem with such comparisons is that the reference method is assumed to be accurate for the particular level of lead in a given matrix. High correlations obtained in this manner may simply indicate that two inaccurate methods are simultaneously performing with the same level of precision. Preferable approaches for assessing accuracy are the use of certified samples determined by a definitive method or direct comparison of different techniques with a definitive proce dure.. For example, Eller and Hartz (1977) compared the precision and accuracy of five availa ble methods for measuring lead in blood: dithizone spectrometry, extraction and tantalum boat AAS, extraction and flame aspiration AAS, direct aspiration AAS, and graphite furnace AAS techniques. Porcine whole blood certified by NBS using IDMS at 1.00 pg/g (0.023) was tested and all methods were found to be equally accurate. The tantalum boat technique was the least precise. The obvious limitation of data from this technique is that they relate to a high blood lead content, suitable for use in measuring the exposure of lead workers or in some other occupational context, but less appropriate for clinical or epidemiological investi gations. 9-16 .1/ *' "M 1 zi. >i Vi 'IP TEH 04U874 DUP050452472 Boone et al. (1979) compared the analytical performance of 113 laboratories using various methods and 12 whole blood samples (blood from cows fed a lead salt) certified as to lead con tent using IDMS at the NBS. Lead content ranged from 13 to 102 pg/dl, determined by ASV and five variations of AAS. The order of agreement with NBS values, i.e., relative accuracy, was as follows: extraction > ASV > tantalum strip > graphite furnace > Delves cup > carbon rod. The AAS methods all showed bias, having positive values at less than 40 pg/dl and negative values at levels greater than 50 pg/dl. ASV showed less of a positive bias problem, although it was not bias free within either of the blood lead ranges. In terms of relative precision, the ranking was: ASV > Delves cup > tantalum strip > graphite furnace > extraction > carbon rod. The overall ranking In accuracy and precision indicated: ASV > Delves cup > extraction > tantalum strip > graphite furnace > carbon rod. As the authors cautioned, the above data should not be taken to indicate that any established laboratory using one particular technique would not perform better; rather, it should be used as a guide for newer facilities choosing among methods. A number of steps in quality assurance pertinent to the routine measurement of lead are necessary in an ongoing program. With respect to internal checks of routine performance, these steps include calibration and precision and accuracy testing. With biological matrices, the use of matrix-matched standards is quite Important, as is an understanding of the range of linearity and variation of calibration curve slopes from day to day. Analyzing a given sample in duplicate is common practice, with further replication carried out if the first two deter minations- vary beyond a predetermined range. A second desirable step is the analysis of sam ples collected in duplicate but analyzed "blind" to avoid bias. Monitoring accuracy within the laboratory Is limited to the availability of control sam ples having a certified lead content in the same medium as the samples being analyzed. Con trols should be as physically close to the media being analyzed as possible. Standard refer ence materials (SRMs), such as orchard leaves and lyophilized bovine liver, are of help in some cases, but NBS-certified blood samples are needed for the general laboratory community. Whole blood samples, prepared and certified by the marketing facility (TOX-EL, A.R. Smith Co., Los Angeles, CA; Kaulson Laboratories, Caldwell, NJ; Behringwerke AG, Marburg, W. Germany; and Health Research Institute, Albany, NY) are available commercially. With these samples, atten tion must be paid to the reliability of the methods used by reference laboratories. The use of such materials, from whatever source, must minimize bias; for example, the attention given control specimens should be the same as that given routine samples. Finally, the most Important form of quality assurance is the ongoing assessment of lab oratory performance by proficiency testing programs using externally provided specimens for analysis. Earlier inter!aboratory surveys of lead measurement in blood and in urine indicated 9-17 TEH 0411875 DUP050452473 that a number of laboratories had performed unsatisfactorily, even when dealing with high con centrations of lead (Keppler et a!., 1970; Donovan et a!., 1971; Berlin et a!., 1973), al though some of the problems may have originated in the preparation and status of the blood samples during and after distribution (World Health Organization, 1977). These earlier tests for proficiency indicated the following: (1) many laboratories were able to achieve a good degree of precision within their own facilities; (2) the greater the number of samples rou tinely analyzed by a facility, the better the performance; and (3) 30 percent of the labora tories routinely analyzing blood lead reported values differing by more than 15 percent from the true level (Pierce et al., 1976). In the more recent, but very limited, study of Paulev et al. (1978), five facilities par ticipated in a survey, using samples to which known amounts of lead had been added. For lead in both whole blood and urine, the interlaboratory coefficient of variation was reported to be satisfactory, ranging from 12.3 to 17.2 percent. Aside from its limited scope, this study used "spiked" instead of jn vivo lead, so that extraction techniques used in most of the labo ratories surveyed would have given misleadingly better results in terms of actual recovery. Maher et al. (1979) described the outcome of a proficiency study involving up to 38 lab oratories that analyzed whole blood pooled from a large number of samples submitted for blood lead testing. The Delves cup technique was the most heavily represented, followed by the che lation-extraction plus flame AAS method and the graphite furnace AAS method. ASV was used by only approximately 10 percent of the laboratories, so that the results basically portray AAS methods. All laboratories had about the same degree of accuracy, with no evidence of consis tent bias, while the inter!aboratory coefficient of variation was approximately 15 percent. A subset of this group, certified by the American Industrial Hygiene Association (AIHA) for air lead, showed a corresponding precision figure of approximately 7 percent. Over time, the sub set of AIHA-certified laboratories remained about the same in proficiency, while the other facilities showed continued improvement in both accuracy and precision. This study indicates that program participation does help the performance of a laboratory doing blood lead determi nations. The most comprehensive proficiency testing program is that carried out by the Centers for Disease Control (CDC) of the U.S. Public Health Service (USPHS). This testing program con sists of two operationally and administratively distinct subprograms, one conducted by the Center for Environmental Health (CEH) and the other by the Licensure and Proficiency Testing Division, Laboratory Improvement Program Office (LIP0). The CEH program is directed at fa cilities involved in lead poisoning prevention and screening, while LIP0 is concerned with laboratories seeking certification under the Clinical Laboratories Improvement Act of 1967 as well as under regulations of the Occupational Safety and Health Administration (OSHA). Both 9-18 TEH 0411876 DUP050452474 the CEH and LIPO protocols involve the use of bovine whole blood certified as to content by reference laboratories (6 in the CEH program, 20-23 in LIPO) with an ad hoc target range of 6 pg/dl for values of 40 pg/dl or less and +15 percent for higher levels. Three samples are provided monthly from CEH, for a total of 36 yearly, while LIPO participants receive three samples quarterly (12 samples yearly). Use of a fixed range rather than a standard deviation has the advantage of allowing the monitoring of overall laboratory improvement. For fiscal year (FY) 1981, 114 facilities were in the CEH program, 92 of them participa ting for the entire year. Of these, 57 percent each month reported all three samples within the target range, and 85 percent on average reported two out of three samples correctly. Of the facilities reporting throughout the year, 95 percent had a 50 percent or better perfor mance, i.e., 18 blood samples or better. Comparing the summary data for FY 1981 with earlier annual reports, one sees considerable improvement in the number of laboratories achieving higher levels of proficiency. For the interval FY 1977-79, there was a 20 percent increase in the number correctly analyzing more than 80 percent of all samples and a 33 percent decrease in those reporting less than 50 percent correct. In the last several years, FY 1979-81, over all performance has more or less stabilized. With the LIPO program for 1981 (Dudley, 1982), the overall laboratory performance aver aged across all quarters was 65 percent of the laboratories analyzing all samples correctly and approximately 80 percent performing well with two of three samples. Over the 4 years of this program, an increasing ability to analyze lead in blood correctly has been demonstrated. Dudley's (1982) survey also indicates that reference laboratories in the LIPO program are be coming more accurate relative to IDMS values, i.e., bias over the blood lead range is con tracting. Current 0SHA criteria for certification of laboratories measuring occupational blood lead levels require that eight of nine samples, 89 percent, be within 6 pg/dl or 15 percent of re ference laboratory means for samples sent over the three previous quarters (U.S. Occupational Safety and Health Administration, 1982). These criteria reflect the ability of a number of laboratories to perform at this level. Note that most proficiency programs, including the CEH and LIPO surveys, are appropriate ly concerned with blood lead levels encountered in such cases as pediatric screening for ex cessive exposure to lead or in occupational exposures. As a consequence, underrepresentation of lead values in the low end of the "normal" range occurs. In the CEH distribution for FY 1981, four samples (11 percent) were below 25 pg/dl. The relative performance of the 114 facilities with these samples indicates outcomes much better than with the whole sample range. This relative distribution of low blood lead samples appears to have continued to the present. 9-19 TEH 0411877 DUP050452475 The National Bureau of Standards has recently made available certified porcine blood lead*' standard reference material (SRM 955) at two levels of blood lead. Certified urine lead; samples are also being offered. 9.3 DETERMINATION OF ERYTHROCYTE PORPHYRIN (FREE ERYTHROCYTE PROTOPORPHYRIN, ZINC PROTOPORPHYRIN) 9.3.1 Methods of Erythrocyte Porphyrin Analysis Lead exposure results in inhibition of the final step in heme biosynthesis, the insertion of iron into protoporphyrin IX to form heme. Inhibition of this step leads to an accumulation of the porphyrin, with zinc (II) occupying the position normally filled by iron. Depending on the particular method of analysis, zinc protoporphyrin (ZPP) itself or the metal-free form,' free erythrocyte protoporphyrin (FEP), is measured. FEP generated as a consequence of chemi cal manipulation should be kept distinct from the metal-free form biochemically produced in the disease, erythropoietic protoporphyria. The chemical or "wet" methods measure FEP or ZPP,f depending upon the relative acidity of the extraction medium. The hematof1uorometer in its- commercially available form measures ZPP. Porphyrins are labile due to photochemical decomposition; hence, samples must be protect- ed from light during collection and handling and analyzed as soon as possible. Hematocrits must also be obtained to adjust for anemic subjects. In terms of methodological approaches for erythrocyte porphyrin (EP) analysis, virtuall all methods now in use exploit the ability of porphyrins to undergo intense fluorescence when excited at the appropriate wavelength of light. Such fluorometrlc techniques can be further classified as wet chemical micromethods or as micromethods using a recently developed instru ment, the hematof1uorometer. The latter Involves direct measurement in whole blood Because the mammalian erythrocyte contains all of the EP in whole blood, either packed cells or whole blood may be used, although the latter is more expedient. Because of the relatively high sensitivity of fluorometrlc measurement for FEP or ZPPS f laboratory methods for spectrofluorometric analysis require a relatively small sample of blood; hence, microtechniques are currently the most popular in most laboratories. These in volve either liquid samples or blood collected on filter paper, the latter used particularly in field sampling. As noted above, chemical methods for EP analysis measure either FEP, where zinc is chemi cally removed, or ZPP, where zinc is retained. The procedures of Piomelli and Davidow (1972)j Granick et al., (1972), and Chisholm and Brown (1975) typify "free" EP methods, while those Lamola et al. (1975), Joselow and Flores (1977), and Chisolm and Brown (1979) Involve mea surement of zinc EP. 9-20 TEH 04118- DUP050452476 In Piomelli and Davidow's (1972) microprocedure, small volumes of whole blood, analyzed either directly or after collection on filter paper, were treated with a suspension of Celite in saline followed by a 4:1 mixture of ethyl acetate to glacial acetic acid. After agitation and centrifugation, the supernatant was extracted with 1.5N HC1. The acid layer was analyzed fluorometrically using an excitation wavelength of 405 nm and measurement at 615 nm. Blood collected on filter paper discs was first eluted with 0.2 ml H20. The filter paper method was found to work just as well as liquid samples of whole blood. Protoporphyrin IX was employed as a quantitative standard. Granick et al. (1972) used a similar microprccedure, but it dif fered in the concentration of acid employed and the use of a ratio of maxima. In Chisolm and Brown's (1975) variation, volumes of 20 pi of whole blood were treated with ethyl acetate/acetic acid (3:1) and briefly mixed. The acid-extraction step was done with 3N HC1, followed by a further dilution step with more acid If the value was beyond the range of the calibration curve. In this procedure, protoporphyrin IX was used as the working standard, with coproporphyrin (a precursor to protoporphyrin) used to monitor the calibration of the fluorometer and any variance with the protoporphyrin standard. Lamola et al. (1975) analyzed the ZPP as such in their procedure. Small volumes of blood (20 pi) were worked up in a detergent (dimethyl dodecylamine oxide) and phosphate buffer solu tion, and fluorescence was measured at 594 nm with excitation at 424 nm. In the variation of Joselow and Flores (1977), 10 pi of whole blood was diluted 1000-fold, along with protoporphy rin (Zn) standards, with the detergent-buffer solution. Note that the ZPP standard is virtu ally impossible to obtain in pure form. Chisolm and Brown (1979) reported the use of proto porphyrin IX plus very pure zinc salt for such standards. In the single-extraction variation of Orfanos et al. (1977), liquid samples of whole blood (40 pi) or blood on filter paper were treated with acidified ethanol. The mixtures were agitated and centrifuged, and the supernatants analyzed directly in fluorometer cuvettes. For blood samples on filter paper, blood was first leached from the paper with saline by soaking for 60 min. Coproporphyrin was used as the quantitative standard. The correlation coeffici ent with the Piomelli and Davidow (1972) procedure (see above) over the range 40-650 pg EP/dl RBCs was r = 0.98. As in the above methods, ZPP itself is measured. Regardless of the extraction methods used, some instrumental parameters are important, including the variation between cut-offs in secondary emission filters and variation among photomultiplier tubes in the red region of the spectrum. Hanna et al. (1976) compared four micromethods for EP analysis: double extraction with ethyl acetate/acetic acid and with HC1 (Piomelli and Davidow, 1972), single extraction with either ethanol or acetone (Chisolm et al., 1974), and direct solubilization with detergent (Lamola et al., 1975). Of these, the ethyl acetate and ethanol procedures were satisfactory; complete extraction occurred only with 9-21 TEH 0411879 DUP050452477 i,* the ethyl acetate/acetic acid method. In the method of Chisholm et al. (1974), the choice of- acid and its concentration appears to be more significant than the choice of organic solvent. The levels of precision with these wet micrcmethods differ with the specifics of analy-V1- sis. Piomelli (1973) reported a coefficient of variation (C.V.) of 5 percent, compared to.,.-* Herder's (1980) observation of 2-4 percent for the methods per se and 6-11 percent total C.v'.^|$p which included precision of samples, standards, and day-to-day variation. The Lamola et a1._ (1975) method for ZPP measurement was found to have a C.V. of 10 percent (same day, presuma-^ bly), whereas Herber (1980) reported a day-to-day C.V. of 9.3-44.6 percent. Herber (1980)Vi also found that the wet chemical micromethod of Piomelli (1973) had a detection limit of 20 u'g V'V EP/dl whole blood, while that of Lamola et al. (1975) was sensitive to 50 pg EP/dl whole V'' blood. The recent development of direct instrumental measurement of ZPP with the hematof1 unrA-^i meter has made it possible to use EP measurement in field screening for lead exposure in large * "W groups of subjects. However, hematof!uorometers were developed for and remain most useful for lead screening programs; they were not meant to be laboratory substitutes for the chemical V; methods of EP analysis. (See Section 9.3.2 for a comparative discussion.) As originally de- veloped by Bell Laboratories (BTumberg et al., 1977) and now produced commercially, the appa ratus employs front-face optics, in which excitation of the fluorophore is at an acute angle to the sample surface, with emitted light emerging from the same surface and thus being de- ""S tected. Routine calibration requires a stable fluorescing material with spectra comparable to ZPP; the triphenylmethane dye Rhodamine B is used for this purpose. Absolute calibration re-^^S 1quires adjusting the microprocessor-controlled readout system to read the known concentration of ZPP in reference blood samples, the latter calibration performed as frequently as possible. AHematof1uorometers are designed for measuring EP in samples containing oxyhemoglobin, i.e., capillary blood. Venous blood, therefore, must first be oxygenated, usually by moderate shaking for approximately 10 min (Blumberg et al., 1977; Grandjean and Lintrup, 1978). A second problem with hematof!uorometer use, in contrast to wet chemical methods, is Interfer ence by bilirubin (Karacid et al., 1980; Grandjean and Lintrup, 1978). This interference oc curs with relatively low levels of EP. At levels normally encountered in lead workers or sub injects with anemia or nonoccupational lead exposure, the degree of such interference is not considered significant (Grandjean and Lintrup, 1978). Karaclc et al. (1980) have found that carboxyhemoglobin (COHb) may pose a potential problem, but its relevance to EP levels of sub jects exposed to lead has not been fully elucidated. Background fluorescence in cover glass may be a problem and should be tested in advance. Finally, the accuracy of the hematoflupro- vcjl meter appears to be affected by hemolyzed blood. \\- Competently employed, the hematof1uorometer appears to be reasonably precise, but its ac curacy may still be biased (see below). Blumberg et al. (1977) reported a C.V. of 3 percent ^ ^ 9-22 - TEH 0411880-1. DUP050452478 over the entire range of ZPP values measured when using a prototype apparatus. Karacic et al. (1980) found the relative standard deviation to vary from 1 percent (0.92 mM ZPP/M Hb) to 5 percent (0.41 mM ZPP/M Hb) depending on concentration. Grandjean and Lintrup (1978) obtained a day-to-day C.V. of 5 percent using blood samples refrigerated for up to 9 weeks. Herber (1980) obtained a total C.V. of 4.1-11.5 percent. A number of investigators have compared EP measured by the hematofluorometer with EP mea sured by the laboratory or wet chemical techniques, ranging from a single, intralaboratory comparison to interlaboratory performance testing. The latter included the EP proficiency testing program of the USPHS1 CDC. Working with prototype instrumentation, Blumberg et al. (1977) obtained correlation coefficients of r = 0.98 (range: 50-800 pg EP/dl RBCs) and 0.99 (range: up to 1000 pg EP/dl RBCs) for comparisons with the Granick and Piomelli methods, respectively. Grandjean and Lintrup (1978), Castoldi et al. (1979) and Karacic et al. (1980) have achieved equally good correlation results. Several reports (Culbreth et al., 1979; Scoble et al., 1981; Smith et al. , 1980) have described the application of high-performance liquid chromatography (HPLC) to the analysis of either FEP or ZPP in whole blood. In one of the studies (Scoble et al., 1981), the protopor phyrins as well as coproporphyrin and mesoporphyrin IX were reported to be determined on-line fluorometrically in less than 6 min using 0.1 ml of blood sample. The HPLC approach remains to be tested in interlaboratory proficiency programs. 9.3.2 Interlaboratory Testing of Accuracy and Precision in EP Measurement In a relatively early attempt to assess inter!aboratcry proficiency in EP measurement, Jackson (1978) reported results of a survey of 65 facilities that analyzed 10 whole blood sam ples by direct measurement with the hematofluorometer or by one of the wet chemical methods. In this survey, the instrumental methods had a low bias compared to the extraction techniques but tended to show better interlaboratory correlation. At present, CDC's ongoing EP proficiency testing program constitutes the most comprehen sive assessment of laboratory performance (U.S. Centers for Disease Control, 1981). Every month, three samples of whole blood prepared at the University of Wisconsin Laboratory of Hygiene are forwarded to participants. Reference means are determined by a group of reference laboratories with a target range of 15 percent across the whole range of EP values. For FY 1981, of the 198 laboratories participating, 139 facilities were involved for the entire year. Three of the 36 samples in the year were not included. Of the 139 year-long participants, 93.5 percent had better than half of the samples within the target range, 84.2 percent per formed satisfactorily with 70 percent or more of the samples within range, and 50.4 percent of all laboratories had 90 percent or more of the samples yielding the correct results. The par ticipants as a whole showed greater proficiency than in the previous year. Of the various 9-23 TEH 0411881 DUP050452479 * ^ Mr methods currently used, the hematofluorometer direct measurement technique was most heavily represented. For example, in the January 1982 survey of the three major techniques, 154 par ticipants used the hematofluorometer, 30 used the Piomelli method, and 7 used the Chisolm/ Brown method. A recent survey by Balamut et al. (1982) raises the troublesome observation that the use of commercially available hematof1uorometers may yield satisfactory proficiency results but still be inaccurate when compared to the wet chemical method using freshly drawn whole blood. Two hematof1uorometers in wide use performed well in proficiency testing but showed an appro ximately 30 percent negative bias with clinical samples analyzed by both instrument and chemi cal microtechniques. This bias leads to false negatives when used in screening. Periodic testing of split samples by both fluorometer and chemical means is necessary to monitor, and correct for, instrument negative bias. The basis of the bias is much more than can be ex plained by the difference between FEP and ZPP. This survey points out precautions noted earlier on the restrictive use of the hematofluorometer to screening situations. Mitchell and Doran (1985) compared EP values measured in their laboratory by the chemical extraction technique with results obtained by the hematofluorometer in 21 other laboratories. These workers found that (a) hematofluorometer results were 11-28 percent lower than the cor responding chemical method values, (b) hematofluorometers demonstrated mean error of up to 3 percent for proficiency samples, and (c) hematofluorometers showed a negative bias of 20 per cent at EP levels of 50 pg/dl and would miss about one third (false negatives) of children at or somewhat above this level. One factor that can be important in the relative accuracy of the hematofluorometer versus wet chemical methods Is the relative stability of ZPP levels as a proportion of total EP across that age range in childhood of most interest in screening. Hammond and coworkers (1984) have observed that the fraction of ZPP versus total EP was at a relative minimum at 3 months of age in 165 children serially tested, and that it increased to 1.0 by around 33 months of age. These observations suggest that this variation of proportionality with age should be taken into account when screening children under approximately 30 months of age and when the hematofluorometer Is the chief means of EP quantification. The technical basis for this age-related change in proportionality may be spectroscopic, i.e., changes in erythrocyte size over this age range would lead to differences in cell packing, which in turn would affect fluorescence yield during front-face irradiation in the hematofluorometer. A second factor noted by the authors may have to do with relative availa bility of zinc. Since zinc deficiency is common at this stage of development (see Chapter 10), bioavailability of zinc for a nonessential complexing with FEP would be restricted by homeostatic sparing of the element for physiological needs. However, since the work of 9-24 TEH 0411882 DUP050452480 Chisolm and Brown (1979), using a chemical method, did not reveal any disparity between the two forms in subjects of the same age range, there is probably an instrumental artifact operating here. 9.4 MEASUREMENT OF URINARY COPROPORPHYRIN The elevation of urinary coproporphyrin (CP-U) with lead intoxication served as a useful indicator of such intoxication in children and lead workers for many years. Although analysis of CP-U has declined considerably in recent times with the development of other testing methods, such as measurement of EP, it still has the advantage of showing active intoxication (Piomelli and Graziano, 1980). The standard method of CP-U determination is the fluorometric procedure described by Schwartz et al. (1951). Urine samples are treated with acetate buffer and aqueous iodine, the latter converting coproporphyrinogen to coproporphyrin (CP). The porphyrin is partitioned into ethyl acetate and back extracted (4 times) with 1.5N HC1. Coproporphyrin is employed as the quantitative standard. Working curves are linear below 5 pg CP/1 urine. In the absorption spectrometric technique of Haeger-Aronsen (1960), iodine is also used to convert coproporphyrinogen to CP. The extractant is ethyl ether, from which the CP is re moved with Q.1N HC1. Absorption is read at three wavelengths, 380, 430, and the Soret maximum at 402 nm. Quantification Is carried out using an equation involving the three wavelengths. 9.5 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID DEHYDRASE ACTIVITY Delta-aminolevulinic acid dehydrase (5-aminolevulinate hydrolase; porphobilinogen synthe tase; E.C. 4.2.1.24; i.e., ALA-D) is an allosteric sulfhydryl enzyme that mediates the con version of two units of 6-aminolevulinic acid (6-ALA) to porphobilinogen, a precursor in the heme biosynthetic pathway to the porphyrins. Lead's inhibition of the activity of this enzyme is the enzymological basis of ALA-D's diagnostic utility In assessing lead exposure using erythrocytes. A number of sampling precautions are necessary when measuring this enzyme's activity. ALA-D activity is modified by the presence of zinc as well as lead. Consequently, blood col lection tubes that have high background zinc content, mainly in the rubber stoppers, must be avoided completely or care must be taken to avoid stopper contact with blood. Nackowski et al. (1977) observed that the presence of zinc in blood collection tubes is a pervasive prob lem, and plastic-cup tubes appear the only practical means to avoid it. To guard against zinc in the tube itself, one should determine the extent of zinc Teachability by blood and use one 9-25 TEH 0411883 DUP050452481 fi 3 /. i ; tube lot, if possible. Heparin is the anticoagulant of choice, because the lead binding','1" * agent, EDTA, or other chelants would affect the lead-enzyme interaction. The relative in- ` stability of the enzyme in blood makes rapid determinations of activity necessary, preferably' ' as soon after collection as possible. Even with refrigeration, analysis of activity should be done within 24 hr (Berlin and Schaller, 1974). Furthermore, porphobilinogen is light labile. which requires that the assay be done under restricted light. Various procedures for ALA-D activity measurement are chemically based on measurement oF"^] ' porphobilinogen generated from the substrate. Delta-ALA porphobilinogen is condensed with pdimethylaminobenzaldehyde (Ehrlich's reagent) to yield a chromophore measured at 553 nm in a f' ' * spectrophotometer. In the European Standardized Method for ALA-D activity measurement (Berlin and Schaller, 1974), developed with the collaboration of nine laboratories for use with blood samples having relatively low lead content, triplicate blood samples (0.2 ml) are hemolyzed, along with a blood blank, with water for 10 min at 37C. Samples are then mixed with 6-ALA ^. solution and incubated for 60 min. The enzyme reaction is terminated by addition of a so'lu- tion of mercury (II) in trichloroacetic acid, followed by centrifugation and filtration. Fil- ' - _ rtrates are mixed with modified Ehrlich's reagent (p-dimethylamincbenzalehyde in trichloro acetic/perchloric acid mixture) and allowed to react for 5 min, followed by chromophore * `r't measurement in a spectrophotometer at 555 nm. Activity is quantified in terms of pM 6-AL * min*l erythrocytes. Note that the amount of phosphate for Solution A in Berlin & Schallr*1 s I.;**.- (1974) report should be 1.78 g, not the 1.38 g stated. In a microscale variation, Granick et MB al. (1973) used only 5 pi of blood and terminated the assay by trichloroacetic acid. In comparing various reports concerning the relationship between lead exposure and ALA-D inhibition, attention should be paid to the units of activity measurement employed with the different techniques. Berlin and Schaller's (1974) procedure expresses activity as pM 6-ALA/ min-1 cells, while Tomokuni's (1974) method expresses activity as pM porphobfHnogen/hr/ml cells. Similarly, when comparing the Bonsignore et al. (1965) procedure to that of Berlin and Schaller (1974), a conversion factor of 3.8 is necessary when converting from Bonsignore to -s i> European Standard Method units (Trevisan et al., 1981). &n Several factors have been shown to affect ALA-D activity. Rather than measuring enzyne activity in blood once, Granick et al. (1973) measured activity before and after treatment -s. with dithiothreitol, an agent that reactivates the enzyme by complexing lead. The ratio of S activated to unactivated enzymes versus blood lead levels accommodates inherent differences in- II: enzyme activity among individuals due to genetic factors and other reasons, Other agents for i Jgj ft, ' such activation include zinc (Finelli et al 1975) and zinc plus glutathione (Mitchell et - r- al., 1977). In the Mitchell et al. (1977) study, nonphysiological levels of zinc were used. 1 Wigfield and Farant (1979) found that enzyme activity is related to assay pH; thus, reduced 9-26 :mMm TEH 0411884 , ^ j 5L DUP050452482 activity from such a pH-activity relationship could be misinterpreted as lead inhibition. These researchers find that pH shifts away from optimal, in terms of activity, as blood lead content increases and the incubation step proceeds. 9.6 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID IN URINE AND OTHER MEDIA Delta-aminolevulinic acid (5-ALA) levels increase with elevated lead exposure, because of the inhibitory effect of lead on the activity of ALA dehydrase and/or the increase of ALA syn thetase activity by feedback derepression. The result is that this intermediate in heme bio synthesis rises in the body and eventually results in increased urinary excretion. The meas urement of this metabolite in urine provides an indication of the level of lead exposure. The ALA content of urine samples (ALA-U)is stable for approximately 2 weeks or more if urine samples are acidified with tartaric or acetic acid and kept refrigerated. Values of ALA-U are adjusted for urine density if concentration is expressed in mg/1 or is measured per gram creatinine. As noted in the case of urinary lead measurement, 24-hr collection is more desirable than spot sampling. Five manual procedures and one.automated procedure for urinary ALA measurement are most widely used. Mauzerall and Granick (1956) and Davis and Andelman (1967) described the most involved procedures, requiring the initial chromatographic separation of ALA. The approach of Grabecki et al. (1967) omitted chromatographic isolation, whereas the automated variation of Lauwerys et al. (1972) omitted prechromatography but included the use of an internal standard. Tomokuni and Ogata (1972) omitted chromatography but employed solvent extraction to isolate the pyrrole intermediate. Mauzerall and Granick (1956) condensed ALA with a p-dicarbonyl compound, acetyl acetone, at pH 4.6 to yield a pyrrole Intermediate (Knorr condensation reaction), which was further re acted with p-dimethylaminobenzaldehyde in perchloric/acetic acid. The samples were then read in a spectrophotometer at 553 nm 15 min after mixing. In this method, both porphobilinogen and ALA are separated from urine by means of a dual-column configuration of cation and anion exchange resins. The latter retains the porphobilinogen and the former separates ALA from urea. The detection limit is 3 pmol/1 urine. In the modification of this method by Davis and Andelman (1967), disposable cation/anion resin cartridges were used, in a sequential configu ration, to expedite chromatographic separation and increase the sample analysis rate. Commer cial (Bio-Rad) disposable columns based on this design are now available and appear satis factory. In these two approaches (Mauzerall and Granick, 1956; Davis and Andelman, 1967), the pro blem of interference due to ami noacetone, a metabolite occurring in urine, is not taken into account. However, Marver et al. (1966) used Dowex-1 in a chromatographic step subsequent to 9-27 TEH 0411885 DUP050452483 the condensation reaction to form the pyrrole. This step separates the ALA derivative from that of the aminoacetone. Similarly, Schlenker et al. (1964) used a cation-exchange column to retain aminoacetone. Tomokuni and Ogata (1972) condensed ALA with ethylacetoacetate and extracted the re sulting pyrrole with ethyl acetate. The extract was then treated with Ehrlich's reagent and the resulting chromophore measured spectrophotometrically. Lauwerys et al. (1972) developed an automated ALA analysis method for lead worker screening in which ALA was added in known amount as an internal standard and the prechromatography was avoided. They reported a high correlation (r = 0.98, no range available) with the procedure of Mauzerall and Granick (1956). Roels et al. (1974) compared the relative proficiency of four methods--those of Mauzerall and Granick (1956), Davis and Andelman (1967), the Lauwerys et al. (1972) automated version, and the Grabecki et al. (1967) method, which omits chromatographic separation and Is normally used with occupational screening. The chromatographic methods gave identical results over the range of 0-60 mg ALA/1 urine, while the automated method showed a positive bias at <6 mg/1. The Grabecki et al. (1967) technique was the least satisfactory of the procedures com pared. Roels et al. (1974) also noted that commercial ion-exchange columns resulted in low variability (<10 percent). Della Fiorentina et al. (1979) combined the Tomokuni and Ogata (1972) extraction method with a correction equation for urine density. Up to 25 mg ALA/1, the C.V. was 4 percent along with a good correlation (r = 0.937) with the Davis and Andelman (1967) technique. While avoiding prechromatography saves time, one must prepare a curve relating urine density to a correction factor for quantitative measurement. Although ALA analysis is normally done with urine as the indicator medium, Haeger-Aronsen (1960) reported a similar colorimetric method for blood and MacGee et al. (1977) described a gas-liquid chromatographic (GLC) method for ALA in plasma as well as urine. Levels of ALA in plasma are much lower than those in urine. In the latter method, ALA was isolated from plasma, reacted with acetyl-acetone, and partitioned Into a solvent (trimethylphenylhydroxide), which also served for pyrolytic methylation in the injection port of the gasliquid . chromatograph; the methylated pyrrole was more amenable to chromatographic isolation than the more polar precursor. For quantification, an Internal standard, 6-amino-5-oxohexanoic acid, was used. The sample requirement is 3 ml plasma. Measured levels ranged from 6.3 to 73.5 ng ALA/ml plasma, and yielded values that were approximately tenfold lower than the colorimetric techniques (O'Flaherty et al., 1980). In comparing the Haeger-Aronsen (1960) and MacGee et al. (1977) methods, a number of dif ferences should be pointed out. First, the colorimetric approach of Haegar-Aronsen does not employ chromatographic steps to separate the ALA from other ami noketones, specifically amino acetone and porphobilinogen. While these other aminoketones are not known to be positively 9-28 ,j. TEH 0411886 DUP050452484 correlated with blood lead, they would add a positive bias to the accuracy of the levels ob tained. The GLC method of MacGee and coworkers does not measure simultaneously these aminoketones in either plasma or urine, and a reading of the published methodology and its applica tion (O'Flaherty et al.( 1980) indicates the procedure is acceptable for urinary ALA and levels of ALA in plasma associated with relatively high blood lead values, i.e., >40 pg/dl. The suitability of the GLC approach for relatively low levels of plasma ALA, i.e., at blood lead levels below 40 pg/dl, remains to be fully evaluated in the field. A careful reading of the MacGee et al. report suggests potential interferences with low levels of ALA measurement, while the methodology has not had wide use or multi-laboratory evaluation. Despite its added cost, a good overall method for assessing the relationship of plasma ALA to blood lead levels below 40 pg/dl, now an issue of controversy (see Chapter 12.3), would be use of the MacGee method in tandem with computerized multiple-ion monitoring in a mass spectrometer. This method is an absolute means of ALA identification as well as a sensitive means of quantifica tion. 9.7 MEASUREMENT OF PYRIMIDINE-5'-NUCLEOTIDASE ACTIVITY Erythrocyte pyrimidine-5'-nucleotidase (5'-ribonucleotide phosphohydrolase, E.C. 3.1.3.5, i.e., Py5N) catalyzes the hydrolytic dephosphorylation of the pyrimidine nucleotides uridine monophosphate (UMP) and cytidinemonophosphate (CMP) to uridine and cytidine (Paglia and Valen tine, 1975). Enzyme inhibition by lead in humans and animals results'in incomplete degrad ation of reticulocyte ribonucleic acid (RNA) fragments, accumulation of the nucleotides, and increased cell hemolysis (Paglia et al., 1975; Paglia and Valentine, 1975; Angle and Mclntire, 1978; George and Duncan, 1982). Two methods are available for measurement of Py5N activity. One is quite laborious in terms of time and manipulation, while the other is shorter but requires the use of radioiso topes and radiometric measurement. In Paglia and Valentine's (1975) method, heparinized venous blood was filtered through cotton or a commercial cellulose preparation to separate erythrocytes from platelets and leukocytes. Cells were given multiple saline washings, packed lightly, and subjected to freeze hemolysis. The hemolysates were dialyzed against a salineTris buffer containing MgCl2 and EDTA to remove nucleotides and other phosphates. The assay system consists of dialyzed hemolysate, MgCl2, Tris buffer at pH 8.0, and either UMP or CMP; incubation is for 2 hr at 37C. Activity is terminated by treatment with 20 percent trichlo roacetic acid, followed by centrifugation. The supernatant inorganic phosphate, P-, is meas ured by the classic method of Fiske and Subbarow (1925), and the phosphomolybdic acid complex is measured spectrophotometrically at 660 nm. A unit of enzyme activity is expressed as 9-29 TEH 0411887 DUP050452485 nmol P^/hr/g hemoglobin. Hemolysates appear to be stable (9Q percent) with refrigeration at 4C for up to 6 days, provided that mercaptoethanol is added at the time of assay. Like the other method, activity measurement requires the determination of hemoglobin. In the simpler approach of Torrance et al. (1977), which can be feasibly applied to much larger numbers of samples, erythrocytes were separated from leukocytes and platelets with a 1:1 mixture of microcrystalline and alphacellulose, followed by saline washing and hemolysis with a solution of mercaptoethanol and EDTA. Hemolysates were incubated with a medium con taining purified 14C-CMP and MgCl2 for 30 min at 37C. The reaction was terminated by sequen tial addition of barium hydroxide and zinc sulfate solution. Proteins and unreacted nucleo tide were precipitated, leaving the labeled cytidine in the supernatant. Aliquots were measured for 14C-activity in a liquid scintillation counter. Enzyme activity was expressed as nM CMP/min/g hemoglobin. The blank activity was determined for each sample by carrying out the precipitation step as soon as the hemolysate was mixed with the labeled CMP, i.e., t = 0. This procedure shows a good correlation (r = 0.94; range: 135-189 enzyme units) with the method of Paglia and Valentine (1975). The two methods express units of enzyme activity dif ferently, so that one must know which method is used when comparing enzyme activity. 9.8 MEASUREMENT OF PLASMA 1,25-DIHYDROXYVITAMIN D The active form of vitamin D in bone mineral metabolism, including absorption of calcium and phosphorus as well as bone resorption of these minerals, is the hormonal metabolite, 1,25-dihydroxyvitamin D (1,25-(0H)2D). Given the growing interest in the adverse effects of lead on the biosynthesis of this crucial metabolite (see Chapters 10, 12 and 13), a brief discussion of the quantitative measurement of this metabolite is merited. Techniques for measurement of 1,25-(0H)2D are all of recent vintage, are all rather lengthy procedurally, and all require a rather high level of laboratory expertise and proficiency. Reported methodology, whatever the differences in specific details, can be broken down into three discrete steps: (1) isolation of the metabolite from plasma or serum by liquidliquid extraction using solvents common in lipid analysis; (2) preconcentration of the ex tracts and chromatographic purification using Sephadex LH-20 or Lipidex 5000 columns along with, in some cases, HPLC; and (3) subsequent quantitation by either of two radiometric bind ing techniques: the more common competitive protein binding (CPB) assay or radioimmunoassay (RIA). The CPB assay normally involves the use of a receptor protein in the intestinal cyto sol of chicks made vitamin D-deficient. Most illustrative of 1,25-(0H)2D measurement is the technique of Shepard et al. (1979), which also includes steps for the analysis of other metabolites not discussed here. Human 9-30 TEH 041 DUP050452486 plasma, 3-5 ml, to which tritiated metabolite is added as tracer internal standard, is ex tracted with a mixture of methanol and methylene chloride, followed by separation of the (0H)2D fraction (to include the 24,25- and 25,26-(0H)2 metabolites) from other metabolites using a Sephadex LH-20 column. Subsequent use of HPLC (straight phase, Zorbax-SIL) separates the 1,25-(0H)Z metabolite from the other two dihydroxylated products. Quantification is by CPB assay. In human adults, the mean metabolite level is 31 pi cograins/ml. Limit of detection is 5 picograms/analytical tube, mean recovery is 58.4 percent, and the within-run and betweenrun coefficients of variation are 17 and 26 percent, respectively. Two interlaboratory surveys of methodology for vitamin D metabolite analysis have recent ly been described (Jongen et al., 1982; Jongen et al., 1984). In the more recent and compre hensive of the two (Jongen et al., 1984), 15 laboratories carried out analyses of eight plasma samples and two standards for 1,25-(0H)2D. Mean interlaboratory coefficient of variation for analysis of 1,25-(GH)2D in the plasma samples was 52 percent. In this survey, nine labora tories used the CPB assay, with six using RIA for quantitation. The major reason, however, for the variance appeared to be differences in methods of purification. The upshot of this survey is that results for a given sample will vary with specifics of procedure. Thus each laboratory should establish its own reference values. 9.9 SUMMARY A complete understanding of a toxic agent's biological effects (including any statement of dose-effect relationships) requires quantitative measurement of either that agent in some biological medium or a physiological parameter associated with exposure to the agent. Quanti tative analysis involves a number of discrete steps, all of which contribute to the overall reliability of the final analytical result: sample collection and shipment, laboratory hand ling, instrumental analysis, and criteria for internal and external quality control. From a historical perspective, the definition of "satisfactory analytical method" for lead has been changing steadily as new and more sophisticated equipment has become available and understanding of the hazards of pervasive contamination along the analytical course has increased. The best example of this change is the current use of the definitive method for lead analysis, isotope-dilution mass spectrometry (IDMS) in tandem with "ultra-clean" facili ties and sampling methods, to demonstrate conclusively not only the true extent of anthropo genic input of lead to the environment over the years but also the relative limitations of most of the methods used today for lead measurement. 9-31 TEH 0411889 nr,^ wirwii,riiirir.ititryntntrtirrTI^^ mnsrn DUP050452487 jgjgsgsggglgfjj'jjajl 9.9.1 Determinations of Lead In Biological Media The low levels of lead in biological media, even in the face of excessive exposure, and the fact that sampling of such media must be done against a backdrop of pervasive lead contam ination necessitates that samples be collected and handled carefully. Blood lead sampling is best done by venous puncture and collection into low-lead tubes after careful cleaning of the puncture site. The use of finger puncture as an alternative method of sampling should be avoided, if feasible, given the risk of contamination associated with the practice in indus trialized areas. While collection of blood onto filter paper enjoyed some popularity in the past, paper deposition of blood requires special correction for hematocrit/hemoglobin level. Urine sample collection requires the use of lead-free containers as well as addition of a bactericide. If feasible, 24-hr sampling is preferred to spot collection. Deciduous teeth vary in lead content both within and across type of dentition. Thus, a specific tooth type should be uniformly obtained for all study subjects and, if possible, more than a single sam ple should be obtained from each subject. Measurements of Lead in Blood. Many reports over the years have purported to offer satisfactory analysis of lead in blood and other biological media, often with severe inherent limitations on accuracy and precision, meager adherence to criteria for accuracy and pre cision, and a limited utility across a spectrum of analytical applications. Therefore, it is only useful to discuss "definitive" and, comparatively speaking, "reference" methods currently in use. In the case of lead in biological media, the definitive method is isotope-dilution mass spectrometry (IDMS). The accuracy and unique precision of IDMS arise from the fact that all manipulations are on a weight basis involving simple procedures, and measurements entail only lead isotope ratios and not the absolute determinations of the isotopes involved, which greatly reduces instrumental corrections and errors. Reproducible results to a precision of one part in 104-105 are routine with appropriately designed and competently operated instru mentation. Although this methodology is still not recognized in many laboratories, it was the first breakthrough, in tandem with "ultra-clean" procedures and facilities, in definitive methods for indexing the progressive increase in lead contamination of the environment over the centuries. Given the expense, required level of operator expertise, and time and effort involved for measurements by IDMS, this method mainly serves for analyses that either require extreme accuracy and precision, e.g., geochronometry, or for the establishment of analytical reference material for general testing purposes or the validation of other methodologies. While the term "reference method" for lead in biological media cannot be rigorously ap plied to any procedures in popular use, the technique of atomic absorption spectrometry (AAS) in its various configurations, or the electrochemical method, anodic stripping voltammetry (ASV), come closest to meriting the designation. Other methods that are generally applied in 9-32 TEH 0411890 DUP050452488 metal analyses are either limited in sensitivity or are not feasible for use on theoretical grounds for lead analysis. AAS, as applied to analysis of whole blood, generally involves flame or flameless micromethods. One macromethod, the Hessel procedure, still enjoys some popularity. Flame micro analysis, the Delves cup procedure, applied to blood lead appears to have an operational sen sitivity of about 10 pg/dl blood and a relative precision of approximately 5 percent in the range of blood lead seen in populations in industrialized areas. The flameless, or electro thermal, method of AAS enhances sensitivity about tenfold, but precision can be more proble matic because of chemical and spectral interferences. The most widely used and sensitive electrochemical method for lead in blood is ASV. For the most accurate results, chemical wet ashing of samples must be carried out, although this process is time-consuming and requires the use of lead-free reagents. The use of metal ex change reagents has been employed in lieu of the ashing step to liberate lead from binding sites, although this substitution is associated with less precision. For the ashing method, relative precision is approximately 5 percent. In terms of accuracy and sensitivity, problems appear at low levels, e.g., 5 pg/dl or below, particularly if samples contain elevated copper levels. Lead in Plasma. Since lead in whole blood is virtually all confined to the erythrocyte, plasma levels are quite low and extreme care must be employed to measure plasma levels relia bly. The best method for such measurement is IDMS, in tandem with ultra-clean facility use. AAS is satisfactory for comparative analyses across a range of relatively high whole blood val ues. Lead in Teeth. Lead measurement in teeth has involved either whole tooth sampling or analysis of specific regions, such as dentine or circumpulpal dentine. In either case, sam ples must be solubilized after careful surface cleaning to remove contamination; solubili zation is usually accompanied by either wet ashing directly or ashing subsequent to a dry ashing step. AAS and anodic stripping have been employed more frequently for such determinations than any other method. With AAS, the high mineral content of teeth argues for preliminary isola tion of lead via chelation/extraction. The relative precision of analysis for within-run mea surement is around 5-7 percent, with the main determinant of variance in regional assay being the initial isolation step. One change from the usual methods for such measurement is the in situ measurement of lead by X-ray fluorescence spectrometry in children. Lead measured in this fashion allows observation of ongoing lead accumulation, rather than waiting for exfolia tion. Lead in Hair. Hair as an exposure indicator for lead offers the advantages of being noninvasive and a medium of indefinite stability. However, the crucial problem of external 9-33 TEH 0411891 DUP050452489 surface contamination is such that it is still not possible to state that any cleaning protocol reliably differentiates between externally and internally deposited lead. Studies that demonstrate a correlation between increasing hair lead and increasing sever ity of a measured effect tend to support arguments for using hair as an external indicator of exposure. Probably, then, such measurement using cleaning protocols that have not been inde pendently validated will overstate the relative accumulation of "internal" hair lead in terms of some endpoint and will also underestimate the relative sensitivity of changes in internal lead content with exposure. One consequence of this would be, for example, an apparent threshold for a given effect in terms of hair lead which is significantly above the actual threshold. Because of these concerns, hair is best used with the simultaneous measurement of blood lead. Lead in Urine. Analysis of lead in urine is complicated by the relatively low levels of the element in this medium as well as the complex mixture of mineral elements present. Urine lead levels are most useful and also somewhat easier to determine in cases of chelation mobil ization or chelation therapy, where levels are high enough to permit good precision and dilu tion of matrix interference. Samples are probably best analyzed by prior chemical wet ashing, using the usual mixture of acids. Both ASV and AAS have been applied to urine analysis, with the latter more routine ly used and usually with a chelation/extraction step. Lead in Other Tissues. Bone samples require cleaning procedures for removal of muscle and connective tissue and chemical solubilization prior to analysis. Methods of analysis are comparatively limited and flameless AAS is the technique of choice. lO lead measurements in bone of lead workers have been reported using X-ray fluores cence analysis and a radioisotopic source for excitation. One problem with this approach with moderate lead exposure is the detection limit, approximately 20 ppm. Soft organ analysis poses a problem in terms of heterogeneity in lead distribution within an organ (e.g., brain and kidney). In such cases, regional sampling or homogenization must be carried out. Both flame and flameless AAS appear to be satisfactory for soft tissue analysis and are the most widely used. Quality Assurance Procedures in Lead Analyses. In terms of available information, the major focus in establishing quality control protocols for lead has involved whole blood meas urements. Translated into practice, quality control revolves around steps employed within the laboratory, using a variety of internal checks, and the further reliance on external checks, such as a formal continuing multi-laboratory proficiency testing program. Within the laboratory, quality assurance protocols can be divided into start-up and rou tine procedures, the former involving establishment of detection limits, within-run and between-run precision, analytical recovery, and comparison with some reference technique 9-34 TEH 0411892 DU P0504 52490 within or outside the laboratory. The reference method is assumed to be accurate for the par ticular level of lead in some matrix at a particular point in time. Correlation with such a method at a satisfactory level, however, may simply indicate that both methods are equally inaccurate but performing with the same level of precision proficiency. More preferable is the use of certified samples having lead at a level established by the definitive method. For blood lead, the Centers for Disease Control (CDC) periodically survey overall accu racy and precision of methods used by reporting laboratories. In terms of overall accuracy and precision, one such survey found that ASV as well as the Delves cup and extraction varia tions of AAS performed better than other procedures. These results do not mean that a given laboratory cannot perform better with a particular technique; rather, such data are of assist ance for new facilities choosing among methods. Of particular value to laboratories carrying out blood lead analysis are the external quality assurance programs at both the State and Federal levels. The most comprehensive proficiency testing program is that carried out by the CDC. This program actually consists of two subprograms, one directed at facilities involved in lead poisoning prevention and screen ing (Center for Environmental Health) and the other concerned with laboratories seeking certi fication under the Clinical Laboratories Improvement Act of 1967 as well as under regulations of the Occupational Safety and Health Administration's (OSHA) Laboratory Improvement Program Office. Judging from the relative overall improvements in reporting laboratories over the years of the programs' existence, the proficiency testing programs have served their purpose well. In this regard, OSHA criteria for laboratory certification require that eight of nine samples be analyzed correctly for the previous quarter. This level of required proficiency reflects the ability of a number of laboratories to actually perform at this level. 9.9.2 Determination of Erythrocyte Porphyrin (Free Erythrocyte Protoporphyrin, Zinc Protoporphyrin) With lead exposure, erythrocyte protoporphyrin IK accumulates because of impaired place ment of divalent iron to form heme. Divalent zinc occupies the place of the native iron. Depending upon the method of analysis, either metal-free erythrocyte porphyrin (EP) or zinc protoporphyrin (ZPP) is measured, the former arising from loss of zinc in the chemical mani pulation. Virtually all methods now in use for EP analysis exploit the ability of the por phyrin to undergo intense fluorescence when excited by ultraviolet light. Such fluorometric methods can be further classified as wet chemical micromethods or direct measuring fluorometry using the hematof1uorometer. Because of the high sensitivity of such measurement, relatively small blood samples are required, with liquid samples or blood collected on filter paper. The most common laboratory or wet chemical procedures now in use represent variations of several common chemical procedures: (1) treatment of blood samples with a mixture of ethyl 9-35 TEH 0411893 DUP050452491 acetate/acetic acid followed by a repartitioning into an inorganic acid medium, or (2) solu bilization of a blood sample directly into a detergent/buffer solution at a high dilution. Quantification has been done using protoporphyrin, coproporphyrin, or zinc protoporphyrin IX plus pure zinc ion. The levels of precision for these laboratory techniques vary somewhat with the specifics of analysis. The Piomelli method has a coefficient of variation of 5 percent, while the direct ZPP method using buffered detergent solution is higher and more variable. The recent development- of the hematofluorometer has made it possible to carry out EP measurements in high numbers, thereby making population screening feasible. Absolute calibra tion is necessary and requires periodic adjustment of the system using known concentrations of EP in reference blood samples. Since these units are designed for oxygenated blood (i.e., capillary blood), use of venous blood requires an oxygenation step, usually a moderate shaking for several minutes. Measurement of low or moderate levels of EP can be affected by interfer ence with bilirubin. Competently employed, the hematofluorometer is .reasonably precise, show ing a total coefficient of variation of 4.11-11.5 percent. While the comparative accuracy of the unit has been reported to be good relative to the reference wet chemical technique, a very recent study has shown that commercial units carry with them a significant negative bias, which may lead to false negatives in subjects having only moderate EP elevation. Such a bias in accuracy has been difficult to detect in existing EP proficiency testing programs. By com parison to wet methods, the hematofluorometer should be restricted to field use rather than becoming a substitute in the laboratory for chemical measurement, and this field use should involve periodic split-sample-comparison testing with the wet method. 9.9.3 Measurement of Urinary Coproporphyrin Although EP measurement has largely supplanted the use of urinary coproporphyrin (CP-U) analysis to monitor excessive lead exposure in humans, this measurement is still of value in that it reflects active intoxication. The standard analysis is a fluorometric technique, whereby urine samples are treated with buffer, and an oxidant (iodine) is added to generate CP from its precursor. The CP-U is then partitioned into ethyl acetate and re-extracted with dilute hydrochloric acid. The working curve is linear below 5 pg CP/dl urine. I' Ml- 9.9.4 Measurement of Delta-Aminolevulinic Acid Dehydrase Activity Inhibition of the activity of the erythrocyte enzyme delta-aminolevulinic acid dehydrase (ALA-D) by lead is the basis for using such activity in screening for excessive lead exposure. A number of sampling and sample handling precautions attend such analysis. Since zinc (II) ion will offset the degree of activity inhibition by lead, blood collecting tubes must have extremely low zinc content, which essentially rules out the use of rubber-stoppered blood 9-36 TEH 0411894 DUP050452492 tubes. Enzyme instability necessitates that the activity measurement be carried out within 24 hr of blood collection. Porphobilinogen, the product of enzyme action, is light labile and requires the assay be done in restricted light. Various procedures for ALA-D measurement are based on measurement of the level of the chromophoric pyrrole (approximately 555 nm) formed by condensation of the porphobilinogen with p-dimethyl aminobenzaldehyde. In the European Standardized Method for ALA-D activity determination, blood samples are hemolyzed with water, ALA solution added, followed by incubation at 37C, and the reaction terminated by a solution of mercury (II) in trichloroacetic acid. Filtrates are treated with modified Ehrlich's reagent (p-dimethylaminobenzaldehyde) in trichloroacetic/perchloroacetic acid mixture. Activity is quantified in terms of micromoles S-ALA/min*l erythrocytes. One variation in the above procedure is the initial use of a thiol agent, such as dithiothreotol, to reactivate the enzyme, giving a measure of the full native activity of the en zyme. The ratio of activated/unactivated activity versus blood lead levels accommodates genetic differences between Individuals. 9.9.5 Measurement of Delta-Aminolevulinic Acid in Urine and Other Media Levels of delta-aminolevulinic acid (6-ALA) in urine and plasma increase with elevated lead exposure. Thus, measurement of this metabolite, generally in urine, provides an index of the level of lead exposure. ALA content of urine samples (ALA-U) is stable for about 2 weeks or more with sample acidification and refrigeration. Levels of ALA-U are adjusted for urine density or expressed per unit creatinine. If feasible, 24-hr collection is more desirable than spot sampling. Virtually all the various procedures for ALA-U measurement employ preliminary isolation of ALA from the balance of urine constituents. In one method, further separation of ALA from the metabolite aminoacetone is done. Ami noacetone can interfere with colorimetric measure ment. ALA is recovered, condensed with a beta-dicarbonyl compound, e.g., acetyl acetone, to yield a pyrrole intermediate. This intermediate is then reacted with p-dimethylaminobenzal dehyde in perchloric/acetic acid, followed by colorimetric reading at 553 nm. In one vari ation of the basic methodology, ALA is condensed with ethyl acetoacetate directly and the re sulting pyrrole extracted with ethyl acetate. Ehrlich's reagent is then added as in other procedures and the resulting chromophore is measured spectrophotometrically. Measurement of ALA in plasma is much more difficult than in urine, since plasma ALA is at nanogram/milliter levels. In one gas-liquid chromatographic procedure, ALA is isolated from plasma, reacted with acetyl acetone and partitioned into a solvent that also serves for pyro lytic methylation of the involatile pyrrole in the injector port of the chromatograph, making the derivative more volatile. For quantification, an internal standard, G-amino-5-oxohexanoic 9-37 TEH 0411895 DUP050452493 acid, is used. While the method is more involved, it is more specific than the older colon'-metric technique. 9.9.6 Measurement of Pyrimidine-5'-Nucleotidase Activity Erythrocyte pyrimidine-5'-nucleotidase (Py5N) activity is inhibited with lead exposure. Currently, two different methods are used for assaying the activity of this enzyme. The old$tSi method is quite laborious in time and effort, whereas the more recent approach is shorter butJ uses radioisotopes and radiometric measurement. -If In the older method, heparinized venous blood is filtered through cellulose to separate 1 erythrocytes from platelets and leukocytes. Cells are then freeze-fractured and the hemcr'", lysates dialyzed to remove nucleotides and other phosphates. This dialysate is then incubated *' in the presence of a nucleoside monophosphate and cofactors, the enzyme reaction being termi- nated by treatment with trichloroacetic acid. The inorganic phosphate isolated from added ` substrate is measured colorimetrically as the phosphoniolybdic acid complex. Jw In the radiometric assay, hemolysates obtained as before are incubated with pure 14C-CMP, By addition of a barium hydroxide/zinc sulfate solution, proteins and unreacted nucleotide are ' precipitated, leaving labeled cytidine in the supernatant. Aliquots are measured for 14C ac tivity in a liquid scintillation counter. This method shows a good correlatibn with the ear lier technique. 9.9.7 Measurement of Plasma 1,25-Dihydrox.yvitamin D Measurement techniques for this vitamin D metabolite, all of recent vintage, consist of three main parts: (1) isolation from plasma or serum by liquid-liquid extraction, (2) precon centration of the extract and chromatographic purification using Sephadex LH-20 or Lipidex 5000 columns, as well as high performance liquid chromatography (HPLC) in some cases, and (3) quantification by either of two radiometric binding techniques, the more common competitive protein binding (CPB) assay or radioimmunoassay (RIA). The CPB assay uses a receptor protein in intestinal cytosol of chicks made vitamin D-deficient. In one typical study, human adults had a mean level of 31 picograms/ml. The limit,Oj" detection was 5 picograms/analytical tube, and within-run and between-run coefficients of.ij1 variation were 17 and 26 percent, respectively. In a recent interlaboratory survey involving 15 laboratories, the level of variance was such that it was recommended that each laboratory,], should establish its own reference values. 9-38 TEH 04! DUP050452494 9.10 REFERENCES Ahlgren, L.; Haeger-Aronsen, B.; Mattson, S.; Schutz, A. (1980) In-vivo determination of lead in the skeleton after occupational exposure to lead. Br. J. Tnd. Med. 37: 109-113. Al-Naimi, T.; Edmonds, M. I.; Fremlin, J. H. (1980) The distribution of lead in human teeth, using charged particle activation analysis. Phys. Med. Biol. 25: 719-726. American Public Health Association. (1955) Methods for determining lead in air and in bio logical materials. New York, NY: American Public Health Association. Angle, C. R.; Mclntire, M. S. (1978) Low level lead and inhibition of erythrocyte pyrimidine nucleotidase. Environ. Res. 17: 296-302. Balamut, R. ; Doran, D.; Giridhar, G.; Mitchell, D.; Soule, S. 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Assoc. J. 38: 63-66. Karacid, V.; Prpfc-Majic, D.; Telisman, S. (1980) The relationship between zinc protoporphyrin (ZPP) and "free" erythrocyte protoporphyrin (FEP) in lead-exposed individuals. Int. Arch. Occup. Environ. Health 47: 165-177. Keppler, J. F. ; Maxfield, M. E.; Moss, W. D.; Tietjen, G.; Linch, A. L. (1970) Interlaborator evaluation of the reliability of blood lead analyses. J. Am. Ind. Hyg. Assoc. 31: 412-429. Kochen, J. A.; Greener, Y. (1973) Levels of lead in blood and hematocrit: implications for the evaluation of the newborn and anemic patient. Pediatr. Res. 7: 937-944. Koizumi, H.; Yasuda, K. (1976) Determination of lead, cadmium, and zinc using the Zeeman ef fect in atomic absorption spectrometry. Anal. Chem. 48: 1178-1182. Kopito, L. E.; Davis, M. A.; Shwachman, H. (1974) Sources of error in determining lead in blood by atomic absorption spectrophotometry. Clin. Chem. (Winston-Salem, NC) 20: 205-211. Kubasik, N. P.; Volosin, M. T.; Murray, M. H. (1972) Carbon rod atomizer applied to measure ment of lead in whole blood by atomic absorption spectrophotometry. Clin. Chem. (Winston Salem, NC) 18: 410-412. 9-43 TEH 0411901 DUP050452499 LaFleur, P. D., ed. (1976) Accuracy in trace analysis: sampling, sample handling, analysis/v 's- 1 C* 1 and 2. proceedings of the 7th materials research symposium; October 1974; Gaither-' ?' sburg, MD. Washington, DC: U.S. Department of Commerce, National Bureau cf` T*' -' Standards; NBS special publication no. 422. Available from: NTIS, Springfield v a- '* <. \ PB-258092. .' . . k *l; Lamola, A.-A.; Joselow, M.; Yamane, T. (1975) Zinc protoporphyrin (ZPP): a simple, sensitive,-,',.-'- 'J'., fluorometric screening test for lead poisoning. Clin. Chem. (Winston-Salem, NC) 21: 93-97i'; m Lauwerys, R. ; Delbroec:kk, R.; Vens, M. D. (1972) Automated analysis of delta- aminolaevfflinfc'# 'it ' acid in urine. Clin. Chim. Acta 40: 443-447. , Lauwerys, R.; Buchet, J.-P.; Roels, H.; Berlin, A.; Smeets, J. (1975) Intercomparison pregram.. VV of lead, mercury, and cadmium analysis in blood, urine, and aqueous solutions. Clin,"'/'* Chem. (Winston Salem, NC) 21: 551-557. ' _^ j1 *i d* I f t ki Lawrence, D. M. (1982) An atomic spectroscopy bibliography for January-June 1982. At. Spe.T>' ' 3: 93-115. `c^ i'/h Lawrence, D. M. (1983) An atomic spectroscopy bibliography for July-December 1982. At. Spec 4: 10-33. .-ix*'* Lee, S. W.; Meranger, J. C. (1980) Direct methods for the determination of lead in whole blood,- ` ' by anodic stripping voltammetry. Am. J. Med. Technol. 46: 853-857. ` ?! .4 i if Legotte, P. A.; Rosa, W. C.; Sutton, D. C. (1980) Determination of cadmium and lead in urine'-'/Y and other biological samples by graphite-furnace atomic-absorption spectrometry. Talant.a.' 1. 27: 39-44. . Lerner, S. (1975) Blood lead analysis--precision and stability. J. Occup. Med. 17: 153-154>r S > 1 ." Lockeretz, W. (1975) Lead content of deciduous teeth of children in different environments. -- Arch. Environ. Health 30: 583-587. , Y"../ MacGee, J.; Roda, S. M. B.; Elias, S. V. j Lington, E. A.; Tabor, M. W.; Hammond, P. B. (1977) / `ij. Determination of 6-aminolevulinic acid in blood plasma and urine by gas-liquid chromato-j -r ' graphy. Biochem. Med. 17: 31-44. P ip'V Machlan, L. A.; Gramlich, J. W.; Murphy, T. J.; Barnes, I. L. (1976) The accurate determina- ** M tion of lead in biological and environmental samples by isotope dilution mass spectro-* 1 f i metry. In: LaFleur, P. D., ed. Accuracy in trace analysis: sampling, sample handling,r ( j aWMnWalys isw . - volume 2.I w c vmiv. _ >P roceediIngs VoIf tvhl Iew 7I tKhM ImIIUaWttue. I rIiUaWls rI eVsWebaUIrcWhII symposium;WJI lll|^WW I Mill) O" -ctobe r 1974;M,-. I Gaithersburg, MD. Washington, DC: National Bureau of Standards; NBS special publication^ no. 422; pp. 929-935. Available from: NTIS, Springfield, VA; PB-258092. -r\ 't|| .... 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Trace substances in environ mental health - IV: [proceedings of University of Missouri's 4th annual conference on trace substances in environmental health]; June 1970; Columbia, M0. Columbia, M0: Uni versity of Missouri-Columbia; pp. 396-406. Mauzerall, D.; Granick, S. (1956) The occurrence and determination of 6-aminolevulinic acid and porphobilinogen in urine. J. Biol. Chem. 219: 435-446. Meranger, J. C. ; hollebone, B. R.; Blanchette, G. A. (1981) The effects of storage times, temperatures and container types on the accuracy of atomic absorption determinations of Cd, Cu, Hg, Pb and Zn in whole heparinized blood. J. Anal. Toxicol. 5: 33-41. Mitchell, D. G.; Doran, D. (1985) Effect of bias in hematofluorometer measurements of proto porphyrin in screening programs for lead poisoning. Clin. Chem. (Winston-Salem, NC) 30: 386-390. Mitchell, D. G.; Ryan, F. J.; Aldous, K. M. (1972) The precise determination of lead in whole blood by solvent extraction-atomic absorption spectrometry. At. Absorpt. Newsl. 11: 120-121. Mitchell, D. G.; Aldous, K. M.; Ryan, F. J. (1974) Mass screening for lead poisoning: capil lary blood sampling and automated Delves-cup atomic-absorption analysis. N.Y. State 0. Med. 74: 1599-1603. Mitchell, R. A.; Drake, J. E.; Wittlin, L. A.; Rejent, T. A. (1977) Erythrocyte porphobi linogen synthase (delta-aminolaevulinate dehydratase) activity: a reliable and quanti tative indicator of lead exposure in humans. Clin. Chem. (Winston-Salem, NC) 23: 105-111. Moller, B.; Carlsson, L.-E; Johannsson, G. I.; Malmqvist, K. G.; Hammarstrom, L,; Berlin, M. (1982) Lead levels determined in Swedish permanent teeth by particle-induced X-ray emmission. Scand. J. Work Environ. Health 8: 267-272. 9-45 TEH 0411903 DUP050452501 Moore, M. R.; Meredith, P. A. (1977) The storage of samples for blood and water lead analysis. Clin. Chim. Acta 75: 167-170. Moore, M. R.; Campbell, B. C.; Meredith, P. A.; Beattie, A. D.; Goldberg, A.; Campbell, D. (1978) The association between lead concentrations in teeth and domestic water lead con centrations. Clin. Chim. Acta 87: 77-83. Morrell, G.; Giridhar, G. (1976) Rapid micromethod for blood lead analysis by anodic stripping voltammetry. Clin. Chem. (Winston-Salem, NC) 22: 221-223. Murphy, T. J. (1976) The role of the analytical blank in accurate trace analysis. In: LaFleur, P. D., ed. Accuracy in trace analysis: sampling, sample handling, analysis - volume 1. Proceedings of the 7th materials research symposium; October 1974; Gaithersburg, MD. Washington, DC: U.S. Department of Commerce, National Bureau of Standards; NBS special publication no. 422; pp. 509-539. Available from: NTIS, Springfield, VA; PB-258092. Nackowski, S. B.; Putnam, R. D.; Robbins, D. A.; Varner, M. 0.; White, L. D.; Nelson, K. W. Trace metal contamination of evacuated blood collection tubes. Am. Ind. Hyg. Assoc. J. 38: 503-508. National Academy of Sciences. (1972) Lead: airborne lead in perspective. Washington, DC: National Academy of Sciences. (Biologic effects of atmospheric pollutants). Needleman, H. L.; Davidson, I.; Sewell, E. M.; Shapiro, I. M. (1974) Subclinical lead exposure in Philadelphia schoolchildren: identification by dentine lead analysis. N. Engl. J. Med. 290: 245-248. Needleman, H. L.; Gunnoe, C.; Leviton, A.; Reed, R.; Peresie, H.; Maher, C.; Barrett, P. (1979) Deficits in psychologic and classroom performance of children with elevated den tine lead levels. N. Engl. J. Med. 300: 689-695. Oehme, M.; Lund, W. (1978) The determination of copper, lead, cadmium and zinc in human teeth by.anodic stripping voltammetry. Anal. Chim. Acta 100: 389-398. 0`Flaherty, E. J.; Hammond, P. B.; Lerner, S. I.; Hanenson, I. B.; Roda, S. M. B. (1980) The renal handling of 6-aminolevulinic acid in the rat and in the human. Toxicol. Appl. Pharmacol. 55: 423-432. Orfanos, A. P.; Murphey, W. H.; Guthrie, R. (1977) A simple fluorometric assay of protopor phyrin In erythrocytes (EPP) as a screening test for lead poisoning. J. Lab. Clin. Med. 89: 659-665. Paglia, D. E.; Valentine, W. N. (1975) Characteristics of a pyrimidine-specific 5`nucleotidase in human erythrocytes. J. Biol. Chem. 250: 7973-7979. Paglia, D. E.; Valentine, W. N.; Dahlgren, J. G. (1975) Effects of low-level lead exposure on pyrimidine 5'-nucleotidase and other erythrocyte enzymes: possible role of pyrimidine 5`-nucleotidase in the pathogenesis of lead-induced anemia. J. Clin. Invest. 56: 1164-1169. Patterson, C. C. (1980) An alternative perspective - lead pollution in the human environment: origin, extent and significance. In: National Academy of Sciences, Committee on Lead in the Human Environment. Lead in the human environment. Washington, DC: National Academy of Sciences; pp. 265-349. 9-46 TEH 0411904 DUP050452502 Patterson, C. C._; Settle, D. M. 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(1982) Temporal trends in the lead concentrations of umbil ical cord blood. Science (Washington, DC) 216: 1429-1431. Rabinowitz, M.; Wetherill, G. W.; Kopple, J. D. (1974) Studies of human lead metabolism by use of stable isotope tracers. Environ. Health Perspect. 7: 145-153. Robinson, M. J.; Karpinski, F. E., Jr.; Brieger, H. (1958) The concentration of lead in plasma, whole blood and erythroctyes of infants and children. Pediatrics 21: 793-796. Roels, H.; Lauwerys, R.; Buchet, J.-P.; Berlin, A.; Smeets, J. (1974) Comparison of four methods for determination of 6-aminolevulinic acid in urine, and evaluation of clinical factors. Clin. Chem. (Winston-Salem, NC) 20: 753-760. Rosen, J. F. ; Zarate-Salvador, C.; Trinidad, E. E. (1974) Plasma lead levels in normal and lead-intoxicated children. J. Pediatr. (St. Louis) 84: 45-48. Schlenker, F. S.; Taylor, N. A.; Kiehn, B. P. (1964) The chromatographic separation, deter mination, and daily excretion of urinary porphobilinogen, amino acetone, and 6-aminolevu linic acid. Am. J. Clin. Pathol. 42: 349-354. 9-47 TEH 0411905 DUP050452503 Schwartz, S.; Zieve, L.; Watson, C. J. (1951) An improved method for the determination of urinary coproporphyrin and an evaluation of factors influencing the analysis. J. Lab. Clin. Med. 37: 843-859. Scoble, H. A.; McKeag, M.; Brown, P. R.; Kavarnos, G. J. (1981) The rapid determination of ery throcyte porphyrins using reversed-phase high performance liquid chromatography. Clin. Chim. Acta 113: 253-265. Settle, D. M.; Patterson, C. C. (1980) Lead in albacore: guide to lead pollution in Americans. Science (Washington, DC) 207: 1167-1176. Shapiro, I. M.; Dobkin, B.; Tuncay, 0. C.; Needleman, H. L. (1973) Lead levels in dentine and circumpulpal dentine of deciduous teeth of normal and lead poisoned children. Clin. Chim. Acta 46: 119-123. Shepard, R. M.; Horst, R. L. ; Hamstra, A. 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(Environmental health criteria 3). 9-49 DUP050452505 10. METABOLISM OF LEAD 10.1 INTRODUCTION This chapter examines the absorption, distribution, retention, and excretion of lead in humans and animals and the various factors that mediate the extent of the toxicokinetic pro cesses of lead. While inorganic lead is the form of the element that has been most heavily studied, organolead compounds are also emitted into the environment and, because they are quite toxic, they are also included in the discussion. Since the preparation of the 1977 Air Quality Criteria Document for Lead (U.S. Environmental Protection Agency, 1977), a number of reports have appeared that have proven particularly helpful in both quantifying the various processes to be discussed in this chapter and assessing the interactive impact of factors such as nutritional status in determining internal exposure risk. 10.2 LEAD ABSORPTION IN HUMANS AND ANIMALS The amounts of lead entering the bloodstream from various routes of absorption are deter mined not only by the levels of the element in the particular media, but also by the various physical and chemical parameters that characterize lead. Furthermore, specific host factors such as age and nutritional status are Important, as is interindividual variability. Addi tionally, to assess absorption rates, one must know whether or not the subject is in "equilibrium11 with respect to a given level of lead exposure. 10.2.1 Respiratory Absorption of Lead The movement of lead from ambient air to the bloodstream is a two-part process: a frac tion of air lead is deposited in the respiratory tract and, of this deposited amount, some fraction is subsequently absorbed directly into the bloodstream or otherwise cleared from the respiratory tract. At present, enough data exist to make some quantitative statements about both of these components of respiratory absorption of lead. The 1977 Air Quality Criteria Document for Lead described the model of the International Radiological Protection Commission (IRPC) for the deposition and removal of lead from the lungs and the upper respiratory tract (International Radiological Protection Commission,. 1966). Briefly, the model predicts that 35 percent of lead inhaled from ambient air by humans is deposited in the respiratory tract, with most of the lead going to the parenchyma and air ways. The IRPC model predicts a total deposition of 40-50 percent for particles with a mass median aerodynamic diameter (MMAD) of 0.5 pm and indicates that the absorption rate would vary 10-1 TEH 0411908 DUP050452506 depending on the solubility of the particular form. More recent data on lead depositfomodeling, however, provide a more precise picture (see next section). 10.2.1.1 Human Studies. Table 10-1 tabulates the various studies of human subjects that pro vide data on the deposition of Inorganic lead in the respiratory tract. Studies of this type' have used diverse methodologies to characterize the inhaled particles in terms of both sie (and size ranges) and fractional distribution. The use of radioactive or stable lead isotopes to directly or Indirectly measure lead deposition and uptake into the bloodstream has bUn particularly helpful in quantifying these processes. From the studies of Kehoe (1961a,b,c) and their update by Gross (1981), as well as data from Chamberlain et al. (1978), Morrow et al. (1980), and Nozaki (1966), the respiratory depo-' sition of airborne lead as encountered in the general population appears to be approximately 30-50 percent, depending on particle size and ventilation rates. Ventilation rate is parti cularly important with submicrometer particles, where Brownian diffusion governs deposition, because a slower breathing rate enhances the frequency of collisions of particles with the ^ alveolar wall. Figure 10-1 (Chamberlain et al., 1978) compares data, both calculated and experimentally measured, on the relationship of percentage deposition to particle size. As particle size Increases, deposition rate decreases to a minimum over the range where Brownian diffusion pre dominates. Subsequently, deposition increases with size (>0.5 pm MMAD) as impaction and sedi mentation become the main deposition factors. In contrast to the ambient air or chamber data tabulated In Table 10-1, higher deposition rates in some occupational settings are associated with relatively large particles. However, much of this deposition is in the upper respiratory tract, with eventual movement to the gas trointestinal tract by ciliary action and swallowing. Mehani (1966) measured total deposition rates of 28-70 percent in battery workers and workers in marine scrap yards. Chamberlain and Heard (1981) calculated an absorption rate of approximately 47 percent for particle sizes en Hi* countered in workplace air. Systemic absorption of lead from the lower respiratory tract occurs directly, while much of the absorption from the upper tract involves swallowing and some uptake in the gut. From the radioactive isotope data of Chamberlain et al. (1978) and Morrow et al. (1980), and the stable isotope studies of Rabinowitz et al. (1977), one can conclude that lead deposited In.? the lower respiratory tract is totally absorbed. Chamberlain et al. (1978) used 203Pb in engine exhaust, lead oxide, or lead nitrate aerosols in experiments where human subjects inhaled the lead from a chamber through a mouth piece or in wind-tunnel aerosols. By 14 days, approximately 90 percent of the label was ffemoved from the lung. Lead movement into the bloodstream could not be described by a simple exponential function; 20 percent was absorbed within 1 hr and 70 percent within 10 hr. 10-2 TEH 0411909 DUP050452507 TABLE 10-1. DEPOSITION OF LEAD IN THE HUMAN RESPIRATORY TRACT TEH 0 4 1 1 9 1 0 u .o ^ 01 rH u to co c rH 01 o> LD rH p CD w 01 rH p W CO o U1 OC 01 O op . CX 01 X c V) o <* % 01 1-- ^ r- p ap o *r *1-- tn p O . p 2 >> <0 01 to -- 2 a 01 c E - E P w (5 a c Si a> o o po P r-* o 01 > p o Cl . o CO to CO cn rH C0 N O z A E 2. 3. tn oo O rH <JD r-- tO HP 01 c *rttj r- ' n P CO ai h HO CD E rH to w JZ PJ 4 <0 p 01 T" 10 r-- S- 00 01 JO CD E rH f0 w JZ CJ 4* 4 2. 2. 2. c m *0* cn ooo 4- o oo co co M P </} 3C CO (0 JC XI X s01 3 JZ Stn ai 01 JO S- p tp o oo i> tn ra 01 u to oc CM O rL o .c 01 rH P CO 3 * 0> tn to ~ >> o 01C3 (0 CL *t- E T3 t/5 X -a \ 4-* LU 3 ao u P 2-P 01 *a to to *<-5 f0 O -Q 01 P in P 3 --I 01 rH 01 to X) P E 5- r-- CM flj O (OH JZ PI 4 CO r- S OS to oi to O EP PU 01 O 01 (0 rH -> N -O 01 - 3 uP w 01 01 *r jJ+J 2 rro 3 P*0 D U 1C o z r-- o tn P O r-- P2 01 "D rO c0 N a> tn U PP 01 01 u rU flj a e *~3 3 (iJX P SZ 3 3 O in O z p r-- 3 XJ (0 4 *> tn P \u cn ai 2*0 -Q O3 rH l/J 1 CM 01 D) S. 1 (0 c 01 ai to x p c0 KJ c -p ai a> 0) 01 rd 01 *r > E <A r- E "D to (0 o C 3+> 0> ai t - -p u O 2. 2. P T--* E XI to 01 -P 01 u 1-5 cr> O P E P CO j Q TJ * 01 p icro 3 01 o rH P 3 t0 to i m ro tn o c o P in r- a. O U*rLf) a. o o *o od m, tn o o> 1- o -p *r* * tn c m e o a. 0> 13 O CD o C <1- 4 (0 o o 01 z 2 P O >> c r~ (0 Z o CO CD rH r-- (0 P 01 5 O . s. io s 01 a *o a -fi- X s- o o s-- -O J= >> a sz ro u d CM CM tn tn CD rH *r C rd jr 01 z u> s~ 01 -X "O P O to 3: *0 -D SP rd tn 01 2>>rP 2O P *-- P tO j P X V) c _o CO c *r* ^ in L ro O tn S- tn P Po s01- po> *ta--i> P i- XI r-- r- 3 f-- tn NO r- in p O VII -- 23 s- -a CM o re o T3 P (0 tn i-- OP 2 P Cl ro pp P CP u 0(0 tn V) ux 2 31 1 i O cn p en cn cn E tn CUE E p-^s P N\ ai Oi 01 p o> cnj-: 2-^ r-- 2 2 p p 3 oo o t j co tn 5 co 3t co CM 00 rH to o p <t to g tn EE s~ 2 a p in CM JC . Po o CO tn ai * 3 P T> H- O 01 -P c tn - in **- <0 P 3 m 73 P *3 3 01 01 *o 01 P tn 01 *i- 01 P UPC to ai v- o P *U P u o z u to 1-- 01 2 OJ T5 U o 3 SZ p o> 1 o c o c: tO f-- s <0 W - to (0ZZ uu P o pp *r tn <0 -X c O Ol e P P ai p ECS r-- rr0 c0 01 >ra> S2- f W N tfl /"-M-- SS ^ to o >> >> ai-r- i p ai oi to o u. (0 3 m-- P tj-- r 01 e CO O O Ul IN O c p C 5- (/) C "O O 01 (0 zo o ox w ^a. o p P PP c ai ai O JD (0 T- U P P2P eo O - op x NP 01 *U O O njr ns E-P _a sa. oi CO (0 01 tr~ f0 P -C Qi O P 0) s. JO r- E O to jocn 0.0 0J o m ns ro P U 1- 01 T3 i-- ro ox a tO 2J2 P tn o .n a. 01 o uN 1 o 01 f 10-3 DUP050452508 Chamberlain et al. (1978) 10-4 ion joC H- "C <-U 9) jx Ux ACOO "Vg 05 O --c3 Oo 0} *- U. eS " cr* J1 g ra cE3 0-2 g 2> S2 -- > T3 S" D> -fCg=OL) J"ngDm 'MCO CO J O o 0NO " ", `35 g- c Eo t; o J >fc jn aC oe ~o 3cr Si 3 .40 it .2 w. S Or*-X->O) 5. 5 .u5SS.'i.*2Co s^e DUP050452509 Rabinowitz et al. (1977) administered 204Pb tracer to adult volunteers and determined (by isotope tracer and balance data) that 14 pg lead was absorbed by these subjects daily at am bient air lead levels of 1-2 pg/m3. Assuming a daily ventilation rate of 20 m3, a deposition rate of 50 percent of ambient air (Chamberlain et al., 1978), and a mean air lead level of 1.5 pg/m3 (2.0 pg/m3 outside the study unit, 1.0 pg/m3 inside, as determined by the authors), then 15 pg lead was available for absorption. Hence, better than 90 percent of deposited lead was absorbed daily. Morrow et al. (1980) followed the systemic uptake of 203Pb in 17 adult subjects using either lead chloride or lead hydroxide aerosols with an average size of 0.25 (0.1) pm MMAD. Half of the deposited fraction of either aerosol was absorbed in 14 hr or less. The radio label data described above are consistent with the data of Hursh and Mercer (1970), who studied the systemic uptake of 212Pb on a carrier aerosol. Given the apparent invariance of absorption rate for deposited lead in the above studies as a function of the chemical form of the element (Chamberlain et al., 1978; Morrow et al., 1980), inhaled lead lodging deep in the respiratory tract seems to be absorbed equally, re gardless of form. Supporting evidence for total human systemic uptake of lead comes from autopsy tissue analysis for lead content.. Barry (1975) found that lead was not accumulated in the lungs of lead workers. This observation is corroborated by the data of Gross et al.' (1975) for nonoccupationally exposed subjects. Dependence of the respiratory absorption rate for lead in humans on the level of lead in air has not been extensively studied, although the data of Chamberlain and coworkers (1978), using human volunteers, show that the lung clearance rate in the adult for single lead pulses did not vary over a lung burden range of 0.3 to 450 pg. In occupational settings, a curvi linear relationship between workplace airborne lead and blood lead results at least partly from particle size changes, i.e., with increasing dust concentration, particle aggregation rate increases and the effective fraction of submicron particles (those penetrating to the lung) compared to total particles steadily lessens (Chamberlain, 1983). All of the available data for lead deposition and uptake from the respiratory tract in humans have been obtained with adults, and quantitative comparisons with the same exposures in children are not possible. Although children 2 years of age weigh one-sixth as much as an adult, they inhale 40 percent as much air lead as adults (Barltrop, 1972). James (1978) has taken into account differences in airway dimensions in adults versus children, and has esti mated that, after controlling for weight, the 10-year-old child has a deposition rate 1.6- to 2.7-fold higher than the adult. Recent studies support the above estimates of James (1978). Hofmann and coworkers (Hofmann, 1982; Hofmann et al., 1979) reported dose calculations for the respiratory tract as a function of age using airway length estimates from the literature and determined that Intake 10-5 TEH 0411912 D UP05045251 of radioactive nuclides into both the tracheobronchial and pulmonary regions was highly agedependent, with maximal intake occurring at about age six. 10.2.1.2 Animal Studies. Experimental animal data for quantitative assessment of lead depo sition and absorption for the lung and upper respiratory tract are limited. The available in formation does, however, support the finding that respired lead is extensively and rapidly absorbed. Morgan and Holmes (1978) exposed adult rats, by nose-only technique, to a 203Pb-labeled engine exhaust aerosol generated in the same manner as by Chamberlain et al. (1978) over a period of 8 days. Exposure was at a level of 21.9 to 23.6 nCi label/liter chamber air. Ad justing for deposition on the animal pelt, 20-25 percent of the label was deposited in the lungs. Deposited lead was taken up extensively in blood (50 percent within 1 hr and 98 per cent within 7 days). The absorption-rate kinetic profile was similar to that reported for humans (Chamberlain et al., 1978). Boudene et al. (1977) exposed rats to 210Pb-labeled aerosols at a level of 1 pg label/m3 and 10 pg label/m3, the majority of the particles being 0.1-0.5 pm in size. At 1 hr, 30 per cent of the label had left the lung; by 48 hr, 90 percent was gone. Bianco et al. (1974) used 212Pb aerosol (^0.2 pm) inhaled briefly by dogs and found a clearance half-time from the lung of approximately 14 hr. Greenhalgh et al. (1979) found that direct instillation of 203Pb-labeled lead nitrate solution into the lungs of rats led to an uptake of approximately 42 percent within 30 min, compared with an uptake rate of 15 percent within 15 min in the rabbit. These instillation data are consistent with the report of Pott and Brockhaus (1971), who noted that Intratracheal instillation of lead in solution (as bro mide) or in suspension (as oxide) serially over 8 days resulted in systemic lead levels in tissues indistinguishable from injected lead levels. Rendall et al. (1975) found that the movement of lead into blood of baboons Inhaling a lead oxide (Pb304) was more rapid and resul ted in higher blood lead levels when coarse (1.6 pm mean diameter) rather than fine (0.8 pm mean diameter) particles were used. 10.2.2 Gastrointestinal Absorption of Lead Gastrointestinal (GI) absorption of lead mainly involves uptake from food and beverages, as well as lead deposited in the upper respiratory tract that is eventually swallowed. It also includes ingestion of nonfood material, primarily in children via normal mouthing activ ity and pica. Two issues of concern with lead uptake from the gut are the comparative rates of such absorption in developing versus adult organisms, including humans, and how the bio availability of lead affects such uptake. 10.2.2.1 Human Studies. Based on long-term metabolic studies with adult volunteers, Kehoe (1961a,b,c) estimated that approximately 10 percent of dietary lead is absorbed from the human 10-6 TEH 0411913 DUP050452511 gut. According to Gross (1981), various balance parameters can vary considerably among sub jects. These studies (Kehoe, 1961a,b,c) did not take into account the contribution of biliary clearance of lead into the gut, which would have affected measurements for both absorption and total excretion. Chamberlain et al. (1978) determined that the level of endogenous fecal lead is approximately 50 percent of urinary lead values. They have estimated that 15 percent of dietary lead is absorbed, if the amount of endogenous fecal lead is taken into account. Following the Kehoe studies, a number of reports determined GI absorption using both sta ble and radioisotopic labeling of dietary lead. Generally, these reports support the observa tion that in the adult human the absorption of lead is limited when taken with food. Harrison et al. (1969) determined a mean absorption rate of 14 percent for three adult subjects ingest ing 203Pb in diet, a figure in accord with the results of Hursh and Suomela (1968). Chamberlain et al. (1978) studied the absorption of 203Pb in two forms (as the chloride and as the sulfide) taken with food. The corresponding absorption rates were 6 percent (sulfide) and 7 percent (chloride), taking into account endogenous fecal excretion. Using adult subjects who ingested the stable isotope 204Pb in their diet, Rabinowitz et al. (1974) reported an average gut absorption of 7.7 percent. In a later study, Rabinowitz et al. (1980) measured an ab sorption rate of 10.3 percent. A number of recent studies indicate that lead ingested under fasting conditions is absor bed to a much greater extent than lead taken with or incorporated into food. For example, Blake (1976) measured a mean absorption rate of 21 percent when 11 adult subjects ingested 203Pb-labeled lead chloride several hours after breakfast. Chamberlain et al. (1978) found that lead uptake in six subjects fed 203Pb as the chloride was 45 percent after a fasting period, compared to 6 percent with food. Heard and Chamberlain (1982) obtained a rate of 63.3 percent using a similar procedure with.eight subjects. Rabinowitz et al. (1980) reported an absorption rate of 35 percent in five subjects when 204Pb was ingested after 16 hr of fasting. These isotope studies support the observations of Barltrop (1975) and Garber and Wei (1974) that lead In between-meal beverages is absorbed to a greater extent than is lead in food. Dependence of the lead absorption rate from the human GI tract on the concentration of lead in diet or water has not been well studied. Recent data from the reports of Blake (1980), Flanagan et al. (1982), and Heard and Chamberlain (1983), however, indicate little concentration dependency across the range of dietary lead content encountered by the general population. For example, Flanagan et al. (1982) found that human volunteers absorbed 4, 40, and 400 pg of ingested lead at about the same rate. The relationship of lead bioavailability in the human gut to the chemical/biochemical form of lead can be determined from available data, although interpretation is complicated by the relatively small amounts administered and the presence of various components of food 10-7 TEH 0411914 DUP050452512 <; % . at-:; iis tfiS 'M its#'' -4 : ' m > -V'-? 4 --r y i already present in the gut. Harrison et al. (1969) found no difference in lead absorption from the human gut when lead isotope was given either as the chloride or incorporated into al ginate. Chamberlain et al. (1978) found that labeled lead as the chloride or sulfide was ab sorbed to the same extent when ingested with food, but the sulfide form was absorbed at a rate of 12 percent compared with 45 percent for the chloride under fasting conditions. Rabinowitz et al. (1980) obtained similar absorption rates for the chloride, sulfide, or cysteine complex forms when administered with food or under fasting conditions. Heard and Chamberlain (1982) found no difference in absorption rate when isotopic lead (203Pb) was ingested with unlabeled meat (sheep's liver and kidney) or when the label was incorporated into the food prior to slaughter. The data of Moore et al. (1979) are of interest with respect to relative GI uptake of lead in adult males and females. Human volunteers (seven males, four females) were given 203Pb in water and whole-body counting was carried out at time points. It appeared that females absorbed somewhat more of the label than males, but the difference did not reach sta tistical significance. Two reports have focused on the question of differences in GI absorption rates between adults and children. Alexander et.al. (1973) carried out 11 balance studies with eight chil dren, aged 3 months to 8 years. Daily intake averaged 10.6 pg Pb/kg body weight (range 5-17). The mean absorption rate determined from metabolic balance studies was 53 percent. A two-part investigation by Ziegler et al. (1978) comprised a total of 89 metabolic balance studies with 12 normal infants aged 2 weeks to 2 years. In the first part, 51 balance studies using 9 children furnished a mean absorption rate of 42.7 percent. In the second, six children were involved in 38 balance studies involving dietary lead intake at 3 levels. Diets were closely controlled and lead content was measured. For all daily intakes of 5 pg Pb/kg or higher, the mean absorption rate was 42 percent. At low levels of lead intake the data were variable, with some children apparently in negative balance, probably because of the difficulty in con trolling low lead intake. In contrast to these reports, Barltrop and Strehlow (1978) found that the results for children hospitalized as orthopedic or "social" admissions were highly variable. A total of 104 balance studies were carried out in 29 children ranging in age from 3 weeks to 14 years. Fifteen of the subjects were in net negative balance, with an average dietary absorption of -40 percent or, when weighted by number of balance studies, -16 percent. Closely comparing these data with those of Ziegler et al. (1978) is difficult. Subjects were inpatients, repre sented a much greater age range, and were not classified in terms of mineral nutrition or weight-change status. As an urban pediatric group, the children in this study may have had higher prior lead exposure so that the "washout" phenomenon (Kehoe, 1961a,b,c; Gross, 1981) may have contributed to the highly variable results. The calculated mean daily lead intake in 10-8 "K TEH 0411915 DUP050452513 the Barltrop and Strehlow group (6.5 pg/kg) was lower than that for all but one study group described by Ziegler et al. (1978). In the latter study, data for absorption became more variable as the daily lead intake was lowered. Finally, in those children classified as or thopedic admissions, whether skeletal trauma was without effect on lead equilibrium between bone and other body compartments is unclear. As typified by the results of the second National Health Assessment and Nutritional Eval uation Survey (NHANES II) (Mahaffey et al., 1979), children at 2-3 years of age show a small peak in blood lead. The question arises whether this peak indicates an intrinsic biological factor, such as increased absorption or retention when compared with older children, or whe ther this age group is exposed to lead in some special way. Several studies are relevant to the question. Zielhuis et al. (1978) reported data for blood lead levels in 48 hospitalized Dutch children, who ranged in age from 2 months to 6 years. Children up to 3 years old had a mean blood lead level of 11.9 pg/dl versus a level of 15.5 in children aged 4-6 years. A sig nificant positive relationship between child age and blood lead was calculated (r = 0.44, p <0.05). In the Danish survey by Nygaard et al. (1977), a subset of 126 children represent ing various geographical areas and age groups yielded the following blood lead values by mean age group: children (N = 8) with a mean age of 1.8 years had a mean blood lead level of 4.3 pg/dl; those with a mean age of 3.7-3.9 years had values ranging from 5.6 to 8.3 pg/dl; and children 4.6-4.8 years of age had a range of 9.2 to 10 pg/dl. These authors note that the youngest group was kept at a nursery, whereas the older kindergarten children had more inter action with the outside environment. Sartor and Rondia (1981) surveyed two population groups in Belgium, one of which consisted of groups of children aged 1-4, 5-8, and 9-14 years. Children under the age of 1 year had a mean blood lead level of 10.7 pg/dl. The 1- to 4-year and 5- to 8-year age groups were comparable, 13.9 and 13.7 pg/dl, respectively, while those 9-14 years old had a blood lead level of 17.2 pg/dl. All of the children in this study were hospital patients. While these European studies suggest that any significant restriction of children in terms of environmental interaction, e.g., in hospitals or nurseries, is associated with an apparently different age-blood lead relationship than the U.S. NHANES II subjects, whether European children in the 2- to 3-year age group show a similar peak remains to be demonstrated. The issue merits further study. The normal mouthing activity of young children, as well as the actual ingestion of non food Items (i.e., pica), is a major concern in pediatric lead exposure, particularly in urban areas with deteriorating housing stock and high automobile density and in nonurban areas con tiguous to lead-production facilities. The magnitude of such potential exposures is discussed in Chapter 7, and an integrated assessment of impact on human intake appears in Chapter 13. Such intake is intensified for children with pica and would include paint, dust, and dirt. 10-9 TEH 0411916 DUP050452514 Drill et al. (1979), using data from Day et al. (1975) and Lepow et al. (1974), have at tempted to quantify the daily intake of soil/dust in young children from such mouthing activi ties as thumb sucking and finger licking. A total of 100 mg/day was obtained for children 2-3 years old, but the amount of lead in this ingested quantity varied considerably from site to site. In the report, a GI absorption rate of 30 percent was estimated for lead in soil and dust. Of relevance to this estimate are the animal data discussed in the next section, which show that lead of variable chemical forms in soil or dust is as available for absorption as lead in food. The Jjn vitro studies relating lead solubility in street dusts with acidity clearly demonstrate that the acidity of the human stomach is adequate to extensively solubi lize lead assimilated from soil and dust. To the extent that Ingestion of such material by children occurs other than at mealtime, the fasting factor in enhancing lead absorption from the human GI tract (vide supra) must also be considered. Hence, a factor of 30 percent for lead absorption from dusts and soils is not an unreasonable value. A National Academy of Sciences (NAS) report on lead poisoning in children has estimated that paint chip ingestion by children with pica occurs with considerable frequency (National Academy of Sciences, 1976). In the case of paint chips, Drill et al. (1979) estimated an ab sorption rate as high as 17 percent. This value may be compared with the animal data in Sec tion 10.2.2.2, which indicate that lead in old paint films can undergo significant absorption in animals. 10.2.2.2 Animal Studies. Lead absorption via the gut of various adult experimental animal species appears to resemble that for the adult human, on the order of 1-15 percent in most cases. Kostial and her coworkers (Kostial and Kello, 1979; Kostial et al., 1978, 1971) re ported a value of 1 percent or less in adult rats maintained on commercial rat chow. These studies were carried out using radioisotopic tracers. Similarly, Barltrop and Meek (1975) reported an absorption rate of 4 percent in control diets, while Aungst et al. (1981) found the value to range from 0.9 to 6.9 percent, depending on the level of lead given in the diet. In these rat studies, lead was ingested with food. Quarterman and Morrison (1978) admini stered 203Pb label in small amounts of food to adult rats and found an uptake rate of appro ximately 2 percent at 4 months of age. Pounds et al. (1978) obtained a value of 26.4 percent with four adult Rhesus monkeys given 210Pb by gastric Intubation. The higher rate, relative to the rat, may reflect various states of fasting at time of intubation or differences in dietary composition (vide infra), two factors that affect rates of absorption. As seen above with human subjects, fasting appears to enhance the rate of lead uptake in experimental animals. Garber and Wei (1974) found that fasting markedly enhanced gut uptake of lead in rats. Forbes and Reina (1972) found that lead dosing by gastric intubation of rats yielded an absorption rate of 16 percent, which is higher than other data for the rat indi cate. Intubation was likely done when little food was in the gut. The data of Pounds et al. 10-10 TEH 0411917 DUP050452515 (1978), as described above, may also suggest a problem with administering lead by gastric in tubation or mixed with water as opposed to food. The bioavailability of lead in the GI tract of experimental animals has been the subject of a number of reports. The designs of these studies differ in regard to how "bioavailability" is defined. In some cases, the dietary matrix was kept constant, or nearly so, while the chemical or physical form of the lead was varied. By contrast, other data described the effect of changes in bioavail ability as the basic diet matrix was changed. The latter case is complicated by the simultaneous operation of lead-nutrient interactive relationships (de scribed in Section 10.5.2). All croft (1950) observed comparable effects when calves were fed lead in the form of the phosphate, oxide, or basic carbonate (PbC03*Pb(0H)2), or incorporated into wet or dry paint. By contrast, lead sulfide in the form of finely ground galena ore was less toxic. Criteria for relative toxicity included kidney and blood lead levels and survival rate over time. In the rat, Barltrop and Meek (1975) carried out a comparative absorption study using lead in the form of the acetate as the reference substance. The carbonate and thallate were absorbed to the greatest extent, while absorption of the sulfide', chromate, napthenate, and octoate was 44-67 percent of the reference agent. Barltrop and Meek (1979) also studied the relationship of the size of lead particles (as the metal or as lead octoate or chromate in powdered paint films) to the amount of gut absorption in the rat; they found an inverse rela tionship between uptake and particle size for both forms. Gage and Litchfield (1968, 1969) found that lead napthenate and chromate can undergo con siderable absorption from the rat gut when incorporated into dried paint films, although less than when given with other vehicles. Ku et al. (1978) found that lead in the form of the ace tate or as a phospholipid complex was equally absorbed from the GI tract of both adult and young rats at a level of 300 ppm. Uptake was assessed by weight change, tissue levels of lead, and urinary aminolevulinic acid (ALA) levels. In a study relevant to the problem of lead bioavailability in soils and dusts, particu larly In exposed children, Dacre and Ter Haar (1977) compared the effects of lead as acetate with lead contained in roadside soil and In house paint soil, at a level of approximately 50 ppm, in commercial rat chow. Uptake of lead was indexed by weight change, tissue lead con tent, and inhibition of aminolevulinic acid dehydrase (ALA-D) activity. None of these para meters differed significantly across the three groups, suggesting that neither the geochemical matrix in the soils nor the various chemical forms (basic carbonate in paint soil, and the oxide, carbonate, and basic carbonate in roadside soil) affect lead uptake. These data are consistent with the behavior of lead in dusts upon acid extraction as re ported by Day et al. (1979), Harrison (1979), and Duggan and Williams (1977). In the Day et al. study, street dust samples from England and New Zealand were extracted with hydrochloric 10-11 TEH 0411918 DUP050452516 acid (HC1) over the pH range of 0-5. At an acidity that may be equalled by gastric sec tions, i.e. , pH of 1, approximately 90 percent of the dust lead was solubilized. Harris (1979) noted that at this same acidity, up to 77 percent of Lancaster, England, street-i lead was soluble, while an average 60 percent solubility was seen in London dust sample (Duggan and Williams, 1977). Because gastric solubilization must occur for lead in th media to be absorbed, the above data are useful in determining relative risk. Kostial and Kello (1979) compared the absorption of 203Pb from the gut of rats maintaii on commercial rat chow versus rats fed such "human" diets as baby foods, porcine liver, and cow's milk. Absorption in the latter cases varied from 3 to 20 percent, compared w <1.0 percent with rat chow. This range of uptake for the nonchow diet compares closely wit that reported for human subjects (vide supra). Similarly, Jugo et al. (1975a) observed t rats maintained on fruit diets had an absorption rate of 18-20 percent. The generally o served lower absorption of lead in the adult rat compared to the adult human appears, then, less reflective of a species difference than of a dietary difference. A number of studies have documented that the developing animal absorbs a relatively ' greater fraction of ingested lead than does the adult, thus supporting studies showing thi age dependency in humans. For example, the adult rat absorbs approximately 1 percent lead or less via diet versus a corresponding value 40-50 times greater in the rat pup (Kostial et al., 1971, 1978; Forbes and Reina, 1972). In the rat, this difference persists through weaning (Forbes and Reina, 1972), at which point uptake resembles that of adults. Part of this dif ference can be ascribed to the nature of the diet (mother's milk versus regular diet), al though the extent of absorption enhancement with milk versus rat chow in the adult rat found by Kello and Kostial (1973) fell short of what is seen in the neonate. An undeveloped, Isss selective intestinal barrier may also exist in the rat neonate. In nonhuman primates, Munra-r' et al. (1975) observed that infant monkeys absorbed 65-85 percent via the gut versus 4 percent in adults. Similarly, Pounds et al. (1978) noted that juvenile rhesus monkeys absorbed appro ximately 50 percent more lead than adults. The question of the relationship of level of lead intake through the GI tract and rate of lead absorption was addressed by Aungst et al. (1981), who exposed adult and suckling rats to-` doses of lead by intubation over the range 1-100 mg/kg or by variable concentrations in drink-.,, ing water. With both age groups and both forms of oral exposure, lead absorption as a percent age of dose decreased, suggesting a saturation phenomenon for lead transport across thewall. Similar data were obtained by Bushnell and DeLuca (1983) for weanling rats given 203Pb b intubation along with carrier doses of 1, 10, 100, or 1000 ppm in diet. The GI absorptio rate was observed to decrease significantly between 10 and 100 ppm carrier lead. Using is lated duodenal loop preparations, Conrad and Barton (1978) reported that lead uptake acros 10-12 TEH 0411 DUP050452517 "HH1 the gut wall was constant from 0.001 to 10 ppm lead, but fell off to 40 percent of the 10-ppm level at the 100-ppm dosing. The above concentration dependency is consistent with a saturable, active transport pro cess for lead in the mammalian gut, based on the kinetic data of Aungst and Fung (1981). Mykk'anen and Wasserman (1981) also noted that lead uptake by chick intestine occurs in two kinetic phases; a rapid uptake is followed by a rate-limiting slow transfer of lead. These kinetic observations agree with an increasingly retarded active transport process as lead con tent increases in the gut; i.e., lead affects its own transport, manifested as an increasingly lower absorption rate at higher lead intake. Of interest here is the comparison of the kinetic behavior of blood lead as a function of oral versus parenteral dosing. With single intravenous injections of 0.5, 1, 5, 10, and 15 mg Pb/kg lead in the rat, Aungst et al. (1981) did not observe any dose dependency of the kinetic rate coefficients governing lead in blood. Integrated exposure, i.e., area under the blood lead curves, increased linearly with dose. On the other hand, injection of lead into rabbits at levels of 5, 10, 25, 50, and 500 pg/kg, by single daily injections for 6 days, resulted in clear curvilinearity to the dose-blood lead curve (Prpic-Majic et al., 1973). The differences in these two reports probably reflect dosing regimen differences: Aungst et al. (1981) used a higher dosing level as single exposures. The implication of these experimental findings for human oral lead exposure is' not clear. As noted earlier, lead intake orally by human subjects up to 400 pg is associated with a rather fixed absorption rate. Direct extrapolation of the animal data described above indi cates that humans would have to ingest 20 to 200 mg lead per day (assuming a 2-kg diet/day at lead contents of 10 or 100 ppm) to have a lowered absorption rate. This value is up to 4500fold above the upper oral Intake guideline for lead (National Academy of Sciences, 1980). 10.2.3 Percutaneous Absorption of Lead Absorption of inorganic lead compounds through the skin appears to be considerably less significant than uptake through the respiratory and GI routes. This observation contrasts with observations for lead alkyls and other organic derivatives (see Section 10.7). Rastogi and Clausen (1976) found that cutaneous or subcutaneous administration of lead napthenate in rat skin was associated with higher lead tissue levels and more severe toxic effects than was the case for lead acetate. Laug and Kunze (1948) applied lead as the acetate, orthoarsenate, oleate, and ethyl lead to rat skin and determined that the greatest levels of kidney lead were associated with the alkyl contact. Moore et al. (1980) studied the percutaneous absorption of 203Pb-labeled lead acetate in cosmetic preparations using eight adult volunteers. Applied in wet or dry forms, absorption was indexed by blood, urine, and whole body counting. Absorption rates ranged from 0 to 0.3 10-13 .ji l TEH 0411920 DUP050452518 percent, with the highest values obtained when the application sites were scratched. These researchers estimated that the normal use of such preparations would result in an absorption of approximately 0.06 percent. 10.2.4 Transplacental Transfer of Lead Lead uptake by the human and animal fetus occurs readily, based on such indices as fetal tissue lead measurements and, in the human, cord blood lead levels. Barltrop (1969) and Horiuchi et al. (1959) demonstrated by fetal tissue analysis that placental transfer in the human occurs by the 12th week of gestation, with fetal lead uptake increasing throughout development. The highest lead levels occur in bone, kidney, and liver, followed by blood, brain, and heart. Cord blood contains significant amounts of lead, which generally correlate with maternal blood values and are slightly but significantly lower in concentration than the mother's (Scanlon, 1971; Harris and Holley, 1972; Gershanik et al., 1974; Buchet et al., 1978; Alexander and Delves, 1981; Rabinowitz and Needleman, 1982). A cross-sectional study of maternal blood lead levels carried out by Alexander and Delves (1981) showed that a significant decrease in maternal blood lead occurs throughout pregnancy, a decrease greater than the dilution effect of the concurrent increase in plasma volume. Hence, during pregnancy there is either an increasing deposition of lead in placental or fetal tissue or an increased loss of body lead via other routes. Increasing absorption by the fetus during gestation, as demonstrated by Barltrop (1969), implies that the former explanation is likely. Hunter (1978) found that summer-born children showed a trend toward higher blood lead levels than those born in the spring, suggesting increased fetal uptake in the summer result ing from increases In circulating maternal lead. This observation was confirmed in the report of Rabinowitz and Needleman (1982). Ryu et al. (1978) and Singh et al. (1978) both reported that infants born to women having a history of lead exposure had significantly elevated blood lead values at birth. if ISll jjlj mHMm 10.3 DISTRIBUTION OF LEAD IN HUMANS AND ANIMALS A quantitative understanding of the sequence of changes in lead levels in various body pools and tissues is essential in interpreting measured lead levels with respect to past expo sure as well as present and future risks of toxicity. This section discusses the distribution kinetics of lead in various portions of the body (blood, soft tissues, calcified tissues, and the "chelatable" or toxicologically active body burden) as a function of such parameters as exposure history and age. IS* i. 10-14 m TEH 0411921 DUP050452519 A given quantity of lead taken up from the GI tract or the respiratory tract into the bloodstream is initially distributed according to the rate of delivery by blood to the various organs and systems. Lead is then redistributed to organs and systems in proportion to their respective affinities for the element. With consistent exposure for an extended period, a near steady state of intercompartmental distribution is achieved. Fluctuations in the near steady state will occur whenever short-term lead exposures are superimposed on a long-term uptake pattern. Furthermore, the steady-state description is im perfect because, on a very short (hourly) time scale, intake is not constant. Lead intake with meals and changes in ambient air lead (outside to inside and vice versa) cause quick changes in exposure levels that may be viewed as short-term alterations in the small, labile lead pool. Metabolic stress could remobilize and redistribute body stores, although documen tation of the extent to which this happens is very limited (Chisolm and Harrison, 1956). 10.3.1 Lead in Blood Viewed from different time scales, lead in whole blood may be seen as residing in several distinct, interconnected pools. More than 99 percent of blood lead is associated with the erythrocytes (DeSilva, 1981; Everson and Patterson, 1980; Manton and Cook, 1979) under typiqal conditions, but it is the very small fraction of lead transported in plasma and extracellular fluid that provides lead to the various body organs (Baloh, 1974). Although the toxicity of lead to the erythrocyte (Raghavan et a!., 1981) is mainly asso ciated with membrane lead content, most of the erythrocyte lead is bound within the cell. Within erythrocytes from nonexposed subjects, lead is primarily bound to hemoglobin, in par ticular HbA2, which binds approximately 50 percent of cell lead while constituting only 1-2 percent of total hemoglobin (Bruenger et al., 1973). A further 5 percent is bound to a 10,000-dalton molecular-weight fraction, about 20 percent to a much heavier molecule, and about 25 percent is considered "free" or bound to lower-weight molecules (Ong and Lee, 1980a; Raghavan and Gonick, 1977). Raghavan et al. (1980) have observed that, among workers exposed to lead, those who develop signs of toxicity at relatively low blood lead levels seem to have a diminished binding of intracellular lead with the 10,000-dalton fraction. This reduction in binding suggests an impaired biosynthesis of a protective species. According to Ong and Lee (1980b), fetal hemoglobin has a higher affinity for lead than adult hemoglobin. Whole blood lead in daily equilibrium with other compartments was found to have a mean life of 35 days (25-day half-life) and a total lead content of 1.9 mg, based on studies with a small number of subjects (Rabinowitz et al., 1976). Chamberlain et al. (1978) established a similar half-life for 203Pb in blood when volunteers were given the label by ingestion, Inha lation, or injection. The lead Inhalation studies in adults described by Griffin et al. 10-15 TEH 0411922 DUP050452520 (1975) permit calculation of half-lives of 28 and 26 days for inhalation of 10.4 and 3.1 pg Pb/m3, respectively. These estimates of biological half-life, based as they are on isotopic study, do not reflect the impact of mobile body burden on half-life. The higher the mobiliza-' ble lead burden, the greater will be the length of the half-life, as clearly seen in thi report of O'Flaherty et al. (1982), where half-life in lead workers was a function of cumula-- tive occupational exposure. Alterations in blood lead levels in response to abrupt changes in exposure apparently oc cur over somewhat different periods, depending on whether the direction of change is greater or smaller. With increased lead intake, blood lead level achieves a new value in approxi mately 60 days (Griffin et al., 1975; Tola et.al., 1973). A decrease may Involve a longer period of time, depending on the magnitude of the past higher exposure (O'Flaherty et al., 1982; Rabinowitz et al. 1977; Gross, 1981). In adulthood, the human's blood lead level appears to Increase moderately. Awad et al. (1981) reported an Increase of 1 pg for each 14 years of age. However, in the NHANES II sur vey (see Chapter 11), white adults showed increasing blood lead until 35-44 years of age, fol lowed by a decrease. By contrast, blacks showed increasing blood lead after 44. In the case of reduced exposure, particularly occupational exposure, the time for re-establishing near steady state depended more upon the extent of lead resorption from bone and the total quanti ty deposited, either of which can extend the "washout" interval. Lead levels in newborn children are similar to but somewhat lower than those of their mothers: 8.3 versus 10.4 pg/dl (Buchet et al., 1978) and 11.0 versus 12.4 pg/dl (Alexander and Delves, 1981). Maternal blood lead levels decrease throughout pregnancy, the decrease being greater than the expected dilution via the concurrent increase in plasma volume (Alexander and Delves, 1981). This decrease in maternal blood lead levels suggests increased fetal uptake during gestation (Barltrop, 1969). Increased tissue retention of lead by the child may also be a factor. HH||| Levels of lead in blood are sex related; adult women invariably show lower levels than adult males (e.g., Mahaffey et al., 1979). Of interest in this regard is the study of Sttiik (1974) showing lower blood lead response in women than in men for an equivalent level of Idad intake. The small but biologically significant lead pool in blood plasma has proven technically difficult to measure, and reliable values have become available only recently (see Chapter 91. Chamberlain et al. (1978) found that injected 203Pb was removed from plasma (and, by infer ence, from extracellular fluid) with a half-life of less than 1 hr. These data support f - observation of DeSilva (1981) that lead is rapidly cleared from plasma. Ong and lee (1980a), in their in vitro studies, found that 203Pb is virtually all bound to albumin and that only 10-16 TEH 04119? DUP050452521 trace amounts are bound to high-weight globulins. To state which binding form constitutes an "active" fraction for movement to tissues is not possible. Although Rosen et al. (1974) reported that plasma lead did not vary across a range of whole blood levels, the findings of Everson and Patterson (1980), DeSilva (1981), and Cavalier! et al. (1978) indicate that there is an equilibrium between red blood cells (RBCs) and plasma, such that levels in plasma rise with levels in whole blood. This observation is consistent with the data of Clarkson and Kench (1958), who found that lead in the RBC is rela tively labile to exchange and a logical prerequisite for a dose-effect relationship in various organs. Ong and Lee (1980c), furthermore, found that plasma calcium is capable of displacing RBC membrane lead, suggesting that plasma calcium is a factor in the cell-plasma lead equilib rium. Several studies concerning the relative distribution of lead between erythrocytes and plasma or serum indicate that the relative percentage of blood lead in plasma versus erythro cytes is relatively constant up to a blood lead concentration of about 50-60 pg/dl, but becomes increasingly greater above this level, i.e., the overall blood lead/plasma lead rela tionship is curvilinear upward. DeSilva (1981) found that the relative fraction of plasma lead versus erythrocytes in 105 Australian lead workers increased at M50 pg/dl. Similarly, Manton and Malloy (1983) observed that a subject having lead Intoxication had serum lead values ranging from 1.6 to 0.3 percent as blood concentration changed from 116 to 31 pg/dl. More recently, Manton and Cook (1984) demonstrated a curvilinear relationship between serum and whole blood lead levels. As de picted in Figure 10-2, the curve indicates that there is a linear segment up to ~50 pg/dl, followed by rather steep increases in relative serum lead content at higher levels. Measurement of lead in plasma by these investigators was carefully carried out, and the Manton reports involved the definitive lead analysis technique of isotope-dilution mass spec trometry (IDMS, see Chapter 9). Given the increased erythrocyte fragility with increasing blood lead content (see Section 12.3), slight hemolysis during sampling might contaminate plasma or serum with high erythrocyte lead and complicate such analyses; however, the reports did not indicate that hemolysis was considered a problem. The biological basis for higher levels of plasma versus whole blood lead with increasing blood lead burden may be related to marked changes in the binding capacity of the erythrocyte at high lead content. These changes may result from alterations in binding sites or in the efficiency of lead movement from membrane to erythrocyte Interior. Fukumoto et al. (1983) have demonstrated changes (in the form of a decrease) in lead-worker erythrocyte-membrane pro teins that may have a role in lead transport. Perhaps more important are the long-known ef fects of lead exposure on erythrocyte morphology and destruction rate (see Section 12.3). 10-17 TEH 0411924 DUP050452522 SERUM LEAD, ^ig/dl Figure 10-2. The curvilinear relationship of serum lead to blood lead. Cross-hatched area represents several overlapping points. Source: Manton and Cook (1984). 10-18 DUP050452523 Changes In cell morphology with increasing blood lead may alter accessibility to binding sites or the relative stability of these sites. Increased cell destruction may increase proteinbound cell lead in plasma, which is only slowly transferred back to cell membrane. In vitro data concerning the concentration dependency of lead partitioning between ery throcytes and plasma are of Interest. Keep in mind, however, that such in vitro data have em ployed normal erythrocytes. Clarkson and Kench (1958) showed that the relative partitioning between normal erythrocytes and plasma is relatively constant up to the highest level tested, equivalent to 100 pg Pb/dl. In the related study of Kochen and Greener (1973), tracer plus carrier lead was added to blood of varying hematocrit up to a maximum addition of 1000 pg/dl. At a normal hematocrit and a higher value (0.65), the percent uptake of lead label by the cells diminished at around 100 pg/dl, consistent with the Clarkson and Kench (1958) data. Onset of curvilinearity at a lower blood lead level in vivo in lead-exposed subjects below the v^ro value of VLOO pg/dl probably reflects in part altered cell morphology and stability (DeSilva, 1981; Manton and Malloy, 1983; Manton and Cook, 1984). The curvilinear relationship of plasma to whole blood lead may well be a factor in Chamberlain's (1983) observation that the relative rate of urinary excretion of lead in human adults increases with blood lead content,, as determined from various published reports provid ing both blood and urinary lead data (see Section 10.4). It may also figure in the apparently better proportionality of tissue lead burdens to dose than blood lead (vide infra) and, equally Important, the curvilinear relationship of chelatable lead to blood lead. That is, at Increasing blood lead, the higher relative rate of plasma lead movement to soft tissues and bone is greater than would be anticipated from simple inspection of blood lead content, the latter rising at a slower rate relative to the Increase in plasma lead. 10.3.2 Lead Levels in Tissues Of necessity, various relationships of tissue lead to exposure and toxicity in humans generally must be obtained from autopsy samples, although in some studies biopsy data have been described. The inherent question then is whether such samples adequately represent the behavior of lead In the living population, particularly in cases where death was preceded by prolonged illness or disease states. Also, victims of fatal accidents are not well character ized as to exposure status and are usually described as having no "known" lead exposure. Finally, these studies are necessarily cross-sectional in design, and, in the case of body ac cumulation of lead, different age groups are assumed to have been similarly exposed. Some im portant aspects of the available data include the distribution of lead between soft and cal cifying tissue, the effect of age and development on lead content of soft and mineral tissue, and the relationship between total and "active" lead burdens in the body. 10-19 TEH 0411926 DUP050452524 10.3.2.1 Soft Tissues. In humans over age 20 most soft tissues do not show age-related changes In lead levels, in contrast to the case with bone (Barry and Mossman, 1970; Barry 1975, 1981; Schroeder and Tipton, 1968; Butt et al., 1964). Kidney cortex also shows creases In lead with age that may be associated with formation of lead nuclear inclusion *. 'V X bodies (Indraprasit et al., 1974). Based on these rates of accumulation, the total body bur-j* `-j* j den may be divided into pools that behave differently. The largest and kinetically slowest pool is the skeleton, which accumulates lead with age. The much more labile lead pool is in` soft tissue. Soft-tissue lead levels generally stabilize in early adult life and show a turnover rate ^ - - $ similar to that for blood. This turnover is sufficient to prevent accumulation except in the.. i ' ? 1 1 renal cortex, which may reflect formation of lead-containing nuclear inclusion bodies (Cramer, 'Vj - ' et al., 1974; Indraprasit et al., 1974). The data of Gross et al. (1975) and Barry (1975) u.s4s Ml indicate that aortic levels rise with age, although this rise may only reflect entrapment of..' lead in atherosclerotic deposits. Biliary and pancreatic secretions, while presumably re-- * fleeting some of the organ levels, have tracer lead concentrations distinct from either blood .. jw ^ or bone pools (Rabinowitz et al., 1973). For levels of lead in soft tissue, the reports of Barry (1975, 1981), Gross et al. 1 (1975) 'V, )/ m and Horiuchi et al. (1959) indicate that soft-tissue content generally is below 0.5 pg/g * wet weight, with higher values for aorta and kidney cortex. The higher values in aorta may or i; .JV- * may not reflect lead in plaque deposits, while higher kidney levels may be associated with the: ^ ^ presence of lead-accumulating tubular cell nuclear inclusions. The relatively constant lead .. concentration in lung tissue across age groups suggests no accumulation of respired lead and is consistent with data for deposition and absorption (see Section 10.2.1). Brain tissue was generally under 0.2 ppm wet weight and appeared to show no change with increasing age. Since these data were collected by cross-sectional study, age-related changes In the low levels of lead in brain would have been difficult to discern. Barry (1975) found that tissues in a small group of samples from subjects with known or suspected occupational exposure showed higher lead levels in aorta, liver, brain, skin, pancreas, and prostate. Analysis of lead levels in whole brain is less illuminating than regional analysis to the issue of sensitivity of certain regions within the organ to toxic effects of lead. The dis--> ' : tribution of lead across brain regions has been reported by various laboratories. The rele-. vant data for humans and animals are set forth in Table 10-2. The data of Grandjean (1978>^j|A|E^W and Niklowitz and Mandybur (1975) for human adults, and those of Okazaki et al. (1963) for autopsy samples from young children who died of lead poisoning, are consistent in showing that lead is selectively accumulated in the hippocampus. The correlation of lead level with potas-. sium level suggests that uptake of lead is greater in cellulated areas. The involvement or ,, mm 10-20 we .'i-jj TEH 041 19?/. DUP050452525 r-N 00 N cn r-i CD c o id e a? 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X 0) c zo to o r <0 l/) PP u to QJ sz 3 *r> TO *o SZ E < 33 to 3= 3 73 O) cn <D TO *73 c c in a> i-- *r- `r-- o *-- *r- c C CL J= o o X J= u to to CD P *r c*r 01 o O J3 5 10 CL CL P O) 73 X> to o c t o TO P a> *r- a; O U'nc <D P o r-j 3 tfi TOp-- to r~* P Ul M3O Pt o PTO to rH CL UU LU ro s5 73 73 CD CD to TO OO Cl CL XX CD CD Cc =3 33 3S T3 r-- o 5~ >, c CM ai $_ in 73 r-- T3 r-- P-- *r*" r- 3 _C Js 73 Oo< tn p TO S- to P rT-O 3 6 73 C C C TO P TO S. P r-- 3 73 n o *i-- P U O) 0) -X `r)\ c cn f- 73 * LT> cr a. TO * *r TO U r-- >v O o -- S- *r- O P TO C -O to o u QJ U ^ LT S- E t o TO CL O P CL CL CD X i-O fl) 73 O rH P 73 O SZ r TO CD TO 1-- "X TO 3 QJ r- TO OJ O O> xs- a. p csj C QJ rH o CJ TO PTO S~ TO cn r-- o TO 73 P TO O) C sz o3 0) o Z8Z >- 10-21 o M r- o X u H DUP050452526 the cerebellum in lead encephalopathy in children (see Section 12.4) and in adult intoxication from occupational exposure indicates that the sensitivity of various brain regions to lead as well as their relative uptake characteristics are factors in lead neuropathology. In adult rats, selective uptake of lead is shown by the hippocampus (Fjerdingstad et al., 1974; Danscher et al., 1975) and the amygdala (Danscher et al., 1975). By contrast, leadexposed neonate rats show greatest uptake of lead Into cerebellum, followed by cerebral cor tex, then brainstem plus hippocampus. Hence, there is a developmental difference in lead dis tribution in the rat with or without increased lead exposure (Klein and Koch, 1981). In studies of young dogs, "unexposed" animals showed highest levels in the cerebellum. Increased lead exposure was associated with selective uptake into gray matter, while cerebel lar levels were relatively low. Unlike the young rat, then, the distribution of lead in brain regions of dogs appears dose-dependent (Stowe et al., 1973). The relationship of lead distribution to various tissues with changes in lead exposure has not been well researched. Available information does suggest that the nature of lead ex posure in experimental animals influences the relationship of tissue lead level to both blood lead level and level of intake. Long-term oral exposure of experimental animals at relatively moderate dosing would appear to result, in tissue values that show more proportionality to dose than do blood lead values, although tissue versus blood lead relationships still appear to be curvilinear. Such is the case with dogs exposed to dietary lead for 2 years (Azar et al., 1973) and rats exposed iji utero and postnatally up to 9 months of age (Grant et al., 1980). By contrast, short-term exposure at various dosing levels yields highly variable data (see Section 12.4.3.5 and Table 12-8). Bull et al. (1979) have reported brain and blood lead data for dam-exposed suckling rats that show marked deviation from linear response to dose when lead was administered in drinking water at 0.0005 to 0.02 percent lead. Over this 40fold oral dosing range, brain lead levels increased only approximately threefold at 21 days of age. Whether this low absorption of lead by brain reflects tissue distribution curvllinearity in the pups or reflects a function of nonlinear milk lead versus maternal dosing relationships cannot be determined. Collins et al. (1982) reported that rats orally exposed to lead from 3 days of age for 4-8 weeks showed a two- to threefold Increase in brain regions when the dosing level was increased to 1.0 mg/kg from 0.1 mg/kg. Blood lead at these two dosing levels showed a concentration ratio of -v2.5, indicating that both brain tissue and blood showed similar non linear response over this 10-fold change in oral exposure. Barry (1975, 1981) compared lead levels in soft tissues of children and adults. Tissue lead of Infants under 1 year old was generally lower than in older children, while children aged 1-16 years had values that were comparable to those for adult women. In Barry's (1981) ! 1 ' mm. Slip: 1 .mm 'fit 10-22 TEH 0411929 DUP050452527 study, the absolute concentration of lead in brain cortex or the ratios of brain cortex to blood lead levels did not appear to be different in infants or older children compared to adults. Such direct comparisons do not account for relative tissue mass changes with age, but this factor is comparatively less with soft tissue than with the skeletal system (see Section 10.4). Subcellular distribution of lead in soft tissue is not uniform, with high amounts of lead being sequestered in the mitochondria and nucleus. Cramer et al. (1974) studied renal biopsy tissue in lead workers having exposures of variable duration. They observed lead-binding nuclear inclusion bodies in the renal proximal tubules of subjects having short exposure, with all showing mitochondrial changes. A considerable body of animal data (see Section 10.3.5) documents the selective uptake of lead into these organelles. Pounds et al. (1982) describe these organellar pools in kinetic terms as having comparatively short half-lives in cultured rat hepatocytes, while McLachlin et al. (1980) found that rat kidney epithelial cells form lead-sequestering nuclear inclusions within 24 hr. 10.3.2.2 Mineralizing Tissue. Biopsy and autopsy data have shown that lead becomes localized and accumulates in human calcified tissues, i.e., bones and teeth. The accumulation begins with fetal development (Barltrop, 1969; Horiuchi et al., 1959). Total lead content in bone may exceed 200 mg in men aged 60 to 70 years, but-in women the accumulation is somewhat lower. Various investigators (Barry, 1975; Horiguchi and Utsunomiya, 1973; Schroeder and Tipton, 1968; Horiuchi et al., 1959) have documented that approximately 95 percent of total body lead is lodged in bone. These reports not only establish the affinity of bone for lead, but also provide evidence that lead increases in bone until 50-60 years of age, the later fall-off reflecting some combination of diet and mineral metabolism changes. Tracer data show accumulation in both trabecular and compact bone (Rabinowltz et al., 1976). In adults, bone lead is the most inert pool as well as the largest, and accumulation can serve to maintain elevated blood lead levels years after past, particularly occupational, ex posure has ended. This fact accounts for the observation that duration of exposure correlates with the rate of reduction of blood lead after termination of exposure (O'Flaherty et al., 1982). The proportion of body lead lodged in bone is reported to be lower in children than in adults, although concentrations of lead In bone increase more rapidly than In soft tissue during childhood (Barry, 1975, 1981). In 23 children, bone lead was 9 mg, or 73 percent of total body burden, versus 94 percent in adults. Expression of lead in bone in terms of con centration across age groups, however, does not accommodate the "dilution" factor, which is quite large for the skeletal system in children (see Section 10.4). The Isotope kinetic data of Rabinowltz et al. (1976) and Holtzman (1978) Indicate biolog ical half-lives of lead in bone on the order of several decades, although it appears that 10-23 TEH 0411930 DUP050452528 there are two bone compartments, one of which is a repository for relatively labile lead (Rabinowitz et al., 1977). Tooth lead levels also increase with age at a rate proportional to exposure (Steenhout and Pourtois, 1981), and are also roughly proportional to blood lead levels in man (Winneke et al., 1981; Shapiro et al., 1978) and experimental animals (Kaplan et al., 1980). Dentine lead is perhaps the most responsive component of teeth to lead exposure because it is laid down from the time of eruption until the tooth is shed. Needleman and Shapiro (1974) have docu mented the usefulness of dentine lead as an indicator of the degree of subject exposure. Fremlin and Edmonds (1980), using alpha-particle excitation and microautoradiography, have shown dentine zones of lead enrichment related to abrupt changes in exposure. The rate of lead deposition in teeth appears to vary with the type of tooth. Deposition is highest in the central incisors and lowest in the molars, a difference that must be taken into account when using tooth lead data for exposure assessment, particularly for low levels of lead exposure (Mackie et al., 1977; Delves et al., 1982). n 10.3.3 Chelatable Lead Mobile lead in organs and systems is potentially more "active" toxicologically in terms of being available to sites of action. Hence, the presence of diffusible, mobilizable, or ex changeable lead may be a more significant predictor of imminent toxicity or recent exposure than total body or whole blood burdens. In reality, however, assays for mobile lead would be quite difficult. In this regard, chelatable urinary lead has been shown to provide an index of this mobile portion of total body burden. Note that "chelatable" lead refers here to the use of calcium disodium ethylenediaminetetraacetic acid (CaNa2EDTA) and body compartments accessible to this chelant. Based mainly on the relationship of chelatable lead to indices of heme bio synthesis impairment, chelation challenge is now viewed as the most useful probe of undue body burden in children and adults (U.S. Centers for Disease Control, 1978; World Health Organiza tion, 1977; Chisolm and Barltrop, 1979; Chisolm et al., 1976; Saenger et al., 1982; Hansen et al., 1981). In adults, chelation challenge is the most reliable diagnostic test for assess ment of lead nephropathy, particularly when exposure is remote in time (Emerson, 1963; Wedeen et al., 1979) or unrecognized (Batuman et al., 1981, 1983). A quantitative description of inputs to the fraction of body lead that is chelatable from various body compartments is difficult to define fully, but it very likely includes a sizable, fairly mobile compartment within bone as well as within soft tissues. This assertion is based on several factors. First, the amount of lead mobilized by chelation is age-dependent in nonexposed adults (Araki, 1973; Araki and Ushio, 1982), while blood and soft-tissue lead levels HK as i-i1is1 fill .V' .:|i AH 10-24 TEH 0411931 DUP050452529 are not (Barry, 1975). This difference Indicates a lead pool labile to chelation but kinetically distinct from soft tissue. Second, studies of chelatable lead in animals (Hammond, 1971, 1973) suggest removal of some bone lead fraction, as does the response of explanted fetal rat bone lead to chelants (Rosen and Markowitz, 1980). Third, the tracer modeling esti mates of Rabinowitz et al. (1977) suggest a mobile bone compartment, and fourth, there is a complex, nonlinear relationship of lead intake by air, food, and water (see Chapter 11) to blood lead, and an exponential relationship of chelatable lead to blood lead (Chisolm et al., 1976). The logarithmic relationship of chelatable lead to blood lead in children (Chisolm et al., 1976) is consistent with the studies of Saenger et al. (1982), who reported that levels of mobilizable lead in "asymptomatic" children with moderate elevations in blood lead were quite similar in many cases to those values obtained in children with signs of overt toxicity. Hansen et al. (1981) reported that lead workers challenged with CaNazEDTA showed 24-hr urine lead levels that in many cases exceeded the accepted limits even though blood lead was only moderately elevated in many of those workers. The action level corresponded, on the regres sion curve, to a blood lead value of 35 pg/dl. Several reports provide insight into the behavior of labile lead pools in children treat ed with chelating agents over varying periods of time. Treatment regimens using CaNa2EDTA or CaNa2EDTA + BAL (British anti-Lewisite, or dimercaprol) for up to 5 days have been invariably associated with a "rebound" in blood lead, ascribed to a redistribution of lead among mobile lead compartments (Chisolm and Barltrop, 1979). Marcus (1982) reported that 41 children given oral D-penici 11 amine for 3 months showed a significant drop in blood lead by 2 weeks (mean initial value of 53.2 pg/dl), then a slight rise that was within measurement error with a peak at 4 weeks, and a fall at 6 weeks, followed by no further change at a blood lead level of 36 pg/dl. Hence, there was a near steady state at an elevated level for 10 of the 12 weeks with continued treatment. This observation could have indicated that re-exposure was occur ring, with oral penicillamine and ingested lead leading to increased lead uptake, as seen by Jugo et al. (1975a). However, Marcus (1982) stated that an effort was made to limit further lead intake as much as possible. From these reports, a re-equilibration does appear to occur, varying in characteristics with type and duration of chelation. The rebound seen in short term treatment with CaNa2EDTA or CaNa2EDTA + BAL, although attributed to soft tissue, could well Include a shift of lead from a larger mobile bone compartment to soft tissues and blood. The apparent steady state between the blood lead pool and other compartments that is achieved In the face of plumburesis, Induced by D-penici11 amine (Marcus, 1982), suggests a rather siza ble labile body pool which, in quantitative terms, would appear to exceed that of soft tissue alone. 10-25 TEH 0411932 DUP050452530 Several studies of EDTA mobilization of lead in children (Saenger et al., 1982; Piomelli et al., 1984) indicate the relative merit of assessing chelatable lead burden in children otherwise characterized as having mild or moderate lead exposure as indicated by blood lead levels. Saenger et al. (1982) noted that significant percentages of children having mild or moderate lead exposure as commonly indexed were found after EDTA challenge to have levels of plumburesis that would qualify them for chelation therapy under U.S. Centers for Disease Control (CDC) guidelines. In the most comprehensive evaluation of this issue to date (Piomelli et al., 1984), 210 children from four different urban lead-poisoning treatment centers were evaluated by EDTA provocation testing. The results showed that at a blood lead level of 30-39 pg/dl, 12 percent (6/52) of children exceed the ratio of 0.6 for pg Pb excreted per mg EDTA per 8 hr. This ratio was selected by the study clinicians as differentiating children with mobile lead bur dens who require further evaluation and/or treatment. Thirty-eight percent of children with blood lead levels of 40-49 pg/dl exceeded the action ratio of 0.6. As indicated in Section 10.3.1, one basis for the curvilinear relationship between chelatable lead and blood lead may be the curvilinear relationship of plasma lead to blood lead. The former increases at a faster rate with exposure increases than blood lead, permitting an increasingly greater rate of lead transfer to the chelatable lead compartment.. 10.3.4 Mathematical Descriptions of Physiological Lead Kinetics To account for observed kinetic data and make predictive statements, a variety of mathe matical models have been suggested, including those describing "steady-state" conditions. Tracer experiments have suggested compartmental models of lead turnover based on a central blood pool (Holtzman, 1978; Rabinowitz et al., 1976; Batschelet et al., 1979). These experi ments have hypothesized well-mixed, interconnected pools and have used coupled differential equations with linear exponential solutions to predict blood and tissue lead exchange rates. Were lead to be retained in these pools in accordance with a power-law distribution of resi dence times, rather than being uniform, a semi-Markov model would be more appropriate (Marcus, 1979). In the model proposed by Rabinowitz et al. (1976), based on the use of stable lead iso tope tracer in adult volunteers, lead biokinetics is envisioned in terms of three body com partments. These compartments, consisting of a central blood compartment as well as softtissue and bone compartments, differ as to biological half-lives or mean-lives (half life = mean-life x 0.693). Blood shows the shortest biological half-life, followed by soft tissue and then the bone compartment. Bone contains most of total body lead burden. 10-26 TEH 0411933 DUP050452531 FWW A more recent approach has been that of Kneip et al. (1983) for multi-organ compartmentalization of lead, based on data obtained with infant and juvenile baboons administered sin gle and chronic lead doses orally. The model proposed for infant baboons is depicted in Figure 10-3. Figure 10-3 acknowledges differences in certain features of lead biokinetics that differ in the developing versus adult organism. One of these differences is the lead transfer rate from blood to bone. In addition, an extracellular space-gut (ECS-Gut) compart ment is included in Figure 10-3. The emphasis is on lead intake through the gut, and a respiratory intake component is not included. In common with other attempts at modeling, the blood compartment in the approach of Kneip et al. (1983) is not further characterized kinetically, which is a limitation in view of the data base concerning such relationships as the curvilinear one between plasma and blood lead (see Section 10.3.2). Most extant steady-state models are deficient because they are based on small numbers of subjects and neglect a dose dependency for some of the interpool transfer coefficients. In this case, a nonlinear dose-indicator response model would be more appropriate when consid ering changes in blood lead levels. For example, the relationship between blood lead and air lead (Hammond et al., 1981; Brunekreef, 1984) as well as that between diet (United Kingdom Central Directorate on Environmental Pollution, 1982) and tap drinking water (Sherlock et al., 1982) are all nonlinear in mathematical form. In addition, alterations in nutritional status or the onset of metabolic stresses can complicate steady-state relationships. In a series of papers, Marcus (1985a,b,c,d) has discussed linear and nonlinear multicompartmental models of lead kinetics and has addressed in particular the relationship between plasma lead and blood lead and the relationship between blood lead and total lead intake. As shown in Figure 10-4, Marcus (1985d) differentiated four discrete pools within the blood com partment: diffusible lead in plasma, protein-bound lead in plasma, a "shallow" red blood cell pool (possibly the erythrocyte membrane), and a "deep" red blood cell pool (probably within the erythrocyte). This model was based on previously published data from a volunteer subject who ingested lead under controlled experimental conditions (DeSilva, 1981). Different ver sions of the model, all assuming steady-state conditions for lead in all tissues, were ana lyzed in terms of three possible mechanisms that might underlie nonlinear blood kinetics: site-limited lead uptake, saturated active absorption, and increased urinary elimination (Marcus, 1985c). The site-limited absorption model provided the best description of a non linear relationship between plasma lead and blood lead. Figure 10-5 shows the fit of the model to data from 103 subjects studied by DeSilva (1981). At relatively high blood lead levels, the fit appears quite satisfactory, but plasma lead is underestimated below 30 pg/dl blood lead (see solid line in Figure 10-5). Adding an intercept term of 0.25 (see broken line in Figure 10-5) improves the fit at low blood lead values. The need for an intercept term can 10-27 TEH 0411934 DUP050452532 INTAKE GUT 0 EXCRETION A,, =0.34 (INFANT) = 0.11 (JUVENILE) Jl,, = 1.73 x 10 3 A,, = 0.10 Aai = 0.03 A,4 = 0.03 Li = 0.07 Aig = 0.08 Aao = 0.01 A,, = 0.23 Figure 10-3. Schematic model of lead metabolism in infant baboons, with compartmental transfer coefficients. Source: Kneip et al. (1983}. 10-28 TEH 0411935 C DUP050452533 rDUP050452534 PLASMA LEAD CONCENTRATION, ^g/dl Figure 10-5. Fitting of nonlinear blood lead model to data of DeSilva (1981). Broken line incorporates an intercept term of 0.25; solid line does not incorporate intercept term. Source: Marcus (1985c). 10-30 be attributed to possible analytic error due to contamination of the plasma samples or to transient fluctuations in plasma lead due to lead exposure just prior to sampling (Marcus, 1985c). In any event, curvilinearity is modest below 30 pg/dl. For individuals without oc cupational or other excessive exposure to lead (>30 pg/dl blood lead), it is not possible to distinguish linear and nonlinear kinetic models (Marcus, 1985c). 10.3.5 Animal Studies The relevant questions to be asked of animal data are those that cannot be readily or fully satisfied by data from human subjects. What is the effect of exposure level on distri bution within the body at specific time points? What is the relationship of age or develop mental stage on the distribution of lead in organs and systems, particularly the nervous sys tem? What are the relationships of physiological stress and nutritional status to the redisbution kinetics? Can the relationship of chelatable lead to such indicator lead pools as blood be defined better? Administration of a single dose of lead to rats produces high initial lead concentrations in soft tissues, which then fall rapidly as the result of excretion and transfer to bone (Hammond, 1971), while the distribution, of lead appears to be Independent of the dose. Castellino and Aloj (1964) reported that single-dose exposure of rats to lead was associated with a fairly constant ratio of erythrocyte lead to plasma lead, a rapid distribution to tissues, and relatively higher uptake in liver, kidney, and particularly bone. Lead loss from olrgans and tissues follows first-order kinetics except from bone. The data of Morgan et al. (1977), Castellino and Aloj (1964), and Keller and Doherty (1980a) document that the skeletal system in rats and mice is the kinetically rate-limiting step in whole-body lead clearance. Subcellular distribution studies involving either tissue fractionation after in vivo lead exposure or jjn vitro data document that lead is preferentially sequestered in the nucleus (Castellino and Aloj, 1964; Goyer et al., 1970) and mitochondrial fractions (Castellino and Aloj, 1964; Barltrop et al., 1974) of cells from lead-exposed animals. Lead enrichment in the mitochondrion is consistent with the high sensitivity of this organelle to the toxic effects of lead. The neonatal animal seems to retain proportionately higher levels of tissue lead compared with the adult (Goldstein et al., 1974; Momcilovic and Kostial, 1974; Mykkanen et al., 1979; Klein and Koch, 1981) and shows slow decay of brain lead levels while other tissue levels sig nificantly decrease over time. This decay appears to result from enhanced entry by lead due to a poorly developed brain barrier system in the developing animals, as well as enhanced body retention in the young animals. The effects of such changes as metabolic stress and nutri tional status have been noted in the literature. Keller and Doherty (1980b) have documented 10-31 TEH 0411938 DUP050452536 1mm that tissue redistribution of lead, specifically bone lead mobilization, occurs3 lactating female mice, with both lead and calcium transfer occurring from mother to pups'f' (Keller and Doherty, 1980c). Changes in lead movement from body compartments, particularly bone, with changes in nutrition are described in Section 10.5. >'|!Wl In animal studies that are relevant both to the issue of chelatable lead versus lead in- s! dicators in humans and to the relative lability of lead in the young versus the adult, Jugo et al. (1975b) and Jugo (1980) studied the chelatability of lead in neonate versus adult rats and'v?1 its lability in the erythrocyte. Challenging young rats with metal chelants yielded prbpor-^.,, tionately lower levels of urinary lead than in the adult, a finding that has been ascribed " tighter binding of lead in the young animal (Jugo et al., 1975b). In a related observation,, -,"1' * * t * m"#r *- the chelatable fraction of lead bound to erythrocytes of young animals given 20SPb was approx-^t ,* 1 imately threefold greater than in the adult rat (Jugo, 1980), although the fraction of dose InV- '~v. the cells was higher in the suckling rat. The difference in the suckling rat erythrocyte garding the binding of lead and relative content compared with the adult may be compared with JL.i' Ong and Lee's (1980b) observation that human fetal hemoglobin binds lead more avidly than does ' '"J,* .if mature hemoglobin. ``v 10.4 LEAD EXCRETION AND RETENTION IN HUMANS AND ANIMALS Dietary lead that is not absorbed in humans and animals passes through the GI tract and is eliminated with feces, as is the deposited fraction of air lead that is swallowed and not , absorbed. Lead absorbed into the blood stream and not retained is excreted through the renal and GI tracts, the latter by biliary clearance. The amounts appearing in urine and fei es appear to be a function of such factors as species, age, and differences In dosing. " ' s'*/1' 10.4.1 Human Studi-es> Booker et al. (1969) found that 212Pb injected into two adult volunteers led to initial " # < 1r v ' appearance of the label in urine (4.4 percent of dose in 24 hr), then in both urine and feces ,, ^ ^ in approximately equal amounts. By use of the stable isotope 204Pb, Rabinowitz et al. (1973) reported that urinary and fecal excretion of the label amounted to 38 and 8 pg/day In adult ' , subjects, accounting for 76 and 16 percent, respectively, of the measured recovery. Fecal ex cretion was thus approximately twice that of all the remaining modes of excretion: hair, * i>. i t i sweat, and nails (8 percent). Perhaps the most detailed study of lead excretion in adult humans was done by ChambeYiain et al. (1978), who administered 203Pb by injection, inhalation, and Ingestion. After injec gjdURHH| tion or oral intake, the amounts in urine (Pb-U) and feces (Pb-Fe, endogenous fecal lead) were SSiliiH 10-32 h V V* TEH 0411939 f w' DUP050452537 compared for the two administration routes. Endogenous fecal lead was 50 percent of that in urines or a 2:1 ratio of urinary to fecal lead. (Increased transit time was allowed for fecal lead to pass through the GI tract.) * Based on the metabolic balance and isotope excretion data of Kehoe (1961a,b,c), Rabino- witz et al. (1976), and Chamberlain et al. (1978), as well as on some recalculations of the Kehoe and Rabinowitz data by Chamberlain et al. (1978), short-term lead excretion amounts to 50-60 percent of the absorbed fraction, the balance moving primarily to bone with some sub sequent fraction (approximately half) of this stored amount eventually being excreted. The rapidly excreted fraction was determined by Chamberlain et al. (1978) to have an excretion half-life of about 19 days. This value is consistent with the estimates of Rabinowitz et al. (1976), who expressed clearance in terms of mean-lives. Mean-lives are multiplied by In 2 (0.693) to arrive at half-lives. The similarity of the blood 203Pb half-life with that of body excretion noted by Chamberlain et al. (1978) indicates a steady rate of clearance from the body. The age dependency of lead excretion rates in humans has not been well studied; all of the above lead excretion data involved only adults. Table 10-3 combines available data from adults (Rabinowitz et al., 1977; Thompson, 1971; Chamberlain et al., 1978) and infants (Ziegler et al., 1978) for purposes of comparison. Intake, urine, fecal, and endogenous fecal lead data from two studies on adults and one report on infants are used. For consistency in the adult data, 70 kg is used as an average adult weight, and a Pb-Fe:Pb-U ratio of 0.5 is used. Daily lead intake, absorption, and excretion values are expressed as pg/kg body weight. For the infant data, daily endogenous fecal lead excretion is calculated using the adult ratio as well as the extrapolated value of 1.5 pg/kg. The respiratory lead intake value for the infants is an upper value (0.2 pg/m3), since Ziegler et al. (1978) found air lead to be <0.2 pg/m3. Compared to the two representative adult groups, infants appear to have a lower total excretion rate, although the excretion of endogenous fecal lead may be higher than for adults. In humans, the dependence of lead excretion rate on level of exposure has been studied in some detail by Chamberlain (1983), who used data from the published reports of King et al. (1979), Williams et al. (1969), Gross (1981), Devoto and Spinazzola (1973), Azar et al. (1975), and Chamberlain et al. (1978). Figure 10-6 reproduces Chamberlain's plots of urinary excretion rate for lead versus blood lead as provided in the various studies. Renal clearance of lead appears to increase as blood lead increases from 25 to 80 pg/dl, the highest blood value reported. Given the earlier discussion concerning the increased fractional partitioning of blood lead into plasma with increasing blood lead burden (see Section 10.3.1), one would anticipate an increasing renal excretion rate for lead over a broad range of blood lead. 10-33 TEH 0411940 DUP050452538 TABLE 10-3. DAILY LEAD EXCRETION AND RETENTION DATA FOR ADULTS AND INFANTS Dietary intake (pg/kg) Fraction of Intake absorbed Diet lead absorbed (pg/kg) Air lead absorbed (pg/kg) Total absorbed lead (pg/kg) Urinary lead excreted (pg/kg) Ratio: urinary/absorbed lead Endogenous fecal lead (pg/kg) Total excreted lead (pg/kg) Ratio: total excreted/absorbed lead Fraction of intake retained Children3 10.76 0.46 (0.55)d 4.95 (5.92) 0.20 5.15 (6.12) 1.00 0.19 (0.16) 0.5 (1.56)f 1.50 (2.56) 0.29 (0.42) 0.34 (0.33) Adult . group A" 3.63 0.15e 0.54 0.21 0.75 0.47 0.62 0.249 0.71 0.92 0.01 Adult group Bc 3.86 Q.15e 0.58 0.11 0.68 0.34 0.50 0.179 0.51 0.75 0.04 Ziegler et al. (1978). bRabinowitz et al. (1977). cjThompson (1971) and estimates of Chamberlain et al. (1978). aEach of the values in parentheses in this column Is corrected for endogenous fecal lead at extrapolated value from Ziegler et al. (1978). Corrected for endogenous fecal lead (Pb-Fe = 0.5 x Pb-U). f Extrapolated value of 1.56 for endogenous fecal Pb. gPb-Fe = 0.5 x Pb-U. Siiiil -11 - .aWM 10-34 TEH 0411941 DUP050452539 RENAL CLEARANCE, kg/day Figure 10-6. Renal clearance (ratio of urinary lead to blood lead) from (A) King et al,, 1979; (B) Williams et al., 1969; (C) Gross, 1981; <D) DeVoto and Spinazzola, 1973; (E) Azar et al., 1975; (G) Chamberlain et al., 1978. Source: Chamberlain (1983). 10-35 TEH 0411942 DUP050452540 Data in Figure 10-6 indicate increased renal excretion of lead only. How the correspon ding biliary excretion rate changes in the face of increasing lead absorption is not known Hence, the overall impact of increasing exposure on total body clearance of the toxicant is difficult to assess. In experimental animals, the relative partitioning of lead between renal and biliary excretion routes has been shown to be dose- and species-dependent (see Section 10.4.2). Lead accumulates in the human body with age, mainly in bone, up to approximately 60 years of age, when a decrease occurs with changes in intake as well as in bone mineral metabolism. Total accumulation by 60 years of age ranges up to approximately 200 mg (see review by Barry, 1978), although occupational exposure can raise this figure several-fold (Barry, 1975) Holtzman (1978) has reviewed the available literature on studies of lead retention In bone. In normally exposed humans a biological half-life of approximately 17 years has been calcula ted, while data for uranium miners yield a range of 1320-7000 days (4-19 years). Chamberlain et al. (1978) have estimated lifetime averaged daily retention at 9.5 pg using data of Barry (1975). Within shorter time frames, however, retention can vary considerably due to such fac tors as disruption of the individual's equilibrium with changes in level of exposure, the dif ferences between children and adults, and, in elderly subjects, the presence of osteoporosis (Gross and Pfitzer, 1974). Lead labeling experiments, such as those of Chamberlain et al. (1978), indicate a short term or Initial retention of approximately 40-50 percent of the fraction absorbed. Much of this retention is by bone. Determining how much lead resorption from bone will eventually occur using labeled lead is difficult, given the extremely small fraction of labeled to unlabeled lead (i.e., label dilution) that would exist. Based on the estimates of Kehoe If' (1961a,b,c), the Gross (1981) evaluation of the Kehoe studies, the Rabinowitz et al. (1976) study, the Chamberlain et- al. (1978) assessments of the aforementioned reports, and the data of Thompson (1971), one can estimate that approximately 25 percent of the lead absorbed daily undergoes long-term bone storage. The above estimates relate either to adults or to long-term retention over most of an in dividual's lifetime. Studies with children and developing animals (see Section 10.4.2) indi cate lead retention in childhood can be higher than in adulthood. By means of metabolic balance studies, Ziegler et al. (1978) obtained a retention figure (as percentage of total in take) of 31.5 percent for infants, while Alexander et al. (1973) provided an estimate of 18 percent. Corrected retention data for both total and absorbed Intake for the pediatric sub" jects of Ziegler et al. (1978) were shown in Table 10-3, using the two values for endogenous fecal excretion as noted. Barltrop and Strehlow (1978) calculated a net negative lead reten tion in their subjects, but problems in comparing this report with the others were notea 10-36 TEH 0411943 DUP050452541 earlier. Given the increased retention of lead in children relative to adults, as well as the greater rate of lead intake on a body-weight basis, increased uptake in soft tissues and/or bone is indicated. Barry (1975, 1981) measured the lead content of soft and mineral tissues in a small group of autopsy samples from children 16 years of age and under, and noted that average soft-tissue values were comparable to those in female adults, while mean bone lead values were lower than in adults. These results suggest that bone in children has less retention capacity for lead than bone in adults. Note, however, that "dilution" of bone lead will occur because of the significant growth rate of the skeletal system through childhood. Trotter and Hixon (1974) studied changes in skeletal mass, density, and mineral content as a function of age, and noted that skeletal mass increases exponentially in children until the early teens, increases less up to the early 20s, levels off in adulthood, and then slowly decreases. From infancy to the late teens, bone mass increases up to 40-fold. Barry (1975) noted an approximate doubling in bone lead concentration over this interval, indicating that total skeletal lead had actually increased 80-fold. He also obtained a mean total bone lead content of approximately 8 mg for children up to 16 years old, compared with a value of approximately 18 mg estimated from both the bone concentrations in his study of children at different ages and the bone growth data of Trotter and Hixon (1974). In a later study (Barry, 1981), autopsy samples from infants and children between 1 and 9 years old showed an approximately 3.5-fold increase in mean bone con centrations across the three bone types studied, compared with a skeletal mass increase from 0-6 months to 3-13 years old of greater than 10-fold, for an estimated increase in total lead of approximately 35-fold. Five reports (see Barry, 1981) noted age versus tissue lead rela tionships indicating that overall bone lead levels in infants and children were less than in adults, whereas four reports observed comparable levels in children and adults. If one estimates total daily retention of lead in the infants studied by Ziegler et al. (1978), using a mean body weight of approximately 10 kg and the corrected retention rate in Table 10-3, one obtains a total daily retention of approximately 40 pg. By contrast, the total reported or estimated skeletal lead accumulated between 2 and 14 years is 8-18 mg (vide supra), which averages out to a daily long-term retention of 2.0 to 4.5 pg/day or 6-13 percent of total retention. Lead retention may be highest In infants up to about 2 years of age (the subjects of the. Ziegler et al. study), then decreases in older children. The mean retention in the Alexander et al. (1973) study was 18 percent, about half that seen by Ziegler et al. (1978). This difference may result from the greater age range in the former study. "Normal" blood lead levels in children either parallel adult male levels or are approxi mately 30 percent greater than adult female levels (Chamberlain et al., 1978), indicating (1) that the soft-tissue lead pool in very young children is not greatly elevated and thus, 10-37 TEH 0411944 DUP050452542 (2) that there is a huge labile lead pool in bone that is still kinetically quite distinct from soft-tissue lead or (3) that in young children, blood lead is a much less reliable indi cator of greatly elevated soft-tissue or labile bone lead than is the case with adults. Barry S!l - J (1981) found that soft-tissue lead levels were comparable in infants ^1 year old and children1! ' * 1-5 and 6-9 years old. . Given the implications of the above discussion--that retention of lead in young child'en' ' 1 * is higher than in adults and possibly older children, while at the same time their skeletal system is less effective for long-term lead sequestration--the very young child is at greatly > elevated risk to a toxicologically "active" lead burden. For further discussion, see Chapter * r, 13 : ' *' to. s Rabinowitz et al. (1976) examined the biokinetics of a stable isotope of lead (204Pb)'^ ` entering human hair after absorption, hair being a mode of lead excretion in humans and otherS L '` i mammals. Feeding adult male volunteers 204Pb daily for about 100 days and analyzing the Iso- - ,, Vt j, 7 1H-v to changes in uptake, with a delay of about 35 days. Hair lead values should be interpreted ' i t' as the integral of the blood lead values over about 100 days. 10.4.2 Animal Studies 1 ' >tf r f 1 In rats and other experimental animals, both urinary and fecal excretion are important `V v j Ill routes of lead removal from the organism. The relative partitioning between the two modes is species- and dose-dependent. Morgan et al. (1977) injected 203Pb into adult rats and noted" rU that lead initially appeared in urine, followed by equivalent elimination in both urine and feces. By 5 days, lead was proportionately higher in feces. Castellino and Aloj (1964), * 1 using 210Pb, observed that fecal excretion was approximately twice that of urine (35.7 versus 15.9 percent) by 14 days. In the report of Klaassen and Shoeman (1974), relative excretion by the two routes was seen to be dose-dependent up to 1.0 mg Pb/kg. Excretion was much higher by biliary clearance into the gut. At 3.0 mg Pb/kg, approximately 90 percent of the excreted :* amount was detected in feces. The relatively higher proportion appearing in feces in the studies of Castellino and Aloj (1964) and Klaassen and Shoeman (1974), compared with the re sults of Morgan et al. (1977), possibly results from use of carrier dosing, since Morgan et al. (1977) used carrier-free injections. Hence, increasing dose does appear to favor bi` liary excretion, as noted by Klaassen and Shoeman (1974). , -> PSP With regard to species differences, Klaassen and Shoeman (1974) found that the amount of biliary clearance in dogs was about 2 percent of that in rats, while rabbits showed 50 percent of the rate of the rat at equivalent dosing. These data for the dog conflict with the results > i-ii IV . 10-38 iS! *#1 *.1 ||TEH 0411945 > * 111111 liiJsLLL DUP050452543 sr t j t bh of Lloyd et al. (1975), who observed 75 percent of the excreted lead eliminated through bili ary clearance. Note that the latter researchers used carrier-free label while the other in vestigators used injections with carrier at levels of 3.0 mg Pb/kg. In mice, Keller and Doherty (1980a) observed that the cumulative excretion rate of 210Pb in urine was 25-50 per cent of that in feces. In nonhuman primates, Cohen (1970) observed that baboons excreted lead at the rate of 40 percent in feces and 60 percent in urine. Pounds et al. (1978) noted that the rhesus monkey lost 30 percent of lead by renal excretion and 70 percent by fecal excre tion. This discrepancy may also reflect a carrier-dosing difference. The extent of total lead excretion in experimental animals given labeled lead orally or parenterally varies, in part due to the time frames for post-exposure observation. In the adult rat, Morgan et al. (1977) found that 62 percent of injected 203Pb was excreted by 6 days. By 8 days, 66 percent of injected 203Pb was eliminated in the adult rats studied by Momcilovic and Kostial (1974), while the 210Pb excretion data of Castellino and Aloj (1964) for the adult rat showed 52 percent excreted by 14 days. Similar data were obtained by Klaassen and Shoeman (1974). Lloyd et al. (1975) found that dogs excreted 52 percent of in jected lead label by 21 days, 83 percent by 1 year, and 87 percent by 2 years. In adult mice (Keller and Doherty, 1980a), 62 percent of injected lead label was eliminated by 50 days. In nonhuman primates, Pounds et al. (1978) measured approximately 18 percent excretion in adult rhesus monkeys by 4 days. Kinetic studies of lead elimination in experimental animals indicate that excretion is described by two or more components. From the elimination data of Momcilovic and Kostial (1974), Morgan et al. (1977) estimated that in the rat the excretion curve obeys a two-compo nent exponential expression with half-lives of 21 and 280 hr. In dogs, Lloyd et al. (1975) found that excretion could be described by three components, i.e., a sum of exponentials with half-lives of 12 days, 184 days, and 4951 days. Keller and Doherty (1980a) reported that the half-life of whole-body clearance of injected 203Pb consisted of an initial rapid and a much slower terminal component, the latter having a half-life of 110 days in the adult mouse. The dependency of excretion rate on dose level has been investigated in several studies. Although Castellino and Aloj (1964) saw no difference in total excretion rate when label was injected with 7 or 100 pg of carrier, Klaassen and Shoeman (1974) did observe that the excre tion rate by biliary tract was dose-dependent at 0.1, 1.0, and 3.0 mg Pb/kg (urine values were not provided for obtaining estimates of total excretion). Momcilovid and Kostial (1974) ob served an increased rate of excretion into urine over the added carrier range of 0.1 to 2.0 pg Pb/kg with no change in fecal excretion. In the report of Aungst et al. (1981), excretion rate in the rat did not change over the injected lead dosing range of 1.0 to 15.0 mg/kg. Rat urinary excretion rates thus seem dose-dependent over a narrow range less than 7 pg, while 10-39 TEH 0411946 jk.! DUP050452544 elimination of lead through biliary clearance is dose-dependent up to an exposure level of 3 mg/kg. Lead movement from lactating animals to their offspring via milk constitutes both a route of excretion for the mother and a route of exposure for the young. Investigations directed at this phenomenon have examined both prior-plus-ongoing maternal lead exposure during lactation and the effects of immediate prior treatment. Keller and Doherty (1980b) exposed two groups of female rats to 2l0Pb: one group for 105 days before mating; the second before and during gestation and nursing. During lactation, there was an overall loss of lead from the bodies of the lactating females compared with controls, while the femur ash weights were inversely re lated to level of lead excretion, indicating that such enhancement is related to bone mineral metabolism. Lead transfer via milk was approximately 3 percent of maternal body burden, in creasing with continued lead exposure during lactation. Lorenzo et al. (1977) found that blood lead levels in nursing rabbits given injected lead peaked rather rapidly (within 1 hr), while milk lead levels showed a continuous increase for about 8 days, at which point the con centration of lead was eightfold higher than in blood. This observation indicates that the transfer of lead to milk can occur against a concentration gradient in blood. Momcilovic (1978) and Kostial and Momcilovic (1974) observed that transfer of 203Pb in the late stage of lactation occurs readily in the rat, with higher overall excretion of lead in nursing versus control females. Furthermore, the rate of lead movement to milk appeared dose-dependent over the added lead carrier range of 0.2 to 2.0 pg. The comparative retention of lead in developing versus adult animals has been investigat ed in several studies using rats, mice, and nonhuman primates. Momcilovic and Kostial (1974) compared the kinetics of lead distribution in suckling and adult rats after injection of 203Pb. Over an 8-day interval, 85 percent of the label was retained in the suckling rat, com pared with 34 percent in the adult. Keller and Doherty (1980a) compared the levels of 210Pb in 10-day-old mice and adults, noting from the clearance half-lives (vide supra) that lead retention was greater in the suckling animals than in the adults. In both adult and young mice, the rate of long-term retention was governed by the rate of release of lead from bone, indicating that in the mouse, skeletal lead retention in the young is greater than in the adult. With infant and adult monkeys orally exposed to 210Pb, Pounds et al. (1978) observed that at 23 days the corresponding amounts of initial dose retained were 92.7 and 81.7 percent, respectively. The studies of Rader et al. (1981a,b) are of particular interest because they demonstrate not only that young experimental animals continue to show greater retention of lead in tissue when exposure occurs after weaning, but also that such retention occurs in terms of either uniform exposure (Rader et al., 1981a) or uniform dosing (Rader et al., 1981b) when compared with adult animals. With uniform exposure, 30-day-old rats given lead in drinking water 10-40 TEH 0411947 DUP050452545 showed significantly higher lead levels in blood and higher percentages of dose retained in brain, femur, and kidney, as well as higher indices of hematopoietic impairment (ALA in urine, erythrocyte porphyrin) when compared to adult animals. As a percentage of dose retained, levels of lead retained in the tissue of the young animals were approximately two- to three fold higher. In part, this difference results from a higher ingestion rate of lead. However, in the uniform dosing study where a higher ingestion rate was not the case, an increased re tention of lead still prevailed, the amount of lead in brain being approximately 50 percent higher in young versus adult animals. Comparison of values in terms of percent retained is more meaningful for such assessments, because the factor of changes in organ mass (see above) is taken into account. Delayed excretion of lead in the young animal may reflect an immature excretory system or a tighter binding of lead in various body compartments. 10.5 INTERACTIONS OF LEAD WITH ESSENTIAL METALS AND OTHER FACTORS Deleterious agents, particularly toxic metals such as lead, do not express their toxlco- kinetic or toxicological behavior in a physiological vacuum, but rather are affected by inter actions of the agent with a variety of. biochemical factors such as nutrients. Growing recog nition of this phenomenon and its implications for lead toxicity in humans has prompted a number of studies, many of them recent, that address both the scope and mechanistic nature of such interactive behavior. Taken collectively, the diverse human and animal data described in this section make it clear that there is heterogeneity in pediatric populations in terms of relative risk for lead exposure and deleterious effects depending on nutritional status. Children having multiple nutrient deficiencies are at greater risk. 10.5.1 Human Studies In humans, the interactive behavior of lead and various nutritional factors is appropri ately viewed as particularly significant for children, since this age group is not only parti cularly sensitive to lead's effects, but also experiences the greatest flux in relative nutri ent status. Such interactions occur against a backdrop of rather widespread deficiencies in a number of nutritional components in children. While such deficiencies are more pronounced in lower-income groups, they exist in all socioeconomic strata. Mahaffey and Michaelson (1980) have summarized the three national nutritional status surveys carried out in the United States for infants and young children: the Preschool Nutrition Survey, the Ten State Nutrition Sur vey, and the Health Assessment and Nutrition Evaluation Survey (HANES 1). The most recent body of data of this type is the second National Health Assessment and Nutrition Evaluation Survey (NHANES II) study (Mahaffey et al., 1979), although the dietary information from it has 10-41 TEH 0411948 DUP050452546 yet to be reported. In the older surveys, iron deficiency was the most common nutritional deficit in children under 2 years of age, particularly children from low-income groups. Re duced vitamin C intake was noted in about one-third of the children, while sizable numbers of them had significantly reduced intakes of calcium. Owen and Lippman (1977) reviewed the regional surveys of low-income groups within Hispanic, white, and black populations. In these groups, iron deficiency was a common finding, and low intakes of calcium and vitamins A and C were observed regularly. Hambidge (1977) concluded that zinc intake in low-income groups is generally inadequate relative to recommended daily allowances. Available data from a number of reports document the association of lead absorption with suboptimal nutritional status. Mahaffey et al. (1976) summarized their studies showing that children with blood lead levels greater than 40 pg/dl had significantly (p <0.01) lower intake of phosphorus and calcium compared with a control group, while iron intake in the two groups was comparable. This study involved children 1-4 years old from an inner-city, low-income population, with close matching for all parameters except the blood lead level. Sorrell et al. (1977), in their nutritional assessment of 1- to 4-year-old children with a range of blood lead levels, observed that blood lead content was inversely correlated with calcium intake, while children with blood lead levels >60 pg/dl had significantly (p <0.001) lower intakes of calcium and vitamin D. Rosen et al. (1980, 1981) found that children with elevated blood lead (33-120 pg/dl) had significantly lower serum concentrations of the vitamin D metabolite 1,25-dihydroxyvitamin D (1,25-(OHJaD) compared with age-matched controls (p <0.001), and showed a negative correlation of serum 1,25-(0H)2D with lead over the range of blood lead levels measured (see Chapter 12, Section 12.5, for further discussion). These observations and animal data (Barton et al., 1978a; see Section 10.5.2) may suggest an increasingly adverse interactive cycle of 1,25-(0H)2D, lead, and calcium in which lead reduces biosynthesis of the vitamin D metabolite. This cycle leads to reduced induction of calcium binding protein (CaBP), less absorption of calcium from the gut, and greater uptake of lead, thus further reducing metabolite levels. Barton et al. (1978a) isolated two mucosal proteins in rat intestine, one of which bound mainly lead and was not vitamin D-stimulated. The second bound mainly calcium and was under vitamin control. The authors suggested direct site-binding competition between lead and cal cium in these proteins. Hunter (1978) investigated the possible interactive role of seasonal vitamin D biosynthesis in adults and children; lead poisoning occurs more often in summer than in other seasons (see Hunter, 1977, for review). Seasonality accounts for 16 percent of ex plained variance of blood lead levels in black children, 12 percent in Hispanic children, and 4 percent in white children. More recently, it has been documented that there is no seasonal variation in circulating levels of 1,25-(0H)2D, the metabolite that affects the rate of lead -IS 10-42 TEH 0411949 |||ii DUP050452547 absorption from the GI tract (Chesney et al., 1981). These results suggest that seasonality is related to changes In exposure. Johnson and Tenuta (1979) determined that calcium intake was negatively correlated (r = -0.327, p <0.05) with blood lead in 43 children aged 1-6 years. The high lead group consumed less zinc than children with lower blood levels. Yip et al. (1981) found that 43 children with elevated blood lead (>30 pg/dl) and erythrocyte protoporphyrin (EP) {>35 pg/dl) had an increased prevalence of iron deficiency as these two parameters increased. Children classed in CDC categories lb and II had a 79 percent iron deficiency rate, while those in Class III were all iron deficient. Chisolm (1981) demonstrated an inverse relationship between chelatable iron and chelatable body lead levels as indexed by urinary ALA levels in 66 children with elevated blood lead. Watson et al. (1980) reported that adult subjects who were iron deficient (determined from serum ferritin measurement) showed a lead absorption rate 2-3 times greater than subjects who were iron replete. In a group of 13 children, Markowitz and Rosen (1981) reported that the mean serum zinc levels in children with plumbism were signifi cantly below the values seen in normal children. Chelation therapy reduced the mean level even further. Chisolm (1981) reported an inverse relationship between ALA in urine (ALA-U) and the amount of chelatable or systemically active zinc in 66 children challenged with EDTA and having blood lead levels ranging from 45 to 60 pg/dl. These two studies suggest that zinc status is probably as important an interactive modifier of lead toxicity as is either calcium or iron. The role of nutrients in lead absorption has been reported in several metabolic balance studies for both adults and children. Ziegler et al. (1978), in their investigations of lead absorption and retention in infants, observed that lead retention was inversely correlated with calcium intake, expressed either as a percentage of total intake (r = -0.284, p <0.01) or on a weight basis (r = -0.279, p <0.01). Interestingly, the calcium intake range measured was within the range considered adequate for infants and toddlers by the National Research Council (National Academy of Sciences, National Research Council, 1974). These data also support the premise that severe deficiency need not be present for an interactive relationship to occur. Using adults, Heard and Chamberlain (1982) monitored the uptake of 203Pb from the gut in eight subjects as a function of the amounts of dietary calcium and phosphorus. Without supplementa tion of these minerals in fasting subjects, the label absorption rate was approximately 60 percent, compared to 10 percent with 200 mg calcium plus 140 mg phosphorus, the amounts pres ent in an average meal. Calcium alone reduced uptake by a factor of 1.3 and phosphorus alone by 1.2; both together yielded a reduction factor of 6. This work suggests that insoluble cal cium phosphate is formed and co-precipitates any lead present. This interpretation is sup ported by animal data (see Section 10.5.2). 10-43 DUP050452548 10.5.2 Animal Studies '-j* Reports of lead-nutrient interactions in experimental animals have generally descrihed - such relationships in terms of a single nutrient, using relative absorption or tissue reten tion in the animal to index the effect. Most of the recent data are concerned with the impact of dietary levels of calcium, iron, phosphorus, and vitamin D. Furthermore, some investiga tors have attempted to elucidate the site(s) of interaction as well as the mechanism(s) ' governing the interactions. Lead's interactions involve the effect of the nutrient on lead uptake, as well as lead's effect on nutrients. The focus of this discussion is on the former. These interaction studies are tabulated in Table 10-4. 10.5.2.1 Interactions of Lead with Calcium. The early report of Sobel et al. (1940) noted that variation of dietary calcium and other nutrients affected the uptake of lead by bone and blood in animals. Subsequent studies by Mahaffey-Six and Goyer (1970) in the rat have demon strated that a considerable reduction in dietary calcium was necessary (from 0.7 percent to 0.1 percent), at which level blood lead was increased fourfold, kidney lead content was ele vated 23-fold, and relative toxicity (Mahaffey et al., 1973) was increased. The changes in calcium necessary to alter lead's effects in the rat appear to be greater than those seen bi Ziegler et al. (1978) in young children, which indicates a species difference in terms of sen sitivity to basic dietary differences as well as to levels of all interactive nutrients. These observations in the rat have been confirmed by Kostial et al. (1971), Quarterman andiifliilplli Morrison (1975), Barltrop and Khoo (1975), and Barton et al. (1978a). The inverse relation ship between dietary calcium and lead uptake has also been noted in the pig (Hsu et al., 1975), horse (Willoughby et al., 1972), lamb (Morrison et al., 1977), and domestic fowl (Berg et al., 1980). 111 The mechanism(s) governing lead's interaction with calcium operate at both the gut wall and within body compartments. Barton et al. (1978a), using everted duodenal sac preparations in the rat, reported the following: (1) interactions at the gut wall require the presence of intubated calcium to affect lead label absorption (pre-existing calcium deficiency in the animal and no added calcium had no effect on lead transport); (2) calcium-deficient animals show increased retention of lead rather than absorption (confirmed by Quarterman et al., 1973); and (3) lead transport may be mediated by two mucosal proteins, one of which has high molecular weight and a high proportion of bound lead, and is affected in extent of lead bind ing with changes in lead uptake. The second protein binds mainly calcium and is vitamin D- dependent. Smith et al. (1978) found that lead is taken up at a different site in the duodenum Of rats than is calcium, but absorption does occur at the site of phosphate uptake, suggesting a complex interaction of phosphorus, calcium, and lead. This observation is consistent with the data of Barltrop and Khoo (1975) for rats and the data of Heard and Chamberlain (1982) for IBP IK' 10-44 TEH 0411951 DUP050452549 TABLE 10-4. EFFECT OF NUTRITIONAL FACTORS ON LEAD UPTAKE IN ANIMALS TEH 0 4 1 1 9 5 2 r-- /--s S- CO a>ot> Pas o a p>01 4SOOoUcO--sS_SS Cro itX/-) P Sjfrrle3 .s4pn(CC3:O-usrr0oH**>>.m't0----11' r'irorwn-^Hs*i' f-- (0 P0) :3Vr) 0rr0~-144 r-- fO Pas. >s r-ro3oC----> rm Ir0T^%N~1.l r-- CO 4a0s sCcoSruO~:s- wrcrrcr^Hosne. aut a>o> *e3 rXC--O31% src--ry( re pas ^ psoiCrOe re *rX-- <4p>a1/3-sc<rm^> S-CrCueO rH r- re pas opcosrae- 'rCrOoH-O-l' r*pCor--" 3rTe PPPu0as) *O>--S 'How&3r-+' t.JcoasCOUa-OS-+.PPPuuaaJsss r0cO--o '3--raot 0 >s p pu(sOTS-3 pc (-4 s>-> UaSs r ta-s (0 pat *Xr-t 3o: suca~oss >auss *Ucrz-Tcc3o 4O Cof-- *P>5CarOs--> -coCpL 3 3o _U(Q0> *T3 r-- *--Cp** E a10s 3 !-- (asUsC- rOca~os t U--coo C 1-4 4o*-CorP *-3rsC>aP--Os-> COPL 3O= JUc3oS I-- x: *Ta3s *P3r~s E3 (asU5sS- *ca0os *Up- rre Ur- U C HH 4- CiooCmoUrP----3L*rj*xf>sca3o--P-=so>s-:> *aOs tp>- 3 US sraUes- "O fa--res *ur- -- ure c c-- aUcrUauoresss- *ocuar-t P*aas CO 3 r *r-- PU PCaass 1-- rue exz CausOs raSes- "cO **uc>UCFaUr-sV- PrpCoQoU"e). >) P"e0OOr)O"1--3CraeOs P*fPoXor-- S(--4 *o3 p-rQe "3 rra--es XaaSur3ess;- ~rra--oes 3 u as ppc*cr C US arauesss l fCco uC *Pr rarsuaUees-Ji O *1- **Pfo33-- coS- -p" Q. US Sous- J2 ra--t >as re *-- Oj re po. 3 at cO xUreS: >ui *TrCau----s 3raeTMs Co *rCo-- P3as Puas Pass pp Co Pas sa-j $- J-H >sco-> 3 P re Pas P u cm >>*3-- (0P P p CO . re OJ P P 30) 4o x0> 3 5c reH-i p UaSs U) *Pui-s *1-- ass>auss 4-> P o u> --as >OS E3 1c O -- *f- QJ u 4- 25 i-- *raos0a^s *0-- 0u 3 U) p -r-- as o u 3 r-- U> U) CO U> r-~ U T- <0 4-> >as >j -y C i-- 03 r* *3 5O *Par-t as3r**0 -j 3 aUsS 4o Tu- 3UuSs *- i--uass -- rUo p C >as r- > sc~o *r 5 -aPs 3 o *- CaOs i-- 3 _i 3 U1 H-- r-- as o a 3us us rre U) r- u *- <D P >at >s - C r-- <0 r- P "OO**a-s TO r-- X3 as p c o r PCat pas s_ T5 as p ?? P c*3 -r- rO a *r-* UJ XO r- p as >as as > *3 -------- as pre i--raei 3 uusj ra-s t- p o r-- I-- C r-- t - re c co CO "43)*Pf" Pr-- 3o r5e- Q.3 re oSu>- *a3s re 3raes as >as Qas. tau ure> p c o *r"* P cas pai S- 3raes __i VS OS *r-- U p(0 OS cx a. CO OS auss S- -Q pP p Po Q. cc CO re re re oc QC Q aust 3O s: s- E o p *p3-- acOs O u. (0 o 3 E 3 3 3 reJ-- ru-- fO O O *re o *p-- U r-- CO O *Ur- c r~ so- o t-- CO i h-H 10-45 c o & 1--J DUP050452550 TABLE 10-4. (continued) o CO 0) <n u r-4 ew 0) i~ r05 4- in CD 3: OS 05 S 05 O m3 r-* O o> p to r~ s--< s- &- Oo o Su p X -a 3 "O ro 3 id 3 id a. E /p o p tn S- ai p P o> !-- S- r-l - id w id 3 CQ cy rH 00 a> r--4 w X> id s3 O o *o 3 id 3 O P 3 id CO O 00 r^- 0CT0t 05 H t--4 vy w r id ro p P 05 05 3 PO *Pr-- P s- E id to CQ m ID r^* cn 05 fH w rH w M C oO o pP XX 3 p U O "D 33 id id .. >l{ pp o S- o t- mwmi pp r--" S- 5. id id 03 ca u? o o 3 CD 3 .W 40 o 3 to a> -x P V) r-- u Id *r- id 05 S~ T5 U r-- c *OP r* CL IO P U p to r- >v 05 P 3 io 3 05 "O P id w!to< 05 a; S o V- s- p co t~ N~ 330 S- CD (ft " 3 1/5 O X) a 05 a .x t 10 r-- u w O 05 S- f-- :''S2I1 V-- U "O a> c C T3 1 to r>. O P 0) ai s. o id P P 05 05 P 3 Id t/1 C P *i-- to Q.P P "O "O P 0> id o +>r-- > o fmCmD u 5- P c ai P 3. t- CsJ O p <y Q.-X P** in "O o -a id P 10 05 CL 05 r-- ar- "O (ft OCX) pp 3 P o id p- p e E3O rd P *r P 3P r-*r- P 05 E 3 O u id s XPXJ 05 *r- Id 05 > 05 C *r P Id P3 *r~ r-- r-- P 3 05 P 1ft 05 Id r~ <y p &. u (^ ? U CD P o u> id p > s- "O 1-- - C 0) O 3 *OCC id r- 3 to O P >s 3 >> 3 (ft o 3 P P f- P 3 O 3 *r- s~ cy P U S- 05 --P 3 r> CD 4- 3 v- p a. P3 5- (55 O rd 05 05 POP3 Id tn o> .Op- <D PuP C 05 05 (ft 3 (ft P i- rd ro c aj tft r-- *o -Q 0) c u o 05 3 3 O (ft 05 Id O 05 u (ft 05 3 U) to Lo -- au 4- 3 Id *r~ (ft P P 05 U 3 CL (ft i- id pp 3 05 a O *f- s- *4'***. 1-- "O p C -X P id o c O S- 3 05 Cl . U 30 r- ro 05 P *o P P 3P 3 ro 05 P *3 P P 3a3 CO s- *o a> O rd s- c ai r-- Q5 3 Id >u P 05 3 >> ct? O 05 r-- > ft 5- **-O P 1-- *o o (ft P CP L o -O P (ft "O <N s- 05 3 ai at*io 3 05 t- `ro (J *p-- r-~ p r-- r- p 3O u 3 id p id 9--1 OS p rM --< CQ -- ca 05 'U C to 40 3*r- CD 05 vHiB r-- P 3 3 id P *o P to to u CJ id id (ft ift u (0 a 05 P r* r0*~) id r" fp u) c *o tft 3 T5 3 rP i'J,ui p r 33 a> E 4- JOo *r-- ro-- 3 O *T O QJ f p p 3 (ft O 05 *r-- p P S- (ft *rO-- P > P ':s--`P8 ,r|| p t- 05 P P P 05 05 P 05 05 P 05 o o S-. P 3 3 5- > 3 S- > 3 U 3^ :Mm CD 3 Id 05 05 05 er O 05 CT O id X o fp id P P P U> *p" (ft i-- (ft P 05 - to 3 Q_ ~a a? 3 05 40 3 05 s- 05 P 05 3 P 05 3 P s- Id 3 P Id C P id P 3 3 p id 05 P *r- o *r- <J -- 3 s_ s- id *0 TJ "O d W 05 X5 (ft 05 XJ "O . VZ!i p a. s- ro id id id 3 p id o p to to -'S <=l1 05 05 CD 05 05 "m (ft 05 Tu- o> p10 p as CO pcd P id OS OS p IB p OSid id OS OS id s. o p u id 3 LL. Os- f--l (ft tft 33 33 OO PP PP (ft (ft o pP a. P (ft 3a i- o p cr" pE to oP p r- a. > 10-46 a 3 E id P *i" > 3 p-- T3 *T" 05 P PO `r- 3 _J P DUP050452551 TEH 0 4 1 1 9 5 4 Low d ie ta ry p ro te in e ith e r Quarterman e t a l. (1978b) reduces or does not a ffe c t retention in various H 00 <7> --s i--l Cs) CO a> P r*H P <11 .O r-- r* ns Q. l/> P 01 a c in (0 S- ai -o r-- r-- c ai < ca , i--i rw CO ro o> r--1 4-* w in a) OJ <0 JQ s~ O t- ro 3 ON _J U- N or a; r0 r*- Q *o o a> C1 rH TJ fO -- re m r-- p #. j-- in x--sx--\ in r--*' 3 CO CO 3 a> c 0> Ncn c d 01 r-- x; -Li r--i rH Jsi in &- a. 3 01 o 00 u o ID x--n r-* CO 00 cn i--i ***<* rH v-y CO 3) T^. C C cn *r rH t- > w ai 01 4-> -J 01 i-- Cu ~a (0 tz x j nS P i--* ai ns r-- u u ai 01 ai X3 XJ - 3 3 in <0 3 3 r-- i"" 03 c >> xs o o <- CD r-- in P *3 ro in s- +J 01 -i* ro ' ai ro a. cn Xf QJ -r- U CL s- <13 O) -r- r-- -O cs o ai t- S as o in s_ ro 01 O -C L> X3 u a. *0 in C (0 cs ai re P 01 c in r-- O N 01 3 o P -o o >> S- _Q P *-- ai ro 4-1 r-- r-- O ai 4- *r- ai ai ai as OC ~ *r- Q. -a r- -l c a; O flJ E S- i- c XS O Oa s- 0) P cl e >>+ >*" J= O P C JWQ oL> ai *f-- 3 re 1 C Q.X3 re 3 U i0mrne1 3 01 01 s- 01 r-- c 01 rew cxx w in p -ac in r- re >> o ai in r- in X3 31 p- iou r* ai ai o +> O 12*r p 01 o c re re re4-> in -- in u x j re e u r-- 4-> 3 r-- o o __i s- re ai c S~ 4- S- ai in ai x: c 4-i -P re re O i- E E -P c V- "O *r- o re qtj 4-> r~ C a> re -Or- <iny 0 0c *ni13O arine su=~ *" S01 sU -sii in ai CJ cre x: m c rai ai > P 01 01 -- "O -Q U D cc N re 3o -Q p 01 *-- XJ x? re 0) C 1-- r" c in o BJ *r OJ m P anj a a. o j so a. o u w Cu Ji3n o3 *r- fO Horr>ac0----n1i 3Ci0nO) Xr0r--e51 t-- co XsCorinpe3-L Xr0eJ1 r-- co X4oQSir-n3e>-. XrrSee XcrCsoi(op--n30.L raoei *cr" 4pic0isrn-e-1- _ r0ae1j s-r*Tc-- "Orce ps03o1. rp4Or--ur---ee>> * 1Oa3c--a) PpcoC0atr-1*i 1--3aicrn--ni `XPSSoorirne3*Z-L "Oraeji pre Pre G QC cn P c 01 c o CL E cO 5u p o f-- L l-- CL s: Pre pre oc DC in P c 0) c o CL E o u fmm *r" 2-> 10-47 <J *y-- fsi Pre ac U r-- rH Pre pre DC DC L. 01 a CL CL r-- O rH C_1 Body lead retention Rat Protein DUP050452552 humans. Thus, the combined action of the two mineral nutrients is greater than the sum their individual effects. Mykkanen and Wassermann (1981) observed that lead uptake in the intestine of the chick occurs in two phases: a rapid uptake (within 5 min) followed by a rate-limiting slow transfer of lead into blood. Conrad and Barton (1978) have observed a similar process in the rat. Hence, either a saturation process occurs (i.e., carrier-mediated transport) or lead sit precipitates in the lumen. In the former case, calcium interacts to saturate the carrier pro' teins as isolated by Barton et al. (1978a) or may precipitate lead in the lumen by initial formation of calcium phosphate. Quarterman et al. (1978a) observed that calcium supplementation of the diet above norma also resulted in increased body retention of lead in the rat. Because both deficiency (Barton et al., 1978a) and excess in calcium intake enhance retention, two sites of influence on retention are suggested. Goyer (1978) has suggested that body retention of lead in calci deficiency, i.e., reduced excretion rate, may result from renal impairment, while Quartern et al. (1978a) suggest that excess calcium suppresses calcium resorption from bone, hence also reducing lead release. 10.5.2.2 Interactions of Lead with Iron. Mahaffey-Six and Goyer (1972) reported that irondeficient rats had increased tissue levels of lead and manifested greater toxicity compared with control animals. This uptake change was seen with but minor alterations in hematocrit, Indicating a primary change in lead absorption over the time of the study. Barton et al. (1978b) found that dietary restriction of iron, using 210Pb and everted sac preparations in the rat, led to enhanced lead absorption, whereas iron loading suppressed the extent of lead uptake, using normal intake levels of iron. This suppression suggests receptor-binding com petition at a common site, consistent with the isolation by these workers of two iron-binding mucosa fractions. While the iron level of diet affects lead absorption, the effect of changes in lead content in the gut on iron absorption is not clear. Barton et al. (1978b) and Dobbins et al. (1978) observed no effect of lead in the gut on iron absorption in the rat, while Flanagan et al. (1979) reported that lead reduced iron absorption in mice. In the mouse, Hamilton (1978) found that body retention of 203Pb was unaffected by iron deficiency, using intraperitoneal administration of the label, while gastric intubation did lead to Increased retention. Animals with adequate iron showed no changes in lead retention at intubation levels of 0.01 to 10 nM. Cerklewski (1980) observed that lead transfer both in' utero and in milk to nursing rats was enhanced compared with controls when dams were maintain- . ed from gestation through lactation on low-iron diets. 10.5.2.3 Lead Interactions with Phosphate. The early studies of Shelling (1932), Grant et al. (1938), and Sobel et al. (1940) documented that dietary phosphate Influenced the extent of lead toxicity and tissue retention of lead in animals. Low levels of phosphate enhanced tf 10-48 TEH 0411955 DUP050452553 p*"' parameters, while excess intake retarded the effects. More recently, Barltrop and Khoo (1975) reported that reduced phosphate increased the uptake of 203Pb approximately 2.7-fold compared with controls. Quarterman and Morrison (1975) found that low dietary phosphate enhanced lead retention in rats but had no effect on skeletal lead mobilization, nor was injected lead label affected by such restriction. In a related study, Quarterman et al. (1978a) found that dou bling the nutrient over normal levels resulted in lowering lead absorption by approximately half. Barton and Conrad (1981) found that reduced dietary phosphorus increased the retention of labeled lead and deposition in bone, in contrast to the results of Quarterman and Morrison (1975). Increasing the intraluminal level of phosphorus reduced lead absorption, possibly by increasing intraluminal precipitation of lead as the mixed lead/calcium phosphate. Smith et al. (1978) reported that lead uptake occurs at the same site as phosphate, suggesting that lead absorption may be more related to phosphate than calcium transport. 10.5.2.4 Interactions of Lead with Vitamin D. Several studies had earlier indicated that a positive relationship might exist between dietary vitamin D and lead uptake, resulting in either greater manifestations of lead toxicity or a greater extent of lead uptake (Sobel et al., 1938, 1940). Using the everted sac technique and testing with 210Pb, Smith et al. (1978) observed that increasing levels of intubated vitamin D in the rat resulted in Increased ab sorption of the label, with uptake occurring at the distal end of the rat duodenum, the site of phosphorus uptake and greatest stimulation by the vitamin. Barton et al. (1980) used 210Pb to monitor lead absorption in the rat under conditions of normal, deficient, and excess amounts of dietary vitamin D. Lead absorption is increased with either low or excess vitamin D. This increased absorption apparently occurs as a result of increased retention ti.me of fecal mass containing the lead due to alteration of Intestinal motility rather than as a re sult of direct enhancement of mucosal uptake rate. Hart and Smith (1981) reported that vita min D repletion of diet enhanced lead absorption (210Pb) in the rat, while also enhancing femur and kidney lead uptake when the label was Injected. 10.5.2.5 Interactions of Lead with Lipids. Barltrop and Khoo (1975) observed that varying the lipid (corn oil) content of rat diet from 5 up to 40 percent resulted in an increase of lead in blood 13.6-fold higher than the normal level. Concomitant increases were observed in lead levels in kidney, femur, and carcass. Reduction of dietary lipid below the 5 percent control figure did not affect the lead-absorption rate. As an extension of this earlier work, Barltrop (1982) has noted that the chemical composition of the lipid is a significant factor in affecting lead absorption. Study of triglycerides of saturated and unsaturated fatty acids showed that polyunsaturated trilinolein Increased lead absorption by 80 percent in rats, when given as 5- or 10-percent loadings in diet, compared with monounsaturated triolein or any of the saturates in the series tricaproin to tristearin. 10-49 TEH 0411956 DUP050452554 10.5.2.6 Lead Interaction with Protein. Quarterman et al. (1978b) have drawn attention one of the inherent difficulties of measuring lead-protein interactions, i.e., the effect protein on both growth and the toxicokinetic parameters of lead, Der et al. (1974) found th' reduction of dietary protein, from 20 to 4 percent, led to increased uptake of lead in tissues, but the approximately sixfold reduction in body weight over the interval of the study' makes it difficult to draw any firm conclusions. Barltrop and Khoo (1975) found that,203Pb' uptake by rat tissue could be enhanced with either suboptimal or excess levels of protein in' diet. Quarterman et al. (1978b) reported that retention of labeled lead in rats maintained on^ a synthetic diet containing approximately 7 percent protein was either unaffected or reduccompared with controls, depending on tissues taken for study. Not only levels of protein but also the type of protein appears to affect tissue le levels. Anders et al. (1982) found that rats maintained on either of two synthetic die' varying only by having casein or soybean meal as the protein source showed significant! higher lead levels in the casein group. 10.5.2.7 Interactions of Lead with Milk Components. For many years, milk was recommended as a counteractant for lead poisoning among lead workers (Stephens and Waldron, 1975). More recen t data, however, pose a mixed picture. Kello and Kostial (1973) found that rats maintained o milk diets absorbed a greater amount of 203Pb than those fed commercial rat chow, phenomenon was ascribed to relatively lower levels of certain nutrients in milk compared with the rat chow. These observations were confirmed by Bell and Spickett (1981), who also observed that lactose-hydrolyzed milk was less effective than the ordinary form in promoting lead absorption, suggesting that, lactose may be the enhancing agent. Bushnell and Deluca' (1981) demonstrated that lactose significantly increased 210Pb absorption and tissue retention by weanling rats when given in high doses by intubation. However, lactose levels close to usual dietary content actually have an inhibiting effect on lead absorption (Bushnell ancl^ DeLuca, 1983). In human studies, moreover, milk consumption is inversely related to blood lead levels, suggesting a net protective effect (Johnson and Tenuta, 1979; Brunekreef et al-., 1983). 10.5.2.8 Lead Interactions with Zinc and Copper. The studies of Cerklewski and Forbes (1976) and El-Gazzar et al. (1978) documented that zinc-deficient diets promote lead absorption in the rat, while repletion with zinc reduces lead uptake. The interaction continues within the body, particularly with respect to ALA-D activity (see Chapter 12, Section 12.3.1.2)* In a study of zinc-lead interactions in female rats during gestation and lactation, Cerklewski (1979) observed that zinc-deficient diets resulted in more transfer of lead through roilk the pups as well as reduced litter body weights. Bushnell and Levin (1983) have shown that 10-50 TEH 0411957 - .-MSiW DUP050452555 rats fed a low-zinc diet (2.0 ppm) containing lead at levels of 10 or 100 ppm had signi ficantly higher retention of lead in brain and calvarium compared to those fed-a diet with 20 ppm zinc. Victery and coworkers (1981) evaluated the acute effects of'lead on the behavior of renal and plasma zinc in the dog. They found that lead enhanced urinary zinc excretion and was related to both increased ultrafilterable plasma zinc and a change in renal tubular zinc transport. Klauder et al. (1973) reported that low dietary copper enhanced lead absorption in rats fed a high-lead diet (5000 ppm). These observations were confirmed by Klauder and Petering (1975) at a level of 500 ppm lead in diet. The same researchers subsequently observed that reduced copper enhanced the hematological effects of lead (Klauder and Petering, 1977), and that both copper and iron deficiencies must be corrected to restore hemoglobin levels to normal. 10.6 INTERRELATIONSHIPS OF LEAD EXPOSURE, EXPOSURE INDICATORS, AND TISSUE LEAD BURDENS Information presented so far in this chapter sets forth the quantitative and qualitative aspects of lead toxicokinetics, including the compartmental modeling of lead distribution in vivo, and leads up to the critical issue of the various interrelationships of lead toxico kinetics to lead exposure, toxicant levels in indicators of such exposure, and exposure-target tissue burdens of lead. Chapter 11 (Sections 11.4, 11.5, 11.6) discusses the various experimental and epidemi ological studies relating the relative impact of various routes of lead exposure on blood lead levels in human subjects, and includes a description of mathematical models for such relation ships. In these sections, the basic question is: what is the mathematical relationship of lead in air, food, water, etc., to lead in blood? This question is descriptive and does not address the biological basis of the observed relationships. Nor does it consider the impli cations for adverse health risks in the sequence leading from external lead exposure to lead in some physiological indicator to lead in target tissues. For purposes of discussion, this section separately considers (1) the temporal character istics of physiological indicators of lead exposure, (2) the biological aspects of the rela tionship of external exposure to Internal indicators of exposure, and (3) Internal indicatortissue lead relationships, including both steady-state lead exposure and abrupt changes in lead exposure. The relationship of internal indicators of body lead, such as blood lead, to biological indicators such as EP or ALA-U is discussed in Chapter 13. 10-51 TEH 0411958 DUP050452556 kUHV-rt-y, 10.6.1 Temporal Characteristics of Internal Indicators of Lead Exposure The biological half-life for blood lead or the nonretained fraction of body lead generally assumed to be rather short, although it in fact depends upon the mobile lead bo burden (O'Flaherty etal., 1982; also see Sections 10.3 and 10.4). Nevertheless, a < blood or urine lead value reflects rather recent exposure compared to tooth or bone /|e values. In cases where lead exposure can be reliably assumed to have occurred at a < level, a blood lead value is more useful than in cases where some intermittent, high level o exposure may have occurred. The former most often occurs with occupational exposure, whil the latter is of particular relevance to young children. Reports have appeared dealing with the stability of individuals' blood lead levels ove time under conditions of ambient exposure. David et al. (1982) followed 29 children, 4-1 years old, with monthly measurements and found the stability to be of a relatively high order (Pearson correlation coefficients of 0.7-0.8). Rabinowitz et al. (1984) sampled more than 200- infants semiannually from birth to 2 years of age and found average changes of about 4 pg/dl. Only 40 percent of these children tended to remain in their previous blood lead category/ (quartile). Within this age range, however, there was a trend toward less fluctuation with increasing age of the young child. Delves et al. (1984) followed 21 adults over 7-11 months with multiple blood lead measurements and found little fluctuation over time (about 1 pg/dl or L less, on average). Hence, there appears to be increasing stability with relatively constant'^ exposure as the individual increases in age. " V.f Accessible mineralizing tissue, such as shed teeth, extend the time frame for assessing.. lead exposure from months to years (Section 10.3), since teeth accumulate lead up to the time';-' of shedding or extraction. Levels of lead in teeth increase with age in proportion to expo^#g sure (Steenhout and Pourtois, 1981). Furthermore, tooth lead levels are correlated with blood lead levels In humans (Shapiro et al., 1978) and animals (Kaplan et al., 1980). The technique - of Fremlin and Edmonds (1980), employing microautoradfography of irradiated teeth, permits the identification of dentine zones high in lead content, thus allowing the disclosure of past periods of abrupt increases in lead intake. rf' While levels of lead in shed teeth are more valuable than blood lead levels in assessing '[ exposure at more remote time points, such Information is retrospective in nature and would not be of use in monitoring current exposure. In this case, serial blood lead measurements must'^If be employed. With the development of methodology for in situ measurement of tooth lead in children (described in Chapter 9), serial ijn situ tooth analysis in tandem with serial blood lead determination would provide comparative data for determining both time-concordant blood' tooth lead relationships as well as which measure is the better indicator of ongoing exposure Given the limitations of an indicator such as blood lead in reflecting lead uptake in target _ organs, as discussed below, the rate of accumulation of lead in teeth measured iri situ may 10-52 TEH 0411959 4;;i! DUP050452557 well be a better index of ongoing tissue lead uptake. This aspect merits further study, espe cially since Shapiro et al. (1978) were able to demonstrate the feasibility of using in situ tooth lead analysis in a large group of children screened for lead exposure. 10.6.2 Biological Aspects of External Exposure/Internal Indicator Relationships Information provided in Chapter 11 as well as the critiques of Hammond et al. (1981) and Brunekreef (1984) indicate that the relationship of lead levels in air, food, and water to lead levels in blood is curvilinear, with the result that as "baseline" blood lead rises (i.e., as one moves up the curve), the relative change in the dependent variable, blood lead, per unit change of lead In some intake medium (such as air) becomes smaller. Conversely, as one proceeds down the curve with reduction in "baseline" lead, the corresponding- change In blood lead becomes larger. One assumption in this "single medium" approach is that the base line Is not integrally related to the level of lead in the particular medium being studied. This assumption is not necessarily appropriate for air versus food lead, nor, in the case of young children, for air lead versus total oral intake of the element. However, it should be noted that Hammond et al. (1981) assigned virtually all of the body compartment lead to the blood, giving blood lead levels in their modeling scheme that were too high. The authors recognized this and later offered a qualification (Hammond et al., 1982). Hammond et al. (1981) have also noted that the shape of the blood lead curves seen in human subjects is similar to that discernible in certain experimental animal studies with dogs, rats, and rabbits (Azar et al., 1973; Prpic-Majid et al., 1973). Similarly, Kimmel et al. (1980), after exposing adult female rats to lead at four levels in drinking water for 6-7 weeks, found values of blood lead that showed a curvilinear relationship to the dose levels. Over the dosing range of 5 to 250 ppm in water, the blood lead range was 8.5 to 31 pg/dl. In a related study (Grant et al., 1980) rats were exposed to lead jn utero, through weaning, and up to 9 months of age at the dosing range used in the Kimmel et al. study (0.5 to 250 ppm in the dams' drinking water until weaning of pups, then the same levels in the weanlings' drink ing water). These animals showed a blood lead range of 5 to 67 pg/dl. One may assume that in all of the above studies the lead in the various dosing groups was near or at equilibrium within the various body compartments. The biological basis of the curvilinear relationship of blood lead to lead intake, across a broad range of blood lead values, may result from a number of factors. In lead workers, as a specific case, increasing workplace air lead level is associated with an Increased particle aggregation rate leading to a lowering of the effective fraction of respirable, submicrometer particles, as suggested by Chamberlain (1983). In studies with human volunteers, there appears to be no change in respiratory absorption rate at lung lead burdens up to 450 pg (Chamberlain et al., 1978). It was noted earlier that oral lead intake up to 400 pg in adults 10-53 TEH 0411960 DUP050452558  '"'"'WHH is associated with unaltered absorption rate. However, animal data relevant to this question indicate that dietary levels between 10 and 100 ppm lead are associated with a decreased ab sorption rate (Bushnell and DeLuca, 1983). If these data were applied directly to humans, a daily intake rate of 20-200 mg lead would be required to produce a similar decrease. The curvilinear blood lead/diet lead relationship may or may not be independent of GI ab sorption rate. The experimental animal studies of Prpic-Majic et al. (1973) indicated a cur vilinear relationship of blood lead to dose of lead when the toxicant was administered by in jection to rabbits. On the other hand, Injection of higher doses into rats does show a linear relationship (Aungst et al., 1981). The data of DeSilva (1981), Manton and Malloy (1983), and Manton and Cook (1984) all sug gest that the increasingly greater fraction of lead in plasma as blood lead increases may be significant (see Section 10.3.1). This increase of lead in plasma would Indicate a relatively greater movement of lead from plasma to tissues and a higher excretion rate, both of which serve to modulate the rate of rise of the whole blood lead with increasing circulating lead. These results are consistent with the report of Chamberlain (1983) showing an apparent in creased urinary excretion rate of lead with rising blood lead. They are also in accord with the observations that tissue lead burdens show a better proportionality to exposure level than does blood lead burden (see Section 10.3.1). Since an increased movement of plasma lead to tissues with increasing blood lead burden would also include deposition in bone, the curvilin ear relationship of chelatable lead to blood lead may also be influenced by the plasma/blood relationship. 10.6.3 Internal Indicator/Tissue Lead Relationships In living human subjects, to determine tissue lead burdens directly (or relate these levels to adverse effects associated with target tissue) as a function of lead intake is not possible. Instead, measurement of lead in an accessible indicator such as blood, along with determination of some biological indicator of impairment (e.g., ALA-U or EP), is used. Evidence continues to accumulate in both the clinical and experimental animal literature that the use of blood lead as an indicator can have limitations in reflecting both the amounts of lead in target tissues and the temporal changes in tissue lead with changes in exposure. Perhaps the best example of the problem is the relationship of blood lead to chelatable lead (see Section 10.3.3). Currently, measurement of the plumburesis associated with challenge by a single dose of a chelating agent such as CaNa2EDTA is considered the best measure of the mo bile, potentially toxic fraction of body lead in children and adults (Vitale et al., 1975; Wedeen et al., 1975; Chisolm et al., 1976; U.S. Centers for Disease Control, 1978; Chisolm and Barltrop, 1979; Hansen et al., 1981). 10-54 TEH 0411961 V DUP050452559 Chisolm et al. (1976) have documented that the relationship of blood lead to chelatable lead is curvilinear, such that a given incremental increase in blood lead is associated with an increasingly larger increment of mobilizable lead. The problems associated with this cur vilinear relationship in exposure assessment are typified by the recent reports of Saenger et al. (1982) and Piomelli et al. (1984) concerning children and Hansen et al. (1981) concerning adult lead workers. Saenger et al. (1982) noted that significant percentages of children having mild to moderate lead exposure, as discernible by blood lead and EP measurements, had urinary outputs of lead upon challenge with CaNa2EDTA that qualified them for chelation thera py under CDC guidelines. Similar data were obtained for 210 children evaluated in four medi cal centers (Piomelli et al., 1984). In adult workers, Hansen et al. (1981) observed that a sizable fraction of subjects with only modest elevations in blood lead levels upon EDTA chal lenge excreted lead in amounts significantly exceeding the upper end of normal. This discrep ancy occurred at blood lead levels of 35 pg/dl and above. The biological basis for the nonlinearity of the relationship between blood lead and che latable lead appears, in major part, to be the existence of a sizable pool of lead in bone that is labile to chelation. Evidence pointing to this explanation was summarized in Section 10.3.3. The question of how long any lead in this compartment of bone remains labile to che lation has been addressed by several investigators in studies of both children and adults. The question is relevant to the issue of the usefulness of EDTA challenge in assessing evi dence for past lead exposure. Chisolm et al. (1976) found that a group (N = 55) of adolescent subjects 12-22 years old, who had a clinical history of lead poisoning as young children and whose mean blood lead was 22.1 pg/dl at the time of study, yielded chelatable lead values that placed them on the same regression curve as a second group of young children with current elevations of blood lead. The results with the adolescent subjects did not provide evidence that they might have had a past history of lead poisoning. According to the authors, this failure to detect prior expo sure suggests that chelatable lead at the time of excessive exposure was not retained in a pool that remained labile to chelation years later, but underwent subsequent excretion or transfer to the inert compartment of bone. One problem with drawing conclusions from this study Is that all of the adolescents apparently had one or more courses of chelation therapy and were removed to housing where re-exposure would be minimal as part of their clinical management after lead poisoning was diagnosed. One must assume that chelation therapy removed a significant portion of the mobile lead burden and that placement in lead-free housing re duced the extent of any further exposure. The obvious question is how this group of adoles cents would compare with subjects who had excessive chronic lead exposure as young children but who did not require or receive chelation therapy. 10-55 TEH 0411962 DUP050452560 Former lead workers challenged with EDTA show chelatable lead values that are signifi cantly above normal years after workplace exposure ceases (e.g., Alessio et a!., 1976; Prerovska and Teisinger, 1970). In the case of former lead workers, blood lead also remains elevated, suggesting that the mobile lead pool in bone remains in equilibrium with lead in blood. The closer correspondence of chelatable lead with actual tissue lead burdens, compared to blood lead, is also reflected in a better correlation of this parameter with such biological indicators of Impairment as EP, although this correlation is seen only in adults. Similarly, Alessio et al. (1976) found that EP in former lead workers was more significantly correlated with chelatable lead than with blood lead. Consideration of both the Intake versus blood lead and the blood lead versus chelatable lead curves leads to the prediction that the level of lead exposure per se is more closely re lated to tissue lead burden than is blood lead. This appears to be the case in experimental animals. Azar et al. (1973) and Grant et al. (1980) reported that levels of lead in brain, kidney, and femur followed more of a direct proportionality with the level of dosing than with blood lead. These observations may relate to the fact that plasma lead rises proportionately faster than whole blood lead. Finally, there is the question of how adequately an internal indicator such as blood lead reflects changes in tissue burden when exposure changes abruptly. In the study of Bjorklund et al. (1981)s lead levels in both blood and brain were monitored over a 6-week period in rats exposed to lead through their drinking water. Blood lead rose rapidly by day 1, during which time brain lead content was only slightly elevated. After day 1, the rate of Increase in blood lead began to taper off, while brain lead began to rise in a nearly linear fashion up to the end of the experiment. From day 7 to 21, blood lead increased from approximately 45 to 55 pg/dl, while brain lead increased approximately twofold. Abrupt reduction in exposure similarly appears to be associated with a more rapid re sponse in blood than in soft tissues, particularly brain. Goldstein and Diamond (1974) reported that termination of Intravenous administration of lead to 30-day-old rats resulted in a sevenfold drop of lead in blood by day 7. At the same time, brain lead levels did not de crease significantly. A similar difference in brain and blood response was reported by Momcilovic and Kostial (1974). In all of the above studies, blood lead was of limited value in reflecting changes in the brain, which is the significant target organ for lead exposure in children. With abrupt in creases in exposure level, the problem concerns a much more rapid approach to steady state in blood than in brain. Conversely, the biological half-time for lead clearance from blood in the young rats of both the Goldstein and Diamond (1974) and Momcilovic and Kostial (1974) studies was much less than it appeared to be for lead movement from brain. 10-56 TEH 0411963 DUP050452561 Despite the limitations in indexing tissue burden and exposure changes, blood lead remains the one readily accessible measure that can demonstrate in a relative way the rela tionship of various effects to increases in exposure. 10.7 METABOLISM OF LEAD ALKYLS The lower alkyl lead compounds used as gasoline additives, tetraethyl lead (TEL) and tetramethyl lead (TML), are much more neurotoxic on an equivalent dose basis than inorganic lead. These agents are emitted in auto exhaust, and their rate of environmental degradation depends on such factors as sunlight, temperature, and ozone levels. There is also some con cern that organolead compounds may result from biomethylation in the environment (see Chapter 6). Finally, a problem arises with the practice among children of sniffing leaded gasoline. The available information dealing with metabolism of lead alkyls is derived mainly from ex perimental animal studies, studies of workers exposed to the agents, and cases of lead alkyl poisoning. 10.7.1 Absorption of Lead Alkyls in Humans and Animals The respiratory intake and absorption of TEL and TML in the vapor state was investigated by Heard et al. (1979), who used human volunteers inhaling 203Pb-labeled TEL and TML. Initial lung deposition rates were 37 and 51 percent for TEL and TML, respectively. Of these amounts, 40 percent of TEL was lost by exhalation within 48 hr, while the corresponding figure for TML within 48 hr was 20 percent. The remaining fraction was absorbed. The effect of gasoline vapor on these parameters was not investigated. In an earlier study Mortensen (1942) reported that adult rats inhaling TEL labeled with 203Pb (0.07-7.00 mg TEL/1) absorbed 16-23 percent of the fraction reaching the alveoli. Gasoline vapor had no effect on the absorption rates. Respiratory absorption of organolead bound to particulate matter has not been specifi cally studied as such. According to Harrison and Laxen (1978), neither TEL nor TML adheres to particulate matter to any significant extent, but the toxicologically equivalent trialkyl derivatives, formed from photolytic dissociation or ozonolysis in the atmosphere, may do so. 10.7.1.1 Gastrointestinal Absorption. Information on the rate of absorption of lead alkyls through the GI tract is not available in the literature. Given the level of gastric acidity (pH l.0) in humans, one would expect TML and TEL to be rapidly converted to,the corresponding trialkyl forms, which are comparatively more stable (Bade and Huber, 1970). Given the simi larity of the chemical and biochemical behavior of trialkyl leads to their Group IV analogs, the trialkyltins, the report of Barnes and Stoner (1958) that triethyltin is quantitatively absorbed from the GI tract indicates that triethyl and trimethyl lead would be extensively ab sorbed via this route. 10-57 TEH DUP050452562 10.7.1.2 Percutaneous Absorption of Lead Alkyls. In contrast to inorganic lead salts, both TEL and TML are rapidly and extensively absorbed through the skin in rabbits and rats (Kehoe and Thamann, 1931; Laug and Kunze, 1948), and lethal effects can be rapidly induced in these animals by merely exposing the skin. Laug and Kunze (1948) observed that systemic uptake of TEL was still 6.5 percent even after most of the TEL had evaporated from the skin surface. The rate of passage of TML was somewhat slower than that of TEL in the study of Davis et al. (1963). Absorption of either agent was retarded somewhat when applied in gasoline. 10.7.2 Biotransformation and Tissue Distribution of Lead Alkyls To understand the in vivo fate of lead alkyls, one must first discuss the biotransforma tion processes of lead alkyls known to occur in mammalian systems. Tetraethyl and tetramethyl lead both undergo oxidative dealkylation in mammals to the triethyl or trimethyl metabolites, which are now accepted as the actual toxic forms of these alkyls. Studies of the biochemical mechanisms for these transformations, as noted by Kimmel et al. (1977), indicate a dealkylation mediated by a P-450 dependent mono-oxygenase system in liver microsomes, with intermediate hydroxylation. In addition to rats (Cremer, 1959; Stevens et al., 1960; Bolanowska, 1968), mice (Hayakawa, 1972), and rabbits (Bolanowska and Garczynski, 1968), this transformation also occurs in humans accidentally poisoned with TEL (Bolanowska et al., 1967) or workers chronically exposed to TEL (Adamiak-Ziemba and Bolanowska, 1970). The rate of hepatic oxidative de-ethylation of TEL in mammals appears to be rather rapid; Cremer (1959) reported a maximum hourly conversion rate of approximately 200 pg TEL/g rat liver. In comparison with TEL, TML may undergo transformation at either a slower rate (in rats) or more rapidly (in mice), according to Cremer and Callaway (1961) and Hayakawa (1972). Other transformation steps involve conversion of triethyl lead to the diethyl form, the process appearing to be species-dependent. Bolanowska (1968) did not report the formation of diethyl lead in rats, while significant amounts of it are present in the urine of rabbits (Arai et al., 1981) and humans (Chiesura, 1970). Inorganic lead is formed in various species treated with TEL, whether the TEL arises from degradation of the diethyl lead metabolite or from some other direct process (Bolanowska, 1968). Degradation appears to occur in rats, since little or no diethyl lead is found, whereas significant amounts of inorganic lead are present. Formation of inorganic lead with lead alkyl exposure may account for the hematological effects seen in humans chronically exposed to the lead alkyls (see Chapter 12, Section 12.3), includ ing children who inhale leaded gasoline vapor. Partitioning of triethyl or trimethyl lead, the corresponding neurotoxic metabolites of TEL and TML, between the erythrocyte and plasma appears to be species-dependent. Byington et al. (1980) studied the partitioning of triethyl lead between cells and plasma in vitro using 10-58 TEH 0411965 ;#s Jfc DUP050452563 washed human and rat erythrocytes and found that human cells had a very low affinity for the alkyl lead while rat cells bound the alkyl lead in the globin moiety at a ratio of three mole cules per hemoglobin tetramer. Similarly, Injected triethyl lead was found to be associated with whole blood levels approximately 10-fold greater than in rat plasma. The available lit erature on TEL poisoning in humans concurs; significant plasma lead values have been routinely reported (Boeckx et al., 1977; Goldings and Stewart, 1982). These data indicate that the rat is a poor model for studying the adverse effects of lead alkyls in human subjects. The biological half-life in blood for the lead alkyls depends on whether clearance of the tetraalkyl or trialkyl forms is being observed. Heard et al. (1979) found that 203Pb-labeled TML and TEL inhaled by human volunteers was rapidly cleared from the blood (by 10 hr), fol lowed by a reappearance of lead. The fraction of lead in plasma initially was quite high, approximately 0.7, suggesting the presence of tetra/trialkyl lead. However, the subsequent rise in blood lead showed all of it essentially present in the cell, which would indicate inorganic or possibly diethyl lead. Triethyl lead in rabbits was more rapidly cleared from the blood (3-5 days) than was the trimethyl form (15 days) when administered as such (Hayakawa, 1972). Tissue distribution of lead in both humans and animals exposed to TEL and TML primarily involves the trialkyl metabolites. Levels are highest in liver, followed by kidney, then brain (Bolanowska et al., 1957; Grandjean and Nielsen, 1979). Nielsen et al. (1978) observed measurable amounts of trialkyl lead in samples of brain tissue from subjects with no known oc cupational exposure. The available studies on tissue retention of triethyl or trimethyl lead provide variable findings. Bolanowska (1968) noted that tissue levels of triethyl lead in rats were almost constant for 16 days after a single Injection of TEL. Hayakawa (1972) found that the halflife of triethyl lead in brain was 7-8 days for rats. The half-time for trimethyl lead was much longer. In humans, Yamamura et al. (1975) reported two tissue compartments for triethyl lead having half-lives of 35 and 100 days (Yamamura et al., 1975). 10.7.3 Excretion of Lead Alkyls The renal tract is the main route of lead excretion in various species exposed to lead alkyls (Grandjean and Nielsen, 1979). The chemical forms of lead in urine suggest that the differing amounts of the various forms are species-dependent. Arai et al. (1981) found that rabbits given TEL parenterally excreted lead primarily In the form of diethyl lead (69 per cent) and inorganic lead (27 percent), triethyl lead accounting for only 4 percent. Bolanowska and Garczynski (1968) found that triethyl lead levels were somewhat higher in the urine of rats than in that of rabbits. In humans, Chiesura (1970) found that trialkyl lead was never greater than 9 percent of total lead content in workers with heavy TEL exposure. 10-59 TEH 0411966 DUP050452564 Adamiak-Ziemba and Bolanowska (1970) reported similar data; the fraction of triethyl lead in"" the urine was approximately 10 percent of total lead. ^* The urinary rates of lead excretion in human subjects with known levels of TEL exposure " were also reported by Adamiak-Ziemba and Bolanowska (1970). In workers involved with U blending and testing of leaded gasoline, workplace air levels of lead (as TEL) ranged froqv^'V 0.037 to 0.289 mg/m3 and the corresponding urine lead levels ranged from 14 to 49 pg/i, of which approximately 10 percent was triethyl lead. ,J`Ni 'K, >\'V 10.8 SUMMARY Toxicokinetic parameters of lead absorption, distribution, retention, and excretion rela- ting external environmental lead exposure to various adverse effects have been discussed in this chapter. Also considered were various influences on these parameters, e.g., nutritional status, age, and stage of development. A number of specific issues in lead metabolism by animals and humans were addressed, including: T-' 1^ J* |& . 1. How does the developing organism from gestation to maturity differ from the adult in toxicokinetic response to lead intake? 2. What do these differences in lead metabolism portend for relative risk for adverse effects? 3. What are the factors that significantly change the toxicokinetic parameters in ways `- 'Vv. relevant to assessing health risk? 4. How do the various interrelationships among body compartments for lead translate to assessment of internal exposure and changes in internal exposure? i-- T*sk 10.8.1 Lead Absorption in Humans and Animals The amounts of lead entering the bloodstream via various routes of absorption are influ enced not only by the levels of the element in a given medium but also by various physical and chemical parameters and specific host factors, such as age and nutritional status. 10.8.1.1 Respiratory Absorption of Lead. The movement of lead from ambient air to the blood stream is a two-part process: deposition of some fraction of inhaled air lead in the deeper part of the respiratory tract and absorption of the deposited fraction. For adult humans, the deposition rate of particulate airborne lead as likely encountered by the general population is around 30-50 percent, with these rates being modified by such factors as particle size and 1M-- ventilation rates. All of the lead deposited in the lower respiratory tract appears to be ab sorbed, so that the overall absorption rate is governed by the deposition rate, i.e., approxi --mBSIm mately 30-50 percent. Autopsy results showing no lead accumulation in the lung indicate total Mlabsorption of deposited lead. 10-60 I-- IK? 4 TEH 04119<*|| V?t l.*,1* l' V DUP050452565 All of the available data for lead uptake via the respiratory tract in humans have been obtained with adults. Respiratory uptake of lead in children, while not fully quantifiable, appears to be comparatively greater on a body-weight basis. A second factor influencing the relative deposition rate in children is airway dimensions. One report has estimated that the 10-year-old child has a deposition rate 1.6- to 2.7-fold higher than the adult on a weight basis. The chemical form of the lead compound inhaled does not appear to be a major determinant of the extent of alveolar absorption of lead. While experimental animal data for quantitative assessment of lead deposition and absorption for the lung and upper respiratory tract are limited, available information from the rat, rabbit, dog, and nonhuman primate support the findings that respired lead in humans is extensively and rapidly absorbed. Over the range of air lead encountered by the general population, absorption rate does not appear to depend on air lead level. 10.8.1.2 Gastrointestinal Absorption of Lead. Gastrointestinal (GI) absorption of lead mainly involves lead uptake from food and beverages as well as lead deposited in the upper respiratory tract and eventually swallowed. It also includes ingestion of non-food material, primarily in children via normal mouthing activity and pica. Two issues of concern with lead uptake from the gut are the comparative rates of such absorption in developing versus adult organisms, including humans, and how the relative bioavailability of lead affects such uptake. By use of metabolic balance and isotopic (radioisotope or stable isotope) studies, var ious laboratories have provided estimates of lead absorption in the human adult on the order of 10-15 percent. This rate can be significantly increased under fasting conditions to 45 percent, compared to lead ingested with food. The latter figure also suggests that beverage lead is absorbed to a greater degree since much beverage ingestion occurs between meals. The relationship of the chemical/biochemical form of lead in the gut to absorption rate has been studied, although Interpretation is complicated by the relatively small amounts given and the presence of various components in food already present in the gut. In general, how ever, chemical forms of lead and their incorporation into biological matrices seem to have a minimal impact on lead absorption in the human gut. Several studies have focused on the ques tion of differences in GI absorption rates for lead between children and adults. Such rates for children are considerably higher than for adults: 10-15 percent for adults versus approx imately 50 percent for children. Available data for the absorption of lead from nonfood items such as dust and dirt on hands are limited, but one study has estimated a figure of 30 percent. For paint chips, a value of about 17 percent has been estimated. Experimental animal studies show that, like humans, the adult animal absorbs much less lead from the gut than the developing animal. Adult rats maintained on ordinary rat chow ab sorb 1 percent or less of the dietary lead. Various animal species studies make it clear that 10-61 TEH 0411968 DUP050452566 the newborn absorbs a much greater amount of lead than the adult, supporting studies showing this age dependency in humans. Compared to an absorption rate of about 1 percent in adult rats, the rat pup has a rate 40-50 times greater. Part, but not most, of the difference can be ascribed to a difference in dietary composition. In nonhuman primates, infant monkeys ab sorb 65-85 percent of lead from the gut, compared to 4 percent for the adults. The bioavailability of lead in the GI tract as a factor in its absorption has been the focus of a number of experimental studies. These data show the following: (1) lead in a number of forms is absorbed about equally, except for lead sulfide; (2) lead in dirt and dust and in different chemical forms is absorbed at about the same rate as pure lead salts added to a diet; (3) lead in paint chips undergoes significant uptake from the gut; and (4) in some cases, physical size of particulate lead can affect the rate of GI absorption. In humans, GI absorption rate of lead appears to be independent of quantity in the gut up to a level of at least 400 pg. In animals, dietary levels between 10 and 100 ppm result in reduced absorption. 10.8.1.3 Percutaneous Absorption of Lead. Absorption of Inorganic lead compounds through the skin is of much less significance than absorption through respiratory and GI routes. In con trast, absorption through skin is far more significant than through other routes for the lead alkyls (see Section 10.7.1.2). One recent study using human volunteers and 203Pb-labeled lead acetate showed that under normal conditions, skin absorption of lead alkyls approached 0.06 percent. 10.8.1.4 Transplacental Transfer of Lead. Lead uptake by the human and animal fetus readily occurs, such transfer going on by the 12th week of gestation in humans, and increasing throughout fetal development. Cord blood contains significant amounts of lead, correlating with, but somewhat lower than, maternal blood lead levels. Evidence for such transfer, be sides the measured lead content of cord blood, includes fetal tissue analyses and reduction in maternal blood lead during pregnancy. There also appears to be a seasonal effect on the fetus, summer-born children showing a trend to higher blood lead levels than those born in the spri ng. Iff; saj$ I* 10.8.2 Distribution of Lead in Humans and Animals In this subsection, the distributional characteristics of lead in various portions of the body (blood, soft tissue, calcified tissue, and the "chelatable" or potentially toxic body burden) are discussed as a function of such variables as exposure history and age. 10.8.2.1 Lead in Blood. More than 99 percent of blood lead is associated with the erythro cytes in humans under steady-state conditions, but it is the very small fraction transported in plasma and extracellular fluid that provides lead to the various body organs. Mos$ (~50 percent) erythrocyte lead is bound within the cell, primarily associated with hemoglobin (par ticularly HbA2), with approximately 5 percent bound to a 10,000-dalton fraction, 20 percent to 10-62 TEH 0411969 NfS DUP050452567 a heavier molecule, and 25 percent to lower-weight species. Several studies with lead workers and patients indicate that the fraction of lead in plasma versus whole blood increases above '<50-60 pg/dl blood lead. Whole blood lead in daily equilibrium with other compartments in adult humans appears to have a biological half-life of 25-28 days and comprises about 1.9 mg in total lead content, based on isotope studies. Other data from lead-exposed workers indicate that half-life depends on mobile lead burden. Human blood lead responds rather quickly to abrupt changes in exposure. With increased lead intake, blood lead achieves a new value in approximately 40-60 days, while a decrease in exposure may be associated with variable new blood values, depending upon the exposure history. This dependence presumably reflects lead resorption from bone. With age, furthermore, a moderate increase occurs in blood lead during adulthood. Levels of lead in blood of children tend to show a peak at 2-3 years of age (probably caused by mouthing activity), followed by a decline. In older children and adults, levels of lead are sexrelated, females showing lower levels than males even at comparable levels of exposure. In plasma, lead is virtually all bound to albumin and only trace amounts to high-weight globulins. Which binding form constitutes an "active" fraction for movement to tissues is impossible to state. The most recent studies of the erythrocyte/plasma relationship in humans indicate an equilibrium between these blood compartments, such that levels in plasma rise with levels in whole blood in fixed proportion up to approximately 50-60 pg/dl, whereupon the relationship becomes curvilinear. 10.8.2.2 Lead Levels in Tissues. Of necessity, various relationships of tissue lead to expo sure and toxicity in humans must generally be obtained from autopsy samples. Limitations on these data include questions of how such samples represent lead behavior in the living popula tion, particularly with reference to prolonged illness and disease states. The adequate char acterization of exposure for victims of fatal accidents is a problem, as is the fact that such studies are cross-sectional in nature, with different age groups assumed to have had similar exposure in the past. 10.8.2.2.1 Soft tissues. After age 20 most soft tissues (in contrast to bone) in humans do not show age-related changes. Kidney cortex shows an increase in lead with age, which may be associated with the formation of nuclear inclusion bodies. Absence of lead accumulation in most soft tissues results from a turnover rate for lead similar to that in blood. Based on several autopsy studies, soft-tissue lead content for individuals not occupa tionally exposed is generally below 0.5 pg/g wet weight, with higher values for aorta and kid ney cortex. Brain tissue lead level is generally below 0.2 pg/g wet weight with no change with increasing age, although the cross-sectional nature of these data would make changes in low brain lead levels difficult to discern. Autopsy data for both children and adults indi cate that lead is selectively accumulated in the hippocampus, a finding that is also consis tent with the regional distribution in experimental animals. 10-63 TEH 0411970 DUP050452568 Comparisons of lead levels in soft-tissue autopsy samples from children with results from adults indicate that such values are lower in infants than in older children, while children aged 1-16 years had levels comparable to those for adult women. In one study, lead content of brain regions did not materially differ for infants and older children compared to adults. Complicating these data somewhat are changes in tissue mass with age, although such changes are less than for the skeletal system. Subcellular distribution of lead in soft tissue is not uniform. High amounts of lead are sequestered in the mitochondria and nucleus of the cell. Nuclear accumulation is consistent with the existence of lead-containing nuclear inclusions in various species, and a large body of data demonstrate the sensitivity of mitochondria to injury by lead. 10.8.2.2.2 Mineralizing tissue. Lead becomes localized and accumulates in human calcified tissues, i.e., bones and teeth. This accumulation in humans begins with fetal development and continues to approximately 60 years of age. The extent of lead accumulation in bone ranges up to 200 mg in men ages 60-70 years, while in women lower values have been measured. Based upon various studies, approximately 95 percent of total body lead is lodged in the bones of human adults, with uptake distributed over trabecular and compact bone. In the human adult, bone lead is both the most inert and the largest body pool, and accumulation can serve to maintain elevated blood lead levels years after exposure, particularly occupational exposure, has ended. By comparison to human adults, only 73 percent of body lead is lodged in the bones of children, which is consistent with other information that the skeletal system of children is more metabolically active than that of adults. Furthermore, bone tissue in children is less dense than in adults. While the increase in bone lead level across childhood is modest, about twofold if expressed as concentration, the total accumulation rate is actually 80-fold, taking into account a 40-fold increase in skeletal mass. To the extent that some significant fraction of total bone lead in children and adults is relatively labile, in terms of health risk for the whole organism it is more appropriate to consider the total accumulation rather than just changes in concentration. The traditional view that the skeletal system was a "total11 sink for body lead (and by implication a biological safety feature to permit significant exposure in industrialized popu lations) never did agree with even older information on bone physiology, e.g., bone remodel ing. This view is now giving way to the idea that there are at least several bone compart ments for lead, with different mobility profiles. Bone lead, then, may be more of an insid ious source of long-term internal exposure than a sink for the element. This aspect of the issue is summarized more fully in the next section. Available information from studies of uranium miners and human volunteers who Ingested stable isotopes indicates that there is a relatively inert bone compartment for lead, having a half-life of several decades, as well as a rather labile compartment that permits an equilibrium between bone and tissue lead. 10-64 tip it |>Pir -wifi*' Vis^lrg' ISP mm # iiie:: TEH 0411971 DUP050452569 Tooth lead also increases with age at a rate proportional to exposure and roughly propor tional to blood lead in humans and experimental animals. Dentine lead is perhaps the most re sponsive component of teeth to lead exposure since it is laid down from the time of eruption until shedding. This characteristic underlies the usefulness of dentine lead levels in asses sing long-term exposure. 10.8.2.2.3 Chelatable lead. Mobile lead in organs and systems is potentially more active lexicologically in terms of being available to biological sites of action. Hence, this frac tion of total body lead burden is a more significant predictor of imminent toxicity. In real ity, direct measurement of such a fraction in human subjects would not be possible. In this regard, chelatable lead, measured as the extent of pluraburesis in response to administration of a chelating agent, specifically CaNa2EDTA, is now viewed as the most useful probe of undue body burden in children and adults. A quantitative description of the inputs to the body lead fraction that is chelant-mobilizable is difficult to define fully, but it most likely includes a labile lead compartment within bone as well as within soft tissues. Support for this view includes the following: (1) the age-dependency of chelatable lead, but not lead in blood or soft tissues; (2) evidence of removal of bone lead in chelation studies with experimental animals; (3) in vitro studies of lead mobilization in bone organ explants under closely defined conditions; (4) tracer modeling estimates in human subjects; and (5) the complex nonlinear relationship of blood lead and lead intake through various media. Data for children and adults showing a logarithmic relationship of chelatable lead to blood lead and the phenomenon of "rebound" in blood lead elevation after chelation therapy regimens (without obvious external re-exposure) offer further support. 10.8.2.2.4 Animal studies. Animal studies have helped to sort out some of the relationships of lead exposure to jjn vivo distribution of the element, particularly the impact of skeletal lead on whole body retention. In rats, lead administration results in an Initial increase of lead levels in soft tissues, followed by loss of lead from soft tissue via excretion and transfer to bone. Lead distribution appears to be relatively independent of dose. Other studies have shown that lead loss from organs follows first-order kinetics except for loss from bone, and that the skeletal system in rats and mice is the kinetically rate-limiting step in whole-body lead clearance. The neonatal animal seems to retain proportionally higher levels of tissue lead compared to the adult and manifests slow decay of brain lead levels while showing a significant decline over time in other tissues. This decay appears to result from enhanced lead entry to the brain because of a poorly developed brain barrier system as well as from enhanced body reten tion of lead by young animals. 10-65 TEH 0411972 DUP050452570 The effects of such changes as metabolic stress and nutritional status on body redistri bution of lead have been noted. Lactating mice, for example, are known to demonstrate tissue redistribution of lead, specifically bone-lead resorption with subsequent transfer of both lead and calcium from mother to pups. 10.8.3 Lead Excretion and Retention in Humans and Animals 10.8.3.1 Human Studies. Dietary lead in humans and animals that is not absorbed passes through the GI tract and is eliminated with feces, as is the fraction of air lead that is swallowed and not absorbed. Lead entering the bloodstream and not retained is excreted through the renal and GI tracts, the latter via biliary clearance. The amounts excreted through these routes are a function of such factors as species, age, and exposure charac teristics. Based upon the human metabolic balance data and Isotope excretion findings of various in vestigators, short-term lead excretion in adult humans amounts to 50-60 percent of the ab sorbed fraction, with the balance moving primarily to bone and some fraction (approximately half) of this stored amount eventually being excreted. This estimated overall retention figure of 25 percent necessarily assumes that isotope clearance reflects that for body lead in all compartments. The rapidly excreted fraction has a biological half-life of 20-25 days, similar to that for lead removal from blood, based on isotope data. This similarity indicates a steady rate of lead clearance from the body. In terms of partitioning of excreted lead between urine and bile, one study indicates that the biliary clearance is about 50 percent that of renal clearance. Lead accumulates in the human body with age, mainly in bone, up to around 60 years of age, when a decrease occurs with changes in intake as well as in bone mineral metabolism. As noted earlier, the total amount of lead in long-term retention can approach 200 mg, and even much higher in the case of occupational exposure. This rate corresponds to a lifetime average retention rate of 9-10 pg Pb/day. Within shorter time frames, however, retention will vary considerably because of such factors as development, disruption in the individuals' equilib rium with lead intake, and the onset of such states as osteoporosis. The age-dependency of lead retention/excretion in humans has not been well studied, but most of the available information Indicates that children, particularly infants, retain a sig nificantly higher amount of lead than adults. While autopsy data Indicate that pediatric sub jects at Isolated points in time actually have a lower fraction of body lead lodged in bone, which probably relates to the less dense bones of children as well as high bone mineral turn over, a full understanding of longer-term retention over childhood must consider the exponen tial growth rate occurring in children's skeletal systems over the time period for which bone lead concentrations have been gathered. This parameter itself represents a 40-fold mass 10-66 TEH 0411973 DUP050452571 increase. This significant skeletal growth rate has an impact on an obvious question: if children take in more lead on a body-weight basis than adults, absorb and retain more lead than adults, and show only modest elevations in blood lead compared to adults in the face of a more active skeletal system, where does the lead go? A second factor is the assumption that blood lead in children relates to body lead burden in the same quantitative fashion as in adults, an assumption that remains to be proven adequately. 10.8.3.2 Animal Studies. In rats and other experimental animals, both urinary and fecal ex cretion appear to be Important routes of lead removal from the organism. The relative parti tioning between the two modes is species- and dose-dependent. With regard to species differ ences, biliary clearance of lead in the dog is but 2 percent of that for the rat, while such excretion in the rabbit is 50 percent that of the rat. Lead movement from laboratory animals to their offspring via milk constituents is a route of excretion for the mother as well as a route of exposure for the young. Comparative studies of lead retention in developing versus adult animals such as rats, mice, and nonhuman primates make it clear that retention is significantly greater in the young animal. These observations support those studies showing greater lead retention in children. Some recent data indicate that a differential retention of lead in young rats persists into the post-weaning period, calculated as either uniform dosing or uniform exposure. 10.8.4 Interactions of Lead with Essential Metals and Other Factors Toxic elements such as lead are affected in their toxicokinetic or toxicological behavior by interactions with a variety of biochemical factors, particularly nutrients. 10.8.4.1 Human Studies. In humans, the interactive behavior of lead and various nutritional factors is expressed most significantly in young children, with such interactions occurring against a backdrop of rather widespread deficiencies in a number of nutritional components. Various surveys have indicated that iron, calcium, zinc, and vitamin deficiencies are wide spread among the pediatric population, particularly the poor. A number of reports have docu mented the association of lead absorption with suboptimal nutritional states for iron and cal cium, reduced intake being associated with increased lead absorption. 10.8.4.2 Animal Studies. Reports of lead-nutrient interactions in experimental animals have generally described such relationships for a single nutrient, using relative absorption or tissue retention in the animal to index the effect. Most of the recent data are for calcium, Iron, phosphorus, and vitamin D. Many studies have established that diminished dietary calci um is associated with increased blood and soft-tissue lead content in such diverse species as the rat, pig, horse, sheep, and domestic fowl. The increased body burden of lead arises from both increased GI absorption and increased retention, indicating that the lead-calcium inter action operates at both the gut wall and within body compartments. Lead appears to traverse 10-67 TEH 0411974 DUP050452572 the gut via both passive and active transfer. It involves transport proteins normally opera ing for calcium transport, but is taken up at the site of phosphorus, not calcium, absorption. Iron deficiency is associated with an increase of lead in tissues and increased toxicity effects that are expressed at the level of lead uptake by the gut wall. In vitro studi Indicate an interaction through receptor-binding competition at a common site, which probabi involves iron-binding proteins. Similarly, dietary phosphate deficiency enhances the exte' of lead retention and toxicity via increased uptake of lead at the gut wall, both lead an phosphate being absorbed at the same site in the small intestine. Results of various studi. of the resorption of phosphate along with lead have not been able to identify conclusively mechanism for the elevation of tissue lead. Since calcium plus phosphate retards lead absorp tion to a greater degree than simply the.sums of the interactions, an insoluble complex of al, these elements may be the basis of this retardation. Unlike the inverse relationship existing for calcium, iron, and phosphate versus lead take, vitamin D levels appear directly related to the rate of lead absorption from the GL tract, since the vitamin stimulates the same region of the duodenum where lead is absorbed. A number of other nutrient factors are known to have an Interactive relationship with lead: c>r 1. Increases in dietary lipids increase the extent of lead absorption, with the extent of the increase being highest with polyunsaturates and lowest with saturated fats, e.g., tristearin. 2. The interactive relationship of lead and dietary protein is not clear cut, and either suboptimal or excess protein intake will increase lead absorption. 3. Certain milk components, particularly lactose, greatly enhance lead absorption in the nursing animal. 4. Zinc deficiency promotes lead absorption, as does reduced dietary copper. Taken collectively, human and animal data dealing with the Interaction of lead and nutri ents Indicate that there are heterogeneous subsets of the human population. In terms of pedatric population risk for lead exposure, children having multiple nutrient deficiencies are in the highest exposure risk category. 10.8.5 Interrelationships of Lead Exposure with Exposure Indicators and Tissue Lead Burdens Three issues involving lead toxicokinetics evolve toward a full connection between lead exposure and its adverse effects: (1) the temporal characteristics of internal indices of lead exposure; (2) the biological aspects of the relationship of lead in various media to various indicators in internal exposure; and (3) the relationship of various internal indica tors of exposure to target tissue lead burdens. 10-68 TEH 0411975 m si? DUP050452573 10.8.5.1 Temporal Characteristics of Internal Indicators of Lead Exposure. The biological half-life for newly absorbed lead in blood may be as short as weeks, or several months. Or, it may be longer, depending on the mobile lead burden in the body. Compared to mineral tissues, this medium reflects relatively recent exposure. If recent exposure is fairly representative of exposure over a considerable period of time, e.g., exposure of lead workers, then blood lead is more useful than for cases where exposure is intermittent or different across time, as in the case of lead exposure of children. Accessible mineralized tissue, such as shed teeth, extend the time frame back to years of exposure, since teeth accumulate lead with age and as a function of the extent of exposure. Such measurements are, however, retrospective in nature, in that Identification of excessive exposure occurs after the fact and thus limits the possi bility of timely medical intervention, exposure abatement, or regulatory policy concerned with ongoing control strategies. Perhaps the most practical solution to the dilemma posed by both tooth and blood lead analyses is iji situ measurement of lead in teeth or bone during the time when active accumu lation occurs, e.g., 2- to 3-year-old children. Available data using X-ray fluorescence anal ysis dc suggest that such approaches are feasible and can be reconciled with such issues as acceptable radiation hazard risk to subjects. 10.8.5.2 Biological Aspects of External Exposure/Internal Indicator Relationships. The literature indicates clearly that the relationship of lead in relevant media for human expo sure to blood lead is curvilinear when viewed over a relatively broad range of blood lead values. This curvilinearity implies that the unit change in blood lead per unit intake of lead in some medium varies across this range of exposure, with comparatively smaller blood lead changes occurring as internal exposure increases. Given our present knowledge, such a relationship cannot be taken to mean that body uptake of lead is proportionately lower at higher exposure, because it may simply mean that blood lead becomes an Increasingly unreliable measure of target-tissue lead burden with increasing exposure. While the basis of the curvilinear relationship remains to be identified, available animal data suggest that it may be related to the Increasing fraction of blood lead in plasma as blood lead increases above approximately 50-60 pg/dl. 10.8.5.3 Internal Indlcator/Tissue Lead Relationships. In living human subjects, direct de termination of tissue lead burdens or how these relate to adverse effects in target tissues is not possible. Some accessible indicator (e.g., lead in a medium such as blood or a biochem ical surrogate of lead such as erythrocyte protoporphyrin), must be employed. While blood lead still remains the only practical measure of excessive lead exposure and health risk, evi dence continues to accumulate that such an index has some limitations in either reflecting tissue lead burdens or changes in such tissues with changes in exposure. 10-69 TEH 0411976 DUP050452574 At present, the measurement of plumburesis associated with challenge by a single dose of a lead-chelating agent such as CaNa2EDTA is considered the best indicator of the mobile, potentially toxic fraction of body lead. Chelatable lead is logarithmically related to blood lead, such that an incremental increase in blood lead is associated with an increasingly larger increment of mobilizable lead. The problems associated with this logarithmic relation ship may be seen in studies of children and lead workers in whom moderate elevation in blood lead levels can disguise levels of mobile body lead. In one recent multi-institution study of 210 children, for example, 12 percent of children with blood lead 30-39 pg/dl, and 38 percent with levels of 40-49 pg/dl, had a positive EDTA-chalTenge response and required further eval uation or treatment. At blood lead levels such as these, the margin of protection against severe intoxication is reduced. The biological basis of the logarithmic chelatable lead/ blood lead relationship rests, in large measure, with the existence of a sizeable bone lead compartment that is mobile enough to undergo chelation removal and, hence, potentially mobile enough to move into target tissues. Studies of the relative mobility of chelatable lead over time indicate that, in former lead workers, removal from exposure leads to a protracted washing out of lead (from bone re sorption of lead) to blood and tissues, with preservation of a bone burden amenable to subsequent chelation. Studies with children are inconclusive, since the one investigation directed to this end employed pediatric subjects who all underwent chelation therapy during periods of severe lead poisoning. Animal studies demonstrate that changes in blood lead with increasing exposure do not agree with tissue uptake in a time-concordant fashion, nor does de crease in blood lead with reduced exposure signal a similar decrease in target tissue, parti cularly in the brain of the developing organism. 10.8.6 Metabolism of Lead Alkyls The lower alkyl lead components used as gasoline additives, tetraethyl lead (TEL) and tetramethyl lead (TML), may themselves poise a toxic risk to humans. In particular, there is among children a problem of sniffing leaded gasoline. 10.8.6.1 Absorption of Lead Alkyls in Humans and Animals. Human volunteers inhaling labeled TEL and TML show lung deposition rates for the lead alkyls of 37 and 51 percent, respectively, values which are similar to those for particulate inorganic lead. Significant portions of these deposited amounts were eventually absorbed. Respiratory absorption of organolead bound to particulate matter has not been specifically studied as such. While specific data for the GI absorption of lead alkyls in humans and animals are not available, their close similarity to organotin compounds, which are quantitatively absorbed, would argue for extensive GI absorption. In contrast to inorganic lead salts, the lower lead 10-70 TEH 0411977 DUP050452575 alkyls are extensively absorbed through the skin and animal data show lethal effects with per cutaneous uptake as the sole route of exposure. 10.8.6.2 Blotransformation and Tissue Distribution of Lead Alkyls. The lower lead alkyls TEL and TML undergo monodealkylation in the liver of mammalian species via the P-450-dependent mono-oxygenase enzyme system. Such transformation is very rapid. Further transformation involves conversion to the dialkyl and inorganic lead forms, the latter accounting for the effects on heme biosynthesis and erythropoiesis observed in alkyl lead intoxication. Alkyl lead is rapidly cleared from blood and shows a higher partitioning into plasma than inorganic lead, with triethyl lead clearance being more rapid than that of the methyl analog. Tissue distribution of alkyl lead in humans and animals primarily involves the trialkyl metabolites. Levels are highest in liver, followed by kidney, then brain. Of interest is the fact that there are detectable amounts of trialkyl lead from autopsy samples of human brain even in the absence of occupational exposure. 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(1979) Detection and treatment of occupational le nephropathy. Arch. Intern. Med. 139: 53-57. Williams, M. K.; King, E.; Walford, J. (1969) An investigation of lead absorption in an ele~ trie accumulator factory with the use of personal samplers. Br. J. Ind. Med. 26: 202-27 Willoughby, R. A.; Thirapatsakun, T.; McSherry, B. J. (1972) Influence of rations low calcium and phosphorus on blood and tissue lead concentrations in the horse. Am. J. Vet. Res. 33: 1165-1173. Winneke, G. ; Brockhaus, A.; Kramer, U.; Ewers, U.; Kujanek, G.; Lechner, H.; Janke, W (1981) Neuropsychological comparison of children with different tooth-lead levels: prelimina report. In: International conference: heavy metals in the environment; Amsterdam, Netherlands. Edinburgh, United Kingdom: CEP Consultants, Ltd.; pp. 553-556. World Health Organization, United Nations Environmental Programme. (1977) Lead. Geneva Switzerland: World Health Organization. (Environmental health criteria 3). Yamamura, Y.; Takakura, J.; Hirayama, F.; Yamauchi, H.; Yoshida, M. (1975) Tetraethyl lea poisoning caused by cleaning work in the aviation fuel tank. Jpn. J. Ind. Health 1.: 223-235. h Yip, R.; Norris, T. N.; Anderson, A. S. (1981) Iron status of children with elevated blocd: lead concentrations. J. Pediatr. (St. Louis) 98: 922-925. 10-90 ' TEH 0411997 DUP050452595 Ziegler, E. E.; Edwards, B. B.; Jensen, R. L.; Mahaffey, K. R.; Fomon, S. J. (1978) Absorption and retention of lead by infants. Pediatr. Res. 12: 29-34. Zielhuis, R. L.; del Castilho, P.; Herber, R. F. M.; Wibowo, A. A. E. (1978) Levels of lead and other metals in human blood: suggestive relationships, determining factors. Environ. Health Perspect. 25: 103-109. 10-91 TEH 0411998 DUP050452596 11. ASSESSMENT OF LEAD EXPOSURES AND ABSORPTION IN HUMAN POPULATIONS 11.1 INTRODUCTION This chapter describes effects on internal body burdens of lead in human populations resulting from exposure to lead in their environment. Particular attention is paid to changes in indices of internal lead exposure that follow changes in external lead exposures. Blood lead is the main index of internal lead exposure discussed here, although other indices, such as levels of lead in teeth and bone, are also briefly discussed. The following terms and definitions are used in this chapter. Sources of lead are those components of the environment (e.g., gasoline combustion, smelters) from which significant quantities of lead are released into various environmental media of exposure. Environmental media are routes by which humans become exposed to lead (e.g., air, soil, food, water, dust). External exposures are levels at which lead is present in any or all of the environmental media. Internal exposures are amounts of lead present in various body tissues and fluids. The present chapter is structured to achieve the following four main objectives: (1) Elucidation of patterns of internal lead exposures in U.S. populations and identification of important demographic covariates. (2) Characterization of relationships between external and internal exposures to lead by exposure medium (air, food, water or dust). (3) Identification of specific sources of lead which result in increased internal exposure levels. (4) Estimation of the relative contributions of various sources of lead in the environment to total internal 'exposure as indexed by blood lead level. The existing scientific literature must be examined in light of the investigators' own objectives and the quality of the scientific investigations performed. Although all studies need to be evaluated in regard to their methodology, the more quantitative studies are evalu ated here in greater depth. A discussion of the main types of methodological points con sidered in such evaluations is presented in Section 11.2. Patterns of internal exposure to lead in human populations are discussed in Section 11.3. This begins with a brief examination of the historical record of internal lead exposure in human populations. These data serve as a backdrop against which recent U.S. levels can be contrasted and define the relative magnitude of external lead exposures in the past and present. The contrast is structured as follows: historical data, recent data from popula tions thought to be isolated from urbanized cultures, and then U.S. populations showing various degrees of urbanization and industrialization. 11-1 TEH 0411999 DUP050452597 The statistical treatment of distributions of blood lead levels in human populations the next topic discussed. As part of that discussion, the empirical characteristics of bV lead distributions in well-defined homogeneous populations are denoted. Important iss'u addressed include the proper choice of estimators of central tendency and dispersion, estiir. tors of percentile values and the potential influence of errors in measurement on statistic estimation involving blood lead data. Then recent patterns of internal exposure in U.S. and other populations showing charige blood lead levels are discussed in detail. Estimates of internal lead exposure and iderit cation of demographic covariates are made. Studies examining the recent past for evidence change in internal exposure levels are presented. Next is an examination of extensive e dence which points towards gasoline lead being an important determinant of changes in blc lead level associated with exposures to airborne lead of populations in the United States elsewhere. Section 11.4 focuses on general relationships between external exposures and levels internal exposure. The distribution of lead in man is diagramatical ly depicted by the coinp nent model shown in Figure 11-1. Of particular importance for this document is the relatio ship between lead in air and lead i`n blood. If lead in air were the only medium of exposure, then the interpretation of a statistical relationship between lead in air and lead in bio . would be relatively simple. However, this is nojt the case. Lead is present in a number c environmental media, as described in Chapter 7 and summarized in Figure 11-1. There are rela tionships between lead levels in air and lead concentrations in food, soil, dust, and wate As shown in Chapters 6, 7, and 8, lead emitted into the atmosphere ultimately comes back contaminate the earth. However, only limited data are currently available that provide quantitative estimate of the magnitude of this secondary lead exposure. The implication i that an analysis involving estimated lead levels in all environmental media may tend to under estimate the relationship between lead in blood and lead in air. The discussion of relationships between external exposure and internal absorption con mences with air lead exposures. Both experimental and epidemiological studies are discuss.d Several studies are identified as being of greatest importance in determining the quantitative relationship between lead in blood and lead in air. The form of the relationship between blood lead and air lead is of particular interest and importance. After discussion of lead versus blood lead relationships, the chapter next discusses the relationship of hVq lead to atmospheric lead found in other environmental media. Section 11.5 describes studies of specific lead exposure situations useful in identifying specific environmental sources lead that contribute to elevated body burdens of lead. The chapter concludes with a summa of key information and conclusions derived from the scientific evidence reviewed. 11-2 TEH 04120 DUP050452598 LIVER) KIDNEY FECES URINE BONES Figure 11-1. Pathways of lead from the environment to and within man. 11-3 TEH 0412001 DUP050452599 11.2 METHODOLOGICAL CONSIDERATIONS * * . i liliSiilliliii&l&li 11.2.1 Analytical Problems \r t ^ Internal lead exposure levels in human populations have been estimated by analyses c,f-Vin`> 5 variety of biological tissue matrices (e.g., blood, teeth, bone, and hair). Lead levels each of these matrices have particular biological meanings with regard to external eyposuie * status; these relationships are discussed in Chapter 10. The principal internal exposure-f - index discussed in this chapter is blood lead concentration. Blood lead concentrations`are 1 most reflective of recent exposure to lead and bear a consistent relationship to levels' of/',* lead in the external environment if the latter have been stable. Blood lead levels arc ously reported as pg/100 g, pg/100 ml, pg/dl, ppm, ppb, and pmol/1. The first four measures ! ^ are roughly equivalent, whereas ppb values are simply divisible by 1000 to be equiv-|t>* 1 Actually there is a small, but not meaningful, difference in blood lead levels reported per volume versus per weight difference. The difference results from the density of blood"1'TjM|g being slightly greater than 1 g/ml. For the purposes of this chapter, data reported on'aV'1 ' weight or volume basis are considered equal. On the other hand, blood lead data reported on ai , * pmol/1 basis must be multiplied by 20.72 to get the equivalent pg/dl value. Data reported*- originally as pmol/1 in studies reviewed here are converted to pg/dl in this chapter. 1 As discussed in Chapter 9, the measurement of lead in blood has been accomplished n succession of analytical procedures over the years. The first reliable analytical methodsJ. available were wet chemistry procedures, succeeded by increasingly automated instrumental procedures. With these changes in technology there has been increasing recognition of the importance' of controlling for contamination in the sampling and analytical procedures. These 4 advances, as well as institution of external quality control programs, have resulted markedly improved analytical results. Data summarized in Chapter 9 show that a generalized.* i, improvement in analytical results across many laboratories occurred during Federal Fiscal Years 1977-1979. No further marked improvement was seen during Federal Fiscal wears'1 * 1979-1981. 1 Because of interest in being able to attribute specific proportions of blood lead as- coming from specific environmental sources, isotopic lead determinations in blood have become an important analytic technique. As difficult as it is to determine blood lead levels accu- i rately, the achievement of accurate lead isotopic determinations is even more difficul* Experience gained from the isotopic lead experiment (ILE) in Italy (reviewed in detail m ^ _ . Section 11.3.6.2.1) has indicated that extremely aggressive quality control and contamination >j f, control programs must be implemented to achieve acceptable results. With proper procedures,,..I ^ meaningful differences on the order of a single nanogram are achievable. 'linHHHi .*1, i* !*. 11-4 f * >* TEH 0412002 4, *~f' * ' DUP050452600 11.2.2 Statistical Approaches Many studies have summarized the distribution of lead levels in humans. These studies usually report measures of central tendency (means) and dispersion (variances). In this chap ter, the term "mean" refers to the arithmetic mean unless stated otherwise. This measure is always an estimate of the average value, but it estimates the center of the distribution (50th percentile) only for symmetric distributions. Many authors provide geometric means, which estimate the center of the distribution if the distribution is lognormal. Geometric means are influenced less by unusually large values than are arithmetic means. A complete discussion of the lognormal distribution is given by Aitchison and Brown (1966), including formulas for'con verting from arithmetic to geometric means. Most studies also give sample variances or standard deviations in addition to the means. If geometric means are given, then the corresponding measure of dispersion is the geometric standard deviation. Aitchison and Brown (1966) give formulas for the geometric standard devi ation and, also, explain how to estimate percentiles and construct confidence intervals. All of the measures of dispersion actually include three sources of variation: population varia tion, measurement variation, and variation due to sampling error. Values for these components are needed in order to evaluate a. study correctly. There are also sources of variation related to the inclusion of predictive variables in the model, or their exclusion. Such vari ables include different lead uptakes attributable to exposure to lead in dust, soil, food, water, paint in deteriorated housing, and other pathways. If included in the model, the remaining sources of variation are due to unmeasured differences in intrinsic metabolism and behavior. It has been the general goal in this chapter to include all attributable sources of variation, thus reducing the estimates of variability to biological differences, uncertainties in exposure, and measurement variations that cannot be further attributed. We recognize that if only air lead exposure is controlled, then there will be additional variation in blood lead response due to imperfectly controlled covariation of lead exposure from related pathways. This additional variation can be dealt with in practice by use of a larger geometric standard deviation. A separate issue is the form of the distribution of blood lead values. Although the nor mal and lognormal distributions are commonly used, there are many other possible distribu tions. The form is important for two reasons: 1) it determines which is more appropriate, the arithmetic or geometric mean, and 2) it determines estimates of the fraction of a popula tion exceeding given internal lead levels under various external exposures. Both of these questions arise in the discussion of the distribution of human blood lead levels and are of importance, ultimately, for deriving a rationale for standard-setting purposes. 11-5 TEH 0412003 DUP050452601 11.2.3 Confounding of Relevant Variables Failure to include relevant variables is the most serious difficulty in evaluating sta ies on lead in human populations. This usually occurs when the blood lead response is who! attributed to some observed variable, e.g., the lead concentration in air, dust, or wate' Typical confounders for air lead include the following: (1) inhalation exposures not captur' by stationary air lead monitors, particularly those that occur from personal expokirf51 leaded gasoline or its combustion products; (2) noninhalation exposures to air lead not cat tured by stationary monitors, e.g., ingestion of food products contaminated by lead fallout leaded dust, and soil; (3) ingestion of lead in water and food that is inadvertantly assdcf ated with air lead exposure. Socioeconomic factors may be important here also. Brunekreef (1984) and Snee (1982b,c) for additional comments. Air lead concentrations are typically highest in urban centers where the concentration o motor vehicles is greatest. (Communities with lead smelters are an exception). Suburban1^ rural areas have much lower air lead concentrations. However, suburban and rural resident, may spend more time in motor vehicles due to longer trips to work, school, and shopping. There is some reason to believe that higher lead concentrations may be found near and inside automobiles (see Spengler et al. , (1984), Section 11.3.6.2.1), thus offsetting the decreas ambient air lead concentrations measured by stationary monitors in non-urban areas, fortunately, there is no way at this time to separate the response to average ambient air le levels from variations in personal lead exposure patterns. Children are known to ingest quantities of dust and soil by normal hand-mouth contact. I studies in which dust lead concentrations or hand lead quantities are measured, their contrir bution is very large -- usually much larger than the lead intake by direct inhalation, smelter communities all of these variables -- ambient air lead, dust lead, soil lead, and lead on children's hands -- are likely to be high. It may then be difficult to separate the contri butions of each of these components, and if any one is not measured, then its influence on blood lead may be attributed to the other variables. This may cause little difficulty when ih;:fact there is a single source for all exposure pathways, but positive confounding may cause difficulty in extrapolating the relationship to situations in which air and dust lead are les strongly coupled. Similarly, the particle size distribution may change with distance from source (smelter, highway, etc.) and particle size is known to affect the fraction of lead sorbed by the lungs. However, air and dust lead concentrations also decrease with dista from the source, thus leading to potential confounding of concentration and size effects. This may be a factor in some smelter studies, e.g., the Silver Valley, Idaho, study discusse later. 11-6 TEH 0412004 DUP050452602 Socioeconomic status (SES), sex, age, and race are also confounded with air lead. Lower SES populations tend to be found in areas with high air lead concentration such as urban cen ters and smelter communities. There may also be systematic SES differences in use of leadsoldered food and beverage cans and in exposure to food products with high lead content and in personal and household cleanliness, as well. The latter is important because dust control can substantially reduce blood lead burdens in children (Charney et a!., 1983). Lower SES is also associated with older housing stocks and increasing risk of encountering lead paint in poor condition and lead pipes in water systems. Lower SES is also more likely to be associated with inadequate dietary calcium, iron, and vitamins, all of which increase lead absorption and the likely toxic effects of any given level of lead exposure. In addition, lower SES is also more likely to imply reduced awareness of lead hazards and reduced resources for dealing with such hazards. Other factors, such as the presence of pets in a household and the amount of time spent playing outside, are not obviously related to SES. Males have higher blood lead levels than females', at least beyond ages 10-11. The most plausible explanations suggest differential exposure, with older boys and men typically spend ing more time in contact with motor vehicles, in jobs with potential lead exposure, and more often outdoors. The risk factors have not been fully identified. Black children also often have higher blood leads than do white children, even after adjusting for SES and other covar iates; the reason for this difference has also not been clarified, but may be related to posi tive confounding factors. For modelling purposes, the appropriate geometric standard deviation removes a portion of the total variation in blood lead due to differences in air lead exposure without removing the variance due to these other factors. Controlling for race, urbanization, age, income, and location may overcontrol in this case, since it may remove variance due to environmental expo sure factors that will remain after air lead is controlled to any given level. It may thus be prudent and conservative to compensate for this overcontrol by increasing the geometric stan dard deviation when only air lead is used as a predictor variable. All of the above factors make it difficult to analyze adequately such a highly confounded environmental exposure variable as air lead. However, there appear to be enough studies in which several of the possible confounding factors were also measured that it is possible to obtain reasonable estimates of blood lead changes in response to differences in concentrations of lead in air, dust, soil, water, and diet, seasonal variations, and personal risk factors such as household quality, occupational exposure, and motor vehicle exposure. The remaining sections of this chapter discuss studies from which such estimates are derived. Experimental studies are much less subject to confounding, and where available, are generally preferred. Unfortunately, experimental studies do not provide information about total environmental air 11-7 TEH 0412005 DUP050452603 lead exposure, which includes multiple exposure pathways and possible time lags of many years due to passage of lead through the soil, the food chain, and water supplies. It is thus also necessary to obtain information about total air lead exposure from observational studies. All observational studies suffer confounding problems. This chapter focuses mainly on those ob servational studies in which a substantial number of the probable important confounding fac tors are either measured or are controlled by the design of the study. Less importance is assigned to those studies in which too many important covariates have been omitted, or which otherwise seem critically deficient. 11.3 LEAD IN HUMAN POPULATIONS 11.3.1 Introduction This descriptive section presents information on dimensions of current internal exposures to lead for United States populations. Several aspects of the current situation regarding internal lead exposures are addressed. First, attention is focused on showing how current in dices of internal exposure compare with indices derived frcm historical samples. Also, the question of how contemporaneous populations compare with one another with respect to internal exposures is addressed. The primary data involved in this discussion are blood lead levels from populations showing varying degrees of urbanization. Blood lead levels are lowest in populations living remotely from urban influences and increase as one goes from rural to urban areas, suggesting that higher blood lead levels are linked to urban lifestyles. Following this discussion, data are presented on several large studies in the United States and a large worldwide study. These data address two principal questions: 1) are there identifiable sub populations in the United States which exhibit higher than average blood lead levels, and 2) how do United States blood lead levels compare with other countries? This section next presents studies which examine recent time trends in blood lead levels in the United States and elsewhere, and then concludes with a discussion of evidence which points towards gasoline lead being an important determinant of changes in blood lead levels associated with exposures to airborne lead of populations in the United States and elsewhere. 11.3.2 Ancient and Remote Populations One question of much interest in understanding environmental pollutants is the extent to which current ambient exposures exceed background levels. Because lead is a naturally occur ring element it can be surmised that some level has been and will always be present in the human body; the question of interest is what is the difference between body burdens of current subgroups of the United States population and those "natural" levels. Information regarding 11-8 TEH 0412006 DUP050452604 this issue has been developed from studies of populations that lived in the past and popula tions that currently live in remote areas far from the influence of industrial and urban lead exposures. Man has used lead since antiquity for a variety of purposes. These uses have afforded the opportunity for some segments of the human population to be exposed to lead and subse quently absorb it into the body. Because lead accumulates over a lifetime in bones and teeth and because bones and teeth stay intact for extremely long times, it is possible to estimate the extent to which populations in the past have been exposed to lead. Because of the prob lems of scarcity of samples and little knowledge of how representative the samples are of con ditions at the time, the data from these studies provide only rough estimates of the extent of absorption. Further complicating the interpretation of these data are debates over proper analytical procedures and the question of whether skeletons and teeth pick up or release lead from or to the soil in which they are interred (Waldron et al. , 1979; Waldron, 1981). Waldron et al. (1979) have argued that any lead found in ancient bones probably is an accurate reflection of exposure during life. They reported a small study which showed no cor relation between bone and soil lead concentrations. Later, however, Waldron (1981) reported a study in which the postmortem bone lead levels appeared to be much too high to have been developed during life. The bones were recovered from lead coffins. Electron microprobe analysis on one bone from a lead coffin showed that the lead was concentrated on the surfaces of the bone. This suggested that the lead in bones came from the lead coffin and led Waldron (1981) to suggest that "in any further study of the lead content of bones from archaeological sites, steps must be taken to assess environmental lead levels and if these are unusually high, the results of the analyses should be viewed with suspicion." Barry and Connolly (1981) express further concern over the use of paleontological remains as doubtful criteria for the in vivo assessment of lead exposure in past populations. Despite these methodological difficulties, several studies provide data by which to esti mate internal exposure patterns among ancient populations, and some studies have included data from both past and current populations for comparisons. Data from specific studies of bone and teeth in ancient populations are summarized below in Section 11.3.2.1. In contrast to the study of ancient populations using bone and teeth lead levels, several studies have looked at the issue of lead contamination from the perspective of comparing blood lead levels in current remote and urbanized populations. These studies using blood lead levels as an indicator found mean blood concentrations in remote populations between 1 and 5 pg/dl (an order of magnitude below current U.S. urban population means), as discussed in Section 11.3.2.2 below. 11-9 TEH 0412007 DUP050452605 11.3.2.1 Ancient Populations. Table 11-1 summarizes several studies that analyzed bones and teeth to yield approximate estimates of lead absorption in the past. Some of these studies- / also analyzed contemporary current samples so that a comparison between past and present couldf be made. Studies summarized in Table 11-1 show an increase of lead levels in bone and teein^* ` from older to contemporary samples. Samples from the Sudan (ancient Nubians) were collected from several different archag'b- ' logical periods (Grandjean et al., 1979). The oldest sample (3300-2900 B.C.) averaged pg/g for bone and 0.9 pg/g for teeth. Data from the later time of 1650-1350 B.C. show a s u d s ' * stantial increase in absorbed lead. Comparison of even the most recent ancient samples wither current Danish sample showed a four- to eightfold increase over time. The Shapiro et al. (1975) study, compared the tooth lead content of ancient population*, ' with that of current remote populations and, also, with current urban populations. Tnsif ancient Egyptian samples (1st and 2nd millenia) exhibited the lowest tooth lead levels, w*tij,w' a mean of 9.7 pg/g. The more recent Peruvian Indian samples (12th century) had similar ltvels-' (13.6 pg/g). The contemporary Alaskan Eskimo samples had a mean of 56.0 pg/g, while Philadelphia samples had a mean of 188.3 pg/g. These data suggest an increasing pattern of - i* lead absorption from ancient populations to current remote and urban populations. Data have also been obtained from ancient Peruvian and Pennsylvanian samples (Becker et al., 1968). The Peruvian and Pennsylvanian samples for American Indian populations were from*1,* approximately the same era (-1200-1400 A.D.). Little lead was used in these cultures as re-,, fleeted by chemical analysis of bone lead content. The values were less than 5 pg/g for both"*,: samples. In contrast, values obtained for modern samples from residents of Syracuse, New; York, ranged from 5 to 110 pg/g. Ericson et al. (1979) also analyzed bone speciments from ancient Peruvians. Samples from 4500-3000 years ago to about 1400 years ago were reasonably constant (<0.2 pg/g). Fosse and Wesenberg (1981) reported a study of Norwegian teeth samples from several eras. The older material from 1200-1800 A.D. was significantly lower in lead (1.22 to 1.81 pg/g) than modern samples (3.73 to 4.12 pg/g). Aufderheide et al. (1981) report a study of 16 skeletons from colonial America. Iwo social groups, identified as plantation proprietors and laborers, had distinctly differen exposures to lead as shown by the analyses of the skeletal samples. The proprietor gr&u averaged 185 pg/g bone ash while the laborer group averaged 35 pg/g. Changes in bone and tooth lead concentrations over time (as determined by the above or other studies) have been evaluated by Angle and Mclntire (1982), as graphically depicted'! Figure 11-2. Lead concentrations in human bones apparently markedly increased among ancient 11-10 TEH 0412008 DUP050452606 TABLE 1 1 -1 . SUMMARY OF REPRESENTATIVE STUDIES OF PAST EXPOSURES TO LEAD TEH 0 4 1 2 0 0 9 *Ol *H KO *CM *IN K * ** *X Mfloro (fiOONU) o h rv h m >u</i >>>>> <e < < < < >s >> > a. CL CL 4Ouus->>- <ooo>J -uLi ouwo> +u* U U <J a aa<D~0> < < < <c < <1L//1l lm/> ll//UH//HU/O1 LLOO <</) L/l l</>s 1</1 >wt>ni>/u>n <c<Ztf < < < <c so ca co a oo oo in < >t.> UUflCOO fl (oMoHHo lrf*l- JoaOmoooOmoOfS^so O (\J rl rl U w ---a >s- m m co e >unj,mt<p. 5Cros S> . fc. <*- Oar*--a aO oai ea> >a> e(u .3tj--.04eJ: .0*ra-04cJ co o Z <_> ,,C hcM43co->) &J(oa8- &fnaocJ.. <C0 UE01 S *-> J4-> 4C-> 4C-? 01 CM O O i-4 ft O O 0i. s. i. -*-a vi <uaz oIB -- X3 c1 n |orfC fsl-j Cai 3Z 11-11 *a>J*-oCr- J| +j a c ai u 2! * co om>r*Ve *>9 j CTi S- <T> *r- rH 4- ** .HOVC 3 *w C 01 JO 1 0) TS . V) l--QJ . )r> ai iq >-cs-r 1 : IB +j 7_*a 4-> <--afl .xoi 3e *oo* VS HI C o aa ru- s<*-. 4* TcO ^01 - " S- <0 ______ ____ 0J 18 U IA <0 ! g>r j $_ OI O X 'r- Sh-J (JfflLLLOUh +-X H N 0) O' +-*- DUP050452607 populations with the introduction of metal!urgic processes and dramatic increases in produc tion and utilization of lead. For example, bone lead concentrations consistently below 3 gg/g were found for premeta11urgic societies in Peru, Egypt, Nubia, and Denmark, whereas concentra tions of lead in bones from England during the early Roman Empire era are reported to be 10-fold higher and to have reached 300 to 400 gg/g by the time of the Norman invasion. The Danish bone lead levels also increased during medieval times and reached peak levels of about 40-50 gg/g in the eighteenth century-. The data available for more recent contemporary popu lations in the twentieth century appear to be widely variable, ranging from 0.1 to 5.4 gg/g reported for contemporary adults in Denmark to 7.5 to 195 gg/g reported for U.S. adults dying in the 1950's. Overall, the available data (despite analytic errors in individual studies) collectively suggest that contemporary Americans, especially urban populations, absorb mani fold higher levels of lead than did members of premetallurgic societies. 11.3.2.2 Remote Populations. Several studies have looked at the blood lead levels in current remote populations (Piomelli et al., 1980; Poole et al., 1980). These studies are important in defining baseline levels of internal lead exposures found in the world today. Piomelli et al. (1980) studied blood lead levels of natives in a remote (far from indus trialized regions) section of Nepal. Portable air samplers were used to determine air lead concentrations in the region. The lead content of the air samples proved to be less than the detection limit, 0.004 gg/m3. A later study by Davidson et al. (1981) found an average air lead concentration of 0.00086 gg/m3 in remote areas of Nepal, thus confirming the low air lead levels reported by Piomelli et al. (1980). Blood lead levels reported by Piomelli et al. (1980) for the Nepalese natives were low; the geometric mean blood lead for this population was 3.4 gg/dl. Adult males had a geometric mean of 3.8 gg/dl and adult females, 2.9 gg/dl. Children had a geometric mean blood lead of 3.5 gg/dl. Only 10 of 103 individuals tested had a blood lead level greater than 10 gg/dl. The blood samples, which were collected on filter paper discs, were analyzed by a modification of the Delves cup atomic absorption spectrophotometric method. Stringent quality control pro cedures were followed for both the blood and air samples. To put these Nepalese values in perspective, Piomelli et al. (1980) reported analyses of blood samples collected and analyzed by the same methods from Manhattan, New York. New York blood leads averaged about 15 gg/dl, fivefold higher than the Nepalese values. Poole et al. (1980) reported another study of a remote population, using contaminationfree micro-blood sampling and chemical analysis techniques. They reported acceptable preci sion at blood lead concentrations as low as 5 gg/dl, using spectrophotometry. One hundred children were sampled from a remote area of Papua, New Guinea. Almost all of the children came from families engaging in subsistence agriculture. The children ranged from 7 to 10 11-13 TEH 0412011 DUP050452608 years and included both sexes. Blood lead levels ranged from 1 to 13 pg/dl with a mean of 5.2. Although the data appear to be somewhat skewed to the right, they are in good agreement with those of Piomelli for Nepalese subjects. 11.3.3 Levels of Lead and Demographic Covariates in LI.S. and Other Populations Several large surveys of blood lead levels give information on the major demographic co- variates in U.S. populations (see also sections 7.3.2.2 and 7.3.2.3.) In addition to the obvious covariates of age, sex, race, and urban-rural differences, there is a more subtle effect of seasonality. Children show a strong midsummer peak (hence the characterization of lead poisoning as "the summer disease" (Hunter, 1978)). This peak may be attributed to many causes: 1) gasoline lead consumption and lead concentrations are higher in the summer; 2) many people, especially children, spend more time outside during the summer; 3) more beverages are consumed in the summer, increasing exposure from lead-soldered beverage cans; and 4) other seasonal variations in diet, climate, and health status may affect blood lead levels. Thus, seasonality has an effect on all of the demographic studies. The extent to which these demo Blip'-' ,SJ' graphic studies adjust for seasonality varies. 11.3.3.1 The NHANES II Study. The National Center for Health Statistics has provided the if: best currently available picture of blood lead levels among United States residents as part of the second National Health and Nutrition Examination Study (NHANES II) conducted from February, 1976 to February, 1980 (Mahaffey et al., 1982; McDowell et al., 1981; Annest et al., 1982; Annest and Mahaffey, 1984). These are the first national estimates of lead levels in whole blood from a representative sample of the non-institutionalized U.S. civilian population aged 6 months to 74 years. From a total of 27,801 persons identified through a stratified, multi-stage probability m 'ifif5mwmm ' fjijjl ill# cluster sample of households throughout the United States, blood lead determinations were scheduled for 16,563 persons including all children ages 6 months to 6 years, and one-half of all persons ages 7-74. Sampling was scheduled in 64 sampling areas over the four-year period according to a previously determined itinerary to maximize operational efficiency and response of participants. Because of the constraints of cold weather, the examination trailers traveled in the moderate climate areas during the winter, and the more northern areas during the summer (McDowell et al., 1981). All reported blood lead levels were based on samples collected by venipuncture. Blood lead levels were determined by atomic absorption spectrophotometry using a modified Delves cup micro-method. Specimens were analyzed in duplicate, with both determinations done independ ently in the same analytical run. Quality control was maintained by two systems, a bench system and a blind insertion of samples. If the NHANES II replicates differed by more than 11-14 TEH 0412012 .f'fl MKJnOTNMMI DUP050452609 7 pg/dl, the analysis was repeated for the specimen (about 0.3 percent were reanalyzed). If the average of the replicate values of either "bench" or "blind" control specimens fell out side previously established 95 percent confidence limits, the entire run was repeated. The estimated coefficient of variation for the "bench" quality control ranged from 7 to 15 percent (Mahaffey et al., 1979). The reported blood lead levels were based on the average of the replicates. Blood lead levels and related data were reported as population estimates; findings for each person were inflated by the reciprocal of selection probabilities, adjusted to account for persons who were not examined and poststratified by race, sex, and age. The final estimates closely ap proximate the U.S. Bureau of Census estimates for the civilian non-institutionalized popula tion of the United States as of March 1, 1978, aged 1/2-74 years. Participation rates varied across age categories; the highest non-response rate (51 percent) was for the youngest age group, 6 months through 5 years. Among medically examined persons, those with missing blood lead values were randomly distributed by race, sex, degree of urbanization, and annual family income. These data are probably the best estimates now available regarding the degree of lead absorption in the general United States population. Forthofer (1983) has studied the potential effects of non-response bias in the NHANES II survey and found no large biases in the health variables. This was based on the excellent agreement of the NHANES II examined data, which had a 27 percent non-response rate, with the National Health Interview Survey data, which had a 4 percent non-response rate. The national estimates presented below are based on 9933 persons whose blood lead levels ranged from 2.0 to 66.0 pg/dl. The median blood lead for the entire U.S. population is 13.0 pg/dl. It is readily apparent that blacks have a higher blood lead level than whites (medians for blacks and whites were 15.0 and 13.0 pg/dl, respectively). Tables 11-2 through 11-4 display the observed distribution of measured blood lead levels by race, sex, and age. The possible influence of measurement error on the percent distribu tion estimates is discussed in Section 11.3.4. Estimates of mean blood lead levels differ substantially with respect to race, age, and sex. Blacks have higher levels than whites, the 6-month to 5-year group is higher than the older age groups, and men are higher than women. Overall, younger children show only a slight age effect, with 2- to 3-year-olds having slight ly higher blood lead levels than older children or adults (see Figure 11-3). In the 6-17 year grouping there is a decreasing trend in lead levels with increasing age. Holding age con stant, there are significant race and sex differences; as age increases, the difference between males and females in mean blood lead concentrations increases. 11-15 TEH 0412013 DUP050452610 TEH 0 4 1 2 0 1 4 Q CO Ol O' tO os LU nO*N <C to o LU S in to o 32 LU <C h- CO <S oa to 10 m co |H COOH LO CO *3* CO rH HOH ro c m r* O O If) tH CO ro o n V CM HCQfs CM VO if) CO O O) VO to cn ro co ro r** o- cn <n IO M KH -- CO to<**o"Hs OS |-- < l/) r>. as i UJ to o 3: n: 5 LO UJ -U s LU >0 UJ >-- --1 OS C9 O o0 O UJ tn c Ul QO 0) JS rH M-u rH CM VO CM eo to cc nco csi CM O' O OOO CO IX) CM CO O OOO O OOO in o <j <t Os 4) . 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O h~- P- rH I 1 co LO tD rH IX) tf) ws. v<n -= &<<U0 rve > ts*r n *. nSH I O tOI r0H0 Lf) U) Stf_) i U 3 tf) O r r-- C a. *0 > 3 Z m tQ j O U TJ 11-16 :Wi DUP050452611 TEH 0 4 1 2 0 1 5 CC VO o nCC Cl ce rH <H o< 3E HC 1/3 O Ui 1-4 O H* < OS LU ** C* o as o r- M- VD ONfO eg cslord CO rH CM 00 rH oo eg c m c m L0 co'sfco Cl record o HtH cn rH LT3 rH CO CO CM CO nvooh*<if O VOLOaO vo oooner OHIO HOiN CO O M* rH O P**C3 CO csi cd cm a a oo id in roco o o OO in *=t* edvo o ooo r~ cn l d'o o < aOS t-H Ni Oas LO Ui ss a li ~j a Ie oz < UJ lU-JJ COHSJ a lu Si --liU _ ts t- o 0 to a> eo so. e <t> s. a> 4-> S- JZ I .c l > 4- l- e esr*-- +e> CaO> cu o a o 0J T*J +> iq id e +j a. Vi O rH 03 C0 in c m in r- c m 3- vo * 'tesjm CO CO CO rH criudoo o ooo o ooo oo 10 00 iO rd u3 00 CM rH V in mrovo f*. CM VO <4* o m <sjo>N cn cn ro rH in co in co rH cn r***^ tHOrej" VO COMO VO CM rHCO HMrt 0vo4 cCoO muf> CM O O CM iH rH 10 rH OiOH rH r^CMCM (H ONft rH COCMtO rH rH CO VO >> e a> u> 0)000 in intI -<0 jyC) n<0s0>1i Hc >>* ONN S rH I | 00 l ID rH m v> s- 01<n vl> Sro- 0a3) JC q j > O<0) t?=*v <0 ONr^. -M r- SHI ;C rr-- <C VO I LO CO rH in trl t vS- ir-tf UI ui CO CU can) j z o> >> c ^ or>rs Ur03 <-- r-C CL T3 >> 10 11-17 i i DUP050452612 < oz ea c (HxX-I iou UJ 3XhS": CQ 3O --2(* vTS >OUCUC a* <CHQI1----S-Q> p* o J> H~ Xz H* (xl ZO l xI Z caC 4-> C IoSe C(g0dios-- ecr0e) 2 i!o uf J= o <+fcJ-- *+fBrlJ>- SC<4>0 Sf E CMCM CM a o ONfO no'o CM s* HOO CM ci o c q 01 c m 01 co m o co cr> a in d cm rO CO O CM d dors id fOOIOI CO VO Cl r-t CO HOID cm p p- OOO tflHH r-H rH rH (0(0 0 ^OH O OOO 0 r- m o o to d d O OOO ID CO 00 o CM d CM CM rM HHrt o 000 co^eo ITHH p p- p. ^ oiors 1X3 CO Lf) WHt H CO O Hmcm-NpP* pOrM Ir-D4 OPvrtps r-4 CQ CM Cl ID ID fc mlNoHm P* ^ CM oo 00 t vo 1100 0I-*5mr-ifO# CM P* ID CO SpCM. vCnM T-i I3 O 30 3 S. Q> 3 o0>. 3</> .4-0 J= U tJ(SA <V>0J0>T) (0 > to U> SU>- UI s<0- <<0u 5e a5*' osrs IBH 0I0 lO IO H 2 -8 5f <t 3: Z 11-18 1 2 346 6 AGE, years Figure 11-3. Geometric mean blood lead levels by race and age for younger children in the NHANES II study. EPA calculations from data furnished by the National Center for Health Statistics. Source: Annest and Mahaffey (1984). 7 11-19 TEH 0412017 DUP050452614 For adults 18-74 years, males have greater blood lead levels than females for both whites and blacks. There is a significant relationship between age and blood lead, but it differs for whites and blacks. Whites have increasing blood lead levels until 35-44 years of age and then decline, while blacks have increasing blood lead levels until 55-64. This study showed a clear relationship between blood lead level and family income group. For both blacks and whites, increasing family income is associated with lower blood lead level. At the highest income level the difference between blacks and whites is the smallest, although blacks still have significantly higher blood lead levels than whites. The racial difference was greatest for the 6-month to 5-year age range. The NHANES II blood lead data were also examined with respect to the degree of urbaniza tion at the place of residence. The -three categories used were urban areas with population greater than one million, urban areas with population less than one million, and rural areas. Geometric mean blood lead levels increased with degree of urbanization for all race-age groups except for blacks 18-74 years of age (see Table 11-5). Most importantly, urban black children aged 6 months - 5 years appeared to have distinctly higher mean blood lead levels than any other population subgroup. 11.3.3.2 The Childhood Blood Lead Screening Programs. In addition to the nationwide picture presented by the NHANES II (Annest et al., 1982) study regarding important demographic corre lates of blood lead levels, Billick et al. (1979, 1982) provide large scale analyses of blood lead values from childhood blood lead screening programs in specific cities that also address this issue. Billick et al. (1979) analyzed data from New York City blood lead screening programs from 1970 through 1976. The data include age in months, sex, race, residence expressed as health district, screening information, and blood lead values expressed in intervals of 10 pg/dl. Only the venous blood lead data (178,588 values), clearly identified as coming from the first screening of a given child, were used. All blood lead determinations were done by the same laboratory. The geometric means of the children's blood lead levels by age, race, and year of collection are presented in Table 11-6. The annual means were calculated from the four quar terly means which were estimated by the method of Hasselblad et al. (1980). The data obtained for New York are generally consistent with the nationwide results from the NHANES II study. For example, all racial/ethnic groups show an increase in geometric mean blood level with age for the first two years and a general decrease in the older age groups. These age-related patterns are seen in Figure 11-4, which shows the trends for all years (1970-1976) combined. Also, the childhood screening data described by Billick etal. (1979) show higher geometric mean blood lead values for blacks than for Hispanics or for whites. Table 11-6 presents these geometric means for the three racial/ethnic groups for seven years. * 11-20 TEH 0412018 DUP050452615 TABLE 11-5. WEIGHTED GEOMETRIC MEAN BLOOD LEAD LEVELS FROM NHANES II SURVEY BY DEGREE OF URBANIZATION OF PLACE OF RESIDENCE IN THE U.S. BY AGE AND RACE, UNITED STATES 1976-80 (micrograms/deciliter) Race and age All races All ages 6 months-5 years 6-17 years 18-74 years - men: women: Whites All ages 6 months-5 years 6-17 years 18-74 years - men: women: B1 acks All ages 6 months-5 years 6-17 years 18-74 years - men: women: Urban, SI million 14.0 16.8 13.1 16.9 12.2 (2,395) (544) (414) (677) ' (760) 14.0 15.6 12.6 16.9 12.4 (1,767) (358) (294) (531) (584) 14.4 20.8 14.6 17.4 11.8 (570) (172) (111) (132) (155) Degree of urbanization Urban, <1 mil 1ion 12.8 15.4 11.7 15.7 11.0 (3,869) (944) (638) (1,050) (1,237) 12.5 14.4 11.4 15.4 10.8 (3,144) (699) (510) (889) (1,046) 14.8 19.2 13.6 18.6 12.4 (612) (205) (113) (134) (160) Rural 11.9 13.0 10.7 15.1 9.8 (3,669) (884) (668) (1,069) (1,048) 11.8 12.7 10.5 14.8 9.8 (3,458) (819) (620) (1,011) (1,008) 14.4 16.5 13.0 18.3 11.3 (150) (42) (39) (38) (31) aNumber with lead determinations from blood specimens drawn by venipuncture. Source: Annest and Mahaffey, 1984; Annest et al., 1982. 11-21 TEH 0412019 DUP050452616 </> LU LO CD 2HH >- Z --I LU 0 LQCUJ LhOU-i L/3 C ^--* ZD O Q O'CO C <D LUU So sH- DC O LL- . O --3 O O <C _c_o1 U*--J t-- C LU 5O*i-DI Q OU< >_-<-Jc--aI 3: o -J UJ UJ ZLCUC OV)Os^. LU j*--z < 00 <zC v-<p-D ZLLr- S < O <- aO sUJa oa) Ll . CO t/) wo zh w J QC LU E UJHS 0 > UJ S- LUZU D1 --J O 3= O UJ |-- &- <OC CD >- -rU-- Ul u --ci a] vE-** ZD CD Q Z LU o <c < H-- Z /~>L/> c <n LU El u rOi---.i CzO: Oiaa/>Ji) Lf) N LO LO H H rCsM nCM ^CM CM r<>M HCsJ raH> rH H CO CO h* ^ CCMOCCM OCsJHCHM rCHMCrHOHN 00 cn CSJ 00 CXi rH rH fCOM CHM COM COM COM MrH rnH <c oE to ro m 05 <t O LO o r- CM CM CM ro in ro M- n cn co I ro lCosJ LCOsl cCoM rCoM iC--Mi rcHo crHo CCMOCMOCsJHCsHJ COM HMH^ hCM crHn nrH crHo rH irnH cd 0 CM 03 rH 00 ^ CM LD ^ CD LT) in CM N l o ro csi r>s in'C cn CsJ 1 LCOM CM CCOM C5fM rCHM rCHM 0rH0 CCMO CCMO HCsl iC--M1 OCM CrHT) LrHD cCMsCiMr-CiMoCoMcrHnrmH Hn o e 0 o'LM1On* oo c m V c m un IC*s"J* CCMD C5Mj* CsJ CCOM rCHM orHo 00(75 00005 00 0 CCMO CCOM rCHM CCMsl rCHsl ct-nH 0rH0 O UD O CO LO 00 CM LCsJOCMHCHSJ HCMOClMOrHLOrH c05 c*sioj* ro ro ro ^ ro oo oo Csj CCMO CCM5 ClOM LCs/Ji *CCM CHM oCM P- CM 00 U0 H CM CM CMt CCSMJ cCsMl CCvMJ OCM 0rH0 CO n CO CSJ H LO LD cCtM* CroM OCM OCM rCHM CrHO LrHO rLoO rH O'* CO O "5f s|- LO OCO CCMD LCDM LCOM iCfM) CCMM OCM l o l d co m r^- cn rH CM CM rCHM CCSMJ CCMM crHn 0rH0 o r^* r^- P^ co H rH LCsOl CCM CsMloCHM HCMLrOH rNH LO CsJ O E O ro O ID in >sr O 00 LD IT> 00 LH ^ c m r-* l d c o p- av c m Cr!oM CCMO C<MD LCDM LCDM LCOM CCMM OCM PCMOCsCJ SCsJl COMHCMricrHOrNH LCOM CCMM rCHSJ rCHSI rC-MH rH CrHO usz>: <c h- hoo-s4 JJUJh Z> -J ^o LZoU i13 i---HJ LCUD a: co LfO o CM rH CsJ O CM O') O 00 (75 LCfM> CdM" CCsMJ CCMJ CCsMJ CiHO rLHO oo cn csi co m o CoM crHn crHo CoM crHn lrHd lrHd rinHin^ON rCHM cCSsJi CdM rCHM CCMD orHn irnH O crHr> rrraH^H.iwrrC^HsJ.crCHOHrr^H'jC.5* <LrHO?iciLr^HOn* rOrOH^'* pcrHHn^crCrHSn^I rcrr^Honrr^c^HnhLcrNHTn) iLcr^HOn OrCrH^D rHrC^HDrcr^HspCri'HDr-rorC-H7''5.tCrrnH^nir<roT^HV Black White U zrcrQ<--o/>_ 11-22 DUP050452617 Figure 11 -4. Geometric mean biood lead values by race and age for younger children in the New York City screening program (1970-1976). Source: Adapted from Hasselblad et al. 1980. 11-23 TEH 0412021 DUP050452618 Using the method of Hasselblad et al. (1980), the estimated geometric standard deviations were I.41, 1.42, and 1.42 for blacks, Hispanics, and whites, respectively. II.3.3.3 Levels of Lead and Demographic Covariates Worldwide. An international study conduct ted under the auspices of the United Nations Environment Program and the World Health Organi zation provides the first analytically comparable blood lead data set available to infer the current similarities and differences in lead absorption from country to country (Friberg ar,-' Vahter, 1983). Extensive attention was paid to quality control issues, with the resulting^ blood lead determinations being very comparable from country to country. School teachers were chosen as study subjects since they would be unlikely to have occupational exposures to lead'j, and also because they would have similarities in socioeconomic characteristics. A detailed interview was administered to the subjects to obtain background data. Figure 11-5, derived from data in the paper, displays the variability from country to country. Unweighted geometric mean blood lead levels ranged from a low of 5.8 pg/dl in Japan to 22.3 pg/dl in Mexico. Teachers in China, Israel, Japan, Sweden, and the United States all i, had geometric mean blood leads below 8.0 pg/dl. In general, males showed higher blood lead levels than females; on the average, male teachers had blood lead levels 30 percent higher than females regardless of cigarette smoking status. In most cases cigarette smokers had 10 percent higher blood lead levels than nonsmokers. 11.3.4 Distributional Aspects of Population Blood Lead Levels ijSSS! The importance of the form of the distribution of blood lead levels was briefly discussed I11I1P11 in Section 11.2.2. The distribution form determines which measure of central tendency (arith llii metic mean, geometric mean, median) is most appropriate. It is even more important in esti mating percentiles in the upper tail of the distribution, an issue of much importance in esti mating percentages (or absolute numbers) of individuals in specific population groups likely to be experiencing various lead exposure levels. Distribution fitting requires large numbers of samples taken from a relatively homo geneous population. A homogeneous population is one in which the distribution of values remains constant when split into subpopulations. These subpopulations could be defined by m :f filip ifli demographic factors such as race, age, sex, income, degree of urbanization, and degree of exposure. Since these factors always have some effect, a relatively homogeneous population w will be defined as one with minimal effects from any factors that contribute to differences in blood lead levels. 11-24 TEH 0412022 -frl.- DUP050452619 ts oU. _-o >_U1J NDa.) nt k <0 o tc <s So a 2i Ol- 95joZ z<usi 2*5 y| z uiuj SO <s S3 u- QUJ O9 S? oy S< 5z3 2 24 22 20 -- 18 16 14 12 -- 10 s 3 <z r* < O-LCUDj oX oz CM CO << Q Zz -UJJ z <GC 22 2 <"a oo XLU s 3cUCcJL UzJ oE 5CO STUDY LOCATION WUi < s1 -I w a HLLI ton 3>3 Z 3 Figure 11 -5. Unweighted geometric mean blood lead level for male and female nonsmoking teachers (mg/dl] for several countries. Source: Derived from Friberg and Vahter (1983). 11-25 TEH 0412023 DUP050452620 Several authors have suggested that the distribution of blood lead levels for any re fa tively homogeneous population closely follows a lognormal distribution (Yankel et al., 19 Tepper and Levin, 1975; Azar et al., 1975). Lognormality has been noted for other mota's such as 90Sr, 144Ce, Pu, and Ti in various tissues of human populations (Cuddihy et al., 19/gSchubert et al., 1967). Yankel et al. (1977), Tepper and Levin (1975), and Angle and Mclntir. (1979) all found their blood lead data to be lognormally distributed. Further analysis by EP of the Houston study of Johnson et al. (1974), the study of Azar et al. (1975), and the N York children screening program reported by Billick et al. (1979) also demonstrated that lognormal distribution provided a good fit to the data. The only nationwide survey of blood lead levels in the U.S. population is the NHANES II survey (Annest et al., 1982). In order to obtain a relatively homogeneous subpopulation of lower environmental exposure, the analysis was restricted to whites not living in an SMSA. (Standard Metropolitan Statistical Area), with a family income greater than $6,000 per year, the poverty threshold for a family of four at the midpoint of study as determined by the U.S. Bureau of Census. This subpopulation was split into four subgroups based on age and sex. The summary statistics for these subgroups are in Table 11-7. TABLE 11-7. SUMMARY OF UNWEIGHTED BLOOD LEAD LEVELS IN WHITES NOT LIVING IN AN SMSA, WITH FAMILY INCOME GREATER THAN $6,000 Subgroup Age 1/2 to 6 Age 6 to 18 Age 18+, men Age 18+, women Sample size 752 573 922 927 Unweighted mean Arith. Geom. mean, mean, pg/dl pg/dl 13.7 11.3 15.7 10.7 12.9 10.6 14.7 10.0 Sample 99th Arith. median, percentile, std. dev., Geom. pg/dl pg/dl pg/dl std. dev. 13.0 10.0 15.0 10.0 32.0 24.0 35.8 23.0 5.03 4.34 5.95 4.14 1.43 1.46 1.44 1.46 Each of these four subpopulations were fitted to five different distributions; normal, lognormal, gamma, Weibull, and Wald (Inverse Gaussian) as shown in Table 11-8. Standard chi-square goodness-of-fit tests were computed after collapsing the tails to obtain an expected cell size of five. The goodness-of-fit test and likelihood functions indicate that the lognormal distribution provides a better fit than the normal, gamma, or Weibull. A histogram and the lognormal fit for each of the four subpopulations appear in Figure 11-6. 11-26 TEH 0412074 DUP050452621 TABLE 11-8. SUMMARY OF FITS TO NHANES II BLOOD LEAD LEVELS OF WHITES NOT LIVING IN AN SMSA, WITH INCOME GREATER THAN $6,000, FOR FIVE DIFFERENT TWO-PARAMETER DISTRIBUTIONS Normal. . Lognormal Gamma Weibull Wald Normal Lognormal Gamma Weibul1 Wald Normal Lognormal Gamma Weibul1 Wald Normal Lognormal Gamma Wei bull Wald Chi-square 75.52 14.75 17.51 66.77 15.71 Chi-square 39.58 3.22 4.88 24.48 2.77 Chi-square 156.98 12.22 34.26 132.91 14.42 Chi-square 66.31 7.70 11.28 56.70 10.26 Children <6 years D.F.* p-value 8 0.0000 10 0.1416 9 0.0413 8 0.0000 10 0.1083 Children 6 years ^17 D.F.* p-value 6 0.0000 8 0.9197 7 0.6745 6 ' 0.0004 8 0.9480 Men S18 years D.F.* p-value 10 0.0000 13 0.5098 12 0.0006 11 0.0000 13 0.3450 Women 18 years D.F.* 5 8 7 6 8 p-value 0.0000 0.4632 0.1267 0.0000 0.2469 loglikelihood -2280.32 -2210.50 -2216.51 -2271.57 -2211.83 loglikelihood -1653.92 -1607.70 -1609.33 -1641.35 -1609.64 loglike!ihood -2952.85 -2854.04 -2864.79 -2934.14 -2855.94 loglikelihood -2631.67 -2552.12 -2553.34 -2611.78 -2556.88 deviation** at 99th percentile 6.61 2.57 4.68 5.51 2.76 deviation** at 99th percentile 2.58 -1.50 -0.64 1.72 -1.30 deviation** at 99th percentile 6.24 1.51 4.00 4.88 1.72 deviation** at 99th percenti le 2.68 -1.18 0.90 1.73 -1.01 *D.F. = degrees of freedom. **observed 99th sample percentile minus predicted 99th percentile. 11-27 TEH 0412025 DUP050452622 FREQUENCY 0 7.5 15.5 23.5 31.5 BLOOD LEAD LEVELS, m/d\. FOR 6-MONTH TO 6-YEAR-OLD-CHILDREN 0 7.5 15.5 23.5 31.5 BLOOD LEAD LEVELS, ng/dl, FOR 6-TO 17-YEAR OLD CHILDREN FREQUENCY BLOOD LEAD LEVELS, ng/dl. FOR MEN ^ 18 YEARS OLD BLOOD LEAD LEVELS, /ig/dl. FOR WOMEN > 18 YEARS OLD Figure 11 -6. Histograms of blood lead levels with fitted lognormal curves for the NHANES II study. All subgroups are white. non-SMSA residents, with family incomes over $6000/year. Source: (EPA calculations from data supplied by National Center for Health Statistics.) 11-28 TEH 0412026 DUP050452623 The Wald distribution is quite similar to the lognormal distribution and appears to provide almost as good a fit. Table 11-8 also indicates that the lognormal distribution estimates the 99th percentile as well as any other distribution. Based on the examination of the NHANES II data, as well as the results of the several other studies discussed above, it appears that the lognormal distribution is the most appro priate for describing the distribution of blood lead levels in homogeneous populations with relatively constant exposure levels. The lognormal distribution appears to fit well across the entire range of the distribution, including the right tail. The lognormal distribution describes both the mean and the variation of the populations under study. It is obvious that even relatively homogeneous populations have considerable variation among individuals. The estimation of this variation is important for determination of the proportion of individuals above a given blood lead level. This variation is the result of both analytic variation and population variation. Analytic variation, which exists in any measurement of any kind, has an impact on the bias and precision of statistical estimates. For this reason, it is important to estimate the magnitude of variation. Analytic variation consists of both measurement variations (vari ation between measurements run at the.same time) and variation created by analyzing samples at different times (days). This kind of variation for blood lead determinations has been discus sed by Lucas (1981). The measurement variation alone does not follow a lognormal distribu tion, as was shown by Saltzman et al. (1983). Values for the variation within groups (or mean square error) are available from several studies discussed above, including the NHANES II Survey, the N.Y. Childhood Screening Study, the Tepper-Leven Seven City Study, and the Azar et al. study. Variation, including analytic variation, ranged from about 1.3 to 1.4 when expressed as a geometric standard deviation. This value depends on the uniformness of the populations and the magnitude of the analytic variation. The NHANES II study provides excellent data for the study of this variation, since it has excellent quality control and extensive information on demographic covariates. In order to minimize the effects of location, income, sex, and age, an analysis of variance procedure was used to estimate the variation for several age-race groups. The variables just mentioned were used as main effects, and the resulting mean square errors of the logarithms are shown in Table 11-9. The estimated geometric standard deviations have been adjusted for sex, age, in come, and place of residence. As a result, the values for geometric standard deviations tend to be smaller than the unadjusted values for specific subgroups as reported by Annest and Mahaffey (1984). 11-29 TEH 0412027 DUP050452624 TABLE 11-9. ESTIMATED MEAN SQUARE ERRORS RESULTING FROM ANALYSIS OF VARIANCE ON VARIOUS SUBPOPULATIONS OF THE NHANES II DATA USING UNWEIGHTED DATA White, White, SMSA, White, Black, Age Non-SMSA not central city central city central c; 1.5 to 6 6 to 18 18+, men 18+, women 0.0916 (1.35)* 0.0814 (1.33) 0.1155 (1-40) 0.1083 (1-39) 0.0839 (1.34) 0.0724 (1.31) - 0.0979 (1.37) 0.0977 (1.37) 0.1074 (1.39) 0. 0790 (1.33) 0.1127 (1.40) 0.0915 (1.35) 0.0978 (1.37) 0.0691 (1.30) 0.1125 (1-40) 0.0824 (1.33) Note: Mean square errors are based on the logarithm of the blood lead levels. ^Estimated geometric standard deviations are given in parentheses. 4 W The analytic variation was estimated specifically for this study by Annest et a!.; (1983b). The analytical variation was estimated as the sum of components estimated from the- high and low blind pool and from the replicate measurements in the study of Griffin et al/ (1975). The overall estimate of analytic variation for the NHANES II study was 0.02033 (estimated mean square error based on logarithms). lia Analytic variation causes a certain amount of misclassification when percent of individuals above or below a given threshold are made. This is estimates of the because the true gffBlHSHI, value of a person's blood lead could be below the threshold, but the contribution from analy tic variation may push the observed value over the threshold. The reverse is also possible. These two types of misclassifications do not necessarily offset each other. Annest et al. (1983b) estimated this misclassification rate for several subpopulations in the NHANES II data using a threshold value of 30 pg/dl. In general, the percent truly greater than this threshold was approximately 24 percent less than the prevalence of blood lead levels equal to or greater than 30 pg/dl, estimated from the weighted NHANES II data. This is less than the values predicted by Lucas (1981) which were based on some earlier studies. The studies reviewed here provide estimates of geometric standard deviations for observed blood lead distributions which consistently fall in the range of 1.3 to 1.4. The NHANE > I study, thought to provide the best available data set in terms of good quality control arid 11-30 TEH 0412028 . 'IJi DUP050452625 other features such as sample size, yields estimates of geometric standard deviations for various subgroups of young children (0.5 to 6 years old) in the range of 1.34 to 1.39 (uncor rected for analytic error). Variations in the site means of log(blood lead) were calculated after controlling for race, income, and degree of urbanization. The remaining standard devi ation of 0.183 for site means indicates substantial variation in baseline exposure after accounting for the major proxies for air lead. The geometric standard deviation attributable to the non-air lead exposure sources can be estimated by adjusting the NHANES II blood lead levels for the impact of gasoline lead by use of linear regression. Since gasoline lead during 1976-1980 accounted for 85 to 90 percent of air lead, the effect at gasoline lead = 0 was reduced by an additional 15 percent to account for all air lead. The resulting geometric standard deviation was 1.428. If this calculation is done only for children with blood lead < 40 pg/dl (who are more likely to be helped by an air lead standard) then the geometric stan dard deviation is 1.419. Thus, a geometric standard deviation for the NHANES II population of children without attribution of any source of lead exposure except gasoline lead and indus trial air lead emissions may be taken as approximately 1.42. 11.3.5 Time Trends in Blood Lead Levels Since 1970 In the past few years a number of reports have appeared that examined trends in blood lead levels during the 1970's. In several of these reports some environmental exposure esti mates are available. 11.3.5.1 Time Trends in NHANES II Study Data. Blood lead data from NHANES II (see section 11.3.3.1 for full discussion of methodology) show a significant downward trend over time for nationwide blood lead levels in the United States (Annest et al., 1983a). After accounting for the effects of race, sex, age, region of country, season, income, and degree of urbaniza tion, a statistically significant negative association with date of sampling was found. Using regression model-predicted blood lead levels, a 37 percent drop from 14.6 to 9.2 pg/dl from the beginning to the end of the study was found. Overall nationwide mean blood lead levels from these data presented in 28-day intervals from February, 1976 to February, 1980 are dis played in Figure 11-7. Similar decreases in average blood lead levels were noted for a number of subgroups which compose the total sample (see Figure 11-8), with the declines ranging from 31 to 42 percent for various subgroups. A variety of possible explanations for the nationwide decline in average blood lead levels were examined. Analysis of quality control samples indicated that laboratory drift was not the cause of the observed decline. Further statistical analyses ruled out the possibility that the decline was entirely due to season, income, geographic region, or urban-rural differ ences. Annest et al. (1983a) suggested that although strong correlation does not prove cause and effect, the most reasonable explanation for this trend appears to be reduction in the 11-31 TEH 0412029 DUP050452626 Vi? ^11 Ifc 11-32 TEH 0412029 001 DUP050452627 PERCENT REDUCTION IN BLOOD LEAD LEVELS RACE SEX AGE IN YEARS Figure 11 -8. Reduction in mean blood lead levels, according to race, sex, and age. Data on sex and age are for whites. Source: Annest et al. (1983a). 11-33 TEH 0412029 .002 DUP050452628 amount of lead used in gasoline production over the same time period (as discussed in more detail in Section 11.3.6.1). 11.3.5.2 Time Trends in the Childhood Lead Poisoning Screening Programs. Billick and col leagues have analyzed the results of blood lead screening programs conducted by the City of New York (Billick et al., 1979; Billick, 1982). Most details regarding this data set were al ready described, but Table 11-10 summarizes relevant methodologic information for these analy ses and for analyses done on a similar data base from Chicago, Illinois. The discussion of the New York data below is limited to an exposition of the time trend in blood lead levels from 1970 to 1977. Geometric mean blood lead levels decreased for all three racial groups and for almost all age groups in the period 1970-76 (Table 11-6). Table 11-11 shows that the downward trend covers the entire range of the frequency distribution of blood lead levels. The decline in blood lead levels showed seasonal variability, but the decrease in time was consistent for each season. The 1977 data were supplied to EPA by Dr. Billick. In addition to this time trend observed in New York City, Billick (1982) examined similar data from Chicago and Louisville. The Chicago data set was much more complete than the Louis ville one, and was much more methodologically consistent. Therefore, the Chicago data will mainly be discussed here. The lead poisoning screening program in Chicago may be the longest continuous program in the United States. Data used in this report covered the years 19671980. Because the data set was so large, only a 1 in 30 sample of laboratory records was coded for statistical analysis (similar to procedures used for New York described above). The blood lead data for Chicago contains samples that may be repeats, confirmatory analy ses, or even samples collected during treatment, as well as initial screening samples. This is a major difference from the New York City data, which had initial screening values only. Chicago blood lead levels were all obtained on venous samples and were analyzed by one labora tory, the Division of Laboratories, Chicago Department of Health. Lead determinations were done by atomic absorption. Racial composition was described in more detail than for New York, but analysis showed there was no difference among the non-blacks, so they were pooled in the final analysis. Table 11-10 displays important characteristics of the Chicago and New York screening pro grams, including the number of observations involved in these studies. From tables in the ap pendices of the report (Billick, 1982), specific data on geometric mean blood lead values, race, sex, and sampling data for both cities are available. Consistency of the data across cities is depicted in Figure 11-9. The long-term trends are quite consistent, although the seasonal peaks are somewhat less apparent. Although the data displayed are only for blacks aged 25 to 36 months, very similar data are available for whites and other groups covered by the study. 11-34 TEH 0412030 DUP050452629 BO i--i--n--i--i--m--i--r YEAR [Beginning Jan. 1) Figure 11-9. Time dependence of blood lead levels for blacks, aged 25-36 months, in New York City and Chicago. Source: Adapted from Billick (1982). 11-35 TEH 0412031 DUP050452630 TABLE 11-10. CHARACTERISTICS OF CHILDHOOD LEAD POISONING SCREENING DATA New York Chicago ' ... Time period 1970 - 1979 1967 - 1980 (QTR 2) Sampling technique Venous Venous Analytic technique AAS (Hasel method) AAS (Hasel method) Laboratory In house In house Screening status Avai1able/unknown Unavailable Race classification and total number of samples used in analysis* Unknown 69,658 White 5,922 Black 51,210 Hispanic 41,364 Other 4,398 TOTAL 172,552 Nonblack 6,459 Black 20,353 TOTAL 26,812 Raw data Decade grouped Ungrouped Gasoline data Tri-state (NY, NJ, CT) 1970 - 1979 SMSA 1974 - 1979 SMSA *New York data set only includes first screens while Chicago includes also confirmatory and repeat samples. ' TABLE 11-11. DISTRIBUTION OF BLOOD LEAD LEVELS FOR 13- TO 48MONTH-OLD BLACKS BY SEASON AND YEAR* FOR NEW YORK SCREENING DATA Year 1970 1971 1972 1973 1974 1975 1976 1977 January - March Percent <15pg/dl 15 - 34pg/dl >34pg/dl (insufficient sample size) 3.8 69.5 26.7 4.4 76.1 19.5 7.3 80.3 12.4 9.2 73.8 17.0 11.1** 77.5** 11.4** 21.1 74.1 4.8 28.4 66.8 4.8 July - September Percent <15pg/dl 15 - 34pg/dl 3.4 1.3 4.3 2.7 8.2 7.3** 11.9 19.9 54.7 56.0 72.2 62.4 65.4 81.3** 75.8 72.9 >34pg/dl 42.0 42.7 23.4 34.9 26.4 11.4** 12.3 7.2 * data provided by I.H. Billick (1982). ^Percentages estimated using- interpolation assuming a lognormal distribution. 11-36 TEH 0412032 DUP050452631 11.3.5.3 Newark. Gause et al. (1977) present data from Newark, New Jersey, that reinforce the findings of Billick and coworkers. Gause et al. studied the levels of blood lead among 5and 6-year-old children tested by the Newark Board of Education during the academic years 1973-74, 1974-75, and 1975-76. All Newark schools participated in all years. Participation rates were 34, 33, and 37 percent of the eligible children for the three years, respectively. Blood samples collected by fingerstick onto filter paper were analyzed for lead by atomic absorption spectrophotometry. The authors point out that fingerstick samples are more subject to contamination than venous samples; and that because erythrocyte protoporphyrin confirmation of blood lead values greater than 50 pg/dl was not done until 1974, data from earlier years may contain somewhat higher proportions of false positives than later years. Blood lead levels declined markedly during the 3-year study period. The percentage of children with blood lead levels less than 30 pg/dl went from 42 percent for blacks in 1973-74 to 71 percent in 1975-76; similarly, the percentages went from 56 percent to 85 percent in whites. The percentage of high risk children (>49 pg/dl) dropped from 9 to 1 percent in blacks and from 6 to 1 percent in whites during the study period. Unfortunately, no com panion analysis was presented regarding concurrent trends in environmental exposures. Foster et al. (1979), however, reported a study from Newark that examined the effective ness of the city's housing deleading program, using the current blood lead status of children who had earlier been identified as having confirmed elevated blood lead levels; according to the deleading program, these children's homes should have been treated to alleviate the lead problem. After intensive examination, the investigators found that 31 of the 100 children studied had lead-related symptoms at the time of Foster's study. Examination of the records of the program regarding the deleading activity indicated a serious lack of compliance with the program requirements. Given the results of Foster's study, it seems unlikely that the observed trend was primarily caused by the deleading program. 11.3.5.4 Boston. Rabinowitz and Needleman (1982) studied umbilical cord blood lead levels from 11,837 births between April, 1979 and April, 1981 in the Boston area. These represented 97 percent of the births occurring in a hospital serving a diverse population. Blood samples were analyzed for lead by anodic stripping voltammetry after stringent quality control proce dures were used. External quality control checks were done by participation in the Blood Lead Reference Program, conducted by the Centers for Disease Control. The average difference between the investigators' results and the reference lab was 1.4 pg/dl. The overall mean blood lead concentration was 6.56 + 3.19 pg/dl (standard deviation) with a range from 0.0 to 37.0 pg/dl. After regression of the individual values of blood lead against the date of birth, a significant downward trend in blood levels was observed (-'-0.89 pg/dl/yr), representing a decrease of 14 percent per year (Figure 11-10). Figure 11-10 also 11-37 TEH 0412033 DUP050452632 SMOOTHED AVERAGE BLOOD LEVEL, f<g/dl MONTH AND YEAR OF COLLECTION Figure 11-10. Modeled umbilical cord blood lead levels by date of sample collection for infants in Boston. Source: Rabinowitz and Needleman {1982). 11-38 TEH 041.7 D-*'1 DUP050452633 illustrates the complicating aspect of seasonal trends in evaluating underlying secular trends. The observed trend is similar to that noted in the NHANES II study described earlier. Rabinowitz and Needleman (1982) list the following as possible causes of the decline: (1) modification of the water supply to decrease the lead content; (2) reduction of the use of lead in gasoline; (3) reduction in contamination of food by solder; and 4) changes in prenatal practices, such as smoking or iron supplementation. Rabinowitz and Needleman (1983) then sought to evaluate statistically possible reasons for the observed two-year downward trend in umbilical cord blood lead levels. The authors used pairwise product moment correlations for the monthly cord lead levels (about 500 per month) and monthly amounts of gasoline lead in Massachusetts. A strong correlation was ob served: with the same month's data, the correlation coefficient was 0.716, which increased to a peak correlation coefficient of 0.758 when a 1-month lag time was used. The authors indi cate that they did not observe similar trends in maternal tobacco smoking, education level, and alcohol consumption. They did observe a positive (instead of negative) trend in tap water lead concentrations. They conclude that gasoline lead exposure changes were probably the cause of the observed trend in blood lead levels. From the ongoing surveillance of consecutive births, Rabinowitz et al. (1984) also iden tified a cohort of 249 infants who were enrolled in an ongoing cohort study after meeting certain eligibility standards. Indoor air was sampled for lead from the homes of children when each child was 6, 18, and 24 months of age. Tapwater was collected after a 4-liter flush, at 1 and 6 months of age. Seasonal biases in indoor/outdoor air lead ratios and the amounts of time spent indoors may have been confounding variables which may have distorted upward the underlying inhalation slope to the observed value near nine. For each month there was generally available a mean air lead from 12 homes, water lead from 23 homes, and blood leads for 500 births. The study period covered March, 1980 to April, 1981. The blood leads were then correlated with gasoline lead sales, indoor air, and tapwater. A linear (although somewhat scattered) trend was found between lead in indoor air and gasoline lead sales. Forty-eight percent of the variance in air lead could be accounted for by the gasoline lead sales. Air lead and blood lead levels were highly correlated. The best linear fit (r = 0.71) has a slope of 9 pg/dl/pg/m3 and an intercept of 4.9 pg/dl. No correla tion was observed between water and blood lead levels. Interestingly, a higher correlation was found between gasoline lead sales and blood lead levels than between air lead and blood lead. Karalekas et al. (1983) report additional data from the Boston metropolitan area. Re sults of the lead screening program indicate that the percentage of screened children with elevated blood lead levels declines over the period 1976-1981. Data on lead in water for this 11-39 TEH 0412035 DUP050452634 fJP period are also presented. Water lead levels began to decline after the decline in blood lead 'd# levels. This relationship in this data warrants further research. 11.3.5.5 Lead Studies in the United Kingdom. There has been a series of publications from various workers in England who have been examining the question of whether or not time trends in blood lead levels exist there as well as in the United States (Oxley, 1982; Elwood, 1983a,b; Quinn, 1983). These papers cover a variety of exposure situations and populations studied. All of them obtained findings analogous to those described above for the United States, in that there has been a general decline in blood lead levels over the decade of the 1970's; they differ, however, with regard to the magnitude of the decline, when the decline 'Wll began, and to what extent the decline may be attributable to a particular source of lead. Oxley (1982) reported an analysis of blood lead levels found in blood samples drawn as a part of preemployment medical examinations conducted by a major U.K.-based oil company during 1967-69 and 1978-80. Blood samples were collected by venipuncture and analyzed for lead by two different methods. A comparative laboratory study also reported by Oxley suggested that the data could be adjusted from one method to the other. Geometric mean blood lead levels de clined from 20.2 to 16.6 pg/dl. Elwood (1983a) reported a time trend analysis of blood lead levels observed in adult women studied over a 10-year period in eight surveys conducted in a variety of locations in Wales. These were analyzed and examined for trends in blood lead levels. All women included >#: # in this analysis came from surveys which were designed to generate representative samples of adult women in residential areas. A high response rate (90 percent or more) was obtained in each of the surveys. Venous blood samples were collected and analyzed for lead. A single laboratory performed all of the analyses with an external reference laboratory performing quality control checks in some of the surveys. Overall mean blood lead levels for the various surveys fell more than 30 percent over the period 1972-1982. Two of the surveys were con ducted in the same area. Between 1974 and 1982, the mean blood lead concentration fell 37 percent. Surveys from mining areas showed that women there had higher blood lead levels than in non-mining areas. Elwood acknowledges that laboratory drift may be present in the data and also that the surveys did not generate strictly comparable samples. Still, the observed decline was thought to be real. Ho statistical analysis of the data is presented to examine the possible reasons . -x. i for the observed decline, but a number of possible environmental reasons were discussed. Re duced gasoline lead exposures as a reason were dismissed on the basis that while the lead con centration in gasoline had indeed declined, the overall use of petrol in England had in creased, therefore balancing the reduction. However, no data regarding traffic patterns or gasoline usage in Wales were presented to verify this reasoning. A portion (amount unspeci- 11-40 TEH 0412036 ri /'Mi- rM^ DUP0504S2635 fied) of the reduction was attributed to a drop in dietary intake of lead due to the reduced use of canned foods. Elwood (1983b) also presents data from a more homogeneous setting. In 1969 a hematologic survey of a random sample of 4070 women was conducted in one town in Wales. Detailed studies were made of 121 of these women whose hemoglobin levels were below 10.5 g/100 ml. Samples of their whole blood were deep frozen, and follow-up samples were obtained for some of the same women in 1982. Follow-up and loss of original samples resulted in there being 26 women with an available blood lead at both times and who were still living at the same address. The mean fall in blood lead levels for these women was 23 percent, representing a fall of 3.5 pg/100 ml. Again Elwood does not attribute the decline to changes in gasoline lead or water supply, but instead suggests that it may be due to changes in dietary intake although noting there are no data on which to base a judgment. King (1983), in commenting on the results of Elwood (1983a), noted that the blood lead values before 1975 were probably falsely elevated due to matrix problems in the chemical ana lysis. This means the magnitude of the observed decline is probably less than that quoted by Elwood (1983b). King (1983) further examined the question of the time trend by controlling for region of Wales and reported that Elwood1s data showed a 50 percent increase in blood lead levels from 1981 to 1982, a most unlikely outcome. Pirkle and Annest (1984) have also criti cized the Elwood (1983a) paper and concluded that various factors make reliable interpreta tions of Elwood1s data extremely difficult. Quinn (1983) reports on the summarized findings of two large-scale survey effects in 1979 and 1981. Broad comparisons within the same authority showed an overall reduction approaching 10 percent (1 pg/100 ml). Quinn himself states, however, that these two survey efforts are not strictly comparable in that the first round focused on representative population groups while the second round focused on areas where lead may have presented a problem. No effort was made to attribute the decline in blood lead levels to a particular source. 11.3.5.6 Other Studies. Okubo et al. (1983) examined a total of 1933 children from 5 to 18 years of age for blood lead using the Hessel method over the period 1975 to 1980 in an urban area of Tokyo and in a nearby suburban area. The analysis of all blood lead was done by the same laboratory. Over the time period of the study an apparent decrease in blood lead is shown. A part of the difference in blood lead between urban and suburban groups is related to the difference in average lead concentrations between the two areas. The difference of blood lead between urban and suburban becomes greater when the comparison of blood lead between the two areas is executed only among children who have lived in the same areas from their birth. In an international study discussed in detail earlier, Friberg and Vahter (1983) compared data on blood lead levels obtained in 1967 with data for 1981 (see Table 11-12). For areas of 11-41 TEH 0412037 DUP050452636 TABLE 11-12. COMPARISON OF MEDIAN BLOOD LEAD LEVELS (pg/dl) IN SEVERAL COUNTRIES FROM STUDIES OF GOLDWATER AND HOOVER (1967) AND FRIBERG AND VAHTER (1983) Country Japan Israel United States Yugoslavia Median blood lead 1967 21.0 15.0 18.0 15.0 Median blood lead 1981 6.0 8.2 7.5 9.2 % change from 1967 7i 45 58 39 i :'j the world where there were data collected by Goldwater and Hoover (1967) as well as the UN/WHO study, there has been a substantial reduction in reported blood lead levels. A cautionary note must be made, however, that the analytic and human sampling procedures are not the same in the two studies. Therefore these data should be thought of as providing further but limited evidence supporting a recent downward trend in blood lead levels worldwide. 11.3.6 Gasoline Lead as an Important Determinant of Trends in Blood Lead Levels As noted in the preceding section, explanations have been sought for declining trends in blood lead levels observed among population groups in the United States and certain other countries since the early 1970s. Also noted was evidence presented by some investigators which strongly suggests that gasoline lead usage is a major determinant of the reported down ward trends in blood lead levels. The present section examines additional, extensive evidence which points towards gasoline lead being an important determinant of changes in blood lead levels associated with exposures to airborne lead of populations in the United States and elsewhere. 11.3.6.1 NHANES II Study Data. Blood lead data from the second National Health and Nutrition Examination survey (NHANES II) were described earlier in Sections 11.3.3.1 and 11.3.5.1. One striking feature of the NHANES II data was a dramatic decline in nationwide average blood lead levels in the United States during the period (1976 to 1980) of the survey. In evaluating possible reasons for the observed decrease in the NHANES II blood lead values, Annest et al. (1983a) found highly significant associations between the declining blood lead concentrations for the overall U.S. population and decreasing amounts of lead used in gasoline in the U.S. during the same time period (see Figure 11-11). The associations persisted after adjusting for race, age, sex, region of the country, season, income, and degree of urbanization (see Table 11-13). Analogous strong associations (r = 0.95; p < 0.001) were also found for blood lead levels for white children aged 6 months to 5 years in the NHANES II sample and gasoline lead usage (Annest et al., 1983a). 11-42 1 I II -'III? ,$jf 'ili*' I * m TEH 0412038 DUP050452637 <N00 su<nE(U -aOIH3d H1N0IAI'9 d3d Q3Sn QV31 IViOi 11-43 110 Figure 11-11. Parallel decreases in blood lead values observed in the NHANESII study and amounts of lead used in gasoline during 1976-1980. CO )0 N9) 9) 09 cn Ui NNO) cc < > DUP050452638 11-13. PEARSON CORRELATION COEFFICIENTS BETWEEN THE AVERAGE BLOOD LEAD LEVELS FOR SIX-MONTH PERIODS AND THE TOTAL LEAD USED IN GASOLINE PRODUCTION PER SIX MONTHS, ACCORDING TO RACE, SEX, AND AGEa Overall (all races) All black6 All whites By sex: Male Female By age: 0.5-5 yr 6-17 yr 18-74 yr Coefficients for 6-month periods*"* January-June April-September . and July-December and 0ctober-Marcha 0.920 0.938 0.678 0.717 0.929 0.955 0.944 0.960 0.912 0.943 0.955 0.969 0.908 0.970 0.920 0.924 Averages 0.929 0.698 0.942 0.952 0.928 0.962 0.939 0.922 "The lead values used to compute the averages were preadjusted by regression analysis to account for the effects of income, degree of urbanization, region of the country, season, and, when appropriate, race, sex, and age. bA11 correlation coefficients were statistically significant (p < 0.001) except those for blacks (p < 0.05). Averages were based on six-month periods, except for the first and last time periods , which covered only February 1976 through June 1976 and January 1980 through February 1980, respectively. j "Averages were based on six-month periods, except for the last time period, which covered only October 1979 through February 1980. eBlacks could not be analyzed according to sex and age subgroups because of inadequate sample sizes. mm: mm Wmti lit t m 4; lap Ijfc 'Si- Questions have been raised by some commentors regarding whether or not (1) the NHANES II survey design was adequate to allow for credible definition of time trends for nationwide average blood lead concentrations, (2) the reported significant associations between NHANES II blood lead data and U.S. gasoline usage are credible and reflect a causal relationship, and (3) the entire decline in blood lead values is attributable to decreased gasoline lead usage versus changes in other sources of lead exposure. These issues and alternative analyses con cerning the NHANES II blood lead/gasoline lead relationships were evaluated by an expert panel (the NHANES II Time-Trend Analysis Review Group) convened by EPA. 11-44 TEH 0412040 DUP050452639 The NHANES II Time-Trend Analysis Review Group (1983) found the following: (1) strong evidence that there was a substantial decline in the average level of blood lead in the U.S. population during the NHANES II survey period; (2) after adjustment for relevant demographic covariables, the magnitude of the change can be estimated for the total U.S. population and for some major subgroups, provided careful attention is given to underlying model assumptions. The Review Group also found a strong correlation between gasoline-lead usage and blood-lead levels, and noted that in the absence of scientifically plausible alternative explanations, the hypothesis that gasoline lead is an important causal factor for blood-lead levels must receive serious consideration. Nevertheless, despite the strong association between the decline in gasoline-lead usage and the decline in blood-lead levels, the survey results and statistical analyses do not confirm the causal hypothesis. Rather, this finding is based on the qualitatively consistent results of extensive analyses done in different but complementary ways. Further support for strong, likely causative, relationships between gasoline lead usage and blood lead levels in the U.S. is provided by analyses carried out by Schwartz et al. (1984). Those analyses not only evaluated NHANES II data, but, also, additional blood lead data such as blood lead values from U.S. childhood lead-screening programs. Results obtained were quite similar to those of Annest et al. (1983b), even after controlling for possible alternative contributors to the blood lead decline, e.g., deleading of lead-painted housing units or decreased food lead intake. Large numbers (thousands) of children were also esti mated by the analysis to have blood lead levels in excess of 30 pg/dl due in part to exposures to lead emitted as a consequence of leaded gasoline usage in the United States. Still further evidence for causative relationships between gasoline lead usage and changes in human blood lead levels is provided by isotope studies of the type described next. 11.3.6.2 Isotope Studies. Two field investigations have attempted to derive estimates of the amount of lead from gasoline that is absorbed by the blood of individuals. Both of these in vestigations used the fact that non-radioactive isotopes of lead are stable. The varying pro portions of the isotopes present in blood and environmental samples can indicate the source of the lead. The Isotopic Lead Experiment (ILE) is an extensive study that attempted to use dif fering proportions of the isotopes in geologic formations to infer the proportion of lead in gasoline that is absorbed by the body. The other study used existing natural shifts in iso topic proportions in an attempt to do the same thing. 11.3.6.2.1 Italy. The ILE is a large-scale community study in which the geologic source of lead for antiknock compounds in gasoline was manipulated to change the isotopic composition of the atmosphere (Garibaldi et al., 1975; Facchetti, 1979; Facchetti, 1985). Preliminary inves tigation of the environment of Northwest Italy, and the blood of residents there, indicated 11-45 TEH 0412041 DUP050452640 that the ratio of 206Pb/207Pb In blood was a constant, about 1.16, and the ratio in gasoline was about 1.18. This preliminary study also suggested that it would be possible to substitute for the currently used geologic sources of lead for antiknock production a geologically dis tinct source of lead from Australia that had an isotopic 206Pb/207Pb ratio of 1.04. It was hypothesized that the resulting change in blood lead 206Pb/207Pb ratios (from 1.16 to a lower value) would indicate the proportion of lead in the blood of exposed human populations attri butable to lead in the air contributed by gasoline combustion in the study area. Baseline sampling of both the environment and residents in the geographic areas of the study was conducted in 1974-1975. The sampling included air, soil, plants, lead stock, gaso line supplies, etc. Human blood sampling was done on a variety of populations within the area. Both environmental and human samples were analyzed for lead concentrations as well as isotopic 206Pb/207Pb composition. In August, 1975, the first switched (Australian lead-labeled) gasoline was introduced; although it was originally intended to get a 100 percent substitution, practical and logisti cal problems resulted in only a 50 percent substitution being achieved by this time. By May, 1977, these problems were worked out and the substitution was practically complete. The sub stitution was maintained until the end of 1979, when a partial return to use of the original sources of lead began. Therefore, the project had four phases: phase zero - background; phase one - partial switch; phase two - total switch; and phase three - switchback. Airborne lead measurements were collected in a number of sites to generate estimates of the lead exposure that was experienced by residents of the area. Turin, the major city of the region, was found to have a much greater level of atmospheric lead than the surrounding coun tryside. There also appeared to be fairly wide seasonal fluctuations. The isotopic lead ratios obtained in the samples analyzed are displayed in Figure 11-12. It can easily be seen that the airborne particulate lead rapidly changed its isotope ratio in line with expectations. Changes in the isotope ratios of the blood samples appeared to lag somewhat behind. Background blood lead ratios for adults were 1.1591 0.0043 in rural areas and 1.1627 0.0022 in Turin in 1975. For Turin adults, a mean isotopic ratio of 1.1325 was obtained in 1979, clearly less than background. Isotopic ratios for Turin schoolchildren, obtained starting in 1977, tended to be somewhat lower than the ratios for Turin adults. Preliminary analysis of the isotope ratios in air lead allowed for the estimation of the fractional contribution of gasoline in the city of Turin, in small communities within 25 km of Turin, and in small communities beyond 25 km (Facchetti and Geiss, 1982). At the time of maximal use of Australian lead isotope in gasoline (1978-1979), about 87.3 percent of the air 11-46 TEH 0412042 DUP050452641 TIME, months onva `k w /'w 1.0411----- !--I------------ 1----------- *----------- 1----------- 1----------- 1-----------1-----------1----------- 1-- 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 YEAR Figure 11-12. Change in 20BPb/207Pb ratjos jn gasoline, blood, and airborne particulate from 1974 to 1984. Source: Facchetti (1985). 11-47 TEH 0412043 DUP050452642 lead in Turin and 58.7 percent of the air lead in the countryside was attributable to gaso line. The determination of lead isotope ratios was essentially independent of air lead con-? centrations. During that time, air lead averaged about 2.0 pg/m3 in Turin (from 0.88-4.54 pg/m3 depending on location of the sampling site), about 0.56 pg/m3 in the nearby communities m (0.30-0.67 pg/m3) and about 0.30 pg/m3 in more distant (> 25 km) locations. It is important m to note that the contribution calculations are for local lead in gasoline, not all lead from' gasoline. Large movements of air masses brought in air lead from other regions, especially for the suburban and urban areas. In the absence of nearby lead industrial sources, this air lead was at least substantially composed of non-Australian gasoline lead and would therefore lead to an underestimate of the total contribution of gasoline lead to blood lead. Blood lead concentrations and isotope ratios for 63 adult subjects were determined on two or more occasions during phases 0-2 of the study. Their blood lead isotope ratios decreased over time and the fraction of lead in their blood attributable to the Australian lead-labeled gasoline could be estimated independently of blood lead concentration (see Appendix C for estimation method). The mean fraction of blood lead attributable to the Australian leadlabeled gasoline ranged from 21.4 + 10.4 percent in Turin to 11.4 7.3 percent in the nearby (< 25 km) countryside and 10.1 9.3 percent in the remote countryside. These likely represent minimal estimates of fractions of blood lead derived from gasoline due to the following ass- is*reasons: (1) use of some non-Australian lead-labeled gasoline brought into the study area sit from outside; (2) probable insufficient time to have achieved steady-state blood lead isotope ratios by the time of the switchback; and (3) probable insufficient time to fully reflect de layed movement of the Australian lead from gasoline via environmental pathways in addition to air. These results can be combined with the actual blood lead concentrations to estimate the HP fraction of gasoline uptake attributable or not attributable to direct inhalation. The results are shown in- Table 11-14 based upon the concept outlined in Facchetti and Geiss (1982). From Section 11.4.1, we conclude that an assumed value of p=1.6 is plausible for predicting the amount of lead absorbed into blood at air lead concentrations less than 2.0 pg/m3. The predicted values for lead from gasoline in air (in the ILE) range from 0.28 to 2.79 pg/dl in blood due to direct inhalation. The total contribution to blood lead from gasoline is much larger, from 3.21 to 4.66 pg/dl, suggesting that the non-inhalation con tribution of gasoline increases from 1.88 pg/dl in Turin to 2.33 pg/dl in the near region and 2.93 pg/dl in the more distant region. The non-inhalation sources include ingestion of dust and soil lead, and lead in food and drinking water. Efforts are being made to quantify the magnitude of these sources. The average direct inhalation of lead in the air from gasoline 11-48 TEH 0412044 DUP050452643 TABLE 11-14. ESTIMATED CONTRIBUTION OF LEADED GASOLINE TO BLOOD LEAD BY INHALATION AND NON-INHALATION PATHWAYS Location Air Pb fraction from gasor , line'3' Turin <25 km >25 km 0.873 0.587 0.587 Mean air Pb (b) cone., ' pg/m3 Blood Pb fraction from SaS07 line'1 ' 2.0 0.56 0.30 0.214 0.114 0.101 Mean blood Pb (d) cone.,v ' pg/dl Blood Pb Non- Pb from inhaled from gaso- Pb from gaso-, line/ , ' !ine. (f) in air,' ' ?lin-seo, (g)' pg/di pg/dl pg/dl Estimated fraction gas-Pb 21.77 25! 06 31.78 4.66 2.86 3.21 2.79 0.53 0.28 1.88 2.33 2.93 0.60 0.19 0.09 'Fraction of air lead in Phase 2 attributable to lead in gasoline. ^Mean air lead in Phase 2, pg/m3. (c}'Mean fraction of blood lead in Phase 2 attributable to lead in gasoline. ^Mean blood lead concentration in Phase 2, pg/dl. 'Estimated blood lead from gasoline = (c) x (d) ' Estimated blood lead from gasoline inhalation = p x (a) x (b), p = 1.6. ('aa)'Estimated blood lead from gasoline, non-inhalation = (f)-(e) v 'Fraction of blood lead uptake from gasoline attributable to direct inhalation = (f)/(e) Data: Facchetti and Geiss (1982); Facchetti (1985). is 9 to 19 percent of the total intake attributable to gasoline in the countryside and an estimated 60 percent in the city of Turin. Note that in this sample, the blood lead con centrations were lowest in the city and highest in the more remote areas. This is not obviously attributable to sex because the city sample was all male. Facchetti (1985) notes that factors unaccounted for are presumably acting on the population of the ILE test area. The lead concentration in tapwater in Turin is approximately 4 pg/1, while it ranges in the country from 12 to 20 pg/1. Also, lead concentrations in Piedmont wines averaged 155 67 pg/1. Daily wine consumption for rural drinkers ranges from 0.5 to 1 liter per day. Thus the importance of wine consumption becomes evident. Other differences between city and county may play a role. A more detailed statistical investigation is needed. Spengler et al. (1984) have developed a modeling approach to try to explain these results. Their hypothesized model suggeststhat in-vehicle lead exposure is important and may explain part of the apparent anomaly of the blood lead levels in this study. That is, Spengler et al. (1984) hypothesized that there is a large component of personal lead exposure associated with gasoline use that is not captured by stationary ambient air lead monitors: 11-49 TEH 0412045 DUP050452644 personal exposure while riding in and working around motor vehicles using leaded gas. Mare' work on this problem is needed, particularly conduction of near- and in-vehicle studies Lead uptake may also be associated with occupation, sex, age, smoking, and drinking habits. The linear exposure model used in Section 11.4 was also used here to estimate the fraction of labeled blood lead from gasoline attributable to exposure via direct inhalation and other pathways. EPA used the data in Facchetti and Geiss (1982) for the 35 subjects whom repeated measurements allowed estimation of the change in isotope ratios in the bio Their blood lead concentrations in Phase 2 were also determined, allowing for estimation of the total gasoline contribution to blood lead. Possible covariates included sex, age, cigarette smoking, drinking alcoholic beverages, occupation, residence location, and work k location. In order to obtain some crude comparisons with the inhalation exposure studies of Section 11.4.1, EPA analyses assigned the air lead values listed in Table 11-15 to various locations. Lower values for air lead in Turin would increase the estimated blood lead inhala tion slope above the estimated value of 1.70. Since the fraction of time subjects were exposed to workplace air was not known, this was also estimated from the data as about 41" percent (i.e., 9.8 hours/ day). The results are shown in Figure 11-13 and Table 11-16. Of all the available variables, only location, sex, and inhaled air lead from gasoline proved statistically significant in predicting blood lead attributable to gasoline. The model predictability is fairly good, with an R2 value of 0.654. It should be noted that a certain amount of confounding of variables was unavoidable in this small set of preliminary data, e.g., no female subjects in Turin or in occupations of traffic wardens, etc. There was a systematic increase in estimated non-inhalation contributions from gasoline use for remote areas, but the cause is unknown. The following interpretation for these results may be offered: The air lead measurements used here represent community or ambient exposures. In addition to the ambient air lead, there may have also been systematic differences in personal exposure. Nevertheless, the estimated non-inhalation contribution of gasoline to blood lead in the ILE study is significant (i.e., 1.8-3.4 pg/dl). TABLE 11-15. ASSUMED AIR LEAD CONCENTRATIONS FOR MODEL Residence or workplace code Location Air lead concentration 1-4 outside Turin (a) Turin residential 1. 0 pg/m3^ Vfi Turin central 2.5 pg/m,,33(C> (a) Use value for community air lead, 0.16 - 0.67 pg/m3. (b) Intermediate between average traffic areas (1.71 pg/m3) and low traffic areas (0.88 pg/m3) in Turin. (c) Intermediate between average traffic areas (1.71 pg/m3) and heavy traffic areas (4.54 pg/m3) in Turin. 11-50 'll!p # 44^1 . * TEH 0412046 DUP050452645 3 '3> 3. ui 2 Ow < o o (<0 3m < o < oo 2 < 2 AVERAGE AIR LEAD CONCENTRATION ATTRIBUTABLE TO GASOLINE ngIm1 Figure 11-13. Estimated direct and indirect contributions of lead in gasoline to blood lead in Italian men, based on EPA analysis of ILE data (Table 11-16). TABLE 11-16. REGRESSION MODEL FOR BLOOD LEAD ATTRIBUTABLE TO GASOLINE Variable Air lead from gas Location Turin <25 km >25 km Sex Coefficient standard error 1.70 1.04 pg/dl per pg/m3 1.82 2.01 pg/dl 2.56 0.59 pg/dl 3.42 t 0.85 pg/dl -2.03 0.48 pg/dl for women TEH 0412047 DUP050452646 The preliminary linear analysis of the overall ILE data set (2161 observations) fouklV,- that total blood lead levels depended on other covariates for which there were plausible ``i -< mechanisms of lead exposure, including location, smoking, alcoholic beverages, age, and occu-v-v pation (Facchetti and Geiss, 1982). The difference between total blood lead uptake and blood1* , lead uptake attributable to gasoline lead has yet to be analyzed in detail, but these analyses *.. suggest that certain i.mportant di.fferences may be found. Some reservations have been expr-_ ! -I sed about the HE study, both by the authors themselves and by Elwood (1983c). These include unusual conditions of meteorology and traffic in Turin, and demographic characteristics of the . 35 subjects measured repeatedly that may restrict the generalizability of the stud_ Facchetti (1985) reports additional analysis which increases the number of blood leads from 35 to 63, alleviating this concern to some extent since the new results confirm the old. How ever, it is clear that changes in air lead attributable to gasoline were tracked by changes in blood lead in Turin residents. The airborne particulate lead isotope ratio quickly achieved new equilibrium levels as the gasoline isotope ratio was changed, and maintained that lev. during the Zh years of Phase 2. The blood lead isotope ratios fell slowly during the change over period, and rose again afterwards as shown in Figure 11-12. Equilibrium was not clearl'. achieved for blood lead isotope ratios, possibly due to large endogenous pools of old lean stored in the skeleton and slowly mobilized over time. Even with such reservations, this study provides a useful basis for relating blood lead and air lead derived from gasoline com bustion. Colombo and Fantechi (1983) have presented an analysis of the ILE study using a dynamic model. The results of their analysis suggest that an appropriate estimate of the con tribution of locally consumed gasoline lead to blood lead is 26, 17, and 14 percent for the subject groups of Turin, and near and far countryside, respectively. These values are similar to but somewhat larger than those presented by Facchetti and Geiss (1982) and Facchetti m (1985). 11.3.6.2.2 United States. Manton (1977) conducted a long-term study of 10 subjects whose blood lead isotopic composition was monitored for comparison with the isotopic composition of the air they breathed. Manton had observed that the ratio of 206Pb/204Pb the al-r varied with seasons in Dallas, Texas; therefore, the ratio of those isotopes should vary in the blood. By comparing the observed variability, estimates could then be made of the amount of lead in air that is absorbed by the blood. Manton took monthly blood samples from all 10 subjects from April, 1974 until June, 1975. JkK m The blood samples were analyzed for both total lead and isotopic composition. The recruited volunteers included a mix of males and females, and persons highly and moderately exposed to M: lead. However, none of the subjects was thought to be exposed to more than 1 pg/m3 of lead in Jit air. Lead in air samples was collected by hi-vol samplers primarily from one site in Dallas. That site, however, had been shown earlier to vary in isotopic composition paralleling another 11-52 TEH 0412048 DUP050452647 site some 16 miles away. All analyses were carried out under clean conditions with care and caution being exercised to avoid lead contamination. The isotope ratio of 206Pb/204Pb increased linearly with time from about 18.45 to 19.35, approximately a 6 percent increase. At least one of the two isotopic lead ratios increased linearly in 4 of the 10 subjects. In one other, they increased, but erratically. In the remainder of the subjects, the isotopic ratios followed smooth curves showing inflection points. The curves obtained for the two subjects born in South Africa were 6 months out of phase with the curves of the native-born Americans. The fact that the isotope ratios in 9 of the 10 subjects varied regularly was thought to indicate that the non-airborne sources of lead varied in isotopic composition very slowly. The blood lead levels exhibited a- variety of patterns, although none of the subjects showed more than a 25 percent change from initial levels. This suggests a reasonably steadystate external environment. Nanton carried his analyses further to estimate the percentage of lead in blood that comes from air. He estimated that the percentage varied from 7 to 41 percent, assuming that dietary sources of lead had a constant isotopic ratio while air varied. He calculated the percent contribution according to the following equation. --9-- 100+q = -ii- , a where (11-1) b = rate of change of an isotope ratio in blood, a = rate of change of the same ratio in the air, and q = constant defined as the number of atoms of the isotope in the denominator of the airborne lead ratio mixed with 100 atoms of the same isotope of lead from non-airborne sources. The results are shown in Table 11-17. Slopes were obtained by least squares regression. Percentages of airborne lead in blood varied between 7+3 and 41 3. Stephens (1981) extended the analysis of data in Manton's study (Table 11-18). He used the observed air lead concentrations based on actual 24-hour air lead exposures in three adults. He assumed values for breathing rate, lung deposition, and absorption into blood to estimate the blood lead uptake attributable to 204Pb by the direct inhalation pathway. Sub jects 5, 6, and 9 absorbed far more air lead in fact than was calculated using the values in Table 11-17. The total air lead contribution for those subjects was 8.4, 4.4, and 7.9 times, respectively, larger than the direct inhalation. These estimates are sensitive to the assumed parameter values. 11-53 TEH 0412049 DUP050452648 TABLE 11-17. RATE OF CHANGE OF 206Pb/204Pb AND 206Pb/207Pb IN AIR AND BLOOD, AND PERCENTAGE OF AIRBORNE LEAD IN BLOOD OF SUBJECTS 1, 3, 5, 6, AND 9 Subject (Air) 1 3 5 6 9* Rate of change per day 206pb/2(Mpb 206pb/'207pb X 10' X 10" 17.60 + 0.77 5.52 0.55 oo 6.53 0.49 3.25 9.97 + 0.42 0.70 0.30 , . 3.13 + 0.34 4.10 0.25 2.01 From 206pb/207pb ... 31.4 + 3.4 .. * 37.1 2.8 18.5 From 206pb/207pb 73 31.4 3.7 41.1 3.0 20.0 Note: Errors quoted are one standard deviation *From slope of tangent drawn to the minima of subject's blood curves. Errors cannot realistically be assigned. H iilj! lit If f* TABLE 11-18. CALCULATEDi BLOOD LEAD UPTAKE FROM AIR LEAD USING MANTON ISOTOPE STUDY Sub Concen ject tration Expo sure* Deposi tion* 5 0.22 pg/m3 15 m3/day 37% 6 1.09 pg/m3 15 m3/day 37% 9 0.45 pg/m3 15 m3/day 37% Absorp tion* 50% 50% 50% Blood uptake from air Calcu lated inhala- tion Observed 0.61 pg/d 3.0 pg/d 1.2 pg/d 5.1 pg/d 13.2 pg/d 9.9 pg/d Fraction of lead uptake from gasoline by direct inhalation 0.120 0.229 0.126 ^assumed rather than measured exposure, deposition and absorption. Source: Stephens, 1981, based on Manton, 1977; Table III. In Manton (1985) the earlier isotope studies were greatly extended and the results were reinterpreted. The recent study emphasized time changes in blood lead and in 206Pb/207pb isotope ratios in three subjects in Dallas, Texas, from 1974 to 1983. Two of the subjects .described earlier (Manton, 1977) were included here, a husband (subject 8) and his first wife (subject 9). The more recent subject was the husband's second wife. The husband 11-54 TEH 0412050 j DUP050452649 had grown up in South Africa and in England; thus he had deep bone pools of lead that reflec ted the Australian lead isotope ratio. As noted earlier, the husband's seasonal minima in isotope ratio appeared to be the opposite of the two women with whom he shared a very similar pattern of environmental exposures. Manton (1985) now attributes this to a large efflux of lead from the skeletal pool. The husband's estimated dietary intake was 55 pg/day. If 10 percent of this is absorbed into blood (5.5 pg/day), mean residence time of 40 days and volume of distribution of 75 dl imply a dietary contribution to blood lead of about 3 pg/dl, much less than his observed average of 17 pg/dl. There was little indication of large changes in diet lead isotope ratio during this period, hence the changes in blood lead isotope ratio may be attributed to changes in the air lead particulate isotope ratio, and to changes in isotope ratio for endogenous sources. Manton attributes the large changes in isotope ratio in the husband to changes in isotope ratio from lead resorbed from bone into the blood. His estimate is that approximately 70 percent of the daily blood input is due to the endogenous skeletal pool of this subject. The subject's wife also exhibited a variety of fluctuations in blood lead level and isotope ratio due to childbirth and to short-term fluctuations in dietary lead. The apparent effect of childbirth was to increase resorption of both skeletal calcium and skeletal lead into blood. The contribution of airborne lead to blood lead isotope ratios thus did not require correction for long-term secular changes in dietary lead isotope ratios. On this basis the direct inhalation contribution was again calculated as about 20 to 60 percent of the total uptake of atmospheric lead using p = 4.1. Manton's calculations are shown in Table 11-19. The cumulative effects of long-term lead absorption on the mobilizable lead pool in the skeleton have been ignored, but are apparently not negligible. In summary, the direct inhalation pathway accounts for only a fraction of the total air lead contribution to blood, the direct inhalation contribution being on the order of 12-23 percent of the total uptake of lead attributable to gasoline, using Stephen's assumptions, and 20-60 percent based on Manton's analysis. This is consistent with estimates from the ILE study, taking into account the much higher air lead levels in Turin. 11.3.6.3 Studies of Childhood Blood Lead Poisoning Control Programs. Billick et al. (1979) presented several possible explanations for the observed decline (described in Section 11.3.5.2) in blood lead levels in New York City children as well as evidence supporting and refuting each. The suggested contributing factors include the active educational and screen ing program of the New York City Bureau of Lead Poisoning Control, the decrease in the amount of lead-based paint exposure as a result of rehabilitation or removal of older housing, and changes in environmental lead exposure. 11-55 TEH 0412051 DUP050452650 CM fN e +v, o o.o uC Cv Da.l XI a a. o </) -cCi-L c *>ma, s o e o CO U v r~ t. o ja = O JZ +rJ- .U u to p a. O o cc l w> - cr? a + * 3U i-- ( (A Oe w3 t*-O- Vufl o~io.- a> e o *-- 'n U5s . CO JS +U > T-P3 +> *-S O CPXJ 3*i- - (/) r-j O XI C cn M3 CO O 11-56 .Ota-Ura*3>*+cJ >v o o *-- 'O Ol '-1 V7 O fUC U *4r-Js- o U- o u DUP050452651 IS 1 Information was only available to partially evaluate the last source of lead exposure and particularly only for ambient air lead levels. Air lead measurements were available during the entire study period for only one station which was located on the west side of Manhattan at a height of 56 m. Superposition of the air lead and blood lead levels indicated a simi larity in seasonal cycle and long-term decline. The authors cautioned against overinterpre tation because of the necessary assumptions in this analysis and because one air monitoring site was used to be representative of the air lead exposure of New York City residents. With this in mind, the investigators fitted a multiple regression model to the data to try to define the important determinants of blood lead levels for this population. Age, ethnic group, and air lead level were all found to be significant determinants of blood lead levels. The authors further point out the possibility of a change in the nature of the population being screened before and after 1973. They reran this regression analysis separately for years both before and after 1973. The same results were still obtained, although the exact coefficients varied. Billick et al. (1980) extended their previous analysis of the data from the single moni toring site mentioned above. The investigators examined the possible relationship between blood lead level and the amount of lead in gasoline used in the area. Figures 11-14 and 11-15 present illustrative trend lines in blood leads for blacks and Hispanics versus air lead and gasoline lead, respectively. Gasoline lead was estimated by multiplying the sales of gasoline by the estimated concentrations of lead in gasoline. Semiannual concentrations of lead for the Mid-Atlantic Coast were interpolated to get quarterly values. Sales were computed using figures for New York, New York plus New Jersey, New York plus Connecticut, or New York plus New Jersey plus Connecticut: all gave similar results. The lead in gasoline trend line ap pears to fit the blood lead trend line better than the air lead trend, especially in the summer of 1973. Multiple regression analyses were calculated using six separate models. The best fitting model had an R2 = 0.745. Gasoline lead content was included rather than air lead. The gaso line lead content coefficient was significant for all three racial groups. Partial correla tions with gasoline alone were not provided. The authors state a number of reasons for gaso line lead providing a better fit than air lead, including the fact that the single monitoring site might not be representative. Nathanson and Nudelman (1980) provide more detail regarding air lead levels in New York City. In 1971, New York City began to regulate the lead content of gasoline sold. Lead in gasoline was to be totally banned by 1974, but supply and distribution problems delayed the effect of the ban. Ultimately, regulation of lead in gasoline was taken over by the U.S. Environmental Protection Agency. !l i ii 11-57 TEH 0412053 DUP050452652 0a.! >iuiii -j Q <ui cc UI <cu(Sci >< Figure 11-14. Geometric mean blood lead levels of New York City children (aged 25-36 months) by ethnic group, and ambient air lead concentration versus quarterly sampling period, 1970-1976. Source: Billick et al. (1980). 11-58 TEH 0412054 DUP050452653 a <u O OV<) Figure 11-15. Geometric mean blood lead levels of New York City children (aged 25-36 months) by ethnic group, and estimated amount of lead present in gasoline sold in New York, New Jersey, and Connecticut versus quarterly sampling period, 1970-1976. Source: Billick et al. (1980). n-59 TEH 0412055 DUP050452654 New York City measured air lead levels during the periods June 1969 to September 1973 an: during 1978 at multiple sites. The earlier monitoring was done by 40 rooftop samplers using i* cellulose filters analyzed by AAS. The latter sampling was done by 27 rooftop samplers using " glass fiber filters analyzed by X-ray fluorescence (XRF). There was excellent agreement between the XRF and atomic absorption analyses for lead (r = 0.985). Furthermore, the XRF analyses were checked against EPA AAS and again excellent agreement was found. The authors t did, however, point out that cellulose filters are not as efficient as glass fiber filters. Therefore, the earlier results tend to be underestimates of air lead levels. \1 m:` i Quarterly citywide air lead averages generally declined during the years 1969-1978. The maximum quarterly citywide average obtained was about 2.5 pg/m3 for the third quarter of 1970. The citywide trend corresponds to the results obtained from the single monitoring site used in />< Billick et al.'s (1979) analysis. The citywide data suggest that the single monitoring site 'Lj /, nfllfi: in Manhattan is a responsible indicator of air lead level trends. The graph in Figure 11-16`'fr reinforces this assertion by displaying the geometric mean blood lead levels for blacks and Hispanics in the 25- to 36-month age groups and the quarterly citywide air lead levels for the periods of interest, A good correspondence was noted. ':t As part of a detailed investigation of the relationship of blood lead levels and lead in gasoline covering three cities, Billick (1982) extended the time trend analyses of New York " S City blood lead data. Figure 11-17 presents the time trend line for geometric mean blood leads for blacks aged 25-36 months extended to 1979. Similar results held for other ages, -f; The downward trend noted earlier was still continuing, although the slopes for both the blood f'r and gasoline lead seem to be somewhat shallower toward the most recent data. A similar picture is presented by the percentage of children with blood lead levels greater than 30 - pg/dl. In the early 70's, about 60 percent of the screened children had these levels; by 1979 . the percentage had dropped between 10 and 15 percent. 11.3.6.4 Frankfurt, West Germany. Sinn (1980; 1981) conducted a study specifically examining the environmental and biological impact of the gasoline lead phasedown implemented in West * Germany on January 1, 1976. Frankfurt am Main provided a good setting for such a study * because of its physical character. CJI; Air and dustfall lead levels at several sites in and about the city were determined be- - fore and after the phasedown was implemented. The mean air lead concentrations obtained during the study are presented in Table 11-20. A substantial decrease in air lead levels was '' noted for the low-level high traffic site (3.18 pg/m3 in 1975-76 to 0.68 pg/m3 in 1978-1979). n1' No change was noted for the background site while only minor changes were observed for the "f other locations. Dustfall levels fell markedly (218 mg/cm2*day for 1972-1973 to 128 !.' mg/cm2*day for 1977-1978). Traffic counts were essentially unchanged in the area during the course of study. ' !;v 11-60 :l$r; TEH 0412056 DUP050452655 Figure 11-16. Geometric mean blood levels for blacks and Hispanics in the 25-to-36-month age group and rooftop quarterly averages for ambient citywide lead levels. Source: Nathanson and Nudelman (1980). 21-61 TEH 0412057 DUP050452656 -TM# l, Figure 11-17. Time-dependence of blood lead and gas lead for blacks, aged 25 to 36 months, in New York. Source: Billick (1982). 11-62 TEH 0412058 DUP050452657 TABLE 11-20. MEAN AIR LEAD CONCENTRATIONS DURING THE VARIOUS BLOOD SAMPLING PERIODS AT THE MEASUREMENT SITES DESCRIBED IN THE TEXT (pg/m3) 1975-1976 1976-1977 1977-1978 1978-1979 Residential low traffic 0.57 0.39 0.32 0.39 High traffic (>20m) 0.59 0.38 0.31 0.31 High traffic (3m) 3.18 1.04 0.66 0.68 Background site 0.12 0.09 0.10 0.12 Source: Sinn (1980, 1981). A number of population groups were included in the study of the blood lead levels; they were selected for having either occupational or residential exposure to high density automo bile traffic. Blood samples were taken serially throughout the study (three phases in December-January 1975-1976, December-January 1976-1977, and December-January 1977-1978). Blood samples were collected by venipuncture and analyzed by three different laboratories. All the labs used AAS although sample preparation procedures varied. A quality control program across the laboratories was conducted. Due to differences in laboratory analyses, attrition, and loss of sample, the number of subjects who could be examined throughout the study was considerably reduced from the initial number recruited (124 out of 300). Preliminary analyses indicated that the various categories of subjects had different blood lead levels, and that males and females within the same category differed. A very com plicated series of analyses then ensued that made it difficult to draw conclusions because the various years' results were displayed separately by each laboratory performing the chemical analysis and by different groupings by sex and category. In Sinn's later report (1981), a downward trend was shown to exist for males and females who were in all years of the study and whose blood levels were analyzed by the same laboratory. 11.4 STUDIES RELATING EXTERNAL DOSE TO INTERNAL EXPOSURE The purpose of this section is to assess the importance of environmental exposures in determining the level of lead in human populations. Of prime interest are those studies that yield quantitative estimates of the relationship between air lead exposures and blood lead levels. Related to this question is the evaluation of which environmental sources of airborne lead play a significant role in determining the overall impact of air lead exposures on blood lead levels. 11-63 TEH 0412059 DUP050452658 A factor that complicates the analysis presented here is that lead does not remain sus pended in the atmosphere but rather falls to the ground, is incorporated into soil, dust, and water, and enters the food chain over time (see Figure 11-1). Since man is exposed to lead from all of these media, as will be demonstrated below, studies that relate air lead levels to blood lead levels (especially experimental exposure studies) may underestimate the overall impact of airborne lead on blood lead levels. In observational studies, on the other hand, the effects of air lead will thus be confounded with lead exposures from other pathways. The simultaneous presence of lead in multiple environmental media requires the use of multiple variable analysis techniques or surrogate assessment of all other external exposures. Virtu ally no assessments of simultaneous exposures to all media have been done. There are several key features that characterize good studies relating external exposure to internal exposure of lead: (1) The study population is well-defined. (2) There is a good measure of the exposure of each individual. (3) The response variable (blood lead) is measured with adequate quality control, preferably with replicates. (4) The statistical analysis model is biologically plausible and is consistent with the data. (5) The important covariates are either controlled for or measured. Some studies of considerable importance do not address all of these factors adequately. Key studies selected for discussion here are those which address enough of these factors suffi ciently well to establish meaningful relationships. The choice of the statistical analysis model is important in determining these relation ships (for a more detailed discussion see Appendix 11B). The model used is especially criti cal in situations where lead is present in relatively low concentrations in one or more environmental media. A large number of statistical models have been used to predict blood lead from various environmental media. For simplicity, let PbB = blood lead, Ej = environmen tal exposure from source j, and b. = the regression coefficient for source j. Using this J notation, the more common models can be written as follows: Linear Model: PbB = bo + bj Ei + ... + b_ E + "error" Linear Model (log form): log(PbB) = log(b0 + bt E,^ + ... + bg Eg) + "error" Log-log Model: log(PbB) = log(b0) + bx log^) + ... + bg log(Eg) + "error" Log Total Exposure Model: log(PbB) = b log(b0 + bj Ex + ... + b s E s ) + "error" (11-2) (11-3) (11-4) (11-5) 11-64 TEH 0412060 DUP050452659 Power-Function Model: PbB = b0 + (bi E[ + ... + bs E s )c + "error" 1/3 Cube-root Model: PbB = b + bt (Ej) + "error" (11-6) (11-7) There is no question that the relationship between blood lead and environmental exposure is nonlinear across the entire range of potential exposures, from very low to high levels. At lower levels of exposure, however, the various models all provide adequate descriptions of the observed data. The choice of a model must be based at least in part on the biological mecha nisms. At the very least, no model should be adopted which is inconsistent with biological reality. The compartment-type metabolic models described in Section 10.3.4 predict a linear response to total lead intake. Compartment models are described by a system of coupled firstorder linear differential equations for the quantity of lead in various kinetically distinct body pools, (see Appendix 11-A). These compartments or kinetic pools may or may not corres pond to distinct physiological systems. It is well known that if the kinetic rate coeffi cients and absorption coefficients in such a model are constant, then the equilibrium blood lead in a steady-intake environment is PbB = (1ead absorbed into blood, pg/d) (Pb mean residence time in blood, d) (PbB volume of distribution, dl) (11-8) The only allowable places for nonlinearity in intake are either in the absorption process, or in the kinetics of lead distribution affecting the residence time. Nonlinearities affecting distribution volume are less plausible. Some of the evidence relating to these mechanisms was reviewed in Chapter 10. Chamberlain (1983) and U.S. EPA (1983) have concluded that after several months of steady exposure to environmental lead, blood lead levels achieve a near equilibrium concentration that increases linearly with the ambient concentration no matter what the exposure pathway (directly by air inhalation, or by ingestion of food, water, dust, soil, or paint), provided the total exposure does not cause blood lead to exceed 30-40 pg/dl. However, when total lead exposure by any pathway becomes so great that blood lead levels greatly exceed 60-80 pg/dl, then the blood lead concentrations increase much more slowly with increasing exposure concentration than they did at lower levels. On the other hand, the log-log and cube root models have slopes which approach infinity as the exposure approaches zero. The curves are so highly nonlinear at low doses that the models attribute nearly all of the increase of blood lead levels to the lowest exposures, and attribute relatively little increase to any additional exposures. However, the data of 11-65 TEH 0412061 DUP050452660 Piomelli et al. (1980) on a population of Nepalese exposed to an air lead of 0.00085 pg/ra3 had a geometric mean blood lead level of 3.4 pg/dl. This is similar to the value predicted by the log-log model of Goldsmith-Hexter. 1 3Mfl The following sections give the models as presented by the original authors. In many (HP cases, EPA has fitted other models in order to show the sensitivity of analysis to the model selected. 11.4.1 Air Studies I ft' The studies emphasized in this section are those most relevant to answering the following mm?. question: If there is moderate change in average ambient air lead concentrations due to changes in environmental exposure (at or near existing EPA air lead standards), what changes are expected in blood lead levels of individual adults and children in the population? Longi iitudinal studies in which changes in blood lead can be measured in single individuals as re sponses to changes in air lead are discussed first. The cross-sectional relationship between iill blood lead and air lead levels in an exposed population provides a useful but different kind of information, since the population "snapshot" at some point in time does not directly mea sure changes in blood lead levels or responses to changes in air lead exposure. In this chapter consideration is also restricted to those individuals without known excessive occupa tional or personal exposures (except, perhaps, for some children in the Kellogg/Silver Valley study). The previously published analyses of relevant studies have not agreed on a single form for the relationship between air lead and blood lead. All of the experimental studies have at least partial individual air lead exposure measures, as does the cross-sectional observational study of Azar et al. (1975). The 1974 Kellogg/Silver Valley study (Yankel et al., 1977) has *also been analyzed using several models. Other population cross-sectional studies have been analyzed by Snee (1981). The most convenient method for summarizing these diverse studies and their several analyses is by use of the blood lead - air lead slope (p), where p measures the change in blood lead that is expected for a unit change in air lead. If determined for indi vidual subjects in a study population, this slope is denoted 0.. If the fitted equation is linear, then p or p. is the slope of the straight line relationship at any air lead level. If the fitted relationship is nonlinear, then the slope of the relationship measures the expected i effect on blood lead of a small change in air lead at some given air lead value and thus will be somewhat different at different air lead levels. A basic assumption here is that the distribution of blood lead in human populations with homogeneous exposure (same geometric mean blood lead) is lognormal; a second assumption is that all such lognormal distributions have the same geometric standard deviation (g.s.d.) or 11-66 TEH 0412062 DUP050452661 coefficient of variation (c.v.) It is then possible to calculate the fraction of the popu lation in excess of any specific level of blood lead. Most subpopulations not occupationally exposed to lead have geometric mean blood lead < 20 pg/dl, at which level the effects of a few pg/dl change in blood lead can be well approximated by a linear function. On the other hand, many important experimental studies involve subjects with much higher blood lead. The re sponse relationships derived from lead-exposed subjects (blood lead > 30 pg/dl) usually show much lower slopes b*.) when blood lead exceeds 40 pg/dl. These two uses of blood lead versus intake models -- to predict the fraction of an exposed population at risk and to predict the change in blood lead of subjects exceeding a criterion blood lead level when blood lead expo sure changes -- may require different blood lead slopes b^. These two uses are not neces sarily inconsistent, e.g., if there was a corresponding increase in biological variability of response to high levels of intake offsetting the decreased slope. For this reason we sepa rately analyze the single-subject and population studies. 11.4.1.1 The Griffin et al. Study. The study of Griffin et al. (1975) has the largest number of human subjects exposed to atmospheric particulate lead at near-ambient conditions, under conditions of long-term controlled exposure. In two separate experiments conducted at the Clinton Correctional Facility in 1971 and 1972, adult male prisoner volunteers were sequest ered in a prison hospital unit and exposed to approximately constant levels of lead oxide (average 10.9 pg/m3 in the first study and 3.2 pg/m3 in the second). Volunteers were exposed in an exposure chamber to an aerosol of submicron-sized particles of lead oxide, which was prepared by burning tetra-ethyl lead in a propane flame. There was an approximate additional 10-15 percent exposure to ambient organic lead vapor. All volunteers were introduced into the chamber 2 weeks before the initiation of the exposure; the lead exposures were scheduled to last 16 weeks, although the volunteers could drop out whenever they wished. Twenty-four vol unteers, including 6 controls, participated in the 10.9 pg/m3 exposure study. Not all volun teers completed the exposure regimen. Blood lead levels were found to stabilize after appro ximately 12 weeks. Among 8 men exposed to 10.9 pg/m3 for at least 60 days, a stabilized mean level of 34.5 5.1 pg/dl blood was obtained, as compared with an initial level of 19.4 3.3 pg/dl. All but two of the 13 men exposed at 3.2 pg/m3 for at least 60 days showed increases and an overall stabilized level of 25.6 3.9 pg/dl was found, compared with an initial level of 20.5 4.4 pg/dl. This represented an increase of about 25 percent above the base level. The aerosols used in this experiment were somewhat less complex chemically, as well as somewhat smaller, than those found in the ambient environment. The particle size obtained was 0.05-0.10 pm, which is smaller than true urban aerosol of 0.3 pm. Griffin et al. (1975), how ever, pointed out that good agreement was achieved on the basis of the comparison of their ob served blood lead levels with those predicted by Goldsmith and Hexter's (1967) equation; that 11-67 TEH 0412063 DUP050452662 is, log10 blood lead = 1.265 + 0.2433 log10 atmospheric air lead. The average diet content of i--f lead was measured and blood lead levels were observed at 1- or 2-week intervals for several pi months. Eight subjects received the maximum 4-month exposure to 10.9 pg/m3; nine subjects !JPv~ * were exposed for 1-3 months. Six subjects had the maximum 4-month exposure to 3.2 pg/m3, and eight others had shorter exposures. iBCompartmental models have been fitted to these data by O'Flaherty et al. (1982) and by EPA. The basis of these models is that the mass of lead in each of several distinct pools or compartments within the body changes according to a system of coupled first-order linear dif ferential equations with constant fractional transfer rates (Batschelet et al., 1979; Rabinc- witz et al., 1976). Such a model predicts that when the lead intake changes from one constant level to another, then the relationship between the mass of lead in each compartment and time with constant intake has a single exponential term. 'mm ilSIllP The subjects at 3.2 pg/m3 exhibited a smaller increase in blood lead, with correspond ingly less accurate estimates of the parameters. Several of the lead-exposed subjects faile^ to show an increase. EPA has reanalyzed these data using a two-compartment model for two reasons: (1) Semi logarithmic plots of blood lead versus time for most subjects showed a twocomponent exponential decrease of blood lead during the postexposure or washout phase of the experiments. Rabinowitz et al. (1977) show that at least two pools are necessary to model blood lead kinetics accurately. The first pool is tenta tively identified with blood and the most labile soft tissues. The second pool probably includes soft tissues and labile bone pools. (2) Kinetic models are needed to account for the subjects' lead burdens not being in equilibrium at any phase of the experiments. Previously published analyses have not used data for all 43 subjects, particularly for the same six subjects (labeled 15-20 in both experiments) who served as controls both years. These subjects establish a baseline for non-inhalation exposures to lead, e.g., in diet and water, and allow an independent assessment of within-subject variability over time. EPA ana lyzed data for these subjects as well as others who received lead exposures of shorter dura tion. The estimated blood lead inhalation slope, p, was calculated for each individual subject according to the formula -Hi1 :"aftpp.l; .ii r = (Change in intake, pg/day) x (mean residence time in blood, day) P (Change in air exposure, pg/m3) x (Volume of distribution, dl) (11-9) 11-68 TEH 0412064 DUP050452663 The changes in air exposure were 10.9-0.15 = 10.75 pg/m3 for 1970-71 and 3.2-0.15 = 3.05 pg/m3 in 1971-72. Paired sample t-tests of equal means were carried out for the six controls and five subjects with exposure both years, and independent sample t-tests were carried out com paring the remaining 12 subjects the first year and nine different subjects the next year. All standard error estimates include within-subject parameter estimation uncertainties as well as between subject differences. The following are observations: (1) Non-inhalation lead intake of the control subjects varied substantially during the second experiment at 3.2 pg/m3, with clear indication of low intake during the 14day pre-exposure period (resulting in a net decrease of blood lead). There was an increase in lead intake (resulting in either equilibrium or net increase of blood lead) during the exposure period. Subjects 16 and 20 had substantial increases, subjects 15 and 19 had moderate increases, and subject 18 had no increase in blood lead during exposure. Subject 17 had a marked decline in blood lead, but the rate of decrease was much faster in the pre-exposure period, suggesting an apparent in crease of intake during exposure periods even for this subject. These subjects had not apparently achieved equilibrium in either blood or tissue compartments. Even though these subjects were not exposed to air lead, the estimated difference between blood lead intake before and during exposure of the other subjects was used to cal culate the apparent inhalation slope at that exposure. The pooled inhalation slope estimated for all six controls (1.48 0.82 s.e.) was significantly positive ( = 1.76, one-tailed p <0.05), as shown in Table 11-21. No explanation for the in creased lead intake during the winter of 1971-72 can be advanced at this time, but factors such as changes in diet orchanges in resorption of bone lead are likely to have had an equal effect on the lead-exposed subjects. No statistically significant changes in the controls were found during the first experiment at 10.9 pg/m3. (2) Among the controls, the estimated mean residence time in blood was slightly longer for the first year than the second year, 41.8 9.2 days versus 34.6 6.5 days, but a paired sample Z-test found that the mean difference for the controls (7.2 11.2 days) was not significantly different from zero (see Table 11-22). (3) Among the five subjects exposed to 10.9 pg/m3 the first year and 3.2 pg/m3 the second year, the mean residence time in blood was almost identical (43.9 9.4 versus 44.7 8.7 days). ! 11-69 TEH 0412065 DUP050452664 TABLE 11-21. GRIFFIN ET AL. (1975) EXPERIMENT INHALATION SLOPE ESTIMATES Group At 3.2 pg/m3 At 10.9 pg/m3 Controls All exposed 1.48 0.82 (n = 6)* 3.00 0.76 (n = 14) -0.20 0.27 (n = 6) 1.57 0.26 (n = Difference (Exposed controls) 1.52 1.12 1.77 0.37 Pooled: (all subjects) (without subjects 1,6)** 1.75 0.35 1.78 0.35 *n = number of subjects. **Subjects 1 and 6 were "non-responders." TABLE 11-22. GRIFFIN ET AL. (1975) EXPERIMENT MEAN RESIDENCE TIME IN BLOOD Control Exposed 3.2 gg/m3 experiment 34.6 6.5 days 40.8 4.4 days 10.9 pg/m3 experiment 41.8 9.2 days 40.6 3.6 days (4) The average inhalation slope for all 17 subjects exposed to 10.9 pg/m3 is 1.77 ^ 0.37 when the slope for the controls is subtracted. The corrected inhalation slope for all 14 subjects exposed to 3.2 pg/m3 is 1.52 1.12, or 1.90 1.14 without subjects 1 and 6 who were "non-responders." These are not significantly different. The pooled slope estimate for all subjects is 1.75 0.35. The pooled mean resi dence time for all subjects is 39.9 2.5 days. Thus, in spite of the large estimation variability at the lower exposure level, the aver age inhalation slope estimate and blood lead half-life are not significantly different at the two exposure levels. This suggests that blood lead response to small changes in air lead in halation is approximately linear at typical ambient levels. 11-70 fit. TEH 041201 DUP050452665 11.4.1.2 The Rabinowitz et al. Study. The use of stable lead isotopes avoids many of the difficulties encountered in the analysis of whole blood lead levels in experimental studies. Five adult male volunteers were housed in the metabolic research wards of the Sepulveda and Wadsworth VA hospitals in Los Angeles for extended periods (Rabinowitz et al., 1974; 1976; 1977). For much of the time they were given low-lead diets with controlled lead content, sup plemented by tracer lead salts at different times. Four subjects were initially observed in the ward for several weeks. Each subject was in the semi-controlled ward about 14 hours per day and was allowed outside for 10 hours per day, allowing the blood lead concentration to stabilize. Subjects 8, D, and E then spent 22-24 hours per day for 40, 25, and 50 days, respectively in a low-lead room with total particulate and vapor lead concentrations that were much lower than in the metabolic wards or outside (see Table 11-23). The subjects were thereafter exposed to Los Angeles air with much higher air lead concentrations than in the ward. The calculated changes in lead intake upon entering and leaving the low-lead chamber are shown in Table 11-24. These were based on the assumption that the change in total blood lead was proportional to the change in daily lead intake. The change in calculated air lead intakes (other than cigarettes) due to removal to the clean room were also calculated indepen dently by the lead balance and labeled tracer methods (Rabinowitz et al., 1976) and are con sistent with these direct estimates. Rabinowitz and coworkers assumed that the amount of lead in compartments within the body evolved as a coupled system of first-order linear differential equations with constant frac tional transfer rates. This compartmental model was fitted to the data. This method of analysis is described in Appendix 11A. Blood lead levels calculated from the three compartment model adequately predicted the observed blood lead levels over periods of several hundred days. There was no evidence to suggest homeostasis or other mechanisms of lead metabolism not included in the model. There was some indication (Rabinowitz et al., 1976) that gut absorption may vary from time to time. The calculated volumes of the pool with blood lead (Table 11-24) are much larger than the body mass of blood (about 7 percent of body weight, estimated respectively as 4.9, 6.3, 6.3, 4.6, and 6.3 kg for subjects A-E). The blood lead compartment must include a substantial mass of other tissue. The mean residence time in blood in Table 11-24 includes both loss of lead from blood to urine and transfer of a fraction of blood lead to other tissue pools. This parameter reflects the speed with which blood lead concentrations approach a new quasi-equilibrium level. Many years may be needed before approaching a genuine equilibrium level that includes lead that can be mobilized from bones. 11-71 TEH 0412067 DUP050452666" TABLE 11-23. AIR LEAD CONCENTRATIONS* (pg/m3) FOR TWO SUBJECTS IN THE RABINOWITZ STUDIES t* a Subject A Subject B Environment Outside (Sepulveda VA) Inside (Sepulveda VA, air-conditioned without filter) Inside (Wadsworth VA, Open air room) (WadswortfTVA) Outside In room (air conditioner with filter, no purifier) In room (with purifiers, "clean air") Open-air room Organic vapor lead Outside "Clean air" Average 1.8 1.5 2.1 2.0 0.97 0.072 1.9 0.10 0.05 Range (1.2-2.4) (1.0-2.7) (1.8-2.6) (1.6-2.4) 1` (0.4-2.1) (0.062-0.087) (1.8-1.9) ' `h - 5-20 days exposure for each particulate lead filter. One of the greatest difficulties in using these experiments is that the air lead expo Sfl sures of the subjects were not measured directly, either by personal monitors or by restric ting the subjects to the metabolic wards. The times when the subjects were allowed outside the wards included possible exposures to ground floor and street level air, whereas the out-* H side air lead monitor was mounted outside the third-floor window of the ward. The VA hospi tals are not far from major streets and the subjects' street level exposures could have been much higher than those measured at about 10 m elevation (see Section 7.2.1.3). Some estimated ratios between air concentrations at elevated and street level sites are given in Table 7-6. A second complication is that the inside ward value of pg/m3 (Rabinowitz et al., 1977)' :t 5 used for subject B may be appropriate for the Wadsworth VA hospital, but not for subject A ' > the Sepulveda VA hospital {see Table 11-23). The changes in air lead values shown in Table 11-24 are thus nominal, and are likely to have systematic inaccuracies much larger than the 11-72 ^MifMlllii TEH 0412068 DUP050452667 TABLE 11-24. ESTIMATES OF INHALATION SLOPE, p, FOR RABINOWITZ STUDIES Changes in intake*, Subject pg/day Volume,** kg Residencet time, days Changes in air lead*', pg/m3 Inhalation+11" slope, pg/d3, per pg/m3 Maximjjjq} slope A 17 5* 7.4 + 0.6 B 16 3 10.0 0.8 C 15 5* 10.1 1** D 9 2 9.9 1.2 E 12 + 2 11.3 1.4 34 5 40 + 5 37 5 40 + 5 27 + 5 2.5ft 2.0 2.2ft 2.0 2.0 2.98 + 1.06 3.56 0.93 2.67 + 1.04 2.02 + 0.60 1.59 0.47 4.38 + 1.55 5.88 1.54 4.16 1.62 3.34 0.99 2.63 + 0.78 *From Rabinowitz et al. (1977), Table VI. Reduced intake by low-lead method for subjects B D, E, tracer method for A, balance method for C. Standard error for C is assumed by EPA to be same as A. **From Rabinowitz et al. (1976), Table II. EPA has assumed standard error with coefficient of variation same as that for quantity of tracer absorbed in Table VI, except for subject C. ^Estimates from Rabinowitz et al. (1976) Table II. Standard error estimate from combined sample. 4*4* 'See text. For A and C, estimated from average exposure. For B, D, and E reduced by 0.2 pg/m3 for clean room exposure. Coefficient of variation assumed to be 10%. Assumed density of blood 1.058 g/cm3. Assuming outside air exposure is 2.1 pg/m3 rather than 4 pg/m3 for 10 hours. nominal 10 percent coefficients of variation stated. The assumption is that for subjects B, D, and E, the exposure to street level air for 10 hours per day was twice as large as the mea sured roof level air, i.e. , 4 pg/m3; and the remaining 14 hours per day were at the ward level of 0.97 pg/m3; thus the time-averaged level was [(10 x 4) + (14 x 0.97)]/24 = 2.23 pg/m3. The average controlled exposures during the "clean room" part of the experiment were 23, 22, and 24 hours respectively for subjects B, D, E; thus averaged exposures were 0.19, 0.28, and 0.12 pg/m3, and reductions in exposure were about 2.0 pg/m3. This value is used to calculate the slope. For subject A, the total intake due to respired air is the assumed indoor average of 1.5 pg/m3 for the Sepulveda VA hospital, combining indoor and outdoor levels [(10 x 4) + (14 x 1.5)]/24 = 2.54 pg/m3. For subject C the Wadsworth average applies. Other than uncertainties in the air lead concentration, the inhalation slope estimates for Rabinowitz's subjects have less internal uncertainty than those calculated for subjects in Griffin's experiment. 11-73 TEH 0412069 DUP050452668 The inhalation slopes thus calculated are the lowest that can be reasonably derived from this experiment, since the largest plausible air lead concentrations have been assumed. The third-floor air monitor average of 2.1 pg/m3 is a plausible minimum exposure, leading to the higher plausible maximum inhalation slopes in the last column of Table 11-24. These are based on the assumption that the time-averaged air lead exposure is smaller by [10(4-2.l)]/24 = 0.79 pg/m3 than assumed previously. It is also possible that some of this difference can be attri buted to dust ingestion while outside the metabolic ward. 11.4.1.3 The Chamberlain et al. Study. A series of investigations were carried out by Chamberlain et al. (1975a,b; 1978) at the U.K. Atomic Energy Research Establishment in Harwell, England. The studies included exposure of up to 10 volunteer subjects to inhaled, ingested, and injected lead in various physical forms. The inhalation exposures included laboratory inhalation of lead aerosols generated in a wind tunnel, or box, of various particle sizes and chemical compositions (lead oxide and lead nitrate). Venous blood samples were taken at several times after inhalation of 203Pb. Three subjects also breathed natural high way exhaust fumes at various locations for times up to about 4.5 hours. The natural respiratory cycles in the experiments varied from 5.7 to 17.6 seconds (4 to 11 breaths per minute) and tidal volumes from 1.6 to 2.3 liters. Lung deposition of lead bearing particles depended strongly on particle size and composition, with natural exhaust particles being more efficiently retained by the lung (30 - 50 percent) than were the chemical compounds (20 - 40 percent). The clearance of lead from the lungs was an extended process over time and depended on particle size and composition, leaving only about 1 percent of the fine wind tunnel aerosols in the lung after 100 hours, but about 10 percent of the carbonaceous exhaust aerosols. The 203Pb isotope reached a peak blood level about 30 hours after inhalation, the blood level then representing about 60 percent of the initial lung burden. A substantial fraction of the lead deposited in the lung appears to be unavailable to the blood pool in the short term, possibly due to rapid transport to and retention in other tis sues including skeletal tissues. In long-term balance studies, some of this lead in the deep tissue compartment would return to the blood compartment. Lead kinetics were also studied by use of injected and ingested tracers, which suggested that in the short term, the mean residence time of lead in blood could be calculated from a one-pool model analysis. Chamberlain et al. (1978) extrapolated these high-level, short-term exposures to longer term ones. The following formula and data were used to calculate a blood-to-air level ratio w m I 11-74 i t# TEH 0412070 DUP050452669 [T, ] [% Deposition] [% Absorption] [Daily ventilation] p = --3---------------------------------------------------------------------------------- [Blood volume] [0.693] where: T',S = biological half life (11-10) With an estimated value of = 18 days (mean residence time T^/0.693 = 26 days), with 50 per cent for deposition in lung for ordinary urban dwellers, and 55 percent of the lung lead re tained in the blood lead compartment (all based on Chamberlain's experiments), with an assumed ventilation of 20 m3/day over blood volume 5400 ml (Table 10-20 in Chamberlain et al., 1978), then r = 26 day X 0.50 X 0.55 X 20 ms/day =2.7 m3/dl p 54 dl (11-11) This value of p could vary for the following reasons: 1. The absorption from lung to blood used here, 0.55, refers to short-term kinetics. In the long term, little lead is lost through biliary or pancreatic secretions, nails, hair, and sweat, so that most of the body lead is available to the blood pool even if stored in the skeleton from which it may be resorbed. Chamberlain suggests an empirical correction to 0.55 X 1.3 = 0.715 absorption. 2. The mean residence time, 26 days, is shorter than in Rabinowitz's subjects, and the blood volume is less, 54 dl. It is possible that in the Rabinowitz study, the mean times are longer and the blood pool size (100 dl) is larger than here because Rabinowitz et al. included relatively fewer labile tissues such as kidney and liver in the pool. Assuming 40 days mean residence time and 100 dl blood volume the slope can be recalculated, ,,P-_---4-0----d---X---0--.-5--0-1X000.15-5---X----2-0---m--3-/--d---_- 2.,,2 ,,m /,,d, l,,. 3. The breathing rate could be much less, for inactive people. (11-12) 11-75 TEH 0412071 DUP050452670 B( B- H.nMw*i iilBll r T- V- 11.4.1.4 The Kehoe Study. Between 1950 and 1971, Kehoe exposed 12 subjects to various levels ill * .. of air lead under a wide variety of conditions. Four earlier subjects had received oral lead i* during 1937-45. The inhalation experiments were carried out in an inhalation chamber at the University of Cincinnati, in which the subjects spent varying daily time periods over extended intervals. The duration was typically 112 days for each exposure level in the inhalation studies, and at the end of this period it was assumed the blood lead concentration had reached a near-equilibrium level. The experiments are described by Kehoe (1961a,b,c) and the data and their analyses by Gross (1981) and Hammond et al. (1981). The studies most relevant to this document are those in which only particles of lead sesquioxide aerosols in the submicron range were used, so that there was at least one air lead exposure (other than control) for which the time-averaged air lead concentration did not exceed 10 pg/m3. Only six subjects met these criteria: LD (1960-63), JOS (1960-63), NK (1963-66), SS (1963-68), HR (1966-67), and DW (1967-69). Subject DH had a rather high initial blood lead concentration (30 pg/dl) that fell illltduring the course of the experiment to 28 pg/dl; apparently daily detention in the inhalation chamber altered DH's normal pattern of lead exposure to one of lesser total exposure. The Kehoe studies did not measure non-experimental airborne lead exposures, and did not measure lead exposures during "off" periods. Subject HR received three exposure levels from 2.4-7.5 Sill .IQs. pg/m3, subject NK seven exposure levels from 0.6-4.2 pg/m3, and subject SS 13 exposure'levels from 0.6-7.2 pg/m3. LD and JOS were each exposed to about 9, 19, 27, and 36 pg/m3 during sequential periods of 109-113 days. gig A great deal of data on lead content in blood, feces, urine and diet were obtained in these studies and are exhibited graphically in Gross (1979) (see Figure 11-18). Apart from the quasi-equilibrium blood lead values and balances reported in Gross (1979; 1981), there has been little use of these data to study the uptake and distribution kinetics of lead in man. EPA analyses used only the summary data in Gross (1981). Data from Gross (1981) were fitted by least squares linear and quadratic regression models. The quadratic models were not significantly better than the linear model except for subjects LD and JOS, who were exposed to air levels above 10 pg/m3. The linear terms predomi nate in all models for air lead concentrations below 10 pg/m3 and are reported in Table 11-25. These data represent most of the available experimental evidence in the higher range of ambient exposure levels, approximately 3-10 pg/m3. Data for the four subjects with statis tically significant relationships are shown in Figure 11-19, along with the fitted regression curve and its 95 percent confidence band. 11-76 TEH 0412072 DUP050452671 1.00 BALANCE $ 0.60 9 0.20 C0aD- -0.20 -0.60 -1.00 >. .ft ... 2.00 $ 1.60 9ffi 1.20 0.80 0 0.40 0.00 1.00 5 0.80 9n 0.60 TM 0.40 2 0.20 0.00 | j j SUBJECT - SS ................ `.....-Vi.-v...--J....1.4."..... 1 ...._________J----- k * .* 4--- --... L--Id--i----*-j --i--i--I--i--i--i---- TIME (days) Figure 11-18. Data plots for individual subjects asa function of time for Kehoe subjects, as presented by Gross (1979). 11-77 TEH 0412073 DUP050452672 TABLE 11-25. LINEAR SLOPE FOR BLOOD LEAD VERSUS AIR LEAD AT LOW AIR LEAD EXPOSURE IN KEHOE'S SUBJECTS Subject DHa HR b jr LD" NKC SSC Linear Slopes 3, mVdl, s.e. Linear Model Quadratic Model -0.34 i 0.28 0.70 0.46 0.67 0.07 0.64 + 0.11 2.60 0.32 1.31 + 0.20 0.14 1.25 0.20 2.14 1.01 0.19 1.29 0.06 1.55 1.28 1.16 0.78 Airi, pg/nr Range_______ Blood, jjg/dje 5.6 - 8.8 2.4 - 7.5 9.4 - 35.7 9.3 - 35.9 0.6 - 4.0 0.6 - 7.2 26 - 31 21 - 27 21 - 46 18 - 41 20 - 30 18 - 29 m, *Also, control = 0. aNo statistically significant relationship between air and blood lead. L High exposures. Use linear slope from quadratic model. c Low exposures. Use lin. ear slope from linear model. 11.4.1.5 The Azar et al, Study. Thirty adult male subjects were obtained from each of five groups: 1) Philadelphia cab drivers; 2) DuPont employees in Starke, Florida; 3) DuPont em ployees in Barksdale, Wisconsin; 4) Los Angeles cab drivers; and 5) Los Angeles office workers (Azar et al., 1975). Subjects carried air lead monitors in their automobiles and in their breathing zones at home and work. Personal variables (age, smoking habits, water samples) were obtained from all subjects, except for water samples from Philadelphia cab drivers. Blood lead, ALAD urine lead, and other variables were measured. From two to eight blood sam ples were obtained from each subject during the air monitoring phase. Blood lead determina tions were done in duplicate. Table 11-26 presents the geometric means for air lead and blood lead for the five groups. The geometric means were calculated by EPA from the raw data pre sented in the authors1 report (Azar et al., 1975). The Azar study has played an important role in setting standards because of the care used in measuring air lead in the subjects' breathing zone. Blood lead levels change in response to air lead levels, with typical time constants of 20-60 days. One must assume that the subjects' lead exposures during preceding months had been reasonably similar to those during the study period. Models have been proposed for these data by Azar et al. (1975), Snee (1981; 1982b), and Hammond et al. (1981) including certain nonlinear models. Azar et al. (1975) used a log-log model for their analysis of the data. The model in cluded dummy variables, C*. C2, C3, C4, C5, which take on the value 1 for subjects in that group and 0 otherwise (see Table 11-26 for the definitions of these dummy variables). The fitted model using natural logarithms was 11-78 4 :h;! !4 ,4; 4'. 'Hr TEH 0412074 ii DUP050452673 BLOOD LEAD, Mg/dl BLOOD LEAD, ng/dt Figure 11-19. Blood level vs. air lead relationships for Kehoe inhalation studies: linear relation for low exposures, quadratic for high exposures, with 95% confidence bands. 11-79 TEH 0412075 DUP050452674 ""****& * * > * HdtqHiBBlit -mm&w ' Group TABLE 11-26. GEOMETRIC MEAN AIR AND BLOOD LEAD LEVELS (pg/100 g) FOR FIVE CITY-OCCUPATION GROUPS (DATA CALCULATED BY EPA) Geometric mean air lead, pg/m3 GSD Geometric mean blood lead, pg/100 g GSD Sample size .......-- _ Code Cab drivers Philadelphia, PA 2.59 1.16 22.1 1.16 30 ci Plant employees Starke, FL 0.59 2.04 15.4 1.41 29 Plant employees Barksdale, WI 0.6i 2.39 12.8 1.43 30 C3 Cabdrivers Los Angeles, CA 6.02 1.18 24.2 1.20 30 C4 Office workers Los Angeles, CA 2.97 1.29 18.4 1.24 30 Cs Source: Azar et al. (1975). vf mm- 111 if f, '% lir M: log (blood Pb) = 2.951 Ca + 2.818 C2 + 2.627 C3 + 2.910 C4 + 2.821 Cs + 0.153 log (air Pb) IP-(11-13) 'Mw Mk :fjflThis model gave a residual sum of squares of 9.013, a mean square error of 0.063 (143 degrees of freedom), and a multiple R2 of 0.502. The air lead coefficient had a standard error of 0.040. The fitted model is nonlinear on air lead, and so the slope depends on both air lead and the intercept. Using an average intercept value of 1.226, the curve has a slope ranging from 10.1 at an air lead level of 0.2 pg/m3 to 0.40 at an air lead level of 9 pg/m3. ip. Snee (1982b) reanalyzed the same data and fitted the following power function model, r, Ipjp log (blood Pb) = log [12.1 (air Pb + 6.00 Cx + 1.46 C2 'Wfc If + 0.44 C3 + 2.23 C4 + 6.26 C5)0-2669] m ft This model gave a residual sum of squares of 9.101, a mean square error of 0.063 (142 degrees of freedom) and a multiple R2 of 0.497. Using an average constant value of 3.28, the slope ilift ranges from 1.29 at an air lead of 0.2 to 0.51 at an air lead of 9. 11-80 < TEH 0412076 - DUP050452675 An important extension in the development of models for the data was the inclusion of separate non-air contributions or background exposures for each separate group. The coeffi cients of the group variables, Cj, in the lead exposure model may be interpreted as measures of total exposure of that group to non-air external sources {cigarettes, food, dust, water) and to endogenous sources (lead stored in skeleton). Water and smoking variables were used to estimate some external sources. (This required deleting another observation for a subject with unusually high water lead.) The effect of endogenous lead was estimated using subject age as a surrogate measure of cumulative exposure, since lead stored in the skeleton is known to increase approximately linearly with age, for ages 20-60 (Gross et al., 1975; Barry, 1975; Steenhout, 1982) in homogeneous populations. In order to facilitate comparison with the constant p ratios calculated from the clinical studies, EPA fitted a linear exposure model to the Azar data. The model was fitted on a loga rithmic scale to facilitate comparison of goodness of fit with other exposure models and to produce an approximately normal pattern of regression residuals. Neither smoking nor water lead provided significantly better fits to the log (blood lead) measurements after the effect of age was removed. Age and air lead may be confounded to some extent because the regression coefficient for age may include the effects of prior air lead exposures on skeletal lead buildup. This would have the effect of reducing the estimated apparent slope p. Geometric mean regressions of blood lead on air lead were calculated by EPA for several assumptions; (1) A linear model analogous to Snee's exposure model, assuming different nonair contributions in blood lead for each of the five subgroups; (2) a linear model in which age of the subject is also used as a surrogate measure of the cumulative body burden of lead that provides an endogenous source of blood lead; (3) a linear model similar to (2), in which the change of blood lead with age is different in different subgroups, but it is assumed that the non-air contribution is the same in all five groups (as was assumed in the 1977 EPA Lead Criteria Document); (4) a linear model in which both the non-air background and the change in blood lead with age may differ by group; and (5) a nonlinear model similar to (4). None of the fitted models are significantly different from each other using statistical tests of hypo theses about parameter subsets in nonlinear regression (Gallant, 1975). 11.4.1.6 Silver Valley/Kellogg, Idaho Study. In 1970, EPA carried out a study of a lead smelter in Kellogg, Idaho (Hammer et al., 1972; U.S. Environmental Protection Agency, 1972). The study was part of a national effort to determine the effects of sulfur dioxide, total sus pended particulate and suspended sulfates, singly and in combination with other pollutants, on human health. It focused on mixtures of the sulfur compounds and metals. Although it was demonstrated that children had evidence of lead absorption, insufficient environmental data were reported to allow further quantitative analyses. 11-81 TEH 0412077 DUP050452676 In 1974, following the hospitalization of two children from Kellogg with suspected acute lead poisoning, the CDC joined the State of Idaho in a comprehensive study of children in the Silver Valley area of Shoshone County, Idaho, near the Kellogg smelter (Vankel et al., 1977; Landrigan et al., 1976). :ii^wMSMM' The principal source of exposure was a smelter whose records showed that emissions aver aged 8.3 metric tons per month from 1955 to 1964 and 11.7 metric tons from 1965 to September, 1973. After a September, 1973 fire extensively damaged the smelter's main emission filtration mm facility, emissions averaged 35.3 metric tons from October, 1973 to September, 1974 (Landrigan ill' et al., 1976). The smelter operated during the fall and winter of 1973-74 with severely liltlimited air pollution control capacity. Beginning in 1971, ambient concentrations of lead in the vicinity of the smelter were determined from particulate matter collected by hi-vol air samples. Data indicated that monthly average levels measured in 1974 (Figure 11-20) were three to four times the levels measured in 1971 (von Lindern and Yankel, 1976). Individual exposures of study participants to lead in the air were estimated by interpolation from these data. Air lead exposures ranged from 1.5 pg/m3 to 30 pg/m3 monthly average (see Figure 11-20). Wlf Soil concentrations were as high as 24,000 pg/g and averaged 7000 pg/g within one mile of the smelter. House dusts were found to contain as much as 140,000 pg/g and averaged 11,000 pg/g in homes within one mile of the complex. The study was initiated in May, 1974 and the blood samples were collected in August, 1974 from children 1-9 years old in a door-to-door survey (greater than 90 percent participation). Social, family, and medical histories were conducted by interview. Paint, house dust, yard and garden soils, grass, and garden vegetable samples were collected. At that time, 385 of the 919 children examined (41.9 percent) had blood lead levels in excess of 40 pg/dl, 41 chil dren (4.5 percent) had levels greater than 80 pg/dl. All but 2 of the 172 children living within 1.6 km of the smelter had levels greater than or equal to 40 pg/dl. Those two children had moved into the area less than six months earlier and had blood lead levels greater than 35 pg/dl. Both the mean blood lead concentration and the number of children classified as exhib iting excess absorption decreased with distance from the smelter (Table 11-27). Blood lead levels were consistently higher in 2- to 3-year-old children than they were in other age groups (Table 11-28). A significant negative relationship between blood lead level and hema tocrit value was found. Seven of the 41 children (17 percent) with blood lead levels greater than 80 pg/dl were diagnosed as being anemic on the basis of hematocrit less than 33 percent, whereas only 16 of 1006 children (1.6 percent) with blood lead levels less than 80 pg/dl were so diagnosed. Although no overt disease was observed in children with higher lead intake, differences were found in nerve conduction velocity. Details of this finding are discussed in Chapter 12. 11-82 Te h 0412078 lir 1 DUP050452677 Figure 11-20. Monthly ambient air lead concentrations in Kellogg. Idaho, 1971 through 1975. Source: von Lindern and Yankei (1976). 11-83 TEH 0412079 DUP050452678 Area 1 2 3 4 5 6 TABLE 11-27. GEOMETRIC MEAN BLOOD LEAD LEVELS BY AREA COMPARED WITH ESTIMATED AIR LEAD LEVELS FOR 1- TO 9-YEAR OLD CHILDREN LIVING NEAR IDAHO SMELTER. (GEOMETRIC STANDARD DEVIATIONS, SAMPLE SIZE, AND DISTANCES FROM SMELTER ARE ALSO GIVEN)3 Mai i -.7 ;,i Geometric mean blood lead, Sample % blood lead Estimated air lead, p"\ Distance fron smelter. V;, , pg/dl GSD size (>40 pg/dl) (pg/m3) Km .* r ^ 65.9 47.7 33.8 32.2 1.30 1.32 1.25 1.29 170 192 174 156 98.9 72.6 21.4 17.8 18.0 14.0 6.7 3.1 0- l.b 1.6- 4.0 4.0-10.0 10.0-24.0 mmmMm igiPil Ms itir' r: 27.5 1.30 188 8.8 1.5 24.0-32.0 IB 21.2 1.29 90 1.1 1.2 about 75 iSiBiB aEPA analysis of data from Yankel et al. (1977). TABLE 11-28. GEOMETRIC MEAN BLOOD LEAD LEVELS BY AGE AND AREA FOR SUBJECTS LIVING NEAR THE IDAHO SMELTER (micrograms per deciliter) 111111111 11111 mgm Area 1 2 3 4 5 6 7 Age group 1 2 3 45 67 8 69* 72 50 51 33 36 31 35 27 35 21 25 28 30 75 75 68 66 63 60 55 46 49 50 47 42 36 35 35 35 31 32 34 31 31 35 30 32 29 29 29 28 25 27 22 23 20 22 20 22 28 32 30 26 37 30 *Error in original publication (Yankel et al., 1977). 9 57 40 32 30 24 17 20 Teenage 39 33 28 35 Adult Mh 37 33 30 34 32 A.'? 32 . -------- ---- - r 11-84 TEH 0412080 DUP050452679 Yankel et al. (1977) fitted the data to the following model. In (blood lead) = 3.1 + 0.041 air lead + (2.1 x 10 + 0.087 dustiness - 0.018 age + 0.024 occupation soil lead) (11-15) where air lead was in pg/m3; soil lead was in pg/g; dustiness was 1, 2, or 3; age was in years; and occupation (parental) was a Hollingshead index. The analysis included 879 sub jects, had a multiple R2 of 0.622, and a residual standard deviation of 0.269 (geometric standard deviation of 1.31). Walter et al. (1980) used a similar model to examine age specific differences of the re gression coefficients for the different variables. Those coefficients are summarized in Table 11-29. The variable that was most significant overall was air lead; its coefficient was ap proximately the same for all ages, corresponding to a change in blood lead of about 1 pg/dl per unit increase of air lead (in pg/m3) at an air exposure of 1 pg/m3 and about 2.4 pg/dl per unit increase in air at an air exposure of 22 pg/m3. TABLE 11-29. AGE-SPECIFIC REGRESSION COEFFICIENTS FOR THE ANALYSIS OF LOG (BLOOD LEAD) LEVELS IN THE IDAHO SMELTER STUDY Age Air Soil Dust Occupation Pica Sex (xlO4) Intercept N 1 0.0467* 0.119T 2 0.0405* 0.106T 3 0.0472* 0.1081 4 0.0366* 0.107T 5 0.0388* 0.052 6 0.0361* 0.070 7 D.0413* 0.053 8 0.0407* 0.051 9 0.0402* 0.081T 0.0323 0.0095 0.0252 0.0348 0.0363T 0.0369T 0.0240 0.0422T 0.0087 0.098 0.225* 0.077 0.117 0.048 0.039 0.106 0.010 0.108 0.055 0.002 0.000 0.032 -0.081 -0.092 -0.061 -0.106T -0.158* 3.5 20.6f 24.2* 32.1* 23.4* 38.4* 21.3f 16.2 11.6 3.017 3.567 3.220 3.176 3.270 3.240 3.329 3.076 3.477 98 94 115 104 130 120 113 105 104 * p <0.01 f p <0.05 The next most important variable that attained significance at a variety of ages was the household dustiness level (coded as low = 0, medium = 1, or high = 2), showing a declining ef fect with age and being significant for ages 1-4 years. This suggested age-related hygiene behavior and a picture of diminishing home orientation as the child develops. For ages 1-4 years, the coefficient indicates the child in a home with a "medium" dust level would have a 11-85 TEH 0412081 DUP050452680 r' blood lead level ~ 10 percent higher than a child in a home with a factors being comparable. The coefficients for soil lead - blood lead relationships exhibited a fairly regular pat tern, being highly significant (p <0.01) for ages 3-6 years, and significant (p <0.05) at ages 2-6 years. The maximum coefficient (at age 6) indicates a 4 percent increase in blood lead per 1000 pg/g increase in soil lead. Pica (coded absent = 0, present = 1) had a significant effect at age 2 years, but was in- significant elsewhere; at age 2 years, an approximate 25 percent elevation in blood lead is predicted in a child with pica, compared with an otherwise equivalent child without pica. Parental occupation was significant at ages 5, 6, and 8 years; at the other ages, how ever, the sign of the coefficient was always positive, consistent with a greater lead burden being introduced into the home by parents working in the smelter complex. Finally, sex (coded male = 0; female = 1) had a significant negative coefficient for ages "fV 8 and 9 years, indicating that boys would have lead levels 15 percent higher than girls at this age, on the average. This phenomenon is enhanced by similar, but nonsignificant, nega tive coefficients for ages 5-7 years. Snee (1982c) also reanalyzed the Idaho smelter data using a log-linear model. He used ji dummy variables for age, work status of the father, educational level of the father, and i household dust level (cleanliness). The resulting model had a multiple R2 of 0.67 and a res.i- dual standard deviation of 0.250 (geometric standard deviation of 1.28). The model showed that 2-year-olds had the highest blood lead levels. The blood lead inhalation slope was es sentially the same as that of-Yankel et al. (1977) and Walter et al. (1980). The above non-linear analyses of the Idaho smelter study are the only analyses which sug gest that the blood lead to air lead slope increases with increasing air lead, contrary to the findings of decreasing slopes seen at high air lead exposures in other studies. An alterna tive to this would be to attempt to fit a linear model as described in Appendix 11-B. Expo sure coefficients were estimated for each of the factors shown in Table 11-30. The results for the different covariates are similar to those of Snee (1982c) and Walter et al. (1980). Because the previous analyses noted above indicated a nonlinear relationship, a similar model with a quadratic air lead term added was also fitted. The coefficients for the other factors remained about the same, and the improvement in the model was marginally significant r- (p = 0.05). This model gave a slope of 1.16 at an air lead of 1 pg/m3, and 1.39 at an air lead of 2 pg/m3. Both the linear and quadratic models, along with Snee's (1982b) model are W shown in Figure 11-21. The points represent mean blood lead levels adjusted for the factors in Table 11-30 (except air lead) for each of the different exposure subpopulations. 11-86 TEH 0412082 DUP050452681 TABLE 11-30. ESTIMATED COEFFICIENTS* AND STANDARD ERRORS FOR THE IDAHO SMELTER STUDY Factor Coefficient Asymptotic standard error Intercept (pg/dl) Air lead (pg/m3) Soil lead (1000 pg/g) Sex'(male=l, female=0) Pica (eaters=l, noneaters=Q) Education (graduate training=0) At least high school No high school Cleanliness of home (clean=0) Moderately clean Dirty Age (1 year old=0) 2 years old 3 years old 4 years old 5 years old 6 years old 7 years old 8 years old' 9 years old Work status (no exposure=0) Lead or zinc worker 13.19 1.53 1.10 1.31 2.22 - 3.45 4.37 - 3.00 6.04 - 4.66 5.48 3.16 2.82 2.74 0.81 -0.19 -1.50 - 3.69 1.90 0.064 0.14 0.59 0.90 1.44 1.51 0.65 1.06 1.48 1.32 1.32 1.25 1.24 1.23 1.28 1.21 0.61 Residual standard deviation = 0.2576 (geometric standard deviation = 1.29). Multiple R2 = 0.662. Number of observations = 860. ^Calculations made by EPA. 11-87 TEH 0412083 DUP050452682 **r-s. ';V i*~ /$. aPPffPBi >', ,> 4 SHH'* ` i` * .i BHU i, j -Vic ;aWMBW :JWHHM Figure 11 -21. Fitted equations to Kellogg Idaho/Silver Valley adjusted blood lead data. m Jjljj & I 11-88 TEH 0412084 ; 'k- DUP050452683 Yankel et al. (1977), Walter et al. (1980), and Snee (1982c) make reference to a follow up study conducted in 1975. The second study was undertaken to determine the effectiveness of control and remedial measures instituted after the 1974 study. Between August, 1974 and August, 1975, the mean annual air lead levels decreased at all stations monitored. In order of increasing distance from the smelter, the annual mean air lead levels for the one year preceding each drawing were 18.0t 10.3 pg/m3, 14.0-8.5 pg/m3, 6.7-4.9 pg/m3, and 3.1-2.5 pg/m3 at 10-24 km. Similar reductions were noted in house dust lead concentrations. In a separate report, von Lindern and Yankel (1976) described reductions in blood lead levels of children for whom determinations were made in both years. A number of factors complicate the interpre tation of the followup study, including the changes in time-varying concentrations of air lead (Figure 11-20) from 1974 to 1975, and relocations of residence. The results demonstrated that significant decreases in blood lead concentration resulted from exposure reductions. 11.4.1.7 Omaha, Nebraska Studies. Exposure from both a primary and secondary smelter in the inner city area of Omaha, Nebraska, has been reported in a series of publications (Angle et al., 1974; Angle and Mclntire, 1977, 1979; Mclntire and Angle, 1973). During 1970-1977, chil dren were studied from these areas: an urban school at a site immediately adjacent to a small battery plant and downwind from two other lead emission sources; from schools in a mixed com mercial-residential area; and from schools in a suburban setting. Children's blood lead levels by venipuncture were obtained by macro technique for 1970 and 1971, but Delves micro assay was used for 1972 and later. The differences for the change in techniques were taken into account in the presentation of the data. Air lead values were obtained by hi-vol sam plers and dustfall values were also monitored. Table 11-31 presents the authors' summary of the entire data set, showing that as air lead values decrease and then increase, dustfall and blood lead values follow. The authors used regression models, both log-linear and semilog, to calculate (air lead)/(blood lead). Specific reports present various aspects of the work. Black children in the two elemen tary schools closest to the battery plant had higher blood leads (34.1 pg/dl) than those in elementary and junior high schools farther away (26.3 pg/dl). Best estimates of the air ex posures were 1.65 and 1.48 pg/m3, respectively (Mclntire and Angle, 1973). The latter study compared three populations: urban versus suburban high school students, ages 14-18; urban black children, ages 10-12, versus suburban whites, ages 10-12; and blacks ages 10-12 with blood lead levels over 20 pg/dl versus schoolmates with blood lead levels below 20 pg/dl (Angle et al., 1974). The urban versus suburban high school children did not differ signifi cantly, 22.3 + 1.2 and 20.2 7.0 pg/dl, respectively, with mean values of air lead concentra tions of 0.43 and 0.29 pg/m3. For 15 students who had environmental samples taken from their homes, correlation coefficients between blood lead levels and soil and housedust lead levels 11-89 TEH 0412085 DUP050452684 TABLE 11-31. AIR, DUSTFALL AND BLOOD LEAD CONCENTRATIONS IN OMAHA, NE STUDY, 1970-1977' Group Al r pg/m3 (N)b Dustfall, pg/m3 - mo (N)c All urban children,, mixed commercial and residential site 1970-71 1972-73 1974-75 1976-77 1.48 0.14(7;65) 0.43 0.08(8;72) 0.10 + 0.03(10;72) 0.52 0.07(12;47) -- 10.6 0.3(6) 6.0 0.1(4) 8.8 (7) Children at school in a commercial site 1970-71 1972-73 1974-75 1976-77 1.69 0.11(7;67) ' 0.63 0.15(8;74) 0.10 + 0.03(10;70) 0.60 0.1G(12;42) -- 25.9 0.6(5) 14.3 4.1(4) 33.9 (7) All suburban children in a residential site 1970-71 1972-73 1974-75 1976-77 0.79 0.06(7;65) 0.29 0.04(8;73) 0.12 0.05(10;73) " -- 4.6 1.1(6) 2.9 0.9(4) Blood, . pg/dl (N)a 31.4 0.7(168) 23.3 0.3(211) 20.4 0.1(284) 22.8 0.7(38) 34.6 1.5(21) 21.9 0.6(54) 19.2 0.9(17) 22.8 0.7(38) -- 19.6 0.5(81) 14.4 0.6(31) 18.2 0.3(185) aBlood lead 1970-71 is by the macro technique, corrected for an established laboratory bias of 3 pg/dl, macro-micro; all other values are by Delves micro assay. bN = Number of months; number of 24-hour samples. CN = Number of months. ^N = Number of blood samples. Source: Adapted from Angle and Mclntire, 1977. m n 111 , '!> lfilltme were 0.31 and 0.29, respectively. Air, dust, and soil lead measurements at 37 sites were inr Ji puted to all children in the vicinity. Wm Suburban 10- to 12-year-olds had lower blood lead levels than their urban counterparts, 17.1 0.7 versus 21.7 0.5 pg/dl (Angle et al., 1974). Air lead exposures were higher in the urban than in the suburban population, although the average exposure remained less than l-Mjf pg/m3. Dustfall lead measurements, however, were very much higher; 32.96 mg/m2/month for urban 10- to-12-year-olds versus 3.02 mg/m2/month for suburban children. Soil lead and house dust lead exposure levels were significantly higher for the urbanblack high-lead group than for the urban low-lead group. A significant correlation (r = 0.49) between blood lead and soil lead levels was found. 11-90 TEH 0412086 1111 .Mu-L ur~ a , DUP050452685 Angle has reanalyzed the Omaha study (Angle et al., 1984) using all of the data on chil dren from all years. There were 1075 samples from which blood lead (pg/dl), air (pg/m3), soil (pg/g), and house dust (gg/g) lead were available. The linear regression model, fitted in logarithmic form, was Pb-Blood = 15.67 + 1.92 Pb-Air + 0.00680 Pb-Soil + 0.00718 Pb-House Dust , (0.40) (+0.60) (0.00097) (0.00090) (N = 1075, R2 = 0.20, S2 = 0.0901, GSD = 1.35) (11-16) Similar models fitted by age category produced much more variable results, possibly due to small ranges of variation in air lead within certain age categories. 11.4.1.8 Roels et al. Studies. Roels et al. (1976, 1978, 1980) have conducted a series of studies in the vicinity of a lead smelter in Belgium. Roels et al. (1980) report a follow-up study in 1975 that included study'populations from a rural-nonindustrialized area as well as from the lead smelter area. The rural group consisted of 45 children (11-14 years). The smelter area group consisted of 69 school children from three schools. These children were divided into two groups; group A (aged 10-13) lived less than 1 km from the smelter and their schools were very close to the smelter; group B consisted of school children living more than 1.5 km from the smelter and attending a school more distant from the smelter. In 1974 the smelter emitted 270 kg of lead and the air lead levels were 1-2 orders of magnitude greater than the current Belgian background concentration for air lead (0.23 pg/m3). Soil and vegetation were also contaminated with lead; within 1 km the soil lead level was 12,250 gg/g. The concentration of lead in drinking water was less than 5 pg/1. Environmental assessment included air, soil, and dust. Air monitoring for lead had been continuous since September, 1973 at two sites, one for each of the two groups. In the rural area, air monitoring was done at two sites for five days using membrane pumps. Lead was ana lyzed by flameless atomic absorption spectrophotometry. Dust and soil samples were collected at the various school playgrounds, and were also analyzed by flameless atomic absorption. A 25 ml blood sample was collected from each child and immediately divided among three tubes. One tube was analyzed for lead content by flameless atomic absorption with background correc tion. Another tube was analyzed for ALA-D activity while the third was analyzed for FEP. FEP was determined by the Roels modification of the method of Sassa. ALA-D was assayed by the European standard method. 11-91 TEH 0412087 DUP050452686 A Air lead levels decreased from area A to area B. At both sites the airborne lead levelslU declined over the two years of monitoring. The amount of lead produced at this smelter durin, this time remained constant, about 100,000 metric tons/year. The median air lead level at th closer site (A) dropped from 3.2 to 1.2 gg/m3, while at the far site (B) the median went froi 1.6 to 0.5-0.8 gg/m3. The rural area exposure levels did not vary over the study period, remaining rather constant at about 0.3 gg/m3. Both smelter vicinity groups showed signs of increased lead absorption relative to the rural population. Blood lead levels for group A were about three times those for the rural ' . population (26 versus 9 pg/dl). The former blood lead levels were associated with about a 5C percent decrease in ALA-D activity and a 100 percent increase in FEP concentration. However, FEP levels were not different for group B and rural area residents. Later surveys of children (Roels et al., 1980) were conducted in 1976, 1977, and 1978; the former two in autumn, the latter in spring. In total there were five surveys conducted > yearly from 1974-1978. A group of age-matched controls from a rural area was studied each * time except 1977. In 1976 and 1978 an urban group of children was also studied. The overall age for the different groups ranged from 9 to 14 years (mean 11-12). The length of residence varied from 0.5 to 14 years (mean 7-10 years). The subjects were always recruited from the same five schools: one in the urban area, one in the rural area and three in the smelter area (two <1 km and one, 2.5 km away). Inall, 661 children (328 boys and 333 girls) were studied 1'jT" over the years. Two hundred fourteen children came from less than 1 km from the smelter, 169 children from 1.5 to 2.5 km from the plant, 55 children lived in the urban area, and 223 chi 1 - dren lived in the rural area. Air lead levels decreased from 1977 to 1978. However, the soil lead levels in the vicinity of the smelter were still elevated (<1 km, soil lead = 2000-6000 gg/g). Dustfall lead in i the area of the near schools averaged 16.4-22.0 mg/m2,day at 500 m from the stack, 5.8-7.2 mg/m2-day at 700 m, about 2 mg/m2*day at 1000 m, and fluctuated around 0.5-1 mg/m2*day at 1.5 km and beyond. The particle size was predominantly 2 gm in diameter with a secondary peak between 4 and 9 gm. The particle size declined with increasing distance from the smelter ? (0.7-2.4 km). The air lead and blood lead results for the five years are presented as Table 11-32. The reported air leads are not calendar year averages. The table shows that blood lead levels (electrothermal atomic absorption spectrophotometry) are lower in the girls than the boys. Within 1 km of the smelter no consistent improvement in air lead levels was noted over the years of the study. The mean blood leads for the children living at about 2.5 km from the smelter never exceeded 20 gg/dl since 1975, although they were higher than for urban and rural children. 11-92 TEH 0412088 DUP050452687 TABLE 11-32. MEAN AIRBORNE AND BLOOD LEAD LEVELS RECORDED DURING FIVE DISTINCT SURVEYS (1974 to 1978) FOR STUDY POPULATIONS OF 11-YEAR-OLD CHILDREN LIVING LESS THAN 1 km OR 2.5 km FROM A LEAD SMELTER, OR LIVING IN A RURAL OR URBAN AREA Study populations 1 Survey (1974) 2 Survey (1975) 3 Survey (1976) 4 Survey (1977) 5 Survey (1978) Pb-Air, Setting pg/m3 < 1 km 2.5 km Rural 4.06 1.00 0.29 <1 km 2.5 km Rural 2.94 0.74 0.31 <1 km 2.5 km Urban Rural 3.67 0.80 0.45 0.30 <1 km 2.5 km 3.42 0.49 < 1 km 2.5 km Urban Rural 2.68 0.54 0.56 0.37 Blood lead concentration. Pfl/dl Total Population Boys Girls n Mean SD n Mean SD n Mean SD 37 30.1 + 5.7 ---- 92 9.4 2.1 40 26.4 + 7.3 29 13.6 + 3.3 45 9.1 + 3.1 14 31.0 5.5 14 21.1 3.4 28 9.7 1.6 19 27.4 6.5 17 14.8 3.6 14 8.2 + 2.3. 23 29.6 5.9 ---- 64 9.3 2.2 21 25.4 8.1 12 11.9 1.9 31 9.5 3.4 38 24.6 8.7 40 13.3 4.4 26 10.4 2.0 44 9.0 2.0 18 28.7 8.0 24 15.6 2.9 17 10.6 + 2.0 21 9.2 2.3 20 20.8 7.6 16 9.8 3.8 9 9.9 2.0 23 8.7 1.7 56 28.9 6.5 50 14.8 + 4.7 27 31.7 9.5 34 15.7 4.8 29 26.4 8.7 16 13.0 4.3 43 27.8 9.3 36 16.0 3.8 29 12.7 + 3.1 42 10.7 + 2.8 20 29.3 + 9.8 26 16.6 + 3.5 18 13.4 2.3 17 11.9 3.0 23 26.5 8.9 10 14.3 4.2 11 11.5 4.0 25 10.0 2.4 Source: Roels et al. (1980). The researchers then investigated the importance of the various sources of lead in deter mining blood lead levels. Data were available from the 1976 survey on air, dust, and hand lead levels. Boys had higher hand dust lead than girls. Unfortunately, the regression analy ses performed on these data were based on the group means of four groups. EPA has reanalyzed the 1976 study using original data provided by Dr. Roels on the 148 children. The air lead, playground dust lead, and hand lead concentrations were all highly correlated with each other. The hand lead measurements are used here with due regard for their limitations, because day-to-day variations in hand lead for individual children are believed to be very large. However, even though repeated measurements were not available, this is among the most usable quantitative evidence on the role of ingested hand dust in childhood lead absorption. 11-93 TEH 0412089 DUP050452688 Total lead content per hand is probably more directly related to ingested lead than is the lead concentration in the hand dust. The linear regression model used above was fitted by EPA using lead in air (pg/m3), lead in hand dust (pg/hand), lead in playground dust (pg/g), and sex as covariates of blood lead. The lead variables were highly correlated, resulting in a statistically significant regression but not statistically significant coefficients. Thus the playground dust measurement was dropped and the following model obtained with almost as small a residual sum of squares, ln(Pb-Blood) = ln(7.37 + 2.46 Pb-Air + 0.0195 Pb-Hand + 2.10 Male) (11-17) (.45)* (.58)* (.0062)* (0.56)* *Standard error of estimated regression coefficients. The fitted model for the 148 observations gave an R2 of 0.654 and a mean square error (S2) of 0.0836 (GSD = 1.335). The significance of the estimated coefficient establishes that intake of lead-bearing dust from the hands of children does play a role in childhood lead ab sorption over and above the role that can be assigned to inhalation of air lead. Individual habits of mouthing probably also affect lead absorption along this pathway. Note too that the estimated inhalation slope, 2.46, is somewhat larger than most estimates for adults. However, the effect of ingestion of hand dust appears to be almost as large as the effect of air lead inhalation in children of this age (9-14 years). Roels et al. (1980), using group means, concluded that the quantitative contribution of hand lead to children's blood lead levels was far greater than that of air lead. The high mutual correlations among air, hand, and dust lead suggest the use of their principal components or principal factors as predictors. Only the first principal component (which accounted for 91 percent of the total variance in lead exposure) proved a statistically significant covariate of blood lead. In this form the model could be expressed as: In(Pb-Blood) = ln(7.42 + 1.56Pb-Air + 0.0120Pb-Hand + 0.00212Pb-Dust + 2.29 Male) (11-18) The estimated standard error on the inhalation slope is 0.47. The difference between these inhalation slope and hand lead coefficients is an example of the partial attribution of the effects of measured lead exposure sources to those sources that are not measured. 11.4.1.9 Other Studies Relating Blood Lead Levels to Air Exposure. The present chapter has thus far evaluated the effects of atmospheric lead on blood lead in a disaggregate manner broken down according to exposure media, including direct inhalation of atmospheric lead, ingestion of particulate lead that has fallen out as dust and surface 11-94 TEH 0412090 DUP050452689 soil, and air lead ingested in consuming food and beverages (including lead absorbed from soil and added during processing and preparation). Disaggregate analyses based on various pathways for environmental lead of the type presented appear to provide a sensitive tool for predicting blood lead burdens under changes of environmental exposure. However, some authors, e.g., Brunekreef (1984) make a strong argument for the use of air lead as the single exposure criterion. Their argument is that exposure to air lead is usually of sufficient duration that the contributions along other pathways have stabilized and are proportional to the air lead concentration. In that case, the ratio between blood lead and air lead plus dust, food, and other proportional increments must be much larger than for air lead by direct inhalation alone. The following studies provide information on the relationship of blood lead to air lead exposures using aggregate analyses that include both direct and indirect air inputs. The first group of studies are population studies which typically employed less accurate estimates of individual exposures. The second group of studies represents industrial exposures at very high air lead levels in which the response of blood lead appears to be substantially different than at ambient air levels. The Tepper and Levin (1975) study included both air and blood lead measurements. House wives were recruited from locations in the vicinity of air monitors. Table 11-33 presents the geometric mean air lead and adjusted geometric mean blood lead values for this study. These values were calculated by Hasselblad and Nelson (1975). Geometric mean air lead values ranged from 0.17 to 3.39 pg/m3, and geometric mean blood lead values ranged from 12.7 to 20.1 pg/dl. Nordman (1975) reported a population study from Finland in which data from five urban and two rural areas were compared. Air lead data were collected by stationary samplers. All levels were comparatively low, particularly in the rural environment, where a concentration of 0.025 pg/m3 was seen. Urban-suburban levels ranged from 0.43 to 1.32 pg/m3. A study was undertaken by Tsuchiya et al. (1975) in Tokyo using male policemen who worked, but not necessarily lived, in the vicinity of air samplers. In this study, five zones were established based on degree of urbanization, ranging from central city to suburban. Air monitors were established at various police stations within each zone. Air sampling was con ducted from September, 1971 to September, 1972; blood and urine samples were obtained from 2283 policemen in August and September, 1971. Findings are presented in Table 11-34. Goldsmith (1974) obtained data for elementary school (9- and 10-year-olds) and high school students in 10 California communities. Lowest air lead exposures were 0.28 pg/m3 and highest were 3.4 pg/m3. For boys in elementary school, blood lead levels ranged from 14.3 to 23.3 pg/dl; those for girls ranged from 13.8 to 20.4 pg/dl for the same range of air lead ex posures. The high school student population was made up of only males from some of the 10 towns. The air lead range was 0.77-2.75 pg/m3,, and the blood lead range was 9.0-12.1 pg/dl. 11-95 TEH 0412091 DUP050452690 TABLE 11-33. GEOMETRIC MEAN AIR LEAD AND ADJUSTED BLOOD LEAD LEVELS FOR 11 COMMUNITIES IN STUDY OF TEPPER AND LEVIN (1975) AS REPORTED BY HASSELBLAD AND NELSON (1975) Community Los Alamos, NM Okeana, OH Houston, TX Port Washington, NY Ardmore, PA Lombard, IL Washington, DC Philadelphia, PA Bridgeport, IL Greenwich Village, NY Pasadena, CA Geometric mean air lead, pg/m3 0.17 0.32 0.85 1.13 1.15 1.18 1.19 . 1.67 1.76 2.08 3.39 Age and smoking adjusted geometric mean blood lead, pg/dl 15.1 16.1 12.7 15.3 17.9 14.0 18.7 20.1 17.6 16.5 17.6 Sample size 185 156 186 196 148 204 219 136 146 139 194 Multiple R2 = 0.240 Residual standard deviation = 0.262 (geometric standard deviation = 1.30) TABLE 11-34. MEAN AIR AND BLOOD LEAD VALUES FOR FIVE ZONES IN TOKYO STUDY Zones 1 2 3 4 5 Air lead pg/m3 0.024 0.198 0.444 0.831 1.157 Blood lead, pg/100 g 17.0 17.1 16.8 18.0 19.7 Source: Tsuchiya et al. 1975. 11-96 TEH 0412092 DUP050452691 V The high school students with the highest blood lead levels did not come from the town with the highest air lead value. However, a considerable lag time occurred between the collection and analysis of the blood samples. In one of the communities the blood samples were refrig erated rather than frozen. Another California study (Johnson et al., 1975, 1976) examined blood lead levels in rela tion to exposure to automotive lead in two communities, Los Angeles and Lancaster (a city in the high desert). Los Angeles residents studied were individuals living in the vicinity of heavily traveled freeways within the city. They included groups of males and females, aged 1 through 16, 17 through 34, and 34 and over. The persons selected from Lancaster represented similar age and sex distributions. On two consecutive days, blood, urine, and fecal samples were collected. Air samples were collected from one hi-vol sampler in Los Angeles, located near a freeway, and two such samplers in Lancaster. The Los Angeles sampler collected for 7 days; the two in Lancaster operated for 14 days. Soil samples were collected in each area in the vicinity of study subjects. Lead in ambient air along the Los Angeles freeway averaged 6.3 + 0.7 pg/m3 and, in the Lancaster area, the average was 0.6 0.2 pg/m3. The mean soil lead in Los Angeles was 3633 pg/g, whereas that found in Lancaster was 66.9 gg/g. Higher blood lead concentrations were found in Los Angeles residents than in individuals living in the control area for all age groups studied. Differences between Los Angeles and Lancaster groups were significant with the sole exception of the older males. Snee (1981) has pointed out a disparity between blood samples taken on consecutive days from the same child in the study. EPA reanalyses using other criteria for outlier detection and removal obtained different inhalation slopes. This calls into question the validity of using this study to quantify the air lead to blood lead relationship. Daines et al. (1972) studied black women living near a heavily traveled highway in New Jersey. The subjects lived in houses on streets paralleling the highway at three distances: 3.7, 38.1, and 121.9 m. Air lead as well as blood lead levels were measured. Mean annual air lead concentrations were 4.60, 2.41, and 2.24 pg/m3, respectively, for the three distances. The mean air lead concentration for the area closest to the highway was significantly differ ent from that in both the second and third, but the mean air lead concentration of the third area was not significantly different from that of the second. The results of the blood lead determinations paralleled those of the air lead. Mean blood lead levels of the three groups of women, in order of increasing distance, were 23.1, 17.4, and 17.6 pg/dl, respectively. Again, the first group showed a significantly higher mean than the other two, but the second and third groups' blood lead levels were similar to each other. Daines et al. (1972), in the same publication, reported a second study in which the distances from the highway were 33.5 11-97 TEH 0412093 DUP050452692 S^.ne weiBSBawwwBag ' * l" '.' fl! > MBs SB and 457 m and in which the subjects were white upper middle class women. The air lead levels were trivially different at these two distances, and the blood lead levels did not differ v either. Because the residents nearest the road were already 33 m from the highway, the dif ferences in air lead may have been insufficient to be reflected in the blood lead levels (see Chapter 7). A summary of linear relationships for other population studies has been extracted from Snee (1981) and is shown in Table 11-35. The Fugas study is described later in Section 11.5.1.3. There is a large range of slope values (-0.1 to 3.1) with most studies in the range of 1.0-2.0. Additional information on the more directly relevant studies is given in the Summary Section 11.4.1.10. TABLE 11-35. BLOOD LEAD-AIR LEAD SLOPES FOR SEVERAL POPULATION STUDIES AS CALCULATED BY SNEE Study No. subjects Tepper & Levin (1975) Johnson et al. (1975) Nordman (1975) Tsuchiya et al. (19.75) Goldsmith (1974) . Fugas (1977) Daines et al. (1972) 1935 65 96 536 478 537 89 79 352 61 Johnson et al. (1975) Goldsmith (1974) 88a 37a 43 486 Sex Female Male Female Male Female Male Male Female Male Female (spring) Female (fall) Male (children) Female (children) Male & female (children) a0utlier results for four subjects deleted. Source: Snee, 1981. 11-98 Slope 1.1 0.8 0.8 1.2 0.6 3.1 -0.1 0.7 2.2 ` 1.6 2.4 1.4 1.1 2.0 95% confidence interval 1.8 0.7 0.6 1.0 0.9 2.2 0.7 0.7 0.7 1.7 1.2 0.6 0.6 1.3 Si!,. f sltr i fll #ftTEH 0412094 DUP050452693 A comprehensive review of studies of blood lead levels in children is presented by Brunekreef (1984). Many of the studies did not include covariates by which air lead slopes could be adjusted for dust or soil ingestion and other factors, leading to aggregate estimates of air lead impacts (direct and indirect) on blood lead levels. The results of some of the studies reviewed by Brunekreef are summarized in Table 11-36. Studies selected for Table 11-36 are those with identified air monitoring methods and reliable blood lead data. The range of p values that Brunekreef (1984) reports is very large, and typical values of 3-5 are larger than those adjusted slopes (1.52-2.46) derived by EPA in preceding sections. If the aggregate approach is accepted, then the blood lead versus total (both direct and indirect) air lead slope for children may be approximately double the slope (~2.0) estimated for the direct contribution due to inhaled air lead alone. There is a great deal of information on blood lead responses to air lead exposures of workers in lead-related occupations. Almost all such exposures are at air lead levels far in excess of typical non-occupational exposures. The blood lead versus air lead slope p is very much smaller at high blood and air levels. Analyses of certain occupational exposure studies are shown in Table 11-37. 11.4.1.10 Summary of Blood Lead versus Inhaled Air Lead Relations. Any summary of the rela tionship of blood lead level and air lead exposure is complicated by the need for reconciling the results of experimental and observational studies. Further, defining the form of the sta tistical relationship is problematical due to the lack of consistency in the range and accu racy of the air lead exposure measures in the various studies. EPA has chosen to emphasize the results of studies that relate lead in air and lead in blood under ambient conditions. At low air lead exposures there is no statistically signifi cant difference between curvilinear and linear blood lead inhalation relationships. Colombo (1985) states that on the basis of experimental biological evidence, theory can provide a steady-state relation of blood Pb to air Pb with a curved response and that the existing PbB vs. PbA data are such that they can be fitted by several algebraically different PbA func tions, including a linear relationship. Colombo concludes, however, that the linear model is preferred because it is consistent with other published models and it is much simpler in its application. Therefore EPA has fitted linear relationships (Tables 11-38, 11-39, and 11-40) to blood lead levels in the studies to be described next with the explicit understanding that the fitted relationships are intended only to describe changes in blood lead due to modest changes (of <3.0 pg/m3) in air lead among individuals whose blood lead levels do not exceed 30 pg/dl. The blood lead inhalation slope estimates vary appreciably from one subject to another in experimental and clinical studies, and from one study to another. The weighted slope and stan dard error estimates from the Griffin study in Table 11-21 (1.75 0.35) were combined with 11-99 TEH 0412095 DUP050452694 TABLE 11-36. CHARACTERISTICS OF STUDIES OH THE RELATIONSHIP BETWEEN AIR LEAD AND BLOOD LEAD IN CHILDREN \ TABLE 11-37. A SELECTION OF RECENT ANALYSES ON OCCUPATIONAL 8-HOUR EXPOSURES TO HIGH AIR LEAD LEVELS Analysis Ashford et al. (1977) King et al. (1979) Gartside et al. (1982) Study Wi 11iams et al., 1969 Globe Union Delco-Remy Factory 1, 1975 Factory 2a, 1975 Factory 3a, 1975 Delco-Remy, 1974-1976 Air lead*. pg/m3 50-300 35-1200 10-350 Bishop and Hill (1983) Battery plants A 1975-1981 B C D E F 20-170 2-200 7-170 7-195 20-140 4-140 Blood lead, pg/dl 40-90 25-90 22-72 12-50 18-72 22-60 24-75 18-60 15-53 P slope 0.19 0.10 0.032 0.07 0.0514 Nonlinear: at 50: 0.081 0.045 0.048 0.022 0.045 0.101 *Assumed 8-hour exposure; divide by 3 for 24-hour equivalent. those calculated similarly for the Rabinowitz study in Table 11-24 (2.14 0.47) and the Kehoe study in Table 11-25 (1.25 0.35, setting subject DH = 0), yielding a pooled weighted slope estimate of 1.64 0.22 pg/dl per pg/m3. There are some advantages in using these experimen tal studies on adult males, but certain deficiencies need to be acknowledged. The Kehoe study exposed subjects to a wide range of exposure levels while they were in the exposure chamber, but did not control air lead exposures outside the chamber. The Griffin study provided rea sonable control of air lead exposure during the experiment, but difficulties in defining the non-inhalation baseline for blood lead (especially in the important experiment at 3.2 pg/m3) add much uncertainty to the estimate. The Rabinowitz study controlled well for diet and other factors and since they used stable lead isotope tracers, they had no baseline problem. How ever, the actual air lead exposure of these subjects outside the metabolic ward was not well determined. Among population studies, only the Azar study provides a slope estimate in which air lead exposures are known for individuals. However, there was no control of dietary lead intake or other factors that affect blood lead levels, and slope estimates assuming only air lead and 11-101 TEH 0412097 DUP050452696 ^ <n rH 2 l CO CM rTC3-J -X L- ZO -o cn o o .o c m oi c m to c m rH v> .*> m * in - c m. * +* 4> +>7, HM<OoHVOrO**HlO<- <30 w-C<Jo>o 5--I Vrft ^CM W )M CM 0* .<71 > U3 * rH . +>CO..C..M..C..O......<.0...C.M..k.T.>..C..M..C..M CM <U + V> >> 1--I CM rH * eH rH 3 r #- <saD" o. rt i> 3 CM . VO o. t ojID. O <o t. > W S- 3 *r-- O <0 JZ 55 f. o 3C (O.. 3: >- wC 01 C^M 10 <30 M3 O r-- CM O eC 00 S. CO CL 030. OfCMliJnUC nCMM- co co r"< r*i <u a-~1 ao a. r-% ao <*> co 03 nu<)n o .l o c Qo. m*~.<M i--Ml r- rV> `rcH\2Ou`rcH,g,~g, r IAi> IBO H0O(ue01-)J*acv6rC>e-.. 4-o>. O C <0 +J c - m&. h>i &w. <e0 0L. 3<a V 41 *5 ^aol /l.*^<a00) *>c1OoC=r.,l 5 (O.: T3IArLL. <0 >0 LO- UC iUt <-PUJ aCO. - CauS>- s-o 4>f--^ Q0>.r--> w <U <ft _*JhS- w<u M r~c*na*.*voOjorv-. -t o - O+ HII Ci-oCa>Co>H>. IOCN1-1 ."9 U 01 co 3 >} I r-- "O f-- TJ O. 3N Vi Q. E S O i- EE -M J +>oi ipF- f<- L 4 i/i rH in CD L < L ZL 11-102 5,5c 4ts o >r* J 3,3C <0 3 CA CO % 5 3OCO. +u5> *f- DUP050452697 TABLE 11-39. CROSS-SECTIONAL OBSERVATIONAL STUDIES ON CHILDREN WITH ESTIMATED AIR EXPOSURES Note: PBB stands fo r blood lead ( p g /d l) ; PBA stands fo r a ir lead (pg/m3) ; slope means ra te o f change o f blood lead per u n it change in a ir lead a t the sta te d a ir lead value. The 95 percent confidence in te rv a ls fo r the slope are given in parentheses. These are approximate and should be used w ith ca u tio n . The analyses labeled "EPA" are c a lc u la te d from the o rig in a l a u th o rs' data. * d .f.= degrees o f freedom. O l> m CM. V0. io r m r-t o q>o A4- CM . I-. ^ m !--I o oO' CM U3> CO XS *- X r- -*-* &o. rue- nw>> ii a. u \ Es- Co 40J1 +t!>o- w Sia.> f- e i~ + LS 4J Oo a. r--<- 4IJfl oC U) 01 *at- ^ i UJ irt O ui Q ,w VI in VI B iiOfl o --c <a0i Oo a rc(a0t O. OcSas d u 4* u + u> O a. c--n <a-g m<1 *a3>ro citH-o4 <a3-0 O UV au 4Sn *ar-. " iH **>. tFO/--iioCMo inLO co II + m ut o w So+. xam3ao3os oC0i+aO* aooaw3a3sri <03 j 0i _< 43 O- c l 0Q3. a. O iO 03 V rt CO H . ci cn fs. re* o o co co T+T+ sc at *c r5<-n: & CO +0J1 <rJ-Ti . O A rt--o UO> Ck. 3 r- J3 i>ft 3v 'to CO C re m v-4 O- ^^2 Q as wi <h CU I re a--s '*+rc-J- CrcooM iO wa>i WosJ r--re e O*- 0.03 4J tfl v> i* s - CX3- l/rl oU<t rWOvim OoiN >s r>. flOro >o o as _ co i fiOHffli-e to 3 CO O 0P c s- u 1 lf- +3J<I- 1s3 OS >T3 O w ' 5. oi O) o/ J3 . a cs in o o r> ig deJ oc) a1 > J=41 *i- tQ-> .OO U "DWl > OnN a Sw>>- i<no in*- OU js jC= -3o'*0"3 "re C33.> *-i m 4-> QOcn) f>a-i+s*J_- 3: C _3Oc r--at > 0C1 *Ua 24S 01 Wl i-- as r r-- O* g>*- 11-103 DUP050452698 fsj dodo o*n!drH in m pH r*4 oo . *3" *'"> 3 o x3o es po: U kj p p ca. uo <v 0i TJPXl C 333 us w o <C cacO._Q ca f<_lua caXC<o<_+ irnv. a. < a. < cao. o co.ca.ca. II li II II ccaoa co aco. eaaos. co cao < o a.c m CO - a. o t o <o iH C C A3 P P <0 s** <M esi oios in* . on m 4JH H V i-l II n. II ca <c OXCM c " g a '<"1K HN . . M Al pUaj pU qi * p19*i~030'^cn lcOo OOS 3tf) U3I0H m H O O R> + tl ca*r.--arfrs-.. ca <caa<cgcpa<a< n r. c m oaa < a<Va<d.^c2a o cam. ax II II li H m as ca ca aca aca aaa caa <3 <3 <J <J ~u -a a; ai pP <0 flj r*. m r4 r-4 6Ok. kSO --I (SJ II II ca ca %% cam. II ll mma ccaaa cam. II II ecao ccoa aa * B 4> _ S E <0 C > g oi (I C V < ixinuj. n; eo. c ns c a scxvsu Of CO xEi rO*S. mos Ucr9 rH Ol -aoCt oli =ss P CroO-s *c*- w< rik~d rrooss 11-104 DUP050452699 ff, \ location as covariables (1.32 + 0.38) are not significantly different from the pooled experi mental studies. Snee and Pfeifer (1983) have extensively analyzed the observational studies, tested the equivalence of slope estimates using pooled within-study and between-study variance com ponents, and estimated the common slope. The result of five population studies on adult males (Azar, Johnson, Nordman, Tsuchiya, Fugas) was an inhalation slope estimate 95 percent confi dence limits of 1.4 0.6. For six populations of adult females [Tepper-Levin, Johnson, Nordman, Goldsmith, Daines (spring), Daines (fall)], the slope was 0.9 0.4. For four popu lations of children [Johnson (male), Johnson (female), Yankel, Goldsmith], the slope estimate was 1.3 0.4. The between-study variance component was not significant for any group so de fined, and when these groups were pooled and combined with the Griffin subjects, the slope estimate for all subjects was 1.2 0.2. The Azar slope estimate was not combined with the experimental estimates because of the lack of control on non-inhalation exposures. Similarly, the other population studies in Table 11-35 were not pooled because of the uncertainty about both inhalation and non-inhalation lead exposures. These studies, as a group, have lower slope estimates than the individual experi mental studies. There are no experimental inhalation studies on adult females or on children. The inha lation slope for women should be roughly the same as that for men, assuming proportionally smaller air intake and blood volume. The assumption of proportional size is less plausible for children. Slope estimates for children from population studies have been used in which some other important covariates of lead absorption were controlled or measured, e.g., age, sex, and dust exposure in the environment or on the hands. Inhalation slopes were estimated for the studies of Angle and Mclntire (1.92 0.60), Roels (2.46 + 0.58), and Yankel et al. (1.53 0.064). The standard error,,of the Yankel study is extremely low and a weighted pooled slope estimate for children would reflect essentially that study alone. In this case the small standard error estimate is attributable to the very large range of air lead exposures of children in the Silver Valley (up to 22 pg/m3). The relationship is in fact not linear, but increases more rapidly in the upper range of air lead exposures. The slope estimate at lower air lead concentrations may not wholly reflet uncertainty about the shape of the curve at higher concentrations. The median slope of the three studies is 1.92. This estimate was not combined with the child population studies of Johnson or Goldsmith. The Johnson study slope estimate used air lead measured at only two sites and is sensitive to assumptions about data outliers (Snee, 1981), which adds a large non-statistical uncertainty to the slope estimate. The Goldsmith slope estimate for children (2.0 0.65) is close to the estimate derived above, but was not used due to non-statistical uncertainties about blood lead collection and storage. 11-105 i! I Ji ii TEH 0412101 DUP050452700 mamm : 'i 'l' ,, One can summarize the situation briefly: ** Ml * , m&SmHr h w<1*1 * 1 n (1) The experimental studies at lower air lead levels, 3.2 pg/m3 or less, and lower blood levels, typically 30 pg/dl or less, have linear blood lead inhalation rela tionships with slopes p. of 0-3.6 for most subjects. A typical value of 1.64 0.22 may be assumed foradults. (2) Population cross-sectional studies at lower air lead and blood lead levels are approximately linear with slopes f3 of 0.8-2.0 for inhalation contributions. (3) Cross-sectional studies in occupational exposures in which air lead levels are higher (much above 10 pg/m3) and blood lead levels are higher (above 40 pg/dl), show a much more shallow linear blood lead inhalation relation. The slope p is in the range 0.03-0.2. (4) Cross-sectional and experimental studies at levels of air lead somewhat above the higher ambient exposures (9-36 pg/m3) and blood leads of 30-40 pg/dl can be described either by a nonlinear relationship with decreasing slope or by a linear relationship with intermediate slope, approximately p = 0.5. Several biological mechanisms for these differences have been discussed (Hammond et al., 1981; 0`Flaherty et al., 1982; Chamberlain, 1983; Chamberlain and Heard, 1981). Since no explanationfor the decrease in steepness of the blood lead inhalation response to higher air lead levels has been generally accepted at this time, there is little basis on which to select an interpolation formula from low air lead to high air lead exposures. The increased steepness of the inhalation curve for the Silver Valley/ Kellogg study is inconsistent with the other studies presented. It may be that smelter situations are unique and must be analyzed differently, or it may be that the curvature is the result of impre cise exposure estimates. (5) The blood lead inhalation slope for children is at least as steep as that for adults, with a median estimate of 1.92 from three major studies (Yankel et al., 1977; Roels et al., 1980; Angle and Mclntire, 1979). (6) Slopes which include both direct (inhalation) and indirect (via soil, dust, etc.) air lead contributions are necessarily higher than those estimates for inhaled air lead alone. Studies using aggregate analyses (direct and indirect air impacts) typically yield slope values in the range 3-5, about double the slope due to inhaled air lead alone. aWM -r>i -i 9 'MW '.111 11.4.2 Dietary Lead Exposures Including Water Another major pathway by which lead en^jrs the body is by ingestion. As noted in Chap ters 6 and 7, the recycling of both natural and anthropogenic lead in the environment results in a certain amount of lead being found in the food we eat and the water we drink. Both of these environmental media provide external exposures to lead that ultimately increase internal exposure levels in addition to internal lead elevations caused by direct inhalation of lead in air. The Nutrition Foundation (1982) report presents a compilation of recent estimates of 11-106 TEH 0412102 DUP050452701 dietary intakes in the United States and Canada. The report gives information on relation ships between external lead exposures and blood lead levels. The mechanisms and absorption rates for uptake of lead from food and water are described in Chapter 10. The purpose of the present section is to establish (analogously to Section 11.4.1) the relationships between external exposures to lead in food and drinking water and resulting internal lead exposures. The establishment of these external and internal lead exposure relationships for the en vironmental media of food and water, however, is complicated by the inherent relationship be tween food and water. First, the largest component of food by weight is water. Second, drinking water is used for food preparation and, as shown in Section 7.3.1.3, provides addi tional quantities of lead that are appropriately included as part of external lead exposures ascribed to food. Third, the quantity of liquid consumed daily by people varies greatly and substitutions are made among different sources of liquid: soft drinks, coffee, tea, etc., and drinking water. Therefore, at best, any values of water lead intake used in drinking water calculations are somewhat problematic. A further troubling fact is the influence of lead in the construction of plumbing facil ities. Studies discussed in Section 7.3.2.1.3 have pointed out the substantial lead exposures in drinking water that can result from the use of lead pipes in the delivery of water to the tap. This problem is thought to occur only in limited geographic areas in the United States. However, where the problem is present, substantial water lead exposures occur. In these areas one cannot make a simplifying assumption that the lead concentration in the water component of food is similar to that of drinking water; rather, one is adding a potentially major addi tional lead exposure to the equation. Studies that have attempted to relate blood lead levels to ingested lead exposure have used three approaches to estimate the external lead exposures involved: duplicate meals, fe cal lead determinations, and market.basket surveys. In duplicate diet studies, estimated lead exposures are assessed by having subjects put aside a duplicate of what they eat at each meal for a limited period of time. These studies probably provide a good, but short term, estimate of the ingestion intake. However, the procedures available to analyze lead in foods have his torically been subject to inaccuracies. Hence, the total validity of data from this approach has not been established. Studies relying on: the use of fecal lead determinations face two major difficulties. First, this procedure involves the use of a mathematical estimate of the overall absorption coefficient from the gut to estimate the external exposure. Until recent ly, these estimates have not been well documented and were assumed to be relatively constant. Newer data discussed later show a much wider variability in the observed absorption coeffici ents than was thought to be true. These new observations cloud the utility of studies using this method to establish external/internal exposure relationships. Secondly, it is difficult to collect a representative sample. 11-107 TEH 0412103 DUP050452702 The last approach is the market basket approach. This approach uses the observed leaflfil concentrations for a variety of food items coupled with estimated dietary consumption of the particular food items. Some studies use national estimates of typical consumption patterns.' upon which to base the estimated exposures. Other studies actually record the daily dietary#! intakes. This approach faces similar analytic problems to those found in the duplicate diet^ approach. It also faces the problem of getting accurate estimates of dietary intakes. The 4, most current total diet study (Pennington, 1983) is described in Section 7.3.1.2. Exposures to lead in the diet are thought to have decreased since the 1940`s. Estimates..! from that period were in the range of 400-500 pg/day for U.S. populations. Khandekar et al. (1984) report a dietary intake of lead to be 245 pg/day. This was calculated from the lead content in different food groups and the amount of each food group consumed by an average resident of Bombay, India. Current estimates for U.S. populations are under 100 pg/day for '* adults. Unfortunately, a good historical record regarding the time course of dietary expo sures is not available. In the years 1978-1982, efforts have been made by the American food canning industry in cooperation with the FDA to reduce the lead contamination of canned fuod. Data presented in Section 7.3.1.2.5 confirm the success of this effort. Seasonal variations in blood lead might also be partially attributable to seasonal variations in the dietary in take of lead. The following evidence suggests that this does not happen. Table 11-41 is taken from Human Nutrition Information Service (1983). The data suggest the following pattern: (1) Consumption of canned vegetables and fruits is much lower in the spring and summer, much higher in the fall and winter, which is the opposite of the pattern of blood lead level variations and suggests that theattributionof seasonal changes to gasoline lead may be an underestimate of its effects. (2) Thepattern is similar for central city, suburban, and nonmetropolitan households. (3) There is. little seasonal variation for fruit and vegetable juices and milk, and a slight increase of soft drink consumption in the summer. The magnitude of such variations is too small to account for blood lead. The specific studies available for review regarding dietary exposures will be organized into three major divisions: lead ingestion from typical diets, lead ingestion from experimen tal dietary supplements, and inadvertent lead ingestion from lead plumbing. 11.4.2.1 Lead Ingestion from Typical Diets. 11.4.2.1.1 Ryu study on infants and toddlers. Ryu et al. (1983) reported a study of four breast-fed infants and 25 formula-fed infants from 8-196 days of age. At 112 days of the study, the formula-fed infants were separated into subgroups based upon how they were to re ceive their milk: homogenized whole cow milk obtained in cartons from a local dairy, a com mercially available milk-based formula supplied in quart cans, and homogenized whole cow milk 11-108 TEH 0412104 DUP050452703 \ TABLE 11-41. HOUSEHOLD CONSUMPTION OF CANNED FOODS (pounds per week) Food Canned fruits* Central city Suburban Nonmetropolitan Canned vegetables* Central city Suburban Nonmetropolitan Fresh fluid milk Central city Suburban Nonmetropolitan Processed milk Central city Suburban Nonmetropolitan Canned veg. juices* Central city Suburban Nonmetropolitan Canned fruit juices* Central city Suburban Nonmetropolitan Soft drinks (total) Central city Suburban Nonmetropolitan Spring 0.65 0.85 0.83 2.37 2.40 2.37 13.44 17.66 15.11 1.14 1.43 1.56 0.39 0.42 0.56 1.34 1.16 1.29 5.50 6.53 5.67 Summer 0.47 0.55 0.62 2.36 2.08 1.94 14.20 17.12 16.17 1.12 1.13 1.36 0.38 0.41 0.38 1.46 1.26 1.22 5.75 6.88 5.89 Fall 0.59 0.84 0.78 2.81 2.57 2.46 14.31 17.38 16.16 1.18 1.10 1.59 0.37 0.54 0.46 1.39 1.25 1.49 5.11 6.22 5.62 Commercially canned. Winter 0.74 0.91 0.85 2.83 2.86 2.89 13.75 17.17 16.70 1.30 1.14 1.90 0.35 0.47 0.53 1.41 1.24 1.35 5.35 5.96 5.25 supplied in quart cans and heat-treated in the same manner as the commercially available for mula. There were 10, 4, and 3 infants in each of these groups, respectively. In addition to food concentrations, data were collected on air, dust, and water lead. Hemoglobin and FEP were also measured. 11-109 TEH 0412105 DUP050452704 The trends in blood lead for the formula-fed infants are shown in Table 11-42. The re sults up to day 112 are averaged for all 25 infants. The estimated average intake was 17 pg/day for this time period. After day 112, the subgroup of seven infants fed either canned formula or heat-treated cow's milk in cans (higher lead), had average estimated lead intake of 61 pg/day. This resulted in an increase of 7.2 pg/dl in the average blood lead level in response to an increase of 45 pg/day in lead intake by day 196. However, since the blood lead levels in this group had not reached equilibirum by this point, the slope calculated from this data of 0.16 should be regarded as an underestimate. TABLE 11-42. BLOOD LEAD LEVELS AND LEAD INTAKE VALUES FOR INFANTS IN THE STUDY OF RYU ET AL. Age, days 8 28 56 84 112 140 168 196 Blood lead of combined group, pg/dl 8.9 5.8 5.1 5.4 6.1 Lower lead Higher lead 6.2 9.3 7.0 12.1 7.2 14.4 Average lead intake of combined group, pg/day 17 17 17 17 17 Lower lead Higher lead 16 61 16 61 16 61 Source: Ryu et al. (1983). 11.4.2.1.2 Rabinowitz infant study. As part of a longitudinal study of the sources of cur rent urban lead exposure, lead was measured in 100 breast milk samples and in 73 samples of the infant formula used by non-nursing mothers (Rabinowitz et al., 1985a). Also, the blood lead levels of the infants fed these diets were determined at birth and at six months of age. Among the infants who were breast-fed, the lead content of their milks correlated very well with their six-month blood lead levels (r = 0.42, p = 0.0003). The mean lead content of in fant formulas and breast milk were not significantly different, nor was the blood lead of children fed one or the other. Lead levels in maternal milk correlated poorly with umbilical cord blood lead (r = 0.18, p = 0.10). Since milk represents much of the diet of young infants and because breast milk lead levels are stable, it is possible to relate blood lead and daily dosage in this population. -Aft 11-110 -IL TEH 0412106 DUP050452705 11.4.2.1.3 Rabinowitz adult study. This study on male adults was described in Section 11.4.1 and in Chapter 10, where ingestion experiments were analyzed in more detail (Rabinowitz et al., 1980). As in other studies, the fraction of ingested stable isotope lead tracers ab sorbed into the blood was much lower when lead was consumed with meals (10.3 2.2 percent) than between meals (35 13 percent). Lead nitrate, lead sulfide, and lead cysteine as car riers made little difference. The much higher absorption of lead on an empty stomach implies greater significance of lead ingestion from leaded paint and from dust and soil when consumed between meals, as seems likely to be true for children. 11.4.2.1.4 Hubermont study. Hubermont et al. (1978) conducted a study of pregnant women liv ing in rural Belgium because their drinking water was suspected of being lead-contaminated. This area was known to be relatively free of air pollution. Seventy pregnant women were re cruited and asked to complete a questionnaire. Information was obtained on lifetime residence history, occupational history, smoking, and drinking habits. First flush tap water samples were collected from each home with the water lead level determined by flameless atomic absorp tion spectrophotometry. Biological samples for lead determination were taken at delivery. A venipuncture blood sample was collected from the mother, as was a fragment of the placenta; an umbilical cord blood sample was used to estimate the newborn's blood lead status. For the entire population, first-flush tap water samples ranged from 0.2 to 1228.5 pg/1. The mean was 109.4, while the median was 23.2. The influence of water lead on the blood lead of the mother and infants was examined by categorizing the subjects on the basis of the lead level of the water sample, below or above 50 pg/1. Table 11-43 presents the results of this study. A significant difference in blood lead levels of mothers and newborns was found for the water lead categories. Placenta lead levels also differed significantly between water lead groups. The fitted regression equation of blood lead level for mothers is given in summary Table 11-51 in section 11.4.2.4. 11.4.2.1.5 Sherlock studies. Sherlock et al. (1982) reported a study from Ayr, Scotland, which considered both dietary and drinking water lead exposures for mothers and children living in the area. In December, 1980, water lead concentrations were determined from kettle water from 114 dwellings in which the mother and child lived less than five years. The adult women had venous blood samples taken in early 1981 as part of a European Economic Community (EEC) survey on blood lead levels. A duplicate diet survey was conducted on a random sample of these 114 women stratified by kettle water lead levels. A study population of 11 mothers with infants less than 4 months of age agreed to parti cipate in the infant survey. A stratified sample of 31 of 47 adult volunteers was selected to participate in the duplicate diet study. Venous blood samples for adults were analyzed for lead immediately before the duplicate diet study; in some instances additional samples were taken to give estimates of long-term 11-111 TEH 0412107 DUP050452706 TABLE 11-43. INFLUENCE OF LEVEL OF LEAD IN WATER ON BLOOD LEAD LEVEL IN BLOOD AND PLACENTA Comparison group Age (years) Pb-B mother (pg/dl) Pb-B newborn (pg/dl) Pb placenta (MS/100 g) Water Pb (pg/i) Water level Low** High*** Low High Low High Low High Low High Mean 25.6 26.3 10.6 13.8 8.8 12.1 9.7 13.3 11.8 247.4 Median 24 25 9.9 13.1 8.5 11.9 8.2 12.0 6.3 176.8 Range 18-41 20-42 5.1-21.6 5.3-26.3 3.4-24.9 2.9-22.1 4.4-26.9 7.1-28 0.2-43.4 61.5-1228.5 Significance NS* <0.005 <0.001 <0.005 Source: Hubermont et al. (1978) *NS means not significant. **Water lead <50 pg/1. ***Water lead >50 pg/1. IPf mm*: ;f^cISlIsP exposure. Venous samples were taken from the infants immediately after the duplicate diet 'W week. Blood lead levels were determined by AAS with a graphite furnace under good quality control. Two other laboratories analyzed .each sample by different methods. The data reported,gii are based on the average value of the three methods.. t'* Dietary intakes for adults and children were quite different; adults had higher intakes than children. Almost one-third of the adults had intakes greater than 3 mg/week while only 20 percent of the infants had that level of intake. Maximum values were 11 mg/week for adults ' and 6 mg/week for infants. The observed blood lead values in the dietary study had the dis- ^ tributions shown in Table 11-44. Table 11-45 presents the crosstabulation of drinking water lead and blood lead level for the 114 adult women in the study. A strong trend of increasing blood lead levels with increa* sing drinking water lead levels is apparent. A curvilinear regression function fits the data better than a linear one. A similar model including weekly dietary intake was fitted to the data for adults and infants. These models are in summary Tables 11-49 and 11-52 in Section 11.4.2.4. 11-112 TEH 0412108 DUP050452707 V TABLE 11-44. DISTRIBUTIONS OF OBSERVED BLOOD LEAD VALUES IN AYR Groups Adults Infants EEC directive >20 pg/dl 55% 100% 50% Blood lead values >30 pg/dl 16% 55% 10% >35 pg/dl 2% 36% 2% Blood lead. pg per 100 ml <10 11-15 16-20 21-25 26-30 31-35 36-40 >40 Total TABLE 11-45. BLOOD LEAD AND KETTLE WATER LEAD CONCENTRATIONS FOR ADULT WOMEN LIVING IN AYR Water lead, pg/1 11- 100- 300- 500- 1000- <10 99 299 499 999 1499 >1500 85 47 3 2 1 13 12 3 3 49 7 5 2442 2122 3 1111 143 3 13 19 28 19 19 8 8 Total 13 17 22 25 12 10 4 11 114 The researchers also developed a linear model for the relationship between dietary intake and drinking water lead. The equation indicates that, when the concentration of lead in water was about 100 pg/1, approximately equal amounts of lead would be contributed to the total week's intake from water and diet; as water lead concentrations increase from this value, the principal contributor would be water. A follow-up study on this same population was made from December, 1982 to March, 1983, as reported by Sherlock et al. (1984). In April 1981, the pH of the water supply was increased from pH 4.5-5.5 to about pH 8.5 by the addition of lime. The result was a decrease in the median blood lead level from 21 to 13 pg/dl. The combined data set was used to give the re gression equation shown in Table 11-52 in Section 11.4.2.4. 11-113 TEH 0412109 DUP050452708 11.4.2.1.6 Central Directorate on Environmental Pollution study. The United Kingdom Centra]>' V Directorate on Environmental Pollution (1982) studied the relationship between blood leaa1'. level and dietary and drinking water lead in infants. Subjects were first recruited by sol c 1 '1 iting participation of all pregnant women attending two hospitals and residing within a single,/)* water distribution system. Each woman gave a blood sample and a kettle water sample. The',.-! . * -i women were then allocated to one of six potential study groups based on the concentration of , water lead. At the start of the second phase (duplicate diet) a total of 155 women volunteered! jgp* (roughly 17-32 per water lead level category). During the course of the study, 24 mothers'"*' withdrew; thus a final study population of 131 mothers was achieved. When the children reached 13 weeks of age, duplicate diet for a week's duration was ob tained for each infant. Great care was exerted to allow collection of the most accurate sample possible. Also, at this time a variety of water samples were collected for subsequent lead analysis. Blood samples were collected by venipuncture from mothers before birth, at delivery, ana about the time of the duplicate diet. A specimen was also collected by venipuncture from die infant at the time of the duplicate diet. The blood samples were analyzed for lead by graph ite furnace AAS with deuterium background correction. Breast milk was analyzed analogously to . the blood sample after pretreatment for the different matrix. Water samples were analyzed by flame atomic absorption; food samples were analyzed after ashing by flameless atomic absorp tion. Both mothers and infants exhibited increased lead absorption by EEC (European Economic Community) directive standards. The infants generally had higher blood leads than the mothers. However, in neither population was there evidence of substantial lead absorption. Water lead samples ranged from less than 50 to greater than 500 pg/1, which was expected due to the sampling procedure used. First draw samples tended to be higher than the other fff samples. The composite kettle samples and the random daytime samples taken during the dupli cate diet week were reasonably similar: 59 percent of the composite kettle samples contained up to 150 pg/1, as did 66 percent of the random daytime samples. Lead intakes from breast milk were lower than from duplicate diets. The lead intakes estimated by duplicate diet analysis ranged from 0.04 to 3.4 mg/week; about 1/4 of the diets ,,,V had intakes less than 1.0 mg/week. The minimum intakes were truncated, as the limit of detec tion for lead was 10 pg/kg and the most common diets weighed 4 kg or more. The central directorate data were reanalyzed by Lacey et al. (1985). Resultsfrom both .T Lacey et al. (1985) and the United Kingdom Central Directorate on Environmental Pollution (1982) are in Tables 11-49 to 11-52 in section 11.4.2.4. The authors used both linear and " cube root models to describe their data. Models relating blood lead levels of infants to 11-114 TEH 0412110 DUP050452709 dietary intake are in Table 11-49 in Section 11.4.2.4. Models relating blood lead levels for both mothers and infants to first flush water lead levels and running water lead levels are in Tables 11-51 and 11-52 in Section 11.4.2.4 respectively. In most cases, the nonlinear (cubic) model provided the best fit. Figure 11-22 illustrates the fit for the two models showing in fant blood lead levels versus dietary lead intake. 11.4.2.1.7 Pocock study. Pocock et al. (1983) have recently reported an important study ex amining the relationship in middle-aged men of blood lead level and water lead levels. Men aged 40-59 were randomly selected from the registers of general practices located in 24 British towns. Data were obtained between January, 1978 and June, 1980. Blood lead levels were obtained on 95 percent of the 7378 men originally selected. The levels were determined by microatomic absorption spectrophotometry. A strict internal and ex ternal quality control program was maintained on the blood lead determinations for the entire study period. Tap water samples were obtained on a small subset of the population. About 40 men were chosen in each of the 24 towns to participate in the water study. First draw samples were collected by the subjects themselves, while a grab daytime and flushed sample were col lected by study personnel. These samples were analyzed by several methods of AAS depending on the concentration range of the samples. Blood lead and water lead levels were available for a total of 910 men from 24 towns. Table 11-46 displays the association between blood lead levels and water lead levels. Blood lead levels nearly doubled from the lowest to highest water lead category. The investigators analyzed their data further by examining the form of the relationship between blood and water lead. This was done by categorizing the water lead levels into nine intervals of first draw levels. The first group (<6 pg/1) had 473 men while the remaining eight intervals had ~ 50 men each. Figure 11-23 presents the results of this analysis. The authors state, "The impression is that mean blood lead increases linearly with first draw water lead except for the last group with very high water concentrations." The regression line shown in the figure is only for men with water lead levels less than 100 pg/1, and is given in Table 11-51 in Section 11.4.2.4. A separate regression was done for the 49 men whose water lead exposures were greater than 100 pg/1. The slope for the second line was only 23 percent of the first line. Additional analyses were done examining the possible influence of water hardness on blood lead levels. A strong negative relationship (r = 0.67) was found between blood lead level and water hardness. There is a possibility that the relationship between blood lead and water hardness was due to the relationship of water hardness and water lead. It was found that a relationship with blood lead and water hardness still existed after controlling for water lead level. 11-115 TEH 0412111 DUP050452710 \ 50 0 1.0 2.0 3.0 4.0 LEAD INTAKE mg/wk Figura 11-22. Blood lead concentrations versus weekly lead intake for bottle-fed infants. (Numbers are coincidental points.) Source: United Kingdom Central Directorate on Environmental Pollution (1982). 11-116 DUP050452711 p \ TABLE 11-46. RELATIONSHIP OF BLOOD LEAD AND WATER LEAD IN 910 MEN AGED 40-59 FROM 24 BRITISH TOWNS First draw water lead, ljg/1 <50 50-99 100-299 300 Number of men 789 69 40 12 Mean blood lead (pg/di) 15.06 18.90 21.65 34.19 Standard deviation 5.53 7.31 7.83 15.27 % with blood lead >35 jjg/dl 0.7 4.3 7.5 41.7 Total Daytime water lead, pg/T <50 50-99 100-299 300 910 845 36 23 5 15.89 15.31 19.62 24.78 39.78 6.57 1.9 5.64 7.89 9.68 15.87 0.7 8.3 17.4 60.0 Total 909 Source: Pocock et al. (1983). 15.85 6.44 1.8 11-117 TEH 0412113 DUP050452712 r \ The authors come to the following conclusion regarding the slope of the relationship be tween blood lead and water lead: This study confirms that the relation is not linear at higher levels. Previous research had suggested a power function relationship--for example, blood lead in creases as the cube root of water lead. Our data, based on a large and more representative sample of men, do not agree with such a curve, particularly at low concentrations of water lead. 11.4.2.1.8 Thomas study. Thomas et al. (1981) studied blood lead levels among residents of a hardwater area in the United Kingdom. They recruited a random sample of voters in an area with 320 ppm calcium hardness. A tap water sample using first draw water was requested and was returned by 70 percent of the selected voters. Sixty women in the dwellings with the highest water blood level and 30 randomly selected women in dwellings in the lowest water lead levels were selected for a blood lead determination; 84 women responded. Blood lead levels were stratified by water lead levels and were compared to data gathered elsewhere from softwater areas. Substantial differences were noted, with the residents of the hardwater areas having meaningfully lower blood lead levels. This is true even for residents in the hardwater area with the lowest (<0.05 mg/1) water lead level. 11.4.2.1.9 Elwood study. Elwood et al. (1983) have investigated the potential of the degree of water hardness to influence the relationship between lead concentrations in drinking water and blood lead level. An experimental model was employed wherein two groups of women were studied both before and after the water hardness of the drinking water for one group was changed to 100 from 10 mg/1. Postconversion blood lead levels were obtained 6 months later. Mean water lead levels fell slightly after the change in the area where the water was hardened, whereas it increased slightly in the central area. Blood lead levels decreased in the experimental areas while increasing in the central area. The decline in blood lead levels was greater with increasing initial water lead levels. 11.4.2.2. Lead Ingestion from Experimental Dietary Supplements. 11.4.2.2.1 Kehoe study. Experimental studies have been used to study the relationship of food lead and blood lead levels. Gross (1981) reanalyzed the results of Kehoe. Oral doses of lead included 300, 1000, 2000, and 3000 pg/day. Each subject had a control period and an ex posure period. Some also had a post-exposure period. Blood samples were collected by veni puncture and analyzed by spectrographic and dithizone methods during the study years. The ingestion doses were in addition to the regular ingestion of lead from the diet. The results of the dose response analysis for blood lead concentrations are summarized in Table 11-47. 11-119 TEH 0412115 DUP050452713 , iSBl` TABLE 11-47. DOSE--RESPONSE ANALYSIS FOR BLOOD LEAD LEVELS IN THE KEH0E STUDY AS ANALYZED BY GROSS (1981) ^Bmam Subject SW MR EB IF2 Added lead, pg/day 300 1000 2000 3000 Difference from control1 Diet, pg/day Feces, pg/day 308 1072 1848 208 984 1547 Urine, pg/day 3 55 80 2981 2581 49 Blood, pg/dl -1 17 33 19 -m ^Each subject servced as his own control. 2Subject did not reach equilibrium. Both subjects MR and EB had long exposure periods, during which time their blood lead levels increased to equilibrium averages of 53 and 60 pg/dl, respectively. The exposure' for- f; / i IF was terminated early before his blood lead had achieved equilibrium. No response in blood lead was seen for subject SW whose supplement was 300 pg/day. -j." 11.4.2.2.2 Stuik study. Stuik (1974) administered lead acetate in two dose levels (20 and 30 > pg/kg*day) to volunteers. The study was conducted in two phases. The first phase was con-. (.> ducted for 21 days during February-March, 1973. Five males and five females aged 18-26 were* exposed to a daily dose of 20 pg Pb2+/kg. Five males served as controls. In the second^ ^ ' phase, five females received 20 pg Pb2+/kg and five males received 30 pg Pb2+/kg. H- H females served as controls. Pre-exposure values were established during the week preceding the exposures in both phases. Blood lead levels were determined by Hessel's method. The results of phase I for blood lead levels are presented in Figure 11-24. Blood lead levels appeared to achieve an equilibrium after 17 days of exposure. Male blood lead levels went from 20.6 to 40.9 pg/g while females went from 12.7 to 30.4 pg/g. The males seemed to respond more to the same body weight dose. .. In phase II, males were exposed to a higher lead dose (30 pg/kg*day). Figure 11-25 dis- ^ .j plays these results. Male blood lead rose higher than in the first study (46.2 versus #4P. 9.' pg/g); furthermore, there was no indication of a leveling off. Females also achieved a higher" blood lead level (41.3 versus 30.4 pg/dl), which the author could not explain. The pre exposure level, however, was higher for the second phase than the first phase (12.7 versus, 17.3 pg/g). 11-120 TEH 0412116 DUP050452714 \ Figure 11-24. Average PbB levels. Exp. I. Source: Stuik (19741. DAYS Figure 11-25. Average PbB levels, Exp. II. Source: Stuik (1974). H-121 TEH 0412117 ~ DUP050452715 \ 11.4.2.2.3 Cools study. Cools et al. (1976) extended the research of Stink (1974) by randc ly assigning 21 male subjects to two groups. The experimental group was to receive a 30 body weight dose of oral lead acetate for a period long enough to achieve a blood lead of 30.0 pg/g, when the lead dose would be adjusted downward to attempt to maintain the sii jects at a blood lead level of 40.0 pg/g. The other group received a placebo. In the pre-exposure phase, blood lead levels were measured three times, while during posure they were measured once a week, except for the first three weeks when they were deter- mined twice a week. Blood lead was measured by flame AAS according to the Westerlund modifi-'| cation of Hessel's method. Pre-exposure blood lead values for the 21 volunteers averaged 172 ppb. The effect of', ingestion of lead acetate on blood lead is displayed in Figure 11-26. After 7 days, mean blood lead levels had increased from 17.2 to 26.2 pg/g. The time to reach a blood lead level of 35.0 pg/g took 15 days on the average (range 7-40 days). 11.4.2.2.4 Schlegel study. Schlegel and Kufner (1979) report an experiment in which two sub- jects received daily oral doses of 5 mg Pb2+ as an aqueous solution of lead nitrate for 6 and 13 weeks, respectively. Blood and urine samples were taken. Blood lead uptake (from 16-60' pg/dl in 6 weeks) and washout were rapid in subject HS, but less so in subject GK (from 12-29 pg/dl in 6 weeks). Time series data on other heme system indicators (FEP, ALA-D, ALA-U, coproporphyrin III) were also reported. 11.4.2.2.5 Chamberlain study.. This study (Chamberlain et al., 1978) was described in Section 11.4.1, and in Chapter 10. The ingestion studies on six subjects showed that the gut absorp tion of lead was much higher when lead was ingested between meals. There were also differ ences in absorption of lead chloride and lead sulfide. 11.4.2.3 Inadvertent Lead Ingestion from Lead Plumbing. 11.4.2.3.1 Early studies. Although the use of lead piping has been largely prohibited in recent construction, occasional episodes of poisoning from this lead source still occur. These cases most frequently involve isolated farms or houses in rural areas, but a surprising urban episode was revealed in 1972 when Beattie et al. (1972a,b) showed the seriousness of the situation in Glasgow, Scotland, which had very pure, but soft, drinking water as its soured. The researchers demonstrated a clear association between blood lead levels and inhibition of IB the enzyme ALA-D in children living in houses with (1) lead water pipes and lead water tanks, r. (2) no lead water tank but with more than 60 ft of lead piping, and (3) less than 60 ft of lead piping. The mean lead content of the water as supplied by the reservoir was 17.9 pg/1; those taken from the faucets of groups 1, 2, and 3 were 934, 239, and 108 pg/1, respectively. lip B 11-122 iV TEH 0412118 DUP050452716 \ PbB. ppb DOSE. Mg/kg DAYS Figure 11-26. Lead in blood (mean values and range) in volunteers. In the lower curve the average daily lead dose of the exposed group is shown. Source: Cools et al. (1976). 11-123 TEH 0412119 DUP050452717 Another English study (Crawford and Crawford, 1969) showed a clear difference between' bone lead contents of the populations of Glasgow and London, the latter having a hard, nons vent water supply. In a study of 1200 blood donors in Belgium (De Graeve et al., 1975 persons from homes with lead piping and supplied with corrosive water had significantly hig blood lead levels. 11.4.2.3.2 Moore studies. Moore and colleagues have reported on several studies relati blood lead levels to water lead levels. Moore (1977) studied the relationship between b lead level and drinking water lead in residents of a Glasgow tenement. The tenement supplied with water from a lead-lined water tank carried by lead piping. Water samples we-e collected during the day. Comparative water samples were collected from houses with coppepipes and from 15 lead-plumbed houses. Blood samples were taken wherever possible from all inhabitants of these houses. The data indicated that if a house has lead-lined pipes, it is' almost impossible to reach the WHO standard for lead in water (100 pg/1). Linear regression equations relating blood lead levels to first flush and running water lead levels are Tables 11-51 and 11-52 in Section 11.4.2.4. Moore (1977) also reported the analysis of blood lead and water lead data collected over a four-year period for different sectors of the Scottish population. The combined data showed consistent increases in blood lead levels as a function of first draw water lead, but the-equation was nonlinear at the higher range. The water lead values were as high as 2000 pg/1. The fitted regression equation for the 949 subjects is in Table 11-51 in Section 11.4.2.4. Moore et al. (1981a,b) reported a study of the effectiveness of control measures for plumbosolvent water supplies. In autumn and winter of 1977, they studied 236 mothers aged 17-37 in a postnatal ward of a hospital in Glasgow with no historical occupational expo sure. Blood lead and tap water samples from the home were analyzed for lead by AAS under sU quality control program. A skewed distribution of blood lead levels was obtained with a median value of 16.6 pg/dl; 3 percent of the values exceeded 41 pg/dl. The geometric mean was 14.5 pg/dl. A cur vilinear relationship between blood lead level and water lead level was found. The log of the maternal blood lead varied as the cube root of both first flush and running water lead concen trations. In Moore et al. (1979), further details regarding this relationship are provided.' Figure 11-27 presents the observed relationship between blood lead and water lead. In April, 1978, a closed loop lime dosing system was installed. The pH of the water was _ . raised from 6.3 to 7.8. Before the treatment, more than 50 percent of random daytime water' samples exceeded 100 pg/1, the WHO standard. After the treatment was implemented, 80 percent of random samples were less than 100 pg/1. It was found, however, that the higher pH was not1 maintained throughout the distribution system. Therefore, in August, 1980, the pH was raised 11-124 TEH 041212 DUP050452718 \ 23.5 25 24 26 25 24 WATER LEAD, mM 23 UP TO IOj M NO IN GROUP Figure 11 -27. Cube root regression of blood lead on first flush water lead. This shows mean S.D. of blood lead for pregnant women grouped in 7 intervals of first flush water lead. Source: Moore et al. (1979). 11-125 TEH 0412121 DUP050452719 to 9 at the source, thereby maintaining the tap water at 8. At this time, more than 95 pe of random daytime samples were less than 100 gg/1. In the autumn and winter of 1980, 475 mothers from the same hospital were studied, median blood lead was 6.6 gg/dl and the geometric mean was 8.1 pg/dl. Comparison of the quency distributions of blood lead between these two blood samplings show a remarkable dr No other source of lead was thought to account for the observed change. Sherlock et al. (1984) report that water treatment produced a sharp fall in water le concentrations and a decrease in the median blood lead concentrations from 21 to 13pg/dl 11.4.2.3.3 Thomas study. Thomas et al. (1979) studied women and children residing on tw adjacent housing estates. One estate was serviced by lead pipes for plumbing while the 6th was serviced by copper pipe. In five of the homes in the lead pipe estate, the lead pipe had been replaced with copper pipe. The source water is soft, acidic, and lead-free. Water samples were collectedfrom the cold tap in the kitchen in each house on three oc casions at two-week intervals. The following water samples were collected: daytime - 1'ui water out of tap at time of visit; running - collected after tap ran moderately for 5 minutes after the daytime sample; and first flush - first water out of tap in morning (collected by residents). Lead was analyzed by a method (unspecified in report) that was reportedly under quality control. Blood samples were collected from adult females (2.5 ml venipuncture) who spent most of the time in the home and from the youngest child (capillary sample). Blood samples were ana lyzed for lead by a quality-controlled unspecified method. Blood lead levels were higher in the residents of the lead estate homes than in the residents of the copper estate homes. Median levels for adult females were 39 and 14.5 pg/dl for the lead and copper estate homes, respectively. Likewise, children's blood lead levels were 37 and 16.6 pg/dl, respectively. Water lead levels were substantially higher for the lead estate than for the copper estate. This was true for all three water samples. The researchers then monitored the effectiveness of replacing the lead pipe on reducing both exposure to lead in drinking water and, ultimately, blood lead levels. This monitcri was done by examining subsamples of adult females for up to 9 months after the change wa implemented. Water lead levels became indistinguishable from those found in the copper estate homes. Blood lead levels declined about 30 percent after 3-4 months and 50 percent at and 9 months. At 6 months the blood lead levels reached those of women living in the copper estates. A small subgroup of copper estate females was also followed during this time. . N. o " decline was noted among them. Therefore, it was very likely that the observed reduction in blood lead levels among the other women was due to the changed piping. 11-126 TEH 0412122 DUP050452720 \ The researchers then analyzed the form of the relationship between blood lead levels and water lead levels. They tried several different shapes for the regression line. Curvilinear models provided better fits. Figure 11-28 depicts the scatter diagram of blood lead and water lead. An EPA analysis of the data is in Table 11-51 in Section 11.4.2.4. A later publication by Thomas (1980) extended his earlier analysis. This more extensive analysis was limited to lead estate residents. Subjects who did not consume the first drawn water from the tap had significantly lower blood lead levels than those who did (10.4 pg/dl difference). No gradient was noted in blood lead levels with increasing water consumption. Furthermore, no gradient in blood lead levels was noted with total beverage consumption (tea ingestion frequency). 11.4.2.3.4 Worth study. In Boston, Massachusetts, an investigation was made of water distri bution via lead pipes. In addition to the data on lead in water, account was taken of socio economic and demographic factors as well as other sources of lead in the environment (Worth et al., 1981). Participants, 771 persons from 383 households, were classified into age groups of less than 6, 6-20, and greater than 20 years of age for analysis. A clear association between water lead and blood lead was apparent (Table 11-48). For children under 6 years of age, 34.6 percent of those consuming water with lead above the U.S. standard of 50 pg/1 had a blood lead value greater than or equal to 35 pg/dl, whereas only 17.4 percent of those con suming water within the standard had blood lead values of greater than or equal to 35 pg/dl. Worth et al. (1981) have published an extensive regression analysis of these data. Blood lead levels were found to be significantly related to age, education of head of household, sex, and water lead exposure. Of the two types of water samples taken, standing grab sample and running grab sample, the former was shown to be more closely related to blood lead levels than the latter. Regression equations are given in Tables 11-51 and 11-52 in Section 11.4.2.4. 11.4.2.4 Summary of Dietary Lead Exposures. Including Water. It is difficult to obtain accu rate dose-response relationships between blood lead levels and lead levels in food or water. Dietary intake must be estimated by duplicate diets or fecal lead determinations. Water lead levels can be determined with some accuracy, but the varying amounts of water consumed by dif ferent individuals add to the uncertainty of the estimated relationships. Studies relating blood lead levels to dietary lead intake are compared in Table 11-49. Two studies had subjects with relatively high dietary lead intakes. In the Sherlock et al. (1982) study, 10 of 31 subjects had lead intake levels greater than 300 pg/day. In the United Kingdom Central Directorate study (1982), 12 of 110 subjects had levels greater than 300 pg/day. These concentrations are high enough that the slope is clearly lower in this range than it is in the 0-100 pg/day range. The estimates of slopes for the cube root models may be overestimates in the low range (0-100 pg/day) for the reasons discussed in section 11.4. 11-127 TEH 0412123 DUP050452721 \ BLOOD LEAD. piM/liter 0 1.0 2.0 FIRST FLUSH WATER LEAD mg liter 3.0 Figure 11 28 Relation of blood lead (adult female) to first flush water lead in combined estates. (Numbers are coincidental points: 9 = 9 or more.) Curve a. present data; curve b. data of Moore eta/. (1979). 11-128 TEH 0412124 DUP050452722 TABLE 11-48. BLOOD LEAD LEVELS OF 771 PERSONS IN RELATION TO LEAD CONTENT OF DRINKING WATER, BOSTON, MA Blood lead levels, pg/dl <35 >35 Total Persons consuming water (standing grab samples) <50 pg Pb/1 No. Percent 50 pq Pb/1 No. Percent Total 622 91 61 9 68 77.3 20 22.7 690 81 683 100 88 100.0 771 X2 = 14.35; df = 1. p <0.01. Source: Worth et al. (1981). Conversely, the linear equation is probably an underestimate. The slope from the Ryu study was estimated directly from changes in infants and is the best estimate available. The esti mates for adults are more accurately estimated from the experimental studies. The experimental studies are summarized in Table 11-50. Most of the dietary intake sup plements were so high that many of the subjects had blood lead concentrations much in excess of 30 pg/dl for a considerable part of the experiment. Blood lead levels thus may not com pletely reflect lead exposure, due to the previously noted nonlinearity of blood lead response at high exposures. The slope estimates for adult dietary intake are about 0.02 pg/dl increase in blood lead per pg/day intake, but consideration of blood lead kinetics may increase this value greatly. Such values are a bit lower than those estimated from the adult population studies extrapolated to typical dietary intakes in Table 11-49, about 0.05 pg/dl per pg/day. The value for infants is much larger. The studies relating first flush and running water lead levels to blood lead levels are in Tables 11-51 and 11-52, respectively. Many of the authors chose to fit cube root models to their data, although polynomial and logarithmic models were also used. Unfortunately, the form of the model greatly influences the estimated contributions to blood lead levels from relatively low water lead concentrations. As indicated in section 11.4, the models producing high estimated contributions are the cube root models and the logarithmic models. All others are polynomial models, either linear, quadratic, or cubic. The slopes of these models tend to be relatively constant at the origin. 11-129 TEH 0412125 DUP050452723 TABLE 11-49. STUDIES RELATING BLOOD LEAD LEVELS ( | ig / d l) TO DIETARY INTAKES (g g /d a y ) XU Q.T3 o 0> TS P P *o i^p SO5OfeI5>-t' u 1o e SfS a2. +uco'5nji r-* d sy P pn xft>. rtJ O E O "D o t-- <-- fO C-J +tf>> J r--4IZ pH d o CO is 10 r- CM d d o ro o + + <c II U CsJ O CO r--t_ 0rH*1 <*-/ JZ v> O CM O CO -- o> U r- sp 0 nj o C s- s- s- P O <- *r* C P > P r-s o<y u c = c m - -I- C O rH o a*>p oc - >,e "IS fc o co <o c sj *a > P 3O . >,J= tj *,55 *S O in T3 iJi XeU rn--] J CM C 5- > --O CcO* D3 p 0e+JcXSs S_ p- C. O 0> P CJ wr- O O < > 5 11-130 >*`4- to r- P 3 W c0 re p p J_ S- l/> C pO ro ) C P psP O 31 UN C Cl CJ QJ CO -- t- cn ' - -- co ,<a p ecn p --o 10 >, P -O p DUP050452724 dc?\otfvlf i- u> r- vsdi o rH <U rH 3. -- WHO SlOls H H rH m * id csj c *-- ss e 4m* Oa? Tr3e It <U <- 4 > +* *0*0 <J 3 5 r- iS$ 05 c c <u 0) 0(0*010 *100 *100 <VoJ -(a0 -- /> *>100> *><0B> *>1p9^ *>100* VI C I/I c-S *v0 a4Jn"O wws +J 4-> V) 01 U) Sp<"tf 'o<*0- Q> S 4J *J *J 333 `OO 'OO 'aQ in m in D Cfl +J -O3 41 5 + V) 3 IO 4-* 4> U) 01 fsa*d-i 4 6id <sR uJ- 4- +* +J s's'a *0<0 *010*O0 mm m *3a *3o OQo *3iod 4J4J4J4J *3 '3 3 3 aor<*9 *<o0 *raa := 13 2 ^f" *3o 4-> l/> *a ro0--1i ai t fCT. ivf>* J < ! VH >VJI-J"I v .2 t Wo Cm ^ 3< O TJ d a s. in xaww Ui u <c <c 11-131 TEH 0 4 1 2 T 2 7 X DUP050452725 TABLE 11-51. STUDIES RELATING BLOOD LEAD LEVELS (p g /d l) TO FIRST-FLUSH WATER LEAD ( g g /I) SIS u 43 +$5 *q *<3o -aQ*. a o -CJ <--<u 3: uj o V0 rat up V0 O crj IH c*> CM v 03 lOOHO cn raj l > in mOQ 00<rirHsp opomcvj o =r M3 c m r*J d -} r-i CM M wo uiood Q CM rtgOIISI ndpo rlHN|\J q-OQQ cm o o cm rn as H rtHrt *m q o p> p*-' <si H H ri cn of rn r-4 O od r*. cv r-t r-4 dd + w <cyn*N&oi ras A> 3: c 4o3. So-*r* PoM <u" oo cUn I 3 JoS=>-4u3Ji a.a. +O -a crt + e CM O r* -- CM 3 <0 QU S wa. o3<u CO so vQ H * a. r-t X . t- tn n- 4<=U T33 C *-> r-- O c- II + o r-sCV CJOOO. 3X>3 PO3 wfl. O * p o co s u Ccn- n33 ra> X&o. 3 a. CM 43 >wen c m a. O LO P* OQHH . . v^f*> rat O O e Oo + + + <~ a MOO |l 2`S.viI a. co - a. WiH CM O VO r-t r-i ii ii ii o.:g as co ai a. XXfl c Q. G. Q. ra- OTHHffl I II II H cCcM CcMc x-s. PIH> Or-t tcfo> W'M'Ol uu 55^ C CM uPuOP S*S3>tf UC re a. Z3 =9 -l UJ t- s <w o *J <- <2 CM O O </) oa> <po 4- C C <-- a o ir-e -o >a> roe -* oo +V3>) ObpS01-0i~3 r-.t tU f3lj . p*. rat 0 r- a 00 P CJ>\ *J 01 I- c o> <- o j ^- zuo C cco E . -ra eg O 3 r-- PH t 44J1 nyft)oV5 *oj -acani xi (on c J 3 41 H 4J 4. /V -- V fc. 3o CM 3C > re tucn o c m C V- o s. O <-- P =3 r- <U CD ? tr^. *r- 4J ' - .j m a S. ONO O BH(*1 ca _ >. CM J- 3>0OU M b -O VlSglD . t Os- --4H-a- CV "V. rs *r o Ol m "0 0 3, HCOO / o> oira m EC0 . ra P3 tUo VCOM *4 cos+> OOCCI * c COlra0>- p =Lra4 un us go. i- . 0.0 CO E i. 4-4 CM O OO O CV L. .O r"> SHV ccov ouroorao aa a H- U--* o o+J vi oV> -Nra. +4 S- t<-u po 3. CM 4u4+ji-v0o E5 POi-Ott-EHJHW p >, or fc. u> o p3 w m *po Pe +j -- c p Jtl VU3 3r CM O O tn 43 4- or w to mtS- Jj o CO a vo c m n --. rat T3 11-132 3>a 00e >- JtCn SaOv* tOra t. ifl >s a S3 a 4J 3 no ra> P P Ml U fJ CO u 3e o SO fljra Cl to s-o a U C 4-4 OU P1 3<40 .Mm 9 ::il iiigiii DUP050452726 TABLE 11-52. STUDIES RELATING BLOOD LEAD LEVELS Mg/<n) TO RUNNING WATER LEAD (Mg/1)( TEH 0 4 1 2 1 2 9 i <5 > m S3* u0o> ****r- c4>1 a. cOy-CrT, to 41 *-> xa ? IBO. CB O 6 0-00 M Ot X lOS eg * o* V CO CO Is rH H e- n. n*. oido ^ tp ^ TOO WNN pC rH rH V h* P. tndo co ro co tfr O O do n ro pdoo ow p- coo* m 10 <o C0 rH ro pv CO P- ddri Oo p - ddd a\ c m co nod CO 10 CO *t cd aj ^ SO 10 to p-T pC CO I-H eg co <d 10 o> ro rd id c m r-H <Tl to <o co c m eg m O O r-I OMH CaO CoO CoT> CM \0 10 rlOH odd c m eg o CM rH CM odd 2c ex. O LO +J CM o y3 P* Hr "C $** s. Q_ p* xUa: 3* +>*/-> AOO +OJ jaa. _+ sui CO HtOPs C m- - a l t j co <- H04J CM ww CQ CO II || --ri0&S'O'" id ph <5 rH 10 (mw o e CO --c oVW 4(oJ0- CO 11 II u Hfiffl Al XI -Q ll a- a- t. xs c c *- ASS w.o a?. + CO O HN ^efi + +~r CO r-C || O WOD'-'O HHg mX cJ3o c i 4Li~ CM CM g (/) sua.n S- U aa cc uat uat soua. -c2* 2- o. ro . WCO N-o O rH Gt CO - w3 . O XI CM CO. P- r-t 03 O II II SQa.^oO CO 03 I CC 0) 41 ou dsdte xxuj 51 a. eM o o -- cn t_ rH o o* O CO r cn uu ta-t 2 S- O > b. C *- .1 e li co u> CTV -U ii ewe> o(c i *c o <A 3> SmSu UaSo rH a r- --* >a co co cu r m r- i. t- <o**s.r4 +aat a-t as_ U <M O g O bO b S- I <UCMM r- +pH a 10 TJ lcn in> 5 IbB. +UJ1V- e -a y to at O 4- W 25S -o-io fc. <*- C t. r- 25 "& H3i *10 O PO* Ifl 01 r- lf> s fj +J 7t tM X3 41 a) osc CT c=ds . *H^ V *= x S , " ^ ts 3 CmJ T3 aW4_J Tm3 ---a U3 r<C0*0CtOie-'vi K IAO 3r 1 aj 2-a -- ao oo 3 OS 11-133 *-- r-- 3 bTIT)JL' DUP050452727 The problem of determining the most appropriate model(s) at low water lead leve (0-25 jjg/1) is extremely difficult. Most data sets estimate a relationship that is primari based on water lead levels of 50-2000 pg/1, and the problem becomes essentially a lowextrapolation problem. The only study which estimates the relationship based primarily lower water lead levels (<100 pg/1) is the Pocock et al. (1983) study. The data from thi study, as well as the authors themselves, suggest that in this lower range of water lea levels, the relationship is linear. Furthermore, the contributions to blood lead levels esti mated from this study are quite consistent with the polynomial models from the other firstflush water lead studies, such as Worth et al. (1981), United Kingdom Central Directorate on Environmental Pollution (1982), and Thomas et al. (1979). For these reasons the Pocock et al. (1983) slope of 0.06 is our best estimate for first-flush water lead studies. The slopes for running water lead studies are about 1.5 to 2.0 times as large. The possibility does exist, however, that the higher initial slopes from the cube-root and logarithmic models are correct. 11.4.3 Studies Relating Lead in Soil and Dust to Blood Lead The relationship of exposure to lead contained in soil and house dust, and the amount of lead absorbed by humans, particularly children, has been the subject of scientific investiga tion for some time (Duggan and Williams, 1977; Barltrop, 1975; Creason et al., 1975; Barltrop et al., 1974; Roberts et al., 1974; Sayre et al., 1974; Ter Haar and Aronow, 1974; Fairey and Gray, 1970). Duggan and Williams (1977) published an assessment of the risk of increased blood lead resulting from the ingestion of lead in dust. Some of these studies have been con cerned with the effects of such exposures (Barltrop, 1975; Creason et al., 1975; Barltrop et al., 1974; Roberts et al., 1974; Fairey and Gray, 1970); others have concentrated on the means by which the lead in soil and dust becomes available to the body (Sayre et al., 1974; Ter Haar and Aronow, 1974; Brunekreef et aT., 1983). 11.4.3.1 Omaha, Nebraska Studies. The Omaha studies were described in Section 11.4.1.7. Soil samples were 2-inch cores halfway between the building and the lot line. Household dust was collected from vacuum cleaner bags. The following analysis was provided courtesy of Dr. Angle. The model is also described in Section 11.4.1.8, and provided the coefficients and standard errors shown in Table 11-53. 11.4.3.2 Stark Study. Stark et al. (1982) used a large-scale lead screening program in New Haven, Connecticut, during 1974-77 as a means of identifying study subjects. The screening program had blood lead levels on 8289 children, ages 1-72 months, that represented about 80 percent of the total city population in that age group. From this initial population, a much smaller subset of children was identified for a detailed environmental exposure study. Using the classifying criteria of residential stability and repeatable blood lead levels (multiple m 11-134 TEH 0-412130 DUP050452728 \ TABLE 11-53. COEFFICIENTS AND STANDARD ERRORS FOR OMAHA STUDV MODEL Factor Coefficient Asymptotic Standard Error Intercept (pg/dl) Air lead (pg/m3) Soil lead (mg/g) House dust (mg/g) 15.67 1.92 6.80 7.18 0.398 0.600 0.966 0.900 Multiple R2 = 0.198 Sample size = 1075 Residual standard deviation = 0.300 (geometric standard deviation = 1.35) measurements fell into one of three previously defined blood lead concentration categories), a potential study population of 784 was identified. Change of residence following identifica tion and refusal to let sanitarians make inspections.resulted in 407 children being dropped; the final study population contained 377 children. With the exception of dietary lead intake, each child's potential total external lead exposure was assessed. Information was obtained on lead in air, house dust, interior and exterior paint, and soil near and far from the home. A two percent sample of homes with children having elevated lead levels had tap water lead levels assessed. No water lead levels above the public health service standard of 50 pg/1 were found. Socioeconomic variables were also obtained. For all children in the study, micro blood samples were taken and analyzed for lead by AAS with Delves cup attachment. Blood lead values were found to follow a lognormal distri bution. Study results were presented using geometric means and geometric standard deviation. Among the various environmental measurements a number of significant correlation coefficients were observed. However, air lead levels were independent of most of the other environmental variables. Environmental levels of lead did not directly follow socioeconomic status. Most of the children, however, were in the lower socioeconomic groups. Multiple regression analyses were performed by Stark et al. (1982) and by EPA*, using all 926 blood lead measurements. Stark and coworkers derived a log-log model with R2 = 0.11, and no significant effects of race or age were found. EPA fitted a linear exposure model in loga rithmic form with results shown in Table 11-54. Significant differences among age groups were *N0TE: The term EPA analyses refers to calculations done at EPA. A brief discussion of the methods used is contained in Appendix 11-B; more detailed information is available at EPA upon request. 11-135 TEH 04T2T31 DUP050452729 TABLE 11-54. MULTIPLE REGRESSION MODELS FOR BLOOD LEAD OF CHILDREN IN NEW HAVEN, CONNECTICUT, SEPTEMBER 1974 - FEBRUARY 1977 Covariate Regression Coefficients and Standard Errors Ages o-:L yr Ages 2-3 yr Ages 4-7 yr Summer - winter Dust, pg/g Housekeeping quality Soil near house, pg/g Soil at curb, pg/g Paint, child's bedroom Paint outside house Paint quality Race = Black 6.33 2.11* 0.00402 0.00170* 4.38 2.02* 0.00223 0.00091* 0.00230 0.00190 0.0189 0.0162 -0.0023 0.0138 0.89 1.71 2.16 2.05 3.28 1.30* 0.00182 0.00066* 1.75 1.17 -0.00016 0.00042 0.00203 0.00082* 0.0312 0.0066* 0.0200 + 0.0069* 3.38 0.96* 0.07 + 1.09 Residual standard deviations Multiple R2 Sample size (blood samples) ' 0.1299 0.289 153 0.0646 0.300 334 ^Significant positive coefficient, one-tailed p <0.05. 2.43 1.38* 0.00022 + 0.00077 -1.61 1.12 0.00060 0.00041 0.00073 0.00079 0.0110 0.0064* 0.0172 0.0067* 4.14 1.15* 5.81 1.00* 0.1052 0.143 439 noted, with considerably improved predictability (R2 = 0.29, 0.30, 0.14 for ages 0-1, 2-3, and 4-7). Sex was not a significant variable, but Race = Black was significant at ages 4-7. Air lead did not significantly improve the fit of the model when other covariates were available, particularly dust, soil, paint, and housekeeping quality. However, the range of air lead levels was small (0.7-1.3 pg/m3) and some of the inhalation effect may have been confounded with dust and soil ingestion. Seasonal variations were important at all ages. ERA analyses of data from children in New Haven (Stark et al., 1982) found substantial evidence for dust and soil lead contributions to blood lead, as well as evidence for increased blood lead due to decreased household cleanliness. These factors are somewhat correlated with each other, but the separate roles of increased concentration and cleanliness could be distin guished. Overall dust, soil, and paint lead levels were not presented in the published papers, but data presented by year of housing construction indicate that meaningful lead expo sures were present. Geometric mean dust lead levels varied from 239 ppm for houses built in 11-136 TEH 0412132 DUP050452730 1960-1969 to 756 ppm for those built in 1910-1919. Soil lead levels varied from 131 ppm to 1273 ppm for 1970-1977 and 1920-1929, respectively. 11.4.3.3 The Silver Valley/Kellogg Idaho Study. The Silver Valley/Kellogg Idaho study was discussed in section 11.4.1.6. Yankel et al. (1977) showed that lead in both soil and dust was independently related to blood lead levels. In their opinion, 1000 pg/g soil lead ex posure was cause for concern. Walter et al. (1980) showed that children aged 3 through 6 showed the strongest relationship between soil lead and blood lead, but 2-year-olds and 7-year olds also had a significant relationship (Table 11-29). The slope of 1.1 for soil lead (1000 pg/g) to blood lead (pg/dl) represents an average relationship for all ages. The Silver Valley-Kellogg Idaho study also gave some information on house dust lead, al though this data was less complete than the other information. Regression coefficients for these data are in Tables 11-29 and 11-30. In spite of the correlation of these predictors, significant regression coefficients could be estimated separately for these effects. 11.4.3.4 Blood Lead Levels of Dutch City Children. Brunekreef et al. (1983) reported on a very extensive study on blood lead and environmental variables in native Dutch children 4-6 years old. Three hundred seventy-one children participated in the blood lead survey and 195 children in the environmental study as well. The environmental evaluation was carried out in April-June 1981 in the cities of Rotterdam, the Hague, and Zoetermeer. Blood was sampled by venipuncture. The environmental variables included: In the home of each child: lead in drinking water (one first-draw sample) lead deposition indoors, using 2 greased deposition plates per home and an averaging time of 4 weeks lead in floor dust, using a special vacuum cleaner to take 2 duplicate samples 4 weeks apart lead in 0-5 cm top soil in gardens, if present In living area: lead deposition outdoors on 5-10 spots per area with an averaging time of 4 weeks lead in street dust using the vacuum cleaner method, taking 30-40 duplicate samples per area on 2 occasions 4 weeks apart In the classroom/school: lead in drinking water (one running sample) lead deposition indoors, applying 2 plates in 2 classrooms per school with an averag ing time of 4 weeks lead in floor dust, taking 2 duplicate samples in 2 different classrooms per school, 4 weeks apart lead in playground dust, using the vacuum cleaner method to take 4 duplicate samples on two occasions 4 weeks apart lead in 0-5 cm top soil in playground lead on dominant hand of child, after playing outdoors for at least 30 minutes in school playground on a dry day. 11-137 TEH 0412133 DUP050452731 Resulting blood lead levels and environmental lead measurements are shown in Tables il; to 11-58. Multiple regression analyses were done by Brunekreef et al. in logarithmic rather linear form. The equation is as follows. In PbB = 1.882 + 0.163c In (lead deposition outdoors) - 0.003b (year of construc tion - 1900) + 0.135k (hand dirtiness) - O.SSO1"* (milk consumption) + 0.1161 3u (presence of pets) + 0.106 (mouthing behavior) - 0.069 (number of rooms) ap <0.01. Dp <0.005. cp <0.001. ap <0.0001. (11-19) Multiple regression analysis for combined inner city and suburban populations give the following: n = 193, R2 = 0.519, F-total = 28.5. Lead deposition outdoors was an important factor, but only in the combined sample, so confounding cannot be ruled out. This appears, however, to be the single most important environmental source, particularly in conjunction with hand dirtiness and with mouthing behavior. Further analyses of these data are proposed. The difference of about 2 pg/dl between city and suburban children (adjusted for all other covariates) can hardly be attri buted to direct inhalation of ambient air lead which differs slightly from city to suburb (0.12-0.13 pg/m3), and hence must be attributed to other pathways. The large coefficient for milk reflects the known importance of calcium in lead metabolism and is also related to mouth ing behaviors, including pica. The presence of pets probably increases the exposure to dirt. This study thus corroborates the importance of various non-inhalation pathways for lead in children, particularly the dust-hand-mouth pathway. Dr. Brunekreef has (personal communication, February 8, 1984) fitted his data on Dutch children to a linear model in logarithmic form, as the Environmental Protection Agency has done elsewhere in the present document. The regression coefficients are all statistically significant, and variables are as in his 1983 paper. The logarithmic linear model had vari ance s2 = 0.06272 and R2 = 0.521; it thus provided an (insignificantly) better description of the data than the original log-log model. 11.4.3.5 Charney Study. Charney et al. (1980) conducted a case control study of children ages 1.5-6 with highly elevated and non-elevated blood lead levels. Cases and controls were initially identified from the lead screening programs of two Rochester, New York, health facilities. Cases were defined as children who had at least two blood lead determinations between 40 and 70 pg/dl and FEP values greater than 59 pg/dl during a 4-month period. Con trols were children who had blood lead levels equal to or less than 29 pg/dl and FEP equal to m 11-138 TEH 0412134 DUP050452732 TABLE 11-55. AIR LEAD LEVELS IN THE ROTTERDAM AREA (BRUNEKREEF ET AL., 1983) Sampling location Rotterdam (center) Maassluis (upwind suburb) Geometric mean air lead level in pg/m3 January-March, 1981 April-June, 1981 0.27 0.22 0.14 0.10 TABLE 11-56. BLOOD LEAD LEVELS IN pg/100 ml FOR CHILDREN WHO PARTICIPATED IN BLOOD SURVEY AND ENVIRONMENTAL SURVEY3 City Rotterdam (center) Rotterdam (suburb) The Hague Zoetermeer Number 54 72 16 53 Geometric mean 13.1 8.2 11.5 7.9 Range 7-31 5-15 7-21 4-15 Percentile 50 90 98 13 19 23 8 11 14 11 19 ' 21 8 11 14 difference between city and suburb significant (t-test on arithmetic means; p <0.001). TABLE 11-57. SCHOOL VARIABLES (ARITHMETIC MEANS) FOR MEASURED LEAD CONCENTRATIONS City Rotterdam3 Rotterdam0 Zoetermeer*3 In drinking water, pg/i 6 1 1 Deposition indoors, pg/m2/d 11.74 4.29 4.59 On floors, pg/m2 100 29 40 On schoolyard, pg/m2 1120 364 337 In sandy playground mg/kg 6 5 6 aInner city. ^Suburb. 11-139 TEH 0412135 DUP050452733 TABLE 11-58. RESULTS OF LEAD MEASUREMENTS REPORTED BY BRUNEKREEF ET AL. (1983) 1 ' ' ;____________________________________________________________________________________________________________ __________________ _ City Concentration Range 2 Lead deposition outdoors (arithmetic mean, ng/m /d) Rotterdam? 643 394-957 Rotterdam" 220 144-315 The Hague3. 369 317-439 Zoetermeer 125 73-278 2 Lead on streets (geometric mean, yg/m ) Rotterdam? 532 168-2304 Rotterdam" 318 113-1155 The Hagueab Zoetermeer0 428 126 81-1339 46-497 n 9 6 5 10 37 36 10 21 t-test ' , ' :ljIfiBiBili p <0.001 --1 p <0.003 s-- p <o.doi p <0.001 IiBHmHI Ii i Ih K p <0.005 p <0.005 mUm p <0.001 p <0.001 Lead in garden soil (geometric mean, mg/kg) Rotterdam? 336 Rotterdam0 43 6-184 The Hague3. 278 35-527 Zoetermeer0 21 3-75 2 Lead deposition indoors (geometric mean, yg/m Vd) Rotterdam? 2.86 0.10-20.86 Rotterdam" 0.99 0.10-8.40 The Hague3. 4.32 1.95-27.05 Zoetermeer0 1.51 0.48-4.40 2 Lead on floors (geometric mean, yg/m ) Rotterdam? 81 5-740 Rotterdam" 30 1-410 The Hague3. 58 22-166 Zoetermeer0 32 3-201 1 56 6 33 48 67 13 49 43 62 11 50 p <0.001 p <0.001 sinni p <0.001 p <0.001 Ih Hh p <0.001 p <0.001 ^*|S p <0.001 p <0.001 p <0.025 p <0.025 i> * tflaKv & Lead in drinking water (geometric mean, jjg/1) Rotterdam? 20 1-126 46 p <0.001 Rotterdam^ 2 1-50 60 p <0.001 The Hague3. 21 1-85 16 p <0.001 Zoetermeer0 1 1-4 53 p <0.001 Lead on hands (geometric mean, yg/hand) Rotterdam? 12 Rotterdam . 5 Zoetermeer" 4 1-96 1-21 1-18 44 p <0.001 65 p <0.001 37 p <0.001 aInner city. ^Suburb. 11-140 i V* -1 'ijpHHi TEH 0412136 I . *uT -U DUP0504S2734 or less than 59 jjg/dl. High-level children were selected first and low-level children were group-matched based on age, area of residence, and social class of the family. Home visits were made to gain permission as well as to gather questionnaire and environmental data. Lead analyses of the various environmental samples were done at several different laboratories. No specification was provided regarding the analytical procedures followed. The matching procedure worked well for age, and mother's educational level and employment status. There were more blacks in the high lead group as well as more Medicaid support. These factors were then controlled in the analysis; no differences were noted between the high and low blood lead groups regarding residence on high traffic density streets (>10,000 vehi cles/ day) or census tract of residence. The two groups differed regarding mean house dust lead levels (1265 pg/sample for high and 123 pg/sample for low). Median values also differed, 149 versus 55 pg/sample. One-third of the children in the low blood lead group had house dust lead samples with more lead than those found in any middle class home previously investigated. There were considerably greater quantities of lead on the hands of the high blood lead group compared with the low lead group (mean values were 49 and 21 pg/sample, respectively). Hand and house dust lead levels were correlated (r = 0.25) but the relationship was not linear. At the low end of the house dust lead values, hand dust was always low but the con verse was not true: not every child exposed to high house dust lead had high hand dust levels. In addition to hand and house dust lead, other factors differentiated the high and low blood lead groups. Although both groups had access to peeling paint in their homes (~2/3), paint lead concentrations exceeding 1 percent were found more frequently in the high as oppo sed to the low group. Pica (as defined in Chapter Seven) was more prevalent in the high lead group as opposed to the low lead group. Since the data suggested a multi factorial contribution of lead, a multiple regression analysis was undertaken. The results suggest that hand lead level, house dust lead level, lead in outside soil, and history of pica are very important in explaining the observed vari ance in blood lead levels. 11.4.3.6 Charleston Studies. In one of the earliest investigations regarding soil lead expo sures, Fairey and Gray (1970) conducted a retrospective study of lead poisoning cases in Charleston, South Carolina. Two-inch core soil samples were collected from 170 randomly selected sites in the city and were compared with soil samples taken from homes where 37 cases of lead poisoning had occurred. The soil lead values obtained ranged from 1 to 12,000 pg/g, with 75 percent of the samples containing less than 500 pg/g. A significant relationship between soil lead levels and lead poisoning cases was established; 500 pg/g was used as the 11-141 TEH 0412137 DUP050452735 cutpoint in the chi-square contingency analysis. Fairey and Gray were the first to examine ~*v this complex problem and, although their data support the soil lead hypothesis, the relatii - ship between soil lead and blood lead levels could not be quantified. Furthermore, because other source of lead was measured, any positive association could have been confounded bvi.ji, |ts| additional sources of lead, such as paint or air. .. A later study by Galke et al. (1975), in Charleston, used a house-to-house survey to re-<p,, 1 cruit 194 black preschool children. Soil, paint, and air lead exposures, as measured by oraf-Vf* fic density, were established for each child. When the population was divided into two groups,/;'* based on the median soil lead value (585 pg/g), a 5 pg/dl difference in blood lead levels was,*", " obtained. Soil lead exposure for this population ranged from 9 to 7890 pg/g. Vehicle traffic' r* patterns were defined by area of recruitment as being high or low. A multiple regression'.. lf analysis of the data showed that vehicle traffic patterns, lead level in exterior siding' ^ paint, and lead in soil were all independently and significantly related to blood lead levels.* > Using the model described in Appendix 11B, the following coefficients and standard errors were;'1}: obtained as shown in Table 11-59. V TABLE 11-59. COEFFICIENTS AND STANDARD ERRORS FROM MODEL OF CHARLESTON STUDY smm Factor Coefficient Intercept (pg/dl) Pica (1 = eater, 0 = otherwise) Traffic pattern (1 = high, 0 = low) Siding paint (mg/cm2) Door paint (mg/cm2) Soil lead (mg/g) 25.92 7.23 7.11 0.33 0.18 1.46 Multiple R2 = 0.386 Residual standard deviation = 0.2148 (geometric standard deviation = 1.24) Asymptotic . standard errof 1.61 1.60 1.48 0.11 0.12 0.59 MW HI IHHl Hh MMj ijJHH 11.4.3.7 Barltrop Studies. Barltrop et al. (1974) described two studies in England- lnvesti-' -ii \ gating the soil lead to blood lead relationship. In the first study, children aged 2 and 3 and their mothers from two towns chosen for their soil lead content had their blood lead levels determined from a capillary sample. Hair samples were also collected and analyzed lead. Lead content of the suspended particulate matter and soil was measured. Soil sam>lc for each home were a composite of several 2-inch core samples taken from the yard of sach j, home. Chemical analysis of the lead content of soil in the two towns showed a 2- to 3-1 ddj difference, with the values in the control town about 200-300 pg/g compared with about /DO-:^ 1000 pg/g in the exposed town. A difference was also noted in the mean air lead content of! 11-142 TEH 0412138 DUP050452736 the two towns, 0.60 compared with 0.29 pg/m3. Although this difference existed, both air lead values were thought low enough not to affect the blood level values differentially. Mean surface soil lead concentrations for the two communities were statistically different, the means for the high and low community being 909 and 398 pg/g, respectively. Despite this difference, no statistically significant differences in maternal blood lead levels or chil dren's blood or hair lead levels were noted. Further statistical analysis of the data, using correlational analysis on either raw or log-transformed blood lead data, likewise failed to show a significant relationship of soil lead with either blood lead or hair lead. The second study was reported in both preliminary and final form (Barltrop et al., 1974; Barltrop, 1975). In the more detailed report (Barltrop, 1975), children's homes were clas sified by their soil lead content into three groups: less than 1,000; 1,000 - 10,000; and greater than 10,000 pg/g. As shown in Table 11-60, children's mean blood lead levels increased correspondingly from 20.7 to 29.0 pg/dl. Mean soil lead levels for the low and high soil exposure groups were 420 and 13,969 pg/g, respectively. Mothers' blood levels, however, did not reflect this trend; nor were the children's fecal lead levels different across the soil exposure areas. TABLE 11-60. MEAN BLOOD AND SOIL LEAD CONCENTRATIONS IN ENGLISH STUDY Category of soil lead (pg/g) <1000 1000-10000 >10000 Sample size 29 43 10 Children's blood lead (pg/dl) 20.7 23.8 29.0 Soil lead (pg/g) 420 3390 13969 Source: Barltrop, 1975. An analysis of the data in Table 11-60 gives the following model blood lead (pg/dl) = 0.64 soil lead (1000 pg/g) + 20.98 (11-20) No confidence intervals were calculated since the calculations were based on means. 11.4.3.8 The British Columbia Studies. Neri et al. (1978) studied blood lead levels in children living in Trail, British Columbia. Capillary blood samples were collected and analyzed for lead by anodic stripping voltammetry. Duplicate samples were analyzed and the 11-143 TEH 0412I39 DUP050452737 f results were discarded whenever the values differed by more than 8 |jg/d1. This procedure probably helped control to some degree the commonly encountered positive bias in blood lead levels observed when capillary samples are used. An episode of poisoning of horses earlier had been traced to ingestion of lead. Environmental monitoring at that time did not suggest that a human health risk existed. However, it was later thought wise to conduct a study of lead absorption in the area. Trail had been the site of a smelter since the turn of the century. The smelter had undergone numerous changes for reasons of both health and productivity. At the time of the blood lead study, the smelter was emitting 300 pounds of lead daily, with ambient air lead levels at about 2 pg/m3 in 1975. Nelson, BC was chosen as the control city. The cities are reasonably close (~30 miles distant), similar in population, and served by the same water basin. The average air lead level in Nelson during the study was 0.5 pg/m3. Initial planning called for the sampling of 200 children in each of three age groups (1-3 years, 1st grade and 9th grade) from each of the two sites. A strike at the smelter at the onset of the study caused parts of the Trail population to move. Hence, the recruited sample deviated from the planned one. School children were sampled in May, 1975 at their schools while the 1- to 3-year olds were sampled in September, 1975 at a clinic or home. This delayed sampling was intentional to allow those children to be exposed to the soil and dus-t for the entire summer. Blood and hair samples were collected from each child. The children in the younger age groups living in Trail had higher blood lead levels than those living in Nelson. An examination of the frequency distributions of the blood lead levels showed that the entire frequency of the distribution shifted between the residents of the two cities. Interestingly, there was no difference in the ninth grade children. Table 11-61 displays the results of the soil lead levels along with the blood lead levels obtained in the earlier study. Blood lead levels were higher for 1- to 3-year olds and first graders in the two nearest-to-smelter categories than in the far-from-smelter category. Again, no difference was noted for the ninth graders. An EPA analysis of the Neri et al. (1978) data gives the following models for children 1to 3-years old 1 life life lilt Blood lead (pg/dl) = 0.0076 soil lead (pg/g) + 15.43, and (11-21) f' Blood lead (pg/dl) = G.C046 soil lead (pg/g) + 16.37 (11-22) for children in grade one. No confidence intervals were calculated since the analysis was based on means. : it 11-144 If TEH 0412140 "ti DUP050452738 TABLE 11-61. LEAD CONCENTRATION OF SURFACE SOIL AND CHILDREN'S BLOOD BY RESIDENTIAL AREA OF TRAIL, BRITISH COLUMBIA Residential area(s) 1 and 2 5 9 3, 4, and 8 6 and 7 Mean soil lead concentration, pg/g, + standard error (and no. of samples) 225 39 (26) 777 239 (12) 570 143 (11) 1674 + 183 (53) 1800 212 (51) Blood lead concentration, pg/dl, mean standard error (and no. of children) 1- to 3- Grade one year olds children 17.2 1 1.1 (27) 19.7 1.5 (11) 20.7 1.6 (19) 27.7 1.8 (14) 30.2 3.0 (16) 18.0 1.9 (18) 18.7 2.3 (12) 19.7 1.0 (16) 23.8 1.3 (31) 25.6 1.5 (26) Total 1320 212 (153) 22.4 1.0 (87) 21.9 0.7 (103) Source: Schmitt et al., 1979. 11.4.3.9 The Baltimore Charney Study: A Controlled Trial of Household Dust Lead Reduction. Charney et al. (1983) selected children from the Lead Poisoning Clinic of the John F. Kennedy Institute in Baltimore. The children were all 15-72 months old at the time of enrollment and had at least two venous blood lead levels between 30 and 49 pg/dl and FEP < 655 [jg/dl. The children were also required to have had thesame place of residence for at least the preceding six months. Their houses had to have been deleadedin accordance with standard procedures used by the Baltimore City Health Department. Experimental control subjects were recruited on the basis of attendance at routine periodic blood lead monitoring. Alternative identification numbers were used for allocation to experimental and control groups. Home visits were made for children in the experimental group and a 930 cm2 area of the floor or windowsill was wiped with an alcohol-treated cloth towel and the dust lead content analyzed. A "dust control team" then visited each home twice monthly and wet-mopped all surfaces with >100 pg Pb per 930 cm2. The child's caretaker was advised to wet-mop these surfaces and other "hot spots" more fre quently, to wash the child's hands before meals and at bedtime, and to restrict access to high1ead areas. Both the 14 experimental subjects receiving the above treatment and the 35 control sub jects started the study with about the same moderately elevated blood lead levels, 38.6 5.2 pg/dl at the start of the experiment. These levels had remained almost stationary for six months before the experiment, increasing only 1 pg/dl on average. After a year of dust con trol, the experimental subjects had reduced their PbB levels by 6.9 pg/dl, whereas the control 11-145 TEH 0412141 DUP050452739 subjects had reduced their PbB levels insignificantly (0.7 jjg/dl). Five of the control `f. , ^ jects actually had increased PbB by 6-12 pg/dl, and one by 20 pg/dl. None of the dust-,?*''' * controlled subjects had any PbB increase, and most showed a decrease of at least 6 tig7vllVi't Four experimental subjects had PbB < 30 gg/dl by the end of the experiment. Dust lead levels in experimentally cleaned homes returned to nearly the m previous hign 9'1i11 +V S111i11p11 vf values within two weeks. There was no significant relation between reduction of leaded dust,'.!*'1 JI|f. * initial level of leaded dust* and the reduction in a child's blood lead level. This latK pf y * apparent correlation may have been due to failure to control or monitor hand washing, finger- sucking and mouthing behavior, access to "hot spots," and time spent in the home. Further- '--''ii.. more, attempts at dust control may have been more successful in some of the control homes than. , in others, resulting in blood lead reduction in at least some individual cases. Since i ii.r t on dust control was offered to caretakers of lead-burdened children visiting the Climc,"i^x'1f may be presumed that some measure of dust control would have occurred in any event. Dust leatl _ values in the experimental homes were high compared to homes in other areas (13/14 had sites.'' ' ' ! >100 pg/930 cm2). While many potentially important factors were not completely controlled, ~ li during the trials, the importance of dust ingestion is evident. This study also points oLt^n, ^ the difficulties in quantifying the dust-hand-mouth pathway using familiar measures of house-'4* - > hold dust lead and concentration. Since the reduction in blood lead levels cannot be'plausi- 4 n * v bly attributed to factors other than household dust control (e.g., relocation of residence or change in diet), the experimental evidence for the importance of household dust in elevation/1- j of blood lead levels in U.S. urban children is very strong. -- 11.4.3.10 Gallacher Study. A report from England (Gallacher etal., 1984) provides add'- i ^ tional informative data on the importance of dust to blood lead levels. They were interested i"-t t in the effect of pica on blood lead levels. Mothers and children aged 1-3 years were recruit-( ; ed from 4 areas of Wales chosen for presumed lead exposure: 1) roadside dwellings; 2) cul ^ de sac dwellings; 3) an old mining area; and 4) a control area. Comprehensive environmental' *' f sampling accompanied the study of blood lead levels. Indoor air samples, soil from areas, pavement dust, house dust, and tap water samples were collected and analyzed for leao^1 , content. Capillary blood samples were collected from the children, while venous samples *en^ collected from the mothers. Blood samples were analyzed for lead by atomic absorption spec-r trophotometry. The accuracy of the capillary sampling was checked; the authors concluded thaU.,,, contamination was not a problem but that the values of the capillary samples were 37 percent^ i/ + higher than venous samples. They attributed the difference as "probably owing to haemoconceti-. * tration of capillary blood." 'I'.ijilif Results from the environmental sampling indicated that for many of the environmental, .ti, ,, f" media, lead exposures were reasonably constant over a several-month period. The authors state ^ 11-146 ` 'V* f>C MBHh I 1 TEH 0412M2 m/r DUP050452740 that, "Coefficient of variation..., based on duplicate pairs and after logarithmic transfor mation, was 9 percent for pavement dwellings (22 dwellings) and 10 percent for housedust (25 dwellings). The coefficient of variation of child hand lead using the 'wet wipe1 tech nique was 19 percent (based on 17 children)." The coefficient of variation of the blood lead sample of venous blood was around 7 percent. In both children and mothers, the mining area differed the most from the control area. The excess of lead in the blood of children was 30 percent for the mining area; in mothers the excess was about 50 percent. Pica as determined by questionnaire showed no consistent association with any area or all areas combined. On the other hand, the analysis of the wet wipe study provided interesting results. Within the roadside dwellings, the cul de sacs, and the control areas, mean lead levels of wet wipe samples were remarkably similar for mothers' hands, children's hands, and kitchen surfaces. But the mining area had a 40 percent excess for mothers' hands, 45 percent for children's hands, and 35 percent for kitchen surfaces, compared to the control area. However, the only difference which was statistically significant was for the children. Correlation analysis was performed between blood lead concentrations and hand lead con centrations. In the mining area, which was the most contaminated area, the correlation co efficient was 0.38, which was statistically significantly different from zero. In the noncontaminated areas, a statistically significant relationship was found between blood lead and kitchen surface. No statistically significant relations were seen for the mothers. Thus these data give additional support to the notion of normal hand-to-mouth activity being a pathway by which lead in dust can get into the blood of children. 11.4.3.11 Other Studies of Soil and Dusts. Rabinowitz et al. (1985c) report in a study dis cussed in Section 11.3.5.4 that lead levels in indoor dust and outdoor soil were strongly pre dictive of blood lead levels. Their sample consisted of Boston urban and suburban infants followed from birth to 2 years of age whose mothers had a mean age of 29 years and 15 years mean schooling. Lepow et al. (1975) studied the lead content of air, house dust, and dirt, as well as the lead content of dirt on hands, food and water, to determine the cause of chronically elevated blood lead levels in 10 children 2 to 6 years old in Hartford, Connecticut. Lead-based paints had been eliminated as a significant source of lead for these children. Ambient air lead con centrations varied from 1.7 to 7.0 pg/m3. The mean lead concentration in dirt was 1,200 pg/g and in dust, 11,000 pg/g. The mean concentration of lead in dirt on children's hands was 2,400 pg/g. The mean weight of samples of dirt from hands was 11 mg, which represented only a small fraction of the total dirt on hands. Observation of the mouthing behavior in these young children led to the conclusion that the hands-in-mouth exposure route was the principal cause of excessive lead accumulation. 11-147 TEH 0412143 DUP050452741 Several studies have investigated the mechanism by which lead from soil and dust g into the body (Sayre et al., 1974; Ter Haar and Aronow, 1974). Sayre et al. (1974) Rochester, New York, demonstrated the feasibility of house dust as a source of lead for c dren. Two groups of houses, one inner city and the other suburban, were chosen for the stiic Lead-free sanitary paper towels were used to collect dust samples from house surfaces and hands of children (Vostal et al., 1974). The medians for the hand and household samples used as the outpoints in the chi-square contingency analysis. A statistically significar difference between the urban and suburban homes for dust levels was noted, as was a rela ship between household dust levels and hand dust levels (Lepow et al., 1975). Ter Haar and Aronow (1974) investigated lead absorption in children that can be tributed to ingestion of dust and dirt. They reasoned that because the proportion of naturally occurring isotope of 210Pb varies for paint chips, airborne particulates, fall.! dust, house dust, yard dirt, and street dirt, it would be possible to identify the sources ingested lead. They collected 24-hour excreta from eight hospitalized children on the>fi day of hospitalization. These children, 1 to 3 years old, were suspected of having eleyat body burdens of lead, and one criterion for the suspicion was a history of pica. Ten chlidfietilfe of the same age level, who lived in good housing in Detroit and the suburbs, were selected i controls and 24-hour excreta were collected from them. The excreta were dried and stable lea as well as 210Pb content determined. For seven hospitalized children, the stable lead value was 22.43 pg/g dry excreta, and the eighth child had a value of 1640 pg/g. The- con trols' mean for stable lead was 4.1 pg/g dry excreta. However, the respective means for-,210P expressed as pCi/g dry matter were 0.044 and 0.040. The authors concluded that because t is no significant difference between these means for 210Pb, the hypothesis that young childir with pica eat dust is not supported. The authors further concluded that children., wit' evidence of high lead intake did not have dust and air suspended particulate as the sources b. their lead. It is clear that air suspended particulate did not account for the lead levels i the hospitalized children. However, the 210Pb concentrations in dust and feces were simi I for all children, making it difficult to estimate the dust contribution. Heyworth et al. (1981) studied a population of children exposed to lead in mine tailings These tailings were used in foundations and playgrounds, and had a lead content ranging fro 10,000 to 15,000 pg/g. In December, 1979, venous blood samples and hair were collected f 181 of 346 children attending two schools in Western Australia. One of the schools was 3 mary school; the other was a combined primary and secondary school. Parents completed'qu tionnaires covering background information as well as information regarding the childre exposure to the tailings. Blood lead levels were determined by the AAS method of Farrely Pybos. Good quality control measures were undertaken for the study, especially for the b-! 11-148 TEH 04121 DUP050452742 lead levels. Blood lead levels were higher in boys versus girls (mean values were 14.0 and 10.4 pg/dl, respectively). This difference was statistically significant. Five percent of the children (n = 9) had blood lead levels greater than 25 pg/dl; five of these children had blood lead levels greater than 30 pg/dl. Blood lead levels decreased significantly with age and were slightly lower in children living on properties on which tailings were used. However, they were higher for children attending the school that used the tailings in the playground. Landrigan et al. (1982) studied the impact on soil and dust lead levels on removal of leaded paint from the Mystic River Bridge in Masschusetts. Environmental studies in 1977 in dicated that surface soil directly beneath the bridge had a lead content ranging from 1300 to 1800 pg/g. Analysis of concomitant trace elements showed that the lead came from the bridge. A concurrent survey of children living in Chelsea (vicinity of bridge) found that 49 percent of 109 children had blood lead levels greater than or equal to 30 pg/dl. Of children living more distant from the bridge, 37 percent had that level of blood lead. These findings prompted the Massachusetts Port Authority to undertake a program to delead the bridge. Paint on parts of the bridge that extended over neighborhoods was removed by abrasive blasting and replaced by zinc primer. Some care was undertaken to minimize both the occupational as well as environmental exposures to lead as a result of the blasting process. Concurrently with the actual deleading work, a program of air monitoring was established to check on the environmental lead exposures being created. In June, 1980, four air samples taken at a point 27 m from the bridge had a mean lead content of 5.32 pg/m3. As a result of these findings air pollution controls were tightened; mean air lead concentrations 12 meters from the bridge in July were 1.43 pg/m3. Samples of the top 1 cm of soil were obtained in July, 1980 from within 30, 30-80, and 100 m from the bridge. Comparison samples from outside the area were also obtained. Samples taken directly under the bridge had a mean lead content of 8127 pg/g. Within 30 m of the bridge, the mean content was 3272 pg/g, dropping to 457 pg/g at 30 to 80 m. At 100 m the soil lead level dropped to 197 pg/g. Comparison samples ranged from 83 to 165 pg/g depending on location. Fingerstick blood samples were obtained on 123 children 1-5 years of age living within 0.3 km of the bridge in Charlestown. Four children (3.3 percent) had blood lead levels greater than 30 pg/dl, with a maximum of 35 pg/dl. All four children lived within two blocks of the bridge. Two of the four had lead paint in their homes but it was intact. None of the 76 children living more than two blocks from the bridge had blood leads greater than or equal to 30 pg/dl, a statistically significant difference. Shellshear's (1973) case report from New Zealand ascribes a medically diagnosed case of lead poisoning to high soil lead content in the child's home environment. Shellshear et al. 11-149 TEH 0412145 DUP050452743 (1975) followed up his case report of increased lead absorption resulting from exposure! i1 lead contaminated soil with a study carried out in Christchurch, New Zealand. Two relal activities comprised the study. First, from May, 1973 to November, 1973, a random study, pediatric admissions to a local hospital was made. Blood samples were taken and analyzed ,ft lead. Homes were visited and soil samples were collected and analyzed for lead. Lead anc yses for both soil and blood were conducted by AAS. Second, a soil survey of the area wa undertaken. Whenever a soil lead value greater than 300 pg/g was found and a child aged 1 was present, the child was referred for blood testing. The two methods of subject recruitment yielded a total of 170 subjects. Eight (4.7 pci cent) of the children had blood lead equal to or greater than 40 pg/dl, and three of them h a blood lead equal to or greater than 80 pg/dl. No correlation with age was noted. The me* blood lead of the pediatric admissions was 17.5 pg/dl with an extremely large range (4-17 pg/dl). The mean blood lead for soil survey children was 19.5 pg/dl. Christchurch was divided into two sections based on the date of development of the area. The inner area had developed earlier and a higher level of lead was used there in the house paints. The frequency distribution of soil lead levels showed that the inner zone samples hao . much higher soil lead levels than the outer zone. Furthermore, analysis of the soil lead '* i levels by type of exterior surface of the residential unit showed that painted exteriors had higher soil lead values than brick, stone, or concrete block exteriors. Analysis of the relationship between soil lead and blood lead was restricted to chilurci . from the sampled hospital who had lived at their current address for at least one year. Table 11-62 presents the analysis, of these results. Although the results were not statistically 1 significant, they are suggestive of an association. * TABLE 11-62. ANALYSIS OF RELATIONSHIP BETWEEN SOIL LEAD AND BLOOD LEAD IN CHILDREN (jMMp Area of city Soi 1 lead (pg/g) Mean Range n Blood lead (ug/dl) Mean Range Inner zone Outer zone Source: Shellshear (1973). 1950 150 30-11000 30-1100 21 47 25.4 18.3 4-170 5-84 ------ -->-- Analysis of the possible effect of pica on blood lead levels showed the mean blood 1ead,^ for children with pica to be 32 pg/dl while those without pica had a mean of 16.8 pg/dl. Th;g pica blood lead mean was statistically significantly higher than the non-pica mean. 11-150 TEH 0412146 DUP050452744 Mielke et al. (1984) reports elevated blood lead and FEP levels among Hmong children living in Minneapolis, Minnesota. The lead sources for these children included soil lead, house paint, and leaded gasoline from vehicle traffic. Fifty percent of children with lead poisoning (FEP > 50 pg/dl, blood lead > 30 pg/dl) inhabited homes which had soil lead levels of 500 to 1000 pg/g. Wedeen et al. (1978) reported a case of lead nephropathy in a black female who exhibited geophagia. The patient, who had undergone chelation therapy, eventually reported that she had a habit of eating soil from her garden in East Orange, New Jersey. During spring and summer, she continuously kept soil from her garden in her mouth while gardening. She even put a sup ply away for winter. The soil was analyzed for lead and was found to contain almost 700 pg/g. The authors estimated that the patient consumed 100-500 mg of lead each year. One month after initial hospitalization her blood lead level was 70 pg/dl. 11.4.3.12 Summary of Soil and Dust Lead . Studies relating soil lead to blood lead levels are difficult to compare. The relationship obviously depends on depth of soil lead, age of the children, sampling method, cleanliness of the home, mouthing activities of the children, and possibly many other factors. Brunekreef et al. (1983) studied a population of urban and rural children in the Netherlands. The analyses are described in detail in Section 11.4.3.4. Blood lead levels increased with increasing outside dustfall, with increased lead on chil dren's hands, and with pets in the household, and decreased with increasing number of rooms (due to dilution or confounded SES effects). Dust lead and its related transport factors sub stantially increased blood lead. Table 11-63 gives some estimated slopes taken from several different studies. The range of these values is quite large, ranging from 0.6 to 6.8. This range is similar to the range of 1.0 to 10.0 reported by Duggan (1980, 1983). Two studies providing good data for slope estimates are the Stark et al. (1982) study and the Angle and Mclntire (1982) study. These two studies gave slope estimates of 2.2 and 6.8 pg/dl per 1000 pg/g, respectively. The relationship of house dust lead to blood lead is even more difficult to obtain. Table 11-64 contains some values for three studies that give data permitting such caculations. The median value of 1.8 pg/dl per 1000 pg/g for children 2-3 years old in the Stark study may also represent a reasonable value for use here. 11.4.4 Paint Lead Exposures A major source of environmental lead exposure for some in the general population comes from lead contained in both interior and exterior paint on dwellings. The amount of lead present, as well as its accessibility, depends upon the age of the residence (because older 11-151 TEH 0412147 DUP050452745 TABLE 11-63. ESTIMATES OF THE CONTRIBUTION OF SOIL LEAD TO BLOOD LEAD Study Range of soil lead values (MQ/g) Angle and Mclntire (1982) study of children in Omaha, NE 16-4792 Stark et al. (1982) study of children in New Haven, CT 30 - 7000 (age 0-1) 30 - 7600 (age 2-3) Vankel et al. (1977) study of children in Kellogg, ID 50 - 24,600 Galke et al. (1975) study of children in Charleston, SC 9 - 7890 Barltrop et al. (1975) study of children in England 420 - 13,969 (group means) Neri et al. (1978) study of children in British Columbia 225-1800 (group means, age 1-3) 225-1800 (group means, age 2-3) Depth of sample 2" h" 3/411 2" 2" NA NA Estimated slope (X103) 6.8 Sample size 1075 2.2 153 2.0 334 1.1 860 1.5 194 0.6 82 7.6 87 4.6 103 *NA means Not Available. 11-152 TEH 0412148 DUP050452746 TABLE 11-64. ESTIMATES OF THE CONTRIBUTION OF HOUSEDUST TO BLOOD LEAD IN CHILDREN Study Range of dust lead values (gg/g) Angle and Mclntire (1979) study in Omaha, NE 18-5571 Stark et al. (1982) study in New Haven , CT 70-7600 40-7600 9-4900 Yankel et al. (1977) study in Kellogg, ID 50-35,600 Age range in years 1-18 6-18 0-1 2-3 4-7 0-4 5-9 Estimated slope (X103) 7.18 3.36 Sample size 1074 832 R2 0.198 0.262 4.02 1.82 0.02 0.19 0.20 153 0.289 334 0.300 439 0.143 185 0.721 246 0.623 buildings contain paint manufactured before lead content was regulated) and the physical con dition of the paint. It is generally accepted by the public and by health professionals that lead-based paint is one major source of overtly symptomatic pediatric lead poisoning in the United States (Lin-Fu, 1973). The level and distribution of lead paint in a dwelling is a complex function of history, geography, economics, and the decorating habits of its residents. Lead pigments were the first pigments produced on a large commercial scale when the paint industry began its growth in the early 1900's. In the 193Q`s lead pigments were gradually replaced with zinc and other opacifiers. By the 1940's, titanium dioxide became available and is now the most commonly used pigment for residential coatings. There was no regulation of the use of lead in house paints until 1955, when the paint industry adopted a voluntary standard that limited the lead content in interior paint to no more than 1 percent by weight of the nonvolatile solids. At about the same time, local jurisdictions began adopting codes and regulations that prohibited the sale and use of interior paints containing more than 1 percent lead (Berger, 1973a,b). In spite of the change in paint technology and local regulations governing its use, in terior paint with significant amounts of lead was still available in the 1970's. Studies by Berger (1973b) and by the U.S. Consumer Product Safety Commission (1974) showed a continuing decrease in the number of interior paints with lead levels greater than 1 percent. By 1974, only 2 percent of the interior paints sampled were found to have greater than 1 percent lead in the dried film (U.S. Consumer Product Safety Commission, 1974). The level of lead in paint in a residence that should be considered hazardous remains in question. Not only is the total amount of lead in paint important, but also the accessibility 11-153 TEH 0412149 DUP050452747 of the painted surface to a child, as well as the frequency of ingestion, must be considered. % '* Attempts to set an acceptable lead level, jn situ, have been unsuccessful, and preventive con- A ' trol measures of lead paint hazards have been concerned with lead levels in currently manufac- tured paint. In one of its reviews, the NAS concluded: "Since control of the lead paint f\* hazard is difficult to accomplish once multiple layers have been applied in homes over two to three decades, and since control is more easily regulated at the time of manufacture, we re- 'f` 1 commend that the lead content of paints be set and enforced at time of manufacture" (National Academy of Sciences, 1976). Legal control of lead paint hazards is being attempted by local communities through Ijjg: health or housing codes and regulations. At the Federal level, the Department of Housing and Urban Development has issued regulations for lead hazard abatement in housing units assisted or supported by its programs. Generally, the lead level considered hazardous ranges from 0.5: to 2.5 mg/cm2, but the level of lead content selected appears to depend more on the sensiti vity of field measurement (using X-ray fluorescent lead detectors) than on direct biological dose-response relationships. Regulations also require lead hazard abatement when the paint is loose, flaking, peeling, or broken, or in some cases when it is on surfaces within reach of a child's mouth. Some studies have been carried out to determine the distribution of lead levels in paint in residences. A survey of lead levels in 2370 randomly selected dwellings in Pittsburgh pro vides some indication of the lead levels to be found (Shier and Hall, 1977). Figure 11-29 > shows the distribution curves for the highest lead level found in dwellings for three age groupings. The curves bear out the statement often made that paint with high levels of lead ass?is most frequently found in pre-1940 residences. One cannot assume, however, that high lead paint is absent in dwellings built after 1940. In the case of the houses surveyed in Pittsburgh, about 20 percent of the residences built after 1960 have at least one surface with more than 1.5 mg/cm2. The distribution of lead within an individual dwelling varies considerably. Lead paint is most frequently found on doors and windows where lead levels greater than 1.5 mg/cm2 were 5V found on 2 percent of the surfaces surveyed, whereas only about 1 percent of the walls had :Jr lead levels greater than 1.5 mg/cm2 (Shier and Hall, 1977). * In a review of the literature, Lin-Fu (1973) found general acceptance that the presence >. , lead in paint is necessary but not sufficient evidence of a hazard. Accessibility in terms ( of peeling, flaking, or loose paint also provide evidence for the presence of a hazard. Of ti- total samples surveyed, about 14 percent of the residences had accessible paint with a lead ^ content greater than 1.5 mg/cm2. As discussed in Section 7.3.2.1.2, one must note that lead oxides of painted surfaces contribute to the lead level of house dust. '< * 11-154 TEH 0412150 B DUP050452748 l FRACTION H AVIN G LEAD LEVEL LEAD LEVEL IX), mg/cm2 Figure 11-2 9. Cumulative distribution of lead levels in dwelling units. Source: Shier and Hall (1977). 11-155 TEH 0412151 DUP050452749 } It is not possible to extrapolate the results of the Pittsburgh survey nationally. However, additional data from a pilot study of 115 residences in Washington, DC, showed similar results (Hall 1974). An attempt was made in the Pittsburgh study to obtain information about the correlation between the quantity and condition of lead paint in buildings, and the blood lead of children who resided there (Urban, 1976). Blood lead analyses and socioeconomic data for 456 children were obtained, along with the information about lead levels in the dwelling. Figure 11-30 is ia plot of the blood lead levels versus the fraction of surfaces within a dwelling with lead levels of at least 2 mg/cm2. Analysis of the data shews a low correlation between the illblood 'rfwmiSVv. lead levels of the children and fraction of surfaces with lead levels above 2 mg/cm2, but there is a stronger correlation between the blood lead levels and the condition of the painted surfaces in the dwellings in which children reside. This latter correlation appeared to be independent of the lead levels in the dwellings. Yaffe et al. (1983) report data that suggests that soil lead possibly derived from exterior paint was an important source for a selected group of children. They used a stable lead isotope ratio technique. Hammond et al. (1981, 1982) conducted a study of Cincinnati children with the dual pur pose of determining whether inner city children with elevated blood lead levels have elevated fecal lead and whether fecal lead correlates with lead-base paint hazard in the home or traf fic density as compared with blood lead. Subjects with high blood lead levels were primarily recruited. Some comparison children with low blood lead levels were also identified. The three comparison children had to be residentially stable so that their low blood lead levels were reflective of the lead intake of their current environment. The subjects from the inner city were usually from families in extremely depressed socio-economic circumstances. Stool samples were collected on a daily basis for up to 3 weeks, then analyzed for lead. Fecal lead levels were expressed both as mg/kg*day and as mg/m2-day. An environmental assessment was made at the home of each child. Paint lead exposure was rated on a three-point scale (high, medium, and low) based on paint lead level and integrity of the painted wall. Air lead exposure was assessed by the point scale (high, medium, and low) based on traffic density, because there are no major point sources of lead in the Cincinnati area. Blood samples were collected on an irregular basis but were taken sufficiently often to have at least one sample from a child from every house studied. The blood samples were analyzed for lead by two laboratories that had different histories of performance in the 0I -proficiency testing program. All blood lead levels used in the statistical analysis were ad* justed to a common base. Because of the variable number of fecal and blood lead levels, the data were analyzed using a nested analysis of variance. 11-156 st TEH 0412152 DUP050452750 a. in --' 30 uj 2> g -J 25 5 X LLI U -I Q 20 -- O O -t CQ 15 .1 --i---------1---------- 1--------- 1----------1--------- 1--------- r SURFACES IN BAD CONDITION, i.e.. PEELING. CHALKING, OR POOR SUBSTRATE ALL SURFACES o a. I -cr JL I 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 FRACTIONS OF SURFACES WITH LEAD >2 mg/cm2 Figure 11 -30. Correlation of children's blood lead levels with fractions of surfaces within a dwelling having lead concentrations > 2 mg Pb/cm2. Source: Urban (1976). ... J 1.0 11-157 TEH 0412153 DUP050452751 The homes of the children were found to be distributed across the paint and traffic lead exposure categories. Both fecal lead levels and blood levels were positively associatedwith interior paint lead hazard. A marginal association between fecal lead levels and exterior paint hazard was also obtained. Neither fecal lead nor blood lead was found to be associated ^ with traffic density; the definition of the high traffic density category, however, began at a ,L>. low level of traffic flow (7500 cars/day). Examination of fecal and blood lead levels by sex and race showed that black males had the highest fecal lead excretion rates followed by white males and black females. White females were only represented by two subjects, both of whom had high fecal lead excretion. Blood lead levels were more influenced by race than by sex. The results suggested that children in high and medium paint hazard homes (high = at least 1 surface with >0.5 percent Pb, peeling or loose) were probably ingesting paint in some form. This could not be con firmed, however, by finding physical evidence in the stools. Long-term stool collection in a subset of 13 children allowed a more detailed examination of the pattern of fecal lead excretion. Two patterns of elevatedfecal lead excretion were noted. The first was a persistent elevation compared with controls; the second was markedly elevated occasional spikes against a normal background. One family moved from a high-hazard home to a low one during the course of the study This allowed a detailed examination of the speed of deleading of fecal and blood lead lever. j|:,s The fecal levels decreased faster than the blood lead levels. The blood leads were still elevated at the end of the collection. Gilbert et al. (1979) studied a population of Hispanic youngsters in Springfield, Massachusetts, in a case control study designed to comparethe presence of sourcesof lead i homes of lead-poisoned children and appropriately matched controls. Cases were defined as children having two consecutive blood lead levels greater than 50 pg/dl. Controls were chil dren with blood lead levels less than or equal to 30 pg/dl who had no previous history of lead ", intoxication and were not siblings of children with blood lead levels greater than 30 pg/dll ^ Study participants had to be residentially stable for at least 9 months and not have movext into their current home from a lead contaminated one. All blood lead levels were analyzed b. Delves cup method of AAS. Cases and controls were matched by age (+3 months), sex, and neigh- u borhood area. The study population consisted of 30 lead intoxication cases and 30 control t',i subjects. Home visits were undertaken to gather interview information and conduct home inspection. i? Painted surfaces were assessed for integrity of the surface and lead content. Lead content was measured by X-ray fluorometry. A surface was scored as positive if the lead content exceeded 1.2 mg/cm2. Drinking water lead was assessed for each of the cases and was found to 11-158 TEH 0412154 DUP050452752 contain less than 50 pg/1, thought by the authors to be sufficiently low so as not to consti tute a hazard. Tap water samples were not collected in the homes of the controls. Soil samples were collected from three sites in the yard and analyzed for lead by X-ray fluorometry. Cases and controls were compared on environmental lead exposures and interview data using McNemar's test for paired samples. The odds ratio was calculated as an estimator of the rela tive risk on all comparisons. Statistically significant differences between cases and con trols were noted for lead in paint and the presence of loose paint. Large odds ratios (>10) were obtained, suggesting a very strong association of blood lead level and paint lead expo sure. There appeared to be little influence of age or sex on the odds ratios. Significant differences between cases and controls were obtained for both intact and loose paint by individual surfaces within specific living areas of the home. Surfaces acces sible to children were significantly associated with lead poisoning status while inaccessible surfaces generally were not. Interestingly, the odds ratios tended to be larger for the in tact surface analysis than for the loose paint one. Median paint lead levels in the homes of cases were substantially higher than those in the homes of controls. The median paint lead for exterior surfaces in cases was about 16-20 pg/cm2 and about 10 pg/cm2 for interior surfaces. Control subjects lived in houses in which the paint lead generally was less than 1.2 pg/cm2 except for some exterior surfaces. Soil lead was significantly associated with lead poisoning; the median soil lead level for homes of cases was 1430 pg/g, while the median soil lead level for control homes was 440 pg/g. Rabinowitz et al. (1985b) report that refinishing activity in homes with high paint lead was associated with elevations of blood lead averaging 69 percent. Blood lead levels of 249 infants were measured semiannually from birth to two years of age. Also, home paint was sampled and any recent home refinishing was recorded. Mean blood lead correlated signifi cantly with the amount of lead in the indoor paint. Two other studies have attempted to relate blood lead levels and paint lead as determined by X-ray fluorescence. Reece et al. (1972) studied 81 children from two lower socioeconomic communities in Cincinnati. Blood leads were analyzed by the dithizone method. There was con siderable lead in the home environment, but it was not reflected in the children's blood lead. Analytical procedures used to test the hypothesis were not described; neither were the raw data presented. Galke et al. (1975), in their study of inner-city black children, measured the paint lead, both interior and exterior, as well as soil and traffic exposure. In a multiple regression analysis, exterior siding paint lead was found to be significantly related to blood lead levels. 11-159 TEH 0412155 DUP050452753 Evidence indicates that a source of exposure in childhood lead poisoning is P*linflW>' ' paint and broken lead-impregnated plaster found in poorly maintained houses. There are a, sof .* .. reports of exposure cases that cannot be equated with the presence of lead paint. F dither,' ` the analysis of paint in homes of children with lead poisoning has not consistently revealed tr t hazardous lead content (Lin-Fu, 1973). For example, one paper reported 5466 samples of jie.fnv'O' obtained from the home environment of lead poisoning cases in Philadelphia between 1%4 ^pa. J? 1968. Among these samples of paint, 67 percent yielded positive findings, i.e., paint^wit'ri. V " more than 1 percent lead (Tyler, 1970). Data published or made available by the Centers for Disease Control also show tha_. ' nificant number of children with undue lead absorption occupy buildings that were i nspLCifecb' ,, j , , . . for lead-based paint hazards, but in which no hazard could be demonstrated (U.S. Centers.JorJl,l Disease Control, 1977a; Hopkins and Houk, 1976). Table 11-65 summarizes the data otitaf bee!..-.'' from the HEW-funded lead-based paint poisoning control projects for Fiscal Years 1981, 19J9,'1''. ` 1978, 1975, and 1974. These data show that in Fiscal Years 1974, 1975, and 1978, in jKhSO. ^ percent of confirmed cases of elevated blood lead levels, a possible source of lead paiid;-^ hazard was not located. In fiscal year 1981, the U.S. Centers for Disease Control (1982a,b); /i screened 535,730 children and found 21,897 with lead toxicity. Of these, 15,472 dwellJ were inspected and 10,666 or approximately 67 percent were found to have leaded paint. -Th^ / - implications of these findings are not clear. The findings are presented in order to place int proper perspective both the concept of total lead exposure and the concept that lead pairv'j,'-is,i - one source of lead that contributes to the total body load. The background contribution of ^ lead from other sources is still not known, even for those children for whom a potential .1^ * ", paint hazard has been identified; nor is it known what proportion of lead came from which. * 4 source. ^jBlllflr p. i k ' - M .-.-T ` Wg/B.g1r lpR Ji - iT M A s t y fi ;' mmm -- 11-160 .l.*i&t* *, . * H\tv y % v* 4- - TEH 041?15>^J DUP050452754 TABLE 11-65. RESULTS OF SCREENING AND HOUSING INSPECTION IN CHILDHOOD LEAD POISONING CONTROL PROJECT BY FISCAL YEAR Results Children screened Children with elevated lead exposure Dwellings inspected Dwellings with lead hazard 1981 535,730 21,897 15,472 10,666 1979 464,751 Fiscal year 1978 397,963 1975 440,650 32,537 17,911 12,461 25,801 36,138 18,536 28,597a 30,227 17,609 Confirmed blood lead level >40 pg/dl. Source: U.S. Centers for Disease Control (1977a, 1979, 1980, 1982a,b); Hopkins and Houk, 1976. 1974 371,955 16,228a 23,096 13,742 11.5 SPECIFIC SOURCE STUDIES The studies reviewed in this section all provide important information regarding specific environmental sources of airborne lead that play a role in population blood lead levels. These studies also illustrate several interesting approaches to this subject. 11.5.1 Primary Smelter Populations Some studies of nonindustry-employed populations living in the vicinity of industrial sources of lead pollution were triggered because evidence of severe health impairment had been found. Subsequently, extremely high exposures and high blood lead concentrations were found. The following studies document the excessive lead exposure that developed, as well as some of the relationships between environmental exposure and human response. 11.5.1.1 El Paso, Texas. In 1972, the Centers for Disease Control studied the relationships between blood lead levels and environmental factors in the vicinity of a primary smelter lo cated in El Paso, Texas emitting lead, copper, and zinc. The smelter had been in operation since the late 1800's (Landrigan et al., 1975; U.S. Centers for Disease Control, 1973). Daily hi-vol samples collected on 86 days between February and June, 1972, averaged 6.6 pg/m3. These air lead levels fell off rapidly with distance, reaching background values approximately 5 km from the smelter. Levels were higher downwind, however. High concentrations of lead in soil and house dusts were found, with the highest levels occurring near the smelter. The geo metric means of 82 soil and 106 dust samples from the sector closest to the smelter were 1791 11-161 TEH 0412157 DUP050452755 and 4022 pg/g, respectively. Geometric means of both soil and dust lead levels near' smelter were significantly higher than those in study sectors 2 or 3 km farther away. Sixty-nine percent of children 1 to 4 years old living near the smelter had blocd"; levels greater than 40 pg/dl, and 14 percent had blood lead levels that exceeded 60 pg Concentrations in older individuals were lower; nevertheless, 45 percent of the children"- 9 years old, 31 percent of the individuals 10 to 19 years old, and 16 percent of the lnfr duals above 19 had blood lead levels exceeding 40 pg/dl. The data presented preclude calc tions of means and standard deviations. Data for people aged 1-19 years of age living near the smelter showed a relatioit between blood lead levels and concentrations of lead in soil and dust. For individuals^ blood lead levels greater than 40 pg/dl, the geometric mean concentration of lead in sbi their homes was 2587 pg/g, whereas for those with a blood lead concentration less thaj pg/dl, home soils had a geometric mean of 1419 pg/g. For house dust, the respective geanjg means were 6447 and 2067 pg/g. Length of residence was important only in the sector . the smelter. Additional sources of lead were also investigated. A relationship was found bet blood lead concentrations and lead release from pottery, but the number of individuals exp to lead-glazed pottery was very small. No relationships were found between blood le^d le and hours spent out-of-doors each day, school attendance, or employment of a smelter. The reported prevalence of pica also was minimal. Data on dietary intake of lead were not obtained because there was no food availab. l1e sources near the smelter since the climate and proximity to the smelter prevented any far in the area. It was unlikely that the dietary lead intakes of the children from.hea1 smelter or farther away were significantly different. It was concluded that the pr- factor associated with elevated blood lead levels in the children was ingestion or inlia'T of dust containing lead. Morse et al. (1979) conducted a follow-up investigation of the El Paso smelter to dete mine whether the environmental controls instituted following the 1972 study had redixdcK-t lead problem described. In November, 1977, all children 1 to 18 years old living with, 1.6 km of the smelter on the U.S. side of the border were surveyed. Questionnaires werc^a1 ministered to the parents of each participant to gather background data. % Venous blood samples were drawn and analyzed for lead by modified Delves cup spectropn- tometry. House dust and surface soil samples, as well as sample pottery items, were tak> from each participant's residence. Dust and soil samples were analyzed for lead byJ nn Pottery lead determinations were made by the extraction technique of Klein. Paint, food, a water specimens were not collected because the earlier investigations of the problem^ demonstrated these media contributed little to the lead problem in El Paso. v, 11-162 DUP050452756 Fifty-five of 67 families with children (82 percent) agreed to participate in the study. There were 142 children examined in these homes. The homes were then divided into two groups. Three children lived in homes within 0.8 km of the smelter. Their mean blood lead level in 1977 was 17.7 pg/dl. By contrast, the mean blood lead level of 160 children who lived within 0.8 km of the smelter in 1972 had been 41.4 pg/dl. In 1977, 137 children lived in homes lo cated 0.8-1.6 km from the smelter. Their mean blood lead level was 20.2 pg/dl. The mean blood level of 96 children who lived in that same area in 1972 had been 31.2 pg/dl. Environmental samples showed a similar improvement. Dust lead fell from 22,191 to 1,479 pg/g while soil lead fell from 1,791 to 427 pg/g closest to the smelter. The mean air lead concentration at 0.4 km from the smelter decreased from 10.0 to 5.5 pg/m3 and at 4.0 km from 2.1 to 1.7 pg/m3. Pottery was not found to be a problem. 11.5.1.2 CDC-EPA Study. Baker et al. (1977b), in 1975, surveyed 1774 children 1-5 years old, most of whom lived within 4 miles of lead, copper, or zinc smelters located in various parts of the United States. Blood lead levels were modestly elevated near 2 of the 11 copper and 2 of the 5 zinc smelters. Although blood lead levels in children were not elevated in the vicinity of three lead smelters, their FEP levels were somewhat higher than those found in controls. Increased levels of lead and cadmium in hair samples were found near lead and zinc smelters; this was considered evidence of external exposure. No environmental determinations were made for this study. 11.5.1.3 Meza Valley, Yugoslavia. A series of Yugoslavian studies investigated exposures to lead from a mine and a smelter in the Meza Valley over a period of years (Fugas et al., 1973; Graovac-Leposavic et al. 1973; Milic et al., 1973; Djuric et al., 1971, 1972). In 1967, 24-hour lead concentrations measured four on different days varied from 13 to 84 pg/m3 in the village nearest the smelter, and concentrations of up to 60 pg/m3 were found as far as 5 km from the source. Mean particle size in 1968 was less than 0.8 pm. Analysis of some common foodstuffs showed concentrations that were 10-100 times higher than corresponding foodstuffs from the least exposed area (Mezica) (Djuric et al., 1971). After January, 1969, when partial control of emissions was established at the smelter, weighted average weekly exposure was cal culated to be 27 pg/m3 in the village near the smelter. In contrast to this, the city of Zagreb (Fugas et al., 1973), which has no large stationary source of lead, had an average weekly air lead level of 1.1 pg/m3. In 1968, the average concentration of ALA in urine samples from 912 inhabitants of 6 vil lages varied by village from 9.8-13 mg/1. A control group had a mean ALA of 5.2 mg/1. Data on lead in blood and the age and sex distribution of the villagers were not given (Djuric et al., 1971). 11-163 TEH 0412159 DUP050452757 ;^'?Tg9 ""i 'u,,'\ V7 v v ^' / Of the 912 examined, 559 had an ALA level greater than 10 mg/1 of urine. In 1969, a mots * extensive study of 286 individuals with ALA greater than 10 mg/1 was undertaken (Graovac- ` Leposavic et al. 1973). ALA-U increased significantly from the previous year. When the clip- ' ' lished data were examined closely, there appeared to be some discrepancies in interpretation, s i The exposure from dust and from food might have been affected by the control devices, blit`no, r data were collected to establish this. In one village, Zerjua, ALA-U dropped from 21.7 ta g.i mg/1 in children 2-7 years of age. Corresponding ALA-U values for 8- to 15-year-olds and adult men and women were reduced from 18.7 to 12.1, from 23.9 to 9.9, and from 18.5 to if mg/1, respectively. Because lead concentrations in air (Fugas et al., 1973), even after 1969", indicated an average exposure of 25 pg/m3, it is possible that some other explanation should^1 be sought. The author indicated in the report that the decrease in ALA-U showed "the depen- * u 1 dence on meteorologic, topographic, and technological factors" (Graovac-Leposavic et dl.f 1973). p Fugas (1977) in a later report estimated the time-weighted average exposure of several1" populations studied during the course of this project. Stationary samplers as well as per-1 sonal monitors were used to estimate the exposure to airborne lead for various parts of the day. These values were then coupled with estimated proportions of time at which these expo sures held. In Table 11-66, the estimated time-weighted air lead values as well as the observed mean blood lead levels for these studied populations are presented. An increase in blood lead values occurs with increasing air lead exposure. TABLE 11-66. MEAN BLOOD LEAD LEVELS IN SELECTED YUGOSLAVIAN POPULATIONS, BY ESTIMATED WEEKLY TIME-WEIGHTED AIR LEAD EXPOSURE Population Rural I Rural II Rural III Postmen Customs officers Street car drivers Traffic policemen N 49 47 45 44 75 43 24 Time-weighted air lead, (pg/m3) 0.079 0.094 0.146 1.6 1.8 2.1 3.0 Blood lead level. (pg/dl) Mean SD 7.9 4.4 11.4 4.8 10.5 18.3 10.4 4.0 9.3 mm 3.3 " , 24.3 10.5 l-"`" 12.2 5,1 Source: Fugas, 1977. 11-164 i &;)!& TEH 0412160 1* DUP050452758 11.5.1.4 Kosovo Province, Yugoslavia. Residents living in the vicinity of the Kosovo smelter were found to have elevated blood lead levels (Popovac et al., 1982). In this area of Yugoslavia, five air monitoring stations had been measuring air lead levels since 1973. Mean air lead varied from 7.8 to 21.7 pg/m3 in 1973; by 1980 the air lead averages ranged from 21.3 to 29.2 pg/m3. In 1978 a pilot study suggested that there was a significant incidence of ele vated blood lead levels in children of the area. Two major surveys were then undertaken. In August, 1978, letters were sent to randomly selected families from the business commu nity, hospitals or lead-related industries in the area. All family members were asked to come to a hospital for primary screening by erythrocyte protoporphyrin. A central population of comparable socioeconomic and dietary background was collected from a town without lead emis sions. Blood levels were determined primarily for persons with EP greater than 8 pg/g Hgb. EP was measured by a hematofluorimeter, while blood lead was determined by the method of Fernandez using atomic absorption with graphite furnace and background correction. Mean EP values were higher in the 1978 survey for exposed residents compared to controls in the average age group. EP values seemed to decline with age. Similar differences were noted for blood lead levels. The observed mean blood leads, ranging from 27.6 in the greater than 15 year age group to 50.9 pg/dl in the 5 to 10 year group, suggest substantial lead ex posure of these residents. In the control group the highest blood lead level was 19 pg/dl. In December, 1980, a second survey was conducted to obtain a more representative sample of persons residing in the area. Letters were sent again, and 379 persons responded. EP levels were higher in all ages in 1980 versus 1978, although the differences were not statistically significant. The air lead levels increased from 14.3 pg/m3 in 1978 to 23.8 pg/m3 in 1980. Comparing the 1980 blood lead results with the 1978 control group shows that the 1980 levels were higher in each age group. Males older than 15 years had higher mean blood lead levels than the females (39.3 versus 32.4 pg/dl). 11.5.1.5 The Cavalleri Study. Cavalleri et al. (1981) studied children in the vicinity of a lead smelter and children from a control area (4 km from the smelter). The exposed population consisted of 85 children aged 3-6 attending a nursery school and 80 primary school children aged 8 to 11. The control population was 25 nursery school children aged 3-6 and 64 primary school children aged 8-11. Since the smelter had installed filters 8 years before the study, the older children living in the smelter area had a much higher lifetime exposure. Blood lead analysis was performed on venous samples using anodic stripping voltammetry by Morrell's method. Precision was checked over the range of 10-100 pg/dl. Reported reproduci bility was also good. All samples were subsequently reanalyzed by AAS using graphite furnace and background correction by the method of Volosen. The average values obtained by the second method were quite similar to those of the first (average difference 1.4 pg/dl; correla tion coefficient, 0.962). 11-165 TEH 0412161 DUP050452759 Air was sampled for lead for 1 month at three sampling sites. The sites were located 150 m, 300 m, and 4 km from the wall of the lead smelter. The average air lead levels 2.32, 3.43, and 0.56 pg/m3, respectively. A striking difference in blood lead levels of the exposed and control populations was served; levels in the exposed population were almost twice that in the control populat There was no significant difference between nursery school and primary school children geometric mean for nursery school children was 15.9 and 8.2 for exposed and control, respec vely. For primary school it was 16.1 and 7.0 pg/dl. In the exposed area, 23 percent of subjects had blood lead levels between 21 and 30 pg/dl and 3 percent greater than 31 pg No control children had blood lead levels greater than 20 pg/dl. The air leads were bei\ 2-3 pg/m3 in the exposed and 0.56 pg/m3 in the control cases. 11.5.1.6 Hartwell Study. Hartwell et al. (1983) report a study of 4 primary smelters; lead and two zinc. Study subjects were recruited in accordance with a statistical samp' l plan based on diffusion modeling. Subjects were recruited to represent a variety of ag 1-5 years, 6-18 years, 20-40 years, and, in two sites, >60 years. Environmental samp covering the important environmental sources of lead were obtained, as were blood s< Unfortunately, air sampling was only conducted for about 1 month in each of the study aV Dust, water, and soil samples were also collected and analyzed for lead. Table 11-67 s marizes the descriptive results of this study in terms of blood lead levels. Table ll presents the Spearman correlation coefficient obtained. 11.5.2 Battery Plants Studies of the effects of storage battery plants have been reported from France and I (Dequidt et al., 1971; De Rosa and Gobbato, 1970). The French study found that children an industrialized area containing such a plant excreted more ALA than those living in a di rent area (Dequidt et al., 1971). Increased urinary excretion of lead and coproporphyrins found in children living up to 100 m from a battery plant in Italy (De Rosa and Gobba 1970). Neither study gave data on plant emissions or lead in air. 11.5.3 Secondary Smelters Zielhuis et al. (1979) studied children living in the vicinity of the Arnhem seconc lead smelter. In 1976 they recruited children to serve as subjects and controls. The chi dren chosen were 2 and 3 years old. Parents were asked to complete a questionnaire for bac ground information. Two-ml venous samples were collected from 17 children living less thar km, from 54 children living 1-2 km, and from 37 children living greater than 2 km from smelter (control group). Blood samples were analyzed for lead by graphite furnace AAS and *1ji1fl 8 MllliMfo M 11-166 TEH 0412165 DUP050452760 TABLE 11-67. LEVELS OF LEAD RECORDED IN HARTWELL ET AL. (1983) STUDY Smelter Bartlesville Palmerton Ajo Anaconda Distance from smelter Air Dust 3.5-24.0 1.3-3.7 0.8-4.3 0.8-1.5 11.0-26.0 5.4-14.5 3.3-9.9 0.3-2.8 3.4-68.0 1.0-6.4 0.5-2.3 0.5-1. 3 10.0-26.0 3.5-21.0 2.0-11.0 2.0-3.5 131 241 203 409 299 386 309 441 361 263 563 201 128 198 278 438 94 74.2 108 60.0 191 64.7 256 116 141 235 176 164 91 210 255 398 Water 6.04 4.56 6.81 7.63 8.7 6.0 2.8 1.8 6.9 11.5 13.3 3.1 3.10 3.52 3.02 3.83 Soil 34.8 243 829 821 532 117 326 331 57.8 64.5 76.5 94.8 75 115 294 424 PbB Ages 1- 5 Ages 6-10 10.5 24.7 39.6 18.8 10.3 11.3 12.6 15.9 9.9 10.6 10.5 9.2 21.0 17.3 18.9 21.5 12.4 12.9 21.8 20.3 12.4 10.2 11.2 10.3 7.8 7.7 6.9 6.9 19.0 11.9 14.3 17.9 TABLE 11-68. SPEARMAN CORRELATIONS OF LEAD IN AIR, WATER, DUST, SOIL, AND PAINT WITH LEAD LEVELS IN BLOOD: BY SITE AND AGE GROUPS, 1978-1979 Bartlesville Palmerton Air Water Dust Soil Paint Air Water Dust Soil Paint 1-5 Blood 0.40* 0.05 0.20 0.33* -0.06 -0.12 -0.06 0.06 0.16 -0.02 6-18 Blood 0.22* 0.14 0.10 0.13 0.06 Age, (yr) 20-40 Blood 0.27* 0.07 0.21 0.07 0.02 0.11 -0.07 0.20 0.06 -0.12 -0.01 -0.05 0.23* Over 60 Blood 0.19 0.23 0.00 -0.06 ^Significantly different from zero at 0.05 level. 11-167 TEH 0412163 DUP050452761 FEP by the method of Piomelli. Air measurements for lead were made in autumn, 1976. SamplmM I were established about 2 km northeast and about 0.4 km north of the plant. Air lead levi el^ >' vi ranged from 0.8 to 21.6 pg/m3 northeast and from 0.5 to 2.5 pg/m3 north of the plant. > '** { Blood leads were statistically significantly higher closer to the smelter. For all ch^l-- dren the mean blood lead level was 19.7 pg/dl for the less than 1 km and 11.8 pg/dl for t-hp V f controls (>2 km). Similarly, FEP levels were higher for the closer (41.9 pg/100 ml erytbro~ cytes) children as opposed to the control (32.5 pg/100 ml RBC). Higher blood levels were^` i associated with lower socioeconomic status. Further investigation of this smelter was undertaken by Brunekreef et al. (1981) 'ard1-; r>( Diemel et al. (1981). In May, 1978, venipuncture blood samples were collected from 95 one-^to | three-year-old children living within 1 km of the smelter. Blood leads were determined.b^* graphite AAS. tfsig*''," 1 Before the blood sampling, an environmental sampling program was conducted. The samples collected are listed in Table 11-69. Questionnaires were administered to collect background and further exposure information. A subset of 39 children was closely observed for 1 or'2 days for mouthing behavior. Table 11-69 also presents the overall results of the enviPbnmejr tal sampling. As can be readily seen, there is a low exposure to airborne lead (geometric mean) 0.41 pg/m3 with a range of 0.28-0.52 pg/m3). Soil exposure was moderate, although high Interior dust was high in lead (geometric mean of 967 pg/g with a maximum of 4741 pg/g). In*a few homes, high paint lead levels were found. Diemel et al. (1981) extended the analysis <^f the environmental samples. They found that indoor pollution was lower than outside, Arnhem, it was found that lead is carried into the homes in particulate form by sticking to" shoes. Most of the lead originated from soil from gardens and street dust. Simple correlation coefficients were calculated to investigate the relationship between log blood lead and the independent variables. Significantly, correlations were found with quantity of house dust, quantity of deposited lead indoors, observational score of dustinessr, age of child, and the average number of times an object is put in the mouth. Multiple regre ssion analyses were calculated on four separate subpopulations. Among children living n houses with gardens, the combination of soil lead level and educational level of the parents explained 23 percent of the variations of blood lead. In children without gardens, the amouqt of deposited lead indoors explained 26 percent of the variance. The authors found that an ir1" > crease in soil lead level from 100-600 pg/g resulted in an increase in blood lead of 6,3. pg/dl. In a Dallas, Texas, study of two secondary lead smelters, the average blood lead level ur ^ exposed children was found to be 30 pg/dl versus an average of 22 pg/dl in control childj^n^ (Johanson and Luby, 1972). For the two study populations, the air and soil lead levels * e, , 3.5and 1.5 pg/m3 and 727 and 255 pg/g, respectively. '"'i/' 11-168 TEH 041216 DUP050452762 r TABLE 11-69. ENVIRONMENTAL PARAMETERS AND METHODS: ARNHEM LEAD STUDY, 1978' ro 3 tO CO to 4-- Po CM CD LO o LO 03 rH CM roC O CM rH t CM rH Q 00 1 CM C30 rH O CM o rH ro t's. LO o LO 1 CM ro 1 rH f** h- O lO CO CM <10* LO CO rH rH O ro* in r- c m ro- in ii CO p". to rH ro* rH Po 1Cl 03 03 m 3- o OV CM V 10 0) c C P (0 10 3r P CL 4- Ta) p "O P to c I3Ds i--C (0 CL r- f0 ra 1-- -r-- c P ro O ro C 00 03 to E <D ' CM r-- r-> LO r-- co CL U CM ro in c m CJY ro o 4^ r*- to o5j- CM oO <73 LO a CL> to O S- (A LO CD H- P r- 3 4- o o P1-- U m 4ro- CO W CD O pP *pi- po <0 Po Z ro >so-> PPP 4- P 3 rao >i 4o- J.2 P P CO q .73 P 0) <D UNO x >,r CD r- P (0 /"-% P (A (ft (ft sz >3 P c to P o c >> ro r4- ro O) C co r- *r- rroo 3 ro 7"ro4rO3o-- 5*rcEr--0o73 o p ro ro up CD 0> to 77<330 <0 c >>S to to pP 3P CD c o CD E 43 CM to 4CD O P S~ > P I U) ^3 CM O C to rro p r-- C CL O U to ~ to P 3 *ri-- to 1 P -*-2 03 (13 CD O E s- ro 3 to S> ro o ro p >> >>-- ro to 73 3 1O 3 c V) P a; c O) o 3U O) E CD p (A r-- to * o to CL CD CD P 73 r- <A 4- CM <TJ CM cr p p (A C 73 I" rt t-- U 3 CULT) O 3 PE VO o 4- IA to Sc aj ro >> 05P O c i~ to i-- O D> to CM r- i-- O r- 03 p CL C E * LO rt c3 o to o r" P 3 P c c: o ro ip s_ ro c p s- o 3U p (A o ro ro e to o r- CO p p >, p ro r"" C r-- ro O 3 c E CL ro 1 o rH Q. to <D p *r to rH CO P ro c/> ro co r-- 0.0 EV ro >> to "o CD 3 r~ P CL tO v> ro p p to O P c ro to o ro 3 f-- O CM OP > 41 co 3C p o 3 *r- OP ro * r-- rH 3 a. " o QU >> O 73 ^3 P X to (A OPP ro O P c P to o o ro to o ro ro p P sro c o r-- r- P CL to >> to P r-- to c 10 ro 0) 3 i-- a 3) ro 3 4- 3 73 3 *rro to P to ro c ro ro o ro u 4. ro p p ro to PEC r-- r- O OX'r OP ro 4- ro 4- Q.rro c c l 3 P o ro c l o v- 73 P CL p ro p >> -- U to 73 to air- 3 r- i-- ro P O r-- > to ro o s- o. u ro p to P o * c jC <A r- tO pro ro -r- i-- P e 3: CLP O !- P s- ro 3 ro to e C ro m to ro c ^ -- * O P U - *-- P ro to c e 73 ro o 3 r- U E 300 U P O rH ro 73 3 P to P o to ro O P c r-- ro r-- CL ro 10 rH c to o ro r3P CO ro to r-- *r-- 3 P CL P CL ro C *r CD ro rH 05 cc -1- 4- r3P 73 ro * 3 to Q. ro o r-- CL CL iro 73 to 3 P r-- tn ro CP a *e-- p 10 4. ro OE a. o OP S- 05 P c ro ro > 4-- 4-- ro ro ia i-- p ro o o tA LO ro c r-- O Q. >v-rS PP r- to ro to 3 1-- 73 3 ro ^ CL o cm a o >> '' pro C3 i- c w p ro ro cu p r-- o r- u P s--' CA to ro ro rH E o r-- E P ro o 3 5- C to P *1" in t/> CO p O > 3: CL > * C >>rH >> P CO 5- <T> P0) S- 73 H a> <D E o P(0 N>> * op 5 r-- , Q. (0 rO p ro n CLP ro O SL. C P CD p r- W U3 CD 73 73 . CL rO <D U5 QJ P ^ P 0> 0) C `f- o 4- o .p P >> CO ** a. 4- 03 S- P U N O CD C 03 w E oh P (0 ro P i-- * Ur- O> LoO rr--o EO 03 P C p ro CL E(0 CD >> CL 73 -* P S-. 4CJ- -IrA- 73 P P 3 CD CO U -C PE4O- *7Ur3- LA tj p-- CD i-- a) r-- M 4CD- CO --t w a. ro c srro--- JQ CfS *--s = COE r- S o> 73 ZL CD 5 P ,-N P >J to CO 733 e7o*3 cs 03 73 CL iO CD *(3TJ * 03 QJ to s- ro3 r- 73 p ro ro 4. P to <*rv c o> rS. 05 73 2. ro '-> ro p s_ o o 73 c 1-- co C 05 73 3. rroo --i ln 73 r-- CO r-- E ro \ P 05 P 3. tO 'w' 3 73 to 4. CO r- o 73 73 C ro *CD P LD P to 3 73 4O P C 05 *r- ^ 05 "r2o - ro p 7--ro P to ro 41-- o *- o ro 73 > fZ ro *r~ >>73 r--* (0 r- ro to 1-- ro UJ CO 4CD P ro 3: D. ro p c *1-- 73 ro ro p , cn U> ro O P P o 10 to ro 3 r-- P to 3 O O rH CD >> 7 -X 5CD- P -->, OCDJ 5 73 Q-P ai as- in E 3 Q) CD 4- c/3 p rt>~o>PO4- 4<D- OO(A ro ro P C CL ro C rt 3s *r- 73 ttOO 03 P ro ^ c u rC-D pu *-ic--x 4rCoD- i-- *f-- v- tA r<- PJQ4D- CCD 11-169 LA tO N 7 O uXi DUP050452763 In Toronto, Canada, the effects of two secondary lead smelters on the blood and hair levels of nearby residents have been extensively studied (Ontario Ministry of the Environm 1975; Roberts et al., 1974). In a'preliminary report, Roberts et al. (1974) stated that and hair lead levels were higher in children living near the two smelters than in chi living in an urban control area. Biologic and environmental lead levels were reported tc crease with increasing distance from the base of the smelter stacks. A later and more detailed report identified a high rate of lead fallout around th secondary smelters (Ontario Ministry of the Environment, 1975). Two groups of children ll within 300 m of each of the smelters had geometric mean blood lead levels of 27 and 28 respectively; the geometric mean for 1231 controls was 17 pg/dl. Twenty-eight percent sample children tested near one smelter during the summer and 13 percent of the sample dren tested near the second smelter during the winter had blood lead levels greater tha pg/dl. Only 1 percent of the controls had blood lead levels greater than 40 pg/dl. For dren, blood lead concentrations increased with proximity to both smelters, but this trie not hold for adults, generally. The report concluded that soil lead levels were the niai, terminant of blood lead levels; this conclusion was disputed by Horn (1976). Blood lead levels in 293 Finnish individuals, aged 15-80, were significantly corre with proximity to a secondary lead smelter (Nordman et al., 1973). The geometric mean lead concentration for 121 males was 18.1 pg/dl; for 172 females, it was 14.3 pg/dl. subjects who spent their entire day at home, a positive correlation was found between lead and distance from the smelter up to 5 km. Only one of these 59 individuals had a lead greater than 40 pg/dl, and none exceeded 50 pg/dl. 11.5.4 Secondary Exposure of Children ms Excessive intake and absorption of lead on the part of children can result whenip who work in a dusty environment with a high lead content bring dust home on their c;l shoes, or even their automobiles. Once they are home, their children are exposed to the dt. Landrigan et al. (1976) reported that the 174 children of smelter workers who lived in 24 km of the smelter had significantly higher blood lead levels, a mean of 55.1 pg/d the 511 children of persons in other occupations living in the same areas who blood lead levels were 43.7 pg/dl. Analyses by EPA of the data collected in Idaho shcwe employment of the father at a lead smelter, at a zinc smelter, or in a lead mine result higher blood lead levels in the children living in the same house as opposed to those chil whose fathers were employed in different locations (Table 11-70). The effect associated parental employment appears to be much more prominent in the most contaminated study nearest to the smelter. This may be the effect of an intervening socioeconomic variable: 11-170 TEH 041216 DUP050452764 TABLE 11-70. GEOMETRIC MEAN BLOOD LEAD LEVELS FOR CHILDREN BASED ON REPORTED OCCUPATION OF FATHER, HISTORY OF PICA, AND DISTANCE OF RESIDENCE FROM SMELTER (micrograms per deciliter) Distance from Area smelter, km 1 1.6 2 1.6 to 4.0 3 4.0 to 10.0 4 10.0 to 24.0 5 24.0 to 32.0 6 75 Lead smelter worker No Pica Pica 78.7 74.2 50.2 52.2 33.5 33.3 - 30.3 - 24.5 -- Lead/zinc mine worker No Pica Pica 75.3 63.9 46.9 46.9 36.7 33.5 38.0 32.5 31.8 27.4 -- Zinc smelter worker No Pica Pica 69.7 59.1 62.7 50.3 36.0 29.6 40.9 - 36.9 - -- Other occupations No Pica Pica 70.8 59.9 37.2 46.3 33.3 32.6 - 39.4 28.0 26.4 17.3 21.4 Source: Landrigan et al. 1976. lowest paid workers, employed in the highest exposure areas within the industry, might be ex pected to live in the most undesirable locations, closest to the smelter. Landrigan et al. (1976) also reported a positive history of pica for 192 of the 919 chil dren studied in Idaho. This history was obtained by physician and nurse interviews of parents. Pica was most common among 2-year-old children and only 13 percent of those with pica were above age 6. Higher blood lead levels were observed in children with pica than in those without pica. Table 11-70 shows the mean blood lead levels in children as they were af fected by pica, occupation of the father, and distance of residence from the smelter. Among the populations living nearest to the smelter, environmental exposure appears to be sufficient at times to more than overshadow the effects of pica, but this finding may also be caused by inadequacies inherent in collecting data on pica. These data indicate that in a heavily con taminated area, blood lead levels in children may be significantly increased by the inten tional ingestion of nonfood materials having a high lead content. Data on the parents' occupation are, however, more reliable. It must be remembered also that the study areas were not homogeneous socioeconomically. In addition, the specific type of work an individual does in an industry is probably much more important than simply being employed in a particular industry. The presence in the home of an industrial employee exposed occupationally to lead may produce increases in the blood lead levels ranging from 10 to 30 percent. 11-171 TEH 0412167 DUP050452765 The importance of the infiltration of lead dusts onto clothing, particularly the und*e .jV' 1 ' garments, of lead workers and their subsequent transportation has been demonstrated in a j iu ij -" ber of studies on the effects of smelters (Martin et al., 1975). It was noted in the Un'isV * Kingdom that elevated blood lead levels were found in the wives and children of workers tevjir], though they resided some considerable distance from the facility. It was most prominent1, '3 the workers themselves, who had elevated blood lead levels. Quantities of lead dust Wdfs,`' found in workers' cars and hemes. It apparently is not sufficient for a factory merely'x<n- provide outer protective clothing and shower facilities for lead workers. In another study-i, ` Bristol, 650-1400 pg/g of lead was found in the undergarments of workers as compared with 3-33.3 pg/g in undergarments of control subjects. Lead dust will remain on the clothing even after" laundering: up to 500 mg of lead has been found to remain on an overall garment after washing (Lead Development Association, 1973). A--* - / Baker et al. (1977a) found blood lead levels greater than 30 pg/dl in 38 of 91 chilcreiv^ whose fathers were employed at a secondary lead smelter in Memphis, TN. House dust, the cnly source of lead in the homes of these children, contained a mean of 2687 pg/g compared with 404 pg/g in the homes of a group of matched controls. Mean blood lead levels in the workers1' children were significantly higher than those for controls and were closely correlated `1*4, the lead content of household dust. In homes with lead in dust less than 1000 pg/g, 18-cHl--* dren had a mean blood lead level of 21.8 + 7.8 pg/dl, whereas in homes where lead in dust was,-' greater than 7000 pg/g, 6 children had mean blood lead levels of 78.3 34.0 pg/dl. See See-/ tion 7.3.2.1.6 for a further discussion of household dust. Other studies have documented increased lead absorption in children of families where "at'j vStaagB# <1 least one member was occupationally exposed to lead (Fischbein et al. , 1980a). The occupa^f, tional exposures involved battery operations (Morton et al., 1982; U.S. Centers for Disease Control, 1977b; Dolcourt et al., 1978, 1981; Watson et al., 1978; Fergusson et al., 1- - well as other occupations (Snee, 1982b; Rice et al., 1978). 1, * In late summer of 1976, a battery plant in southern Vermont provided the setting for'the first documented instance of increased lead absorption in children of employees in the battery industry. The data were first reported by the U.S. Centers for Disease Control (197/t>)ra1^f more completely by Watson et al. (1978). Reports of plant workers exposed to high levelsjal/. lead stimulated a study of plant employees and their children in August and September, In the plant, lead oxide powder is used to coat plates in the construction of batteries* Before the study, the work setting of all 230 employees of the plant had been examinea and 2" workers (22 percent) were identified as being at risk for high lead exposure. All high-risk workers interviewed reported changing clothes before leaving work and 90 percentjOt-fV. them reported showering, washed at home. However, 87 percent of them stated that their work clothes ' 11-172 .-V !i-- mKm TEH DUP050452766 Of the high-risk employees, 24 had children between the ages of 1 and 6 years. A casecontrol study was conducted in the households of 22 of these employees. Twenty-seven children were identified. The households were matched with neighborhood controls, including 32 control children. None of the control family members worked in a lead industry. Capillary blood specimens were collected from all children and the 22 battery plant employees had venous spec imens taken. All blood samples were analyzed for lead by AAS. Interviewers obtained back ground data, including an assessment of potential lead exposures. About 56 percent of the employees' children had blood leads greater than 30 pg/dl com pared with about 13 percent of the control children. Mean blood lead levels were signifi cantly different, 31.8 pg/dl and 21.4 pg/dl, respectively. Blood lead levels in children were significantly correlated with employee blood lead levels. House dust lead levels were measured in all children's homes. Mean values were 2239.1 pg/g and 718.2 pg/g for employee and control homes, respectively; this was a statistically significant difference. Examination of the correlation coefficient between soil lead and blood lead levels in the two sets of homes showed a marginally significant coefficient in the employee households but no correlation in the control homes. Tap water and paint lead levels did not account for the observed difference in blood leads between children of workers and neighborhood controls. It is significant that these findings were obtained despite the chang ing of clothes at the plant. Morton et al. (1982) conducted their study of children of battery plant workers and con trols during February-March, 1978. Children were included in the study if one parent had at least 1 year of occupational exposure, if they had lived at the same residence for at least 6 months, and if they were from 12-83 months of age. Children for the control group had to have no parental occupational exposure to lead for 5 years, and had to have lived at the same ad dress at least 6 months. Thirty-four children were control-matched to the exposed group by neighborhoods and age (1 year). No matching was thought necessary for sex because in this age group blood lead levels are unaffected by sex. The selection of the control population attempted to adjust for both socioeconomic status as well as exposure to automotive lead. Capillary blood specimens were collected concurrently for each matched pair. Blood lead levels were measured by the CDC lab using a modified Delves cup AAS procedure. Blood lead levels for the employees for the previous year were obtained from company records. Question naires were administered at the same time as the blood sampling to obtain background informa tion. The homemaker was asked to complete the interview to try to get a more accurate picture of the hygiene practices followed by the employees. 11-173 TEH 0412169 DUP050452767 K HI mm \ i ' Children's blood lead levels differed significantly between the exposed and contra], groups. Fifty-three percent of the employees' children had blood lead levels greater than io pg/dl, while no child in the control population had a value greater than 30 pg/dl. The ir.^ar. blood lead for the children of the employees was 49.2 pg/dl with a standard deviation of 8.3 pg/dl. These data represent the population average for yearly individual average levels. j- employees had an average greater than 60 pg/dl. Still, this is lower than the industry' average. Of the eight children with blood levels greater than 40 pg/dl, seven had father^ with blood lead greater than 50 pg/dl. Yet there was not a significant correlation between children's blood lead level and father's blood lead level. ' Investigations were made into the possibility that other lead exposures could account jor the observed difference in blood lead levels between children of employees and control chjl- dren. In II of the 33 pairs finally included in the study, potential lead exposures c. .. t than fathers' occupations were found in the employee child of the matched pair. These yicluded a variety of lead sources such as automobile body painting, casting of lead, and playing with spent shell casings. The control and exposed populations were again compared after removing these 11 pairs from consideration. There was still a statistically significant difference in blood lead level between the two groups of children. i An examination of personal hygiene practices of the workers showed that within high': posure category jobs, greater compliance with recommended lead containment practices resull in lower mean blood lead levels in children. Mean blood leads were 17.3, 36.0, and 41.9 pg for good, moderately good, and poor compliance groups, respectively. In fact, there was di a small difference between the good hygiene group within the high-exposure category and mean of the control group (17.3 pg/dl versus 15.9 pg/dl). Insufficient sample sizes available to evaluate the effect of compliance on medium and low lead exposures for fath Dolcourt et al. (1978) investigated lead absorption in children of workers in a pl?j$ that manufactures lead-acid storage batteries. The plant became known to these researchers^ a result of finding an elevatedblood lead level in a 20-month-old child during ro screening. Although the child was asymptomatic, his mother proved not to be. Two sibli were also found to have elevated blood lead levels. The mother was employed by the plant; work involved much hard labor and brought her into continual contact with powdery lead ox No uniforms or garment covers were provided by the company. As a result of these findin screening was offered to all children of plant employees. During February to May, 1977, 92 percent of 63 eligible children appeared for screeni Age ranged from 10 months to 15 years. About equal numbers of girls and boys unde screening. Fingerstick blood samples were collected on filter paper and were analyzed lead by AAS. Children with blood lead levels equal to or greater than 40 pg/dl were refer III 11-174 ''il TEH Q412170 DUP050452768 for more detailed medical evaluation including an analysis of a venous blood specimen for lead. Dust samples were collected from carpeting in each home and analyzed for lead by gra phite furnace AAS. Home tap water was analyzed for lead by AAS, and house paint was analyzed for lead by XRF. Of the 58 children who had the initial fingerstick blood lead elevation, 69 percent had blood lead levels equal to or greater than 30 pg/dl. Ten children from six families had blood lead levels equal to or greater than 40 pg/dl, and blood lead levels were found to vary markedly with age. The 0- to 3-year-old category exhibited the highest mean (48.6 pg/dl) with the 3- to 6-year-olds the next highest (38.2 pg/dl). Lowest mean values were found in the equal to or greater than 10-year-old group (26.7 pg/dl). More detailed investigation of the six families with the highest blood lead levels in their children revealed the following: five of the six lived in rural communities, with no pre-existing source of lead from water supply, house paint, industrial emissions, or heavy automobile traffic. However, dust samples from the carpets exhibited excessively high lead concentrations. These ranged from 1700 to 84,050 pg/g. Fergusson et al. (1981) sampled three population groups: general population, employees of a battery plant, and children of battery plant employees, using hair lead levels as indices of lead. Hair lead levels ranged from 1.2 to 110.9 pg/g in the 203 samples from the general population. The distribution of hair lead levels was nearly lognormal. Employees of the bat tery factory had the highest hair lead levels (median ~250 pg/g), while family members (median ~40 pg/g) had a lesser degree of contamination and the general population (median ~5 pg/g) still less. Analysis of variance results indicated a highly significant difference between mean lead levels of the general survey and family members of the employees, and a significant difference between the mean lead levels in the hair of the employees and their families. No significant differences were found comparing mean hair lead levels among family members in terms of age and sex. The analyses of the house dust suggested that the mechanism of exposure of family members is via the lead in dust that is carried home. Mean dust lead level among the homes of factory employees was 5580 pg/g while the dust inside of houses along a busy road was only 1620 pg/g. Both of these concentrations are for particles less than 0.1 mm. Dolcourt et al. (1981) reported two interesting cases of familial exposure to lead caused by recycling of automobile storage batteries. The first case was of a 22-member, fourgeneration family living in a three-bedroom house in rural eastern North Carolina. The great grandfather of the index case worked at a battery recycling plant. He had two truckloads of spent casings delivered to the home to serve as fuel for the wood stove; the casings were burned over a 3-month period. 11-175 TEH 0412171 r DUP050452769 The Index case presented with classic signs of acute lead encephalopathy, the most seVej'i and potentially fatal form of acute lead poisoning. The blood lead level was found to be pg/dl. Three months after initial diagnosis and after chelation therapy, she conti nued'-to have seizures and was profoundly mentally retarded. Dust samples were obtained by va^iV.m cleaner and analyzed for lead by flameless AAS. Dust from a sofa near the wood stove tog? tained 13,283 pg/g lead, while the kitchen floor dust had 41,283 pg/g. There was no pUnjt lead. All other members of the family had elevated blood lead levels ranging from 27;?55 fjg/dl. IfpgflKr 3 The other case involved a truck driver working in a low-exposure area of,a battn^ recycling operation in rural western North Carolina. He was operating an illegal battery^re*cycling operation in his home by melting down reclaimed lead on the kitchen stove. No faijffljy: i'j member was symptomatic for lead symptoms but blood lead levels ranged from 24 to 72 pg/tfl., Soil samples taken from the driveway, which was paved with fragments of the discarded*bat!tl|w||, casings, contained 12-13 percent lead by weight. In addition to families being exposed as a result of employment at battery plants, stu j1, dies have been reported recently for smelter worker families (Rice et al., 1978; Snee, 1982m. Rice et al. studied lead contamination in the homes of secondary lead smelters. Homes of em ployees of secondary smelters in two separate geographic areas of the country were examinedj;o determine whether those homes had a greater degree of lead contamination than homes of wor i in the same area not exposed to lead. Both sets of homes (area I and II) were examined at the same time of the year. Thirty-three homes of secondary smelter employees were studied; 19 homes in the Saih3j` similar neighborhoods were studied as controls. Homes studied were in good condition and weje one- or two-family dwellings. Blood lead levels were not obtained for children in' tq|p homes. In the homes of controls, a detailed occupational history was obtained for aach employed person. Homes where one or more residents were employed in a lead-contakirated environment were excluded from the analysis. t a,, House dust samples were collected by VostaVs method and were analyzed for lead by 'h AS. In one of the areas, samples of settled dust were collected from the homes of employees and controls. Dust was collected over the doorways. In homes where the settled dust was collec ted, zinc protoporphyrin (ZPP) determinations were made in family members of the lead workers' and in the controls. r' In both areas, the wipe samples were statistically significantly higher in the homes.^^ employees compared to controls (geometric mean 79.3 61.8 pg/g versus 28.8 7.4 pg/g 112.0 2.8 pg/g versus 9.7 3.9 pg Area II). No significant differences were found beUten workers1 homes or controls between Area I and Area II. Settled dust lead was significant;i/ 11-176 -XL- i9| TEH 04121/2 -- 4J DUP050452770 higher in the homes of employees compared to controls (3300 versus 1200 pg/g). Lead contents of particulate matter collected at the curb and of paint chips collected in the home were not significantly different between employee homes and controls. Zinc protoporphyrin determina tions were done on 15 children, 6 years or younger. ZPP levels were higher in employee chil dren than in control children. Mean levels were 61.4 pg/ml and 37.6 pg/ml, respectively. It should be noted again that the wipe samples were not different between employee homes in the two areas. Interviews with employees indicated that work practices were quite similar in the two areas. Most workers showered and changed before going home. Work clothes were washed by the company. Obviously, much closer attention needs to be paid to other potential sources of lead introduction into the home (e.g., automobile surfaces). From Mexico (Molina-Ballesteros et al., 1983) comes a report of yet another occupation which can contribute to the lead burden of children whose parents work in settings contami nated by lead. One hundred and fifty-three children belonging to pottery-making families with home workshops were studied, as well as 80 randomly selected children serving as controls. Venipuncture blood samples were collected and analyzed by atomic absorption spectrophotometry. Mean blood lead levels were 15 pg/dl higher for children whose parents had the home pottery workshops than for control children. The mean blood lead level in the exposed children was 39.5 pg/dl, which indicates a high degree of lead absorption in these children. 11.5.5 Miscellaneous Studies 11.5.5.1 Studies Using Indirect Measures of Air Exposure. 11.5.5.1.1 Studies in the United States. A 1973 Houston study examined the blood lead levels of parking garage attendants, traffic policemen, and adult females living near freeways (Johnson et al., 1974). A control group for each of the three exposed populations was selec ted by matching for age, education, and race. Unfortunately, the matching was not altogether successful; traffic policemen had less education than their controls, and the garage employees were younger than their controls. Females were matched adequately, however. It should be noted that the mean blood lead values for traffic policemen and parking garage attendants, two groups regularly exposed to higher concentrations of automotive exhausts, were significantly higher than the means for their relevant control groups. Statistically significant differ ences in mean values were not found, however, between women living near a freeway, and control women living at greater distances from the freeway. A study of the effects of lower-level urban traffic densities on blood lead levels was undertaken in Dallas, Texas, in 1976 (Johnson et al., 1978). The study consisted of two phases. One phase measured air lead values for selected traffic densities and conditions, ranging from equal to or less than 1,000 to about 37,000 cars/day. The second phase consisted 11-177 TEH 0412173 DUP050452771 of an epidemiological study of traffic density and blood lead levels among residents. 11-31 shows the relationship between arithmetic means of air lead and traffic density, be seen from the graph, a reasonable fit was obtained. " *' Figure As cLi 'llll .ggSgSHli iiiifiii Figure 11-31. Arithmetic mean of air lead levels by traffic volume. Dallas, 1976. Source: Johnson et al. (1978). Wm In addition, for all distances measured (1.5-30.5 m from the road), air lead concentra tions declined rapidly with distance fromthe street. At 15 m, concentrations were aboJt 55 percent of the street concentrations. In air lead collections from 1.5 to 30.5 m fron the street, approximately 50 percent of the airborne lead was in the respirable range (<1 pin), the proportions in each size class remained approximately the same as the distance from t(ie street increased. Soil lead concentrations were higher in areas with greater traffic density, ranging from 73.6 pg/g at less than 1,000 cars per day to a mean of 105.9 at greater than 19,500 cars- per day. The maximum soil level obtained was 730 pg/g. Dustfall samples for 28 days from 'nine locations showed no relationship to traffic densities, but outdoor levels were at least times the indoor concentration in nearby residences. 11-178 TEH 0412174 DUP050452772 In the second phase, three groups of subjects, 1 to 6 years old, 18 to 49 years old, and 50 years and older, were selected in each of four study areas. Traffic densities selected were less than 1,000, 8,000-14,000, 14,000-20,000, and 20,000-25,000 cars/day. The study groups averaged about 35 subjects, although the number varied from 21 to 50. The smallest groups were from the highest traffic density area. No relationship between traffic density and blood lead levels in any of the age groups was found (Figure 11-32). Blood lead levels were significantly higher in children, 12-18 pg/dl, than in adults, 9-14 pg/dl. Caprio et al. (1974) compared blood lead levels and proximity to major traffic arteries in a study reported in 1971 that included 5226 children in Newark, New Jersey. Over 57 per cent of the children living within 30.5 m of roadways had blood lead levels greater than 40 pg/dl. For those living between 30.5 and 61 m from the roadways, more than 27 percent had such levels, and at distances greater than 61 m, 31 percent exceeded 40 pg/dl. The effect of automobile traffic was seen only in the group that lived within 30.5 m of the road. No other sources of lead were considered in this study. However, data from other studies on mobile sources indicate that it is unlikely that the blood lead levels observed in this study resulted entirely from automotive exhaust emissions. In 1964, Thomas et al. (1967) investigated blood lead levels in 50 adults who had lived for at least 3 years within 76 m of a freeway (Los Angeles) and those of 50 others who had lived for a similar period near the ocean or at least 1.6 km from a freeway. Mean blood lead levels for those near the freeway were 22.7 + 5.6 for men and 16.7 7.0 pg/dl for women. These concentrations were higher than for control subjects living near the ocean: 16.0 8.4 pg/dl for men and 9.9 4.9 pg/dl for women. The higher values, however, were similar to those of other Los Angeles populations. Measured mean air concentrations of lead in Los Angeles for October, 1964, were as follows: 12.25 + 2.70 pg/m3 at a location 9 m from the San Bernardino freeway; 13.25 + 1.90 pg/m3 at a fourth-floor location 91.5 m from the freeway; and 4.60 1.92 pg/m3 1.6 km from the nearest freeway. The investigators concluded that the dif ferences observed were consistent with coastal inland atmospheric and blood lead gradients in the Los Angeles basin and that the effect of residential proximity to a freeway (7.6-76 m) was not demonstrated. Ter Haar and Chadzynski report a study of blood lead levels of children living near three heavily travelled streets in Detroit (Ter Haar, 1981; Ter Haar and Chadzynski, 1979). Blood lead levels were not found to be related to distance from the road but were related to condi tions of housing and age of the child after multiple regression analyses. 11.5.5.1.2 British studies. In a Birmingham, England, study, mean blood lead levels in 41 males and 58 females living within 800 m of a highway interchange were 14.41 and 10.93 pg/dl, respectively, just before the opening of the interchange in May, 1972 (Waldron, 1975). From 11-179 TEH 0412175 DUP050452773 BLOOD LEAD CONCENTRATION, jxg/dl Figure 11-32. Blood lead concentration and traffic density by sex and age, Dallas, 1976. Source: Johnson et al. {1978). 11-180 i October, 1972, to February, 1973, the respective values for the same individuals were 18.95 and 14.93 pg/dl. In October, 1973, they were 23.73 and 19.21 pg/dl. The investigators noted difficulties in the blood collection method during the baseline period and changed from capil lary to venous blood collection for the remaining two sets of samples. To interpret the significance of the change in blood collection method, some individuals gave both capillary and venous blood at the second collection. The means for both capillary and venous bloods were calculated for the 18 males and 23 females who gave both types of blood samples (Barry, 1975). The venous blood mean values for both these males and females were lower by 0.8 and 0.7 pg/dl, respectively. If these differences were applied to the means of the third series, the mean for males would be reduced to 24.8 pg/dl and that for the females to 18.7 pg/dl. These adjusted means still show an increase over the means obtained for the first series. Comparing only the means for venous bloods, namely series two and three, again shows an in crease for both groups. The increase in blood lead values was larger than expected following the model of Knelson et al. (1973), because air lead values near the road were approximately 1 pg/m3. The investigators concluded that either the lead aerosol of very small particles behaved more like a gas so that considerably more than 37 percent of inhaled material was absorbed, or that ingestion of lead-contaminated dust might be responsible. Studies of taxicab drivers have employed different variables to represent the drivers' lead exposure (Flindt et al., 1976; Jones et al., 1972): one variable was night versus dayshift drivers (Jones et al., 1972); the other was mileage driven (Flindt et al. , 1976). No difference was observed, in either case. The studies reviewed show that automobiles produce sufficient emissions to increase air and nearby soil concentrations of lead as well, and to increase blood lead concentrations in children and adults. The problem is of greater importance when houses are located within 100 ft (30 m) of the roadway. 11.5.5.2 Miscellaneous Sources of Lead. The habit of cigarette smoking is a source of lead exposure. Shaper et al. (1982) report that blood lead concentration is higher for smokers than nonsmokers and that cigarette smoking makes a significant independent contribution to blood lead concentration in middle-aged men in British towns. A direct increase in lead in take from cigarettes is thought to be responsible. Hopper and Mathews (1983) comment that current smoking has a significant effect on blood lead level, with an average increase of 5.8 percent in blood lead levels for every 10 cigarettes smoked per day. They also report that past smoking history had no measurable effect on blood lead levels. Hasselblad and Nelson (1975) report an average increase in women's blood lead levels of 1.3 pg/dl for smokers com pared to nonsmokers in the study of Tepper and Levin (1975). 11-181 TEH 0412177 DUP050452775 Although no studies are available, it is conceivable that destruction of lead-cantainijkj plastics (to recover copper), which has caused cattle poisoning, also could become a source jf lead exposure for humans. Waste disposal is a more general problem because lead-containing materials may be incinerated and may thus contribute to increased air lead levels. 2 source of lead has not been studied in detail. Tyrer (1977) cautions of the lead hazard "m the recycling of waste. -! The consumption of illicitly distilled liquor has been shown to produce clinical cases,^; lead poisoning. Domestic and imported earthenware (De Rosa et al., 198Q) with improperly fired glazes have also been related to clinical lead poisoning. This source becomes important when foods or beverages high in acid are stored in earthenware containers, because the `actd: releases lead from the walls of the containers. Particular cosmetics, popular among some Oriental and Indian ethnic groups, contain hi:Jh percentages of lead that sometimes are absorbed by users in quantities sufficient to be toxic. Ali et al. (1978) and Attenburrow et al. (1980) discuss the practice of surma and lead poison ing. In addition to lead-containing cosmetics causing lead poisoning, folk remedies have also been linked to lead poisoning (U. S. Centers for Disease Control, 1983a,b). Two Mexican folk remedies, Azarcon and greta, have been implicated as causing lead poisoning in children (U...S. Centers for Disease Control, 1983a). These products have a high lead content (70-90 percent) and are primarily lead tetroxide and lead oxide for Azarcon and greta, respectively. Thffe have been a minimum of 15 reported cases of lead poisoning associated with these products.^.A survey of Mexican-Hispanics living in Los Angeles estimated that 7.1-21.1 percent of Mexicar- Hispanic households had at some time used these products. ^31' A folk medicine used by Hmong refugees from Northern Laos has also been imp!icated>in lead poisoning of children (U.S. Centers for Disease Control, 1983b). The product, "pay-lqir ah," has a variable composition and texture, making control more difficult, Other sources jcf lead are presented in Table 11-71. Source Gasoline sniffing Colored gift wrapping Gunshot wound Drinking glass decorations Electric kettles Hair dye Snuff use Firing ranges Glazed pottery TABLE 11-71. SOURCES OF LEAD References 11-182 Kaufman and Wiese (1978) Coodin and Boeckx (1978) Hansen and Sharp (1978) Bertagnolli and Katz (1979) Diliman et al. (1979) Anonymous (1979) Wigle and Charlebois (1978) Searle and Harnden (1979) Filippini and Simmler (1980) Fischbein et al. (1979, 1980b) Acra et al. (1981) "I ISIS TEH 0412178 DUP050452776 11.6 SUMMARY AND CONCLUSIONS Using the bones and teeth of ancient populations, studies show that levels of internal exposures of lead today are substantially elevated over past levels. Studies of current populations living in remote areas far from urbanized cultures show blood lead levels in the range of 1-5 pg/dl. In contrast to the blood lead levels found in remote populations, data from current U.S. populations have geometric means ranging from <10 to 20 pg/dl depending on age, race, sex, and degree of urbanization. These higher current exposure levels appear to be associated with industrialization and widespread commercial use of lead, e.g., in gasoline combustion. Age appears to be one of the single most important demographic covariates of blood lead levels. Blood lead levels in children up to six years of age are generally higher than those in non-occupationally exposed adults. Children aged two to three years tend to have the high est levels, as shown in Figure 11-33. Blood lead levels in non-occupationally exposed adults may increase slightly with age due to skeletal lead accumulation. Sex has a differential impact on blood lead levels depending on age. No significant dif ferences exist between males and females less than seven years of age. Males above the age of seven generally have higher blood lead levels than females. Race also plays a role, in that blacks generally have higher blood lead levels than either whites or Hispanics and urban black children (aged 6 months-5 years) have markedly higher blood lead concentrations than any other racial or age group. Possible genetic factors associated with race have yet to be fully untangled from differential exposure levels and other factors as important determinants of blood lead levels. Blood lead levels also generally increase with degree of urbanization. Data from NHANES II show blood lead levels in the United States, averaged over 1976-1980, increasing from a geometric mean of 11.9 pg/dl in rural populations to 12.8 pg/dl in urban populations of less than one million, and increasing.again to 14.0 pg/dl in urban populations of one million or more. Blood lead levels, examined on a population basis, have similarly skewed distributions. Blood lead levels, from a population thought to be homogeneous in terms of demographic and lead exposure characteristics, approximately follow a lognormal distribution. The geometric standard deviations, an estimation of dispersion, for four different studies are shown in Table 11-72. The values, including analytic error, are about 1.4 for children and possibly somewhat smaller for adults. This allows an estimation of the upper tail of the blood lead distribution, the group at higher risk. A somewhat larger geometric standard deviation of 1.42 may be derived from the NHANES II study when only gasoline and industrial air lead emission exposures are assumed to be controllable sources of variation. 11-183 TEH 0412179 DUP050452777 40 35 30 TJ a. Q< 25 ao o / ------ ---- NEW YORK SCREENING - HISPANICS ----------- NHANES II STUDY - BLACKS ----------- NHANES II STUDY WHITES Si.'1;.; 20 v s: \ 15 sill! 01 2345678 AGE, yr i______i 10 Figure 11-33. Geometric mean blood lead levels by race and age for younger children in the NHANES II study, and the Kellogg/Silver Valley and New York Childhood Screening Studies. US 11-184 TEH 04i: DUP050452778 TABLE 11-72. SUMMARY OF BLOOD LEAD POOLED GEOMETRIC STANDARD DEVIATIONS AND ESTIMATED ANALYTIC ERRORS Study Pooled geometri<: standard deviations Inner city Inner city black children white children NHANES II 1.37a 1. 39a N.Y. Childhood Screening Study 1.41 1.42 Tepper-Leven - - Azar et al. - - Adult females 1.36b - 1.30 - Adult males 1.40b Estimated analytic error 0.021 _c - 1.29 0.056d 0.042d Note: To calculate an estimated person-to-person GSD, compute Exp [((In(GSD))2 Analytic Error)1//2^ aA geometric standard deviation of 1.42 may be derived when only gasoline and industrial air lead emission exposures are assumed to be controllable sources of variability. ^Pooled across areas of differing urbanization cNot known, assumed to be similar to NHANES II dTaken from Lucas (1981). Recent U.S. blood lead levels show a downward temporal trend occurring consistently across race, age, and geographic location. The downward pattern commenced in the early part of the 1970's and has continued into 1980. The downward trend has occurred from a shift in the entire distribution and not through a truncation in the high blood lead levels. This con sistency suggests a general causative factor, and attempts have been made to identify the causative element. Reduction in lead emitted from the combustion of leaded gasoline is a prime candidate. Studies of data from blood lead screening programs (i.e., New York City) suggest that the downward trend in blood lead levels noted earlier is due to the reduction in air lead levels, which has been attributed to the reduction of lead in gasoline. The NHANES II analysis found a highly significant association between the declining blood lead concentrations for the over all U.S. population and decreasing amounts of lead used in gasoline in the United States during the same time period. Two studies used isotope ratios of lead to estimate the relative proportion of lead in the blood coming from airborne lead. From one study, by Manton, it can be estimated that between 7 and 41 percent of the blood lead in study subjects in Dallas 11-185 TEH 0412181 DUP050452779 , resulted from airborne lead. Additionally, these data provide a means of estimating Lhp-whV- `'o direct contribution of air lead to blood lead. By one estimate, only 10 - 20 percent of thf- . \ total airborne contribution in Dallas is from direct inhalation. =i' From the ILE data in Facchetti and Geiss (1982) and Facchetti (1985), as shown in Taele y 11-73, the direct inhalation of air lead may account for 60 percent of the total adult bbod'?,' V lead uptake from leaded gasoline in a large urban center, but inhalation is a much less impjr-/ tant pathway in suburban parts of the region (19 percent of the total gasoline lead cuntrfbu-. rV tion) and in the rural parts of the region (9 percent of the total gasoline lead ccntribu-r'~}s 'V tion). EPA analyses of the preliminary results from the ILE study separated the inhalation"!^ " and non-inhalation contributions of leaded gasoline to blood lead into the following tb>et . " parts: (1) an increase of about 1.7 pg/dl in blood lead per pg/m3 of air lead, attributable Vi to direct inhalation of the combustion products of leaded gasoline; (2) a sex difference-t, about 2 pg/dl attributable to lower exposure of women to indirect (non-inhalation) patnw^f * for gasoline lead; and (3) a non-inhalation background attributable to indirect gasoline leag11 * pathways, such as ingestion of dust and food, increasing from about 2 pg/dl in Turin to '3 pg/dl in remote rural areas. The non-inhalation background represents only two to three yeajra.^ ^ of environmental accumulation at the new experimental lead isotope ratio. It is not clear htw ^ to numerically extrapolate these estimates to U.S. subpopulations; but it is evident that eye^ in rural and suburban parts of a metropolitan area, the indirect (non-inhalation) pathways Jotf'l exposure to leaded gasoline make a significant contribution to blood lead. This can be seen'.in; Table 11-73. It should also be noted that the blood lead isotope ratio responded fa"rljj rapidly when the lead isotope ratio returned to its pre-experimental value, but it is notjjg't ?r P w possible to estimate the long-term change in blood lead attributable to persistent exposure# t to accumulated environmental lead. ,1* The strongest kind of scientific evidence about causal relationships is based on an ex\ periment in which all possible extraneous factors are controlled. The evidence derived fr$Z the Isotopic Lead Experiment (ILE) comes very close to this ideal. The experimental intej^ vention consisted of replacing the normal 206Pb/207Pb isotope ratio by a very different ratin-TJ There is no plausible mechanism by which other concurrent lead exposure variables (food, wate^;and beverages, paint, and industrial emissions) could have also changed their isotope ratios.*^ Hence the very large changes in isotope ratios in blood were responding to the change/ gasoline. There was no need to carry out detailed aerometric and ecological modeling to fcracjt,-, * the leaded gasoline isotopes through the various environmental pathways. In fact, our ana'Jy:1^ ? ses (Section 11.3.6.2.1) show that consideration of inhalation of community air lead '' will substantially under estimate the total effect of gasoline lead, at least in the 35 sulf : ff jects whose blood leads were tracked in the ILE Preliminary Study. This may be partia|fjSpwJg explained by the differences in the lead concentration measured by stationary monitors 11-186 Vr' ' * ' jVi '' TEH 041218 DU PC'5*0452780 TABLE 11-73. ESTIMATED CONTRIBUTION OF LEADED GASOLINE TO BLOOD LEAD BY INHALATION AND NON-INHALATION PATHWAYS Location Turin <25 tan >25 km Air lead fraction from gasoline3 0.873 0.587 0.587 Blood lead fraction from gasoline13 0.214 0.114 0.101 Blood lead from gasoline in airc (pg/dl) 2.79 0.53 0.28 Blood lead not inhaled from .gaso line0 (pg/dl) 1.88 2.33 2.93 Estimated fraction gas-lead inhalation6 0.60 0.19 0.09 ?Fraction of air lead in Phase 2 attributable to lead in gasoline. "Mean fraction of blood lead In Phase 2 attributable to lead in gasoline. jEstimated blood lead from gasoline inhalation = p x a x b, p = 1.6. "Estimated blood lead from gasoline, non-inhalation = f-e. "Fraction of blood lead uptake from gasoline attributable to direct inhalation = f/e. Source: Facchetti and Geiss (1982), pp. 52-56; Facchetti (1985). compared to those that would be measured by personal monitors, expecially if higher exposures occur in certain microenvironments. Diet lead is also an explanation for the large excess of gasoline lead isotope ratio in blood beyond that expected from inhalation of ambient air lead, both from gasoline lead entering the food chain and added by food processing and preparation. The subjects in the ILE study cannot be said to represent some defined population, and it is not clear how the results can be extended to U.S. populations. Turin's unusual meteorology, high lead levels, and "reversed" urban-rural gradient of the subjects in the ILE study indi cate the need for future research. But in spite of the variable gasoline lead exposures of the subjects, there is strong evidence that changes in gasoline lead produce large changes in blood lead. Because the main purpose of this chapter is to examine relationships of lead in air and lead in blood under ambient conditions, the results of studies most appropriate to this area have been emphasized. A summary of the most appropriate studies appears in Table 11-74. At air lead exposures of 3.2 pg/m3 or less, there is no statistically significant difference be tween curvilinear and linear blood lead inhalation relationships. At air lead exposures of 10 pg/m3 or more, either nonlinear or linear relationships can be fitted. Thus, a reasonably consistent picture emerges in which the blood lead to air lead relationship by direct inhala tion was approximately linear in the range of normal ambient exposures of 0.1-2.0 pg/m3 (as discussed in Chapter 7). Differences among individuals in a given study (and among several 11-187 TEH 0412183 DUP050452781 TABLE 11-74. SUMMARY OF BLOOD INHALATION SLOPES, (p) (jg/dl per pg/m3 MSf Population Children Children Children Adult males Adult males Adult males Adult males Study Study type Angle and Population Mclntire, 1979 Omaha, NE Roels et al. (1980) Belgium Population Yankel et al. Population (1977); Walter et al. (1980) Idaho Azar et al. (1975). Five groups Population Griffin et al. (1975), NY prisoners Experiment Gross (1979) Experiment Rabinowitz et Experiment al. (1973,1976, 1977) (P) Slope, N pg/dl per pg/m3 1074 1.92 148 2.46 879 1.52 Model sensitivity of slope* (1.40 - 4.40)a'b'c~ mm iM. (1.55 - 2.46)a,L jjl (1.07 - 1.52)a,b,c 149 1.32 43 1.75 6 1.25 5 2.14 (1.08 - 2.39) (1.52 - 3.38) (1.25 - 1.55)' (2.14 - 3.51)' ^Selected from among the most plausible statistically equivalent models, For nonlinear models, slope at 1.0 pg/m3. ^Sensitive to choice of other correlated predictors such as dust and soil lead. "'Sensitive to linear versus nonlinear at low air lead. 'Sensitive to age as a covariate. ^Sensitive to baseline changes in controls. ^Sensitive to assumed air lead exposure. 11-188 TEH 0412H DUP050452782 studies) are large, so that pooled estimates of the blood lead inhalation slope depend upon the weight given to various studies. Several studies were selected for analysis, based upon factors described earlier. EPA analyses* of experimental and clinical studies (Griffin et a!., 1975; Rabinowitz et a!., 1974, 1976, 1977; Kehoe 1961a,b,c; Gross, 1981; Hammond et al., 1981) suggest that blood lead in adults increases by 1.64 0.22 pg/dl from direct inhalation of each additional pg/m3 of air lead. EPA analysis of Azar's population study (Azar et al., 1975) yields a slope of 1.32 0.38 for adult males. EPA analyses of population studies (Yankel et al., 1977; Reels et al., 1980; Angle and Mclntire, 1979) suggest that, for chil dren, the median blood lead increase is 1.97 pg/dl per pg/m3 for inhaled air lead. These slope estimates are based on the assumption that an equilibrium level of blood lead is achieved within a few months after exposure begins, This is only approximately true, since lead stored in the skeleton may return to blood after some years. Chamberlain et al. (1978) suggest that long-term inhalation slopes should be about 30 percent larger than these estima tes. Inhalation slopes quoted here are associated with a half-life of blood lead in adults of about 30 days. 0`Flaherty et al. (1982) suggest that the blood lead half-life may increase slightly with duration of exposure, but this has not been confirmed (Kang et al., 1983). One possible approach would be to regard all inhalation slope studies as equally infor mative and to calculate an average slope using reciprocal squared standard error estimates as weights. This approach has been rejected for two reasons. First, the standard error estima tes characterize only the internal precision of an estimated slope, not its representativeness (i.e., bias) or predictive validity. Secondly, experimental and clinical studies obtain more information from a single individual than do population studies. Thus, it may not be appro priate to combine the two types of studies. Estimates of the inhalation slope for children are only available from population studies. The importance of dust ingestion as a non-inhalation pathway for children is estab lished by many studies. A pooled slope estimate, 1.97 0.39, has been derived for air lead inhalation based on those studies (Angle and Mclntire, 1979; Roels et al., 1980; Yankel et al., 1977) from which the air inhalation and dust ingestion contributions can both be esti mated. Aggregate analyses of data from these and several other studies typically yield slope estimates in the range of 3-5 for the combined impact of both direct (inhaled) and indirect (via dust, etc.) contributions of air lead to blood lead in children. *Nate: The term EPA analyses refers to calculations done at EPA. A brief discussion of the methods used is contained in Appendix 11-B; more detailed information is available at EPA upon request. 11-189 TEH 0412185 DUP0S0452783 While direct inhalation of air lead is stressed, this is not the only air lead corcritun't tion that needs to be considered. Smelter studies allow partial assessment of the air "itati/ contributions to soil, dust, and finger lead. Conceptual models allow preliminary estimation* of the propagation of lead through the total food chain as shown in Chapter 7. Useful mat he-* matical models to quantify the propagation of lead through the food chain need to be devbj-, oped. The direct inhalation relationship does provide useful information on changes in bjcoif, lead as responses to changes in air lead on a time scale of several months. The indirdti` pathways through dust and soil and through the food chain may thus delay the total blood leaa^* response to changes in air lead, perhaps by one or more years. The Italian ILE study 1 ac11 tates partial assessment of this delayed response from leaded gasoline as a source. Dietary absorption of lead varies greatly from one person to another and depends on the*1 physical and chemical form of the carrier, on nutritional status, and on whether lead is ih1"1' gested with food or between meals. These distinctions are particularly important for consuirp-, tion by children of leaded paint, dust, and soil. Typical values of 10 percent absorption of ingested lead into blood have been assumed for adults and 25 to 50 percent for childi i It is difficult to obtain accurate dose-response relationships between blood lead level's1' and lead levels in food or water. Dietary intake must be estimated by duplicate diets oft fecal lead determinations. Water lead levels can be determined with some accuracy, but the varying amounts of water consumed by different individuals add to the uncertainty of the esti mated relationships. C Quantitative analyses relating blood lead levels and dietary lead exposures have been reported. Studies on infants provide estimates that are in close agreement. Only one indi vidual study is available for adults (Sherlock et al. 1982); another estimate from a number* df' . 1 pooled studies is also available. These two estimates are in good agreement. Most of the subjects in the Sherlock et al. (1982) and United Kingdom Central Directorate on Environme'r^S Pollution (1982) studies received quite high dietary lead levels (>300 pg/day). The fitted cube root equations give high slopes at lower dietary lead levels. On the other hand, tjer linear slope of the United Kingdom Central Directorate on Environmental Pollution (1982) stu^j is probably an underestimate of the slope at lower dietary lead levels. For these reasors,^ the Ryu et al. (1983) study is the most believable, although it only applies to infant ^ also probably underestimates to some extent the value of the slope. Estimates for adults \ should be taken from the experimental studies or calculated from assumed absorption and haifr . life values. Most of the dietary intake supplements were so high that many of the subject#* had blood lead concentrations much in excess of 30 pg/dl for a considerable part of the - periraent. Blood lead levels thus may not completely reflect lead exposure, due to >8* *- previously noted nonlinearity of blood lead response at high exposures. The slope estirate?.. llMHi 11-190 V Ullf * ' TEH 0412186 | A DUP050452784 for adult dietary intake are about 0.02 pg/dl increase in blood lead per pg/day intake, but consideration of blood lead kinetics may increase this value to about 0.04. Such values are a bit lower than slopes of about 0.05 pg/dl per pg/day estimated from the population studies ex trapolated to typical dietary intakes. The value for infants is larger. The relation between blood lead and water lead is not clearly defined and is often de scribed as nonlinear. Water lead intake varies greatly from one person to another. It has been assumed that children can absorb 25-50 percent of lead in water. Many authors chose to fit cube root models to their data, although polynomial and logarithmic models were also used. Unfortunately, the form of the model greatly influences the estimated contributions to blood leads from relatively low water lead concentration. Although there is close agreement in the quantitative analyses of the relationship bet ween blood lead level and dietary lead, there is a larger degree of variability in results of the various water lead studies. The relationship is curvilinear, but its exact form is yet to be determined. At typical levels for U.S. populations, the relationship appears linear. The only study that determines the relationship based on lower water lead values (<100 pg/1) is the Pocock et al. (1983) study. The data from this study, as well as the authors themselves, suggest that in this lower range of water lead levels, the relationship is linear. Further more, the estimated contributions to blood lead levels from this study are quite consistent with the polynomial models .from other studies. For these reasons, the Pocock et al. (1983) slope of 0.06 is considered to represent the best estimate. The possibility still exists, however, that the higher estimates of the other studies may be correct in certain situations, especially at higher water lead levels (>100 pg/1). Studies relating soil lead to blood lead levels are difficult to compare. The relation ship obviously depends on depth of soil lead, age of the children, sampling method, cleanli ness of the home, mouthing activities of the children, and possibly many other factors. Var ious soil sampling methods and sampling depths have been used over time, and as such they may not be directly comparable and may produce a dilution effect of the major lead concentration contribution from dust which is located primarily in the top 2 cm of the soil. Increases in soil dust lead significantly increase blood lead in children. From several studies (Yankel et al., 1977; Angle and Mclntire, 1979) EPA estimates an increase of 0.6-6.8 pg/dl in blood lead for each increase of 1000 pg/g in soil lead concentration. Values of about 2.0 pg/dl per 1,000 pg/g soil lead from the Stark et al. (1982) study may represent a reasonable median estimate. The relationship of housedust lead to blood lead is difficult to obtain. House hold dust also increases blood lead, as children from the cleanest homes in the Silver Valley/ Kellogg Study had 6 pg/dl less lead in blood, on average, than those from the households with the most dust. 11-191 TEH 0412187 DUP050452785 A number of specific environmental sources of airborne lead have been identsit having a direct influence on blood lead levels. Primary lead smelters, secondary, smelters, and battery plants emit lead directly into the air and ultimately increase.soil1 dust lead concentrations in their vicinity. Adults, and especially children, have been ' to exhibit elevated blood lead levels when living close to these sources. Blood lead;!' in these residents have been shown to be related to air, as well as to soil or dust expos The habit of cigarette smoking is a source of lead exposure. 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A mathematical model is helpful in estimating the new apparent equilibrium level even when the duration of the experiment is not sufficiently long for this equilibrium level to have been achieved. The model assumes that lead in the body is held in some number of homogeneous and well-mixed pools or compartments. The compartments have similar kinetic properties and may or may not correspond to identifiable organ systems. In a linear kinetic model it is assumed that the rate of change of the mass of lead in compartment i at time t, denoted X|(t), is a linear function of the mass of lead in each compartment. Denote the frac tional rate of transfer of lead into compartment i from compartment j by K.. (fraction per 1J day), and let I.(t) be the total external lead input into compartment i at time t in units such as pg/day. The elimination rate from compartment i is denoted KQ.. The compartmental model is for each of the n compartments. If the inputs are all constant, then each X..<t) is the sum of (at most) n exponential functions of time (see for example, Jacquez, 1972). For the one-compartment model dX.(t)/dt = It - k q1 Xx(t) with an initial lead burden X1(0) at time 0, Xi(t) = xa(0) exp(-KoXt) + [(Ii/Kjji) (l-exp(-K0lt)] (11-24) (11-25) The mass of lead at equilibrium is Ii/Kq X pg. We may think of this pool as "blood lead". If the pool has volume Vx then the equilibrium concentration is Ii/Kq1 Vx pg/dl. Intake from several pathways will have the form Ix = Ax (Pb-Air) + A2 (Pb-Diet)+ * ` * (11-26) 11A-1 TEH 0412208 DUP050452806 so that the long-term concentration is Ii/K0i Vx = Pb-Air + ' (11-27) The inhalation coefficient is p = Aj/KgiVj.. The blood lead half-life is 0.693/Kq j . Models with two or more compartments will still have equilibrium concentrations in blood and other compartments that are proportional to the total lead intake, and thus increase linearly with increasing concentrations in air, dust, and diet. The relationship between the exponential parameters and the fractional transfer coefficients will be much more complicated, however. Models with two or three pools have been fitted by Rabinowitz et al. (1976, 1977) and by Batschelet et al. (1979). The pools are tentatively identified as mainly blood, soft tissue and bone. But as noted in Section 11.4.1.1, the "blood" pool is much larger than the volume of blood itself, and so it is convenient to think of this as the effective volume of distri bution for pool 1. A five-pool model has been proposed by Bernard (1977), whose pools are mainly blood, liver, kidney, soft bones and hard bone. The major conclusion of this Appendix is that linear kinetic mechanisms imply linear relationships between blood lead and lead concentrations in environmental media. An'extended discussion of nonlinear kinetic mechanisms is given in Chapter 10, based on analyses in Marcus (1985). One important mechanism involves an apparent limitation on the amount of lead that can be absorbed by the red blood cells. However, at blood lead levels <30 pg/dl this limitation does not greatly affect the linearity of the relationship between blood lead and lead exposure. 11A-2 TEH 0412209 DUP050452807 APPENDIX 11B FITTING CURVES TO BLOOD LEAD DATA The relationship between blood lead and the concentrations of lead in various environ mental media is a principal concern of this chapter. It is generally accepted that the geo metric mean blood lead is some function, f, of the concentration of air lead and of lead in diet, dust, soil, and other media. It has been observed that blood lead levels have a highly skewed distribution even for populations with relatively homogeneous exposure, and that the variability in blood lead is roughly proportional to the geometric mean blood lead or to the arithmetic mean (constant coefficient of variation). Thus, instead of the usual model in which random variations are normally distributed, a model is assumed here in which the random deviations are multiplicative and lognormally distributed with geometric mean 1 and geometric standard deviation (GSD) eCT. The model is written Pb-Blood = f (Pb-Air, etc.) eaz (11-28) where 2 is a random variable with mean 0 and standard deviation 1. It has a Gaussian or normal distribution. The model is fitted to data in logarithmic form In(Pb-Blood) = In (f) (11-29) even when f is assumed to be a linear function, e.g., f = P Pb-Air + PQ + Pi Pb-Dust + ... (11-30) The nonlinear function, fitted by most authors (e.g., Snee, 1982b), is a power function with shape parameter A., f = (p Pb-Air + pQ + pi Pb-Dust + ...)X (11-31) These functions can all be fitted to data using nonlinear regression techniques. Even when the nonlinear shape parameter A has a small statistical uncertainty or standard error as sociated with it, a highly variable data set may not clearly distinguish the linear function (A = 1) from a nonlinear function (A 4 1). In particular, for the Azar data set, the residual sum of squares is shown as a function of the shape parameter A, in Figure 11B-1. When only a 11B-1 TEH 0412210 DUP050452808 RESIDUAL SUM OF SQUARES Figure 11 B-1. Residual sum of squares for nonlinear regression models for Azar data (N = 149). 11B-2 Wsm St TEH 0412211 DUP050452809 separate intercept (background) is assumed for each subpopulation, the best choice is X = 0.26; but when age is also used as a covariate for each subpopulation, then the linear model is better. However, the approximate size of the difference in residual sum of squares required to decide at the 5 percent significance level that a nonlinear model is better (or worse) than a linear model is larger than the observed difference in sum of squares for any K>0.2 (Gallant, 1975). Therefore, a linear model is used unless evidence of nonlinearity is very strong, as with some of Kehoe's studies and the Silver Valley/Kellogg study. Non linearity is detectable only when blood lead is high (much above 35 or 40 pg/dl), and intake is high, e.g., air lead much above 10 pg/m3. Additional research is needed on the relation ship between lead levels and lead intake from all environmental pathways. 11B-3 TEH 0412212 DUP050452810 APPENDIX 11C ESTIMATION OF GASOLINE LEAD CONTRIBUTIONS TO ADULT BLOOD LEAD BURDENS BASED ON ILE STUDY RESULTS As discussed in Chapter 11 (pp. 11-118 to 11-123) the results of the Isotopic Lead Ex periment (ILE) carried out in Northern Italy provide one basis by which to estimate contribu tions of lead in gasoline to blood lead burdens of populations exposed in the ILE study area. Figures 11C-1 to 5 of this appendix, reprinted from Facchetti and Geiss (1982), illustrate changes in isotopic 206Pb/207Pb ratios for 35 adult subjects, for whom repeated measurements were obtained over time during the ILE study. The percent of total blood lead in those sub jects contributed by Australian lead-labeled gasoline (petrol) used in automotive vehicles in the ILE study area was estimated by the approach reprinted below verbatim from Appendix 17 of Facchetti and Geiss (1982): The main purpose of the ILE project was the determination of the contribution of petrol lead to total lead in blood. A rough value for the fraction of petrol lead in blood can be derived from the following equations: Ri X + f (1-X) = R' R2 X + f (1-X) = R" (1) (11) each of them referring to a given time at which equilibrium conditions hold. R1 and R" represent the blood lead isotopic ratios measured at each of the two times; if R-|_ and R represent the local petrol lead isotopic ratios measured at the same times, X is the fraction of local petrol lead in blood due to petrols affected by the change in the lead isotopic ratio, irrespective of its pathway to the blood i.e., by inhalation and ingestion (e.g., from petrol lead fallout). The term (1-X) represents the fraction of the sum of all other external sources of lead in the blood (any other>> petrol lead included), factor f being the unknown isotopic ratio of the mixture of these sources. It is assumed that X and f remained constant over the period of the experiment, which implies a reasonable constancy of both the lead contributing sources in the test areas and the living habits which, in practice, might not be entirely the case. Data from individuals sampled at the initial and final equilibrium phases of the ILE study together with petrol lead isotopic ratios measured at the same times, would ideally provide a means to estimate X for Turin and countryside adults. However, for practical reasons, calculations were based on the initial and final data of the subjects whose first llC-1 TEH 0412213 DUP050452811 sampling was done not later than 1975 and the final one during phase 2. Their complete follow-up data are shown in Table 27. For R^ and R^ the values measured in the phases 0 and'2 of ILE were used (R^ = 1.186, R,, = 1.060). Hence, as averages of the individual X and f results, we obtain: Turin countryside <25 km countryside >25 km Xi = 0.237 0.054 fx * 1.1560 0.0033 X2 = 0.125 0.071 f2 * 1.1542 0.0036 X3 = 0.110 0.058 f3 * 1.1576 0.0019 i.e 24% i.e. 12% i.e 11% Figure 11C-1. Individual values of blood Pb-206/Pb-207 ratio for subjects follow-up in Turin {12 subjects). Source: Facchetti and Geiss (1982). 11C-2 TEH 0412214 DUP050452812 q<wqd9oS qdm/qdso? Figure 11C-2. Individual values of blood 206Pb/207Pb ratio for subjects follow-up in Castagnetto {4 subjects). Figure 11C-3. Individual values of blood 206Pb/207Pb ratio for subjects follow-up in Oruento and Fiano (6 subjects). Source: Facchetti and Geiss (1982). 11C- 3 TEH 0412215 DUP050452813 206pb/207pb Figure 11C-4. Individual values of blood 206Pb/207Pb ratio for subjects follow-up in Note and Santena (9 subjects). JO fipb/20/pb Figure 11C-5. Individual values of blood 20BPb/207Pb ratio for subjects follow-up in Viu (4 subjects). Source; Facchetti and Geiss (1982). 11C-4 ijU.S GOVERNMENT PRINTING OFFICE: 198 6- 64 6-116^40643 TEH DUP050452814 00 ID <inN ro cc o c u DUP050452815 Official Business Penalty for Private Use, $300