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ANALYSIS OF NHANES 11 BLOOD LEAD STUDY PLMR-5S-83 l M. PIERRARD PETROLEUM LABORATORY E. 1. DU PONT DE NEMOURS & CO. SEPTEMBER 21, 1983 TEH 0532477 DUP050033743 Notts'. The U.S. Government's second National Health and Nu trition Examination Survey - known as NHANES II - was de signed to assess nutritional status of the population based on questionaires and examinations administered in 64 sample areas over a 4 year period. As an added part of the study, venous blood lead measurements were made on 9936 persons (1). The study was designed for cross-sectional analysis that is, to obtain a value for each measured variable repre sentative at the study midpoint - and not for chronological analysis. However, an apparent blood lead decrease of 37? over the 4 year study period prompted attempts to analyze the time trend (2), TEH 0532478 DUP050033744 NHANESH Assessment of National Health Status February 1976 to February 1980 64 Sampling Sites 6 Months to 74 Years of Age 27,801 Persons Selected -- 20,322 Examined 9,936 Venous Blood Lead Levels Determined Not Designed for Chronological Trend Analysis Apparent 37 Percent Reduction in Blood Lead TEH 0532479 DUP050033745 Attention was drawn to this representation of the par allel declines of six month average blood lead and total U.S. gasoline lead use (3). This figure might well have led some to infer that the blood lead decline was solely due to the decline in total gasoline lead use. TEH 0532480 DUP050033746 Average Blood Lead Levels (//g/dl') Gasoline Lead and NHANESU Blood Lead Levels (Feb. 1976 -- Feb. 1980) TEH 0532481 DUP050033747 i Once the basic data became available, further exami nation showed that there is substantial confounding because of nonuniformity of subject characteristics over the 4 year course of the NHANES II study. This figure shows one example of such confounding (4). These considerations resulted in a number of more de tailed analyses, including our own. to contrast the fea tures of the various analyses, it is helpful to consider the identifiable factors which might affect apparent blood lead. TEH 0532482 DUP050033748 Average Blood Lead Levels (//g/dl) Urban Dwellers Sampled and NHANES XI Blood Lead Levels (Feb. 1976 -- Feb. 1980) TEH 0532483 DUP050033749 It is generally agreed that exposure to lead may occur via a number of routes. In several analyses of the NHANES II data conducted or sponsored by government groups, it was assumed that only exposure to lead from gasoline decreased during the study period (5,6,7). Their assumption that food lead was un changed was justified on the basis of calculated lead content for a constant market basket of foods (8). However, 6U% of the U.S. households surveyed in 1979 by the Economics and Statistics service of the U.S. Department of Agriculture reported diet changes during the period 1977 to 1979 (9). Furthermore, alumi num cans were displacing soldered cans during this period (10). Therefore, we made provision in our analysis for possible changes due to these or other unquantifiable factors. Returning to gasoline lead, it should be noted that the other analyses referred to used total national gasoline lead use as the index of exposure. Yet, the 6H sites visited dur ing NHANES II had a wide range of lead exposures as shown by air lead data. To account for this variability, we calculated the site-specific gasoline lead density for each location vis ited. Each site consisted of one or more counties. The gaso line lead consumed in the site county at the time of the visit was calculated from state gasoline consumption and lead dosage, and county and state populations, using the fact that gasoline consumption is highly correlated with population in most of the U.S. (11). The site-specific lead density then was calculated by dividing county lead use by county area. This approach allows for exposure to gasoline lead by ingestion as well as in hat ion. The study design factors listed in the chart were treated as classification variables. Caravan itinerary covers region of the country and season. Personal variables are sex, age, and race, and residence variables are size of city or town and in or outside of the core city of a Standard Metropolitan Sta tistical Area. Quality control data on the laboratory analysis of blood leads for the last 3 years of NHANES II do not indicate any significant problem. However, there were no check samples car ried through the sequence of field collection, storage, ship ment and final analysis at the home laboratory, so we allowed for a possible trend contribution from this source. TEH 0532484 DUP050033750 identifiable Factors Potentially influencing Blood Lead Trend Exposure Air Lead from Gasoline Food and Beverages Water Paint Dust Study Design Caravan Itinerary Personal Variables Residence Characteristics Study Execution Laboratory Analysis Sample Handling TEH 0532485 DUP050033751 Identifiable Factors Potentially Influencing Blood Lead Trend Exposure Air Lead from Gasoline Food and Beverages Water Study Design Caravan Itinerary Personal Variables Residence Characteristics Study Execution Laboratory Analysis Sample Handling TEH 0532485 DUP050033752 We investigated the time trend contribution attributable to the demographic factors alone, for demographics and gasoline lead, and for demographies, gasoline lead and time, which was used as a surrogate for unquantiftable time-related blood lead effects. Details are given in our paper (12) which is appended to this report. Of particular interest is this comparison of national gaso line lead use and site-specific lead density. National gasoline use is not statistically significant as a blood lead predictor in the presence of the time surrogate for other time-related blood lead effects. On the other hand, site-specific lead den sity and its logarithm retain their Significance, TEH 0532486 DUP050033753 Significance of National Gasoline Lead and Site Specific Lead Density Gasoline Lead Exposure Variable National Site Density Log (Site Density) Significance Level* Variable 0.6850 0.0022 0.0019 Time <0.0001 < 0.0001 <0.0001 *AII models included the full set of 30 demographic terms. TEH 0532487 DUP050033754 The histogram shows the frequency distribution of the correlations with time of the site-specific lead densities at each of the NHANES II sites over the 4 years of the study. The arrow at A shows that total national gasoline lead use is highly correlated with time. But, as indicated by the arrow at B, the site-specific lead densities at the sites when they were actually visited is poorly correlated with time. Thus, national gasoline lead use not only fails to re produce the time history of lead exposure as the caravans moved from site to site, but it also obscures the influence of other potential time-related effects because it is highly correlated with time. TEH 0532488 DUP050033755 Correlation ot Gasoline Lead Density and Time Correlation Coefficient TEH 0532489 DUP050033756 Using site-specific lead density as the measure of ex posure to gasoline lead, stepwise regression analysis showed that Over half the apparent blood lead decrease can be accounted for by changing demographics, About one-tenth of the apparent blood lead de crease can be accounted for by gasoline lead exposure, A significant time trend still remains after accounting for demographies and gasoline lead exposure. TEH 0532490 DUP050033757 Contributions to Blood Lead Decrease 1976-80 TEH 0532491 DUP050033758 To complement the stepwise regression analysis reported in (12), we analyzed the NHANES II blood lead data by the method of split-plot covariance analysis (13). This method takes its name from agricultural applications, where a field or "plot" is "split" and planted with two varieties of plant. To validly compare performance of the two varieties grown un der the same conditions "within-plot" corrections - such as for different numbers of the plant varieties - must be made. To compare performance of the varieties in different fields, or plots - say under different climatic conditions - "betweenplot" corrections are required. The situation is analogous for the NHANES II blood lead data set. Here, corrections are required for within-site differences in the characteristics of the subjects. The within-site analysis adjusts the raw observed blood lead value of each individual at a Site to the value he would have if his personal and residence characteristics were the average values for the site. The between-site analysis amounts to an adjustment of the site-adjusted blood leads to the value each would have if every site had the same value of each of the personal, residence and itinerary variables. After these adjustments all observations are on a common basis relative to demographics, and the remain ing time trend is attributable to lead exposure factors and/or other trend influences. By omitting or including site-specific lead density in the adjustment process, we were able to estimate the contribution of gasoline lead to the blood lead decrease. TEH 0532492 DUP050033759 Steps in Blood Lead Trend Analysis Adjust for Differing Characteristics of individual Subjects Further Adjust for Differing Site Characteristics -- With and Without Gasoline Lead Quantify Unexplained time Trend Compare Unexplained Time Trend With and Without Gasoline Lead Exposure TEH 0532493 DUP050033760 The split-plot analytical approach was applied to 216 models for blood lead as listed. An important result is that use of the NHANES II blood lead weighting factors, or the basis of residual weighting, or the transformation of the dependent variable blood lead did not affect the overall results * which were consistent throughout. TEH 0532494 DUP050033761 Analyses for Residual Time Trend Factor _________ ___________ BPb and In BPb P, R, I and 26 combinations of current and lagged site specific gasoline lead density and their logarithms With and without BPb weighting factors Residuals weighted according to 1/S2 and N Options 2 27 2 2 Number of models = 2x27 x 2x2 = 216 Consistent results regardless of BPb weights, residual weighting, and BPb or In BPb TEH 0532495 DUP050033762 Because the results were consistent, the overall picture can be grasped by examining a few cases. For untransformed blood lead as the dependent variable, before adjustment to remove any effects, the 4-year decrease is 5.8 ug/dl. After within-site and between-site adjustment for itinerary, personal, and residence (DEM) variations, this is reduced to about 1.6 pg/dl, with R|=0.53. Including current site-specific lead density (G Pb) or its lagged values (G Pb3Q - 30 days lag, G Pbjjc - 45 days, lag) in the model accounts for up to 0.5 jug/m3 of the 4-year decrease. Note that the addition of lagged lead density terms after the first one has little effect on either the blood lead decrease attributable to gasoline lead or on R?. Also note in the last two lines that making the adjustment for gasoline lead before any adjustment for demographics reduces the 4-year decrease by less than 1 jug/dl, but with R? of only 0.20 to 0.21. TEH 0532496 DUP050033763 Typical Model Results* ciiecis nemoveci None DEM DEM, GPb DEM. GPb, GPb.,0 DEM. GPb. GPb;i0. GPb45 DEM. log GPb DEM. tog GPb. log GPb30 DEM. log GPb. log GPb30. log GPb45 GPb tog GPb Blood Lead,i/g/dl Remaining Pour Year Attributable 9 Gasoline Lead 5.80 1.62* 1,27 0.35 1.21 0.41 1.19 0.43 1.48 0.14 1.10 0.52 1.09 0.53 5.17 4.93 R* 0.53 0.59 0.59 0.58 0.57 0.60 0,59 0.20 0.21 `Dependent variable !3Pt> residuals weighted by 1 /S' no BPb weights TEH 0532497 DUP050033764 ___________' ` ' Typical Model Results* Effects Removed None DEM DEM. GPb DEM. GPb. GPb30 DEM. GPb. GPb30. GPb45 DEM. log GPb DEM, log GPb. log GPb3p DEM. log GPb. log GPb30. log GPb45 GPb log GPb Blood Lead,jjg/dl Remaining Pour Year Attributable Decrease to Gasoline Lead 5.80 I.Gf 1.27 0.35 1.21 0.41 1.19 0.43 1.48 014 1.10 0.52 1.09 0.53 5.17 4.93 R* 0.53 0.59 0.59 0.58 0.57 0.60 0.59 0.20 0.21 "Dependent variable BPb. residuals weighted by t/S? no BPb weights TEH 0532497 DUP050033765 From the site-by-site analysis (12) and from the additional split-plot analysis of covariance on the individual observations just discussed, we conclude that national gasoline lead use is not a valid index because it does not reflect the exposures due to lead use at the NHANES II sites at the times they were sampled. Further, confounding of total national gasoline lead use with time precludes estimation of other unquantifiable, time-related effects. We found that over half of the apparent blood lead decrease is traceable to changes in site subject demographics. From a large number of models we estimate, that 5 to 10? (or 0.3 to 0.6 yug/dl) of the blood lead decrease is attri butable to gasoline lead exposure. This estimate is consistent with the existing literature. It agrees with the estimate based on an air lead decrease of about 0.3 an cC value in the range 1 to 2 (14,15). It is also consistent with the Frankfurt study (16). Finally, after adjustment for both demographics and gasoline lead exposure, a significant blood lead time trend remains. TEH 0532498 DUP050033766 Conclusions National gasoline lead use is not a valid index of exposure at NHANESII sites Over 50% of the apparent blood lead decrease is attributable to demographics 5 to 10% of the apparent blood lead decrease is attributable to gasoline lead exposure The blood lead decrease of 0.3 to 0 6//g/dl attributable to gasoline lead is consistent with the observed air lead decrease A significant blood lead time trend remains after accounting for demographics and gasoline lead exposure TEH 0532499 DUP050033767 REFERENCES 1. United States. National Center for Health Statistics. Plan and operation of the second National Health and Nutrition Examination Survey, 1976-1980. Programs and Collection Procedures, Series 1, No. 15. 2. United States. Center for Disease Control, Morbidity and Mortality Weekly Report 30, 132 (1982). 3. Houk, V. Statement at Environmental Protection Agency Hearing on Regulation of Fuel and Fuel Additives, Lead Phasedown Regulation, Notice of Proposed Rulemaking, April 15, 1982. 4. Petroleum Chemicals Division, E. I. du Pont de Nemours & Co., Inc. Statement presented to Environmental Protection Agency, Science Advisory Board, Environmental Health Committee at an Open Meeting on Public Health Impacts Associated with Lead in Gasoline Phasedown Program, July 7, 1982, 5. Schwartz, J. U.S. EPA Memorandum "Health Effects of Gasoline Lead Emissions", May 11, 1982. 6. ICF Incorporated "The Relationship Between Gasoline Lead Usage and Blood Lead Levels in Americans: A Statistical Analysis of the NHANES II Data", Report to EPA, December, 1982. 7. Pirkle, J.L. U.S, CDC Memorandum "Comments on the Dupont , .(sic) Analysis of the NHANES II Blood Lead Data", December 1 1982 8. Jelinek, C.F. "Levels of Lead in the United States Food Supply", J. Assoc. Off, Anal. Chem. 65, 9h2-6 (1982). 9. "Growing Concern for Nutrition", Food processing, p.40, March, 198I. 10. "Beverage Can Shipments", Modern Metals, p. 34, July, I960. 11. Pierrard, J.M., et al, "Vehicle Emissions Controls and Ambient Air Quality", SAE Australia, Jubilee Tear Conference, Melbourne (1977). 12. Pierrard, J.M. et al, "Assessment of Blood Lead Levels in the U.S.A. from NHANES II Data", Proceedings of the Inter national Conference on Heavy Metals in the Environment, p. 421-4, September, 1983. TEH 0532500 DUP050033768 13 Kempthorne, 0. Design and Analysis of Experiments> John Wiley and Sons, New York, 1952. '' 14 U.S. EPA Office of Air Quality Standards. National Air Quality and Emissions Trend Report, 1981. 15. Snee, R.D. "Evaluation of Studies of the Relationship Between Blood Lead and Air Lead", Int. Arch. Occup. Environ. Health 48, 219-42 (1981). 16. Sinn, W. "On the Relationship Between Lead in Air and Blood Lead Content of Persons Living and Working in the Centre of a City (Frankfurt Blood Lead Study)", Int. Arch. Occup. Environ. Health 47, 93-118 (1980), 48; 1-23 (1981). I Pt ist I*0 m I X M TEH 0532501 DUP050033769 Proceedings, international Conference on Heavy Metals in the Environment, p. 421 - 424, Sept. 1983. 421 ASSESSMENT OF BLOOD LEAD LEVELS ZD THE U.S.A. FROM NHANESII n*TA John M Pierrerd*, Cherles C Pfeifer+ and Ronald 0 Snee+ ABSTRACT Changing demographics of the subject groups st the 64 sites sampled dur ing NHANESII accounts for over half the apparent 5.61 ug/dl blood lead decrease from 1976 to 1980, Site-specific gasoline lead exposure accounts for 0.51 ug/dl of the blood lead decrease. In agreement with the change expected due to the decrease of 0.32 ug/a* in average air lead and the accepted range 1 jfoi < 2 for blood lead response to air lead change, INTRODUCTION The U.S. Government'* second National Health and Nutritional Examination Survey (NHANESII) %s a cross-sectional study designed to esses* national health statu*. Venous blood laad levels (BPb) vers measured for 9,936 of the 20,333 examinees. Mobile caravan teams visited 64 sites in th* contlnguous U.S.A. and Hawaii between 1976 and 1980. A preliminary analysis reported e 36.72 reduction in BPb over the four-year study period and noted that the decrease in BPb reflects the decreese in national use of lead in gasoline production (ref 1). Because the NHANESII sample was not selected to insure valid yithln-study time analyses, several categories of demographic variables were evaluated in the present study to examine their effect on the reported BPb decline. Three alternative measures of exposure to lead from gasoline were tested for their utility as indicators of BPb response. Finally, time was intro duced to represent ell other time-related BPb effects that may be present. ADJUSTMENT FOR DEMOGRAPHICS The effect of changing site demographics on the BPb time trend was inves tigated by classifying each examinee in terms of 6 personal variables (P) describing race, sex, age end family income, 3 residence variables (R) describing degree of urbanisation, and 6 caravan Itinerary variables (I) describing season of the year and region of the U.S.A. These classifica tion Variables assume a value of 1 if the descriptor applies to the exam inee, 0 otherwise. Means were computed for each site based on examinee records with a venous BPb, and the 64 site means further analysed. Three BPb adjustments were evaluated corresponding to different selection sets of candidate explanatory terms for variation among site mean BPb'*. The first set included the 6 P variables and their 15 two-way interactions; the second set added the .3 R variables to the first set; end, the third set added the 6 1 variables to tbe second set. A weighted least squares stepwise regression procedure was applied to each full eat of selection candidates. Weighting was by number of BPb values at each site. *E. I. du Pont de Nemours & Co., Inc., Wilmington, DE, USA, Petroleum Laboratory, -t- Engineering Department TEH 0532502 DUP050033770 Terms were retained, if their significance with BPb satisfied the p <0.15 criterion. Adjusted site mean BPb's were obtained by adding the weighted site mean BPb to the residuals from the final regression model. Each adjusted set of values, along with the unadjusted BPb's, then was regressed on site mean examination date. Values of BPb were predicted at the first and last site mean examination date in NHANESII to evaluate the influence of dif ferential site demographics. The results of the time analyses on the unadjusted and adjusted site mean BPb'a are glvan in Table 1. They Illustrate the confounding inherent among BPb, site demographics and time during the study period. Each group of demographic variables was able to explain some of the time trend with terms from the third selection set reducing the unadjusted decrease by store than half . Table 1 Time Trend and Four Tear Change of Blood Lead Unadjusted and Adjusted for Demographics Unadjusted Adjusted for P for P and R for P, R and I Time Trend ug/dl/yr Std. Error -1,4$ 0.18 -1.09 -0.74 -0.57 0.18 0.17 0.14 Remaining Four Tear Decrease BPb. ue/dl % 5.61 32.7 4.29 2.92 2.26 26.0 18.4 14.5 ADJUSTMENT FOR GASOLINE LEAD AND DEMOGRAPHICS Gasoline lead (GPb) is the best documented of the Identified sources of lead which Include food, water, paint and dust. National GPb use has been claimed to explain the decrease In unadjusted BPb (ref 2), and so was eva luated as one GPb exposure variable. National GPb use (tonnes) was com puted from data by State on lead content and consumption of gasoline. To reflect site to site variation, a GPb density (tonnes/wi*) for each site Was computed by multiplying the relevant state GP use by the ratio of population in the site counties to state population, and dividing by land area of the site counties. The basis for this definition is the correla tion between population and gasoline use (ref 3), Subsite GPb density was calculated similarly but based on each BPb examinee's residence char acteristics, Applicable data permitted calculation of all 3 GPb exposures for 55 of the original 64 sites. Kean BPb's from the 55 sites ware adjusted as before for 5 selection sets, each containing all of the P,R and I demographic terms and one of the GPb exposure variables or its logarithm. The adjusted BPb'a then were regres sed' on site mean examination date. These results, along with the signifi cance levels of the GPb exposure terms, are given in Table 2. In all cases inclusion of a GPb term further reduced the BPb decrease from the 2,26 ug/dl unaccounted for by demographics. The remaining trend was con sistent for all but national GPb use. TEH 0532503 DUP050033771 422 Terns were retained if their significance with BPb satisfied the p <0.15 criterion. Adjusted site mean BPb's were obtained by adding the weighted site mean BPb to the residuals from the final regression nodal. Each adjusted set of values, along with the unadjusted BPb's, then was regressed on site wean examination date. Values of BPb were predicted at the first and last site mean examination date in NHANESXX to evaluate the influence of dif ferential site demographics. The results of the tine analyses on the unadjusted and adjusted site mean BPb's are given in Table 1. They Illustrate the confounding inherent among BPb, Site demographics and tine during the study period. Each group of demographic variables was able to explain some of the time trend with terms from the third selection set reducing the unadjusted decrease by more than half. Table 1 Time Trend and Four Tear Change of Blood Lead Unadjusted end Adjusted for Demographics Unadjusted Adjusted for P for P and R for P, R and 1 Time Trend Std. ug/dl/yr Error -1.43 0.18 -1.09 -0.74 -0.57 0.18 0.17 0.14 Remaining Four Tear Decrease BPb, ug/dl X~ 5.61 32.7 4.29 2.92 2.26 26.0 18.4 14.5 a d j u s t me n t f o r g a s o l in e l e a d AND DEMOGRAPHICS Gasoline lead (GFb) is the best documented of the identified sources of lead which Include food, water, paint and dust. National GPb use has been claimed to explain the decrease in unadjusted BPb (ref 2), and so was eva luated as one GPb exposure variable. National GPb use (tonnes) was com puted from data by state on lead content and consumption of gasoline* To reflect site to site variation, a GPb density (tonnes/mi- ) for each site was computed by multiplying the relevant state GP use by the ratio of population in the site counties to state population, and dividing by land area of the site counties. The basis for this definition is the correla tion between population and gasoline use (ref 3), Subsite GPb density was calculated similarly but based on each BPb examinee's residence char acteristics. Applicable data permitted calculation of all 3 GPb exposures for 55 of the original 64 sites. Mean BPb's from the 55 sites were adjusted as before for 5 selection sets, each containing all of the P,R and X demographic terms and one of the GPb exposure variables or its logarithm. The adjusted BPb's then were regres sed on site mean examination date. These results, along with the signifi cance levels of the GPb exposure terms, are given in Table 2. In all cases Inclusion of a GPb term further reduced the BPb decrease from the 2.26 ug/dl unaccounted for by demographics. The remaining trend W3S con sistent for all but national GPb use. TEH 0532503 DUP050033772 423 Table 2 Ti>a Trend and Four Tear Change of Blood Lead Adjusted for Demographies and Gasoline Lead Exposure GPb Exposure Variable Slgnif. Level P Mational o.oooi Site Density 0.0001 Subsite Density 0.0311 Log (Site Density) 0.0001 Log (Subsite Density) 0.1076 Time Trend Std * uft/dl/yr Error -0.14 -0,44 -0.47 -0.52 -0.39 0.12 0.13 0.12 0.13 0.13 Remaining Four Tear Decrease BPb. ua/dl 1 0.57 1.75 1.85 2.05 1.55 3.8 11.3 11.9 13.1 10.1 TIME-RELATED BLOOD LEAD EFFECTS In the absence of credible and suitable data on lead sources besides gaso line, a tine variable, reflecting site mean examination date, was adopted as a surrogate for other tine-related BPb effects. A stepwise regression procedure was used on each of 5 selection sets again containing the full set of demographic terns, one of the GPb exposure variables and the sur rogate, tine. First, the model Was forced to include both time and the GPb variable used; In companion analyses the selection of all terms was allowed to proceed solely on the basis of the inclusion criterion. As shown in Table 3, under both forced and unforced conditions the time vari able was significant for all cases, but only Site GPb Density retained significance. When time is taken into account as a surrogate for un quantified time-related BPb effects, national GPb use Is no longer signi ficant. These results suggest other time-related BPb effects are present in MHANESII. Table 3 Significance Levels of Gasoline Lead Exposure and Time Terms in Models Including Demographics Forced Unforced Gpb Exposure Variable GPb Slgnif. Level Time Slgnif. Level GPb Slgnif. Level Time Signlf. Level National Site Density Subsite Density Log (Site Density) Log (Subsite Density) 0.8850 0.0022 0.6276 0.0019 0.7520 0.0001 0.0001 0.0001 0.0001 0.0001 MS 0.0022 MS 0.0019 MS NS * Mot Selected, p>0.15 O.OOOI < 0.0001 0.0001 0.0001 0.0001 TEH 0532504 DUP050033773 424 CONCLUSIONS This analysis has shown that many factors related to personal and resi dence characteristics and sampling Itinerary significantly affect NHANESII BPb values, and can account for 3.35 ug/dl of the apparent decrease be tween 1976 and 1980. Of the CPb exposure variables only Site GPb Density and its logarithm had a significant effect on BPb in the presence of the time surrogate. The portion of the four-year decrease due to Bite GPb Density was determined by the analysis to be 0.5 ug/dl. This is consis tent with the observed national average air lead decrease of 0.3 ug/m3 over the same period (ref 4), and the well-documented air lead/blood lead relationship (ref 5,6). Figure 1 shows the relative contributions to the four-year blood lead decrease. The unexplained portion of the BPb decrease, 1.75 ug/ dl, is reflected by the time variable and may be due to improved sample handling over the course of the NHANES1I study, effectiveness of numerous government programs to reduce lead intake through food, paint and water (ref 7), or other unquanti fied causes. REFERENCES 1. Centers for Disease Control, Morbidity and Morality Weekly Rep 30, 132 (1982) ~ 2. New Scientist, 94, 570 (1982) 3. J M Pierrard et al. Vehicle Emissions Controls and Ambient Air Quality, SAE Australasia, Jubilee Year Conference, Melbourne (1977) 4. EPA Office of Air Quality Standards, National Trend in the Maximum Quarterly Average Lead Levels, 1970-1979 5. R D Snee, Int Arch Occup Environ Health 48, 219 (1981) 6. W Sinn, Int Arch Occup Environ Health 47, 93 (1980) and 48, (1981) 7. National Academy of Sciences, Lead in the Human Environment Washington, D.C. 1980) p. 477 t f h nj&osnf; DUP050033774