Document 4vakpbpVVR988yR0Jg87n09Lj

A REVIEW OF THE RECENT LITERATURE CONCERNING THE RELATIONSHIP OF FREE ERYTHROCYTE PROTOPORPHYRIN, ZINC PROTOPORPHYRIN AND BLOOD LEAD LEVEL By Alan H, Purdy, Ph.D., C.C.E. Kenneth Bridbord, M.D, Department of Health, Education, and Welfare Center for Disease Control National Institute for Occupational Safety and Health Office of Extramural Coordination and Special Projects to? \ N 30681 DUP040013614 A REVIEW OF THE RECENT LITERATURE CONCERNING THE RELATIONSHIP OF FREE EP.y Th r o c y i'E PAorORQRf'H'mihvi, ziNc' ;PR5T0?QR1?i7gin' WBIO'Od Te M) TEVeL" Lead intoxication (Pbl) in humans dates to antiquity. This is because lead was readily available* had a low-melting point, and was easily cast. Lead being relatively Soft as well, could be fabricated by simple means. Early history shows that humans worked with and used lead, and that they were poisoned by it1. In early mining, lead deposits were often found near the surface of the ground. The lead occurred as oxides and carbonates. These compounds were readily absorbed and did cause lead intoxication in great numbers of lead miners.2 Today, acute severe cases of lead poisoning are less apt to be seen although they still occur. Instead, chronic low-level lead intoxication is more apt to be encountered. However, the population risk is much greater at the present time than in the past due in part to the wide scale use of leaded gasolines, leaded plastics, and the wide distribution of automobile batteries. ` The effects of lead intoxication are varied: gastro-intestinal sequelae, { ^peripheral and central nervous system effects; encepalopathy, including psychosis, neuropathy, anemia; and interference with the synthesis of heme, causing an accumulation of heme precusors in the blood. These precusors are suspected of being toxic in their own right , It Is the interference with the heme biosynthetic pathway that produces a number of substances useful for measuring the degree of lead intoxication, as well as the quantity cf lead absorbed into the body. The problem of measurement of lead in the human body is a critical one. Much of the historical data on lead intoxication is related to measurements of blood Vo3 DUP040013615 levels of lead. This constitutes a large pool of information on the subject. 4' 5 Recent experimentation by Rabinowitz et al and Riegert and Whitlock show that there are significant short-term variations of approximately plus or minus 10 percent in a given individual's blood-lead level, even under the best of laboratory conditions. These variations are thought to be brought about by illness, dehydration, acidosis, or parathyroid hormone, as well as dietary variations in ' calcium and phosphorous ratios'' * * . Further, blood lead levels tend to represent recent absorption.. To add to these biological difficulties, the direct analysis .of blood for blood-lead content is hampered by the high level of skill required in analytical techniques, and the great care demanded to avoid the risk of sample contamination. Generally, the proficiency record of laboratories in blood-lead J t 10,11,12., 32,33 " > determinations has been poor . It, therefore, appears that the 'i ' measurement of blood-lead level for an individual presents difficult problems. However, most clinical measures of lead toxicity have been related to blood-lead measurements, making blood-lead levels a commonly used measure of lead toxicity and absorption. Carefully done blood-lead procedures are therefore valuable on a statistical basis and can be used to evaluate and .cal ibrate other methods of lead: intoxication measurement provided chelation therapy is taken into account. 'A Research to date has shown that the most biologically significant, sensitive, and stable measurements of lead intoxication are the by-products of blocked heme biosynthesis. The most conveniently measured of these by-products are: delta-aminolevulinic acid (ALA), delta-aminolevulinic acid dehydratase (ALAD), free erythrocyte protoporphyrin (FEP) and zinc chelated erythrocyte protoporphyrin (ZPP). The heme biosynthetic pathway is shown in Figure 1. This figure is taken 3 from Perbroth et al . The exact manner that lead inhibits the synthesis is unknown, but it is apparent from the effects on precusors that the interference takes place in at least 2 sites. One site lowers the production of the enzyme ALAD Yoy I ; t. DUP040013616 oT I j best avalliable copy,. * r' iii * > * * -CHj-COOK; P S -CHj-CHj-COOH j " s'CMf VsCHspij j Tk -X Diagrammatic representation of the major Hcpt in porphyrin biosynthesis. TCA cycle m tricarboxylic acid cycle; Bi -- POs *" pyridoxal phosphate; ALA S i-aminoicvulinic acid syn thetase (ALA synthetase); S-ALA i-aminoicvulinic acid; ALA D m i-aminoicvulinic acid dehvdrase (ALA dehydrate); PBG * porphobilinogen: "PBGase" is a term used to represent the 'nzymatic activity involved in the conversion of PUG to uroporphyrinogen rtt. Two enzymes are er-tu rPy insoUcd in this conversion, PBG deaminase and an isomcrizing enzyme [20]: URO'GEN or uroporphyrinogen nt (hexahydtourpporphyrin ml; UROD u URO'CEN' decarboxylase; *i*JPRO'G.EN til " coproporphyrinogen in; COPRO-OK w COPRO'GF.N' oxidase. The rr-'.c- two shown probably involves two enzymatic step! IJOU PROTO * protoporphyrin; HI.Nib bVN* - heme synthetase (ferrocheiatase). Enzymes represented within the rectangle are located within tiistoehondria. lii| ill; :111 "II a Has' j > /. DUP040013617 leading to an increase of ALA, At the other site, lead interferes with the insertion of iron in the protoporphyrin ring, leading to an accumulation of protoporphyrins in the blood. Both ALAD and the substrate ALA have been used as parameters in determinations of exposure to lead. Blood levels of the enzyme and Substrate, or urine levels of the substrate (ALA-U} are sometimes utilized in determining the amount of exposure to lead. The protoporphyrins are generally either extracted from the red blood cells (free erythrocyte protoporphyrin) or are measured directly in the blood in the form of zinc protoporphyrin. The protoporphyrins, therefore, measure the same phenomena; their ratio of magnitude with respect to lead is determined by the method of measurement. Since the correlation of blood-lead level with individual lead intoxication is difficult and often does not reflect the true biological status of the individual,* a logical approach to lead intoxication would be to examine the more sensitive and stable by-products of heme biosynthesis caused by lead interference. The most sensitive of these is the enzyme ALAD 13 * 14 . Research by Hernberg et al, has Shown that there is a direct relationship between ALAD and blood lead. The 15 health significance of ALAD, however, remains to be proven . In addition, the jtest for ALAD, while accurate, is difficult and time-consuming. I The next most sensitive detectable biological disturbance induced by lead in vivo 12 is the increased concentration of FEP . Research has shown that a significant 16,3 increase of free circulating porphyrins is not well tolerated in the body. Fp is detected by fluoresence- The concentration of FEP is affected by hematocrit levels and iron deficiency anemia, and therefore, hematocrit and Hb readings should be taken in conjunction with positive FEP results^,!*!. f /- Vot, y' / DUP040013618 Extensive research has shown that FEP has a Togarhythmic or exponential relationship with blood lead ' ' ' * . The logarhythmic or exponential relationship has been shown to be true in both male and female adults, as well as in children, 16 although the slope of the response curve is different for each of these groups . The largest data base is on children, with male adults, and female adults having considerably less data in that order. Recent investigations show that free erythrocyte protoporphyrin in patients with 23 lead intoxication is, in fact, not free but is chelated with zinc . Research by Lamola, Ooselow, and Yamane^4; and Fischbein, Eisinger, and Blumberg'^ has i- . shown that the measurement of fluorescence ac 495 nm wave length of blood directly, without any extraction steps, can serve as a simple and specific screening test \ for lead intoxication. * i i \ ! The outstanding advantage of using zinc protoporphyrin for lead intoxication measurements Is that it can be detected with a portable field instrument called a hematoflurometer . This instrument only requires that a drop of the subject's whole blood be placed on a slide and be directly assayed for lead effects. The read out of the instrument is not subject to dilution errors or extraction errors, as in FEP measurement; nor is it as subject to contamination errors, laboratory technique errors, or day-to-day biological variability, as in the base of blood lead levels. The only significant sources of variability are the calibration samples, which can be rigidly controlled on a broad scale., plus individual hematocrit and hemoglobin levels. Low hematocrit and hemoglobin would manifest themselves as a small percentage of false positives which can be easily segregated. The hematoflurometer was specifically designed by Bell laboratories to give an almost instantaneous reading of the biological effects of lead intoxication. It has been field-tested by Fischbein et al, and found to be convenient and accurate. Vo 7 i 7- -II . i '1 DUP040013619 -Thus, the methodology exists to simply end Inexpensively monitor the biological effects of lead intoxication for those workers exposed to lead hazards. The question now arises, "Do v/e have enough dose-response information for screening purposes to determine the acceptable upper limits of IP? in the blood due to lead intoxication?" A search of the literature shows a considerable inconsistency in the relationship between FEP and blood-lead levels between different investigators (See Tables I, II, and III). The variations of these ratios between the investigators, is apparently due to the following: a) mean age b) sex or ratio of sexes in studies of children c) race or ratio of races '* d) extraction method e) type of regression equation fitted to data Observation of Table III indicates that the combination of extraction method and regression equation is capable of producing an nrrfpr of mannitude variation between similar age and sex groups. If the uniform method of ZPP analysis using the hernatoflurometer is adopted, the regression equation could be the last large source of variability. The regression equations used in the major studies of lead intoxication using protoporphyrin.thus far take three forms: 1. quadratic 2. logarhythmic 3. logistic In the Quadratic and logarhythmic protoporphyrin vs. blood-lead level equations, the protoporphyrin tends toward infinity with increasing blood lead. Living systems generally do not exhibit this type of dose-response relationship; instead the response tends to level off with increasing dose. The logistic equation exhibits this leveling off characteristic at relatively high lead doses while exhibiting a rapid rise at medium doses similar to the quadratic and logarhythic equations. In some recent studies., the data exhibits the logistic 20,22,34 form i A number of the investigators listed in Tables I and II have been able to recommend upper limits of FEP tnat are consistent with blood-lead limits to prevent lead intoxication; however, because of the variations'#it is not possible to directly translate these recommendations into limits for ZPP, Therefore,. to make the FEP information useful, it must be correlated directly with ZPP 25,26 readings with respect to blood-lead levels. Fischbein et al are in process , 30 of establishing this relationship. (See Figure 2). In addition, Latnola et al have made a quanitative determination of erythrocyte zinc protoporphyrin. This work should lead to a standardized base line for all investigators in this field. 24 In plotting the regression equations of Lamola et al for ZPP (See Fig. 3), an obvious inflection point occurs on these curves at about 13.5 ug/100ml ZPP for both children and adult males. This would appear to be the threshold biological response (as determined by ZPP) to lead intoxication. In children, this would be approximately 22 ug/100 ml Pb.B and for adult males, it would be approximately 35 ug/lOOml Pb.B. The 35 ug/lOOml of blood lead coincides with Zielhurs lower estimate of the threshold of biological response for adult males (as determined by protoporphyrin in erythrocytes, method of Schwartz 3 Wikoff), %? DUP040013621 10 A PHSj CDC Report dated March 1977 in a study of five lead smelters found the threshold of clinically detectably pathology to be a blood-lead level of 60 ug/100 ml. The ZPP equivalent level should be established by the results of current research. / \ There is adequate evidence that female adults show increased sensitivity to 19 27 28 ' lead intoxication as compared with male adults * * . This is based upon responses of the hemopoietic system to increased blood-lead levels. The relationship of ZPP and bicod lead in adult famales is yet to be well-established however. '1 \ j In summary, all current evidence suggests that an advantageous way to assess lead intoxication is by analysis of the by-products of lead interference with the heme biosynthetic pathway; and that the by-product of choice for analysis is zinc protoporphyrin. In addition, the common methodology used in ZPP analysis should allow pooling of the data of different investigators for statistical analysis. Hl3 DUP040013624 n AVAILABLE DATA, FgP v s BLOOD LEAD Table I 1. Reels, Arch. Env. Hlth., Dec. 76 Method: modified Granick 2. Reels, Int. Arch, Arbeitsmed 34:97-103 1974 Method: Granick Children Log FEP - 1.311 + O.C25 (Pb-8) Graph, Fig, 2, pg, 313, K=?l,>-.728 Female adult '' Log FEP = 1.243 + G.0259 (Pb-D) N=26, r=.743 Male adult Log FEP = 1.4777 + 0.0106 (Pb-B) N*40, 4=.544 ;3. To.TCs-.yni Arch. Env. Hlth., Dec. 75 Method; nod. Piomelli Children Log FEP = 1.454 + 0.0211 i=37, 4=,592 Graph* Fig. 2, pg. 102 (Pb-B) Adult males Graph, Fig. 1, pg. 589, K--65, r=.72 4. Pic-elii, Pediatrics 51:2, Feb. 1973 Method: Piomelli Children Log FEP = 1.623 + .0177 (Pb-B) Graph, Fig. 1, pg. 255, M-1038, 4=,72 5. Landrigan, Pediatrics 89:6, Dec, 76 Method: Granick Chi1dran ? FEP = 0.043 x (Pb-B) + 0.45 (Pb-B)-2.14 Graph, Fig. 3, pg, 907, fi=1056 r=. 79 6. Reigart, Pediatrics 57:1, Jan.76 Method:: Chisolm Children Tables IV, V, pg. 57 7. Chisolm, Pediatrics, 84:4, Apr. 76 Method: Chisolm Children Relationship Linear between log FEP and Pb-B Graph, Fig, 1, pg. 492, R=115, r=.60 8. Joselow, illOSH Symp. 76 Method: Piomelli Children, Male ad 'Its Adapted from Piomelli Pediatrics 51:254-257, 1973 Fig. 5, pg. 33, Graph Ln FEP=3.0219 + .0245 Pb-B 9. CDC, EP 1-76-33-2 Method: Piomelli Adult Males Graph, Fig. 2, pg. 7 N-73, 4-.76 Ln FEP * 3.685 + .0276 Pfc-3 V/j DUP040013625 AVAILABLE DATA, FEP vs. BLOOD LEAD (Cont.) 10. CDC, EP1-76-83-2 Method: Plomelli 11. Levine, et al, Am. J Pub. Kith, 66:6, June 76 Method: Granick 12. L. Alessio, et al Int. Arch. Occ. Envvron.Hlth 37:73-83, 1976 Method: Schwartz 3 Wikoff Adult males Table 2, pg, 5 Table 3,4, pg, 6 Table 5, pg. 7 N38, 4=, 79 Adult Rales Tables 1,2,pg. 549 Adult Males FEP = 230 1 + expl S.34 -.079 Pb-B) fl=201, 4-. 904 ' j DUP040013626 13 AVAILABLE DATA, ZPP vs BLOOD LEAD Table II 1. Joselow, HIOSH Syirp. 76 Method: Lamola Graphs Fig. 6, pg. 34: Adapted from Lamola, Joselow, Yamane, Clin. Chem. 21:92-97, 1973 2. Lamola, Clin. Chem. 21:93-97, 1975 Method: Lamola Equa. Children Log ZPP = 0.52 + 0.027 Pb-B 8*250, r=,77 . Equa. Men Log ZPP = 0.54 + 0.017 Pb-B H=35, r=.87 3. Fischbein, fit. Sinai .J, Med. 43:3, May, June 76 Methods: Lamola, Sassa, (Granick) Graph, Fig. 4, pg. 298 Correlation ZPP and FEP N=33, 4=,93 4. Lilis & Fischbein Report to HIOSH, ES-00928,May 15,1976 Method: Lamola Chelated Lead Smelter Workers Graph, Fig. 8, pg. 59 11=158 5. Fischbein, Proceedings Int. Conf. oh Heavy Metals in Envirn., Toronto, Oct., 1975 Method: Lamola, Sassa (Granick) Correlation ZPP & FEP 6. Kellogg Report HIOSH March 1977 Method: Lamola Equa. Women Loo ZPP = .946 + (.019 x Pb-B) 8*189, r=.5$ Equa. Men Log ZPP * .820 + (.018 x Pb-B) H=710, r=.79 v/r DUP040013627 COMPARISON OF BLOOD LEAD VS. PEP FOR DIFFERENT INVESTIGATORS 6 .3 7 9 .3 5 1 9 .8 2 8 ,4 5 5 .8 9 9 .2 f 260. A ll c a lc u la tio n s based on regression equations in Tables I & I I o& r- cr> 4/1 </> o CM- 5 CM +-* 00 tO O. CO * UJ I CM cn :V> in VO CO f-- CM | *--* o> co in O H CM 1 .r- 1 CM crv cn VO |M> O in o IM vo IM ro :r CM CM ro 'sr vo CM I CO CM LD c ro ' uJcu a- i VO CO M3 CM CO r>> 900 t CM S3- VO crv CM 1 ST cn C\ *r CM sO cx> in vo CO sr CO co f-- r- CM C 4- C3 V3 ^ QJ t-- CM o ro r>. h-- CO `sr c; Cpv crv o CO cc 1O CM r** 1 uo. CM VO 1 oOo i i 1 CTi r>^ o CM sr 1 CM cn O o vo CM r-- in r>* o CO vo r-- .^r CM CM ro CO r*. to c r*^ a. CD a ro m ccUJ o u. o tz O cr soS- r>* r-- *o c CM rS c o p * r* -o p |M CJ .zc CO CO jr O VO o% o r-- a. ; tc o r-. o tX CM rr>o. CM vo VO XT' CM vO CM VO I o r*. o M*' p*. cj: 1 tn <p f--* I o in 1 CM sr | 'j-- ' 1 CM CM < o sr VC VO CM o Cf% r~ in co CM o ID .r-- oVO fs CO r-- OJ CO VD P-. 1 sr co O p-- Cr p*. CO CO CM CO O CO rs r-- CM .to CO sr 1 r" CM CM cj* CO CM scrr> S3* S3- STVD CM co sr h- o VD sr *-- ** CM f c% CM CM CO o O O o CM N, ro ID VD o a> p-- o r*- CM CM r-* CO CM VO to 1 CO cr> CO CM in CM tn CO to vo uo in VD r-- co in co CO CM VO. r-- CM CO O X) a.1 o CM in CM o<o in c? CO S' o vn o VC o o r*** CO oo cr [ o r-* V5 a o o m B CoUD> ouu JiVaAO < c- CM Ulj o!I HU DUP040013628 15 COMPARISON OF BLOOD LEAD VS. ZPP FOR DIFFERENT INVESTIGATORS ICUtl tr* <zo G\ *Tw ?T* f-- o ro o * cm a to p*" r*. uo r**- r-- CM CM CTi CM CO . fO o CO CO f--- co to ru CM *9" CM <7 CO o vo VO o -J C7 S'* UJ C' O . -sr to .Pv O' C_' * M1. CO O CJ to CSI r-- CO CO sr VO co e-- ST 51 r^. CM co CO CO r-* Cl . **T *- CM w VO C. c cr* c -- r>* *?.CO fs s- Is o L."Y pa Oi CM CO 1^* CO CO LO O o> f^a #- VO CO o CM CM CO to U2=J m r<-* cc C\J LO r**. VO CD VO *?* r- VO O r-- CM CM CM CO VO vo CO o\ CO 3- fd .* r* *- CM CO to Ni I-- Cn . fmm CO 1 o O LO o to o o o O o .Q c m CM n CO * to VO CO <? o. r-- qn DUPO40013629 16 i REFERENCES 1. GilfilTam, S.C.; "Lead Poisoning and the Fall of Rome," J. Occup. Med. 7:53-60, 1965. i 2. Nelson, K.; "Industrial Hygiene of Lead Production, A Brief Review''; Health Effects of Occ. Lead and Arsenic Exposure, a Symposium HEW, CDC, HIOSH, Feb. 76. 3. Perlroth, M.G,; Tschudy, D.P.; Marver, H.S,, et al; "Acute Intermittent Porphyria: New Morphologic and Biochemical Findings," Am. J. Med 41:149-62, 1966. " 4. Rabinowitz, M.; Wetherrill, G.W.; Kopple, J.D.; "Studies of Lead Metabolism bv Use of Stable Isotope Tracers," Env. tilth. Perspectives 145-153, Hay'74. 5. Riege.rt, J.R.; Whitlock:, M.S.; "Longitudinal Observations of the Relationship Between Free Erythrocyte Porphyrins and Whole Blood Lead," Pediatrics 57:54-59, Jan. 76. ] 6. Coyer, R. A.; Mahaffey, K. R.; "Susceptibility to Lead Toxicity," Environ. Health Perspect., 2:73, 1972. 7. Hardy, H. L.; "What is the Status of Knowledge of the Toxic Effects of Lead on Indent ifiable Groups in the Population?"; Clin. Pharmacol. Ther. 7:713, 1966, 8. Aub, J.C.; Fairhall, L.T.; Minot, A.S.; Reznikoff, P.; "Lead Poisoning," Medicine 4:1, 1925. 9. Hunter, D.; Aub, O.C.; "Lead Studies XV: the Effects of Parathyroid Hormone on the Excretion of Lead and Calcium in Patients Suffering from Lead Poisoning," Q.J. Med. 20:1, 1927. 10. Keppler, O.F., et al; "Interlaboratory Evaluation of the Reliability of Blood Lead Analysis," Amer. Ind. Hyg, Assn. J. 70:412-429, 1970, 11. Anderson, D.C., Chief, Lead Poisoning Control Section, CDC, DHEW; Letter September 19, 1974 to Participants in the CDC Blood Lead Proficiency Testing Program. 12. Joseiow, M.H.; "Biological Problems of Blood Lead Levels," Health Effects of Occ. Lead and Arsenic Exposure, Symposium, HEW, CDC, HIOSH, Feb. 76. 13. Hernberg, S.; Tola, S.; Nikkanen, J.; Valkonen, S.v "Erythrocyte Deltaaminolevulinic Acid Dehydratase in New Lead Exposure," Arch, Environ. Health 25:109-113, Aug. 72. i -./ DUP040013630 REFERENCES (Continued) 14. Koeis, H.; Bucneu, o.?.; Lauwerys, R.; Hubermont, G.; "Impact of Air Pollution by Lead on the Heme Biosynthetic Pathway in School-Age Children," Arch. Environ. Health, -310-316 Nov., Dec. 76. 15. National Academy of Sciences, Cornnittee on Biologic Effects of Atmospheric Pollutants; "Lead: Airborne Lead in Perspective," National Academy Sciences, p. 139, 1972. 16. Zielhuis, R.L.; "Dose-response Relationships for Inorganic Lead: I. Biochemical Haematolcgical Responses. II. Subjective and Functional Responses - Chronic Sequelae - No-response Levels," Int. Arch. Occup. Environ. Health, 35:1-18 and 19-35, 1975. 17. Chisolm, 0.J.; Nellitisl E.D.; Keil, J.E.; Barrett, H.B. ; "A Simple Protoporphyrin Assay-microhematocrit Procedure as a Screening Technique for Increased Lead Absorption in Young Children," 0. Pediatrics 84:4, 490-496, April 74. ^ 18. A Statement by the Center for Disease Control: "Increased Lead Absorption and Lead Poisoning in Young Children," J. Pediatrics 87:5, 824-830, Nov. 75. .19. Reels, H.A.; Lauwerys, R.R.; Buchet, <J.P.; Urelust, M.T.; "Response of Free Erythrocyte Porphyrin and Urinary Delta-aminolevulinic Acid in Man and Women Moderately Exposed to Lead," Int. Arch, Arbeitsmed. 34:97-108, 1974. 20. Tomokuni, K.; Osaka, I.; Ogata, M,; "Erythrocyte Protoporphyrin Test for Occupational Lead Exposure," Arch, Environ. Health 30:583-590, Dec. 75. 21, Piomelli, S.; Davidow, B.; Guinee, V.T.; Young, P.; Giselle, 6.; "The FEP (Free Erythrocyte Porphyrins) Test: A Screening Micromethod for Lead Poisoning," Pediatrics 51:2, 254-259, 1973, 22, Landrigan, P.J.; Baker, E.L.; Feldman, R.6.; Cox, D.H.; Eden, K, V.; Orenstein, VLA.; Mather, d.A.; Yankel, A.J.; Von Lindern, O.H.: "Increased Lead Absorption with Anemia and Slowed Nerve Conduction in Children Near a Lead Smelter," J. Pediatrics 89:6, 904-910, Dec. 75. j 23. Laraola, A.A.; Yatnani, T.: "Zinc Protoporphyrin in the Erythrocytes of Patients with Lead Intoxication and Iron Deficiency Anemia," Science, 186:936-933, 1974. ; 24. Larnola, A,A.; Joselow, M.; Yamane, T.; "Zinc Protoporphyrin (ZPP): A Simple, Sensitive, Fluorometeric Screening Test For Lead Poisoning," Clin. Chem. 21:1, 93-97, 1975. 25, Fischbein, A.; Eisinger, 0.; Blumberg, U.E.; "Zinc Protoporphyrin Determination: . A Rapid Screenino Test for the Detection of Lead Poisoning,"; Mount Sinai; . J. Mad, 43:3, 294-299, May-June 76. V/ 9 I / DUP040013631 REFERENCES (Continued) 13 26, Fischbein, A,; Sassa, S.; Eisinger, J.; Blumberg, Vi.E.: "Blood Lead and Protoporphyrin Levels in Lead Exposed Workers - The Application of a New Method for the Detection of Lead Poisoning*" Proc. of the Int. Conf. on Heavy Metals in the Environment, Toronto, Canada, October 27-31, 1975. 27. Stuick, E. J.: "Biological Response of Male and Female Volunteers to Inorganic Lead," Int. Arch, Arbeitsmed. 33:83-97, 1974. 25. Boulos, B.: "Special Problems of Lead in Women Workers," Health Effects of Occ. Lead and Arsenic Exposure, a Symposium, HEW, CDC; NIOSH, Feb. 76. 29. Lilis, R.; Fischbein, A.: "Lead Disease Among Workers in Secondary Lead Smelters," Report ES 00928, Mount Sinai School of Medicine for NIOSH, May 1976, 30. Lamol.a, A.A.; Eisinger, J.; Blumberg, W.E,; Kometani, T.; Burnham, B.F,: "Quanitative Determination of Erythrocyte Zinc Protoporphyrin," 0. Lab. Clin, Men. (In Press), '0 31. PKS, CDC, Report =Pl-76-33-2, March 5, 1976, "Occupational Lead Poisoning in Tennessee". 32. Baloh, R.W.: "Laboratory Diagnosis of Increased Lead Absorption" Arch. Environ. Hlth., 23:193, 1974. 33. Berlin, A.; Buchet, J.P.; del Castilho, P.; Lauwerys, R.; Reels, H., Smeets,J.: "Intercomparison Programme on Analysis of Pb, Cd and Hg in Biological Fluids," Int. Symp. Recent Advances in Assessment of Health Effects-of Environmental Pollution, ECE-EPA-HHO;, Paris 1974, 34. Alessio, L.; Bertatzi, P.A.; Toffoletto, F.; Foa, V.: "Free Erythrocyte Protoporphyrin as an Indicator of the Biolooical Effect of Lead in Adult | Males,!." Int. Arch, Occup. Environ. Hlth, 37:73-83, 1976. 33,j :-HS, CDC Report "A Report of Recent Medical Studies of Five U.S. Lead Plants " March 1977. ' ilO ! DUP040013632