Pleura mesothelioma and exposure to asbestos

Summary The author reviewed literature data on the relationship between lead in blood levels (PbB) and various biochemical and haematological responses. PbB levels may be regarded as representative for internal dose. The percentage of subjects with a specified intensity of a specified response in groups of subjects has been calculated in relation to PbB. This Dose-Response (D-R) relationship portrays the increase of biological effects with increasing internal dose, qualitatively and quantitatively, and can be used to evaluate the health significance of Pb exposure in occupational and public health. D-R-curves have been calculated for -aminolaevulinic acid dehydratase activity in erythrocytes (ALAD), -aminolaevulinic acid excretion in urine (ALAU), protoporphyrin in erythrocytes (PPE), Na⁺-K⁺-ATPase activity in erythrocytes and reduced glutathion content of erythrocytes. Various other biochemical and haematological responses are discussed in regard to their relationship with PbB. In a subsequent paper the prevalence of functional effects in relation to PbB will be discussed.     

Lead exposure from conventional and cottage lead smelting in Jamaica

A survey was conducted to determine the distribution and determinants of environmental and blood lead levels near a conventional and several cottage lead smelters and to assess the relationship between environmental and blood lead levels in a tropical, developing-country setting. Fifty-eight households were studied in the Red Pond community, the site of the established smelter and several backyard smelters, and 21 households were studied in the adjacent, upwind Ebony Vale community in Saint Catherine Parish, Jamaica. Households were investigated, using questionnaires, soil and housedust lead measurements, and blood lead (PbB) measurements from 372 residents. Soil lead levels in Red Pond exceeded 500 parts per million (ppm) at 24% of households (maximum-18,600 ppm), compared to 0% in Ebony Vale (maximum 150 ppm). Geometric mean PbB in Red Pond, where 44% of children <6 years of age had PbB levels 25 micrograms per deciliter (g/dL), was more than twice that Ebony Vale in all age groups (p < 0.0005). Within Red Pond, proximity to backyard smelters and to the conventional smelter were independent predictors of soil lead (p < 0.05). Soil lead was the strongest predictor of PbB among Red Pond subjects under 12 years of age. The blood lead-soil lead relationship in children differed from that reported in developed countries; blood lead levels were higher than expected for the household-specific soil lead levels that were observed. These data indicate that cottage lead smelters, like conventional ones, are a hazard for nearby residents and that children exposed to lead contamination in tropical, developing countries may be at higher risk for developing elevated blood lead levels than similarly-exposed children in developed countries.The results of this investigation were presented at the APHA annual meeting in Boston, MA, November, 1988.     

An effect of erythrocyte protoporphyrin on blood manganese in lead-exposed children and adults

Summary In one study in 2- and 3-year-old children (geom. average 143 g Pb/1) and in two studies in workers (geom. average 483 pg Pb/1 and 323 g Pb/1) manganese in blood levels increased with blood lead and with free erythrocyte porphyrin (FEP). The zero-order correlation between PbB and MnB disappeared when FEP was kept constant. The conclusion is drawn that the increase of MnB with increasing PbB is probably not due to simultaneous exposure, neither to direct interaction between Pb and Mn, but mediated through a relationship between Mn and porphyrin in erythrocytes.This study was supported by a grant from the Dutch Prevention Fund     

Free erythrocyte protoporphyrin as an indicator of the biological effect of lead in adult males

In previous research we established that FEP is a suitable and valid test for evaluating the metabolic damage caused by lead absorption.In this study, in the same sample consisting of adult male subjects with PbB levels ranging from 15 to 150 g/100 ml, we examined the relationship existing between PbB and the other indicators of effect so as to compare their behavior with that of FEP and establish whether there is a field of application where the erythrocyte metabolite is to be preferred.     

Assessment and comparison of human exposure to lead between Belgium,Malta, Mexico and Sweden

Summary This is a follow-up study of UNEP/WHO Pilot Project on Assessment of Human Exposure to Lead and Cadmium through Biological Monitoring, carried out in 1983/1984. The main objectives of the follow-up study were: to study whether differences in blood-lead levels found between countries in the Biological Monitoring Project were confirmed and were primarily due to exposure via ingested lead (oral intake) or via inhaled lead; to make a preliminary survey, in selected areas, of the possible sources of high exposure (Malta, Belgium). Four countries participated: Belgium, Malta, Mexico, Sweden. To insure comparability between the populations, certain categories were monitored: teachers for socio-economic status, non smoking males, aged between 25 and 50 years old. The blood-lead concentration (PbB) was measured to determine the current exposure and the feces-lead excretion (PbF) was determined to find out the part of the exposure due to ingestion. Blood-lead levels and feces-lead excretion were very different between the four countries. Median values for PbB, in g Pb/1, were, in decreasing values 247 in Malta, 188 in Mexico, 135 in Belgium and 53 in Sweden. Median values for PbF, in g Pb/day, were 361 in Malta, 159 in Mexico, 82 in Belgium and 22 in Sweden. Oral intake seems to be the major exposure route in the four countries. The relationship between PbB and PbF is curvilinear. To investigate the possible source of high exposure, a preliminary survey was made in Malta and Belgium; lead in air suspended and sedimenting particles was monitored as well as the lead concentration in some food and street dust samples. Concerning the comparison of lead concentrations in these environmental samples between Belgium and Malta, no major differences were detected. The high internal exposure to lead in Maltese people, as measured by PbB, is probably due to a combination of several factors.     

Exposure to lead and cadmium of children living in different areas of North-West Germany: results of biological monitoring studies 1982–1986

Summary Between 1982 and 1986 several surveys were carried out to determine the levels of lead and cadmium in blood, urine, and shed deciduous teeth (incisors only) of children living in rural, suburban, urban, and industrial areas of North-West Germany. Blood lead (PbB) and blood cadmium (CdB) were measured in about 4000 children. In rural, suburban and urban areas the median PbB levels vary between 5.5 and 7 g/dl, with 98th percentiles varying between 10 and 13 g/dl. The median CdB levels are between 0.1 and 0.2 g/dl, with 95th percentiles between 0.3 and 0.4 g/l. Children from urban areas have significantly higher PbB levels than children from rural and suburban areas. Regarding CdB no differences could be detected. Children living in areas around lead and zinc smelters, particularly those living very close to the smelters, have substantially increased PbB and CdB levels. Children from lead worker families also have substantially increased PbB and CdB levels. The lead levels in shed milk teeth (PbT) were determined in about 3000 children. In rural, suburban and urban areas the median PbT levels are between 2 and 3 g/g, with 95th percentiles between 4 and 7 g/g. Children from urban areas have significantly higher PbT levels than children from rural and suburban areas. The highest PbT levels (on a group basis) are in children from nonferrous smelter areas. The median levels of lead in urine (PbU) are between 6 and 10 g/g creatinine, with 95th percentiles between 20 and 30 g/g creatinine. Children from polluted areas have higher PbU levels than children from less polluted areas. The median levels of cadmium in urine (CdU) are in the order of 0.1 g/g creatinine, with 95th percentiles being in the range of 0.5 and 1.0 g/g creatinine. Girls have higher CdU levels than boys. There are no differences between groups of children from different areas. Children from lead worker families have higher PbU and CdU levels than otherwise comparable children. The results of the present studies indicate a further decrease of PbB in children from North-West Germany since the CEC blood lead campaigns carried out in 1979 and 1981. The decrease of lead exposure also seems to be reflected by a decrease of tooth lead levels.The studies presented in this communication were supported by the Ministry of Work, Health and Social Affairs and the Ministry of Environment and Agriculture of Nordrhein-West-falen, FRG     

Maternal Low-Level Lead Exposure and Fetal Growth

Background

Limited epidemiologic studies have examined the association between maternal low-level lead exposure [blood lead (PbB) < 10 μg/dL] and fetal growth.

Objective

We examined whether maternal low-level lead exposure is associated with decreased fetal growth.

Methods

We linked New York State Heavy Metals Registry records of women who had PbB measurements with birth certificates to identify 43,288 mother–infant pairs in upstate New York in a retrospective cohort study from 2003 through 2005. We used multiple linear regression with fractional polynomials and logistic regression to relate birth weight, preterm delivery, and small for gestational age to PbB levels, adjusting for potential confounders. We used a closed-test procedure to identify the best fractional polynomials for PbB among 44 combinations.

Results

We found a statistically significant association between PbB (square root transformed) and birth weight. Relative to 0 μg/dL, PbBs of 5 and 10 μg/dL were associated with an average of 61-g and 87-g decrease in birth weight, respectively. The adjusted odds ratio for PbBs between 3.1 and 9.9 μg/dL (highest quartile) was 1.04 [95% confidence interval (CI), 0.89–1.22] for preterm delivery and 1.07 (95% CI, 0.93–1.23) for small for gestational age, relative to PbBs ≤ 1 μg/dL (lowest quartile). No clear dose–response trends were evident when all of the quartiles were assessed.

Conclusions

Low-level PbB was associated with a small risk of decreased birth weight with a supralinear dose–response relationship, but was not related to preterm birth or small for gestational age. The results have important implications regarding maternal PbB.     

Free erythrocyte protoporphyrin as an indicator of the biological effect of lead in adult males

Summary The relationship between FEP and the indicators of dose (PbB, PbU, PbU-EDTA) was examined in a group of male subjects who had left lead-exposing jobs more than 12 months previously.In these subjects, FEP and PbB and FEP and PbU were correlated to a distinctly lower degree compared to previous findings in currently exposed subjects, although the correlations were still statistically significant. In the previously exposed subjects the erythrocyte metabolite displayed definitely higher values than those found in currently exposed subjects at the same PbB or PbU levels.A very close correlation was found between FEP and PbU-EDTA, as was found in exposed subjects. The regression curve assumed an identical profile in the two situations. From these results it may be concluded that FEP persists at high levels for a long time after cessation of exposure due to a direct inhibition of heme synthetase caused by lead released from the tissue deposits.It should be noted that FEP proved to be a valid test for predicting the amount of lead storage, even a long time after cessation of exposure.Abbreviations PbB blood lead (g/100 ml) - PbU lead in urine (g/l) - PbU-EDTA amount of chelatable lead excreted with 24 h urine after administration of Ca NA₂ EDTA (1 g intravenously) - FEP free erythrocyte protoporphyrin (g/100 ml RBC) - ALAU urinary delta-aminolevulinic acid (mg/l) - CPU urinary coproporphyrin (g/l)     

The Influence of Declining Air Lead Levels on Blood Lead–Air Lead Slope Factors in Children

Background: It is difficult to discern the proportion of blood lead (PbB) attributable to ambient air lead (PbA), given the multitude of lead (Pb) sources and pathways of exposure. The PbB–PbA relationship has previously been evaluated across populations. This relationship was a central consideration in the 2008 review of the Pb national ambient air quality standards.Objectives: The objectives of this study were to evaluate the relationship between PbB and PbA concentrations among children nationwide for recent years and to compare the relationship with those obtained from other studies in the literature.Methods: We merged participant-level data for PbB from the National Health and Nutrition Examination Survey (NHANES) III (1988–1994) and NHANES 9908 (1999–2008) with PbA data from the U.S. Environmental Protection Agency. We applied mixed-effects models, and we computed slope factor, d[PbB]/d[PbA] or the change in PbB per unit change in PbA, from the model results to assess the relationship between PbB and PbA.Results: Comparing the NHANES regression results with those from the literature shows that slope factor increased with decreasing PbA among children 0–11 years of age.Conclusion: These findings suggest that a larger relative public health benefit may be derived among children from decreases in PbA at low PbA exposures. Simultaneous declines in Pb from other sources, changes in PbA sampling uncertainties over time largely related to changes in the size distribution of Pb-bearing particulate matter, and limitations regarding sampling size and exposure error may contribute to the variability in slope factor observed across peer-reviewed studies.Citation: Richmond-Bryant J, Meng Q, Davis A, Cohen J, Lu SE, Svendsgaard D, Brown JS, Tuttle L, Hubbard H, Rice J, Kirrane E, Vinikoor-Imler LC, Kotchmar D, Hines EP, Ross M. 2014. The Influence of declining air lead levels on blood lead–air lead slope factors in children. Environ Health Perspect 122:754–760; http://dx.doi.org/10.1289/ehp.1307072     

Behaviour of some indicators of biological effect in female lead workers

Summary The relationships between certain indicators of internal dose and of biological effect were studied in 93 adult women with varying degrees of exposure to lead (PbB levels ranging from 8 to 74 g/ 100 ml). The results were compared with those obtained in a group of 95 males with more of less similar exposure. In both groups a good correlation was found between PbB and ALAD, EP, CPU taken singularly and the trend of the indicators of effect, depending on PbB levels, was similar: the decrease in ALAD values was already clear at PbB levels which do not cause an elevation of EP and the erythrocyte metabolite increased earlier than CPU. Considering the same levels of internal lead load (measured by both PbB and PbU-EDTA) in women, EP values were higher than in the men. No significant difference was established between the two sexes regarding ALAD and CPU values, when considered at the same PbB levels. Validity of ALAD and EP in the females, as already shown in our previous studies on males, was moderate in predicting PbB levels 40 g/100 ml, while it clearly improved at PbB levels 50–60 g/ 100 ml. This indicates that for screening women of child-bearing age the two indicators of effect must be used with caution, since a value of 40 g/100 ml has been proposed as the permissible PbB limit.Abbreviations PbB blood lead (g/100 ml) - PbU-EDTA amount of chelatable lead excreted with 24 hours urine after administration of CaNa₂ EDTA (1 g intravenously) - ALAD -aminolevulinic acid dehydratase activity of erythrocytes (mU/ml RBC) - EP erythrocyte protoporphyrin (g/100 ml RBC) - ALAU urinary -aminolevulinic acid (mg/1) - CPU urinary coproporphyrin (g/1)     

Lead exposure in battery-factory workers is not associated with anemia

Anemia is a manifestation of lead toxicity. However, there are conflicting reports of its prevalence among lead-exposed workers, and it is uncertain whether they should be monitored by periodic hemoglobin (Hb) examinations. To explore the relationship between Hb and lead exposure, we examined the correlation between Hb, blood lead (PbB), and zinc protoporphyrin (ZPP) levels in 961 blood samples obtained from 94 workers in a lead-acid battery plant in Israel between 1980 and 1993. Blood lead levels exceeded 60 micrograms/dL (2.90 mumol/L) in 105 (14%) of the blood samples. The correlation between PbB and logZPP was 0.594. Hb levels did not correlate with PbB or ZPP. We conclude that (a) periodic Hb determinations are not a useful indicator of lead exposure in Israeli industrial workers; (b) the discrepancies between the reported correlation between PbB and Hb levels remain unexplained and in need of further study; and (c) a finding of anemia in a person with PbB levels of up to 80 micrograms/dL should be considered to be due to lead toxicity only after other causes for anemia have been excluded.     

Relationship between blood lead levels and renal function in lead battery workers

OBJECTIVES: The aim of this study was to investigate the correlation between blood lead (PbB) levels and renal function indices of blood-urea nitrogen (BUN), serum creatinine (SC) and uric acid (UA) among lead battery workers with exposure to lead. METHODS: A total of 229 workers of both genders from two lead battery factories were recruited in this cross-sectional study. The personal airborne and blood samples were collected on the same day. The airborne lead (PbA) and PbB levels, and individual renal function parameters were measured and statistically analyzed. RESULTS: A positive correlation between PbB levels and individual renal function index of BUN, SC, and UA was found ( P<0.01). The PbB levels and renal function indices showed significant difference between male and female workers. Based on a multiple regression model, an increment of 10 micro g/dl PbB produced an increase of 0.62 mg/dl BUN, after being adjusted for work duration and age, and an increase of 0.085 mg/dl UA, after being adjusted for gender and body weight. Workers with PbB 60 microg/dl showed a positive dose-effect relationship with significant difference in BUN ( P<0.001) and UA ( P<0.05), and the percentage of workers with BUN and UA over the reference value also showed an increasing trend. CONCLUSION: Blood-urea nitrogen and uric acid could be considered as suitable prognostic indicators of renal dysfunction in lead-exposed workers. Our results showed that PbB levels higher than 60 micro g/dl had increasing chances of inducing adverse renal effects.     

Determinants of Blood Lead Levels across the Menopausal Transition

In this study, the authors sought to evaluate the impact of menopause on lead remobilization from bone-lead stores. The study was conducted between 1993 and 1995 in Mexico City and included 903 women (mean age = 46.8 y [standard deviation = 8.2 y]). Participants provided information about reproductive variables and known risk factors for high PbB levels. PbB levels were determined with graphite furnace atomic absorption spectrophotometry. The authors used linear-regression models to describe the relationship between PbB levels and variables of interest. PbB levels ranged from 1.0 μg/dl to 43.8 μg/dl (mean = 11.0 μg/dl). Menopausal women at baseline had the highest PbB levels; the mean difference between pre- and postmenopausal women was 0.76 μg/dl (95% confidence interval = 0.024, 1.48). We observed an inverted U-shaped relationship between PbB level and age. The highest PbB levels were observed in women aged 47-50 y. Other important predictors of PbB levels were use of lead-glazed ceramics, number of pregnancies, history of cigarette smoking, and height. Our results support the hypothesis that bone lead may be mobilized during menopause and may constitute an important source of exposure.     

Determinants of blood lead levels across the menopausal transition

In this study, the authors sought to evaluate the impact of menopause on lead remobilization from bone-lead stores. The study was conducted between 1993 and 1995 in Mexico City and included 903 women (mean age = 46.8 y [standard deviation = 8.2 y]). Participants provided information about reproductive variables and known risk factors for high PbB levels. PbB levels were determined with graphite furnace atomic absorption spectrophotometry. The authors used linear-regression models to describe the relationship between PbB levels and variables of interest. PbB levels ranged from 1.0 microg/dl to 43.8 microg/dl (mean = 11.0 microg/dl). Menopausal women at baseline had the highest PbB levels; the mean difference between pre- and postmenopausal women was 0.76 microg/dl (95% confidence interval = 0.024, 1.48). We observed an inverted U-shaped relationship between PbB level and age. The highest PbB levels were observed in women aged 47-50 y. Other important predictors of PbB levels were use of lead-glazed ceramics, number of pregnancies, history of cigarette smoking, and height. Our results support the hypothesis that bone lead may be mobilized during menopause and may constitute an important source of exposure.     

Estimated burden of blood lead levels 5 microg/dl in 1999-2002 and declines from 1988 to 1994

In light of recent data suggesting adverse health effects at blood lead levels (PbB) <10 μg/dl, lowering the current definition of elevated blood lead (10 μg/dl) has been recommended. To ascertain the population level impact of such a change, we calculated the prevalence of PbB 5 μg/dl in 1–21-year-old population in the United States. Furthermore, we characterized changes in PbB between 1988–1994 and 1999–2002.We analyzed data from the National Health and Nutrition Examination Survey (NHANES) III (n=10,755) and NHANES 1999–2002 (n=8013).In 1999–2002, about 91.7% of study children had detectable levels of lead in the blood. Among them, 7.3%, 2.8%, and 1.0% children and adolescents aged 1–5, 6–11, and 12–21 years, respectively, had PbB between 5 and 9.9 μg/dl. This number translates to approximately 2.4 million individuals. Between 1988–1994 and 1999–2002, the geometric mean PbB declined from 2.88 to 1.94 μg/dl in children 1–5 years, 1.80 to 1.36 μg/dl in children 6–11 years, and 1.24–1.02 μg/dl in children and adolescents 12–21 years of age. Also, the prevalence of PbB 5 μg/dl declined from 25.7% to 8.8%, 12.8% to 3.0%, and 7.5% to 1.2% in these age groups, respectively.A substantial proportion of children may be at risk for adverse health effects from lead exposure below 10 μg/dl and a large number of children will be classified as having elevated PbB if 5 μg/dl is considered the threshold. Significant public health resources will have to be mobilized for intervention, screening, and case management of these children.     

Correlation between lead in plasma and other indicators of lead exposure among lead-exposed workers

In order to clarify the bioavailability of lead in plasma (PbP), we performed a study on five workers in a Japanese factory manufacturing lead glass-based paints. Blood and urine samples were obtained over a period of 15 months, during which time the workers took it in turns to perform sifting work (with the highest level of lead exposure) for 1-month periods. A total of 75 sets of blood and urine samples were thus obtained. We determined whole blood lead (PbB), PbP, Urinary coproporphyrin (CPU), urinary -aminolevulinic acid (ALAU), urinary lead (PbU) and ALA in plasma (ALAP). In the 15 sets of samples obtained at the end of the period with a high level of lead exposure, PbP correlated significantly with ALAU, CPU, PbU and ALAP, but PbB correlated significantly only with PbU. In the 60 sets of samples obtained following a low level of lead exposure, correlation coefficients between the concentrations of PbP and of ALAU, CPU and PbU exceeded those between the concentrations of PbB and of ALAU, CPU and PbU. These findings indicate that PbP is a better dose indicator of lead biochemically available for heme synthesis and that PbU has a closer correlation with PbP than with PbB.     

Recovery of slowed nerve conduction velocity in lead-exposed workers

Summary Maximum motor nerve conduction velocities in the median nerve (MCV) and blood lead (PbB) were repeatedly measured in 14 lead exposed workers with an initial PbB from 0.7 to 4.0 mol/kg (median 2.3 mol/kg) for a period from 3 months to 7 years: A certain dose of Calcium Disodium Ethylenediaminetetraacetic Acid (CaEDTA) was injected intravenously into most of the subjects during the period.In seven subjects, MCV improved by more than 4 m/s during the observation period which involved the first two successive measurements of MCV and PbB, but the remaining seven subjects showed the minimal alteration (within ± 4.0 m/s). The initial value of MCV was significantly slower (P < 0.01) and the decrease in PbB was significantly greater (P < 0.05) in the group of subjects having shown the improvement of MCV by more than 4 m/s.The initial value of MCV was significant in determining the alteration in MCV in multiple regression analysis and, together with the change in PbB, explained 31% of the alteration in MCV between the first two successive measurements. The initial level of PbB, dose of CaEDTA, time interval between the measurements and age played no essential part in the alteration in MCV.The alteration in MCV throughout the whole observation period in each subject significantly correlated with the concurrent change in PbB (r=–0.573, P < 0.001).     

Fecal lead excretion in young children as related to sources of lead in their environments

Summary Fecal lead excretion (PbF) was studied in young children with elevated lead exposure. PbB was generally 40–70 g/dl. The children's home environments were classified as to lead-base paint hazard and traffic density. There was a significant correlation between paint hazard classification and PbF but not between traffic density and PbF. There also was a correlation of PbB with paint hazard classification. Long-term fecal collections were instituted using 10 children who lived in high hazard homes and three children with low PbB's, whose PbF's were considered normal. Among the children living in high hazard homes, median fecal lead excretion generally was only moderately elevated. Grossly elevated amounts of lead were found only occasionally and only in a few of the children. Movement of two children from a high hazard home to a low hazard home resulted in prompt and substantial reduction in PbF. By contrast, PbB fell only very slowly.This study was supported by a grant from the US National Science Foundation—RANN Program, Grant 77-22186     

Relationship between blood lead level and urinary ALA level in workers exposed to very low levels of lead

The relationship between blood lead (PbB) level and urinary delta-aminolevulinic acid (ALAU) level was examined in a total of 3,636 lead-exposed workers in a periodic medical examination in 1992, in accordance with the Ordinance on Prevention of Lead Poisoning. The results were consistent with previously reported results in that ALAU level was found to increase with an increase in PbB level above 22.4 micrograms/dl (1.35 as a logarithmic value) and to rise markedly above 35.5 micrograms/dl (1.55). On the contrary, the geometric means of ALAU levels appeared to decrease with an increase in PbB levels within a range between a logarithmic value of 0.15 (1.4 micrograms/dl) and 1.25 (17.8 micrograms/dl). Because the earliest sign of the adverse health effects of lead is reported to occur at a PbB level of of 20 micrograms/dl, the relationship between PbB level and ALAU level was examined at PbB levels below 20 micrograms/dl. A regression formula was obtained, Y (log ALAU (mg/l)) = -0.0570X (log PbB (microgram/dl) + 0.4099. This result indicates that ALAU level decreases with a concomitant increase in PbB level lower than 20 micrograms/dl.     

Psychological performance of workers with blood-lead concentration below the current threshold limit value

Summary The effects of lead exposure on psychological test performance and subjective feelings of well-being were investigated in 40 exposed workers whose PbB levels had never exceeded 60 g/100 ml and in 20 controls matched for sex, age and educational level. The exposed workers were divided into two groups of 20, with recent PbB levels in the range 45–60 g/100 ml or below 35 g/100 ml. The group of workers with the higher PbB levels showed significantly poorer performance and reported more physical symptoms than the other two groups. These differences were unrelated to socio-demographic and personality characteristics. A principal component analysis suggested that the poorer performance was mainly due to an impairment of general functioning and only to some extent to a deterioration in specific functions, such as verbal reasoning and abstraction. Higher lead concentrations were correlated with poorer performance and a higher number of physical complaints. These results indicate that in exposed workers the threshold for impaired performance lies below the blood-lead concentration of 60 g/100 ml, which is the current threshold limit value (TLV).This study was supported by the Consiglio Nazionale delle Ricerche (CNR, Roma), Gruppo Nazionale Scienze del Comportamento (Grant no. 81.00083.04 and no. 82.02117.04)