Evaluation of lead exposure in workers at secondary lead smelters in South Korea: with focus on activity of erythrocyte pyrimidine 5'-nucleotidase (P5N)

To evaluate lead exposure among secondary lead-smelting workers with a focus on erythrocyte pyrimidine 5'-nucleotidase (P5N) activity, blood lead concentration (PbB), activity of P5N and other biological variables were examined in 88 exposed workers in five secondary lead smelters and in 24 non-exposed workers in Korea. All of the mean values of air lead concentration (PbA) in the three processes, scrap pretreatment, blast furnace smelting, and refining and casting of the secondary lead smelters, markedly exceeded 0.05 mg/m3. In this survey, 29 (97%) of 30 air samples for lead exceeded 0.05 mg/m3. The highest mean PbA and PbB values were found in the section of blast furnace smelting. All of the mean PbB values in all the sections were higher than 30 microg/dl. PbB of 71 (81%) of the 88 exposed workers exceeded 30 microg/dl. In 31 (35%) of the exposed workers, PbB was above 60 microg/dl. Compared with the non-exposed group, zinc protoporphyrin (ZPP) in the exposed group was significantly increased, whereas erythrocyte P5N activity and activity of erythrocyte delta-aminolevulinic acid dehydratase (ALAD) were significantly inhibited. Erythrocyte P5N activity had valid biological correlation with PbB and with other biological variables, such as ALAD activity or ZPP. Lead exposure affected hemoglobin levels via inhibition of P5N activity, as well as the heme biosynthetic pathway, in the high-exposure state.     

Benchmark dose approach for low-level lead induced haematogenesis inhibition and associations of childhood intelligences with ALAD activity and ALA levels

Lead (Pb) levels, delta-aminolevulinic acid dehydratase (ALAD) activities, zinc protoporphyrin (ZPP) levels in blood, and urinary delta-aminolevulinic acid (ALA) and coproporphyrin (CP) concentrations were measured for 318 environmental Pb exposed children recruited from an area of southeast China. The mean of blood lead (PbB) levels was 75.0 μg/L among all subjects. Benchmark dose (BMD) method was conducted to present a lower PbB BMD (lower bound of BMD) of 32.4 μg/L (22.7) based on ALAD activity than those based on the other three haematological indices, corresponding to a benchmark response of 1%. Childhood intelligence degrees were not associated significantly with ALAD activities or ALA levels. It was concluded that blood ALAD activity is a sensitive indicator of early haematological damage due to low-level Pb exposures for children.     

Low level lead exposure and intelligence in the preschool years

Definitive evidence of neuropsychological effects of low level Pb exposure continues to be sought in prospective studies of child development. The period from mid-infancy to age three years is important because behavioral and physiological characteristics of that age are associated with the intake and retention of environmental Pb. In the Cleveland study, we measured blood Pb (PbB) at ages six months, two years, and three years. At ages six months, one year and two year, the Mental Development Index (MDI) of the Bayley Scales of Infant Development was administered. The Stanford Binet Intelligence Scale IQ was obtained at age three years. Eight multiple regression analyses tested the relationship of each of the three PbB measures with the respective current and each ensuring developmental assessment. Demographic data and measures of the caretaking environment were selected as covariates for the control of confounding factors. Six months PbB was not related significantly to any of five assessments with or without control of confounding variables. The remaining three analyses were significant in the initial analyses, but the effect was completely attenuated with statistical control of confounding variables. These results suggest that obtained correlations between lead exposure and preschool intelligence depend on the caretaking environment.     

Extremely low frequency-magnetic fields (ELF-EMF) occupational exposure and natural killer activity in peripheral blood lymphocytes

Extremely Low Frequency-Magnetic Fields (ELF-MF) are possible carcinogens to humans and some data suggest that they can act as promoters or progressors. Since NK cells play a major role in the control of cancer development, an adverse effect on ELF-MF on NK function has been hypothesized. We examined NK activity in 52 workers exposed to different levels of ELF-MF in various activities. Individual exposure was monitored during 3 complete work-shifts using personal dosimeters. Environmental exposure was also monitored. ELF-MF levels in the workers were expressed as Time-Weighted Average (TWA) values. NK activity was measured in peripheral blood lymphocytes (PBL). In the whole group the median occupational TWA was 0.21 microT. According to the TWA levels, workers were classified as low exposed (26 subjects, TWA < or =0.2 microT) and higher exposed workers (26 subjects; TWA >0.2 microT). In higher exposed workers, we observed a trend to reduce NK activity compared to low exposed, but the difference was not significant. Then we selected a subgroup of highest exposed workers (12 subjects; TWA >1 microT); no difference was observed between low and highest exposed subjects in the main personal variables. Considering both E:T ratios from 12:1 to 50:1 and Lytic Units, a significant reduction in NK activity was observed in the highest exposed workers compared to the low exposed. Multivariate analysis showed a significant negative correlation between exposure and LU, while no correlation was evidenced with other personal characteristics. ELF-MF are considered possible carcinogens, and existing data suggest that they can act as promoters. Due to the role of NK activity in host defence against cancer, the results obtained in this study in workers exposed to ELF-MF levels exceeding 1 microT are in agreement with this hypothesis, and support the need for further investigation in this field.     

Epidemiological monitoring of environmental lead exposures in California State Hospitals

Blood lead screening of 8062 state hospital residents in California revealed 143 residents with excessive lead levels (greater than or equal to 30 micrograms/dL). This screening was part of the Childhood Lead Project and was performed in 1978. The purpose of this study was to identify "critical" lead sources in California State Hospitals. Accurate identification is crucial if subsequent abatement programs are to be effective. The strategy involved the following sequence of steps: 1) Selection of cases based on blood lead and erythrocyte protoporphyrin screening. 2) Determination of pica habits and environmental exposures through interviews with ward's staff and/or parents. 3) Measurement of lead levels in environmental samples reflecting exposures. 4) Interpreting these data in order to identify critical lead sources. 5) Reducing exposure to critical lead sources. 6) Following up of cases and controls to validate the effects of this strategy. A group of 36 lead-burdened cases with pica (30-60 micrograms Pb/dL blood) and 36 matched controls (PbB less than 20 micrograms/dL) were selected from among the developmentally disabled residents of two California State Hospitals. These subjects were studied in order to identify the lead sources to which they were exposed and to abate the major ones. Three major lead sources were found in the state hospitals: wall and furniture paints (100-45,400 micrograms Pb/g paint); surface soil (33-570 micrograms Pb/g soil); educational format was presented to all involved staff. The results have indicated a trend towards lower lead intake by the lead-burdened cases. In one of the two hospitals a "lead-free unit" had been established. All the lead-burdened cases were transferred to this unit in August 1981. A few months later the blood lead levels of all the cases dropped below 30 micrograms/dL. Initial epidemiological monitoring indicated where there were preventable hazards, which abatement efforts succeeded in reducing. Further monitoring of such problems is indicated in this and other developmentally-disabled populations.     

Effect of the delta-aminolevulinic acid dehydratase gene polymorphism on renal and neurobehavioral function in workers exposed to lead in China

Effects of delta-aminolevulinic acid dehydratase (ALAD) polymorphisms on the renal and neurobehavioral functions were investigated in Chinese workers from a storage battery plant exposed to inorganic lead. Blood and urine were collected from each worker to determine the ALAD genotypes, blood lead levels (PbB), urinary β2-MG and urinary NAG activity. The World Health Organization Neurobehavioral Core Test Battery (WHO-NCTB) was used. Of the 135 lead workers tested for ALAD genotype, 126 were ALAD1-1, 9 were ALAD1-2 but none were ALAD2-2. The gene frequencies of ALADl-1 and ALADl-2 were 93.33% and 6.67%, respectively. The workers with ALAD1-2 genotype had significantly higher concentrations of PbB (62.52 µg/dl vs. 41.02 µg/dl), urinary NAG (22.01 U/gCr vs. 13.49 U/gCr), urinary β2-MG (194.98 μg/gCr vs. 112.88 μg/gCr), and digit span backward (DSB) score (6.67 vs. 5.33) than those of ALAD1-1 genotype. Urinary NAG of ALAD1-2 genotype carriers was significantly higher than that of ALAD1-1 genotype under the same blood lead level (b_i 0.75 vs. b_i 0.29). Interaction between PbB and ALAD genotypes has a significant influence on NAG (P = 0.02) and β₂-MG (P = 0.01). It is postulated that the workers with the ALAD2 allele appear to be more susceptible to the effects of lead on renal injury, whereas neurobehavioral functions in ALAD1 homozygote tend to be more vulnerable.     

Tests available for assessing recent exposure to inorganic lead compounds and their use for screening purposes.

This paper indicates the tests available for measurement of inorganic lead uptake by the body. The tests are listed and then considered individually. In the light of recent great interest in lead as a health hazard, the best methods for screening are considered: this includes biological and biochemical tests. It is emphasized that the U.K. favours blood lead estimation, the EEC countries other than Britain use blood lead but are considering more widespread use of delta-amino laevulinic acid dehydratase estimation in blood. Some authorities in the United States of America, on the other hand, favour a free erythrocyte protoporphyrin test. The advantages and disadvantages are brought out and some tests are mentioned only in order to exclude them as unsuitable. Suitability of tests for industrial checks and general screening of the population are differentiated. The conclusion is that blood lead still provides the best overall check of lead uptake.     

Biomonitoring of the adverse effects induced by the chronic exposure to lead and cadmium on kidney function: usefulness of alpha-glutathione S-transferase

A successful prevention of renal diseases induced by occupational exposure to lead (Pb) and/or cadmium (Cd) largely relies on the capability to detect nephrotoxic effects at a stage when they are still reversible or at least not yet compromising renal function. Hence, the aim of this cross-sectional study was to evaluate the usefulness of a set of early biological markers of oxidative stress or nephrotoxicity for the biomonitoring of workers occupationally exposed to Pb and/or Cd in a non-ferrous metal smelter, and gender, age, socioeconomic status, smoking habits, and drug use-matched control individuals. In exposed subjects, mean levels of Pb in blood and urine were also 387.1+/-99.1 microg Pb/L (1.868+/-0.478 micromol Pb/L) and 217.7+/-117.7 microg Pb/g creatinine (1.051+/-0.568 micromol Pb/g creatinine), and mean levels of Cd in blood and urine were 3.26+/-2.11 microg Cd/L (0.029+/-0.019 micromol Cd/L) and 2.51+/-1.89 microg Cd/g creatinine (0.022+/-0.017 micromol Cd/g creatinine), suggesting thereby relatively low occupational exposure levels. Statistically significant variations in zinc protoporphyrin, malondialdehyde, retinol binding protein, alpha-glutathione S-transferase, and urinary protein levels were reported between the two groups, and were closely correlated with Pb and/or Cd exposure levels. Variations in alphaGST levels were closely associated with Pb exposure. Taken together, these results suggest the use of alpha-glutathione S-transferase excretion in urine as a hallmark of early changes in the proximal tubular integrity.     

Alterations of heme metabolism in lymphocytes and metal content in blood plasma as markers of diesel fuels effects on human organism

Workers in the diesel fuel distribution trade are intensively exposed to fuel vapours. Diesel fuel presents the main source of air pollution by benzene at a marine diesel fuel terminal. Levels of benzene are used to evaluate the external exposure to diesel fuel. Since benzene causes alterations in porphyrin metabolism, and some of these may lead to the generation of tumours, heme synthesis is proposed as a biomarker of early health effects of diesel fuel. A group of 20 workers exposed to diesel fuel and a group of 20 unexposed persons were examined and interviewed using structured questionnaires. The levels of 5-aminolevulinic acid (ALA) and protoporphyrin (PP), activities of ALA synthase and ferrochelatase, as well as levels of PP associated with DNA were determined in lymphocytes spectrophotometrically. Amounts of the metals Cd, Mn, Zn, Cu and Ca were measured in blood plasma by flame atomic absorption spectrometry method. Both ALA and PP levels were significantly increased in marine terminal workers: 3.0 +/- 0.4 vs. 0.8 +/- 0.2 nmol/10(6) lymphocytes: and 511 +/- 164 vs. 389 +/- 77 pmol/10(6) lymphocytes in exposed and control individuals, respectively. ALA-synthase activity was 2.5 fold higher in lymphocytes of workers exposed to diesel fuels (P < 0.01). At the same time ferrochelatase activity was decreased and protoporphyrin level was accordingly elevated. The amount of porphyrin associated with DNA increased 1.4 fold in exposed workers (P = 0.05). Among all investigated metals in blood plasma of exposed workers only zinc levels were statistically significantly increased (P < 0.05). The disturbances of heme metabolism in lymphocytes and zinc level in blood plasma caused by diesel fuel exposure seems to be a useful biomarkers for carcinogenic risk assessment.     

Approaches to the assessment of long term exposure to radon and its progeny

In recent years, a number of case-control epidemiological studies have taken place and others are in progress to evaluate the lung cancer risk to the general population from exposure to radon and its short-lived progeny in the indoor residential environment. While it is actually long term exposure over past decades to radon progeny by inhalation that dominates lung doses, for a number of practical reasons it is radon gas that is measured in these studies. Because the risk from radon and its progeny results from cumulative exposure over past decades rather than from contemporary exposure, it is necessary to reconstruct the historical exposures of subjects. A number of factors limit the accuracy of this approach of which the following are perhaps the most important: the mobility and residential history of the subjects; radon exposures elsewhere; and changes that may have occurred in the radon levels in current and previous residences. Measurement techniques to assist in making more direct retrospective assessments of radon exposure have appeared in the recent past and are the subject of this paper. These are based on the measurement of the long-lived radon progeny 210Po trapped in household artefacts such as glass or porous and spongy materials. In vivo measurements of skeletal 210Pb in exposed persons is also a method that is currently being investigated as a means to assess historical exposures to radon. The advantages and disadvantages of these methods are described here as well as their potential in future radon epidemiological studies.     

Adverse health effects of lead exposure on children and exploration to internal lead indicator

Our research on adverse effects of lead exposures on physical and neurobehavioral health of children aged 6–12 years in 4 villages, labeled as K, M, L, and X, in rural China, was reported in this article. Lead in blood (PbB), urine (PbU), hairs (PbH), and nails (PbN) were measured by graphite furnace atomic absorption spectrometry. Abbreviated Symptom Questionnaire of Conner's instruments and Revised Raven's Standard Progressive Matrices were applied to evaluate childhood attention deficit/hyperactivity disorders (ADHD) and intelligences. Geometric means (SD) of PbB, PbU, PbH and PbN concentrations were 71.2 μg/L (1.56), 11.7 μg/g (1.75), 12.5 μg/g (2.82), and 25.3 μg/g (2.79), respectively. 54 (17.0%) children had PbB levels of ≥ 100 μg/L. Boys, the 6–10 years old, and living in village K were 2.11, 2.48, and 9.16 times, respectively, more likely to be poisoned by lead than girls, aged 11–12 years, and residing in X. 18 (5.7%) and 37 (11.7%) subjects had ADHD and mental retardations, respectively. Inverse relationships between intelligences and natural log transformed PbU and PbH levels were observed with respective odds ratios (95%CI) of 1.79 (1.00–3.22) and 1.46 (1.06–2.03) or 1.28 (1.04–1.58) and 1.73 (1.18–2.52) by binary or ordinal logistic regression modeling. ADHD prevalence was different by gender and age of subjects. PbU, PbH, and PbN related to PbB positively with respective correlation coefficients of 0.530, 0.477, and 0.181. Receiver operating characteristic (ROC) curves of the three measurements reveled areas under curves (AUCs) being 0.829, 0.758, and 0.687, respectively. In conclusion, children had moderate levels of lead exposures in this rural area. Intelligence declines were associated with internal lead levels among children. ROC analysis suggests PbU an internal lead indicator close to PbB.     

Occupational exposure to noise and the cardiovascular system: A meta-analysis

The aim of our meta-analysis is to evaluate the association between the modifications of the cardiovascular system and chronic exposure to noise in occupationally exposed subjects.We considered the articles published from 1950 to May 2008. Only 15 papers were conforming to the inclusion criteria identified for this meta-analysis. A total of 18,658 workers were divided in three groups according to the level of noise exposure as measured in the original studies (High Exposure, HE, Intermediate Exposure, IE, Low Exposure, LE). A preliminary evaluation of the type of data allowed for a classification of the type of performed measurements. Two classes of variables were identified: Class I, composed by continuous variables (systolic blood pressure, SBP, diastolic blood pressure, DBP, and heart rate, HR) and Class II, composed by not continuous variables (prevalence of hypertension and prevalence of ECG abnormalities). For each variable the calculation of heterogeneity was performed. For continuous variables the calculation of ES and its significance were performed while Odds Ratio (OR) and its significance were calculated for not continuous variables.The results show a statistically significant increase of SBP and DBP in HE workers compared to LE and IE workers while HR is statistically higher in HE participants compared to LE participants. The prevalence of both hypertension and ECG abnormalities is statistically higher in HE workers compared to LE and IE workers.Taking into account both the extremely high heterogeneity among studies and the ES/OR values we suggest a particular attention to the measurement and evaluation of SBP, DBP and HR in workers with chronic exposure to noise. Also ECG for workers with chronic exposure to noise is suggested in order to identify and evaluate possible abnormalities noise could be a concurrent cause of.     

Hair can be a good biomarker of occupational exposure to mercury vapor: simulated experiments and field data analysis

Generally, urine mercury (U-Hg) is widely used for assessment of inorganic mercury (I-Hg) exposure in humans. The reliability of scalp hair as an indicator of mercury vapor exposure is contentious. However, significant correlations were found between hair total mercury (T-Hg) and U-Hg and between hair I-Hg and total gaseous mercury (TGM) in ambient air in our previous studies. Simulated experiments were designed to assess the contribution of direct absorption/adsorption of mercury vapor in the hair. Results indicated that the increases of hair T-Hg concentrations were less than 1 μg/g, which was negligible compared with hair T-Hg concentrations in occupationally exposed workers. The β-mercaptoethanol washing can remove 30% of mercury (Hg) in the exposed hair samples. The inhaled Hg constituted the major fraction (97.4%) of I-Hg exposure for the artisanal Hg mining workers. From the simulated experiments and field data analysis, we can conclude that hair I-Hg can be a useful tool for monitoring occupational exposure to Hg vapor.     

Occupational exposure to lead in ancient times

The uses and regional production of lead in ancient times are summarized. Since there is no evidence to suggest that any deliberate attempts were made to curtail personal exposure to the mine dusts or the emissions from the forges and crucibles, it is surmised that many of the ancient artisans who worked with lead probably contracted plumbism. The number of workers so exposed is estimated to be over 140,000 per year during the Roman Empire. The ancient literary records of work-related plumbism, however, are surprisingly sparse.     

Pesticide exposure of non-occupationally exposed subjects compared to some occupational exposure: a French pilot study

Data about non-dietary exposure to different chemical classes of pesticides are scarce, especially in France. Our objective was to assess residential pesticide exposure of non-occupationally exposed adults, and to compare it with occupational exposure of subjects working indoors. Twenty unexposed persons, five gardeners, seven florists and nine veterinary workers living in Paris area were recruited. Nineteen residences, two greenhouses, three florist shops and three veterinary departments were then sampled. Thirty-eight insecticides, herbicides and fungicides were measured in indoor air with an air sampler for 24 h, and on hands by wiping them with isopropanol-wetted swabs. After extraction, samples were analysed by gas and high-performance liquid chromatography. Seventeen different pesticides were detected at least once in indoor air and twenty-one on the hands. An average of 4.2+/-1.7 different pesticides was detected per indoor air sample. The organochlorines lindane, alpha-endosulfan and alpha-HCH were the most frequently detected compounds, in 97%, 69% and 38% of the samples, respectively. The organophosphates dichlorvos and fenthion, the carbamate propoxur and the herbicides atrazine and alachlor were detected in more than 20% of the air samples. Indoor air concentrations were often low, but could reach 200-300 ng/m(3) in residences for atrazine and propoxur. Propoxur levels significantly differed between the air of veterinary places and other places (Kruskal-Wallis test, p<0.05) and dieldrin levels between residences and workplaces (p<0.05). There was a greater number of pesticides on hands than in air, with an average of 6.3+/-3.3 different pesticides detected per sample, the most frequently detected being malathion, lindane and trifluralin, in more than 60% of the subjects. Maximal levels (up to 1000-3000 ng/hands) were observed either in the general population or in workers, depending on the pesticide. However, no significant difference was observed between workers and general population handwipe pesticide levels. As expected, gardeners were exposed to pesticides sprayed in greenhouses. Florists and veterinary workers, whose pesticide exposure had not been described until now, were also indirectly exposed to pesticides used for former pest control operations. Overall, general population was exposed to more various pesticides and at levels sometimes higher than in occupational places. The most frequent pesticides in residences were not the same as in US studies but levels were similar. These preliminary results need to be confirmed in a greater number of residences from different parts of the country, in order to better assess pesticide exposure of the general population and its influencing factors.     

Feasibility of assessing dermal exposure to PAHs of workers on gaswork sites--the SOLEX study

Population exposure to pollutants in soil is an important public health concern. Difficult to measure, it is usually estimated using multimedia models. Modeling data predict that the skin surface is a predominant exposure route in roughly 15% of the US Superfund sites. Nonetheless, no study has confirmed these predictions. The SOLEX study was an opportunity to study the feasibility of estimating the cutaneous polycyclic aromatic hydrocarbons (PAHs: all 16 of the United States Environmental Protection Agency list) load of workers at three former manufactured gas sites, one of those being under remediation. Over two measurement periods (November 1997 and June 1998), 30 and 28 volunteers, respectively, were equipped for a single day work with five pads that collected soil particles and were placed at the neck, shoulder, wrist, groin, and ankle. Pad contamination was observed for six of the nine workers on the site being remediated but not on other sites. The wrist pad was most often affected, followed by the neck pad, these are, the exposed regions of the body. The PAHs most frequently identified were anthracene, fluoranthene, naphthalene, phenanthrene, and pyrene, at concentrations relatively high. In conclusion, this study showed that estimating skin exposure to soil pollutants is feasible. Secondly, it suggested that only subjects in close contact with the soil had a detectable exposure to PAHs. Extension of this approach to other exposure settings is warranted, especially among children playing in polluted public or private gardens, because their games lead to frequent contact with the soil.     

Blood lead screening in Ontario children: blood lead and free erythrocyte protoporphyrin levels

A blood lead survey was conducted on samples from 2459 children aged 3-6 years to determine the prevalence of lead poisoning in children of this age in the Province of Ontario. Lead poisoning, defined as a blood lead concentration greater than or equal to 1.21 mumol 1-1 (25 micrograms dl-1), was found in 26 subjects (1.1% of the samples). The mean blood lead concentration for children from southern Ontario was 0.50 mumol l-1, and for those from northern Ontario it was 0.37 mumol l-1. Stringent quality controls and independent cross-checks of finger-prick capillary blood sampling were employed in the study. The free erythrocyte protoporphyrin levels were also monitored to detect the presence of iron deficiency in the children.     

Levels of selenium and antioxidative enzymes following occupational exposure to inorganic mercury

Levels of selenium and mercury in blood and urine were analysed in 37 male workers exposed to elemental mercury vapour in a chloralkali plant and in 39 unexposed controls of the same age. Mean urinary Hg was 223 nmol l-1 (15 nmol/mmol creatinine) in the exposed group and 26 nmol l-1 (2.0 nmol/mmol creatinine) in the controls. Mean blood and plasma Hg levels were 46 and 36 nmol l-1, respectively, in the exposed group, as compared with 17 and 7 nmol l-1 in the controls. The concentrations of Se in plasma and erythrocytes did not differ between the two groups. Urinary Se levels were, however, slightly but significantly lower in the exposed group (median values 23 vs 29 nmol/mmol creatinine), and there was a negative correlation between urinary Se and plasma Hg in the exposed group. This may be due to a retention of Se in the kidneys. In a subgroup of exposed workers and controls, glutathione peroxidase, superoxide dismutase and catalase were also analysed. No differences were found between the groups with respect to these antioxidative enzymes. The effect on Se status of moderate Hg exposure seems to be of minor clinical importance.     

Cadmium in blood and urine after cessation of exposure.

A plant for the synthesis and packaging of cadmium oxide was operated for 32 months (1982-84) in a small chemical factory producing zinc and copper oxide. The cumulative exposure of 6 workers was from 12 to 190 days. Five years after cessation of exposure the blood cadmium levels in the exposed were, on average, 4-10 times higher than those of a reference group and the urinary cadmium levels were 1-6-times higher. In view of the long half-life of cadmium in the human body, the choice of normal reference values requires particular care since brief and sometimes forgotten exposures to cadmium may be a confounding factor to set reference values.     

Contributions of risk factors to elevated blood and dentine lead levels in preschool children.

The relationship between blood lead level (PbB) and an array of socio-demographic, behavioral, caregiving and environmental risk factors was investigated in a cohort of socioeconomically disadvantaged urban children at ages 2, 3 and 4 years and 10 months. The risk factors were also related to dentine lead level (PbD) from shed deciduous teeth. Strong persistent pairwise relationships with PbB and PbD were observed for maternal IQ, parental education, examiner ratings of the condition and cleanliness of the physical environment, and the HOME scale, which assesses the quality of the caretaking environment. The association between dirt pica and PbB was strong at 2 years (r = 0.30), but was less pronounced in subsequent assessments as the prevalence of pica decreased. Insignificant or weak relationships were found for maternal assessments of paint-and-plaster peeling in the home and non-dirt pica. The HOME scale and the ratings of the condition of the physical environment were significantly related to PbB and PbD even after adjustment for socio-demographic factors. These two measures were also strongly related to an array of developmental outcomes. The results indicate that statistical adjustment specifically for the quality of the caretaking environment can lead to substantial reductions in estimates of adverse lead effects.