Lead exposure is associated with a delay in the onset of puberty in South African adolescent females: Findings from the Birth to Twenty cohort

Introduction

One of the suggested, yet under-researched, causes of pubertal delay is lead exposure. In South Africa blood lead levels are generally higher than in resource-rich countries. Thus the effects of lead exposure on pubertal development may be significant.

Objective

The objective of this study is to determine the association between lead exposure and pubertal development in adolescent females in the Birth to Twenty cohort (Bt20).

Methods

Bt20 is a Johannesburg based birth cohort study that commenced in 1990 and includes 1682 girls. At 13 years of age venous blood samples were collected from 725 adolescent female participants for lead content analyses; of these, 712 had menarche data. Pubertal measurement was based on age of menarche and self-reported Tanner staging for pubic hair (n = 684) and breast development (n = 682).

Results

The mean blood lead level for the sample was 4.9 μg/dl. Fifty percent had blood lead levels < 5.0 μg/dl, 49% were ≥ 5.0 μg/dl and 1% was > 10.0 μg/dl. The average age of menarche was 12.7 years. At 13 years, 4% and 7% had reached Tanner stage 5 for pubic hair and breast development, respectively. Analyses showed that higher blood lead levels were associated with significant delays in the onset of puberty (p < 0.001).

Conclusion

The study found that higher blood lead levels were associated with a delay in the onset of puberty, after adjustment for confounders. Lead exposure in resource-poor countries is generally higher compared to resource-rich countries and thus the effects of high blood levels have personal and public health significance.     

Predicting blood lead levels from current and past environmental data in Europe

The present case study on lead in Europe illustrates the use of the Integrated Monitoring Framework Strategy to assess the health outcome of environmental pollution by evaluating the associations between lead in various environmental compartments (air, soil, dust, drinking water and diet) and lead concentrations in blood (B-Pb) for various age-related sub-populations. The case study was aimed to investigate whether environmental, exposure and biomonitoring data at general population level, covering all EU member states, could be integrated. Although blood lead has been monitored extensively in Europe, consistent datasets are not yet available. Data diverge with regard to objectives, regional scale, sampling years, gender, age groups and sample size.Significant correlations were found between B-Pb and the concentrations of Pb in air and diet. The significant decrease of the Pb in air over time from 0.31 μg/m³ (P95: 0.94; n = 98) prior to 1990 to 0.045 μg/m³ (P95: 0.11; n = 256) in 2007 (latest observations included) (Δ = − 85%) corresponds to a decline in B-Pb by 48% and 57% in adult women and adult men, respectively. For pre-school children a more shallow decline in B-Pb of 16% was calculated over the same period. Similarly, the reduction in Pb-dietary intake from on average 68.7 μg/d (P95: 161.6; n = 19) in 1978 to 35.7 μg/d (P95: 82.3; n = 33) in the years post 2000 (Δ = − 48%) is paralleled by a decline in B-Pb of 32, 33 and 19% in adult women, primary- and pre-school children, respectively. Insufficient data exist for other age groups to calculate statistically significant correlations.Although regression models have been derived to predict B-Pb for different sub-populations in Europe based on Pb concentrations in air and soil as well as dietary intake, it is concluded that the available data are insufficient to accurately predict actual and future simultaneous exposure to Pb from various environmental compartments, and as a consequence the health impact of Pb for various target populations at EU scale. At least due to data availability, air Pb remains the best predictor of B-Pb in the population. However, lead emission sources have largely been reduced and inhalation of lead in air is not causal to B-Pb levels. Therefore, there is a need of adequate data for Pb in soil and house dust, and in diet and drinking water as these are causal exposure sources with a longer Pb half-life than air. An extended and more harmonized surveillance system monitoring B-Pb, especially in children, is urgently required in order to identify, quantify and reduce still remaining sources of Pb exposure.     

Assessing remedial effectiveness through the blood lead:soil/dust lead relationship at the Bunker Hill Superfund Site in the Silver Valley of Idaho

The 21 square mile Bunker Hill Superfund Site in northern Idaho includes several thousand acres of contaminated hillsides and floodplain, a 365-acre abandoned lead/zinc smelter and is home to more than 7000 people in 5 residential communities. Childhood lead poisoning was epidemic in the 1970s with >75% of children exceeding 40 microg/dl blood lead. Health response activities have been ongoing for three decades. In 1991, a blood lead goal of 95% of children with levels less than 10 microg/dl was adopted. The cleanup strategy, based on biokinetic pathways models, was to reduce house dust lead exposure through elimination of soil-borne sources. An interim health intervention program, that included monitoring blood lead and exposures levels, was instituted to reduce exposures through parental education during the cleanup. In 1989 and 2001, 56% and 3% of children, respectively, exceeded the blood lead criteria. More than 4000 paired blood lead/environmental exposure observations were collected during this period. Several analyses of these data were accomplished. Slope factors derived for the relationship between blood lead, soil and dust concentrations are age-dependent and similar to literature reported values. Repeat measures analysis assessing year to year changes found that the remediation effort (without intervention) had approximately a 7.5 microg/dl effect in reducing a 2-year-old child's mean blood lead level over the course of the last ten years. Those receiving intervention had an additional 2-15 microg/dl decrease. Structural equations models indicate that from 40 to 50% of the blood lead absorbed from soils and dusts is through house dust with approximately 30% directly from community-wide soils and 30% from the home yard and immediate neighborhood. Both mean blood lead levels and percent of children to exceed 10 microg/dl have paralleled soil/dust lead intake rates estimated from the pathways model. Application of the IEUBK model for lead indicates that recommended USEPA default parameters overestimate mean blood lead levels, although the magnitude of over-prediction is diminished in recent years. Application of the site-specific model, using the soil and dust partitions suggested in the pathways model and an effective bioavailability of 18%, accurately predicts mean blood lead levels and percent of children to exceed 10 microg/dl throughout the 11-year cleanup period. This reduced response rate application of the IEUBK is consistent with the analysis used to originally develop the cleanup criteria and indicates the blood lead goal will be achieved.     

Particle size distributions, size concentration relationships, and adherence to hands of selected geologic media derived from mining, smelting, and quarrying activities

Hand-to-mouth activity, especially in children, is a potentially significant pathway of exposure to soil contaminants. Hand-mouthing behavior is of particular concern in areas impacted by mining, smelting, and quarrying activities as these activities may lead to elevated levels of heavy metals in soil. In order to estimate potential exposures to contaminated geologic media attributable to hand-to-mouth contact, it is useful to characterize adherence of those media to skin, as contaminant concentrations in adhered media may differ greatly from unfractionated, whole media concentrations. Such an investigation has been undertaken to aid estimation of exposures to arsenic, cadmium, lead, and zinc in nine different geologic media collected in the Pacific Northwest region of the United States. After establishing the particle size distribution of each medium (fractions < 63 μm, 63-150 μm, 150-250 μm, and 250 μm-2 mm were determined) and target elemental concentrations within each particle size fraction, an active handling protocol involving six volunteers was conducted. Wet media always adhered to a greater extent than dry media and adhered media generally had higher elemental concentrations than bulk media. Regression analyses suggest smaller particle fractions may have higher elemental concentrations. Results of application of a maximum likelihood estimation technique generally indicate that handling of dry media leads to preferential adherence of smaller particle sizes, while handling of wet media does not. Because adhered material can differ greatly in particle size distribution from that found in bulk material, use of bulk concentrations in exposure calculations may lead to poor estimation of actual exposures. Since lead has historically been a metal of particular concern, EPA's Integrated Exposure Uptake Biokinetic (IEUBK) Model was used to examine the potential consequences of evaluating ingestion of the selected media assuming concentrations in adhering versus bulk media.     

Prenatal exposure to lead in Spain: cord blood levels and associated factors

Introduction and Objective

Lead is a known neurotoxic. Fetuses and infants are very vulnerable to lead exposure, since their blood-brain barrier is not completely formed. Hence, there is an importance for monitoring of blood lead levels prenatally and during early infancy. The aim of this study is to evaluate the prenatal exposure to lead and its association with maternal factors in four population based mother-child cohorts in Spain. The present research was carried out within the framework of the INMA project INfancia y Medio Ambiente (Environment and Childhood).

Methods

A total of 1462 pregnant women were recruited between 2004 and 2008. Lead was analyzed in a sample of cord blood by thermal decomposition, amalgation, and Atomic Absorption Spectrometry. Maternal sociodemographic, lifestyle and dietary factors were obtained by questionnaires during pregnancy. A multivariate logistic regression model was constructed. The dependent variable was a dichotomous lead level variable (detected vs no detected, i.e. ≥ vs < 2 μg/dL).

Results

A low percentage of cord blood samples with lead levels ≥ 2 μg/dL were found (5.9%). Geometric mean and maximum were 1.06 μg/dL and 19 μg/dL, respectively. Smoking at the beginning of pregnancy, age, social class, weight gain during pregnancy, gravidity, and place of residence were the maternal factors associated with detectable cord blood lead levels. Mother's diet does not appear to be a determining factor of lead exposure. Nevertheless, daily intake of iron and zinc may act as a protective factor against having cord blood lead levels ≥ 2 μg/dL.

Conclusion

In the different regions of Spain taking part in this study, lead levels to which newborns are exposed are low. Mobilization of lead from bones may be the main contributor to the cord blood levels.     

Childhood lead exposure and uptake in teeth in the Cleveland area during the era of leaded gasoline

Childhood uptake of lead from exposure to atmospheric leaded gasoline in the United States has been studied using mainly blood lead levels. Since reliable blood lead techniques were used only after the peak use of leaded gasoline, the prior exposure history is unclear. The well-documented decline in blood lead levels after the mid-1970s could represent the continuation of a historic steady decline in exposure from many sources. Alternatively, the post-1970s decline might represent the declining phase of a unimodal rise and fall corresponding closely to usage of leaded gasoline. To assess these possibilities, lead concentration and 207Pb/206Pb isotope ratios were measured in the enamel of permanent molar teeth formed between 1936 and 1993 in mainly African-American donors who grew up in the Cleveland area. Tooth enamel preserves the lead concentration and isotope ratio that prevails during tooth formation. Historical trends in enamel lead concentration were significantly correlated with surrogates of atmospheric lead exposure: lead in sediments of two dated Lake Erie cores, and lead consumed in gasoline. About two-thirds of the total lead uptake into enamel in this period was attributable to leaded gasoline, and the remainder to other sources (e.g. paint). Enamel 207Pb/206Pb isotope ratios were similar to those of one lake sediment. Multivariate analysis revealed significant correlation in neighborhoods with higher levels of traffic, and including lake sediment data, accounted for 53% of the variation in enamel lead levels. Enamel lead concentration was highly correlated with reported African-American childhood blood levels. The extrapolated peak level of 48 μg/dL (range 40 to 63) is associated with clinical and behavioral impairments, which may have implications for adults who were children during the peak gasoline lead exposure. In sum, leaded gasoline emission was the predominant source of lead exposure of African-American Cleveland children during the latter two-thirds of the 20th century.     

An evaluation of recent blood lead levels in Port Pirie,South Australia

The Port Pirie Lead Program commenced in 1984. The abatement program involves identification of children with elevated blood lead levels, house decontamination, soil treatment, development of heavily vegetated buffer zones around the smelter, family education and support and community education. Since 1984 the smelter has also implemented substantial new emission controls and environmental improvements. Blood lead and air monitoring programs as well as investigations of emission sources, ongoing household contamination and infant exposure mechanisms are in place. Although capillary blood lead monitoring has shown a significant decrease in the mean blood lead levels of the children, 61% of children aged 1-4 years still exceed 10 microg/dl, with 28% at or above 15 microg/dl. Re-entrainment of lead from the contaminated areas within the city is only a small contributor to air-borne lead levels compared with that from the smelter and its environs. The smelter has undertaken extensive work to reduce windborne fugitive emissions. While attempts to demonstrate reductions in air lead have been hampered by large annual variations in wind speed and direction, air lead studies have confirmed that only small losses are now arising from the stockpile area of the smelter site. Evidence suggests that worker hygiene improvements, relocation of children to lower exposure suburbs, community education, house decontamination, specific measures for individual children with elevated blood lead, and avoidance of tank rainwater have all been partially successful. A substantial investigation program has refocused intervention efforts towards reducing exposure from indoor environments during the first year of life and contributed to improved identification and ranking of ongoing smelter emission sources.     

A comparative study of manganese and lead levels in human umbilical cords and maternal blood from two urban centers exposed to different gasoline additives

Manganese (Mn) and lead (Pb) are two neurotoxic chemicals and experimental evidence suggests that they can cross the placental barrier. Tetraethyl lead was still in use as an antiknock agent in Paris during the sampling period of the study, while it has been replaced by methylcyclopentadienyl manganese tricarbonyl (MMT) in Canada since 1977. By 1990, MMT was in 100% of gasoline in Canada. In a study of 160 pairs of mothers-neonates in Montreal and 206 pairs in Paris, we compared levels of Mn and Pb in the umbilical cord and in maternal blood. Neonates and mothers had significantly higher Pb levels in Paris where lead additives were still used in gasoline. Geometric mean maternal blood Pb levels were 5.4 microg/dl compared to 2.1 microg/dl in Montreal and cord blood Pb levels were 3.2 microg/dl in Parisian mothers compared to 1.7 microg/dl in Montreal. The prevalence of Paris Pb values superior to the 95th percentile of the Montreal distribution was highly elevated in all media studied. The prevalence of high Mn levels in umbilical cord blood was also significantly higher in Montreal. Surveillance programs are important to limit Pb overexposure and associated neurological effects in neonates where tetraethyl Pb is still in use as a gasoline additive. Since Mn is an essential element and dietary Mn intake may differ between Montreal and Paris, the difference observed with regard to high Mn values between Montreal and Paris cannot, at this time, be attributed to MMT in Montreal's gasoline. Further studies are needed to infer an association between Mn emissions from MMT and prenatal exposure to Mn.     

Blood lead levels in Taiwanese adults: distribution and influencing factors

Five-thousand nine-hundred thirteen Taiwanese adults were selected by multistage sampling methods to investigate environmental lead exposure in Taiwan. The blood specimens were distributed to six laboratories for blood lead levels (BLL) measurement. The mean BLL of the 5913 Taiwanese adults was 8.28 ± 5.39 μg/dl, with a maximum level of 57.6 μg/dl. The median was 7.0 μg/dl and 90th percentile was 15.0 μg/dl. BLLs were associated with gender, ethnic group, education level, smoking, alcohol consumption, herbal drug consumption, milk consumption, sources of drinking water, level of urbanization, and occupational lead exposure. These results showed that BLLs in Taiwanese adults were stable during the 2-year study. Most of the influencing factors were consistent with other studies, while local risk factors, such as Chinese herbal drug consumption are important ways of preventing the general population from overexposure to lead.     

Blood lead levels in Jamaican school children

Blood lead levels are reported for a total of 421 schoolchildren in 13 schools in rural and urban environments in Jamaica, including one highly contaminated community. In the rural areas blood lead levels ranged from 3 to 28.5 microg dl(-1), with a median of 9.2 microg dl(-1); the range and median in the urban schools were 4-34.7 and 16.6 microg dl(-1), respectively. Forty-two percent of the rural and 71% of the urban blood lead levels exceeded the US Centers for Disease Control and Prevention intervention level of 10 microg dl(-1). Except in the contaminated area, the relationship between soil lead levels, which in Jamaica are in general typical of tropical lateritic soils, and blood lead levels is not clear-cut. Very high blood lead levels of 18 to > 60 microg dl(-1) with a median of 35 microg dl(-1) were observed among children in the contaminated area, the site of a former lead ore processing plant. These high blood lead levels were significantly reduced, by the implementation of relatively simple mitigation strategies which involved isolation of the lead, education, and a food supplementation programme, to levels similar to those observed in the urban schools. These values, however, remain higher than are desirable and unfortunately, all the sources of lead are not yet identified. The recent discontinuation of the use of leaded petrol is expected to result in significant reductions in exposure to lead.     

Evaluation of home lead remediation in an Australian mining community

In 1994 a comprehensive program was established to reduce children's blood lead levels in Broken Hill, NSW, Australia. Home remediation (abatement of lead hazards in a child's home) was included as part of a case management strategy for children with blood lead levels ≥ 15 µg/dL. Children with blood lead levels ≥ 30 µg/dL were offered immediate home remediation. Children with blood lead levels of 15-29 µg/dL were allocated to ‘immediate’ or ‘delayed’ home remediation; a subset of these participated in a randomized controlled trial (RCT) to evaluate the effectiveness of home remediation for reducing blood lead levels. One hundred and seventeen children received home remediation. One hundred and thirteen returned for follow-up blood tests, 88 of whom participated in the RCT. On average children's blood lead levels decreased by 1.7 µg/dL (10%) in the 6 months after remediation and by 2.2 µg/dL (13%) in the 6-12 months after remediation. However, remediation did not significantly change the rate of decline in blood lead levels (P = 0.609). There was no evidence of association between change in children's blood lead levels and changes in lead loading in their homes. The results are consistent with the published literature, which suggests that home remediation does not reduce children's exposure to lead sufficiently to cause a moderate or greater decrease in their blood lead level. In communities where lead is widely dispersed, the study suggests that it is important to assess potential sources and pathways by which children are exposed to lead when developing an intervention plan, and the need for multiple interventions to effectively reduce blood lead levels. The findings reinforce the ongoing need for rigorous epidemiological evaluation of lead management programs to improve the evidence base, and for effective primary prevention to avoid children being exposed to lead in the first place.     

Blood lead and associated risk factors in Ontario children

The purpose of this study was to determine blood levels in Ontario children and to identify those risk factors associated with higher blood lead levels. A random sample of 1315 children aged 7 and younger from urban, suburban and rural Ontario was selected. Blood lead concentration was determined in finger prick blood samples by graphite furnace atomic absorption spectrophotometry. Measurements of lead in air, tap water, soil, and gasoline were also established. Traffic pattern were determined in each area. A questionnaire was administered to a random sample of 800 families of the children tested to assess the presence of other risk factors. Urban children had higher geometric mean blood lead levels (12.02, S.D. = 4.4 micrograms/dl) than suburban children (9.95, S.D. = 3.5 micrograms/dl), and they, in turn, had higher blood lead levels than rural children (8.91, S.D. = 3.9 micrograms/dl). Each of these differences is statistically significant (p less than 0.001). Fifty four (4.3%) of all children were at or above the alert level of 20 micrograms/dl. The proportion above the alert level did not differ significantly between urban, suburban and rural children. Blood lead levels were slightly higher for males than females and for pre-schoolers aged 3 and 4, compared to school age children aged 5 and 6. The blood lead levels of these children were significantly lower than that of children surveyed near a point source of industrial emissions. Multivariate statistical modelling resulted in a set of characteristics which best explained the differences in children's blood lead levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood lead levels and risk factors for lead poisoning among children in Jakarta,Indonesia

The phase-out of leaded gasoline began in Jakarta, Indonesia on July 1, 2001. We evaluated mean blood lead levels (BLLs) and the prevalence of elevated BLLs of Jakarta school children and assessed risk factors for lead exposure in these children before the beginning of the phase-out activities. The study involved a population-based, cross-sectional blood lead survey that included capillary blood lead sampling and a brief questionnaire on risk factors for lead poisoning. A cluster survey design was used. Forty clusters, defined as primary schools in Jakarta, and 15 2nd- and 3rd-grade children in each cluster were randomly selected for participation in the study. The average age of children in this study was 8.6 years (range 6-12) and the geometric mean BLL of the children was 8.6 microg/dl (median: 8.6 microg/dl; range: 2.6-24.1 microg/dl) (n=397). Thirty-five percent of children had BLLs > or =10 microg/dl and 2.4% had BLLs > or =20 microg/dl. Approximately one-fourth of children had BLLs 10-14.9 microg/dl. In multivariate models, level of education of the child's primary caregiver, water collection method, home varnishing and occupational recycling of metals, other than lead, by a family member were predictors of log BLLs after adjustment for age and sex. BLLs of children who lived near a highway or major intersection were significantly higher than those of children who lived near a street with little or no traffic when level of education was not included in the model. Water collection method was a significant predictor of BLLs > or =10 microg/dl after adjustment for age and sex. BLLs in children in this study were moderately high and consistent with BLLs of children in other countries where leaded gasoline is used. With the phase-out of leaded gasoline, BLLs of children in Jakarta are expected to rapidly decline as they have in other countries that have phased lead out of gasoline.     

Manganese and lead in children's blood and airborne particulate matter in Durban, South Africa

Despite the toxicity and widespread use of manganese (Mn) and lead (Pb) as additives to motor fuels and for other purposes, information regarding human exposure in Africa is very limited. This study investigates the environmental exposures of Mn and Pb in Durban, South Africa, a region that has utilized both metals in gasoline. Airborne metals were sampled as PM_2.5 and PM₁₀ at three sites, and blood samples were obtained from a population-based sample of 408 school children attending seven schools. In PM_2.5, Mn and Pb concentrations averaged 17 ± 27 ng m^− 3 and 77 ± 91 ng m^− 3, respectively; Mn concentrations in PM₁₀ were higher (49 ± 44 ng m^− 3). In blood, Mn concentrations averaged 10.1 ± 3.4 μg L^− 1 and 8% of children exceeded 15 μg L^− 1, the normal range. Mn concentrations fit a lognormal distribution. Heavier and Indian children had elevated levels. Pb in blood averaged 5.3 ± 2.1 μg dL^− 1, and 3.4% of children exceeded 10 μg dL^− 1, the guideline level. Pb levels were best fit by a mixed (extreme value) distribution, and boys and children living in industrialized areas of Durban had elevated levels. Although airborne Mn and Pb concentrations were correlated, blood levels were not. A trend analysis shows dramatic decreases of Pb levels in air and children's blood in South Africa, although a sizable fraction of children still exceeds guideline levels. The study's findings suggest that while vehicle exhaust may contribute to exposures of both metals, other sources currently dominate Pb exposures.     

Environmental exposure of lead and iron deficit anemia in children age ranged 1-5 years: A cross sectional study

Iron (Fe) deficiency is the most common nutritional problem among children and lead (Pb) toxicity is the most common environmental health threat to children all over the world. The objective of this study was to determine blood lead (BPb) levels and prevalence of Fe deficient anemia among 1 to 5 year old children attending day care clinic in pediatric ward of civil hospital Karachi, Pakistan. A total of 340 children of both genders participating in this study, were screened for anemia. Among them 215 were anemic and 125 non-anemic. The anemic group was further divided in two groups on the basis of % hemoglobin (Hb), mild (Hb < 10 g/dL) and severe anemic group (Hb < 8 g/dL), while non-anemic as referent children (Hb > 10 g/dL). The blood samples were analysed for Pb and Fe, along with hematological parameters. The result indicated that anemic children had a higher mean values of Pb in blood than referent children with Hb > 10 g/dL. The Pb levels < 100 μg/L were detected in 40% referent children while 60% of them had > 10 μg/dL. The BPb concentration in severe anemic children (53%) was found in the range of 100-200 μg/L, whereas 47% had > 200 μg/L. The significant negative correlations of BPb level with % Hb (r = −0.514 and r = −0.685) and Fe contents (r = −0.522, r = −0.762, p < 0.001) were observed in mild and severe anemic children respectively. While positive correlation was observed between BPb and age of both group and genders (r = 0.69, p < 0.01). The BPb levels were significantly associated with biochemical indices in the blood which have the potential to be used as biomarkers of Pb intoxication and Fe deficient anemia.     

Nonlinear associations between blood lead in children, age of child, and quantity of soil lead in metropolitan New Orleans

Previous studies identified a curvilinear association between aggregated blood lead (BL) and soil lead (SL) data in New Orleans census tracts. In this study we investigate the relationships between SL (mg/kg), age of child, and BL (μg/dL) of 55,551 children in 280 census tracts in metropolitan New Orleans, 2000 to 2005. Analyses include random effects regression models predicting BL levels of children (μg/dL) and random effects logistic regression models predicting the odds of BL in children exceeding 15, 10, 7, 5, and 3 μg/dL as a function of age and SL exposure. Economic benefits of SL reduction scenarios are estimated. A unit raise in median SL^0.5 significantly increases the BL level in children (b = 0.214 p = < 0.01), and a unit change in Age^0.5 significantly increases child BL (b = 0.401, p = < 0.01). A unit change in Age^0.5 increases the odds of a child BL exceeding 10 μg/dL by a multiplicative factor of 1.23 (95% CI 1.21 to 1.25), and a unit (mg/kg) addition of SL increases the odds of child BL > 10 μg/dL by a factor of 1.13 (95% CI 1.12 to 1.14). Extrapolating from regression results, we find that a shift in SL regulatory standard from 400 to 100 mg/kg provides each child with an economic benefit ranging from $4710 to $12,624 ($US 2000). Children's BL is a curvilinear function of both age and level of exposure to neighborhood SL. Therefore, a change in SL regulatory standard from 400 to 100 mg/kg provides children with substantial economic benefit.     

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.     

Blood lead and its effect on Cd, Cu, Zn, Fe and hemoglobin levels of children

The levels of heavy metals, such as Pb, Cd, Cu, Zn and Fe, in whole blood samples of Mumbai and Hyderabad children have been determined. In the present study, 576 blood samples of children (3-6 years old) were collected during 1996-1998 and analyzed for heavy metal contents by anodic stripping voltammetry and atomic absorption spectrometry. The geometric mean concentrations of Pb, Cd, Cu and Zn in blood of Mumbai children were 8.0, 0.10, 86.5 and 398.9 microg dl(-1), while those for Hyderabad children were 13.3, 0.13, 100.6 and 483.4 microg dl(-1) respectively. The geometric mean concentrations of Fe in the blood of Mumbai and Hyderabad children were 21.9 and 34.5 mg dl(-1), respectively. Of the Mumbai children, 61.8% were found to have a blood lead concentration lcss than 10 microg dl(-1), while the corresponding proportion of Hyderabad children was 27.4%. Higher concentrations of Pb in the children's blood were observed at high traffic areas in both cities. A decreasing trend in the hemoglobin content with increasing blood lead levels was observed for Mumbai children. A good negative correlation (-0.61) between the blood lead and iron has been observed for Mumbai children The hemoglobin content of 85% of the study population was found to vary between 8 and 14 g%.     

Effect of smelter emission reductions on children's blood lead levels

Trail, British Columbia has been the site of an active lead-zinc smelter for approximately 95 years. Since 1989, the community has been monitoring blood lead levels in children, studying exposure pathways and conducting comprehensive education and case management programs. From 1989 through 1996, mean blood lead levels of pre-school children declined at an average rate of 0.6 microg/dl per year. From 1996 to 1999, mean blood lead levels fell at an average rate of 1.8 microg/dl per year, from 11.5 in 1996 to 5.9 in 1999. The recent rapid decline appears to be mainly attributable to the start-up of a new lead smelter using modern flash-smelting technology in May of 1997. In 1998, the annual arithmetic mean air lead level in Trail was 0.28 microg/m(3), compared with 1.1 microg/m(3) in 1996. Reductions of approximately 50% were observed in lead loadings and concentrations in outdoor dustfall, street dust and indoor dustfall after smelter emissions were reduced. Slight reductions (statistically insignificant) have been observed in carpet dust and soil lead concentrations. During the summer of 2001, the smelting and refining operations at Trail were shut down completely for 3 months. During this period, average air lead levels in Trail dropped to 0.03 microg/m(3). The average blood lead level in Trail pre-school children at the end of the shutdown was 4.7 microg/dl. These results challenge prevailing theories about the relative importance of various environmental lead sources. For example, the US EPA Integrated Biokinetic Uptake Model for Lead (IEUBK), with its emphasis on soil concentrations, would not have predicted the dramatic decline in children's blood lead levels seen in Trail following the reductions in air lead levels. The Trail experience suggests that increased attention should be paid to the importance of active sources of highly bioavailable and mobile lead bearing dusts.     

Study on CO2 global recycling system

This presentation describes the development of a prototype Monte Carlo module for the physiologically-based pharmacokinetic (PBPK) model for lead, created by Dr Ellen O'Flaherty. The module uses distributions for the following: exposure parameters (soil and dust concentrations, daily soil and ingestion rate, water lead concentration, water ingestion rate, air lead concentration, inhalation rate and dietary lead intake); absoption parameters; and key pharmacokinetic parameters (red blood binding capacity and half saturation concentration). Distributions can be specified as time-invariant or can change with age. Monte Carlo model predicted blood levels were calibrated to empirically measured blood lead levels for children living in Midvale, Utah (a milling/smelting community). The calibrated model was then evaluated using blood lead data from Palmerton, Pennsylvania (a town with a former smelter) and Sandy, Utah, (a town with a former smelter and slag piles). Our initial evaluation using distributions for exposure parameters showed that the model accurately predicted geometric (GM) blood lead levels of Palmerton and Sandy and slightly over predicted the GSD. Consideration of uncertainty in red blood cell parameters substantially inflated the GM. Future model development needs to address the correlation among parameters and the use of parameters for long-term exposure derived from short-term studies.