Testing the dose-response specification in epidemiology: public health and policy consequences for lead

The contribution of environmental pollutants to the risk of autism and other neurodevelopmental disorders: A systematic review of case-control studies

Exposure to environmental pollutants, such as metals, pesticides, and air pollutants during early life, is a risk factor for neurodevelopmental disorders (NDDs), including Autism Spectrum Disorder (ASD). Our systematic review aimed to select and summarize more recent case-control studies that examined the association between prenatal and early postnatal exposure to environmental pollutants and NDDs. We searched five databases (Web of Science, PubMed, Embase, Scopus, Ovid), screened 2261 records, and included 24 eligible case-control studies. Meta-analyses were conducted on subgroups of at least three studies that shared both the outcome and the exposure. A noteworthy discovery from this literature review is the existence of non-linear or non-monotonic dose-response relationships between the exposure to certain metals and the risk of ASD. The meta-analysis revealed a significant association between exposure to particular matter (PM)10 during the first year of life and the risk of ASD. Overall, studies included in our systematic review indicate that exposure to several pollutants within the first three years of life was significantly associated with the risk of NDDs.

Awareness Level About Lead Poisoning Among the Saudi Population in Arar City, Saudi Arabia: A Cross-Sectional Study

OBJECTIVES

This study aimed to evaluate the awareness regarding lead poisoning among the Saudi population of Arar, Saudi Arabia.

METHODS

A cross-sectional, online self-administered questionnaire-based method was utilized for data collection through convenience sampling from Arar, Saudi Arabia. The collected data were analyzed using descriptive and inferential statistics.

RESULTS

The study included 389 participants, with a majority (302 participants (77.6%)) of females with a mean age of 31.7 years (range 18-54 years). The source of information about lead poisoning was reported as the media in 264 participants (67.8%). The participants (197, 50.6%) reported children as the age group most at risk for lead poisoning. All suggested sources of exposure to lead were identified by 190 participants (48.9%). As for the most common effect of lead poisoning, mental impairment was reported by 101 participants (26%), while 107 (27.6%) participants reported nerve problems. Kidney problems were reported by 181 participants (46.4%). Gender significantly (P = 0.001) affects the participants' knowledge about the sources of lead poisoning, while knowledge about the routes of poisoning was significantly affected by the participants' age (P = 0.010).

CONCLUSION

In Saudi Arabia, there is limited knowledge of risk factors, route of poisoning, and management and prevention of lead poisoning. A comprehensive lead-poisoning prevention strategy must include a high level of public knowledge of lead hazards as a key component.

Prenatal and Childhood Exposure to Organophosphate Pesticides and Behavior Problems in Adolescents and Young Adults in the CHAMACOS Study

BACKGROUND

We previously reported associations of prenatal exposure to organophosphate (OP) pesticides with poorer neurodevelopment in early childhood and at school age, including poorer cognitive function and more behavioral problems, in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS), a birth cohort study in an agriculture community.

OBJECTIVE

We investigated the extent to which early-life exposure to OP pesticides is associated with behavioral problems, including mental health, in youth during adolescence and early adulthood.

METHODS

We measured urinary dialkylphosphates (DAPs), nonspecific OP metabolites, in urine samples collected from mothers twice during pregnancy (13 and 26 wk) and at five different times in their children (ages 6 months to 5 y). We assessed maternal report and youth report of externalizing and internalizing behavior problems using the Behavior Assessment System for Children, 2nd edition (BASC-2), when the youth were ages 14, 16, and 18 y. Because there was evidence of nonlinearity, we estimated associations across quartiles of DAPs and modeled repeated outcome measures using generalized estimating equations.

RESULTS

There were 335 youths with prenatal maternal DAP measures and 14-. 16-, or 18-y BASC-2 scores. Prenatal maternal DAP concentrations (specific gravity-adjusted median, Q 1 - Q 3 = 159.4 , 78.7 - 350.4  nmol / L ) were associated with higher T-scores (more behavior problems) from maternal report, including more hyperactivity [fourth vs. first quartile of exposure β = 2.32 ; 95% confidence interval (CI): 0.18, 4.45], aggression (β = 1.90 ; 95% CI: 0.15, 3.66), attention problems (β = 2.78 ; 95% CI: 0.26, 5.30), and depression (β = 2.66 ; 95% CI: 0.08, 5.24). Associations with youth report of externalizing problems were null, and associations with depression were suggestive (fourth vs. first quartile of exposure β = 2.15 ; 95% CI: - 0.36 , 4.67). Childhood DAP metabolites were not associated with behavioral problems.

DISCUSSION

We found associations of prenatal, but not childhood, urinary DAP concentrations with adolescent/young adult externalizing and internalizing behavior problems. These findings are consistent with prior associations we have reported with neurodevelopmental outcomes measured earlier in childhood in CHAMACOS participants and suggests that prenatal exposure to OP pesticides may have lasting effects on the behavioral health of youth as they mature into adulthood, including their mental health. https://doi.org/10.1289/EHP11380.

The relationship between childhood blood lead levels below 5 µg/dL and childhood intelligence quotient (IQ): Protocol for a systematic review and meta-analysis

BACKGROUND

The causal association between childhood lead (Pb) exposure and decrements in intelligence quotient (IQ) is well-established, and no safe blood lead level (BLL) in children has been identified. An international pooled analysis of seven prospective studies published by Lanphear et al. in 2005 quantified the relationship between childhood BLL and IQ. Further studies of Pb and IQ have been published more recently with mean BLLs generally lower than in the studies analyzed by Lanphear et al. In this article, we present the protocol for a systematic review to estimate an updated Pb-IQ relationship focusing on BLLs below 5 µg per deciliter (µg/dL).

STUDY QUESTION

What is the quantitative relationship between childhood BLLs and IQ at ages 3-17 years at BLLs below 5 μg/dL?

DATA SOURCES

A comprehensive search of the scientific literature will utilize citation mapping and key word searching. In the citation mapping approach, we will identify seed references that are relevant to our study question, and will then identify more recent references that have cited at least one of the seed references. The key word search will be conducted in the PubMed, Biosis Previews, Scopus, and Web of Science databases. We will also search electronic grey literature databases for conference proceedings, dissertations, and preprints.

STUDY ELIGIBILITY CRITERIA, STUDY SCREENING AND DATA EXTRACTION

We will include studies that measured BLL in children at any age, assessed full-scale IQ of the same children (concurrent with or subsequent to BLL sample collection) at ages 3-17, and estimated a continuous quantitative relationship between BLL and IQ. We will consider only studies with a central tendency BLL < 10 µg/dL. The title and abstract of each record will be reviewed independently by two authors to determine whether the study in question satisfies the inclusion criteria. The full text of each article remaining after title-abstract screening will be reviewed independently by two authors to determine whether the study in question satisfies the inclusion criteria. Two authors will independently extract study characteristics and data from each included study.

RISK OF BIAS ASSESSMENT

Studies meeting inclusion criteria will be evaluated for risk of bias (RoB) using the Navigation Guide method applied in a previous systematic review of neurodevelopmental effects (Lam et al., 2017), with adaptation to our study question. Each study will be independently evaluated by two review authors.

DATA ANALYSIS AND SYNTHESIS

We intend to conduct a random-effects meta-analysis to summarize the effects of children's exposure to Pb on IQ scores. Additionally, we plan to perform sensitivity analyses using sub-group analyses and/or meta-regression techniques to assess the impact of study design and study population characteristics to examine potential heterogeneity of results across studies. We will assign a confidence level rating (high, moderate, low, or very low) to the effect estimate from the meta-analyses/meta-regressions.

Heavy Metal Contamination of Soil in Preschool Facilities around Industrial Operations, Kuils River, Cape Town (South Africa)

The contamination of soil by heavy metals is a potential health risk, especially among susceptible populations. The aim of this study was to measure the levels of heavy metals, identify the contamination levels and possible sources of heavy metals, and evaluate the health risk caused by heavy metals to the children living in Kuils River. Composite samples of soil were collected at 34 preschools. A portable X-ray fluorescence spectrometer was used to measure the levels of metals. Contamination levels were evaluated using a geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (CF) and pollution load index (PLI). The spatial distribution of the Igeo contamination levels was assessed using ArcGIS. Sources of heavy metals and the correlation among metals were assessed using factor analysis and Pearson correlation, respectively. The measured concentrations of metals were used to estimate the health risk for children. The average levels of the metals were 16, 4469, 137, 30, 176, 1547 and 232 mg/kg for arsenic (As), iron (Fe), manganese (Mn), lead (Pb), strontium (Sr), titanium (Ti) and zinc (Zn), respectively. According to Igeo, EF, CF and PLI contamination exist in the study area. The health index (HI) for non-carcinogenic effects showed the ingestion route as the main contributor to the total risk, with the accumulative carcinogenic risk exceeding the maximum acceptable level. To protect the affected communities, and children in particular, this study provides evidence of the need for action, including the institution of mandatory buffer zones between pollutant-generating activities and human settlements.

The effect of confounding variables in studies of lead exposure and IQ

Methods proposed to address confounding variables frequently do not adequately distinguish confounding from covariation. A confounder is a variable that correlates both with the outcome and the major exposure variable. Accurate treatment of confounding is crucial to low dose extrapolation of the effects of chemical exposures based on epidemiology studies. This study explores the limitations of current regression models in extrapolation to the low dose region of the dose-response curve due to the existence of unrecognized and uncontrolled confounding, using epidemiological data for lead. Based on the reported data in analyses by Lanphear and colleagues and Crump and colleagues, and drawing on other studies, Wilson and Wilson considered maternal IQ, HOME score, SES, parental education, birthweight, smoking, and race as characteristic variables which may have interaction effects. This analysis identifies confounding variables based on the seven longitudinal cohorts in analyses conducted by Lanphear and colleagues and by Crump and colleagues and confirms maternal IQ, HOME score, maternal education and maternal marital status at birth are "Highly Likely" confounders, while race is a "Likely" confounder. The cohort data were reanalyzed using the methods presented by Crump and colleagues while also considering the interaction among the identified confounding variables. This analysis determined that confounders influence IQ estimates in a quantifiable way that may exceed or at least obscure previously-reported effects of blood lead on IQ with blood lead levels below 5 µg/dL; however, limitations in the datasets make predictions of the low dose dose-response analysis questionable.

Do Low Levels of Blood Lead Reduce Children's Future Test Scores?

We construct a unique individual-level dataset linking preschool blood lead levels with third grade test scores for Rhode Island children born 1997-2005. Using two identification strategies, we show for the first time that reductions of lead from even historically low levels have significant positive effects. A one-unit decrease in average blood lead levels reduces the probability of being substantially below proficient in reading (math) by 0.96 (0.79) percentage points on a baseline of 12 (16) percent. Since disadvantaged children have greater exposure to lead, lead poisoning may be one of the causes of continuing disparities in test scores.

Economic Valuation of Selected Illnesses in Environmental Public Health Tracking

BACKGROUND

In benefit-cost analysis of public health programs, health outcomes need to be assigned monetary values so that different health endpoints can be compared and improvement in health can be compared with cost of the program. There are 2 major approaches for estimating economic value of illnesses: willingness to pay (WTP) and cost of illness (COI). In this study, we compared these 2 approaches and summarized valuation estimates for 3 health endpoints included in the Centers for Disease Control and Prevention's National Environmental Public Health Tracking Network-asthma, carbon monoxide (CO) poisoning, and lead poisoning.

METHOD

First, we compared results of WTP and COI estimates reported in the peer-reviewed literature when these 2 methods were applied to the same study participants. Second, we reviewed the availability and summarized valuations using these 2 approaches for 3 health endpoints.

RESULT

For the same study participants, WTP estimates in the literature were higher than COI estimates for minor and moderate cases. For more severe cases, with substantial portion of the costs paid by the third party, COI could exceed WTP. Annual medical cost of asthma based on COI approach ranged from $800 to $3300 and indirect costs ranged from $90 to $1700. WTP to have no asthma symptoms ranged from $580 to $4200 annually. We found no studies estimating WTP to avoid CO or lead poisoning. Cost of a CO poisoning hospitalization ranged from $14 000 to $17 000. For patients who sustained long-term cognitive sequela, lifetime earnings and quality-of-life losses can significantly exceed hospitalization costs. For lead poisoning, most studies focused on lead exposure and cognitive ability, and its impact on lifetime earnings.

CONCLUSION

For asthma, more WTP studies are needed, particularly studies designed for conditions that involve third-party payers. For CO poisoning and lead poisoning, WTP studies need to be conducted so that more comprehensive economic valuation estimates can be provided. When COI estimates are used alone, it should be clearly stated that COI does not fully capture the nonmarket cost of illness, such as pain and suffering, which highlights the need for WTP estimates.

Confounding and causation in the epidemiology of lead

The National Health and Medical Research Council recently reported that there were not enough high-quality studies to conclude that associations between health effects and blood lead levels <10 μg/dL were caused by lead. It identified uncontrolled confounding, measurement error and other potential causal factors as common weaknesses. This paper supports those findings with evidence of uncontrolled confounding by parental education, intelligence or household management from several papers. It suggests that inappropriate statistical tests and aggregation of data representing different exposure routes partly explain why confounding has been overlooked. Inadequate correction of confounding has contributed to incorrect conclusions regarding causality at low levels of lead. Linear or log-linear regression models have tended to mask any threshold. While the effects of higher levels of lead exposure are not disputed, overestimation of health effects at low lead exposures has significant implications for policy-makers endeavouring to protect public health through cost-effective regulations.

Shape of concentration-response curves between long-term particulate matter exposure and morbidities of chronic bronchitis: a review of epidemiological evidence

Numerous studies have assessed the concentration-response (C-R) relationships between long-term exposure to particulate matter (PM) and mortality from cardiopulmonary diseases, but few studies have evaluated the C-R relationships between PM exposure and morbidity of chronic respiratory diseases or their symptoms, and to date no systematic review has been published on the characteristics of the C-R curves between PM exposure and respiratory disease morbidity. Screening of all available studies in Medline identified ten studies with figures or scatter plots showing the C-R relationships between PM exposure and chronic bronchitis or chronic cough/phlegm. The C-R relationships showed ballistic 'S' shaped curves, linear in the low to moderate PM range and flattening out in the high PM range. Moreover, the shape and level of the C-R curves differed markedly between susceptible and nonsusceptible populations. New evidence from a prospective cohort study confirmed that the C-R relationship between PM reduction and beneficial effects on respiratory health may be due to the decreased incidence of respiratory symptoms and increased recovery in individuals with symptoms of bronchitis. Additional studies are needed to assess the C-R relationships between different PM contents and chronic health parameters, especially in geographic areas with high PM pollution and in more susceptible populations. Evidence from prospective cohort studies in developing countries with areas of high PM pollution may help evaluate the burden of chronic respiratory disease attributable to PM pollution and air quality standards.

Identification of lead sources in residential environments: Sydney Australia

Interior and exterior dust, soil and paint were analysed at five brick urban Sydney homes over 15 months to evaluate temporal variations and discriminate sources of lead (Pb) exposure. Exterior dust gauge Pb loading rates (μg/m(2)/28 days), interior vacuum dust Pb concentrations (mg/kg) and interior petri-dish Pb loading rates (μg/m(2)/28 days), were correlated positively with soil Pb concentrations. Exterior dust gauge Pb loading rates and interior vacuum dust Pb concentrations peaked in the summer. Lead isotope and Pb speciation (XAS) were analysed in soil and vacuum dust samples from three of the five houses that had elevated Pb concentrations. Results show that the source of interior dust lead was primarily from soil in two of the three houses and from soil and Pb paint in the third home. IEUBK child blood Pb modelling predicts that children's blood Pb levels could exceed 5 μg/dL in two of the five houses.

Assuring access to data for chemical evaluations

BACKGROUND

A database for studies used for U.S. Environmental Protection Agency (EPA) pesticide and chemical reviews would be an excellent resource for increasing transparency and improving systematic assessments of pesticides and chemicals. There is increased demand for disclosure of raw data from studies used by the U.S. EPA in these reviews.

OBJECTIVES

Because the Information Quality Act (IQA) of 2001 provides an avenue for request of raw data, we reviewed all IQA requests to the U.S. EPA in 2002-2012 and the U.S. EPA's responses. We identified other mechanisms to access such data: public access databases, the Freedom of Information Act (FOIA), and reanalysis by a third party.

DISCUSSION

Only two IQA requests to the U.S. EPA were for raw data. Both of these were fulfilled under FOIA, not the IQA. Barriers to the U.S. EPA's proactive collection of all such data include costs to the U.S. EPA and researchers, significant time burdens for researchers, and major regulatory delays. The U.S. EPA regulatory authority in this area is weak, especially for research conducted in the past, not funded by the U.S. government, and/or conducted abroad. The U.S. EPA is also constrained by industry confidential business information (CBI) claims for regulatory testing data under U.S. chemical and pesticide laws. The National Institutes of Health Clinical Trials database systematically collects statistical data about clinical trials but not raw data; this database may be a model for data from studies of chemicals and pesticides.

CONCLUSIONS

A database that registers studies and obtains systematic sets of parameters and results would be more feasible than a system that attempts to make all raw data available proactively. Such a proposal would not obviate rights under the IQA to obtain raw data at a later point.

Sex and rearing condition modify the effects of perinatal lead exposure on learning and memory

Developmental lead (Pb) exposure is associated with cognitive impairments in humans and rodents alike. In particular, impaired spatial learning and memory, as assessed using the Morris water maze (MWM), has been noted in developmentally Pb-exposed rats. Although sex and rearing environment can influence MWM performance in normal animals, the interactions of sex and rearing environment on the impact of developmental Pb exposure on hippocampal-dependent processes has not been well characterized. The present study examined the effects of perinatal exposure (i.e., gestation through weaning) to different levels of Pb (250, 750 and 1500 ppm Pb acetate in food) in males and females raised in a non-enriched environment (standard cage with 3 animals and no toys) or an enriched environment (large cage containing a variety of toys that were changed twice weekly). Testing in the MWM began at postnatal day 55. Behavioral outcomes were influenced by sex and rearing environment, with complex interactions with Pb exposure. In non-Pb exposed control animals, beneficial effects of environmental enrichment on spatial learning and memory were observed in males and females, with greater effects in females. Pb exposure in females mitigated at least some of the benefits of enrichment on learning, particularly at the lowest and highest exposure levels. In males, enrichment conferred a modest learning advantage and for the most part, Pb exposure did not affect this. However, in males with the highest Pb exposure, enrichment did help to overcome detrimental effects of Pb on learning. In females, any potential benefit to reference memory contributed by enrichment was muted by exposure to Pb and for the most part, this was not reproduced in males. Thus, there are complex interactions between sex, environment, and Pb exposure on spatial learning and memory. Environmental manipulation is a potential risk modifier of developmental Pb exposure and interacts with other factors including sex and amount of Pb exposure to affect the functional influences of Pb on the brain.

Comparison of total suspended particulate concentration-response relationships for respiratory symptoms between Chinese children with a different susceptibility status

Few studies have explored concentration-response (C-R) relationships between levels of particulate matter (PM) and respiratory morbidity in terms of the susceptibility of children to respiratory diseases. We sought to determine whether the shapes of C-R curves for comparing total suspended particle (TSP) concentration versus the adjusted prevalence of bronchitis (persistent cough or phlegm) and asthma (current wheeze or asthma) symptoms between children with a different susceptibility status. We used the restricted cubic spline (RCS) function to characterize the C-R relationships between TSP and the adjusted prevalence rates of four respiratory symptoms, after controlling for possible confounding by SO(2) and NO(2) levels, in 11,860 children selected from 18 districts of six cities in Liaoning province. Susceptible children exhibited a 2- to 3-fold elevation in the prevalence of all four respiratory symptoms across the entire TSP range (188-689μg/m(3)). Significant differences in the shapes of C-R curves were evident in children with symptoms of bronchitis (ballistic "S"-shaped curves) and asthma (flattened "U"-shaped curves), as well as between the low and high TSP ranges of such curves, when children were grouped by susceptibility status. A significant linear association between TSP levels and current asthma prevalence was found only among susceptible children exposed to high levels of TSP. The shapes and properties of the TSP-morbidity C-R curves differed significantly by type of respiratory symptom, susceptibility status, and TSP range. More work is required to characterize CR relationships in terms of susceptibility status in countries with different PM levels.

Seven-year neurodevelopmental scores and prenatal exposure to chlorpyrifos, a common agricultural pesticide

BACKGROUND

In a longitudinal birth cohort study of inner-city mothers and children (Columbia Center for Children's Environmental Health), we have previously reported that prenatal exposure to chlorpyrifos (CPF) was associated with neurodevelopmental problems at 3 years of age.

OBJECTIVE

The goal of the study was to estimate the relationship between prenatal CPF exposure and neurodevelopment among cohort children at 7 years of age.

METHODS

In a sample of 265 children, participants in a prospective study of air pollution, we measured prenatal CPF exposure using umbilical cord blood plasma (picograms/gram plasma) and 7-year neurodevelopment using the Wechsler Intelligence Scale for Children, 4th edition (WISC-IV). Linear regression models were used to estimate associations, with covariate selection based on two alternate approaches.

RESULTS

On average, for each standard deviation increase in CPF exposure (4.61 pg/g), Full-Scale intelligence quotient (IQ) declined by 1.4% and Working Memory declined by 2.8%. Final covariates included maternal educational level, maternal IQ, and quality of the home environment. We found no significant interactions between CPF and any covariates, including the other chemical exposures measured during the prenatal period (environmental tobacco smoke and polycyclic aromatic hydrocarbons).

CONCLUSIONS

We report evidence of deficits in Working Memory Index and Full-Scale IQ as a function of prenatal CPF exposure at 7 years of age. These findings are important in light of continued widespread use of CPF in agricultural settings and possible longer-term educational implications of early cognitive deficits.

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 SL⁰·⁵ significantly increases the BL level in children (b=0.214 p= or <0.01), and a unit change in Age⁰·⁵ significantly increases child BL (b=0.401, p= or <0.01). A unit change in Age⁰·⁵ 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 100mg/kg provides children with substantial economic benefit.

A blood lead benchmark for assessing risks from childhood lead exposure

Lead exposure is an insidious problem, causing subtle effects in children at low exposure levels where clinical signs are not apparent. Although a target blood lead concentration (Pb(B)) of ten micrograms per deciliter (10 microg/dL) has been used as the basis for environmental decision-making in California for nearly two decades, recent epidemiologic evidence suggests a relationship between cognitive deficits and Pb(B) at concentrations < 10 microg/dL. Based on a published meta-analysis of children's IQ scores and their blood lead concentrations, we developed a new blood lead benchmark: an incremental increase in blood lead concentration (DeltaPb(B)) of 1 microg/dL, an increase that we estimate could decrease the IQ score in an average school child in California by up to one point. Although there is no evidence to date for a threshold for the neurobehavioral effects of lead, a one-point IQ decrement was chosen to represent a de minimus change. To safeguard the intellectual potential of all children, additional efforts to reduce or eliminate multiple-source exposures to lead are warranted.

Children's blood lead and standardized test performance response as indicators of neurotoxicity in metropolitan New Orleans elementary schools

This study analyzes pre-Katrina variation in aggregate student performance and children's blood lead (BPb) in 117 elementary school districts in metropolitan New Orleans. Fourth grade student achievement on Louisiana Educational Assessment Program (LEAP) tests were analyzed as a function of BPb for children 1-6 years old within school districts, controlling for student-teacher ratios, percent of students eligible for a free or discounted lunch, and school racial demography. Measures of performance across subject areas (English Language Arts, Science, Mathematics, and Social Studies) include school Achievement Test Scores (ATS) and indices of agreement and variation in student achievement. ATS are measured on a 5-point scale, corresponding to achievement categories of advanced=5 to unsatisfactory=1. Regression results show that median BPb (microg/dL) and percent of children with BPb > or =10 microg/dL are significantly associated with reductions in test scores across all subjects and depress variation in student performance across achievement categories. These data suggest that assisting children with improved school performance requires alleviation of pre-school Pb exposure and its associated neurotoxic damage. Cost-benefit calculations suggest that it is more cost effective to pay for onetime primary prevention instead of paying continuous expenses focused on reversing neurotoxic damage.

Emerging aspects of assessing lead poisoning in childhood

This review covers the epidemiology of lead poisoning in children on a global scale. Newer sources of lead poisoning are identified. The methods that are used to assess a population of children exposed to lead are discussed, together with the ways of undertaking an exposure risk assessment; this includes assessing the time course and identifying sources of lead exposure. Human assessment measures for lead toxicity, such as blood lead concentrations, deciduous tooth lead, and use of zinc protoporphyrin estimations are evaluated. The role of isotopic fingerprinting techniques for identifying environmental sources of exposure is discussed. Among emerging data on the cognitive and behavioral effects of lead on children, the review considers the growing evidence of neurocognitive dysfunction with blood lead concentrations even below 10 µg/dl. The challenge of assessing and explaining the risk that applies to an individual as opposed to a population is discussed. Intervention strategies to mitigate risk from lead are examined together with the limited role for and limitations of chelation therapy for lead. Lessons learned from managing a population lead-dust exposure event in Esperance, Western Australia in 2007 are discussed throughout the review.

Soil metal concentrations and toxicity: associations with distances to industrial facilities and implications for human health

Urban and rural areas may have different levels of environmental contamination and different potential sources of exposure. Many metals, i.e., arsenic (As), lead (Pb), and mercury (Hg), have well-documented negative neurological effects, and the developing fetus and young children are particularly at risk. Using a database of mother and child pairs, three areas were identified: a rural area with no increased prevalence of mental retardation and developmental delay (MR/DD) (Area A), and a rural area (Area B) and an urban area (Area C) with significantly higher prevalence of MR/DD in children as compared to the state-wide average. Areas were mapped and surface soil samples were collected from nodes of a uniform grid. Samples were analyzed for As, barium (Ba), beryllium (Be), chromium (Cr), copper (Cu), Pb, manganese (Mn), nickel (Ni), and Hg concentrations and for soil toxicity, and correlated to identify potential common sources. ArcGIS was used to determine distances between sample locations and industrial facilities, which were correlated with both metal concentrations and soil toxicity. Results indicated that all metal concentrations (except Be and Hg) in Area C were significantly greater than those in Areas A and B (p< or =0.0001) and that Area C had fewer correlations between metals suggesting more varied sources of metals than in rural areas. Area C also had a large number of facilities whose distances were significantly correlated with metals, particularly Cr (maximum r=0.33; p=0.0002), and with soil toxicity (maximum r=0.25; p=0.007) over a large spatial scale. Arsenic was not associated with distance to any facility and may have a different anthropogenic, or natural source. In contrast to Area C, both rural areas had lower concentrations of metals, lower soil toxicity, and a small number of facilities with significant associations between distance and soil metals.

Human geography of New Orleans' high-lead geochemical setting

Previous soil lead studies in New Orleans focused on the geochemical footprint and its health impacts. This study examines the human geography of race, income, and age in pre-Katrina metropolitan New Orleans within the context of lead accumulation in soils. Sample points of soil lead data (n = 5,467) collected in 1998-2000 were mapped in a geographic information system (GIS), binned into 9 ranges, and queried by (1) 2000 Census racial demographic data, (2) 1999 median household income, and (3) 2000 age data. The absolute population generally declines as lead levels increase except at lead levels from 200-400 to 400-1,000 mg/kg when population increases; the African-American population comprises a disproportionate share of this cohort. The high-lead areas occur in the inner city, home to the largest populations of African-Americans in New Orleans. The mean household income curve indicates that lower economic groups are at risk to higher levels of lead. A total of 44,701 children under the age of 5 years, plus 123,579 children aged 5-17, lived in census block groups containing at least one sample point with over 100 mg/kg lead, and these include 23,124 and 64,064 young people, respectively, who live near at least one point over 400 mg/kg. Lead exposure affects a panoply of outcomes that influence the health and welfare of the community. Unless corrected, children are likely to return to the same or, because of lack of lead-safe practices during renovation, even higher exposure risks than before the flooding of New Orleans.

Soil lead (Pb) in residential transects through Lubbock, Texas: a preliminary assessment

Residential lead (Pb) contamination, resulting from decades-long use of leaded gasoline and lead-based paint, is likely to be present in soils in most urban areas. A screening level sampling effort demonstrated that Lubbock, Texas, USA, like other cities of its age and size, has areas of elevated soil Pb. This effort was based on soil sampling performed on residential, commercial and thoroughfare properties. The focus of this study was to investigate that component of soil contamination due to combustion of leaded gasoline. Soils were collected from the 1-2 cm surface layer from street-side property borders, well away from buildings that might lead to soil contamination from leaded paint chips. All samples were analyzed for Pb after a 1 M HNO(3) mild extraction to determine the amount of bioavailable Pb. Two of three transects through the city demonstrated significant trends of decreasing Pb concentrations with distance from the city center, paralleling a decrease in developed property age. Peak soil Pb concentrations outside city development was 4.9 +/- 0.6 mg/kg while the median concentration for the city was 35.4 mg/kg. Peak soil Pb concentrations in the city center ranged from 90.0 to 174.0 mg/kg and decreased exponentially to 6.0-9.0 mg/kg at the furthest terminus of the residential transects.

Epidemiologic evidence of relationships between reproductive and child health outcomes and environmental chemical contaminants

This review summarizes the level of epidemiologic evidence for relationships between prenatal and/or early life exposure to environmental chemical contaminants and fetal, child, and adult health. Discussion focuses on fetal loss, intrauterine growth restriction, preterm birth, birth defects, respiratory and other childhood diseases, neuropsychological deficits, premature or delayed sexual maturation, and certain adult cancers linked to fetal or childhood exposures. Environmental exposures considered here include chemical toxicants in air, water, soil/house dust and foods (including human breast milk), and consumer products. Reports reviewed here included original epidemiologic studies (with at least basic descriptions of methods and results), literature reviews, expert group reports, meta-analyses, and pooled analyses. Levels of evidence for causal relationships were categorized as sufficient, limited, or inadequate according to predefined criteria. There was sufficient epidemiological evidence for causal relationships between several adverse pregnancy or child health outcomes and prenatal or childhood exposure to environmental chemical contaminants. These included prenatal high-level methylmercury (CH(3)Hg) exposure (delayed developmental milestones and cognitive, motor, auditory, and visual deficits), high-level prenatal exposure to polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and related toxicants (neonatal tooth abnormalities, cognitive and motor deficits), maternal active smoking (delayed conception, preterm birth, fetal growth deficit [FGD] and sudden infant death syndrome [SIDS]) and prenatal environmental tobacco smoke (ETS) exposure (preterm birth), low-level childhood lead exposure (cognitive deficits and renal tubular damage), high-level childhood CH(3)Hg exposure (visual deficits), high-level childhood exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (chloracne), childhood ETS exposure (SIDS, new-onset asthma, increased asthma severity, lung and middle ear infections, and adult breast and lung cancer), childhood exposure to biomass smoke (lung infections), and childhood exposure to outdoor air pollutants (increased asthma severity). Evidence for some proven relationships came from investigation of relatively small numbers of children with high-dose prenatal or early childhood exposures, e.g., CH(3)Hg poisoning episodes in Japan and Iraq. In contrast, consensus on a causal relationship between incident asthma and ETS exposure came only recently after many studies and prolonged debate. There were many relationships supported by limited epidemiologic evidence, ranging from several studies with fairly consistent findings and evidence of dose-response relationships to those where 20 or more studies provided inconsistent or otherwise less than convincing evidence of an association. The latter included childhood cancer and parental or childhood exposures to pesticides. In most cases, relationships supported by inadequate epidemiologic evidence reflect scarcity of evidence as opposed to strong evidence of no effect. This summary points to three main needs: (1) Where relationships between child health and environmental exposures are supported by sufficient evidence of causal relationships, there is a need for (a) policies and programs to minimize population exposures and (b) population-based biomonitoring to track exposure levels, i.e., through ongoing or periodic surveys with measurements of contaminant levels in blood, urine and other samples. (2) For relationships supported by limited evidence, there is a need for targeted research and policy options ranging from ongoing evaluation of evidence to proactive actions. (3) There is a great need for population-based, multidisciplinary and collaborative research on the many relationships supported by inadequate evidence, as these represent major knowledge gaps. Expert groups faced with evaluating epidemiologic evidence of potential causal relationships repeatedly encounter problems in summarizing the available data. A major driver for undertaking such summaries is the need to compensate for the limited sample sizes of individual epidemiologic studies. Sample size limitations are major obstacles to exploration of prenatal, paternal, and childhood exposures during specific time windows, exposure intensity, exposure-exposure or exposure-gene interactions, and relatively rare health outcomes such as childhood cancer. Such research needs call for investments in research infrastructure, including human resources and methods development (standardized protocols, biomarker research, validated exposure metrics, reference analytic laboratories). These are needed to generate research findings that can be compared and subjected to pooled analyses aimed at knowledge synthesis.

Nonlinear association between soil lead and blood lead of children in metropolitan New Orleans, Louisiana: 2000-2005

Metropolitan New Orleans is unique because it has a universal blood lead (BL) screening dataset (n=55,551) from 2000-2005 spatially coupled with a soil lead (SL) dataset (n=5467) completed in 2000. We evaluated empirical associations between measurements of SL and BL exposure responses of children in New Orleans by stratifying the databases by Census Tracts and statistically analyzing them with permutation methods. A consistent curvilinear association occurred annually between SL and BL with robust significance (P-values<10(-23)). The mathematical model of the pooled BL datasets for 2000-2005 is: BL=2.038+0.172 x (SL)(0.5) (agreement (R) of 0.534, an r(2) of 0.528, and a P-value of 1.0 x 10(-211)) indicating that chance alone cannot explain the association. Below 100 mg/kg SL children's BL exposure response is steep (1.4 microg/dL per 100 mg/kg), while above 300 mg/kg SL the BL exposure response is gradual (0.32 microg/dL per 100 mg/kg). In 1995, the BL prevalence was 37%>or=10 microg/dL for the most vulnerable poor and predominantly African-American children. In the era of universal screening the prevalence of elevated BL is 11.8%>or=10 microg/dL for the general population of children. The SL map describes community variations of potential BL exposure. If health effects occur at BL>or=2 microg/dL, then 93.5% of the children in New Orleans are at risk. These results reinforce the proposal that prevention of childhood Pb exposure must include SL remediation as demonstrated by a New Orleans pilot project and a proactive Norwegian government program.

Probabilistic modeling of young children's overall lead exposure in France: integrated approach for various exposure media

OBJECTIVES

Emissions of lead into the environment (and thus its environmental concentrations) have decreased in recent years. We sought to estimate the overall lead exposure of children aged 6 months to 6 years (the population group most exposed and most sensitive to lead) in France through the various media (air, food, water, soils, and dust) and the respective contributions of each medium to the total dose. We have focused on the general population, leaving aside specific risk factors such as deteriorated lead paints.

METHODS

We used the most recent French intake data for food and water, and a daily ingested quantity selected from the literature for soils and dust. Contamination data came from the first total diet study of contaminant levels in France (2000-2001), from regulatory testing of tap water (2004), a literature review of lead in urban soils, and a pilot study (2005) of lead in dust. Air quality monitoring measurements showed that the contribution of air could now be safely ignored. Weekly exposure doses were estimated with Monte Carlo simulations.

RESULTS

Median weekly exposure dose was 7.5 microg/kg bw.week for children aged 6 months to 3 years and 4.7 for those aged from 3-6 years. 95th percentiles were 13.5 and 8.7 microg/kg bw.week. Exposure came mainly from food. The principal uncertainties are associated with quantification limits in food and water, representativeness and traceability of tap water samples, and absence of recent data about urban soil contamination.

CONCLUSIONS

These results differ quite notably from earlier estimates and highlight the need, especially for policy-making purposes, to update exposure measurements for this metal.

Mycophenolate mofetil administration reduces renal inflammation, oxidative stress, and arterial pressure in rats with lead-induced hypertension

Hypertension is a likely consequence of chronic lead exposure in humans, especially in association with reduced renal function and in high risk populations. Numerous studies have demonstrated that oxidative stress plays an important role in the pathogenesis of experimental lead-induced hypertension and we have shown recently that tubulointerstitial immune cell infiltration is a feature of chronic low-dose lead exposure. Since oxidative stress, renal inflammation, and angiotensin activity are closely linked characteristics in experimental models of hypertension, we decided to investigate whether lead-induced hypertension would be ameliorated by suppressing renal inflammation with the immunosuppressive drug mycophenolate mofetil (MMF). We studied rats exposed for 14 wk to lead acetate (100 ppm in the drinking water) that, in addition, received either MMF, 20 mg.kg(-1).day(-1) by gastric gavage (Pb.MMF group, n = 12) or vehicle (Pb group, n = 12). Control rats received MMF alone (n = 5) or neither lead nor MMF (n = 6). All rats were killed at the end of the experiment. Low-dose lead exposure resulted in mild to moderate tubular cell damage and a progressive increment in blood pressure, oxidative stress, interstitial accumulation of lymphocytes and macrophages, NF-kappaB activation, and increased renal angiotensin II level. The administration of MMF suppressed the tubulointerstitial accumulation of lymphocytes and macrophages and prevented the hypertension, oxidative stress, and NF-kappaB activation and reduced the heightened renal angiotensin content associated with chronic lead exposure. We conclude that interstitial inflammation plays an important role in lead-induced hypertension.

Update on the clinical management of childhood lead poisoning

Childhood lead poisoning is still an enormous public health issue in the United States, affecting thousands of children and their families. New evidence suggests that even very low blood lead levels, less than 10 microg/dL, can be associated with neurologic injury. This article discusses characteristics of children at high risk for lead poisoning, unusual sources of lead contamination, and new aspects of lead's pathophysiology. It includes current thinking on the clinical management and prevention of childhood lead poisoning.

Questionnaire survey of exposure to lead in the domestic environment in Nigeria

Environmental exposure to lead is a significant cause of morbidity and mortality in developed countries, particularly in children, but remains understudied in developing countries. While prevention is acknowledged as the best public health option, the level of knowledge about lead exposure in many developing countries is not known. We conducted a survey to evaluate the knowledge about lead exposure in Nigeria. Survey questionnaires were developed from the results of focus group discussions and published literature. 600 questionnaires were randomly distributed to adults living in Ibadan, South Western Nigeria in 2004. In addition, the knowledge of lead exposure was measured using a modified version of the Chicago Lead Knowledge Test (CLKT). Information on lead abatement and sources of household lead exposure were also obtained. Most respondents did not have a satisfactory level of knowledge about lead exposure in the domestic environment, how to prevent it and the role of nutrition in diminishing the impact of exposure. Younger people, female and increased years of schooling predict higher scores in the CLKT. Most respondents lived in rented homes; the majority of which were either built or last refurbished in the 1990s. Home owners and people living in homes built or last refurbished within 4 years of the study had higher mean CLKT scores. Our study showed that our respondents had very low levels of knowledge about the risk of domestic exposure to lead, particularly to children. We recommend that efforts should be made to increase awareness of this condition and that in Nigeria as in most development countries; this should be done through the maternal and child health care programs.

Longitudinal associations between blood lead concentrations lower than 10 microg/dL and neurobehavioral development in environmentally exposed children in Mexico City

OBJECTIVE

Increasing evidence suggests that 10 microg/dL, the current Centers for Disease Control and Prevention screening guideline for children's blood lead level, should not be interpreted as a level at which adverse effects do not occur. Using data from a prospective study conducted in Mexico City, Mexico, we evaluated the dose-effect relationship between blood lead levels and neurodevelopment at 12 and 24 months of age.

METHODS

The study population consisted of 294 children whose blood lead levels at both 12 and 24 months of age were < 10 microg/dL; blood lead levels were measured by graphite furnace atomic absorption spectroscopy; Bayley Scales of Infant Development II were administered at these ages. The outcomes of interest were the Mental Development Index and the Psychomotor Development Index.

RESULTS

Adjusting for covariates, children's blood lead levels at 24 months were significantly associated, in an inverse direction, with both Mental Development Index and Psychomotor Development Index scores at 24 months. Blood lead level at 12 months of age was not associated with concurrent Mental Development Index or Psychomotor Development Index scores or with Mental Development Index at 24 months of age but was significantly associated with Psychomotor Development Index score at 24 months. The relationships were not altered by adjustment for cord blood lead level or, in the analyses of 24-month Mental Development Index and Psychomotor Development Index scores, for the 12-month Mental Development Index and Psychomotor Development Index scores. For both Mental Development Index and Psychomotor Development Index at 24 months of age, the coefficients that were associated with concurrent blood lead level were significantly larger among children with blood lead levels < 10 microg/dL than it was among children with levels > 10 microg/dL.

CONCLUSIONS

These analyses indicate that children's neurodevelopment is inversely related to their blood lead levels even in the range of < 10 microg/dL. Our findings were consistent with a supralinear relationship between blood lead levels and neurobehavioral outcomes.

Reduced intellectual development in children with prenatal lead exposure

OBJECTIVE

Low-level postnatal lead exposure is associated with poor intellectual development in children, although effects of prenatal exposure are less well studied. We hypothesized that prenatal lead exposure would have a more powerful and lasting impact on child development than postnatal exposure.

DESIGN

We used generalized linear mixed models with random intercept and slope to analyze the pattern of lead effect of the cohort from pregnancy through 10 years of age on child IQ from 6 to 10 years. We statistically evaluated dose-response nonlinearity.

PARTICIPANTS

A cohort of 175 children, 150 of whom had complete data for all included covariates, attended the National Institute of Perinatology in Mexico City from 1987 through 2002.

EVALUATIONS/MEASUREMENTS

We used the Wechsler Intelligence Scale for Children-Revised, Spanish version, to measure IQ. Blood lead (BPb) was measured by a reference laboratory of the Centers for Disease Control and Prevention (CDC) quality assurance program for BPb.

RESULTS

Geometric mean BPb during pregnancy was 8.0 microg/dL (range, 1-33 microg/dL), from 1 through 5 years was 9.8 microg/dL (2.8-36.4 microg/dL), and from 6 through 10 years was 6.2 microg/dL (2.2-18.6 microg/dL). IQ at 6-10 years decreased significantly only with increasing natural-log third-trimester BPb (beta=-3.90; 95% confidence interval, -6.45 to -1.36), controlling for other BPb and covariates. The dose-response BPb-IQ function was log-linear, not linear-linear.

CONCLUSIONS

Lead exposure around 28 weeks gestation is a critical period for later child intellectual development, with lasting and possibly permanent effects. There was no evidence of a threshold; the strongest lead effects on IQ occurred within the first few micrograms of BPb.

RELEVANCE TO CLINICAL PRACTICE

Current CDC action limits for children applied to pregnant women permit most lead-associated child IQ decreases measured over the studied BPb range.

An examination of knowledge, attitudes and practices related to lead exposure in South Western Nigeria

BACKGROUND

Lead is a highly toxic and pervasive metal. Chronic exposure to low levels is responsible for significant health effects, particularly in children. Prevention remains the best option for reducing childhood lead exposure, however the knowledge, attitudes and practices to lead exposure in many developing countries is not known.

METHODS

We conducted four focus group discussions (FGD) to evaluate knowledge attitudes and practices to lead exposure in Nigeria. An FGD guide was developed from the literature and preliminary discussion with members of the public. Participants in the FGD were randomly selected from adults living in Ibadan, South Western Nigeria in 2004.

RESULTS

We found that there was limited awareness of the sources of lead exposure in the domestic environment and participants had little knowledge of the health effects of chronic low-dose lead exposure.

CONCLUSION

We conclude that the findings of this study should be used, in conjunction with others, to develop appropriate health education intervention for lead exposure in the domestic environment.