Early Childhood Lead Exposure Research Articles

Spatial Variability in Relationships between Early Childhood Lead Exposure and Standardized Test Scores in Fourth Grade North Carolina Public School Students (2013-2016).

Exposure to lead during childhood is detrimental to children's health. The extent to which the association between lead exposure and elementary school academic outcomes varies across geography is not known. Estimate associations between blood lead levels (BLLs) and fourth grade standardized test scores in reading and mathematics in North Carolina using models that allow associations between BLL and test scores to vary spatially across communities. We link geocoded, individual-level, standardized test score data for North Carolina public school students in fourth grade (2013-2016) with detailed birth records and blood lead testing data retrieved from the North Carolina childhood blood lead state registry on samples typically collected at 1-6 y of age. BLLs were categorized as: (reference), , and . We then fit spatially varying coefficient models that incorporate information sharing (smoothness), across neighboring communities via a Gaussian Markov random field to provide a global estimate of the association between BLL and test scores, as well as census tract-specific estimates (i.e., spatial coefficients). Models adjusted for maternal- and child-level covariates and were fit separately for reading and math. The average BLL across the 91,706 individuals in the analysis dataset was . Individuals were distributed across 2,002 (out of 2,195) census tracts in North Carolina. In models adjusting for child sex, birth weight percentile for gestational age, and Medicaid participation as well as maternal race/ethnicity, educational attainment, marital status, and tobacco use, BLLs of , and were associated with overall lower reading test scores of [95% confidence interval (CI): , ], (, ), and (, ), respectively. For BLLs of , , and , spatial coefficients-that is, tract-specific adjustments in reading test score relative to the "global" coefficient-ranged from to 2.52, to 3.90, to 7.85, and to 4.33, respectively. Results for mathematics were similar to those for reading. The association between lead exposure and reading and mathematics test scores exhibits considerable heterogeneity across North Carolina communities. These results emphasize the need for prevention and mitigation efforts with respect to lead exposures everywhere, with special attention to locations where the cognitive impact is elevated. https://doi.org/10.1289/EHP13898.

Making the case for lead safe housing: Downstream effects of lead exposure on outcomes for children and youth

Lead based paint is a predominate source of lead exposure in children, which has a documented negative effect on their health and development. Despite public health efforts, the housing stock in disinvested neighborhoods in many cities continues to present significant risk of childhood lead exposure. In this article, we describe how a multi-agency integrated data system was used to document the impact of lead exposure on indicators of child and youth development as recorded in educational and human service systems. By tracking administrative data for two cohorts of Cleveland, Ohio children from birth to early adulthood and using rigorous matching methods to reduce confounders when comparing those with and without elevated blood lead levels, we document negative effects on developmental, behavioral and socio-economic outcomes due to early childhood lead exposure. The magnitude of disparities between individuals who had elevated blood lead levels (≥5 μg/dL) in early childhood, compared to their matched counterparts, is in the ranges of 20–40%. The analysis is framed by clarifying the context, assumptions and limitations associated with the use of administrative data. This type of information has been useful in illuminating the burden of lead exposure for children, families and youth serving agencies and engaging public officials, landlords and residents in initiatives to bring housing up to lead safe standards.

Early childhood lead exposure is not reflected in adult bone lead: Results of a sub-cohort of African American women in the Cincinnati lead study

IntroductionPb in bone may serve as a biomarker for cumulative Pb dose over decades. We hypothesized that adult female bone Pb concentrations (BoPb) would be significantly associated with average childhood blood Pb levels (BlPb) in a birth cohort exposed to relatively high levels of Pb from Pb paint residues. Methods94 African American women with a mean age of 32.7 years were recruited from the Cincinnati Lead Study (CLS) cohort. Subjects were born to women residing where there had been a high incidence of childhood Pb poisoning. Biomarkers of Pb exposure were serial BlPb concentrations spanning the prenatal period to approximately 6.5 years of age. BoPb was assessed in the tibia using the McMaster 109Cd K-XRF fourth generation system. Covariates included nutritional variables related to bone health. ResultsBlPb concentrations began to rise around 6 months of age and declined at later ages. Study participants were obese with a mean Body Mass Index of 34.4 and suboptimal vitamin D status as indicated by a mean 25-OH-D of 18.5 ng/ml. Average tibia Pb was −2.0 ± 8.6 μgPb/g bone mineral. In multiple linear regression, there was no significant association between BoPb at approximately age 30 and childhood cumulative BlPb(CumBlPb). DiscussionCollectively, BoPb of this group of subjects was not detectable. We suggest that the reason these subjects’ BoPb did not reflect their early exposure was that a significantly smaller proportion of Pb body burden resides in bone in young children. As the child grows what Pb there was in bone is diluted and any remaining signal is weak. It has been claimed that BoPb in older children, adolescents, and adults can recapitulate historical exposure to Pb during earlier development; however, in some populations, BoPb at later ages may not be an adequate biomarker to capture childhood exposure to Pb.

Racial residential segregation shapes the relationship between early childhood lead exposure and fourth-grade standardized test scores

Racial/ethnic disparities in academic performance may result from a confluence of adverse exposures that arise from structural racism and accrue to specific subpopulations. This study investigates childhood lead exposure, racial residential segregation, and early educational outcomes. Geocoded North Carolina birth data is linked to blood lead surveillance data and fourth-grade standardized test scores (n = 25,699). We constructed a census tract-level measure of racial isolation (RI) of the non-Hispanic Black (NHB) population. We fit generalized additive models of reading and mathematics test scores regressed on individual-level blood lead level (BLL) and neighborhood RI of NHB (RINHB). Models included an interaction term between BLL and RINHB. BLL and RINHB were associated with lower reading scores; among NHB children, an interaction was observed between BLL and RINHB. Reading scores for NHB children with BLLs of 1 to 3 µg/dL were similar across the range of RINHB values. For NHB children with BLLs of 4 µg/dL, reading scores were similar to those of NHB children with BLLs of 1 to 3 µg/dL at lower RINHB values (less racial isolation/segregation). At higher RINHB levels (greater racial isolation/segregation), children with BLLs of 4 µg/dL had lower reading scores than children with BLLs of 1 to 3 µg/dL. This pattern becomes more marked at higher BLLs. Higher BLL was associated with lower mathematics test scores among NHB and non-Hispanic White (NHW) children, but there was no evidence of an interaction. In conclusion, NHB children with high BLLs residing in high RINHB neighborhoods had worse reading scores.

Low level lead exposure in early childhood and parental education on adolescent IQ and working memory: a cohort study.

The independent effect of lead exposure and parental education on children's neurocognition is well-documented. However, few studies have examined the combined effect of childhood lead exposure and parental education on adolescent neurocognition, especially in China. Examine both the combined and interactive effect of childhood blood lead levels (BLLs) and parental education on early adolescent neurocognition. 417 children from a longitudinal cohort study in Jintan, China had BLLs measured at 3-5 years and 12 years, parental education levels assessed at 3-5 years, and neurocognitive outcomes tested at 12 years. BLLs at 3-5 years were inversely associated with adolescent IQ (β -0.55 95% CI: -0.97, -0.13) but not working memory (β -0.06 95% CI: -0.23, 0.11) and parental education was positively associated with adolescent IQ (β 0.68 95% CI: 0.19, 1.17) and working memory (β 0.24 95% CI: 0.04, 0.44). BLLs and parental education evidenced combined effects on neurocognition, where children with higher BLLs and lower fathers' education had mean IQ scores 7.84 (95% CI: -13.15, -2.53) points lower than children with lower BLLs and higher fathers' education. There were significant associations between parental education and working memory, however, not with BLLs. The interaction between mother and father high school education and BLLs was insignificant for effects on IQ and working memory. Childhood lead exposure and parental education levels have a combined and long-term impact on IQ, evidence that may partially explain disparities in lead exposure associated outcomes and highlight those children at greatest risk for neurocognitive deficits. Children continue to be exposed to low-levels of environmental lead in China and globally, warranting examination of the impact of such exposures. This paper demonstrates that even relatively low-level lead exposure in early childhood significantly influences adolescent neurocognitive functioning. Furthermore, co-existing social determinant of health-related variables, measured here as parental education, have a combined impact on neurocognition. These results highlight children at greater risk for neurocognitive deficits and demonstrate the need to examine the influence of lead exposure within the broader socio- ecological environment, as these factors work in tandem to influence longer-term neurocognitive outcomes.

Longitudinal association of early childhood lead exposure and adolescent heart rate variability: influence of parental education

Lead exposure has been shown to dysregulate physiological stress responses. However, few studies have investigated the effect of lead exposure on later heart rate variability (HRV), an indicator of a stress response, in large samples of children. Furthermore, the interaction between social environmental factors and lead exposure in childhood, which commonly co-occur, remains understudied. This study examined relationships between childhood lead exposure and early adolescent physiological stress responses at different levels of parental education. Participants were 406 children from Jintan, China. Blood lead levels (BLLs) and parental education data were collected at 3–5 years of age, and HRV outcomes assessed at 12 years via frequency domain measures (LF/HF ratio) collected during an induced stress test. Results show a significant interaction between parental education and BLLs at 3–5 years. This relationship was found to be most consistent for the interaction between BLLs and mother’s years of education for both the planning (β = 0.12, p = 0.046) and speaking (β = 0.11, p = 0.043) phase of the stress task, suggesting that increasing years of mother’s education may enhance the deleterious influence of lead exposure on the HRV frequency measure, LF/HF ratio. This research highlights the complexity in lead exposure induced outcomes.

Early childhood lead exposure and adolescent heart rate variability: A longitudinal cohort study

Lead is a known neurotoxicant with many detrimental health effects, including neurocognitive deficits and cardiovascular and metabolic disorders. However, few studies have tested the association between lead exposure and the physiological stress response, which in and of itself may act as a precursor to and/or underlying mechanism of detrimental health outcomes. The purpose of this study was to examine the influence of early childhood and early adolescent low-level lead exposure on early adolescent heart rate variability, a widely-used measure of physiological stress. Participants were 408 children from Jintan, China for whom blood lead levels were measured between 3 and 5 years (early childhood) and again at 12 years (early adolescence). Heart rate variability was assessed at 12 years while participants underwent an induced stress task utilizing the ratio of low to high frequency (LF/HF) ECG measures. Mean blood lead levels in the cohort were 6.63 mcg/dl and 3.10 mcg/dl at 3–5 years and 12 years, respectively. Blood lead levels at 3–5 years of age (β 0.06, p = 0.027), but not at age 12 (β −0.05, p = 0.465), were significantly associated with LF/HF measures while controlling for multiple sociodemographic variables, potentially reflecting a dysregulated stress response with a shift towards sympathetic dominance. These findings suggest that early childhood lead exposure may have a detrimental influence on early adolescent autonomic responses to acute stress, which holds implications for cardiovascular health and overall growth and development.

Prenatal and Early Childhood Lead Exposure and Metabolic Syndrome Risk Indicators in 6 to 8 year-old Children

BACKGROUND AND AIM: Exposure to lead (Pb) during early life stages has been associated with the development of metabolic syndrome (MS). Longitudinal studies in children are limited. We aimed to examine the association between prenatal and early childhood exposure to Pb and risk indicators of MS between 6 and 8 years of age. METHODS: Our study included 601 mother-child dyads participating in the PROGRESS birth cohort, children included were full term. Blood lead levels (BLLs) were assessed prenatally, during the second and third trimesters, in cord blood at delivery, and postnatally in early childhood at ages 1, 2 and 4 years of age. To account for cumulative exposure, we created scores (prenatal, postnatal, and overall) dichotomizing BLLs at each stage visit and categorized as: always above if BLLs was above the median (AA), never above if all BLLs was below the median (NA), and sometimes above otherwise (SA). We analyzed fasting glucose, HbA1c, triglycerides, total cholesterol, HDL cholesterol, LDL cholesterol, body mass index, waist circumference, body fat percentage, systolic and diastolic blood pressure at 72 and 96 months of age. Mixed-effects models were used to analyze each outcome longitudinally for prenatal, postnatal, and overall BLLs scores, adjusting for socioeconomic status, sex, size for gestational age, parity, maternal and children’s age. RESULTS:We observed associations for total cholesterol with SA prenatally (β: -6.13, 95% CI: -11.0, -1.23), postnatally (β: -6.16, 95% CI: -11.8, -0.46) and overall (β: -6.66, 95% CI: -11.2, -2.10); LDL cholesterol and prenatal SA (β: -4.901, 95% CI: -9.13, -0.66); systolic blood pressure and overall AA (β: -1.851, 95% CI: -3.60, -0.09); HbA1c and postnatal SA (β: -0.10, 95% CI: -0.20, -0.001). CONCLUSIONS:Early life exposure to Pb may alter early indicators of MS. Follow-up of these children will allow for more definition on the longer-term impact of exposure. KEYWORDS: Lead Exposure, Prenatal Exposure, Metabolic Syndrome, Early Childhood

Early childhood lead exposure and the persistence of educational consequences into adolescence

BackgroundThere is consensus that early childhood lead exposure causes adverse cognitive and behavioral effects, even at blood lead levels (BLL) below 5 μg/dL. What has not been established is to what extent the effects of childhood lead exposure persist across grades. ObjectiveTo measure the effects of early childhood lead exposure (BLL 1–10 μg/dL) on educational performance from grades 3–8; to determine if effects in lower grades persist as a child progresses through school; and if so, to characterize the pattern of persistence. MethodsWe examine data from 560,624 children living in North Carolina between 2000 and 2012 with a BLL ≤10 μg/dL measured between age 0–5 years. Children are matched to their standardized math and reading scores for grades 3–8, creating an unbalanced panel of 2,344,358 student-year observations. We use socio-economic, demographic, and school information along with matching techniques to control for confounding effects. ResultsWe find that early childhood exposure to low lead levels caused persistent deficits in educational performance across grades. In each grade (3–8), children with higher blood lead levels had, on average, lower percentile scores in both math and reading than children with lower blood lead levels. In our primary model, we find that children with BLL = 5 μg/dL in early childhood ranked 0.90–1.20 (1.35–1.55) percentiles lower than children with BLL ≤ 1 μg/dL on math (reading) tests during grades 3–8. As children progressed through school, the average percentile deficit in their test scores remained stable. ConclusionsOur study shows that the adverse effects of early childhood exposure to low lead levels persist through early adolescence, and that the magnitude of the test-score percentile deficit remains steady between grades 3–8.

Early lead exposure and pubertal development in a Mexico City population

BackgroundPrevious studies have examined the association between blood lead levels and pubertal timing in adolescent girls; however, the evidence is lacking on the role of lead exposure during sensitive developmental periods on sexual maturation. ObjectivesTo examine the association of prenatal and early childhood lead exposure with pubertal stages among 264 boys and 283 girls aged 9.8–18.0 years in Mexico City. MethodsWe measured maternal bone lead (a proxy for cumulative fetal exposure to lead from maternal bone stores mobilized during pregnancy) at 1 month postpartum. Blood lead was measured annually from 1 to 4 years. Pubertal stage was assessed by a pediatrician. We examined the association between lead and pubertal stages of breast, pubic hair and genitalia using ordinal regression. Age at menarche was evaluated using Cox proportional-hazard models. ResultsMultivariate models showed that maternal patella lead and early childhood blood lead were inversely associated with breast growth (patella OR = 0.72, 95% CI: 0.51–1.00; blood OR = 0.70, 95% CI: 0.53–0.93) in girls. Girls with maternal patella lead in the 3rd tertile and child blood lead in the 2nd tertile had a later age at menarche compared with girls in the 1st tertile (patella HR = 0.60, 95% CI: 0.41–0.88; blood HR = 0.65, 95% CI 0.46–0.91). Additionally, early childhood blood lead was negatively associated with pubic hair growth (OR = 0.68, 95% CI: 0.51–0.90) in girls. No associations were found in boys. ConclusionsThese data suggest that higher prenatal and early childhood exposure to lead may be associated with delayed pubertal development in girls but not boys. Our findings are consistent with previous analyses and reinforce the reproductive effects of lead for girls.

Lead exposure and academic achievement: evidence from childhood lead poisoning prevention efforts

Though the adverse consequences of lead exposure in children have been well known for over a century, the recent Flint water crisis has drawn renewed attention to the impacts of lead exposure on human health and development. This study considers connections to educational outcomes, asking whether population-level lead exposure in early childhood influences later academic achievement and racial achievement gaps. It assesses the effectiveness of recent local- and state-level lead hazard control programs in mitigating exposure and uses this source of exogenous variation in early childhood exposure across birth cohorts to draw inferences about the long-term effects of lead on mean student test scores. Our findings indicate that lead hazard control grants reduced lead poisoning incidents by over 70% of the baseline prevalence. And each one percentage point reduction in lead poisoning in early childhood translated to a growth of 0.04 standard deviations in student math test scores and 0.08 standard deviations in student reading scores. This same reduction in lead poisoning narrowed both the white-Hispanic math achievement gap and white-Hispanic reading achievement gap by 0.06 standard deviations, implying important downstream consequences for economic inequality.

A Prospective Birth Cohort Study on Early Childhood Lead Levels and Attention Deficit Hyperactivity Disorder: New Insight on Sex Differences

To investigate the prospective associations between early childhood lead exposure and subsequent risk of attention deficit hyperactivity disorder (ADHD) in childhood and its potential effect modifiers. We analyzed data from 1479 mother-infant pairs (299 ADHD, 1180 neurotypical) in the Boston Birth Cohort. The child's first blood lead measurement and physician-diagnosed ADHD was obtained from electronic medical records. Graphic plots and multiple logistic regression were used to examine dose-response associations between lead exposure and ADHD and potential effect modifiers, adjusting for pertinent covariables. We found that 8.9% of the children in the Boston Birth Cohort had elevated lead levels (5-10 µg/dL) in early childhood, which was associated with a 66% increased risk of ADHD (OR, 1.66; 95% CI, 1.08-2.56). Among boys, the association was significantly stronger (OR, 2.49; 95% CI, 1.46-4.26); in girls, the association was largely attenuated (P value for sex-lead interaction = .017). The OR of ADHD associated with elevated lead levels among boys was reduced by one-half if mothers had adequate high-density lipoprotein levels compared with low high-density lipoprotein, or if mothers had low stress compared with high stress during pregnancy. Elevated early childhood blood lead levels increased the risk of ADHD. Boys were more vulnerable than girls at a given lead level. This risk of ADHD in boys was reduced by one-half if the mother had adequate high-density lipoprotein levels or low stress. These findings shed new light on the sex difference in ADHD and point to opportunities for early risk assessment and primary prevention of ADHD.

From Lead Exposure in Early Childhood to Adolescent Health: A Chicago Birth Cohort.

To assess the relationships between childhood lead exposure and 3 domains of later adolescent health: mental, physical, and behavioral. We followed a random sample of birth cohort members from the Project on Human Development in Chicago Neighborhoods, recruited in 1995 to 1997, to age 17 years and matched to childhood blood test results from the Department of Public Health. We used ordinary least squares regression, coarsened exact matching, and instrumental variables to assess the relationship between average blood lead levels in childhood and impulsivity, anxiety or depression, and body mass index in adolescence. All models adjusted for relevant individual, household, and neighborhood characteristics. After adjustment, a 1 microgram per deciliter increase in average childhood blood lead level significantly predicts 0.06 (95% confidence interval [CI] = 0.01, 0.12) and 0.09 (95% CI = 0.03, 0.16) SD increases and a 0.37 (95% CI = 0.11, 0.64) point increase in adolescent impulsivity, anxiety or depression, and body mass index, respectively, following ordinary least squares regression. Results following matching and instrumental variable strategies are very similar. Childhood lead exposure undermines adolescent well-being, with implications for the persistence of racial and class inequalities, considering structural patterns of initial exposure.

The Impact of Low-Level Lead Toxicity on School Performance among Hispanic Subgroups in the Chicago Public Schools.

Background: Environmental lead exposure detrimentally affects children’s educational performance, even at very low blood lead levels (BLLs). Among children in Chicago Public Schools (CPS), the severity of the effects of BLL on reading and math vary by racial subgroup (White vs. Hispanic vs. non-Hispanic Black). We investigated the impact of BLL on standardized test performance by Hispanic subgroup (Mexican, Puerto Rican, and Other Hispanic). Methods: We examined 12,319 Hispanic children born in Chicago between 1994 and 1998 who were tested for BLL between birth and 2006 and enrolled in the 3rd grade at a CPS school between 2003 and 2006. We linked the Chicago birth registry, the Chicago Blood Lead Registry, and 3rd grade Illinois Standard Achievement Test (ISAT) scores to examine associations between BLL and school performance. Primary analyses were restricted to children with BLL below 10 µg/dL (0.483 µmol/L). Results: BLLs below 10 µg/dL (0.483 µmol/L) were inversely associated with reading and math scores in all Hispanic subgroups. Adjusted Relative Risks (RRadj) and 95% confidence intervals (CI) for reading and math failure were 1.34 (95% CI = 1.25, 1.63) and 1.53 (95% CI = 1.32, 1.78), respectively, per each additional 5 µg/dL of lead exposure for Hispanic children; RRadj did not differ across subgroups. We estimate that 7.0% (95% CI = 1.8, 11.9) of reading and 13.6% (95% CI = 7.7, 19.2) of math failure among Hispanic children can be attributed to exposure to BLLs of 5–9 µg/dL (0.242 to 0.435 µmol/L) vs. 0–4 µg/dL (0–0.193 µmol/L). The RRadj of math failure for each 5 µg/dL (0.242 µmol/L) increase in BLL was notably (p = 0.074) stronger among black Puerto Rican children (RRadj = 5.14; 95% CI = 1.65–15.94) compared to white Puerto Rican children (RRadj = 1.50; 95% CI = 1.12–2.02). Conclusions: Early childhood lead exposure is associated with poorer achievement on standardized reading and math tests in the 3rd grade for Mexican, Puerto Rican, and Other Hispanic children enrolled in Chicago Public Schools. While we did not see interactions between BLL and ISAT performance by Hispanic subgroup, the stronger association between BLL and math failure for Black Puerto Rican children is intriguing and warrants further study.

Lead Exposure during Early Human Development and DNA Methylation of Imprinted Gene Regulatory Elements in Adulthood.

Background:Lead exposure during early development causes neurodevelopmental disorders by unknown mechanisms. Epidemiologic studies have focused recently on determining associations between lead exposure and global DNA methylation; however, such approaches preclude the identification of loci that may alter human disease risk.Objectives:The objective of this study was to determine whether maternal, postnatal, and early childhood lead exposure can alter the differentially methylated regions (DMRs) that control the monoallelic expression of imprinted genes involved in metabolism, growth, and development.Methods:Questionnaire data and serial blood lead levels were obtained from 105 participants (64 females, 41 males) of the Cincinnati Lead Study from birth to 78 months. When participants were adults, we used Sequenom EpiTYPER assays to test peripheral blood DNA to quantify CpG methylation in peripheral blood leukocytes at DMRs of 22 human imprinted genes. Statistical analyses were conducted using linear regression.Results:Mean blood lead concentration from birth to 78 months was associated with a significant decrease in PEG3 DMR methylation (β = –0.0014; 95% CI: –0.0023, –0.0005, p = 0.002), stronger in males (β = –0.0024; 95% CI: –0.0038, –0.0009, p = 0.003) than in females (β = –0.0009; 95% CI: –0.0020, 0.0003, p = 0.1). Elevated mean childhood blood lead concentration was also associated with a significant decrease in IGF2/H19 (β = –0.0013; 95% CI: –0.0023, –0.0003, p = 0.01) DMR methylation, but primarily in females, (β = –0.0017; 95% CI: –0.0029, –0.0006, p = 0.005) rather than in males, (β = –0.0004; 95% CI: –0.0023, 0.0015, p = 0.7). Elevated blood lead concentration during the neonatal period was associated with higher PLAGL1/HYMAI DMR methylation regardless of sex (β = 0.0075; 95% CI: 0.0018, 0.0132, p = 0.01). The magnitude of associations between cumulative lead exposure and CpG methylation remained unaltered from 30 to 78 months.Conclusions:Our findings provide evidence that early childhood lead exposure results in sex-dependent and gene-specific DNA methylation differences in the DMRs of PEG3, IGF2/H19, and PLAGL1/HYMAI in adulthood.Citation:Li Y, Xie C, Murphy SK, Skaar D, Nye M, Vidal AC, Cecil KM, Dietrich KN, Puga A, Jirtle RL, Hoyo C. 2016. Lead exposure during early human development and DNA methylation of imprinted gene regulatory elements in adulthood. Environ Health Perspect 124:666–673; http://dx.doi.org/10.1289/ehp.1408577

Late effects of low blood lead concentrations in children on school performance and cognitive functions

BackgroundAlthough it is known that lead is a neurotoxin that negatively impacts cognitive functions at low blood concentrations (B-Pb), little is known about the impact of early exposure on later cognitive functions. ObjectivesThis study assesses the effects of very low lead exposure in early childhood on teenage cognitive performance. MethodsUsing data collected between 1978 and 2007, we analyzed B-Pb (median 30μg/L; six-fold decrease over time) in 3176 Swedish children (age 7–12). School performance in grade 9 (age 16; boys and girls) and over-all IQs measured during conscription examinations (age 18–19; mainly boys) were obtained from registers. In multivariate models, potential confounders (age at blood sampling, sex, parents’ education, family economy, and country of birth of child and parents) and effect modifiers (socioeconomic; father's IQ at conscription examination) were included. ResultsThere were statistically significant adjusted negative associations between school performance (Grades up to 1991: P<0.0001; Merits 1992-2007:P<0.0001) and IQ (P=0.03) and B-Pb. The dose–response relationships were non-linear. Effects were more pronounced for B-Pb≤50μg/L than for higher levels. In the B-Pb range 5–50μg/L, the average IQ loss corresponded to about 5 IU. There was no significant effect modification associated with socioeconomic factors. ConclusionsLead causes neurotoxic effects at very low exposures (B-Pb<50μg/L) in childhood and these effects remain for many years.

The impact of low-level lead toxicity on school performance among children in the Chicago Public Schools: a population-based retrospective cohort study.

BackgroundEnvironmental lead exposure poses a risk to educational performance, especially among poor, urban children. Previous studies found low-level lead exposure was a risk factor for diminished academic abilities, however, this study is distinct because of the very large sample size and because it controlled for very low birth weight and early preterm birth–two factors closely associated with lower academic performance. In this study we examined the association between lead concentration in whole blood (B-Pb) of Chicago Public School (CPS) children and their performance on the 3rd grade Illinois Standard Achievement Tests (ISAT) reading and math scores.MethodsWe examined 58,650 children born in Chicago between 1994 and 1998 who were tested for blood lead concentration between birth and 2006 and enrolled in the 3rd grade at a CPS school between 2003 and 2006. We linked the Chicago birth registry, the Chicago Blood Lead Registry, and 3rd grade ISAT scores to examine associations between B-Pb and school performance.ResultsAfter adjusting for other predictors of school performance including poverty, race/ethnicity, gender, maternal education and very low birth weight or preterm-birth, we found that B-Pbs below 10 μg/dL were inversely associated with reading and math scores in 3rd grade children. For a 5 μg/dL increase in B-Pb, the risk of failing increased by 32% for reading (RR = 1.32, 95%CI = 1.26, 1.39) and math (RR = 1.32, 95%CI = 1.26, 1.39). The effect of lead on reading was non-linear with steeper failure rates at lower B-Pbs. We estimated that 13% of reading failure and 14.8% of math failure can be attributed to exposure to blood lead concentrations of 5 to 9 vs. 0 to 4 μg/dL in Chicago school children.ConclusionsEarly childhood lead exposure is associated with poorer achievement on standardized reading and math tests in the third grade, even at very low B-Pbs. Preventing lead exposure in early childhood is critical to improving school performance.

LEAD EXPOSURE AND BEHAVIOR: EFFECTS ON ANTISOCIAL AND RISKY BEHAVIOR AMONG CHILDREN AND ADOLESCENTS

It is well known that exposure to lead has numerous adverse effects on behavior and development. Using data on two cohorts of children from the National Longitudinal Survey of Youth (NLSY), this paper investigates the effect of early childhood lead exposure on behavior problems from childhood through early adulthood. I find large negative consequences of early childhood lead exposure, in the form of an unfolding series of adverse behavioral outcomes: behavior problems as a child, pregnancy and aggression as a teen, and criminal behavior as a young adult. At the levels of lead that were the norm in United States until the late 1980s, estimated elasticities of these behaviors with respect to lead range between 0.1 and 1.0. (JEL I18, J13, K49, Q53, Q58)

Application of Propensity Scores to a Continuous Exposure: Effect of Lead Exposure in Early Childhood on Reading and Mathematics Scores

The estimation of causal effects in observational studies is usually limited by the lack of randomization, which can result in different treatment or exposure groups differing systematically with respect to characteristics that influence outcomes. To remove such systematic differences, methods to ”balance” subjects on observed covariates across treatment or exposure levels have been developed over the past three decades. These methods have been primarily developed in settings with binary treatment or exposures. However, in many observational studies, the exposures are continuous instead of being binary or discrete, and are usually considered as doses of treatment. In this manuscript we consider estimating the causal effect of early childhood lead exposure on youth academic achievement, where the exposure variable blood lead concentration can take any values that are greater than or equal to 0, using three balancing methods: propensity score analysis, non-bipartite matching, and Bayesian regression trees. We find some evidence that the standard logistic regression analysis controlling for age and socioeconomic confounders used in previous analyses (Zhang et al. (2013)) overstates the effect of lead exposure on performance on standardized mathematics and reading examinations; however, significant declines remain, including at doses currently below the recommended exposure levels.

Quantile regression in environmental health: Early life lead exposure and end-of-grade exams

Conditional means regression, including ordinary least squares (OLS), provides an incomplete picture of exposure–response relationships particularly if the primary interest resides in the tail ends of the distribution of the outcome. Quantile regression (QR) offers an alternative methodological approach in which the influence of independent covariates on the outcome can be specified at any location along the distribution of the outcome. We implemented QR to examine heterogeneity in the influence of early childhood lead exposure on reading and math standardized fourth grade tests. In children from two urban school districts (n=1,076), lead exposure was associated with an 18.00 point decrease (95% CI: −48.72, −3.32) at the 10th quantile of reading scores, and a 7.50 point decrease (95% CI: −15.58, 2.07) at the 90th quantile. Wald tests indicated significant heterogeneity of the coefficients across the distribution of quantiles. Math scores did not show heterogeneity of coefficients, but there was a significant difference in the lead effect at the 10th (β=−17.00, 95% CI: −32.13, −3.27) versus 90th (β=−4.50, 95% CI: −10.55, 4.50) quantiles. Our results indicate that lead exposure has a greater effect for children in the lower tail of exam scores, a result that is masked by conditional means approaches.