Evaluation of Uncontrolled Confounding in Studies of Environmental Exposures and Neurobehavioral Testing in Children

Associations of Perinatal Metal and Metalloid Exposures with Early Child Behavioral Development Over Time in the New Hampshire Birth Cohort Study

Research on the neurodevelopmental effects of metal(loid)s has focused mainly on outcomes assessed at one time point, even though brain development progresses over time. We investigated biomarkers of perinatal exposure to metals and changes in child behavior over time. We followed 268 participants from the prospective New Hampshire Birth Cohort Study between birth and age 5 years. We measured arsenic (As), copper (Cu), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in toenails from 6-week-old infants. The Behavioral Symptoms Index (BSI), externalizing, and internalizing symptoms were assessed using the Behavior Assessment System for Children, 2nd edition (BASC-2) at ages 3 and 5 years. Multivariable linear regression was used to estimate associations of metals with behavior change, calculated as the difference in symptom raw scores between 3 and 5 years, in addition to the associations for symptom scores at 3 and 5 years separately. Sex-specific associations were also explored using stratified models and a sex-metal interaction term. Adjusted associations of metals and change in behavior varied by exposure and outcome. Each 1 μg/g increase in ln toenail Cu was associated with improved behavior between 3 and 5 years [BSI: β = - 3.88 (95%CI: - 7.12, - 0.64); Externalizing problems: β = - 2.20 (95%CI: - 4.07, - 0.33)]. Increasing Zn was associated with increased externalizing behavior over time (β = 3.42 (95%CI: 0.60, 6.25). Sex-stratified analyses suggested more pronounced associations among boys compared to girls. Perinatal exposure to metals may alter behavioral development between ages 3 and 5 years. Findings support the need for more research on associations between metals and neurodevelopment over longer time periods.

Association of maternal and cord blood barium exposure with preschoolers' intellectual function: Evidence from the Ma'anshan Birth Cohort (MABC) study

OBJECTIVES

Barium is widely involved in drilling fluids, plastics, and personal care products. Although the neurodevelopmental toxicity of barium has been reported in animals, human data are scarce. This study aimed to investigate the effect of prenatal barium concentrations on preschoolers' intellectual function based on a birth cohort study.

METHODS

A total of 2164 mother-child pairs from Ma'anshan city, China were included in this study. We measured serum barium concentrations in the first, second, and third trimesters and in cord blood. Intellectual function in children aged 3.0-6.0 years old was assessed using the Chinese version of the Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition (WPPSI-IV). Linear regression models were used to analyze the association between averaged barium exposure during pregnancy and intellectual function. Multiple informant models were performed to jointly test for differences in associations between four repeated barium exposure and intellectual function. All models were further stratified by child sex.

RESULTS

Collectively, we observed significant inverse associations of average maternal barium exposure levels with verbal comprehension index (VCI), visual spatial index (VSI), processing speed index (PSI), and full-scale intelligence quotient (FSIQ) scores. Maternal serum log₁₀-transformed barium levels in the second trimester were inversely associated with VCI [-2.33 (95%CI: -4.02, -0.64)], VSI [-2.30 (95%CI: -4.08, -0.52)], working memory index (WMI) [-2.09 (95%CI: -3.71, -0.46)], PSI [-2.23 (95%CI: -3.82, -0.65)], and FSIQ scores [-2.73 (95%CI: -4.23, -1.22)]. Prenatal barium exposure was inversely associated with VCI, VSI, WMI, PSI, and FSIQ in girls, except for the fluid reasoning index (FRI). Additionally, inverse associations were found between prenatal barium exposure and VSI, PSI, and FSIQ in boys.

CONCLUSIONS

Prenatal barium exposure had detrimental effects on intellectual function in preschoolers and girls drove these inverse associations more than boys. The second trimester may be the critical window of neurotoxicity to barium exposure.

Prenatal exposure to polycyclic aromatic hydrocarbons is not associated with behavior problems in preschool and early school-aged children: A prospective multi-cohort study

BACKGROUND

Epidemiological study findings are inconsistent regarding associations between prenatal polycyclic aromatic hydrocarbon (PAH) exposures and childhood behavior. This study examined associations of prenatal PAH exposure with behavior at age 4-6 years in a large, diverse, multi-region prospective cohort. Secondary aims included examination of PAH mixtures and effect modification by child sex, breastfeeding, and child neighborhood opportunity.

METHODS

The ECHO PATHWAYS Consortium pooled 1118 mother-child dyads from three prospective pregnancy cohorts in six U.S. cities. Seven PAH metabolites were measured in prenatal urine. Child behavior was assessed at age 4-6 using the Total Problems score from the Child Behavior Checklist (CBCL). Neighborhood opportunity was assessed using the socioeconomic and educational scales of the Child Opportunity Index. Multivariable linear regression was used to estimate associations per 2-fold increase in each PAH metabolite, adjusted for demographic, prenatal, and maternal factors and using interaction terms for effect modifiers. Associations with PAH mixtures were estimated using Weighted Quantile Sum Regression (WQSR).

RESULTS

The sample was racially and sociodemographically diverse (38% Black, 49% White, 7% Other; household-adjusted income range $2651-$221,102). In fully adjusted models, each 2-fold increase in 2-hydroxynaphthalene was associated with a lower Total Problems score, contrary to hypotheses (b = -0.80, 95% CI = -1.51, -0.08). Associations were notable in boys (b = -1.10, 95% CI = -2.11, -0.08) and among children breastfed 6+ months (b = -1.31, 95% CI = -2.25, -0.37), although there was no statistically significant evidence for interaction by child sex, breastfeeding, or neighborhood child opportunity. Associations were null for other PAH metabolites; there was no evidence of associations with PAH mixtures from WQSR.

CONCLUSION

In this large, well-characterized, prospective study of mother-child pairs, prenatal PAH exposure was not associated with child behavior problems. Future studies characterizing the magnitude of prenatal PAH exposure and studies in older childhood are needed.

Endocrine disruptors: Challenges and future directions in epidemiologic research

Public concern about the impact of endocrine disrupting chemicals (EDCs) on both humans and the environment is growing steadily. Epidemiologic research provides key information towards our understanding of the relationship between environmental exposures like EDCs and human health outcomes. Intended for researchers in disciplines complementary to epidemiology, this paper highlights the importance and challenges of epidemiologic research in order to present the key elements pertaining to the design and interpretation of an epidemiologic study on EDCs. The conduct of observational studies on EDCs derives from a thoughtful research question, which will help determine the subsequent methodological choices surrounding the careful selection of the study population (including the comparison group), the adequate ascertainment of exposure(s) and outcome(s) of interest, and the application of methodological and statistical concepts more specific to epidemiology. The interpretation of epidemiologic results may be arduous due to the latency occurring between EDC exposure and certain outcome(s), the complexity in capturing EDC exposure(s), and traditional methodological and statistical issues that also deserve consideration (e.g., confounding, effect modification, non-monotonic responses). Moving forward, we strongly advocate for an integrative approach of expertise in the fields of epidemiology, exposure science, risk assessment and toxicology to adequately study the health risks associated with EDCs while tackling their challenges.

DNA Methylation Biomarkers of IQ Reduction are Associated with Long-term Lead Exposure in School Aged Children in Southern China

Although lead associated with intelligence decline in children has long been reported, studies combining intelligence determination, molecular mechanisms exploration, and biomarker screen are quite rare. In this study, based on 333 children aged 9-11, we determined the role of DNA methylation (DNAm) in the relationship of lead exposure with children's intelligence. DNAm was measured from children's blood DNA specimens, and mediation analysis was performed to identify DNAm biomarkers mediating the lead-intelligence relationship. We identified forty-three differentially methylated regions (DMRs), and two fragments (FAM50B1 and PTCHD3) significantly mediated the lead-intelligence relationship, with contribution rates of 30.36% (p = 0.010) and 60.36% (p < 0.001), respectively. In addition, blood lead levels (BLLs) lower than 100 μg/L still adversely affected children's IQs and DNAm of the two fragments. Our data suggests that DNAm mediates lead-associated cognitive delay in children and blood lead reference value for school-aged children (100 μg/L) should be revised, and the candidate biomarkers can be used in related neurological diseases in future.

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.

Effects of early and recent mercury and lead exposure on the neurodevelopment of children with elevated mercury and/or developmental delays during lactation: A follow-up study

This follow-up study of 82 children investigated the potential impact of early and recent exposure to mercury and lead on their neurodevelopmental performance at 5-8 years of age (2017-2018). Early exposure of these children to mercury, methylmercury, and lead was assessed during lactation at 3-12 months old, as well as their mother's exposure using measurements from a cross-sectional study (2011-2013). Only infants who failed to pass the neurodevelopment screening tools and/or had elevated mercury were included in this study. Urine and hair were sampled during the follow-up study to assess the children's recent exposure to mercury, methylmercury, and lead. Their cognitive performance and visual-motor integration were also measured using the Test of Non-Verbal Intelligence (TONI) and the Beery-Visual-Motor Integration (Beery VMI), respectively. The association between alterations in urinary porphyrins excretion and exposure to metals was analyzed and their influence on the children's neurodevelopment was explored. Linear regression models revealed a significant negative association between the infants' mercury exposure during lactation and the TONI Quotient (β = -0.298, 95%CI = -4.677, -0.414) and Beery VMI Age Equivalent scores at age 5-8 (β = -0.437, 95%CI = -6.383, -1.844). The mothers' blood methylmercury was inversely and significantly associated with their children's TONI Quotient (β = -0.231, 95%CI = -8.184, -0.331). In contrast, the children's Beery VMI Age Equivalent scores were positively and significantly associated with the hair methylmercury of the mothers (β = 0.214, 95%CI = 0.088, 3.899) and their infants (β = 0.256, 95%CI = 0.396, 4.488). These relationships suggest the presence of negative confounding that we did not take into account. Unlike mercury, there was some evidence that lead in breast milk had an inverse relationship with the children's visual-motor coordination skills. Our study did not show a clear association between children's recent exposure to metals and neurodevelopment. However, a significant inverse association was observed between the TONI Quotient and the interaction of hair methylmercury × ∑porphyrins (ß = -0.224, 95%CI = -0.86, -0.049), implying that porphyrins are a sensitive measure of low body-mercury burden. Although lead induced higher ∑porphyrins excretion in urine (β = 0.347, 95%CI = 0.107, 0.525), their interaction did not influence children's neurodevelopmental scores. The interactions between metals and porphyrins might provide insights into their potential contributory role in the pathogenesis associated with neurological disorders or other diseases. Despite the small sample size of the present study, its findings about the association between toxic metal exposure and the high risk of poor neurodevelopmental performance are worrying, particularly at an early age, and additional research is needed using larger sample sizes.

Domain- and trimester-specific effect of prenatal phthalate exposure on preschooler cognitive development in the Ma'anshan Birth Cohort (MABC) study

BACKGROUND

Phthalates are a group of heavily produced endocrine disruptors that are widely used in personal care products, food packaging, building materials, and medical device. Few epidemiological studies have examined the effect of repeated prenatal exposure to multiple phthalates on preschooler cognitive development.

OBJECTIVES

This study aimed to examine the association between prenatal phthalate exposure measured at multiple time points and the intelligent quotient (IQ) scores of preschoolers, and to further identify the critical windows and specific intelligence domains in which phthalate exposure would affect preschooler cognitive development.

METHODS

The current study was based on the Ma'anshan Birth Cohort (MABC) study. Seven phthalate metabolites were measured in 2128 maternal urine samples collected during the first, second, and third trimesters of pregnancy. The IQ score of preschool-aged children were assessed with the Chinese version of the Wechsler Preschool and Primary Scale of Intelligence, Fourth edition (WPPSI-Ⅳ CN). Linear mixed models (LMMs) were used to assess the longitudinal effects of repeated prenatal phthalate exposure on children's IQ score. Multiple linear regression models were fitted to determine whether critical window phthalate exposure would affect cognitive development of children.

RESULTS

Overall, the repeated measures analysis indicated that the verbal comprehension index (VCI), visual space index (VSI) and full-scale intelligence quotient (FSIQ) decreased by 0.30 (95% CI: -0.60, 0; p = 0.05), 0.32 (95% CI: -0.62, -0.01; p = 0.04), and 0.31 (95% CI:-0.57, -0.04; p = 0.02) points, respectively, with each ln-transformed increase in the metabolite concentration of MBP. The fluid reasoning index (FRI) and processing speed index (PSI) increased by 0.30 (95% CI: 0.07, 0.54; p = 0.01) and 0.28 (95% CI: 0.06, 0.51; p = 0.01) points, respectively, with each ln-concentration increase in MEP. Trimester-specific regression models stratified by the sample collection time during pregnancy generated consistent results. In the first trimester, each ln-transformed MBP increase was associated with reductions in VCI, VSI and FSIQ of 0.56 (95% CI:-1.09, -0.02; p = 0.04), 0.60 (95% CI:-1.15, -0.05; p = 0.03) and 0.49 (95% CI:-0.97, -0.01; p = 0.04) points, respectively. In the third trimester, we observed that only MBzP exposure was associated with an increase in VCI (β: 0.48, 95% CI: 0.03, 0.92; p = 0.04). The gender-stratified analyses revealed that boys drove these associations.

CONCLUSIONS

Our results suggest that prenatal phthalate exposure impairs the cognitive development of preschoolers. The first trimester of pregnancy might be the most vulnerable period in terms of neurotoxicitydue to phthalate exposure. These findings warrant further confirmation.

The effects of maternal and children phthalate exposure on the neurocognitive function of 6-year-old children

The primary purpose of this study was to investigate the effects of phthalate exposure on the intelligence and attentional performance of 6-year old children when adjusting each other as covariates. We also investigated the differential effects of phthalate exposure on the intelligence and attention according to exposure period (maternal or children). Urine concentrations of mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-n-butyl phthalate (MBP) were analyzed. Multivariable linear regression models were used to investigate the relationship between exposure to various phthalates with IQ scores and continuous performance test (CPT) variables. There were robust associations between child MEHHP and MEOHP levels with full scale IQ (FSIQ) even after adjusting for demographic variables and CPT scores (MEHHP -9.27, 95% CI: -17.25, -1.29; MEOHP -9.83, 95% CI: -17.44, -2.21). Child MEHHP and MEHOP levels negatively affected omission errors (MEHHP -20.36, 95% CI: -34.17, -6.55; MEOHP -18.93, 95% CI: -32.58, -5.28) and the response time variability (MEHHP -21.07, 95% CI: -39.04, -3.10; MEOHP -20.41, 95% CI -38.14, -2.69) of the CPT after adjusting for demographic variables and IQ. Maternal phthalate exposure had no effects on IQ or CPT variables. These results suggest that children phthalate exposure, but not maternal exposure, has an adverse effect on IQ and attentional performance, and these associations were found to be independent of each other.

Statistical design considerations applicable to clinical trials of iodine supplementation in pregnant women who may be mildly iodine deficient

No large, randomized, placebo-controlled trial of iodine supplementation in pregnant women in a region of mild or moderate iodine deficiency has been completed in which a primary outcome measure was an assessment of the neurobehavioral development of the offspring at age ≥2 y. In this article, I discuss considerations for the design of such a trial in a region of mild iodine deficiency, with a focus on statistical methods and approaches. Exposure and design issues include the ethics of using a placebo, the potential for overexposure to iodine, and the possibility of community randomization. The main scientific goal of the trial is important in determining the follow-up period. If the goal is to determine whether iodine supplementation during pregnancy improves neurobehavioral development in the offspring, then follow-up should continue until a reasonably reliable assessment can be conducted, which might be at age ≥2 y. Once the timing of assessment is decided, the impact of potential loss to follow-up should be considered so that appropriate statistical methods can be incorporated into the design. The minimum sample size can be calculated by using a sample size formula that incorporates noncompliance and assumes that a certain proportion of study participants do not have any outcome observed. To have sufficient power to detect a reasonably modest difference in neurobehavioral development scores using an assessment tool with an SD of 15, a large number of participants (>500/group) is required. The minimum adequate number of participants may be even larger (>1300/group) depending on the magnitude of the difference in outcome between the supplementation and placebo groups, the estimated proportion of the iodine-supplementation group that fails to take the supplement, and the estimated proportion of pregnancies that do not produce outcome measurements.

The impact of thyroid abnormalities during pregnancy on subsequent neuropsychological development of the offspring: a meta-analysis

OBJECTIVE

To investigate the relationship between specific thyroid abnormalities in women during pregnancy and the subsequent neuropsychological development of their offspring.

METHODS

A systematic literature search of PubMed, Embase and Web of Science was conducted. Eligible studies were case-control or cohort study that explored this association with euthyroid thyroid abnormalities during pregnancy. The outcomes included intelligence scores and motor scores. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated and heterogeneity was assessed with Cochrane Q chi-square test and I(2) statistics. A fixed-effects or random-effects model was used to pool the estimates according to the heterogeneity among the included studies.

RESULTS

Six studies, involving 4449 participants, were included. Children of women with thyroid abnormalities had mean intelligence score of 6.27 points and motor score of 5.99 points lower than that of children of euthyroid women. Subgroup analysis suggested that, children of women with hypothyroxinaemia, subclinical hypothyroidism and positive TPOAb had mean intelligence scores of 5.69 points, 8.76 points and 10.55 points, and mean motor scores of 4.19 points, 9.98 points and 9.03 points lower than those of the controls, respectively.

CONCLUSIONS

The thyroid abnormalities in pregnant women may adversely affect neuropsychological development of their offspring.

Constructing and Adapting Causal and Formative Measures of Family Settings: The HOME Inventory as Illustration

Measures of the home environment are frequently used in studies of children's development. This review provides information on indices composed of causal and formative indicators (the kind of indicators often used to capture salient aspects of family environments) and to suggest approaches that may be useful in constructing such measures for diverse populations. The HOME Inventory is used to illustrate challenges scholars face in determining what to include in useful measures of family settings. To that end, a cross-cultural review of research on relations among HOME, family context, and child outcomes is presented. The end of the review offers a plan for how best to further research on relations between the home environment and child development for diverse populations.

Prenatal Docosahexaenoic Acid Supplementation and Offspring Development at 18 Months: Randomized Controlled Trial

OBJECTIVE

We evaluated the effects of prenatal docosahexaenoic acid (DHA) supplementation on offspring development at 18 months of age.

DESIGN

Randomized placebo double-blind controlled trial.

SETTINGS

Cuernavaca, Mexico.

PARTICIPANTS AND METHODS

We followed up offspring (n = 730; 75% of the birth cohort) of women in Mexico who participated in a trial of DHA supplementation during the latter half of pregnancy. We assessed the effect of the intervention on child development and the potential modifying effects of gravidity, gender, SES, and quality of the home environment.

INTERVENTIONS OR MAIN EXPOSURES

400 mg/day of algal DHA.

OUTCOME MEASURES

Child development at 18 months of age measured using the Spanish version of the Bayley Scales of Infant Development-II. We calculated standardized psychomotor and mental development indices, and behavior rating scale scores.

RESULTS

Intent-to-treat differences (DHA-control) were: Psychomotor Developmental Index -0.90 (95% CI: -2.35, 0.56), Mental Developmental Index -0.26 (95% CI: -1.63, 1.10) and Behavior Rating Scale -0.01 (95% CI: -0.95, 0.94). Prenatal DHA intake attenuated the positive association between home environment and psychomotor development index observed in the control group (p for interaction = 0.03) suggesting potential benefits for children living in home environments characterized by reduced caregiver interactions and opportunities for early childhood stimulation.

CONCLUSIONS

Prenatal DHA supplementation in a population with low intakes of DHA had no effects on offspring development at 18 months of age although there may be some benefit for infants from poor quality home environments.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00646360.

Environmental tobacco smoke exposure and children's intelligence at 8-11 years of age

BACKGROUND

Evidence supporting a link between postnatal environmental tobacco smoke (ETS) exposure and cognitive problems among children is mounting, but inconsistent.

OBJECTIVES

We examined the relationship between ETS exposure, measured using urine cotinine, and IQ scores in Korean school-aged children.

METHODS

The participants were 996 children 8-11 years of age recruited from five administrative regions in South Korea. We performed a cross-sectional analysis of urinary cotinine concentrations and IQ scores obtained using the abbreviated form of a Korean version of the Wechsler Intelligence Scales for Children. Associations were adjusted for potential confounders, and estimates were derived with and without adjustment for mother's Full-Scale IQ (FSIQ) score.

RESULTS

After adjusting for sociodemographic and developmental covariates, urinary cotinine concentrations were inversely associated with FSIQ, Verbal IQ (VIQ), Performance IQ (PIQ), vocabulary, math, and block design scores. Following further adjustment for maternal IQ, only the VIQ scores remained significantly associated with urinary cotinine concentration (B = -0.31; 95% CI: -0.60, -0.03 for a 1-unit increase in natural log-transformed urine cotinine concentration; p = 0.03).

CONCLUSION

Urine cotinine concentrations were inversely associated with children's VIQ scores before and after adjusting for maternal IQ. Further prospective studies with serial measurements of cotinine are needed to confirm our findings.

Multilevel analysis of air pollution and early childhood neurobehavioral development

To investigate the association between the ambient air pollution levels during the prenatal and postnatal stages and early childhood neurobehavioral development, our study recruited 533 mother-infant pairs from 11 towns in Taiwan. All study subjects were asked to complete childhood neurobehavioral development scales and questionnaires at 6 and 18 months. Air pollution, including particulate matter ≤10 μm (PM10), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), and hydrocarbons, was measured at air quality monitoring stations in the towns where the subjects lived. Multilevel analyses were applied to assess the association between air pollution and childhood neurobehavioral development during pregnancy and when the children were 0 to 6 months, 7 to 12 months, and 13 to 18 months old. At 18 months, poor subclinical neurodevelopment in early childhood is associated with the average SO2 exposure of prenatal, during all trimesters of pregnancy and at postnatal ages up to 12 months (first trimester β = -0.083, se = 0.030; second and third trimester β = -0.114, se = 0.045; from birth to 12 months of age β = -0.091, se = 0.034). Furthermore, adverse gross motor below average scores at six months of age were associated with increased average non-methane hydrocarbon, (NMHC) levels during the second and third trimesters (β = -8.742, se = 3.512). Low-level SO2 exposure prenatally and up to twelve months postnatal could cause adverse neurobehavioral effects at 18 months of age. Maternal NMHC exposure during the 2nd and 3rd trimesters of pregnancy would be also associated with poor gross motor development in their children at 6 months of age.

Predictors of intelligence at the age of 5: family, pregnancy and birth characteristics, postnatal influences, and postnatal growth

Parental education and maternal intelligence are well-known predictors of child IQ. However, the literature regarding other factors that may contribute to individual differences in IQ is inconclusive. The aim of this study was to examine the contribution of a number of variables whose predictive status remain unclarified, in a sample of basically healthy children with a low rate of pre- and postnatal complications. 1,782 5-year-old children sampled from the Danish National Birth Cohort (2003–2007) were assessed with a short form of the Wechsler Preschool and Primary Scale of Intelligence – Revised. Information on parental characteristics, pregnancy and birth factors, postnatal influences, and postnatal growth was collected during pregnancy and at follow-up. A model including study design variables and child’s sex explained 7% of the variance in IQ, while parental education and maternal IQ increased the explained variance to 24%. Other predictors were parity, maternal BMI, birth weight, breastfeeding, and the child’s head circumference and height at follow-up. These variables, however, only increased the explained variance to 29%. The results suggest that parental education and maternal IQ are major predictors of IQ and should be included routinely in studies of cognitive development. Obstetrical and postnatal factors also predict IQ, but their contribution may be of comparatively limited magnitude.

Neurodevelopment evaluation in children with congenital hypothyroidism by Bayley-III

BACKGROUND

Congenital hypothyroidism is the most common reason of mental retardation, and normal neurological development can be provided by early and effective treatment. In this present study, it is aimed to compare neurological developments of patients in 6-42 months of age with congenital hypothyroidism and healthy controls of the same age group prospectively by Bayley III test.

METHODS

In this present study, neurological developments of 41 congenital hypothyroidism cases and 39 healthy controls, who applied to Pediatric Endocrinology Section of Mersin Children Hospital and Pediatric Neurology Outpatient Clinic of the Medical School at Mersin University between years 2009 and 2011, were evaluated by Bayley III test.

RESULTS

Cognitive, language and global motor scores in addition to receptive communication, expressive communication, fine motor and gross motor subscores in children with congenital hypothyroidism were statistically significantly lower than those in the control group (p<0.05). It is detected that initiation dose and day of treatments, severity of hypothyroidism and time to normalization thyroid stimulating hormone had no statistically significant effects on neurological development of the study group (p>0.05). In both groups, as the education levels of mothers are increased, language development scores are also increased (p<0.05). Additionally, statistically significant increases in Bayley III scores except cognitive scores have been observed in both groups as the level of income is increased (p<0.05).

CONCLUSIONS

Despite early and effective treatment in newborns with congenital hypothyroidism, retardation in neurological developmental has been detected. This situation can be related to influences on neurodevelopment in intrauterine period. According to our present knowledge, this study is the first case-control study in the literature that neurological developments of congenital hypothyroidism patients are evaluated with Bayley-III score.

Effect of environmental manganese exposure on verbal learning and memory in Mexican children

Manganese (Mn) is an essential metal, but in excess it becomes neurotoxic. Children's developing nervous system may be especially vulnerable to the neurotoxic effects of overexposure to this metal. The aim of this study was to assess the effect of Mn exposure on verbal memory and learning in 7- to 11-year-old children. We tested 79 children living in the Molango Mn-mining district and 95 children from a non-exposed community in the same State of Mexico. The Children's Auditory Verbal Learning Test (CAVLT) was administered. Blood and hair samples were obtained to determine Mn concentrations using atomic absorption spectrophotometry. CAVLT performance was compared between the two groups and multilevel regression models were constructed to estimate the association between biomarkers of Mn exposure and the CAVLT scores. The exposed group presented higher hair and blood Mn (p<0.001) than the non-exposed group (median 12.6 vs. 0.6μg/g, 9.5vs. 8.0μg/L respectively), as well as lower scores (p<0.001) for all the CAVLT subscales. Hair Mn was inversely associated with most CAVLT subscales, mainly those evaluating long-term memory and learning (β=-0.47, 95% CI -0.84, -0.09). Blood Mn levels showed a negative but non-significant association with the CAVLT scores. These results suggest that Mn exposure has a negative effect on children's memory and learning abilities.

The effects of low to moderate prenatal alcohol exposure in early pregnancy on IQ in 5-year-old children

OBJECTIVE

To examine the effects of low to moderate maternal alcohol consumption during early pregnancy on children's intelligence (IQ) at age 5 years.

DESIGN

Prospective follow-up study.

SETTING

Neuropsychological testing in four Danish cities 2003-2008.

POPULATION

A cohort of 1628 women and their children sampled from the Danish National Birth Cohort.

METHODS

Participants were sampled based on maternal alcohol consumption during pregnancy. At 5 years of age, children were tested with the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R). Parental education, maternal IQ, maternal smoking in pregnancy, the child's age at testing, gender, and tester were considered core confounding factors, whereas the full model also controlled for maternal binge drinking, age, BMI, parity, home environment, postnatal smoking in the home, health status, and indicators for hearing and vision impairments.

MAIN OUTCOME MEASURES

The WPPSI-R.

RESULTS

No differences in test performance were observed between children whose mothers reported consuming between one and four or between five and eight drinks per week at some point during pregnancy, compared with children of mothers who abstained. For women who reported consuming nine or more drinks per week no differences were observed for mean differences; however, the risks of low full-scale IQ (OR 4.6; 95% CI 1.2-18.2) and low verbal IQ (OR 5.9; 95% CI 1.4-24.9) scores, but not low performance IQ score, were increased.

CONCLUSIONS

Maternal consumption of low to moderate quantities of alcohol during pregnancy was not associated with the mean IQ score of preschool children. Despite these findings, acceptable levels of alcohol use during pregnancy have not yet been established, and conservative advice for women continues to be to avoid alcohol use during pregnancy.

Assessing windows of susceptibility to lead-induced cognitive deficits in Mexican children

BACKGROUND

The identification of susceptible periods to Pb-induced decrements in childhood cognitive abilities remains elusive.

OBJECTIVE

To draw inferences about windows of susceptibility using the pattern of associations between serial childhood blood lead (BPb) concentrations and children's cognitive abilities at 4 years of age among 1035 mother-child pairs enrolled in 4 prospective birth cohorts from Mexico City.

METHODS

Multiple longitudinally collected BPb measurements were obtained from children (1, 2, 3, and 4 years) between 1994 and 2007. Child cognitive abilities were assessed at 4 years using the general cognitive index (GCI) of the McCarthy Scales of Children's Abilities. We used multivariable linear regression to estimate the change in cognitive abilities at 4 years of age with a 10 μg/dL increase in childhood BPb concentrations adjusting for maternal IQ, education, marital status, child sex, breastfeeding duration, and cohort.

RESULTS

In separate models for each BPb measurement, 2 year BPb concentrations were most strongly associated with reduced GCI scores at 4 years after adjusting for confounders (β: -3.8; 95% confidence interval CI: -6.3, -1.4). Mutual adjustment for other BPb concentrations in a single model resulted in larger, but less precise estimate between 2 year BPb concentrations and GCI scores at 4 years of age (β: -7.1; 95% CI: -12, -2.0). The association between 2 year BPb and GCI was not heterogeneous (p=0.89), but some BPb and GCI associations varied in magnitude and direction across the cohorts. Additional adjustment for child hemoglobin, birth weight, gestational age, gestational BPb concentrations, or test examiner did not change the pattern of associations.

CONCLUSIONS

Higher BPb concentrations at 2 years of age were most predictive of decreased cognitive abilities among these Mexico City children; however, the observed pattern may be due to exposure, outcome, or cohort related factors. These results may help developing countries more efficiently implement childhood Pb prevention strategies.

Mid-gestational maternal free thyroxine concentration and offspring neurocognitive development at age two years

CONTEXT

Lower neurocognitive development scores at age 2 yr have been reported in association with euthyroid hypothyroxinemia during early pregnancy.

OBJECTIVE

The objective of this study was to further explore this association with euthyroid hypothyroxinemia during early pregnancy.

DESIGN

This was an observational, nested case-control study.

SETTING

The study was conducted at physician offices and prenatal clinics throughout Maine.

STUDY SUBJECTS

Between May 2004 and March 2006, TSH was measured in 5734 women in conjunction with second-trimester Down syndrome screening. After completion of pregnancy, free T(4) was measured in stored second-trimester sera from euthyroid women (TSH 0.1-3.5 mIU/ml; n = 5560). Women with free T(4) at the third centile or less (n = 99) were matched with women whose free T(4) was at the 10th to the 90th centile (n = 99).

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Bayley Scales of Infant Development (BSID III) were administered to the 198 offspring at age 2 yr. Scores for cognitive, language, and motor development were compared between matched pairs of offspring from the two groups before and after correcting for relevant variables.

RESULTS

Unadjusted BSID-III scores (cognitive, language, and motor) were lower by about 3% at age 2 yr among offspring of 98 hypothyroxinemic women (cases), reaching borderline significance for cognitive and motor scores. After adjustment for gestational age, the child's age at testing, maternal weight, and education, all differences diminished and became nonsignificant. Scores less than 85 were more frequent among case children but did not reach statistical significance (P = 0.14).

CONCLUSIONS

Isolated hypothyroxinemia during the second trimester is not associated with significantly lower BSID-III scores at age 2 yr, compared with scores for offspring of matched euthyroxinemic women.

Prenatal exposure to phthalates and infant development at 6 months: prospective Mothers and Children's Environmental Health (MOCEH) study

BACKGROUND

There are increasing concerns over adverse effects of prenatal phthalate exposure on the neurodevelopment of infants.

OBJECTIVES

Our goal was to explore the association between prenatal di(2-ethylhexyl) phthalate and dibutyl phthalate exposure and the Mental and Psychomotor Developmental Indices (MDI and PDI, respectively) of the Bayley Scales of Infant Development at 6 months, as part of the Mothers and Children's Environmental Health Study.

METHODS

Between 2006 and 2009, 460 mother-infant pairs from Seoul, Cheonan, and Ulsan, Korea, participated. Prenatal mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-n-butyl phthalate (MBP) were measured in one urine sample acquired from each mother during the third trimester of pregnancy. Associations with log-transformed creatinine-corrected phthalate concentrations were estimated using linear regression models adjusted for potential confounders.

RESULTS

MDI was inversely associated with the natural log concentrations (micrograms per gram creatinine) of MEHHP [β = -0.97; confidence interval (CI), -1.85 to -0.08] and MEOHP (β = -0.95; CI, -1.87 to -0.03), and PDI was inversely associated with MEHHP (β = -1.20; CI, -2.33 to -0.08). In males, MDI was inversely associated with MEHHP (β = -1.46; CI, -2.70 to -0.22), MEOHP (β = -1.57; CI, -2.87 to -0.28), and MBP (β = -0.93; CI, -1.82 to -0.05); PDI was inversely associated with MEHHP (β = -2.36; CI, -3.94 to -0.79), MEOHP (β = -2.05; CI, -3.71 to -0.39), and MBP (β = -1.25; CI, -2.40 to -0.11). No significant linear associations were observed for females.

CONCLUSIONS

The results suggest that prenatal exposure to phthalates may be inversely associated with the MDI and PDI of infants, particularly males, at 6 months.

Review of the epidemiologic literature on residential exposure to perchloroethylene

Perchloroethylene is a solvent that is widely used for dry cleaning. There has been considerable interest in the toxicity of this chemical because of the potential for low-level exposure among a large portion of the US population. Although substantial epidemiologic literature exists on high-level occupational exposure to perchloroethylene, there are relatively few studies dealing with lower-level residential exposure. In the current paper, the author reviews this limited residential literature, with special emphasis on strengths, limitations, and consistency. Reviewed studies primarily address neurobehavioral, cancer, and reproductive endpoints. Most studies used an ecological or cross-sectional design, with exposure defined by either drinking-water contamination or proximity to dry cleaning. In general, reviewed studies were highly exploratory, with inconsistencies and potential for bias that detract from interpretation of study findings. The magnitudes of reported effects are frequently incompatible with the effects reported from much higher occupational and human-chamber exposures. Overall, few reliable conclusions can be drawn from this sparse and highly limited body of literature.

Intellectual function in Mexican children living in a mining area and environmentally exposed to manganese

BACKGROUND

Excessive exposure to manganese (Mn), an essential trace element, has been shown to be neurotoxic, especially when inhaled. Few studies have examined potential effects of Mn on cognitive functions of environmentally exposed children.

OBJECTIVE

This study was intended to estimate environmental exposure to Mn resulting from mining and processing and to explore its association with intellectual function of school-age children.

METHODS

Children between 7 and 11 years of age from the Molango mining district in central Mexico (n = 79) and communities with similar socioeconomic conditions that were outside the mining district (n = 93) participated in the cross-sectional evaluation. The revised version of the Wechsler Intelligence Scale for Children adapted for the Mexican population was applied. Concentrations of Mn in blood (MnB) and hair (MnH) were used as biomarkers of exposure.

RESULTS

Exposed children had significantly higher median values for MnH (12.6 μg/g) and MnB (9.5 μg/L) than did nonexposed children (0.6 μg/g and 8.0 μg/L, respectively). MnH was inversely associated with Verbal IQ [β = -0.29; 95% confidence interval (CI), -0.51 to -0.08], Performance IQ (β = -0.08; 95% CI, -0.32 to 0.16), and Total Scale IQ (β = -0.20; 95% CI, -0.42 to 0.02). MnB was inversely but nonsignificantly associated with Total and Verbal IQ score. Age and sex significantly modified associations of MnH, with the strongest inverse associations in young girls and little evidence of associations in boys at any age. Associations with MnB did not appear to be modified by sex but appeared to be limited to younger study participants.

CONCLUSIONS

The findings from this study suggest that airborne Mn environmental exposure is inversely associated with intellectual function in young school-age children.

Relationship between environmental phthalate exposure and the intelligence of school-age children

BACKGROUND

Concern over phthalates has emerged because of their potential toxicity to humans.

OBJECTIVE

We investigated the relationship between the urinary concentrations of phthalate metabolites and children's intellectual functioning.

METHODS

This study enrolled 667 children at nine elementary schools in five South Korean cities. A cross-sectional examination of urine phthalate concentrations was performed, and scores on neuropsychological tests were obtained from both the children and their mothers.

RESULTS

We measured mono-2-ethylhexyl phthalate (MEHP) and mono(2-ethyl-5-oxohexyl)phthalate (MEOHP), both metabolites of di(2-ethylhexyl)phthalate (DEHP), and mono-n-butyl phthalate (MBP), a metabolite of dibutyl phthalate (DBP), in urine samples. The geometric mean (ln) concentrations of MEHP, MEOHP, and MBP were 21.3 microg/L [geometric SD (GSD) = 2.2 microg/L; range, 0.5-445.4], 18.0 microg/L (GSD = 2.4; range, 0.07-291.1), and 48.9 microg/L (GSD = 2.2; range, 2.1-1645.5), respectively. After adjusting for demographic and developmental covariates, the Full Scale IQ and Verbal IQ scores were negatively associated with DEHP metabolites but not with DBP metabolites. We also found a significant negative relationship between the urine concentrations of the metabolites of DEHP and DBP and children's vocabulary subscores. After controlling for maternal IQ, a significant inverse relationship between DEHP metabolites and vocabulary subscale score remained. Among boys, we found a negative association between increasing MEHP phthalate concentrations and the sum of DEHP metabolite concentrations and Wechsler Intelligence Scale for Children vocabulary score; however, among girls, we found no significant association between these variables.

CONCLUSION

Controlling for maternal IQ and other covariates, the results show an inverse relationship between phthalate metabolites and IQ scores; however, given the limitations in cross-sectional epidemiology, prospective studies are needed to fully explore these associations.

Prenatal bisphenol A exposure and early childhood behavior

BACKGROUND

Prenatal exposure to bisphenol A (BPA) increases offspring aggression and diminishes differences in sexually dimorphic behaviors in rodents.

OBJECTIVE

We examined the association between prenatal BPA exposure and behavior in 2-year-old children.

METHODS

We used data from 249 mothers and their children in Cincinnati, Ohio (USA). Maternal urine was collected around 16 and 26 weeks of gestation and at birth. BPA concentrations were quantified using high-performance liquid chromatography-isotope-dilution tandem mass spectrometry. Child behavior was assessed at 2 years of age using the second edition of the Behavioral Assessment System for Children (BASC-2). The association between prenatal BPA concentrations and BASC-2 scores was analyzed using linear regression.

RESULTS

Median BPA concentrations were 1.8 (16 weeks), 1.7 (26 weeks), and 1.3 (birth) ng/mL. Mean (+/- SD) BASC-2 externalizing and internalizing scores were 47.6 +/- 7.8 and 44.8 +/- 7.0, respectively. After adjustment for confounders, log(10)-transformed mean prenatal BPA concentrations were associated with externalizing scores, but only among females [beta = 6.0; 95% confidence interval (CI), 0.1-12.0]. Compared with 26-week and birth concentrations, BPA concentrations collected around 16 weeks were more strongly associated with externalizing scores among all children (beta = 2.9; 95% CI, 0.2-5.7), and this association was stronger in females than in males. Among all children, measurements collected at <or= 16 weeks showed a stronger association (beta = 5.1; 95% CI, 1.5-8.6) with externalizing scores than did measurements taken at 17-21 weeks (beta = 0.6; 95% CI, -2.9 to 4.1).

CONCLUSIONS

These results suggest that prenatal BPA exposure may be associated with externalizing behaviors in 2-year-old children, especially among female children.

The effect of maternal smoking during pregnancy on intellectual disabilities among 8-year-old children

Prenatal tobacco smoke exposure has been implicated as a risk factor for cognitive deficits in children. The purpose of this study is to examine the association between prenatal tobacco smoke exposure and diagnosis of intellectual disabilities (ID) among 8-year-old children living in Arkansas, Georgia, North Carolina and Utah. In 2002 and 2004, 965 ID case children were identified through a surveillance network and compared with the population of children born in the surveillance region during the same period (n = 104 607). Prenatal tobacco smoke exposure was determined from birth certificates. We estimated the effect of prenatal tobacco smoke exposure (none, <10, 10-19 and > or =20 cigarettes per day) on ID using logistic regression. Generally, the risk of ID was mildly elevated among children whose mothers smoked > or =20 cigarettes per day during pregnancy [RR 1.34; 95% (confidence interval) CI 0.96, 1.87] after adjustment for maternal education, maternal race, maternal age, marital status, child sex, birth year and study site. However, the effect of exposure to > or =20 cigarettes per day significantly differed for males [RR 1.77, 95% CI 1.20, 2.62] compared with females [RR 0.81, 95% CI 0.44, 1.50]. Supplemental analyses reveal substantial confounding of this relationship by socio-economic indicators. A differential effect of tobacco smoke exposure on the risk of ID is suggested for males and females and deserves further investigation; however, the interpretation is tempered by the potential for residual confounding.

Estimating uncertainty in observational studies of associations between continuous variables: example of methylmercury and neuropsychological testing in children

BACKGROUND

We suggest that the need to account for systematic error may explain the apparent lack of agreement among studies of maternal dietary methylmercury exposure and neuropsychological testing outcomes in children, a topic of ongoing debate.

METHODS

These sensitivity analyses address the possible role of systematic error on reported associations between low-level prenatal exposure to methylmercury and neuropsychological test results in two well known, but apparently conflicting cohort studies: the Faroe Islands Study (FIS) and the Seychelles Child Development Study (SCDS). We estimated the potential impact of confounding, selection bias, and information bias on reported results in these studies using the Boston Naming Test (BNT) score as the outcome variable.

RESULTS

Our findings indicate that, assuming various degrees of bias (in either direction) the corrected regression coefficients largely overlap. Thus, the reported effects in the two studies are not necessarily different from each other.

CONCLUSION

Based on our sensitivity analysis results, it is not possible to draw definitive conclusions about the presence or absence of neurodevelopmental effects due to in utero methylmercury exposure at levels reported in the FIS and SCDS.

In utero p,p'-DDE exposure and infant neurodevelopment: a perinatal cohort in Mexico

BACKGROUND

Evidence suggests that p,p'-dichlorodiphenyldichloroethene (DDE) affects neurodevelopment in infants, although a critical exposure window has not yet been identified.

OBJECTIVES

Our goal was to assess the prenatal DDE exposure window and its effect on the psychomotor development index (PDI) and mental development index (MDI) during the first year of life.

METHODS

We recruited 244 children whose pregnancies and deliveries were uncomplicated, and whose mothers were monitored throughout the pregnancy. Participating mothers were not occupationally exposed to DDT (dichlorodiphenyltrichloroethane) but were residents of a zone in Mexico with endemic malaria. We measured serum levels of DDE before pregnancy and during each trimester of the pregnancy. We evaluated PDI and MDI of the Bayley Scales for Infant Development (BSID-II), at 1, 3, 6, and 12 months of age. We adjusted for quality of the home environment and maternal intellectual coefficient (IQ). We used generalized mixed-effects models for statistical analysis.

RESULTS

Third-trimester DDE level (7.8 +/- 2.8 ppb) was significantly higher than the level at baseline, first, and second trimesters, but the differences never exceeded 20%. Only DDE levels during the first trimester of pregnancy were associated with a significant reduction in PDI (every doubled increase of DDE level reduced the PDI 0.5 points). DDE was not associated with MDI.

CONCLUSIONS

A critical window of exposure to DDE in utero may be the first trimester of the pregnancy, and psychomotor development is a target of this compound. Residues of DDT metabolites may present a risk of developmental delay for years after termination of DDT use.

In utero exposure to background concentrations of DDT and cognitive functioning among preschoolers

p,p'-DDT (bis[p-chlorophenyl]-1,1,1-trichloroethane) is a persistent organochlorine compound that has been used worldwide as an insecticide. The authors evaluated the association of cord serum levels of DDT and its metabolite, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE), with neurodevelopment at age 4 years. Two birth cohorts in Ribera d'Ebre and Menorca (Spain) were recruited between 1997 and 1999 (n = 475). Infants were assessed at age 4 years by using the McCarthy Scales of Children's Abilities. Organochlorine compounds were measured in cord serum. Children's diet and parental sociodemographic information was obtained through questionnaire. Results showed that DDT cord serum concentration at birth was inversely associated with verbal, memory, quantitative, and perceptual-performance skills at age 4 years. Children whose DDT concentrations in cord serum were >0.20 ng/ml had mean decreases of 7.86 (standard error, 3.21) points in the verbal scale and 10.86 (standard error, 4.33) points in the memory scale when compared with children whose concentrations were <0.05 ng/ml. These associations were stronger among girls. Prenatal exposure to background, low-level concentrations of DDT was associated with a decrease in preschoolers' cognitive skills. These results should be considered when evaluating the risk and benefits of spraying DDT during antimalaria and other disease-vector campaigns.

Neurobehavioral performance in preschool children from agricultural and non-agricultural communities in Oregon and North Carolina

Organophosphate (OP) pesticides produce acute toxic effects but little is known about low-level chronic exposures. Latino children of agricultural workers have a high risk of exposure to pesticides because of the close proximity of their homes to fields where pesticides are applied and from take-home exposure. Neurobehavioral performance of preschool children from agricultural (AG) communities was compared to performance of those from non-agricultural (Non-AG) communities in Oregon and North Carolina. Seventy-eight children aged 48-71 months completed a battery of neurobehavioral tests two times, approximately 1 month apart. Multiple regression revealed that the AG children performed poorer on measures of response speed (Finger Tapping) and latency (Match-to-Sample) compared to the Non-AG children. These results demonstrate modest differences in AG children compared to Non-AG children that are consistent with functional effects seen in adults exposed to low concentrations of OP pesticides. Just as was the case following early research on adults poisoned by pesticides, this study points to the need for additional investigations to test the hypothesis that low-concentration OP exposures affect acquisition of test performance, response speed and latency in children of agricultural workers.

In utero exposure to background levels of polychlorinated biphenyls and cognitive functioning among school-age children

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants. In utero exposure to background levels of PCBs has been associated with intellectual impairment among children in most, but not all, studies. The authors evaluated prenatal PCB exposure in relation to cognitive test (intelligence quotient (IQ)) scores on the Wechsler Intelligence Scale for Children at age 7 years. Pregnant women were recruited from 12 US study centers from 1959 to 1965, and their children were followed until age 7 years (the Collaborative Perinatal Project). Third trimester serum was analyzed for PCBs in 1997-1999 for 732 women selected at random and for an additional 162 women whose children had either a low or a high IQ score. The PCB-IQ association was examined in multivariate models. Among those in the lowest exposure category (<1.25 microg of PCB/liter of serum), the fully adjusted mean IQ score was 93.6 (standard error: 1.8); among those in the highest category (> or =5 microg of PCB/liter), the mean IQ was 97.6 (standard error: 1.2); and overall the increase in IQ per unit increase in PCB level (microg/liter) was 0.22 (95% confidence interval: -0.28, 0.71). In these data, in utero exposure to background levels of PCBs was not associated with lower IQ at age 7 years.

Neurocognitive impairment in lead-exposed children of Andean lead-glazing workers

OBJECTIVE

The level of lead (Pb) exposure necessary to induce intellectual impairment has not been firmly established. Some studies using conventional language-based intelligence tests have reported that pediatric blood lead (PbB) levels lower than 10 microg/dL (0.483 micromol/L) are associated with neurocognitive impairment. However, these tests may introduce cultural biases in the assessment of intellectual functioning. The objective of this study was to assess the effects of PbB concentration on nonverbal intelligence in Andean children with chronic environmental Pb exposure using a nonlanguage-based test of cognitive functioning.

METHODS

Using Raven Colored Progressive Matrices (RCPM) as a measure of nonverbal intelligence, this study investigated the effects of Pb exposure (biomarker: PbB levels) on intellectual functioning in 188 chronically Pb-exposed children (age range: 5.33-11.67 years) of Ecuadorian Andean Pb-glazing workers.

RESULTS

The mean PbB level of the 188 children was 29.3 microg/dL (range: 3.5-94.3 microg/dL). Forty-seven children had PbB levels <10 microg/dL (Centers for Disease Control and Prevention [CDC] I classification), of which 30 had abnormal (ie, < or =25th percentile) RCPM standard scores. Of the 141 children with PbB levels > or =10 microg/dL, 97 had abnormal RCPM scores. A regression analysis revealed a statistically significant negative association (r = -0.331, P < 0.0001) between PbB level and RCPM standard score. Conversion of RCPM standard scores to estimated IQ scores showed an approximate two-point decrease in IQ for each 10-microg/dL increment in PbB level from 10 to >70 microg/dL.

CONCLUSIONS

Performance on a test of nonverbal intelligence was inversely associated with chronic Pb exposure in Andean children with PbB levels below and above the CDC risk management level of 10 microg/dL, with the decline in test scores suggesting a dose-response relationship.