Latent subgroups of cognitive performance in lead- and manganese-exposed Uruguayan children: Examining behavioral signatures

A comprehensive analysis of children's blood lead levels in Latin America and the Caribbean over the last eight years: Progress and recommendations

In 2017 we published a review on blood lead levels (BLL) in children from Latin America and the Caribbean (LAC) for data available up to 14th of March 2014 and recommended the identification and control of "lead hot spots". In the present study, an evaluation of progress toward reducing BLL in the region was carried out. A systematic review of the latest literature on lead exposure in the LAC region held on the PubMed, Web of Science and LILACS databases (January 2014 to March 2022) was conducted using the PRISMA methodology. Only original papers published in peer-reviewed English, Spanish, or Portuguese journals were eligible. A total of 558 papers were retrieved, 77 of which met the selection criteria and 31 (40.25 %) were carried out in Mexico. The prevalence of children with BLL above 10 μg. dL-1 was 22.08 % in the previous review versus 6.78 % in the current study. In the present review, the prevalence of children with BLL above 5 μg. dL-1 was 29.62 %, and only one study reported a BLL prevalence rate between 3.3 and 5 μg. dL-1. The highest BLLs were associated with well-known sources or occupational exposures. The number of countries (n = 13) that published data on BLL in children was lower compared to the previous review (n = 16). Most studies were conducted in areas with known lead exposure sources, similar to the earlier review. The percentage of children at risk of lead poisoning in the region remains unknown because few studies have published data on environmental exposure levels and most samples were relatively small. The recommendation to identify and control sources of lead exposure was maintained, while further suggestions for establishing a systematic public health surveillance system for lead were proposed to help reduce the knowledge gap and inform public health policy-making in LAC.

Blood lead levels and math learning in first year of school: An association for concern

Lead is a well-known neurotoxicant that continues to affect children's cognition and behavior. With the aim to examine the associations of lead exposure with math performance in children at the beginning of formal schooling, we conducted a cross-sectional study of first-grade students from 11 schools in Montevideo, Uruguay. Math abilities were assessed with tests from the Batería III Woodcock-Muñoz (Calculation, Math Facts Fluency, Applied Problems, Math Calculation Skills and Broad Maths). Separate generalized linear models (GLM) tested the association of blood lead level (BLL) and each math ability, adjusting for key covariates including age and sex, maternal education, household assets and Home Observation for Measurement of the Environment Inventory score. In a complete-case of 252 first-grade students (age 67-105 months, 45% girls), mean ± SD blood lead level was 4.0 ± 2.2 μg/dL. Covariate-adjusted logistic models were used to examine the association between childhood BLLs and the odds of low math performance. BLL was negatively associated with scores on the Calculation test (β (95% CI): -0.18 (-0.33, -0.03)), Math Calculation Skills (-1.26 (-2.26, -0.25)), and Broad Maths cluster scores (-0.88 (-1.55, -0.21)). Similarly, performance on the Calculation test, as well as cluster scores for Broad Maths and Math Calculation Skills differed between children with BLLs <5 and ≥ 5 μg/dL (p < 0.01), being lower in children with higher BLLs. Finally, considering the likelihood of low test performance, each 1 μg/dL higher B-Pb was related to 27% higher likelihood for Maths Facts Fluency, 30% for Broad Math and Math Calculation Skills, and 31% for Calculation (p < 0.05). These results suggest that lead exposure is negatively associated with several basic skills that are key to math learning. These findings further suggest that the cognitive deficits related to lead exposure impact student achievement at very early stages of formal education.

Secular trends in blood lead concentrations of school-age children in Montevideo, Uruguay from 2009 to 2019

Lead exposure continues to be a public health problem globally, yet very few countries perform systematic biomonitoring or surveillance of children's blood lead levels (BLLs). Secular trends in children's BLLs have not been well characterized outside North America and Europe. In 2009-19, we conducted a series of non-representative cross-sectional surveys in Montevideo, Uruguay, enrolling children living in areas of the city with known or suspected lead contamination. Lead was measured with atomic absorption spectrometry on fasting venous blood samples. Of the 856 children representing independent (non-sibling) observations, 759 had BLL measures. Other missing data were imputed. Using linear and logistic regression models, we estimated the covariate-adjusted year to year difference in mean BLL and the likelihood of having BLL ≥5 and BLL ≥3.5 μg/dL. At the start of the study, mean ± SD BLL was 4.8 ± 2.6 μg/dL, and at the end 1.4 ± 1.4 μg/dL. The prevalence of BLL ≥5 and BLL ≥3.5 μg/dL also differed markedly between 2009 and 2019 (30.8% vs. 2.7% and 53.8% vs. 5.8%). Similarly, where 80.8% of children had BLL ≥2 μg/dL in 2011, in 2019 that number was 19.3%. The estimated year to year difference in BLL was ∼0.3 μg/dL. Despite this progress, pediatric lead exposure remains a problem in Montevideo. In years 2015-19, between 19 and 48% of school children had BLL ≥2 μg/dL, a level at which adverse neurobehavioral outcomes continue to be reported in the literature. Continued prevention and risk-reduction efforts are needed in Montevideo, including systematic surveillance of BLLs in all children.

Biomonitoring of arsenic, lead, manganese and mercury in hair from a presumably exposed Uruguayan child population

Aim: To perform an exposure assessment of arsenic, manganese, mercury and lead levels in hair samples from children from poor neighborhoods. Materials & methods: A total of 38 Caucasian children were recruited with the consent of their parents or tutors. Determinations were performed by atomic absorption spectrometry. Results & conclusion: Results were 0.045-0.12 μg/g-1 (arsenic), 0.56-2.05 μg/g-1 (manganese) and 0.34-27.8 μg/g-1 (lead). Lead results did not correlate with those previously reported in blood from the same individuals, suggesting that hair is not useful for exposure assessment of this contaminant. Mercury was determined for the first time in Uruguayan children showing levels <0.083 μg/g-1. Results revealed low-to-moderate metal exposure, except for some high lead findings.

Environmental Exposure Disparities and Neurodevelopmental Risk: a Review

PURPOSE OF REVIEW

Neurotoxicant exposures are of particular concern in historically marginalized communities. Often a consequence of structural racism, low-income minoritized populations experience a disproportionate burden of hazardous exposures through proximity to industrial facilities, high traffic roads, and suboptimal housing. Here, we summarize reports on exposures and neurodevelopment focused on differences by education, income, race/ethnicity, or immigration status from 2015 to 2022, discuss the importance of such investigations in overburdened communities, and recommend areas for future research.

RECENT FINDINGS

We found 20 studies that investigated exposure disparities and neurodevelopment in children. Most were conducted in the USA, and many focused on air pollution, followed by metal exposures and water contamination. Although several studies showed differences in exposure-outcome associations by income and education, many examining differences by race/ethnicity did not report notable disparities between groups. However, measures of individual race and ethnicity are not reliable measures of discrimination experienced as a consequence of structural racism. Our review supports scientific evidence that the reduction of individual and widespread municipal exposures will improve child development and overall public health. Identified research gaps include the use of better indicators of economic status and structural racism, evaluations of effect modification and attributable fraction of outcomes by these factors, and considerations of multidimensional neighborhood factors that could be protective against environmental insults. Considering that vulnerable populations have disparities in access to and quality of care, greater burden of exposure, and fewer resources to incur associated expenses, such populations should be prioritized.

Reducing the complexity of high-dimensional environmental data: An analytical framework using LASSO with considerations of confounding for statistical inference

PURPOSE

Frameworks for selecting exposures in high-dimensional environmental datasets, while considering confounding, are lacking. We present a two-step approach for exposure selection with subsequent confounder adjustment for statistical inference.

METHODS

We measured cognitive ability in 338 children using the Woodcock-Muñoz General Intellectual Ability (GIA) score, and potential associated features across several environmental domains. Initially, 111 variables theoretically associated with GIA score were introduced into a Least Absolute Shrinkage and Selection Operator (LASSO) in a 50% feature selection subsample. Effect estimates for selected features were subsequently modeled in linear regressions in a 50% inference (hold out) subsample, first adjusting for sex and age and later for covariates selected via directed acyclic graphs (DAGs). All models were adjusted for clustering by school.

RESULTS

Of the 15 LASSO selected variables, eleven were not associated with GIA score following our inference modeling approach. Four variables were associated with GIA scores, including: serum ferritin adjusted for inflammation (inversely), mother's IQ (positively), father's education (positively), and hours per day the child works on homework (positively). Serum ferritin was not in the expected direction.

CONCLUSIONS

Our two-step approach moves high-dimensional feature selection a step further by incorporating DAG-based confounder adjustment for statistical inference.

Pyrethroid and Chlorpyrifos Pesticide Exposure, General Intellectual Abilities, and Executive Functions of School Children from Montevideo, Uruguay

Children's developing brains are susceptible to pesticides. Less is known about the effect of exposure to chlorpyrifos and pyrethroids on executive functions (EF). We measured urinary 3,5,6-trichloro-2-pyridinol (TCPy), a metabolite of chlorpyrifos, and urinary 3-phenoxybenzoic acid (3-PBA), a general, nonspecific metabolite of pyrethroids in first-grade children from Montevideo, Uruguay (n = 241, age 80.6 ± 6.4 months, 58.1% boys). EFs were assessed with the Intra-dimensional/Extra-dimensional shift (IED), Spatial Span (SSP), and Stockings of Cambridge (SOC) tests from the Cambridge Neuropsychological Test Automated (CANTAB) Battery. General intellectual ability (GIA) was assessed using the Woodcock-Muñoz Cognitive battery. Median (range) urinary TCPy and 3-PBA levels were 16.7 (1.9, 356.9) ng/mg of creatinine and 3.3 (0.3, 110.6) ng/mg of creatinine, respectively. In multivariable generalized linear models, urinary TCPy was inversely associated with postdimensional errors on the IED task β [95% CI]: -0.11 [-0.17, -0.06]. Urinary 3-PBA was inversely associated with the total number of trials -0.07 [-0.10, -0.04], and the total number of errors -0.12 [-0.18, -0.07] on the IED task. When TCPy and 3-PBA were modeled together, the associations did not differ from single-metabolite models. We found no evidence of effect modification by blood lead level (BLL). Pesticide exposure may affect EF performance in urban children.

Exposure to metal mixtures and neuropsychological functioning in middle childhood

Elevated exposure to multiple trace metals can be neurotoxic even at relatively low levels. These findings are primarily evident from adult occupational studies as well as in children exposed prenatally or in early childhood. Less research has focused on the neurodevelopmental impacts of exposure to metals among school-aged children. We examined associations between exposure to a mixture of four metals (arsenic, cadmium, manganese, lead) measured in hair and markers of cognition, attention, and behavior among 222 6-12 year old children who participated in a 2009-2010 neurodevelopmental follow-up to the C8 Health Project. Using quantile-based g-computation we estimated the adjusted overall metal mixture effect ψ (95 % CI) as the change in outcome per decile increase in all metals in the mixture. Hair metal levels varied by metal, with cadmium being lowest (median 0.007, interquartile range (IQR) 0.013 μg/g) and lead the highest concentration (median 0.152, IQR 0.252 μg/g). Children's cognitive skills and development, attention/impulsivity, and behavior were all close to standardized population means. Each decile increase in all metals was associated with a Full Scale IQ reduction of 1.01 points (95 % confidence interval (CI) -1.88, -0.15) and Verbal IQ reduction of 1.11 points (95 % CI -1.97, -0.25), adjusted for child age, sex, secondhand smoke exposure, HOME score, maternal education, maternal IQ, and examiner. Maternal report of ADHD-like behaviors and executive functioning also showed adverse associations with the metal mixture. Our findings suggest that similar to exposure during prenatal and early childhood periods, recent exposure to metals during middle childhood is associated with adverse neurodevelopmental consequences. Middle childhood may also be a developmental window of susceptibility to the negative consequences of exposure to environmental neurotoxicants.

Executive functions in school-aged children exposed to airborne manganese: A multilevel analysis

Neuropsychological alterations have been identified in populations heavily exposed to metals with neurotoxic potential, such as manganese (Mn). This study examined the associations between Mn environmental exposure in school-aged children and executive functions, using structural equation modeling. Children, aged between 7 and 12 years (N = 181), were recruited from four elementary schools located in a region that is under the influence of atmospheric emissions from a ferro-manganese alloy plant in the municipality of Simões Filho, Bahia, Brazil. The following cognitive functions were evaluated: Intelligence, Inhibitory Control, Cognitive Flexibility, Verbal and Design Fluency, Verbal and Visual Working Memory and Attention. We performed structural equation modeling to identify the following executive functions latent variables: working memory, inhibitory control and cognitive flexibility. We further analyzed the relations between executive functions and Mn measured in hair (MnH) and toenails (MnTn) with linear mixed models, after controlling for co-variables. A positive effect at the individual level on working memory, inhibition control and cognitive flexibility was observed with MnTn after controlling for co-variables, but no association was found with MnH levels. However, children attending school most environmentally exposed to Mn emissions, which had the highest rate of Mn dust deposition, had the poorest scores on working memory. These findings suggest both benefits and risk of Mn on children's cognitive development.

A mixed methods study examining neighborhood disadvantage and childhood behavior problems in Montevideo, Uruguay

BACKGROUND

Neighborhood disadvantage (ND) is a risk factor for child behavior problems (CBPs), but is understudied outside the United States and Europe. Our mixed methods study aims to (1) create a culturally meaningful measure of ND, (2) test cross-sectional associations between ND and CBPs and (3) qualitatively explore life in the neighborhoods of families participating in the Salud Ambiental Montevideo (SAM) study.

METHODS

The quantitative study (Study 1) comprised 272, ~7-year-old children with geolocation and complete data on twelve behavioral outcomes (Conner's Teachers Rating Scale - Revised Short Form: CTRS-R:S and Behavioral Rating Inventory of Executive Functioning: BRIEF). A ND factor was created at the census segment level (1,055 segments) with 19 potential indicators of ND downloaded from the Municipality of Montevideo Geographic Services. Children were assigned ND scores based on the location of their household within a census segment. Multilevel models tested associations between ND and all CBP scales, controlling for confounders at the individual level. The qualitative study (Study 2) comprised 10 SAM caregivers. Photovoice alongside semi-structured interviews in Spanish were used to foster conversations about neighborhood quality, activities, and raising children. Thematic analysis with inductive coding was used to summarize qualitative study findings.

RESULTS

The ND factor consisted of 12 census-based indicators related to education, employment, ethnicity, housing quality, and age characteristics, but unrelated to home ownership and some ethnicity variables. In multivariable models, ND was associated with greater conduct problems (β = 1.37, p < .05), poor shifting (β = 1.56, p < .01) and emotional control problems (β = 2.36, p < .001). Photovoice and semi-structured interviews yielded four themes: physical disorder, recreation, safety and crime, and community resources. Residents discussed improving waste management and transportation, updating playgrounds, and ensuring neighborhood safety.

CONCLUSIONS

ND in Montevideo comprised a unique set of census indicators. ND was primarily related to behavioral regulation problems. Hypothesized pathways whereby ND affects CBPs are discussed.

Lead exposure and indices of height and weight in Uruguayan urban school children, considering co-exposure to cadmium and arsenic, sex, iron status and dairy intake

Child growth depends on complex factors including diet, nutritional status, socioeconomic, and sanitary conditions, and exposure to environmental chemicals. Lead exposure is known to impair growth in young children but effects in school-age children are less clear. The effects of co-exposure to low-level lead and other toxic metals on child growth are not well understood. We examined cross-sectional associations of blood lead (BLL) with growth indices (Z scores of body mass index for age, BAZ, and height for age, HAZ) in Uruguayan urban school children (n = 259; ~7 y). Potential differences in these associations in children with lower vs. higher urinary inorganic arsenic metabolites (U-As), urinary cadmium (U-Cd), sex (42% girls), iron deficiency (ID, 39% children), or intake of dairy foods below recommended levels were examined. BLL was measured using AAS, U-As using HPLC-HGICP-MS, and U-Cd using ICP-MS. Dietary information was obtained by two 24-h recalls completed by caregivers. Children's linear growth was within age and sex-appropriate reference values. Overweight (BAZ > 1 2 SD) was found in 20.1%, and obesity (BAZ > 2 SD) in 18.5%, of children. Ranges (5th, 95th percentile) of biomarker concentrations were: BLL, 0.8-7.8 μg/dL; U-Cd, 0.01-0.2 μg/L, and U-As, 4.0-27.3 μg/L. BLL was inversely associated with HAZ ([95% CI]: 0.10 [-0.17, -0.03]) in covariate-adjusted models. Although this association was slightly more pronounced in girls, children without ID, and children with lower U-As, there was little evidence of effect modification due to overlapping CIs in stratified models. BLLs were not associated with BAZ, except for a suggestion of a negative relationship in girls (-0.10 [-0.23, 0.02]) but not boys [0.001 [-0.11, 0.12]). Our findings indicate that exposure to low levels of lead was associated with lower HAZ in apparently normally growing urban school children. Larger future studies should help elucidate if these associations persist over time and across populations.

Proximity to sources of airborne lead is associated with reductions in Children's executive function in the first four years of life

Although policies to remove lead from gasoline have resulted in a substantial reduction in airborne lead, multiple industries are known to generate lead that is released in the air. The present study examines the extent to which residential proximity to a documented source of airborne lead is associated with intellectual and executive function in children. Data were available for n = 849 children from the Family Life Project. Geolocation for children's residences between birth and 36 months were referenced against the Environmental Protection Agency's Risk Screening Environmental Indicators (RSEI) database, which estimates exposure for each ½ mile grid in the contiguous United States. Instrumental variable models were employed to estimate causal associations between exposure and cognitive outcomes measured at 36, 48, and 60 months, using census-documented density of manufacturing employment as the instrument. Models of continuous lead dosage indicated small negative effects for both child IQ and executive function (EF). These results indicate that RSEI estimates of airborne lead exposure are meaningfully associated with decrements in cognitive development.

Exposure to environmental neurotoxic substances and neurodevelopment in children from Latin America and the Caribbean

Environmental (and occupational) exposure to neurotoxic substances is a worldwide problem that can affect children's neurodevelopment (ND). In Latin American and Caribbean (LAC) countries there are over 300 million children living under the threat of neurodevelopmental delays due to toxic environmental exposure. Large industrial centers, intense mining and agricultural activities, along with changing complex ecosystems constitute a mosaic that drives contamination of air, water and the food chain. Neurotoxic contaminants such as pesticides (organochlorines, organophosphates, carbamates, pyrethroids, neonicotinoids, and manganese fungicides), chemicals of industrial use (phthalates), and metals (Hg, Pb, Al, As, F, Cd, Mo, Mn) are at the center of environmental exposure studies. Exposure to neurotoxic substances singly or in combination with other compounds or socioeconomic stressors (maternal education, socio-economic and nutritional status) intertwined with occupational and para-occupational exposure can affect ND (motor, cognition, behavior) of children. Significant negative effects of pesticides and neurotoxic elements on ND were found in all studied countries, affecting especially the less-privileged children from laboring families. Studies showed that exposures to the neurotoxicants in human milk are secondary to their more lasting effects during prenatal exposure. This review integrates exposure (prenatal and breastfeeding), metabolism, and ND effects of neurotoxicants. It highlights the overwhelming evidence showing that current levels of exposures are hazardous and detrimental to children's ND in LAC countries. The evidence indicates that a reduction in neurotoxicant exposure is essential to protect children's ND. Therefore, it is urgent to adopt policies and actions that prevent and remediate region-specific children's ND issues.

(Ascorb)ing Pb Neurotoxicity in the Developing Brain

Lead (Pb) neurotoxicity is a major concern, particularly in children. Developmental exposure to Pb can alter neurodevelopmental trajectory and has permanent neuropathological consequences, including an increased vulnerability to further stressors. Ascorbic acid is among most researched antioxidant nutrients and has a special role in maintaining redox homeostasis in physiological and physio-pathological brain states. Furthermore, because of its capacity to chelate metal ions, ascorbic acid may particularly serve as a potent therapeutic agent in Pb poisoning. The present review first discusses the major consequences of Pb exposure in children and then proceeds to present evidence from human and animal studies for ascorbic acid as an efficient ameliorative supplemental nutrient in Pb poisoning, with a particular focus on developmental Pb neurotoxicity. In doing so, it is hoped that there is a revitalization for further research on understanding the brain functions of this essential, safe, and readily available vitamin in physiological states, as well to justify and establish it as an effective neuroprotective and modulatory factor in the pathologies of the nervous system, including developmental neuropathologies.

Associations of metals and neurodevelopment: a review of recent evidence on susceptibility factors

PURPOSE OF REVIEW

Epidemiologic evidence exists that many metals are associated with adverse neurobehavioral effects in young children, including lead (Pb), methylmercury (meHg), manganese (Mn) and arsenic (As)5-8. Importantly, chemical insult can vary depending on host factors and exposure circumstance. This systematic review summarizes the recent literature investigating modifying factors of the associations between metals and neurodevelopment, including immutable traits (sex or genetics) or exposure conditions (timing or co-exposures).

RECENT FINDINGS

Of the 53 studies included in this review, the number investigating modification of exposure effects were: 30 for sex, 21 for co-exposures, 12 for timing of exposure, and six for genetic modifiers. Sex-specific effects of metal-neurobehavioral associations were inconclusive for all metals, likely due to the heterogeneity of outcome domains assessed and the exposure time points measured. Seven studies evaluated both sex and exposure timing as modifying factors using deciduous teeth or other biomarkers with repeated measures to characterize metals exposure over time. Only five studies used statistical methods for mixtures to evaluate associations of more than two metals with neurobehavioral domains.

SUMMARY

Despite the expansion of research on susceptibility to the neurodevelopmental effects of metals exposure, considerable gaps remain. This work remains critical, as characterizing susceptible subpopulations can aid in identifying biological mechanisms and is fundamental for the protection of public health.

Catching flame retardants and pesticides in silicone wristbands: Evidence of exposure to current and legacy pollutants in Uruguayan children

Children are exposed to many potentially toxic compounds in their daily lives and are vulnerable to the harmful effects. To date, very few non-invasive methods are available to quantify children's exposure to environmental chemicals. Due to their ease of implementation, silicone wristbands have emerged as passive samplers to study personal environmental exposures and have the potential to greatly increase our knowledge of chemical exposures in vulnerable population groups. Nevertheless, there is a limited number of studies monitoring children's exposures via silicone wristbands. In this study, we implemented this sampling technique in ongoing research activities in Montevideo, Uruguay which aim to monitor chemical exposures in a cohort of elementary school children. The silicone wristbands were worn by 24 children for 7 days; they were quantitatively analyzed using gas chromatography with tandem mass spectrometry for 45 chemical pollutants, including polychlorinated biphenyls (PCBs), pesticides, polybrominated diphenyl ethers (PBDEs), organophosphorus flame retardants (OPFRs), and novel halogenated flame-retardant chemicals (NHFRs). All classes of chemicals, except NHFRs, were identified in the passive samplers. The average number of analytes detected in each wristband was 13 ±3. OPFRs were consistently the most abundant class of analytes detected. Median concentrations of ΣOPFRs, ΣPBDEs, ΣPCBs, and dichlorodiphenyltrichloroethane (DDT) and its metabolites (dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD)) were 1020, 3.00, 0.52 and 3.79 ng/g wristband, respectively. Two major findings result from this research; differences in trends of two OPFRs (TCPP and TDCPP) are observed between studies in Uruguay and the United States, and the detection of DDT, a chemical banned in several countries, suggests that children's exposure profiles in these settings may differ from other parts of the world. This was the first study to examine children's exposome in South America using silicone wristbands and clearly points to a need for further studies.

Biomarkers of environmental manganese exposure and associations with childhood neurodevelopment: a systematic review and meta-analysis

BACKGROUND

Although prior studies showed a correlation between environmental manganese (Mn) exposure and neurodevelopmental disorders in children, the results have been inconclusive. There has yet been no consistent biomarker of environmental Mn exposure. Here, we summarized studies that investigated associations between manganese in biomarkers and childhood neurodevelopment and suggest a reliable biomarker.

METHODS

We searched PubMed and Web of Science for potentially relevant articles published until December 31th 2019 in English. We also conducted a meta-analysis to quantify the effects of manganese exposure on Intelligence Quotient (IQ) and the correlations of manganese in different indicators.

RESULTS

Of 1754 citations identified, 55 studies with 13,388 subjects were included. Evidence from cohort studies found that higher manganese exposure had a negative effect on neurodevelopment, mostly influencing cognitive and motor skills in children under 6 years of age, as indicated by various metrics. Results from cross-sectional studies revealed that elevated Mn in hair (H-Mn) and drinking water (W-Mn), but not blood (B-Mn) or teeth (T-Mn), were associated with poorer cognitive and behavioral performance in children aged 6-18 years old. Of these cross-sectional studies, most papers reported that the mean of H-Mn was more than 0.55 μg/g. The meta-analysis concerning H-Mn suggested that a 10-fold increase in hair manganese was associated with a decrease of 2.51 points (95% confidence interval (CI), - 4.58, - 0.45) in Full Scale IQ, while the meta-analysis of B-Mn and W-Mn generated no such significant effects. The pooled correlation analysis revealed that H-Mn showed a more consistent correlation with W-Mn than B-Mn. Results regarding sex differences of manganese associations were inconsistent, although the preliminary meta-analysis found that higher W-Mn was associated with better Performance IQ only in boys, at a relatively low water manganese concentrations (most below 50 μg/L).

CONCLUSIONS

Higher manganese exposure is adversely associated with childhood neurodevelopment. Hair is the most reliable indicator of manganese exposure for children at 6-18 years of age. Analysis of the publications demonstrated sex differences in neurodevelopment upon manganese exposure, although a clear pattern has not yet been elucidated for this facet of our study.

Environmental exposure to low-level lead (Pb) co-occurring with other neurotoxicants in early life and neurodevelopment of children

Lead (Pb) is a worldwide environmental contaminant that even at low levels influences brain development and affects neurobehavior later in life; nevertheless it is only a small fraction of the neurotoxicant (NT) exposome. Exposure to environmental Pb concurrent with other NT substances is often the norm, but their joint effects are challenging to study during early life. The aim of this review is to integrate studies of Pb-containing NT mixtures during the early life and neurodevelopment outcomes of children. The Pb-containing NT mixtures that have been most studied involve other metals (Mn, Al, Hg, Cd), metalloids (As), halogen (F), and organo-halogen pollutants. Co-occurring Pb-associated exposures during pregnancy and lactation depend on the environmental sources and the metabolism and half-life of the specific NT contaminant; but offspring neurobehavioral outcomes are also influenced by social stressors. Nevertheless, Pb-associated effects from prenatal exposure portend a continued burden on measurable neurodevelopment; they thus favor increased neurological health issues, decrements in neurobehavioral tests and reductions in the quality of life. Neurobehavioral test outcomes measured in the first 1000 days showed Pb-associated negative outcomes were frequently noticed in infants (<6 months). In older (preschool and school) children studies showed more variations in NT mixtures, children's age, and sensitivity and/or specificity of neurobehavioral tests; these variations and choice of statistical model (individual NT stressor or collective effect of mixture) may explain inconsistencies. Multiple exposures to NT mixtures in children diagnosed with 'autism spectrum disorders' (ASD) and 'attention deficit and hyperactivity disorders' (ADHD), strongly suggest a Pb-associated effect. Mixture potency (number or associated NT components and respective concentrations) and time (duration and developmental stage) of exposure often showed a measurable impact on neurodevelopment; however, net effects, reversibility and/or predictability of delays are insufficiently studied and need urgent attention. Nevertheless, neurodevelopment delays can be prevented and/or attenuated if public health policies are implemented to protect the unborn and the young child.