Lead, mercury, and cadmium exposure and attention deficit hyperactivity disorder in children

Association between heavy metals exposure and risk of attention deficit hyperactivity disorder (ADHD) in children: a systematic review and meta-analysis

Heavy metals can negatively affect children's neurodevelopment, yet the relationship between heavy metals exposure and attention deficit hyperactivity disorder (ADHD) in children remains unclear. We aimed to examine associations between exposure to five common heavy metals (lead, arsenic, mercury, cadmium, and manganese) with neurodevelopmental toxicity and the risk of ADHD in children. Online databases of PubMed, Web of Science, and Embase were searched before February 29, 2024. A total of 31 studies involving 25,258 children were included in the final analysis. Our findings revealed that lead exposure was positively associated with ADHD risk in children (OR = 1.95, 95% CI: 1.57-2.41) overall, while the associations varied among different WHO regions, with the strongest in the Americas. Sensitivity analyses revealed significant associations between arsenic (OR = 1.53, 95% CI: 1.01-2.32) and manganese (OR = 1.79, 95% CI: 1.28-2.49) exposure and ADHD risk after omitting one study. Arsenic exposure was positively associated with ADHD risk in studies conducted in the Americas and adjusted for environmental smoke exposure. Positive associations between manganese exposure and ADHD risk were also found in several subgroup analyses. No significant associations were found for mercury and cadmium exposure. Dose-response meta-analysis suggested that children with higher blood lead levels exhibited a higher probability of ADHD diagnosis. Lead exposure consistently increases the risk of ADHD in children, while arsenic and manganese exposure may be associated with ADHD under different occasions. More research is required to understand heavy metals' impact on ADHD across varying exposure levels, particularly in less contaminated regions.

A systematic review of exposure to toxic elements and neurocognitive development in children

Exposure to potentially toxic elements (PTEs) has been implicated in neurodevelopmental disorders and cognitive deficits in children. However, the extent of this association and the underlying mechanisms remain poorly understood. The objective of this systematic review is to consolidate the current body of research concerning the connection between exposure to PTEs and the neurocognitive development of children. Adhering strictly to the MOOSE guidelines, the methodological framework of this review was meticulously structured. A comprehensive and thorough search strategy was implemented across Web of Science and PubMed, with a specific focus on articles published in English up to April 15, 2024. The assessment of the identified studies was systematically carried out using the evaluation method described by Gascon et al. in 2016. Fifteen studies meeting the inclusion criteria were ultimately incorporated into the review. These studies collectively involved 8391 participants and utilized various methodologies to assess exposure to PTEs and neurodevelopmental outcomes in children. Findings from the reviewed studies suggest that exposure to PTEs such as lead, arsenic, mercury, and fluoride may be associated with adverse effects on neurocognitive development, including deficits in IQ, attention, memory, and behavioral problems. Despite the limitations of the existing literature, including study design constraints and geographic disparities, the findings highlight the need for continued research to better understand the impact of PTEs on neurocognitive development in children. Future research should employ longitudinal designs, utilize alternative biomarkers for exposure assessment, consider exposure pathways and sources, investigate cumulative effects of multiple PTEs, and ensure broader geographical representation.

Association between some environmental risk factors and attention-deficit hyperactivity disorder among children in Egypt: a case-control study

BACKGROUND

Attention-Deficit Hyperactivity Disorder (ADHD) is a complex disease that negatively impacts the social and academic/occupational activities of children and is more common in boys than in girls.

METHODS

This case-control study aimed to assess the association between some environmental risk factors and ADHD among children in Alexandria, Egypt. It was carried out at the outpatient clinics of El Shatby Pediatric University Hospital in Alexandria, Egypt, with 252 children (126 cases and 126 controls). Hair samples were collected for analysis of lead and manganese levels using Atomic Absorption Spectrophotometer. A pre-designed interview questionnaire was used to determine the important environmental risk factors that may be related to ADHD.

RESULTS

Children from parents with low levels of education, living in crowded houses, and occupational exposure to chemical agents were found to be risk factors for ADHD. The mean ± SD hair lead level in ADHD children was 2.58 ± 1.95, while in controls was 1.87 ± 0.92, with a statistically significant difference (p < 0.001). The mean ± SD hair manganese level in ADHD children was 2.10 ± 1.54, while in controls was 1.11 ± 0.69, with a statistically significant difference (p < 0.001). The logistic regression model revealed that six factors had a significant association with ADHD: using of newspapers to wrap food 3 or more times a week (adjusted odds ratio (AOR) = 105.11, 95% CI: 11.18-988.26), daily TV watching by child for more than 5 h (AOR = 63.96, 95% CI: 2.56-1601.32), child's eating commercially packed noodles 3 times or more per week (AOR = 57.73, 95% CI: 3.77-593.93), using unpackaged flour in cooking (AOR = 44.47, 95% CI: 1.83-629.80), eating sweets daily by child (AOR = 6.82, 95% CI: 1.23-37.94), and lastly elevated hair Manganese level (AOR = 3.57, 95% CI: 1.24-10.29).

CONCLUSIONS

ADHD is a multi-factorial disorder, where many environmental risk factors contribute to its development. Future efforts to determine the best preventive strategy in Egypt must be based on a better knowledge of the role of environmental risk factors in the etiology of the disorder. Eliminating non-essential uses of lead and providing public education regarding the importance of safe disposal of lead-acid batteries and computers are necessary.

Early postnatal and concurrent exposure to metals and neurobehavioral outcomes at 5 years: Associations with individual environmental exposures and mixtures

BACKGROUND

Little is known about the effect of postnatal exposure to heavy metals on children's behavior problems. This study aimed to investigate the association between metal exposure during different stages of postnatal life and neurobehavioral outcomes in preschool children.

METHODS

Urinary concentrations of six metals (arsenic, cadmium, chromium, lead, manganese, and vanadium) were measured using inductively coupled plasma mass spectrometry in 220 participants at two time points: before 1 year and at 5 years of age. Mothers completed the Child Behavior Checklist when the children were 5 years old. Multivariable linear and logistic regression analyses were used to evaluate the association between metal concentrations and behavioral outcomes. We employed Bayesian kernel machine regression (BKMR) to assess possible joint effects and potential interactions between metal mixtures and behavioral outcomes.

RESULTS

Concentrations of urinary arsenic (As) in infants were associated with higher scores for anxious/shy behavior problems (β ranging from 0.03 to 0.23). Further analyses showed that As exposure increased the odds of scores falling into the borderline or clinical range on anxious/depressed, affective, and pervasive developmental problems (ORs: 2.45-3.40). Stratification by sex indicated significance in girls but not in boys. BKMR analysis showed that, among the metal mixtures, As displayed a major effect on behavior scores. Concentrations of urinary cadmium in infants were also associated with higher behavioral scores but did not increase the risk of clinical problems. A cross-sectional survey in 5-year-olds did not show a significant association between concurrent metal exposure and behavioral outcome.

CONCLUSION

Our results showed that exposure to As and Cd during infancy was associated with emotional problems in children. The effect of arsenic exposure was more pronounced among female infants. We suggest reducing exposure to toxic metals during early postnatal life to prevent behavioral problems in children."

Childhood lead exposure increases the risk of attention-deficit-hyperactivity disorder: A meta-analysis

Environmental lead exposure has been a much-discussed risk factor for the development of ADHD for decades. However, due to methodological shortcomings, the existing research on this topic is highly inconsistent. We will attempt to clarify this question by performing a meta-analysis based on a systematic literature search until February 2024 including different databases such as Pubmed and Google Scholar. The effects of environmental lead exposure were synthesized by odds ratios. A random effects model was deployed with a Paule-Mandel estimator using Hedges' invariance weighting. In addition, we carried out sensitivity analyses to examine the robustness of effects, including the detection of outliers, publication bias, p-hacking and moderating variables. In total, 14 studies with 14 effect sizes were included which had investigated the effects of lead exposure on the development of ADHD. The analyses were based on a final sample size of N = 7618 with n = 2554 ADHD cases (33,53 %) and n = 5064 healthy controls (66.47 %). Our results show that lead exposure was significantly associated with a higher risk of ADHD development. Regression analyses demonstrated that increased age of participants and increased lead significantly enhanced the risk of ADHD. Summing up we present novel results concerning the relationship between environmental lead exposure and the development of ADHD, while discussing underlying pathomechanisms as well as limitations. Finally, we provide recommendations for future studies and public health policies.

Effects of Blood Lead Levels <10 µg/dL in School-Age Children and Adolescents: A Scoping Review

CONTEXT

Lead exposures among school-age children are a major public health issue. Although the harmful effects of lead exposure during the first years of life are well known, there is not as much understanding of the effects of low levels of lead exposure during later childhood.

OBJECTIVES

To review the effects of blood lead levels (BLLs) <10 µg/dL in school-age children and adolescents.

DATA SOURCES

We searched Medline, Embase, Global health, CINAHL, Scopus, and Environmental Science Collection databases between January 1, 2000, and May 11, 2023.

STUDY SELECTION

We included peer-reviewed English-language articles that presented data on the effects of BLLs <10 µg/dL in individuals ages 5 through 18 years.

DATA EXTRACTION

Data on country, population, analytic design, sample size, age, BLLs, outcomes, covariates, and results were extracted.

RESULTS

Overall, 115 of 3180 screened articles met the inclusion criteria. The reported mean or median BLL was <5 µg/dL in 98 articles (85%). Of the included articles, 89 (77%) presented some evidence of an association between BLLs <10 µg/dL during school age and detrimental outcomes in a wide range of categories. The strongest evidence of an association was for the outcomes of intelligence quotient and attention-deficit/hyperactivity disorder diagnoses or behaviors.

LIMITATIONS

Few articles controlled for BLLs at age <5 years, limiting conclusions about the relation between later BLLs and outcomes.

CONCLUSIONS

BLLs <10 µg/dL in school-age children and adolescents may be associated with negative outcomes. This review highlights areas that could benefit from additional investigation.

Prenatal Tobacco Exposure and Behavioral Disorders in Children and Adolescents: Systematic Review and Meta-Analysis

Prenatal tobacco exposure has been implicated in increased risk of the development of behavioral disorders in children and adolescents. The purpose of the current study was to systematically examine the association between prenatal tobacco exposure and diagnoses of Attention Deficit/Hyperactivity Disorder, Oppositional Defiant Disorder, and Conduct Disorder in childhood and adolescence. We searched Medline, Psychinfo, ERIC, Proquest, Academic Search Complete, PsychArticles, Psychology and Behavioral Sciences Collection, Web of Science, CINAHL Plus, and Google Scholar databases through October 2022. The authors screened studies and extracted data independently in duplicate. Ten clinical studies examining diagnoses of Attention Deficit/Hyperactivity Disorder, Oppositional Defiant Disorder, and Conduct Disorder between the ages of 4 and 18 years old were included. There was insufficient evidence to synthesize outcomes related to Conduct Disorder and Oppositional Defiant Disorder. The meta-analysis found a significant effect of prenatal tobacco exposure in increasing the likelihood of an Attention Deficit/Hyperactivity Disorder diagnosis in childhood and adolescence. Implications for future research are discussed.

Exploring the link between toxic metal exposure and ADHD: a systematic review of pb and hg

INTRODUCTION

Attention-Deficit/Hyperactivity Disorder (ADHD) is a recognized neurodevelopmental disorder with a complex, multifactorial origin. Lead (Pb) and mercury (Hg) are highly toxic substances that can potentially impair brain development and have been implicated in the development of ADHD. This systematic review aims to analyze the epidemiological literature regarding the association between Pb and Hg exposure and the diagnosis of ADHD.

METHODS

From November 1983 to June 2, 2023, a comprehensive search was conducted in multiple databases and search engines, including PubMed, Web of Science, Scopus, and Google Scholar. Observational studies (case-control, cohort, and cross-sectional) measuring Pb and Hg levels in various biological samples (blood, hair, urine, nail, saliva, teeth, and bone) of children with ADHD or their parents and their association with ADHD symptoms were included.

RESULTS

Out of 2059 studies, 87 met the inclusion criteria and were included in this systematic review. Approximately two-thirds of the 74 studies investigating Pb levels in different biological samples reported associations with at least one subtype of ADHD. However, most studies examining Hg levels in various biological samples found no significant association with any ADHD subtype, although there were variations in exposure periods and diagnostic criteria.

CONCLUSION

The evidence gathered from the included studies supports an association between Pb exposure and the diagnosis of ADHD, while no significant association was found with Hg exposure. Importantly, even low levels of Pb were found to elevate the risk of ADHD. Further research is needed to explore the comprehensive range of risk factors for ADHD in children, considering its significance as a neurodevelopmental disorder.

Differentiated impacts of short-term exposure to fine particulate constituents on infectious diseases in 507 cities of Chinese children and adolescents: A nationwide time-stratified case-crossover study from 2008 to 2021

This study assesses the association of short-term exposure to PM2.5 (particles ≤2.5 μm) on infectious diseases among Chinese children and adolescents. Analyzing data from 507 cities (2008-2021) on 42 diseases, it focuses on PM2.5 components (black carbon (BC), ammonium (NH4+), inorganic nitrate (NO3-), organic matter (OM), and sulfate (SO42-)). PM2.5 constituents significantly associated with incidence. Sulfate showed the most substantial effect, increasing all-cause infectious disease risk by 2.72 % per interquartile range (IQR) increase. It was followed by BC (2.04 % increase), OM (1.70 %), NO3- (1.67 %), and NH4+ (0.79 %). Specifically, sulfate and BC had pronounced impacts on respiratory diseases, with sulfate linked to a 10.73 % increase in seasonal influenza risk and NO3- to a 16.39 % rise in tuberculosis. Exposure to PM2.5 also marginally increased risks for gastrointestinal, enterovirus, and vectorborne diseases like dengue (7.46 % increase with SO42-). Sexually transmitted and bloodborne diseases saw an approximate 6.26 % increase in incidence, with specific constituents linked to diseases like hepatitis C and syphilis. The study concludes that managing PM2.5 levels could substantially reduce infectious disease incidence, particularly in China's middle-northern regions. It highlights the necessity of stringent air quality standards and targeted disease prevention, aligning PM2.5 management with international guidelines for public health protection.

Environmental pollution and extreme weather conditions: insights into the effect on mental health

Environmental pollution exposures, including air, soil, water, light, and noise pollution, are critical issues that may implicate adverse mental health outcomes. Extreme weather conditions, such as hurricanes, floods, wildfires, and droughts, may also cause long-term severe concerns. However, the knowledge about possible psychiatric disorders associated with these exposures is currently not well disseminated. In this review, we aim to summarize the current knowledge on the impact of environmental pollution and extreme weather conditions on mental health, focusing on anxiety spectrum disorders, autism spectrum disorders, schizophrenia, and depression. In air pollution studies, increased concentrations of PM2.5, NO2, and SO2 were the most strongly associated with the exacerbation of anxiety, schizophrenia, and depression symptoms. We provide an overview of the suggested underlying pathomechanisms involved. We highlight that the pathogenesis of environmental pollution-related diseases is multifactorial, including increased oxidative stress, systematic inflammation, disruption of the blood-brain barrier, and epigenetic dysregulation. Light pollution and noise pollution were correlated with an increased risk of neurodegenerative disorders, particularly Alzheimer's disease. Moreover, the impact of soil and water pollution is discussed. Such compounds as crude oil, heavy metals, natural gas, agro-chemicals (pesticides, herbicides, and fertilizers), polycyclic or polynuclear aromatic hydrocarbons (PAH), solvents, lead (Pb), and asbestos were associated with detrimental impact on mental health. Extreme weather conditions were linked to depression and anxiety spectrum disorders, namely PTSD. Several policy recommendations and awareness campaigns should be implemented, advocating for the advancement of high-quality urbanization, the mitigation of environmental pollution, and, consequently, the enhancement of residents' mental health.

Early childhood exposure to environmental phenols and parabens, phthalates, organophosphate pesticides, and trace elements in association with attention deficit hyperactivity disorder (ADHD) symptoms in the CHARGE study

BACKGROUND

A growing body of literature investigated childhood exposure to environmental chemicals in association with attention-deficit/hyperactivity disorder (ADHD) symptoms, but limited studies considered urinary mixtures of multiple chemical classes. This study examined associations of concurrent exposure to non-persistent chemicals with ADHD symptoms in children diagnosed with autism spectrum disorder (ASD), developmental delay (DD), and typical development (TD).

METHODS

A total of 549 children aged 2-5 years from the Childhood Autism Risks from Genetics and Environment (CHARGE) case-control study were administered the Aberrant Behavior Checklist (ABC). This study focused on the ADHD/noncompliance subscale and its two subdomains (hyperactivity/impulsivity, inattention). Sixty-two chemicals from four classes (phenols/parabens, phthalates, organophosphate pesticides, trace elements) were quantified in child urine samples, and 43 chemicals detected in > 70% samples were used to investigate their associations with ADHD symptoms. Negative binomial regression was used for single-chemical analysis, and weighted quantile sum regression with repeated holdout validation was applied for mixture analysis for each chemical class and all chemicals. The mixture analyses were further stratified by diagnostic group.

RESULTS

A phthalate metabolite mixture was associated with higher ADHD/noncompliance scores (median count ratio [CR] = 1.10; 2.5th, 97.5th percentile: 1.00, 1.21), especially hyperactivity/impulsivity (median CR = 1.09; 2.5th, 97.5th percentile: 1.00, 1.25). The possible contributors to these mixture effects were di-2-ethylhexyl phthalate (DEHP) metabolites and mono-2-heptyl phthalate (MHPP). These associations were likely driven by children with ASD as these were observed among children with ASD, but not among TD or those with DD. Additionally, among children with ASD, a mixture of all chemicals was associated with ADHD/noncompliance and hyperactivity/impulsivity, and possible contributors were 3,4-dihydroxy benzoic acid, DEHP metabolites, MHPP, mono-n-butyl phthalate, and cadmium.

CONCLUSIONS

Early childhood exposure to a phthalate mixture was associated with ADHD symptoms, particularly among children with ASD. While the diverse diagnostic profiles limited generalizability, our findings suggest a potential link between phthalate exposure and the comorbidity of ASD and ADHD.

Heavy Metal and Thiol/Disulfide in Children with Attention-Deficit and Hyperactivity Disorder

Background

In the etiology of attention-deficit and hyperactivity disorder (ADHD), oxidative stress and heavy metal exposure are still controversial topics. In this study, our goal was to examine heavy metal levels and oxidative balance in newly diagnosed patients with ADHD and reveal whether heavy metal levels have an effect on the oxidation balance.

Methods

The study included 35 patients with newly diagnosed ADHD and 31 healthy control groups of similar age and gender. Participants' parents or caregivers completed a semi-structured questionnaire regarding their children's breastfeeding and prenatal and postnatal smoking exposures. The levels of heavy metals lead (Pb), mercury (Hg), and cadmium were measured with inductively coupled plasma optical emission spectroscopy, and a unique automated spectrophotometric approach was used to quantify serum total thiol, native thiol, and disulfide quantities and ratios.

Results

The rate of smoking during pregnancy was significantly higher in the ADHD group than in the control group (P = .030). Compared to the control group, the native and total thiol levels of children with ADHD were significantly higher (P < .001). Likewise, the ADHD group had significantly higher Hg levels compared to the control group (P = .002). Cadmium levels were substantially greater in the control group compared to the ADHD group (P < .001). However, there was no significant difference between Pb levels in the ADHD and the control group (P = .844).

Conclusion

Exposure to Hg and prenatal smoking may contribute to the development of ADHD in childhood. In response to oxidative stress, the young brains of children with ADHD may enhance their antioxidant levels.

Heavy metal contamination in duck eggs from a mercury mining area, southwestern China

Objective

Mercury (Hg) contamination in the environment around mercury mines is often accompanied by heavy metal contamination.

Methods

Here, we determined concentrations of chromium (Cr), zinc (Zn), strontium (Sr), barium (Ba), and lead (Pb) in duck eggs from a Hg mining area in Southwest China to assess the contamination and health risk.

Results

Duck eggs obtained from the mining area exhibit higher concentrations of Cr, Zn, Sr, Ba, and Pb compared to those from the background area, with egg yolks containing higher metal levels than egg whites. Specifically, the mean Cr, Zn, Sr, Ba, and Pb concentrations of duck eggs from the Hg mining area are 0.38, 63.06, 4.86, 10.08, and 0.05 μg/g, respectively, while those from the background area are only 0.21, 24.65, 1.43, 1.05, and 0.01 μg/g. Based on the single-factor contamination index and health risk assessment, heavy metal contamination in duck eggs poses an ecological risk and health risk.

Conclusion

This study provides important insight into heavy metal contamination in duck eggs from Hg mining areas.

An Industry-Relevant Metal Mixture, Iron Status, and Reported Attention-Related Behaviors in Italian Adolescents

BACKGROUND

Exposure to environmental metals has been consistently associated with attention and behavioral deficits in children, and these associations may be modified by coexposure to other metals or iron (Fe) status. However, few studies have investigated Fe status as a modifier of a metal mixture, particularly with respect to attention-related behaviors.

METHODS

We used cross-sectional data from the Public Health Impact of Metals Exposure study, which included 707 adolescents (10-14 years of age) from Brescia, Italy. Manganese, chromium, and copper were quantified in hair samples, and lead was quantified in whole blood, using inductively coupled plasma mass spectrometry. Concentrations of Fe status markers (ferritin, hemoglobin, transferrin) were measured using immunoassays or luminescence assays. Attention-related behaviors were assessed using the Conners Rating Scales Self-Report Scale-Long Form, Parent Rating Scales Revised-Short Form, and Teacher Rating Scales Revised-Short Form. We employed Bayesian kernel machine regression to examine associations of the metal mixture with these outcomes and evaluate Fe status as a modifier.

RESULTS

Higher concentrations of the metals and ferritin were jointly associated with worse self-reported attention-related behaviors: metals and ferritin set to their 90th percentiles were associated with 3.0% [β = 0.03 ; 95% credible interval (CrI): - 0.01 , 0.06], 4.1% (β = 0.04 ; 95% CrI: 0.00, 0.08), and 4.1% (β = 0.04 ; 95% CrI: 0.00, 0.08) higher T -scores for self-reported attention deficit/hyperactivity disorder (ADHD) index, inattention, and hyperactivity, respectively, compared with when metals and ferritin were set to their 50th percentiles. These associations were driven by hair manganese, which exhibited nonlinear associations with all self-reported scales. There was no evidence that Fe status modified the neurotoxicity of the metal mixture. The metal mixture was not materially associated with any parent-reported or teacher-reported scale.

CONCLUSIONS

The overall metal mixture, driven by manganese, was adversely associated with self-reported attention-related behavior. These findings suggest that exposure to multiple environmental metals impacts adolescent neurodevelopment, which has significant public health implications. https://doi.org/10.1289/EHP12988.

Early-Life Lead Exposure: Risks and Neurotoxic Consequences

BACKGROUND

Lead (Pb) does not have any biological function in a human, and it is likely no safe level of Pb in the human body. The Pb exposure impacts are a global concern for their potential neurotoxic consequences. Despite decreasing both the environmental Pb levels and the average blood Pb levels in the survey populations, the lifetime redistribution from the tissues-stored Pb still poses neurotoxic risks from the low-level exposure in later life. The growing fetus and children hold their innate high-susceptible to these Pb-induced neurodevelopmental and neurobehavioral effects.

OBJECTIVE

This article aims to evaluate cumulative studies and insights on the topic of Pb neurotoxicology while assessing the emerging trends in the field.

RESULTS

The Pb-induced neurochemical and neuro-immunological mechanisms are likely responsible for the high-level Pb exposure with the neurodevelopmental and neurobehavioral impacts at the initial stages. Early-life Pb exposure can still produce neurodegenerative consequences in later life due to the altered epigenetic imprints and the ongoing endogenous Pb exposure. Several mechanisms contribute to the Pb-induced neurotoxic impacts, including the direct neurochemical effects, the induction of oxidative stress and inflammation through immunologic activations, and epigenetic alterations. Furthermore, the individual nutritional status, such as macro-, micro-, or antioxidant nutrients, can significantly influence the neurotoxic impacts even at low-level exposure to Pb.

CONCLUSION

The prevention of early-life Pb exposure is, therefore, the critical determinant for alleviating various Pb-induced neurotoxic impacts across the different age groups.

Bacterial tolerance and detoxification of cyanide, arsenic and heavy metals: Holistic approaches applied to bioremediation of industrial complex wastes

Cyanide is a highly toxic compound that is found in wastewaters generated from different industrial activities, such as mining or jewellery. These residues usually contain high concentrations of other toxic pollutants like arsenic and heavy metals that may form different complexes with cyanide. To develop bioremediation strategies, it is necessary to know the metabolic processes involved in the tolerance and detoxification of these pollutants, but most of the current studies are focused on the characterization of the microbial responses to each one of these environmental hazards individually, and the effect of co-contaminated wastes on microbial metabolism has been hardly addressed. This work summarizes the main strategies developed by bacteria to alleviate the effects of cyanide, arsenic and heavy metals, analysing interactions among these toxic chemicals. Additionally, it is discussed the role of systems biology and synthetic biology as tools for the development of bioremediation strategies of complex industrial wastes and co-contaminated sites, emphasizing the importance and progress derived from meta-omic studies.

Urinary heavy metals and attention-deficit/hyperactivity symptoms of preschool children: a mixed-exposure analysis

The neurotoxic effects of certain heavy metals are well established, but only a few studies have investigated the joint effect of concurrent exposure to multiple ones. The study aims to evaluate the association between mixed exposure to neurotoxic metals and the psychosocial behavior of preschool children. Using a stratified sampling strategy, we recruited participants from 105 kindergartens in 41 townships of Taiwan and excluded those with blood lead levels ≥ 3.5 µg/L. The first-morning void urines were collected and analyzed for cadmium, manganese, arsenic, chromium, lead, and nickel concentrations using inductively coupled plasma mass spectrometry. We applied the parentally reported Strengths and Difficulties Questionnaire (SDQ) and Swanson, Nolan, and Pelham IV (SNAP-IV) scales to evaluate the psychosocial behaviors. Multiple linear regressions were utilized to evaluate the associations between each heavy metal and the outcomes, while the mixed effect of concurrent exposure was estimated by using a Quantile g-computation approach. A total of 977 preschool children were included in the study, and the mean (SD) age was 5.7 (0.7) years old. In single pollutant models, we observed adverse effects of urinary manganese, nickel, arsenic, and lead on the specific subsets of SDQ. Furthermore, the combined effect of six heavy metals significantly affected the hyperactivity/inattention symptoms (beta = 0.46, 95% CI: 0.13-0.78, with all metals increased by one quartile), and chromium and lead were the two major contributors. Similar detrimental effects of urinary cadmium and lead were also observed in the SNAP-IV subsets, although the joint effect analysis was not significant. The study provided evidence that concurrent exposure to multiple heavy metals may exert increased risks of hyperactivity/inattention in children compared to single pollutant exposure. Further studies are needed to verify our findings regarding mixed exposure to multiple neurotoxic metals.

Examining the effects of cumulative environmental stressors on Gulf Coast child and adolescent health

This study examines how community-level cumulative environmental stress affects child and adolescent emotional distress and chronic health conditions both directly and indirectly through stressors at the household, family, and individual levels. Data comes from the Women and their Children's Health (WaTCH) Study, which sought to understand the health implications of exposure to the 2010 Deepwater Horizon oil spill (DHOS) among a cohort of 596 mothers with children ages 10 to 17 in southeastern Louisiana. Community-level environmental stress was measured using a newly developed geospatial index. Household-level stressors included previous hurricane impacts, impacts of DHOS, degree of financial difficulty, and degree of housing physical decay. Family stressors included maternal depression, self-rated physical health, and degree of parenting stress. Child stress was based on perceived stress; child mental health was based on serious emotional disturbance; and child physical health was based on diagnosis of chronic illness. Structural equation modeling used weighted least squares means and variance and theta parameterization. Results showed a significant negative direct path between community-level cumulative environmental stress and child/adolescent serious emotional disturbance and chronic illness. However, the indirect relationship through household, family, and individual-level stressors was significant and positive for both child/adolescent serious emotional disturbance and chronic illness. These findings point to the centrality of the household and family in determining child and adolescent physical and mental health outcomes in communities exposed to frequent disasters and ongoing environmental stressors.

Disparities in Toxic Chemical Exposures and Associated Neurodevelopmental Outcomes: A Scoping Review and Systematic Evidence Map of the Epidemiological Literature

BACKGROUND

Children are routinely exposed to chemicals known or suspected of harming brain development. Targeting Environmental Neuro-Development Risks (Project TENDR), an alliance of > 50 leading scientists, health professionals, and advocates, is working to protect children from these toxic chemicals and pollutants, especially the disproportionate exposures experienced by children from families with low incomes and families of color.

OBJECTIVE

This scoping review was initiated to map existing literature on disparities in neurodevelopmental outcomes for U.S. children from population groups who have been historically economically/socially marginalized and exposed to seven exemplar neurotoxicants: combustion-related air pollution (AP), lead (Pb), mercury (Hg), organophosphate pesticides (OPs), phthalates (Phth), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs).

METHODS

Systematic literature searches for the seven exemplar chemicals, informed by the Population, Exposure, Comparator, Outcome (PECO) framework, were conducted through 18 November 2022, using PubMed, CINAHL Plus (EBSCO), GreenFILE (EBSCO), and Web of Science sources. We examined these studies regarding authors' conceptualization and operationalization of race, ethnicity, and other indicators of sociodemographic and socioeconomic disadvantage; whether studies presented data on exposure and outcome disparities and the patterns of those disparities; and the evidence of effect modification by or interaction with race and ethnicity.

RESULTS

Two hundred twelve individual studies met the search criteria and were reviewed, resulting in 218 studies or investigations being included in this review. AP and Pb were the most commonly studied exposures. The most frequently identified neurodevelopmental outcomes were cognitive and behavioral/psychological. Approximately a third (74 studies) reported investigations of interactions or effect modification with 69% (51 of 74 studies) reporting the presence of interactions or effect modification. However, less than half of the studies presented data on disparities in the outcome or the exposure, and fewer conducted formal tests of heterogeneity. Ninety-two percent of the 165 articles that examined race and ethnicity did not provide an explanation of their constructs for these variables, creating an incomplete picture.

DISCUSSION

As a whole, the studies we reviewed indicated a complex story about how racial and ethnic minority and low-income children may be disproportionately harmed by exposures to neurotoxicants, and this has implications for targeting interventions, policy change, and other necessary investments to eliminate these health disparities. We provide recommendations on improving environmental epidemiological studies on environmental health disparities. To achieve environmental justice and health equity, we recommend concomitant strategies to eradicate both neurotoxic chemical exposures and systems that perpetuate social inequities. https://doi.org/10.1289/EHP11750.

Quantitative Proteomic Analysis of Cyanide and Mercury Detoxification by Pseudomonas pseudoalcaligenes CECT 5344

The cyanide-degrading bacterium Pseudomonas pseudoalcaligenes CECT 5344 uses cyanide and different metal-cyanide complexes as the sole nitrogen source. Under cyanotrophic conditions, this strain was able to grow with up to 100 μM mercury, which was accumulated intracellularly. A quantitative proteomic analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been applied to unravel the molecular basis of the detoxification of both cyanide and mercury by the strain CECT 5344, highlighting the relevance of the cyanide-insensitive alternative oxidase CioAB and the nitrilase NitC in the tolerance and assimilation of cyanide, independently of the presence or absence of mercury. Proteins overrepresented in the presence of cyanide and mercury included mercury transporters, mercuric reductase MerA, transcriptional regulator MerD, arsenate reductase and arsenical resistance proteins, thioredoxin reductase, glutathione S-transferase, proteins related to aliphatic sulfonates metabolism and sulfate transport, hemin import transporter, and phosphate starvation induced protein PhoH, among others. A transcriptional study revealed that from the six putative merR genes present in the genome of the strain CECT 5344 that could be involved in the regulation of mercury resistance/detoxification, only the merR2 gene was significantly induced by mercury under cyanotrophic conditions. A bioinformatic analysis allowed the identification of putative MerR2 binding sites in the promoter regions of the regulatory genes merR5, merR6, arsR, and phoR, and also upstream from the structural genes encoding glutathione S-transferase (fosA and yghU), dithiol oxidoreductase (dsbA), metal resistance chaperone (cpxP), and amino acid/peptide extruder involved in quorum sensing (virD), among others. IMPORTANCE Cyanide, mercury, and arsenic are considered very toxic chemicals that are present in nature as cocontaminants in the liquid residues generated by different industrial activities like mining. Considering the huge amounts of toxic cyanide- and mercury-containing wastes generated at a large scale and the high biotechnological potential of P. pseudoalcaligenes CECT 5344 in the detoxification of cyanide present in these industrial wastes, in this work, proteomic, transcriptional, and bioinformatic approaches were used to characterize the molecular response of this bacterium to cyanide and mercury, highlighting the mechanisms involved in the simultaneous detoxification of both compounds. The results generated could be applied for developing bioremediation strategies to detoxify wastes cocontaminated with cyanide, mercury, and arsenic, such as those generated at a large scale in the mining industry.

Endocytosis-Mediated Transport of Pb in Rat Blood Cells

Blood is an important reservoir for Pb storage in living organisms, and the storage of Pb in blood cells inhibits its discharge from blood. However, the mechanism and molecular targets of Pb entry and exit from blood cells have not been elucidated, which is the major barrier to reducing blood Pb levels in normal human beings. In this study, we explored the effect of Pb-binding proteins on blood Pb levels in rats at environmentally relevant concentrations (0.32 μg/g) by identifying the functions of Pb-binding proteins and validating them with inhibitors. The results showed that Pb-binding proteins in blood cells were mainly related to phagocytosis, while in plasma, they were mainly involved in the regulation of endopeptidase activity. Meanwhile, at the normal population Pb levels, endocytosis inhibitors, endopeptidase activity inhibitors, and coadministration of both can reduce the level of Pb in MEL (mouse erythroleukemia cells) cells by up to 50, 40, and 50%, respectively, while in rat blood, the reduction can reach up to 26, 13, and 32%, respectively. Collectively, these findings reveal that endocytosis increases blood Pb levels and provides a possible molecular target for Pb excretion at ambient concentrations.

Early childhood exposure to environmental phenols and parabens, phthalates, organophosphate pesticides, and trace elements in association with attention deficit hyperactivity disorder (ADHD) symptoms in the CHARGE study

Background

Agrowing body of literature investigated childhood exposure to environmental chemicals in association with attention deficit hyperactivity disorder (ADHD) symptoms, but limited studies considered urinary mixtures of multiple chemical classes. This study examined associations of concurrent exposure to non-persistent chemicals with ADHD symptoms in children diagnosed with autism spectrum disorder (ASD), developmental delay, and typical development.

Methods

A total of 574 children aged 2-5 years from the Childhood Autism Risks from Genetics and Environment (CHARGE) case-control study was administered the Aberrant Behavior Checklist (ABC). This study focused on the Hyperactivity subscale and its two subdomains (hyperactivity/impulsivity, inattention). Sixty-two chemicals from four classes (phenols/parabens, phthalates, organophosphate pesticides, trace elements) were quantified in child urine samples, and 43 chemicals detected in >70% samples were used in statistical analyses. Weighted quantile sum regression for negative binomial outcomes with repeated holdout validation was performed to investigate covariate-adjusted associations between mixtures and ABC scores in 574 children. The mixture analyses were further restricted to 232 children with ASD.

Results

Phthalate metabolite mixtures, weighted for mono-n-butylphthalate (MNBP), mono-2-heptyl phthalate, and mono-carboxy isononyl phthalate, were associated with the Hyperactivity subscale (mean incidence rate ratio [mIRR] = 1.11; 2.5th, 97.5th percentile: 1.00, 1.23), especially the hyperactivity/impulsivity subdomain (mIRR = 1.14; 2.5th, 97.5th percentile: 1.06, 1.26). These associations remained similar after restricting to children with ASD. The inattention subdomain was associated with a phenols/parabens mixture, weighted for several parabens and bisphenols (mIRR = 1.13; 2.5th, 97.5th percentile: 1.00, 1.28) and a total mixture, weighted for 3,4-dihydroxy benzoic acid, MNBR and mono-(2-ethyl-5-carboxypentyl) phthalate (mIRR = 1.11; 2.5th, 97.5th percentile: 1.01,1.25) only among children with ASD.

Conclusions

Concurrent exposure to phthalate mixtures was associated with hyperactivity in early childhood. Though causal inference cannot be made based on our cross-sectional findings, this study warrants further research on mixtures of larger number of chemicals from multiple classes in association with ADHD-related behaviors in young children.

Lead-induced neurodevelopmental lesion and epigenetic landscape: Implication in neurological disorders

Lead (Pb) was implicated in multiple genotoxic, neuroepigenotoxic, and chromosomal-toxic mechanisms and interacted with varying synaptic plasticity pathways, likely underpinning previous reports of links between Pb and cognitive impairment. Epigenetic changes have emerged as a promising biomarker for neurological disorders, including cognitive disorders, Alzheimer's disease (AD), and Parkinson's disease (PD). In the present review, special attention is paid to neural epigenetic features and mechanisms that can alter gene expression patterns upon environmental Pb exposure in rodents, primates, and zebrafish. Epigenetic modifications have also been discussed in population studies and cell experiment. Further, we explore growing evidence of potential linkage between Pb-induced disruption of regulatory pathway and neurodevelopmental and neurological disorders both in vivo and in vitro. These findings uncover how epigenome in neurons facilitates the development and function of the brain in response to Pb insult.

Meals, Microbiota and Mental Health in Children and Adolescents (MMM-Study): A protocol for an observational longitudinal case-control study

Recent studies indicate that the interplay between diet, intestinal microbiota composition, and intestinal permeability can impact mental health. More than 10% of children and adolescents in Iceland suffer from mental disorders, and rates of psychotropics use are very high. The aim of this novel observational longitudinal case-control study, "Meals, Microbiota and Mental Health in Children and Adolescents (MMM-Study)" is to contribute to the promotion of treatment options for children and adolescents diagnosed with mental disorders through identification of patterns that may affect the symptoms. All children and adolescents, 5-15 years referred to the outpatient clinic of the Child and Adolescent Psychiatry Department at The National University Hospital in Reykjavik, Iceland, for one year (n≈150) will be invited to participate. There are two control groups, i.e., sex-matched children from the same postal area (n≈150) and same parent siblings (full siblings) in the same household close in age +/- 3 years (n<150). A three-day food diary, rating scales for mental health, and multiple questionnaires will be completed. Biosamples (fecal-, urine-, saliva-, blood samples, and buccal swab) will be collected and used for 16S rRNA gene amplicon sequencing of the oral and gut microbiome, measurements of serum factors, quantification of urine metabolites and host genotype, respectively. For longitudinal follow-up, data collection will be repeated after three years in the same groups. Integrative analysis of diet, gut microbiota, intestinal permeability, serum metabolites, and mental health will be conducted applying bioinformatics and systems biology approaches. Extensive population-based data of this quality has not been collected before, with collection repeated in three years' time, contributing to the high scientific value. The MMM-study follows the "Strengthening the Reporting of Observational Studies in Epidemiology" (STROBE) guidelines. Approval has been obtained from the Icelandic National Bioethics Committee, and the study is registered with Clinicaltrials.gov. The study will contribute to an improved understanding of the links between diet, gut microbiota and mental health in children through good quality study design by collecting information on multiple components, and a longitudinal approach. Furthermore, the study creates knowledge on possibilities for targeted and more personalized dietary and lifestyle interventions in subgroups. Trial registration numbers: VSN-19-225 & NCT04330703.

Impacts of Neonatal Methylmercury on Behavioral Flexibility and Learning in Spatial Discrimination Reversal and Visual Signal Detection Tasks

Early postnatal development in rodents is sensitive to neurotoxic effects of the environmental contaminant, methylmercury. While juvenile and adolescent exposure also produce long-term impairments in behavior, the outcome of neonatal exposure is less understood. Neural development during the neonatal period in rodents is akin to that seen in humans during the third trimester of pregnancy but methylmercury exposure occurring during the neonatal period has not been modeled, partly because breast milk is a poor source of bioavailable methylmercury. To examine this developmental period, male Long-Evans rats were exposed to 0, 80, or 350µg/kg/day methylmercuric chloride from postnatal days 1 to 10, the rodent neonatal period. As adults, behavioral flexibility, attention, memory, and expression of the dopamine transporter in these rats was assessed. Rats exhibited changes in behavioral flexibility assessed in a spatial discrimination reversal procedure. Those rats exposed to the highest dose of methylmercury displayed subtly altered patterns of perseveration compared to control animals. During acquisition of the attention/memory procedure, rats exposed to this dose also had slower acquisition, and achieved lower overall accuracy during training, compared to controls despite neither attention nor memory being affected once the task was acquired. Finally, dopamine transporter expression in the striatum, prefrontal cortex, and hippocampus was unchanged in these adult rats. The results of this study replicate the trend of findings seen with exposure during gestation or during adolescence.

Exposure to multiple metals and the risk of dyslexia - A case control study in Shantou, China

Environmental heavy metal exposure has been considered to be the risk factor for neurodevelopmental disorders in children. However, the available data on the associations between multiple metals exposure and the risk of dyslexia in China are limited. The purpose of our study was to examine the associations between urinary metal concentrations and Chinese dyslexia risk. A total of 56 Chinese dyslexics and 60 typically developing children were recruited. The urinary concentration of 13 metals were measured by inductively coupled plasma-mass spectrometer (ICP-MS). Binary logistic regression and the Probit extension of Bayesian kernel machine regression (BKMR-P) were used to explore the associations between multiple metal exposure and the risk of Chinese dyslexia. Our results indicated that Co, Zn and Pb were significantly associated with Chinese dyslexia in the multiple-metal exposure model. After adjusting the covariates, a positive association was observed between Pb and the risk of Chinese dyslexia, with the odds ratio (OR) in the highest quartiles of 6.81 (95%CI: 1.07-43.19; p-trend = 0.024). Co and Zn were negatively associated with the risk of Chinese dyslexia. Compared to the lowest quartile, the ORs of Co and Zn in the highest quartile are 0.13 (95%CI: 0.02-0.72; p-trend = 0.026) and 0.18 (95%CI: 0.04-0.88; p-trend = 0.038), respectively. In addition, BKMR-P analysis indicated that with the cumulative level across Co, Zn and Pb increased, the risk of Chinese dyslexia gradually declined and then rebounded, albeit non-significantly, and Pb was the major contributor in this association. In general, the urinary concentrations of Co, Zn and Pb were significantly associated with Chinese dyslexia. More prospective studies are needed to confirm the health effects of multiple metals exposure in children with Chinese dyslexia.

Attention deficit among preschool and school-aged children living near former metal-processing plants in Romania

Industrial areas affected by high and long-term heavy metal pollution have a great impact on health of the resident population. Children represent a group at high-risk with an increased susceptibility to chronic heavy metal intoxication. Our work included the assessment of attention particularities through a case-control study in pre-school and school-aged children (4-6 years and 8-11 years) from two study areas, Copşa Mică and Zlatna, compared to a non-polluted locality with no history of heavy metal pollution. Copşa Mică and Zlatna are two of the most polluted heavy metals regions in Romania due to non-ferrous metallurgy for a long period of time. Recruitment of participants was made by a random selection of an entire class for each age within the schools and kindergartens from the study areas (Copşa Mică and Zlatna) and from the non-polluted region. Interpretation of data was performed using statistical analysis (ANOVA and Student's t-test). Preschool children (4-6 years) were tested using Wechsler Preschool and Primary Scale of Intelligence (WPPSI) tests, Animal House and labyrinth samples. The results of the attention tests applied to pre-school children were lower in the study areas compared to the control group, but no statistical differences were found. The results of the attention tests applied to children aged between 8 and 11 years (Toulouse-Pieron test and Traffic light test) indicate lower average scores within the study groups from polluted areas, compared to the control group. Differences with statistically significance were registered for the 8 years age group (p = 0.037). In these areas efficient strategies and precise intervention measures are needed in order to limit or remove the heavy metal exposure and protect the human health, especially the groups exposed to a high level of risk.

Cellular and genetic mechanism of bacterial mercury resistance and their role in biogeochemistry and bioremediation

Mercury (Hg) is a highly toxic element that occurs at low concentrations in nature. However, various anthropogenic and natural sources contribute around 5000 to 8000 metric tons of Hg per year, rapidly deteriorating the environmental conditions. Mercury-resistant bacteria that possess the mer operon system have the potential for Hg bioremediation through volatilization from the contaminated milieus. Thus, bacterial mer operon plays a crucial role in Hg biogeochemistry and bioremediation by converting both reactive inorganic and organic forms of Hg to relatively inert, volatile, and monoatomic forms. Both the broad-spectrum and narrow-spectrum bacteria harbor many genes of mer operon with their unique definitive functions. The presence of mer genes or proteins can regulate the fate of Hg in the biogeochemical cycle in the environment. The efficiency of Hg transformation depends upon the nature and diversity of mer genes present in mercury-resistant bacteria. Additionally, the bacterial cellular mechanism of Hg resistance involves reduced Hg uptake, extracellular sequestration, and bioaccumulation. The presence of unique physiological properties in a specific group of mercury-resistant bacteria enhances their bioremediation capabilities. Many advanced biotechnological tools also can improve the bioremediation efficiency of mercury-resistant bacteria to achieve Hg bioremediation.

Assessment of Copper and Zinc Levels in Hair and Urine of Children With Attention Deficit Hyperactivity Disorder: A Case-Control Study in Eastern India

Background

Attention deficit hyperactivity disorder (ADHD) is a neuro-developmental ailment diagnosed with inattention and hyperactivity-impulsivity. It is one of the most prevalent neurodevelopmental disorders and has complex aetiology, both genetic and environmental. There is a perceived decrease in skill acquirement, leading to insufficient income and job opportunities as adults, which drives them towards poor physical and mental outcomes compared to their contemporaries without ADHD. The impact of heavy metals on ADHD is a topic of interest but is much less studied. Copper has been implicated as a pro-oxidant and in the metal accelerated production of free radicals that may affect oxidative stress. Zinc also serves as an antioxidant, and changes in its concentrations may impact the homeostasis of oxidative stress.

Methods

Twenty-four children diagnosed with ADHD were taken as cases and matched with 24 healthy controls. Hair and urine samples were collected from all the study participants. The samples were collected in sterile containers according to established protocols. Acid digestion of hair samples was done using 65% nitric acid and 30% hydrogen peroxide. Urine samples were extracted by a solution of 0.1% Triton-X-100 and 1% ultrapure nitric acid. The levels of zinc and copper were determined in both samples by inductively coupled plasma optical emission spectrometry (ICP-OES). The copper/zinc ratio (Cu/Zn) was calculated from these values. Mann Whitney U Test and receiver operating characteristic (ROC) analysis were done to estimate statistical significance.

Results

The median age of the study population was eight years. Overall, 34 male and 14 female subjects participated. There was no significant difference in height, weight and BMI between the cases and controls. Hair zinc levels in the ADHD group (198.49 µg g^-1 of hair) was significantly lower than the control group (527.05 µg g^-1 of hair). However, hair copper levels were increased significantly in the ADHD children (14.01 µg g^-1 of hair) compared to the controls (7.43 µg g^-1 of hair). Urine zinc levels were significantly lower in cases than controls (525.7 µg g^-1 of spot urine creatinine vs 1374.09 µg g^-1 of spot urine creatinine). However, copper levels in urine were higher in the ADHD children (17.01 µg g^-1 of spot urine creatinine compared to 7.26 µg g^-1 of spot urine creatinine in controls). Both hair and urine copper to zinc ratio was significantly higher in the ADHD group. On ROC analysis, the hair Cu/Zn ratio had an area under the curve (AUC) of 0.920 (p-value <0.001), and the urine Cu/Zn ratio had an AUC of 0.967 (p-value <0.001). When used as a diagnostic classifier for ADHD based on the cut-off value determined by ROC, both hair and urine Cu/Zn ratio had high sensitivity and specificity.

Conclusion

Low zinc levels in the urine and hair of children and higher levels of copper may impact the aetiology of ADHD in these children. At an early stage, the Cu/Zn ratio in both hair and urine samples may be used as a precise biomarker to identify and monitor such children.

RELATIONSHIP BETWEEN LEAD AND CADMIUM LEVELS IN BLOOD AND REFRACTORY CHRONIC CONSTIPATION AMONG IRANIAN CHILDREN

BACKGROUND

There is limited research examining reasons causing refractory chronic constipation (RCC) in children. The effects of lead (Pb) and cadmium (Cd) exposures on this condition have been even less clear. However, some related factors may contribute to evaluation of blood lead levels (BLLs) and blood cadmium levels (BCLs).

OBJECTIVE

The present study aimed to examine the relationship between Pb and Cd exposures and RCC in children living in the city of Ahvaz, Khuzestan Province, in Southwestern Iran.

METHODS

This study was performed on a total number of 48 children aged 2-13 years, including 36 medically-diagnosed RCC cases and 12 controls referring to a pediatric clinic in the city of Ahvaz. Their BLLs and BCLs were then determined using a graphite furnace atomic absorption spectrophotometer. The data from the researcher-designed questionnaire were also recoded and the related risk factors were analyzed through Spearman's correlation and logistic regression analysis.

RESULTS

The findings revealed that the geometric means of Pb and Cd in blood samples in the control group were 58.95 µg/dL and 0.45 µg/dL; respectively. These values in the case group were equally 45.26 µg/dL and 0.26 µg/dL; respectively. A significant difference was additionally observed between BCLs in the case and control groups (P<0.01). All children in both groups also had BLLs greater than the permissible limit endorsed by the World Health Organization (WHO) (≤10 µg/dL). On the other hand, 8.3% of the individuals in the case group and 33.3% of those in the control group had BCLs higher than the acceptable range mentioned by WHO (≤0.5 µg/dL).

CONCLUSION

Pb and Cd exposures due to environmental pollution and susceptibility to heavy metals may not be associated with RCC in children living in the city of Ahvaz. Although this research was the first one providing data on BLLs and BCLs in children with RCC, the findings could be useful for designing future epidemiologic studies.

Sex-specific neurotoxic effects of heavy metal pollutants: Epidemiological, experimental evidence and candidate mechanisms

The heavy metals lead (Pb), mercury (Hg), and cadmium (Cd) are ubiquitous environmental pollutants and are known to exert severe adverse impacts on the nervous system even at low concentrations. In contrast, the heavy metal manganese (Mn) is first and foremost an essential nutrient, but it becomes neurotoxic at high levels. Neurotoxic metals also include the less prevalent metalloid arsenic (As) which is found in excessive concentrations in drinking water and food sources in many regions of the world. Males and females often differ in how they respond to environmental exposures and adverse effects on their nervous systems are no exception. Here, we review the different types of sex-specific neurotoxic effects, such as cognitive and motor impairments, that have been attributed to Pb, Hg, Mn, Cd, and As exposure throughout the life course in epidemiological as well as in experimental toxicological studies. We also discuss differential vulnerability to these metals such as distinctions in behaviors and occupations across the sexes. Finally, we explore the different mechanisms hypothesized to account for sex-based differential susceptibility including hormonal, genetic, metabolic, anatomical, neurochemical, and epigenetic perturbations. An understanding of the sex-specific effects of environmental heavy metal neurotoxicity can aid in the development of more efficient systematic approaches in risk assessment and better exposure mitigation strategies with regard to sex-linked susceptibilities and vulnerabilities.

Polygenic risk of genes involved in the catecholamine and serotonin pathways for ADHD in children

It is general acknowledged that genes play a vital role in the etiology of attention deficit/hyperactivity disorder (ADHD). The relationship between the genes involved in catecholamine (dopamine, noradrenaline)/serotonin transmissions and ADHD has been widely described in medical literature. A pathway-based study was conducted in this study to test the association of gene-gene interaction and the cumulative effect of genetic polymorphisms within the dopamine, norepinephrine, and serotonin neurotransmitter pathways with ADHD susceptibility. A case-control study was conducted among Chinese children, and 168 ADHD patients and 233 controls were recruited using a combination diagnosis according to the DSM-IV ADHD rating scale. Classification and regression tree (CART) analysis was conducted to explore the gene-gene interaction, and logistic regression modal was applied to estimate the polygenic risk of the potential multiple genetic variants. The results of CART analyses indicated that the children carrying the combination of ADRA2A rs553668GG/GA and SLC6A4 rs6354 GG/GT genotypes displayed a 6.15-fold increased risk of ADHD, compared to those with the combination of ADRA2A rs553668 AA and ANKK1 rs1800497 AA genotypes. The unfavorable alleles of ADRA2A rs553668 G, DRD2 rs1124491 G and SLC6A4 rs6354 G showed cumulative effects on ADHD, and the OR for ADHD may increase by 1.42 times when the number of unfavorable allele number increased by one. Those findings reveal the importance of the gene-gene interactions and polygenic effects of many common variants to ADHD susceptibility, even the effect of each variant is very small.

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.

Environmental health risk assessment of heavy metal exposure among children living in an informal e-waste processing village in Viet Nam

This study was conducted to compare the exposure levels of five heavy metals via different pathways based on the field samplings and questionnaire surveys of children residing in an informal e-waste processing village and a reference village in Viet Nam. The findings revealed that levels of the total average daily intake (ADI) of the five heavy metals collected from a child at the exposed village were 3.90 times higher (p < 0.01) than that of a child at the reference village. Ingestion of cooked rice was the largest contributor to the total ADI of the children tested at both villages. However, the risks from water drinking and dermal contact of soil were negligible. The total non-carcinogenic risk and carcinogenic risk in an exposed child were significantly higher (p < 0.01) than their respective risks in a reference child. The non-carcinogenic risk to an exposed child was likely to occur, while the risk to a reference child was negligible. The carcinogenic risks found in children from both of the villages, however, were higher than the acceptable values, indicating the potential health risks to the children from both villages. The susceptibility of children to heavy metal contaminations shown in this study suggests that a mitigating measure need to be initiated jointly by a public agency and a private organization to prevent children from the risks of being exposed to the contaminants.

Comparative Study of Heavy Metal Concentration in Eggs Originating from Industrial Poultry Farms and Free-Range Hens in Kosovo

The aim of the present study was to determine the most significant heavy metal concentration in hen eggs, in particular to compare the heavy metal concentration in eggs originating from industrial poultry farms versus free-range hens. The sampling process was carried out between October and December 2018, in the Republic of Kosovo. In total, 22 random egg samples were collected, with 54.5% and 45.5% of samples coming from poultry farms and free-range hens, respectively. The measurements of the heavy metals were taken by inductively coupled plasma mass spectrometry (ICP-MS), using a wide range of elements, and only the most important elements were reported, such as Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg, and Pb within the range of 0.48–8.45, 38.77–289, 4286.59–15383.74, 0.45–144.74, 61.68–550.59, 1078.04–11378.56, 0.29–35.42, 0.27–6.54, and 0.04–1.41 μg kg−1, respectively. This study revealed that the heavy metals in eggs from free-range hens are richer in essential elements such as Mn, Fe, and Zn, while poultry farm eggs contain a higher contribution of Cr, Cd, As, and Pb. However, the daily intake of heavy metals from egg consumption was lower than the WHO-FAO advised provisional daily intake. Therefore, egg consumption does not exceed the safety levels of toxic metals and does not pose any risk to human health.

Relationship between ambient PM2.5 exposure and blood cadmium level in children under 14 years in Beijing, China

Ambient PM_2.5 pollution is a global environmental problem. PM_2.5 can act as a carrier of heavy metals. However, the relationship between PM_2.5 exposure and blood cadmium (Cd) level in children was less understood. Based on the data of hourly collected PM_2.5 and blood Cd level of 13,626 children aged 0-14 years from Apr. 2008 to Feb. 2013 in Beijing of China, we investigated the short-term effects of PM_2.5 exposure on blood Cd level. Generalized linear mixed models (GLMMs) were utilized to explore the potential association between PM_2.5 exposure and blood Cd level of children. The results showed that the mean blood Cd level was 0.64 μg/L. There was a significant association between PM_2.5 exposure and blood Cd level (P < 0.05). Age was negatively associated with blood Cd level (P < 0.05), and the younger children were more sensitive to Cd from PM_2.5 exposure. There wasn't a significant difference in PM_2.5 concentration between heating and non-heating seasons in winter (P > 0.05); there was also no gender difference of children on blood Cd level (P > 0.05). The present study demonstrates the importance of controlling the PM_2.5 bound Cd exposure, and environmental countermeasures should be implemented stringently to reduce their impact on children's health.

Blood lead and mercury levels are associated with low resting heart rate in community adolescent boys

While the neurotoxic effects of heavy metals at even low levels have been well-studied, few studies have examined the cardiovascular effects of heavy metals on resting heart rate and these have focused on adult populations. The present study aimed to examine the association between low-level environmental lead and mercury exposure and resting heart rate in community adolescents. As part of the China Jintan Cohort Study, 532 adolescents aged 12 years (SD = 0.6) were tested for blood levels of lead (BLL) and mercury (BML) and resting heart rate (RHR). Generalized linear models were conducted to test the relationship between BLL and BML and RHR, controlling for children's sex, age, and socioeconomic status. Analyses were clustered at the preschool level when the children were recruited to adjust for standard error. The mean (SD) BLL and BML were 3.14 (SD = 1.19) μg/dL and 1.26 (SD = 0.68) μg/L at age 12 years, respectively. After adjusting for confounders, we found a significant interaction between BML and BLL in predicting RHR in boys (B = -1.27, SE = 0.49, p < 0.01, n = 289). We created BLL and BML groups in boys based on median cut-offs. Boys in the High BLL/High BML group had significantly lower RHR (mean = 84.22 beats per minute [bpm], SD = 8.77, n = 61) than boys in the Low BLL/Low BML group (mean = 89.03 bpm, SD = 10.75, n = 69; p < 0.05). BML and BLL did not interact to predict RHR in girls (B = -0.18, SE = 0.88, p > 0.05, n = 242). Combined high BLL and BML were associated with low RHR in community adolescent boys. Low RHR is an indication of chronic under-arousal and has been implicated in psychopathology, particularly for externalizing behavior. Our findings may stimulate further communication and research in this area.

(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.

Ethnic and border differences on blood cancer presentation and outcomes: A Texas population-based study

BACKGROUND

The Texas/Chihuahua (US/Mexico) border is a medically underserved region with many reported barriers for health care access. Although Hispanic ethnicity is associated with health disparities for many different diseases, the population-based estimates of incidence and survival for patients with blood cancer along the border are unknown. The authors hypothesized that Hispanic ethnicity and border proximity is associated with poor blood cancer outcomes.

METHODS

Data from the Texas Cancer Registry (1995-2016) were used to investigate the primary exposures of patient ethnicity (Hispanic vs non-Hispanic) and geographic location (border vs non-border). Other confounders and covariates included sex, age, year of diagnosis, rurality, insurance status, poverty indicators, and comorbidities. The Mantel-Haenszel method and Cox regression analyses were used to determine adjusted effects of ethnicity and border proximity on the relative risk (RR) and survival of patients with different blood cancer types.

RESULTS

Hispanic patients were diagnosed at a younger age than non-Hispanic patients and presented with increased comorbidities. Whereas non-Hispanics had a higher incidence of developing blood cancer compared with Hispanics overall, Hispanics demonstrated a higher incidence of acute lymphoblastic leukemia (RR, 1.92; 95% CI, 1.79-2.08; P < .001) with worse outcomes. Hispanics from the Texas/Chihuahua border demonstrated a higher incidence of chronic myeloid leukemia (RR, 1.28; 95% CI, 1.07-1.51; P = .02) and acute myeloid leukemia (RR, 1.17; 95% CI, 1.04-1.33; P = .0009) compared with Hispanics living elsewhere in Texas.

CONCLUSIONS

Hispanic ethnicity and border proximity were associated with a poor presentation and an adverse prognosis despite the younger age of diagnosis. Future studies should explore differences in disease biology and treatment strategies that could drive these regional disparities.

Multiple exposure pathways of first-year university students to heavy metals in China: Serum sampling and atmospheric modeling

In this study, we collected 308 serum samples from 17 to 20 year old first-year university students who were recruited from Lanzhou University in China a few days after their enrollment to measure the serum Pb, Cd, Hg, and As levels, and specific questionnaires for age, sex, settlement and dietary structure were designed. A 3-D atmospheric transport model was used to simulate the atmospheric concentration and dry deposition across China based on gridded Pb emission inventory to examine the association between the spatial distribution of serum concentrations and environmental fates of Pb. The mean serum Pb, Cd, Hg, and As concentrations averaged over all participating young students were 21.38, 1.46, 3.86, and 4.69 μg/L, respectively. The Pb, Cd, and Hg levels in 3%, 7%, and 20% serum samples exceeded the standards. The minimum serum As and Hg concentrations and the maximum serum Pb and Cd concentrations occurred in urban areas. Seafood diet habits (P < 0.05), sex (P < 0.05), and relocation (P < 0.01) caused significant differences in serum As, Pb, and Cd concentrations. A cluster analysis was carried out to classify the exposure pathways for target contaminants. The results indicated that 4 heavy metals in the serum of volunteers from northern China could be grouped into the same category, in which significant positive correlations were found between the serum heavy metal levels and background concentrations of surface soil. However, in other provinces and metropolises, the atmospheric pollution level played a critical role involving in the inhalation exposure pathway. We demonstrated that serum Pb levels in freshman students were related to the atmospheric transport and dry deposition of Pb.

E-waste lead exposure and children's health in China

China is one of the countries worldwide confronted with serious e-waste pollution and associated detrimental health effects, which has aroused public, academic and governmental concerns. Most local residents are exposed to hazardous substances such as lead (Pb) and other persistent organic pollutants because of informal e-waste recycling activities. This study reviews recent studies on children exposed to e-waste Pb in China focusing on health-related effects in children (e.g. growth and development, cardiovascular, immune, nervous, respiratory, reproductive, skeletal, and urinary systems) and evaluating the evidence for the association between e-waste Pb exposure and the children health outcomes in China. Children are one of most sensitive and vulnerable groups when facing e-waste Pb exposure. Previous data indicate that exposure to e-waste Pb has adverse effect on human health such as delayed and damaged physical and nervous development. It is the time to take effective measures, such as upgrading e-waste recycling technology, enhancing government policy guidance and support, and strengthening environmental protection and health awareness of the local inhabitants, to prevent the adverse effects of e-waste.

Interaction between lead and noradrenergic genotypes affects neurocognitive functions in attention-deficit/hyperactivity disorder: a case control study

BACKGROUND

Lead is known to be associated with attention-deficit/hyperactivity disorder (ADHD) even at low concentrations. We aimed to evaluate neurocognitive functions associated with lead in the blood and the interactions between lead and dopaminergic or noradrenergic pathway-related genotypes in youths with ADHD.

METHODS

A total of 259 youths with ADHD and 96 healthy controls (aged 5-18 years) enrolled in this study. The Korean Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime version was conducted for psychiatric diagnostic evaluation. Blood lead levels were measured, and their interaction with dopaminergic or noradrenergic genotypes for ADHD; namely, the dopamine transporter (DAT1), dopamine receptor D4 (DRD4), and alpha-2A-adrenergic receptor (ADRA2A) genotypes were investigated. All participants were assessed using the ADHD Rating Scale-IV (ADHD-RS). Participants also completed the continuous performance test (CPT) and Stroop Color-Word Test (SCWT). Analysis of covariance was used for comparison of blood lead levels between ADHD and control groups. A multivariable linear regression model was used to evaluate the associations of blood lead levels with the results of ADHD-RS, CPT, and SCWT; adjusted for intelligence quotient (IQ), age, and sex. A path analysis model was used to identify the mediating effects of neurocognitive functions on the effects of blood lead on ADHD symptoms. To evaluate the effect of the interaction between blood lead and genes on neuropsychological functions, hierarchical regression analyses were performed.

RESULTS

There was a significant difference in blood lead levels between the ADHD and control groups (1.4 ± 0.5 vs. 1.3 ± 0.5 μg/dL, p = .005). Blood lead levels showed a positive correlation with scores on omission errors(r = .158, p = .003) and response time variability (r = .136, p = .010) of CPT. In the multivariable linear regression model, blood lead levels were associated with omission errors (B = 3.748, p = .045). Regarding the effects of lead on ADHD symptoms, hyperactivity-impulsivity was mediated by omission errors. An interaction effect was detected between ADRA2A DraI genotype and lead levels on omission errors (B = 5.066, p = .041).

CONCLUSIONS

Our results indicate that neurocognitive functions at least partly mediate the association between blood lead levels and ADHD symptoms, and that neurocognitive functions are affected by the interaction between blood lead levels and noradrenergic genotype.

Dietary contributions to increased background lead, mercury, and cadmium in 9-11 Year old children: Accounting for racial differences

BACKGROUND

Initial interest in the adverse consequences of exposure to lead (Pb), mercury (Hg), and cadmium (Cd) focused on relatively high exposures through environmental or occupational sources; however, recent evidence suggests even low-level background exposure to non-essential metals might be detrimental, particularly for children's health and development. One potentially important source of increased background levels of non-essential toxic metals is diet.

OBJECTIVES

We considered whether differences in diet are associated with levels of non-essential metals in blood and whether racial differences in metals are mediated by dietary differences.

METHODS

We assessed blood levels of Pb, Hg, and Cd in a sample of 9-11 year-old children (N = 295) comprised of 42% European Americans (EAs), 58% African American (AAs), and 47% female. Diet was assessed using 24-h dietary recalls during phone interviews administered to parents on two consecutive days (Friday and Saturday). The Healthy Eating Index-2105 (HEI-2015) was calculated to assess diet quality.

RESULTS

The current study identified significant dietary sources of non-essential metal exposure - namely total fruit for Pb, total protein for Hg, and greens and beans for Cd. Moreover, AAs were found to have significantly higher blood levels of Pb and Hg than EAs and these racial differences were significantly mediated by these dietary differences.

DISCUSSION

This study is one of very few to consider total diet in children and exposure to the non-essential metals Pb, Hg, and Cd, and the first to demonstrate that racial differences in increased background blood levels of non-essential toxic metals can be accounted for by racial differences in diet. Given regional differences in food consumption patterns and specific farm and store sources for the foods, the generalizability of the current findings has yet to be determined; however, commonly consumed foods appear to be a significant source of low-level non-essential metals.

Association between exposure to urban waste and emotional and behavioral difficulties in schoolchildren

OBJECTIVE

To evaluate the association between living near waste recycling sites and emotional or behavioral difficulties in schoolchildren.

METHODOLOGY

A cross-sectional study with schoolchildren aged 6-13 years old from disadvantaged communities in a Brazilian city, divided between those who live less than 100m away from the central point of the recycling site and those that live more than 150m away from the site, as a control group and classified through georeferencing. The emotional and behavioral difficulties were investigated using the Strengths and Difficulties Questionnaire tool. Other variables were analyzed through logistic regression to determine their contribution to the outcomes.

RESULTS

Children living near waste recycling sites had a higher prevalence of emotional and behavioral problems than children living farther away. In the logistic regression model, no other covariates had a significant impact on the results, except for attending preschool. As expected, the families of the exposed group had lower income and lower levels of schooling, thus being characterized as a highly vulnerable population.

CONCLUSION

The association between living near waste recycling sites and lower test performance raises concerns about the impact of inappropriate waste management in urban centers on children's health.

Bioaccessibility and health risk assessment of Pb and Cd in urban dust in Hangzhou, China

Heavy metals in urban dust can enter the human body through a variety of ways, thus endangering human health. Understanding the bioaccessibility of heavy metals in urban dust is a key to its risk assessment. After the G20 summit in 2016, Hangzhou city has received much attention, including its environmental health risk. The surface dust collected from three different functional areas in Hangzhou were subjected to the in vitro physiologically based extraction test (PBET) to measure the bioaccessibility of Pb and Cd. In terms of spatial variation, the distribution of Pb bioaccessibility was in the order of residential areas > city parks > main roads > the Botanic Garden, while for Cd ordered in city parks > residential areas > main roads > the Botanic Garden. For temporal variation, the bioaccessibility of Pb was higher in autumn and winter, and the bioaccessibility of Cd was higher in spring and autumn. Based on multiple linear statistical analysis, the relationship between the spatial and temporal distribution differences of the bioaccessibility of Pb and Cd in the city and the main components was discussed. Meanwhile, the non-carcinogenic hazard quotients of Pb and the carcinogenic risk of Cd were calculated and showed no harm to human health, except the total Pb in the surface dust with a high non-carcinogenic risk for infants. Urban dust in Hangzhou city has a slight pollution and health risk from Pb. Currently, controlling and reducing the city's Pb emission is the key to maintain Hangzhou city's air quality and matching with its international tourism city.

An integrative approach to identify the impacts of multiple metal contamination sources on the Eastern Andean foothills of the Ecuadorian Amazonia

Currently, several concerns have been raised over metal contamination in the upper Amazon basin. Rivers that flow from the high Andes to the lowland Amazon are threatened by anthropogenic activities, which may, in turn, lead to increased metal concentrations in both water and sediments. In the present study, the impacts of multiple metal contamination sources in these ecosystems were identified. The degree of metal contamination was assessed in water and sediment and seed phytotoxicity analyses were carried out in samples taken from 14 sites located in upper Napo River tributaries, combining geochemical and ecotoxicological techniques. These tributaries were chosen based on their degree of anthropogenic contamination and proximity to known sources of relevant pollution, such as small-scale gold mining (MI), urban pollution (UP), fish farming (FF) and non-functional municipal landfill areas (LF). Our results suggest that anthropogenic activities are introducing metals to the aquatic ecosystem, as some metals were up to 500 times above the maximum permissible limits for the preservation of aquatic life established by Ecuadorian and North American guidelines. Sites located close to small-scale gold mining and sanitary landfills presented 100 to 1000 times higher concentrations than sites classified as "few threats". In water, Cd, Pb, Cu, Zn and Hg were mostly above the maximum permissible limits in the samples, while Cd in sediment reached concentrations 5-fold above the probable effect level (PEL). Phytotoxicity was associated through the diffuse contamination present in urban and landfill areas. Overall, metal concentrations and phytotoxicity assessments suggest anthropogenic effects to environmental contamination, even though natural sources cannot be disregarded. Anthropogenic effects in the eastern Andean Rivers need to be constantly monitored in order to build a complete picture on how pollution sources may affect this strategic Amazon basin area.

The potential role of clock genes in children attention-deficit/hyperactivity disorder

BACKGROUND

Attention deficit/ hyperactivity disorder (ADHD) is a chronic neurodevelopmental disorder and is thought to be associated with circadian system.

METHODS

We performed a pathway-based study to test individual single nucleotide polymorphisms (SNPs) and the overall evidence of genetic polymorphisms involved in the circadian pathway in association with children ADHD susceptibility among a Chinese population. A community-based case-control study was conducted among Chinese children, and 168 ADHD patients and 233 controls were recruited using a combination diagnosis based on the diagnostic and statistical manual of mental disorders iv (DSM-IV) ADHD rating scale, Swanson, Nolan, and Pelham rating scale (SNAP-IV) rating scale, and semi-structured clinical interview.

RESULTS

The results of single-loci analyses identified that PER1 rs2518023 and ARNTL2 rs2306074 were nominally association with ADHD susceptibility (P < 0.05). Next, we applied multifactor dimensionality reduction (MDR), and classification and regression tree (CART) analyses to explore high-order gene-gene interactions among the functional SNPs to ADHD risks. The results indicated that interactions among the PER1 rs2518023, ARNTL2 rs2306074 and NR1D1 rs939347 were associated with the risk of ADHD in children. Individuals carrying the combination genotypes of the PER1 rs2518023 GG or GT, ARNTL2 rs2306074 TC or TT and NR1D1 rs939347 GA or AA displayed a significantly higher risk for ADHD than who carry the PER1 rs2518023 TT and CRY2 rs2292910 CA/CC genotypes (adjusted OR = 4.37, 95% CI = 2.16-8.85, P < 0.001).

CONCLUSIONS

These findings revealed the importance of genetic variations related to the circadian clock system to the susceptibility of children ADHD.

Oxidative stress caused by lead (Pb) induces iron deficiency in Drosophila melanogaster

Toxic elements exposure disturbs the homeostasis of essential elements in organisms, but the mechanism remains elusive. In this study, we demonstrated that Drosophila melanogaster exposed to Lead (Pb, a pervasive environmental threat to human health) exhibited various health defects, including retarded development, decreased survival rate, impaired mobility and reduced egg production. These phenotypes could be significantly modulated by either intervention of dietary iron levels or altering expression of genes involved in iron metabolism. Further study revealed that Pb exposure leads to systemic iron deficiency. Strikingly, reactive oxygen species (ROS) clearance significantly increased iron uptake by restoring the expression of iron metabolism genes in the midgut and subsequently attenuated Pb toxicity. This study highlights the role of ROS in Pb induced iron dyshomeostasis and provides unique insights into understanding the mechanism of Pb toxicity and suggests ideal ways to attenuate Pb toxicity by iron supplementation therapy or ROS clearance.

Persistent Effects on Cardiorespiratory and Nervous Systems Induced by Long-Term Lead Exposure: Results from a Longitudinal Study

Long-term lead (Pb) exposure alters the normal development of the nervous system and physiology. It affects multiple organ systems, causing hypertension, cardiorespiratory dysfunction, being a well-known neurotoxin, inducing changes in neurogenesis, neurodegeneration, and glial cells. However, studies of the developmental effects of lead and its outcomes throughout life are lacking. Determine morphofunctional, behavioral, and cognitive developmental effects of long-term lead exposure at three different ages. Wistar rats were exposed to a Pb-acetate solution from fetal period until adulthood and compared to a non-exposed control group. General behavior and cognitive skills were evaluated by behavioral tests and physiological data and cardiorespiratory reflexes measured. Neurodegeneration, neuroinflammation, and synaptic activity were assessed by immunohistochemistry. Lead exposure caused long-lasting anxiety-like behavior and strong long-term memory impairment without changes in locomotor and exploratory activity. Hypertension was observed at all time points, concomitant with baroreflex impairment and increased chemoreflex sensitivity. Persistent neuroinflammation, transient synaptic overexcitation without neurodegeneration was observed. Long-term Pb exposure, since fetal period, causes long-lasting anxiety-like behavior, concomitant with hypertension, without general motor skills impairment. Synaptic overexcitation, reactive astrogliosis, and microgliosis could underlie behavioral and long-term memory changes, which might have been caused during developmental phases and consolidated during adulthood. Also, alterations observed in the cardiorespiratory reflexes can explain persistent hypertension. This longitudinal study identifies and characterizes lead toxicity nature and magnitude, important to devise and test potential interventions to attenuate the long-term harmful effects of lead on the nervous and cardiovascular systems.