The Relationship Between the Level of Copper, Lead, Mercury and Autism Disorders: A Meta-Analysis

Environmental pollutant exposure and adverse neurodevelopmental outcomes: An umbrella review and evidence grading of meta-analyses

BACKGROUND

Exposure to environmental pollutants during foetal and childhood development has been associated with neurodevelopmental disorders; however, existing evidence remains fragmented and lacks comprehensive credibility assessments.

METHODS

PubMed, Embase, PsycINFO, and the Cochrane Database of Systematic Reviews were systematically searched from database inception through January 2025, supplemented by reference list searches. Eligible studies were meta-analyses of observational research examining the associations between environmental pollutant exposure and adverse neurodevelopmental outcomes, with quality assessment performed using the AMSTAR 2 tool. Summary effect estimates were re-analysed using random-effects models, accompanied by heterogeneity I² statistics, 95 % prediction intervals, and evaluations of small-study effects and excess significance bias. Evidence was graded according to established criteria as follows: convincing, highly suggestive, suggestive, weak, or not significant. Reporting adhered to PRISMA guidelines, and the study protocol was pre-registered with PROSPERO (CRD42022339292).

RESULTS

A total of 45 studies, comprising 256 unique meta-analyses, were included in the umbrella review. Of these, 88 meta-analyses demonstrated statistical significance; however, 62 % of these exhibited small-study effects and/or excess significance bias. According to the quantitative grading criteria, highly suggestive evidence was identified for the association between PM2.5 exposure and attention deficit hyperactivity disorder (ADHD) (odds ratio [OR] 1.82 [1.52, 2.18]), as well as for lead (Pb) exposure (OR 1.96 [1.57, 2.46]) and ADHD. Childhood fluoride exposure was also graded as highly suggestive evidence for cognitive deficit (OR 3.80 [2.42, 5.97]). Suggestive evidence included the associations between pregnancy O3 exposure and autism spectrum disorder (ASD), childhood lead exposure with decreased intelligence quotient (IQ), decreased blood magnesium (Mg) levels in children with ADHD, and first-trimester pregnancy exposure to PM2.5 and ASD. Sensitivity analyses indicated that results derived from the Restricted Likelihood Maximum (REML) estimator demonstrated greater robustness compared to the widely used DerSimonian and Laird (DL) estimator, reflecting a 13 % increase in significant associations.

CONCLUSIONS AND RELEVANCE

Neurodevelopmental disorders associated with environmental pollutants from industrial and human activities pose a critical public health challenge. Future research necessitates cautious analytical strategies and enhanced methodological transparency to improve the credibility of findings.

Mercury exposure and childhood outcomes: An overview of systematic reviews

OBJECTIVE

The objective of this review was to summarize recent and relevant systematic reviews (SRs) that assessed relationships between mercury (Hg) exposure during pregnancy, lactation, and childhood and child outcomes.

EVIDENCE REVIEW

Three electronic databases were searched for SRs published between January 2018 to December 2024 about Hg exposure (of any form or source, including seafood), during pregnancy, lactation or childhood and child outcomes including: anthropometrics, neurodevelopment, attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), exposure biomarkers, cardiometabolic health, immunity, and birth outcomes. All articles were screened at title/abstract and full-text levels by two independent reviewers. A MeaSurement Tool to Assess systematic Reviews (AMSTAR) 2 critical appraisal tool was used to assess the methodological quality of the included SRs.

FINDINGS

Twenty-nine SRs of observational studies were identified that assessed Hg during pregnancy (n = 19) and/or childhood (n = 17). During pregnancy, results from the SRs suggested that higher Hg may be associated with higher risk of birth defects, pre-term birth, ADHD, ASD, and low birth weight, length, and head circumference. Results varied for neurodevelopment outcomes in the child, likely due to co-exposure with seafood during pregnancy, variation in response by sex of the child, and etiological differences among developmental domains. During childhood, SRs suggested that higher Hg may be associated with higher risk of ADHD and adverse neurodevelopment, growth, and body composition outcomes. Also, Hg concentrations were higher in children with ASD than those without in case-control studies but longitudinal data were lacking. Evidence on methylmercury exposure from seafood during pregnancy and childhood was limited and inconclusive.

CONCLUSION AND RELEVANCE

Mercury exposure during pregnancy and childhood is recognized as a major public health concern. However, more research is needed that specifically examines methylmercury from seafood to better inform future dietary recommendations.

Assessment of Essential and Toxic Element Levels in the Toenails of Children with Autism Spectrum Disorder

Autism spectrum disorder (ASD) has become a global public health concern, impacting the quality of life. The question of gene-environment interaction in the emergence of ASD remains a subject of ongoing debate, and exploring its pathophysiology is thoroughly related to metals as a risk factor. Therefore, this study aims to assess the levels of toxic (Al, Cd, Hg, and Pb) and essential (Cr, Mn, Fe, Ni, Cu, Zn, and Se) elements in toenail samples collected in children with ASD and neurotypical children, by ICP-MS. Parallelly, we will discuss the use of toenails as an exposure indicator. The study involved 208 children aged 3 to 14 from Marrakech, Morocco. One hundred two were diagnosed with ASD and 106 were neurotypical children. Significant statistical differences in the concentration of Cr, Mn, and Fe were documented between the two groups. Higher levels of Pb in toenails compared to reference values have been reported. No association was established between concentrations of elements and age. Spearman correlation coefficients revealed a significantly different pattern of mutual dependence for toxic and essential elements between the two groups. The strongest positive correlations were found in the neurotypical group (Fe-Mn (ρ = 0.750), and Se-Zn (ρ = 0.800)). These results provide additional, although inconclusive, evidence on the probable role of element disturbance in the pathogenesis of ASD. Further studies should be performed to explore other nutritional, cultural, sociodemographic, environmental, and methodological factors that may impact the levels of these elements in the nails and their possible correlation with the incidence of ASD.

Association of weight and dietary habits with high blood mercury levels in Korean adolescents: data from the KoNEHS cycle 4, 2018-2020

BACKGROUND

Humans are exposed to mercury primarily in its highly toxic form, methyl mercury, which is known to have adverse effects on various organs and systems. The negative impact of mercury exposure on the growth, development, and mental health of children, from infancy to adolescence, is well-documented. However, there are no internationally standardized safe limits for mercury exposure. This study investigated the impact of dietary habits and higher body mass index (BMI) on blood mercury levels in adolescents.

METHODS

This study analyzed the data from the 4th Korean National Environmental Health Survey (KoNEHS) 2018-2020. The focus was on 825 middle and high school students aged 13-18 years, whose blood mercury levels were measured. A survey on dietary and lifestyle habits was also conducted. Blood mercury levels were categorized by geometric median values, and associations with overweight status and seafood consumption were examined using a generalized linear model.

RESULTS

The geometric mean blood mercury level for the entire sample was 1.37 μg/L, with levels of 1.31 μg/L in normal-weight individuals and 1.43 μg/L in overweight individuals, showing a statistically significant difference between the two groups. After adjusting for other variables, blood mercury levels were significantly associated with overweight status (estimate: 0.084; p = 0.018; 95% confidence interval [CI]: 0.015-0.153), consumption of large fish and tuna more than once a week (estimate: 0.18; p = 0.001; 95% CI: 0.077-0.284), and consumption of fish once a week or more (estimate: 0.147; p = 0.004; 95% CI: 0.043-0.250).

CONCLUSIONS

In adolescents, a higher BMI and an increased consumption of large fish, tuna, and fish were associated with higher blood mercury levels. Notably, a stronger association was found between large fish consumption and blood mercury levels in the overweight group. These findings suggest the need to moderate seafood consumption and establish more proactive mercury exposure standards for adolescents.

Combined Exposure to Folate and Lead during Pregnancy and Autistic-Like Behaviors among Canadian Children from the MIREC Pregnancy and Birth Cohort

BACKGROUND

Folic acid (FA) supplementation may attenuate the associations between gestational exposure to certain chemicals and autism or autistic-like behaviors, but to our knowledge, this has not been assessed for lead.

OBJECTIVES

We examined whether the relationship between gestational blood-lead levels (BLLs) and autistic-like behaviors was modified by gestational plasma total folate concentrations, FA supplementation, and maternal methylenetetrahydrofolate reductase (MTHFR) 677C>T genotype.

METHODS

We used data from the Maternal-Infant Research on Environmental Chemicals study (2008-2011), a Canadian pregnancy and birth cohort study. Childhood autistic-like behaviors were documented in 601 children 3-4 y of age with the Social Responsiveness Scale-2 (SRS-2), where higher scores denote more autistic-like behaviors. We measured BLLs and plasma total folate concentrations during the first and third trimesters of pregnancy. We also estimated gestational FA supplementation via surveys and genotyped the maternal MTHFR 677C>T single nucleotide polymorphism (SNP). We estimated the confounder-adjusted associations between log 2 -transformed BLLs and SRS-2 scores by two indicators of folate exposure and maternal MTHFR 677C>T genotype using linear regression.

RESULTS

Third-trimester BLLs were associated with increased SRS-2 scores [β a d j = 3.3 ; 95% confidence interval (CI): 1.1, 5.5] among participants with low (< 10 th percentile), third-trimester, plasma total folate concentrations, but BLL-SRS-2 associations were null (β a d j = - 0.3 ; 95% CI: - 1.2 , 0.5) among those in the middle category (≥ 10 th and < 80 th percentiles) (p-interaction < 0.001 ). FA supplementation also attenuated these associations. Both folate indicators modified first-trimester BLL-SRS-2 associations, but to a lesser extent. Third-trimester BLL-SRS-2 associations were slightly stronger among participants who were homozygous for the T (minor) allele of the MTHFR 677C>T SNP (β a d j = 0.9 ; 95% CI: - 1.2 , 3.1) than those without the T allele (β a d j = - 0.3 ; 95% CI: - 1.3 , 0.7), but the difference was not statistically significant (p -interaction = 0.28 ).

DISCUSSION

Folate may modify the associations between gestational lead exposure and childhood autistic-like behaviors, suggesting that it mitigates the neurotoxic effects of prenatal lead exposure. https://doi.org/10.1289/EHP14479.

Blood and hair copper levels in childhood autism spectrum disorder: a meta-analysis based on case-control studies

OBJECTIVES

The association between copper levels and autism spectrum disorder (ASD) has been a controversial topic. This study investigated relationship between copper levels and ASD.

CONTENT

The following databases are searched until April 2022: PubMed, EMBASE and Web of Science. Combined effect size standardized mean differences (SMD) and 95% confidence intervals (95% CI) were calculated with Stata 12.0. In this meta-analysis, 29 case-control studies were included, which included 2,504 children with ASD and 2,419 healthy controls. The copper levels in hair (SMD: -1.16, 95% CI: -1.73 to -0.58) was significantly lower in ASD children than healthy controls. The copper levels in blood (SMD: 0.10, 95% CI: -0.12 to 0.32) not significantly compare ASD with controls.

SUMMARY AND OUTLOOK

Copper may be associated with the development of ASD in children.

Reduction of Glyoxalase 1 Expression Links Fetal Methylmercury Exposure to Autism Spectrum Disorder Pathogenesis

Glyoxalase 1 (Glo1) is an essential enzyme to detoxify methylglyoxal (MGO), a cytotoxic byproduct of glycolysis. Accumulating studies have shown an important role of Glo1 in regulating cortical development and neurogenesis, potentially contributing to the pathogenesis of autism spectrum disorder (ASD) when impaired. We have previously shown that prenatal exposure to non-apoptotic low-dose methylmercury (MeHg), an environmental pollutant, induces premature cortical neurogenesis and ASD-like behaviors in a rodent model. In this study, we aimed to determine the underlying molecular mechanisms that mediate prenatal MeHg-induced premature neuronal differentiation and abnormal neurodevelopment. Using single-cell RNA sequencing (scRNA-seq) and real-time quantitative PCR (RT-qPCR), we found that prenatal MeHg exposure at a non-apoptotic dose significantly reduced Glo1 gene expression in embryonic cultured radial glia precursors (RGPs). In cultured RGPs, the knockdown of Glo1 expression increased neuronal production at the expense of the cultured RGPs population, while overexpression of Glo1 restored MeHg-induced neuronal differentiation back to normal levels. Furthermore, we found that co-treatment with both MeHg and multiple MGO scavengers or a CREB inhibitor (iCREB) mitigated MeHg-induced premature neuronal differentiation, reinforcing the role of Glo1 and CREB in mediating MeHg-induced neuronal differentiation. Our findings demonstrate a direct link between MeHg exposure and expression of an ASD risk gene Glo1 in cortical development, supporting the important role of gene-environment interaction in contributing to the etiology of neural developmental disorders, such as ASD.

Reversal of Autism Symptoms among Dizygotic Twins through a Personalized Lifestyle and Environmental Modification Approach: A Case Report and Review of the Literature

The prevalence of autism has been increasing at an alarming rate. Even accounting for the expansion of autism spectrum disorder diagnostic (ASD) criteria throughout the 1990's, there has been an over 300% increase in ASD prevalence since the year 2000. The often debilitating personal, familial, and societal sequelae of autism are generally believed to be lifelong. However, there have been several encouraging case reports demonstrating the reversal of autism diagnoses, with a therapeutic focus on addressing the environmental and modifiable lifestyle factors believed to be largely underlying the condition. This case report describes the reversal of autism symptoms among dizygotic, female twin toddlers and provides a review of related literature describing associations between modifiable lifestyle factors, environmental exposures, and various clinical approaches to treating autism. The twins were diagnosed with Level 3 severity ASD "requiring very substantial support" at approximately 20 months of age following concerns of limited verbal and non-verbal communication, repetitive behaviors, rigidity around transitions, and extensive gastrointestinal symptoms, among other common symptoms. A parent-driven, multidisciplinary, therapeutic intervention involving a variety of licensed clinicians focusing primarily on addressing environmental and modifiable lifestyle factors was personalized to each of the twin's symptoms, labs, and other outcome measures. Dramatic improvements were noted within several months in most domains of the twins' symptoms, which manifested in reductions of Autism Treatment Evaluation Checklist (ATEC) scores from 76 to 32 in one of the twins and from 43 to 4 in the other twin. The improvement in symptoms and ATEC scores has remained relatively stable for six months at last assessment. While prospective studies are required, this case offers further encouraging evidence of ASD reversal through a personalized, multidisciplinary approach focusing predominantly on addressing modifiable environmental and lifestyle risk factors.

Environmental Risk Factors in Autism Spectrum Disorder: A Narrative Review

Existing evidence indicates that environmental factors might contribute up to 50% of the variance in autism spectrum disorder (ASD) risk. This structured narrative review offers a comprehensive synthesis of current knowledge on environmental risk factors in ASD, including evaluation of conflicting evidence, exploration of underlying mechanisms, and suggestions for future research directions. Analysis of diverse epidemiological investigations indicates that certain environmental factors, including advanced parental age, preterm birth, delivery complications, and exposure to toxic metals, drugs, air pollutants, and endocrine-disrupting chemicals, are linked to an increased ASD risk through various mechanisms such as oxidative stress, inflammation, hypoxia, and its consequences, changes in neurotransmitters, disruption of signaling pathways and some others. On the other hand, pregnancy-related factors such as maternal diabetes, maternal obesity, and caesarian section show a weaker association with ASD risk. At the same time, other environmental factors, such as vaccination, maternal smoking, or alcohol consumption, are not linked to the risk of ASD. Regarding nutritional elements data are inconclusive. These findings highlight the significance of environmental factors in ASD etiology and emphasize that more focused research is needed to target the risk factors of ASD. Environmental interventions targeting modifiable risk factors might offer promising avenues for ASD prevention and treatment.

Hair Trace Elements and Mineral Content in Moroccan Children with Autism Spectrum Disorder: a Case-Control Study

The prevalence of autism spectrum disorder (ASD) around the world continues to increase while the pathophysiology remains insufficiently elucidated. Genetics, environment, and epigenetic changes are often implicated. Abnormal level in trace elements and minerals is among environmental factors assumed to be involved. The purpose of this article is to assess hair concentrations of toxic and essential elements in children with ASD and children with neurotypical development in the city of Marrakech. Two hundred and twenty-seven children (107 with ASD and 120 controls) aged 3 to 14 years old were recruited. The results of analysis by ICP-MS showed a significant decrease in hair levels of copper, zinc, iron, and selenium (25%, 13%, 17%, 11%) of children with ASD. The most significantly reduced concentrations in children with ASD are that of manganese by 34%. Hair aluminum level was significantly elevated by 29% in ASD compared to controls. Multiple linear regression analysis revealed that copper, selenium, and iron content in hair were significantly inversely associated with ASD, similarly, hair aluminum content was significantly associated with ASD. Adjusted model for demographic parameters increased the predictive ability of the model, father's age was a significant predictor. In addition, ASD and gender were significant predictors of hair levels of aluminum, selenium, and manganese.These results support the hypothesis of the disparity of trace elements and minerals levels in children with ASD and highlight the potential interest of micronutrient supplementation in the eventual improvement of ASD symptoms. Future research should explore the pathophysiology of these micronutrient deficiencies.

Synthesis, spectroscopic findings, SEM/EDX, DFT, and single-crystal structure of Hg/Pb/Cu-SCN complexes: In silico ADME/T profiling and promising antibacterial activities

This work contemplates synthesizing M-SCN crystal compounds (M = Hg/Pb/Cu) in the presence of respective metal salts and exogenous ancillary SCN^- ion by slowly evaporating the mixed solvent (CH₃OH + ACN). The complexes were characterized by spectroscopy, SEM/EDX, and X-ray crystallography. The Hg-Complex, Pb-Complex, and Cu-Complex crystallize in the monoclinic space group (Z = 2/4). The crystal packing fascinatingly consists of weak covalent bonding and Pb⋯S contacts of tetrel type bond. Here are the incredible supramolecular topographies delineated by the Hirshfeld surface and 2D fingerprint plot. The B3LYP/6-311++G (d, p) level calculations in the gas phase optimized the compound's geometry. The energy difference (Δ) between HOMO-LUMO and global reactivity parameters investigates the complex's energetic activity. MESP highlights the electrophilic/nucleophilic sites and H-bonding interactions. Molecular docking was conceded with the Gram- + ve bacterium Bacillus Subtilis (PDB ID: 6UF6) and the Gram-ve bacterium Proteus Vulgaris (PDB ID: 5HXW) to authenticate the bactericidal activity. ADME/T explains the various pharmacological properties. In addition, we studied the antibacterial activity with MIC (μg/mL) values and time-kill kinetics against Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6635) as Gram-positive, Pseudomonas aeruginosa (ATCC 27853) and Escherichia coli (ATCC 25922) as Gram-negative bacteria.

Prenatal low-dose methylmercury exposure causes premature neuronal differentiation and autism-like behaviors in a rodent model

Aberrant neurodevelopment is a core deficit of autism spectrum disorder (ASD). Here we ask whether a non-genetic factor, prenatal exposure to the environmental pollutant methylmercury (MeHg), is a contributing factor in ASD onset. We showed that adult mice prenatally exposed to non-apoptotic MeHg exhibited key ASD characteristics, including impaired communication, reduced sociability, and increased restrictive repetitive behaviors, whereas in the embryonic cortex, prenatal MeHg exposure caused premature neuronal differentiation. Further single-cell RNA sequencing (scRNA-seq) analysis disclosed that prenatal exposure to MeHg resulted in cortical radial glial precursors (RGPs) favoring asymmetric differentiation to directly generate cortical neurons, omitting the intermediate progenitor stage. In addition, MeHg exposure in cultured RGPs increased CREB phosphorylation and enhanced the interaction between CREB and CREB binding protein (CBP). Intriguingly, metformin, an FDA-approved drug, can reverse MeHg-induced premature neuronal differentiation via CREB/CBP repulsion. These findings provide insights into ASD etiology, its underlying mechanism, and a potential therapeutic strategy.

Multiple exposure to methylmercury aggravates DNA damage in the BTBR T + Itpr3 tf/J autistic mouse model: the role of DNA repair efficiency

Environmental and genetic factors have been recognized to play major roles in the pathogenesis of autism. Here we examined the BTBR T⁺Itpr3^tf/J (BTBR) mice's susceptibility, an autistic model, to the genotoxic effects and DNA repair dysregulation of methylmercury. Micronuclei formation and oxidative DNA damage were analyzed using the micronucleus/fluorescence in situ hybridization test and modified comet assay, respectively. The results showed higher centromeric-positive micronuclei and oxidative DNA damage in BTBR mice exposed to methylmercury than the unexposed mice, which indicates that mutagenesis aggravated in BTBR mice after methylmercury exposure. Lipid peroxides in BTBR mice were significantly elevated, with a decrease in reduced/oxidized glutathione ratio after methylmercury exposure, indicating an augmenting oxidant-antioxidant imbalance. The expression of several genes involved in DNA repair was markedly altered in BTBR mice after methylmercury exposure as evaluated via PCR array and RT-PCR analyses. Declining of the antioxidant defense and dysregulation in DNA repair process after methylmercury exposure may explain the aggravated genotoxic susceptibility of BTBR mice. Thus, autistic individuals exposed to methylmercury must be under regular medical follow-up through standard timetabled medical laboratory inquiry to allow for early recognition of any mutagenic changes. Additionally, strategies that elevate cellular antioxidants/DNA repair efficiency may counteract methylmercury-induced genotoxicity.

Sulfur amino acid metabolism and related metabotypes of autism spectrum disorder: A review of biochemical evidence for a hypothesis

There are multiple lines of evidence for an impaired sulfur amino acid (SAA) metabolism in autism spectrum disorder (ASD). For instance, the concentrations of methionine, cysteine and S-adenosylmethionine (SAM) in body fluids of individuals with ASD is significantly lower while the concentration of S-adenosylhomocysteine (SAH) is significantly higher as compared to healthy individuals. Reduced methionine and SAM may reflect impaired remethylation pathway whereas increased SAH may reflect reduced S-adenosylhomocysteine hydrolase activity in the catabolic direction. Reduced SAM/SAH ratio reflects an impaired methylation capacity. We hypothesize multiple mechanisms to explain how the interplay of oxidative stress, neuroinflammation, mercury exposure, maternal use of valproate, altered gut microbiome and certain genetic variants may lead to these SAA metabotypes. Furthermore, we also propose a number of mechanisms to explain the metabolic consequences of abnormal SAA metabotypes. For instance in the brain, reduced SAM/SAH ratio will result in melatonin deficiency and hypomethylation of a number of biomolecules such as DNA, RNA and histones. In addition to previously proposed mechanisms, we propose that impaired activity of "radical SAM" enzymes will result in reduced endogenous lipoic acid synthesis, reduced molybdenum cofactor synthesis and impaired porphyrin metabolism leading to mitochondrial dysfunction, porphyrinuria and impaired sulfation capacity. Furthermore depletion of SAM may also lead to the disturbed mTOR signaling pathway in a subgroup of ASD. The proposed "SAM-depletion hypothesis" is an inclusive model to explain the relationship between heterogeneous risk factors and metabotypes observed in a subset of children with ASD.