Prenatal exposure to methylmercury and PCBs affects distinct stages of information processing: an event-related potential study with Inuit children

Developmental exposure to methylmercury alters GAD67 immunoreactivity and morphology of endothelial cells and capillaries of midbrain and hindbrain regions of adult rat offspring

INTRODUCTION

Methylmercury (MeHg) is an environmental contaminant that is of particular concern in Northern Arctic Canadian populations. Specifically, organic mercury compounds such as MeHg are potent toxicants that affect multiple bodily systems including the nervous system. Developmental exposure to MeHg is a major concern, as the developing fetus and neonate are thought to be especially vulnerable to the toxic effects of MeHg. The objective of this study was to examine developmental exposure to low doses of MeHg and effects upon the adult central nervous system (CNS). The doses of MeHg chosen were scaled to be proportional to the concentrations of MeHg that have been reported in human maternal blood samples in Northern Arctic Canadian populations.

METHOD

Offspring were exposed to MeHg maternally where pregnant Sprague Dawley rats were fed cookies that contained MeHg or vehicle (vehicle corn oil; MeHg 0.02 mg/kg/body weight or 2.0 mg/kg/body weight) daily, throughout gestation (21 days) and lactation (21 days). Offspring were not exposed to MeHg after the lactation period and were euthanized on postnatal day 450. Brains were extracted, fixed, frozen, and sectioned for immunohistochemical analysis. A battery of markers of brain structure and function were selected including neuronal GABAergic enzymatic marker glutamic acid decarboxylase-67 (GAD67), apoptotic/necrotic marker cleaved caspase-3 (CC3), catecholamine marker tyrosine hydroxylase (TH), immune inflammatory marker microglia (Cd11b), endothelial cell marker rat endothelial cell antigen-1 (RECA-1), doublecortin (DCX), Bergmann glia (glial fibrillary acidic protein (GFAP)), and general nucleic acid and cellular stains Hoechst, and cresyl violet, respectively. Oxidative stress marker lipofuscin (autofluorescence) was also assessed. Both male and female offspring were included in analysis. Two-way analysis of variance (ANOVA) was utilized where sex and treatment were considered as between-subject factors (p* <0.05). ImageJ was used to assess immunohistochemical results.

RESULTS

In comparison with controls, adult rat offspring exposed to both doses of MeHg were observed to have (1) increased GAD67 in the cerebellum; (2) decreased lipofuscin in the locus coeruleus; and (3) decreased GAD67 in the anterior CA1 region. Furthermore, in the substantia nigra and periaqueductal gray, adult male offspring consistently had a larger endothelial cell and capillary perimeter in comparison to females. The maternal high dose of MeHg influenced RECA-1 immunoreactivity in both the substantia nigra and periaqueductal gray of adult rat offspring, where the latter neuronal region also showed statistically significant decreases in RECA-1 immunoreactivity at the maternal low dose exposure level. Lastly, males exposed to high doses of MeHg during development exhibited a statistically significant increase in the perimeter of endothelial cells and capillaries (RECA-1) in the cerebellum, in comparison to male controls.

CONCLUSION

Findings suggest that in utero and early postnatal exposure to MeHg at environmentally relevant doses leads to long-lasting and selective changes in the CNS. Exposure to MeHg at low doses may affect GABAergic homeostasis and vascular integrity of the CNS. Such changes may contribute to neurological disturbances in learning, cognition, and memory that have been reported in epidemiological studies.

Postnatal methylmercury exposure and neurodevelopmental outcomes at 7 years of age in the Seychelles Child Development Study Nutrition Cohort 2

BACKGROUND

Consumption of fish yields many nutritional benefits, but also results in exposure to methylmercury (MeHg). The developing brain is known to be particularly susceptible to MeHg toxicity in high doses. However, the potential impact of low-level environmental exposure from fish consumption on children's neurodevelopment remains unclear.

METHODS

We investigated postnatal MeHg exposure at 7 years and its association with a battery of 17 neurodevelopmental outcomes in a subset of children (n = 376) from 1535 enrolled mother-child pairs in Nutrition Cohort 2 of the Seychelles Child Development Study (SCDS NC2). Each outcome was modeled in relation to postnatal MeHg exposure using linear regression, adjusting for prenatal MeHg exposure, levels of maternal polyunsaturated fatty acids (PUFA), and several other covariates known to be associated with neurodevelopmental outcomes.

RESULTS

Median postnatal MeHg exposure at 7 years was 2.5 ppm, while the median prenatal MeHg exposure was 3.5 ppm. We found no statistically significant associations between postnatal MeHg exposure and any of the 17 neurodevelopmental outcomes after adjusting for prenatal MeHg exposure and other covariates.

CONCLUSIONS

These findings are consistent with previous cross-sectional analyses of the SCDS Main Cohort. Continued follow-up of the entire NC2 cohort at later ages with repeated exposure measures is needed to further confirm these findings.

Our evolved understanding of the human health risks of mercury

Mercury (Hg) is a chemical of health concern worldwide that is now being acted upon through the Minamata Convention. Operationalizing the Convention and tracking its effectiveness requires empathy of the diversity and variation of mercury exposure and risk in populations worldwide. As part of the health plenary for the 15th International Conference on Mercury as a Global Pollutant (ICMGP), this review paper details how scientific understandings have evolved over time, from tragic poisoning events in the mid-twentieth century to important epidemiological studies in the late-twentieth century in the Seychelles and Faroe Islands, the Arctic and Amazon. Entering the twenty-first century, studies on diverse source-exposure scenarios (e.g., ASGM, amalgams, contaminated sites, cosmetics, electronic waste) from across global regions have expanded understandings and exemplified the need to consider socio-environmental variables and local contexts when conducting health studies. We conclude with perspectives on next steps for mercury health research in the post-Minamata Convention era.

Neuropsychological effects and cognitive deficits associated with exposure to mercury and arsenic in children and adolescents of the Mojana region, Colombia

The present study aims to explore the neuropsychological performance and exposure to mercury (Hg) and arsenic (As) in Colombian children and adolescents considering biomarkers in hair and blood. The total sample consisted of 70 participants from the Mojana region, Colombia. A neuropsychological evaluation protocol was used, consisting of 11 internationally recognized tests, with evidence of national validation and use for measurement in neurotoxicology contexts. A 57.1% of the sample presented levels above the reference value according to the USEPA, the WHO, and the ATSDR for total mercury in hair (HgH), blood mercury (HgB), and/or blood arsenic (AsB). The mean values reported for HgH were 1.76 ± 3.1 μg/g (95% CI 1.02-2.50) with ranges between 0.23 and 17.20; for HgB: 4.11 ± 5.93 μg/l (CI 2.69-5.52), ranging between 0.25 and 25.80, and for AsB: 1.96 ± 2.73 (CI 1.31-2.61) ranging between 0.50 and 15.50. In the comparison of groups in relation to the level of exposure, a significant difference was found (p < 0.05) for the subtest The Boston Naming Test (BNT). Correlation analyses found, on the one hand, significant negative relationships in tests integrated within the verbal (CVB) and executive function (EF) components as well as evidence of positive relationships in the manifestation of errors in their performance with the levels of Hg and/or As transformed by biomarker (Log10). In the linear regression analyses it was found that for each increase in the concentration of HgH, HgB, and AsB it is estimated that, both for the models with and without data adjustment, there is a loss of scores in integrated measures within the CVB and EF for the transformed levels of HgH, HgB, and AsB; and an increase in the reported errors in their processing within these functions. According to these results, exposure to mercury and/or arsenic is related with performance in verbal neuropsychological skills and executive functioning.

Impact of chronic exposure to legacy environmental contaminants on the corpus callosum microstructure: A diffusion MRI study of Inuit adolescents

Exposure to environmental contaminants is an important public health concern for the Inuit population of northern Québec, who have been exposed to mercury (Hg), polychlorinated biphenyls (PCBs) and lead (Pb). During the last 25 years, the Nunavik Child Development Study (NCDS) birth cohort has reported adverse associations between these exposures and brain function outcomes. In the current study, we aimed to determine whether contaminant exposure is associated with alterations of the corpus callosum (CC), which plays an important role in various cognitive, motor and sensory function processes. Magnetic resonance imaging (MRI) was administered to 89 NCDS participants (mean age ± SD = 18.4 ± 1.2). Diffusion-weighted imaging was assessed to characterize the microstructure of the CC white matter in 7 structurally and functionally distinct regions of interest (ROIs) using a tractography-based segmentation approach. The following metrics were computed: fiber tract density, fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD). Multiple linear regression models adjusted for sex, age, current alcohol/drug use and fish nutrients (omega-3 fatty acids and selenium) were conducted to assess the association between diffusion-weighted imaging metrics and Hg, PCB 153 and Pb concentrations obtained at birth in the cord blood and postnatally (mean values from blood samples at 11 and 18 years of age). Exposures were not associated with fiber tract density. Nor were significant associations found with cord and postnatal blood Pb concentrations for FA. However, pre- and postnatal Hg and PCB concentrations were significantly associated with higher FA of several regions of the CC, namely anterior midbody, posterior midbody, isthmus, and splenium, with the most pronounced effects observed in the splenium. FA results were mainly associated with lower RD. This study shows that exposure to Hg and PCB 153 alters the posterior microstructure of the CC, providing neuroimaging evidence of how developmental exposure to environmental chemicals can impair brain function and behavior in late adolescence.

The impact of mercury contamination on human health in the Arctic: A state of the science review

The 2021 Arctic Monitoring and Assessment Programme (AMAP) Mercury (Hg) Assessment is motivated by Arctic populations, and most notably Indigenous Peoples in the region, who are particularly vulnerable to Hg pollution. The objective of this review paper is to answer the following AMAP policy-relevant question: what is the human health impact of Hg pollution in the Arctic? In doing so, this state of the science review paper builds on information published 10 years ago in the last AMAP Hg assessment. The synthesized results demonstrate that: a) global influences (e.g., sources and transport pathways, biogeochemical processes, climate change, globalization) drive Hg exposures into human communities; b) Hg exposures are realized through dietary intake of certain country food items, and that new exposure science approaches are helping to deepen understandings; c) the nutritional and cultural benefits of country foods are immense, though a dietary transition is underway raising concerns over metabolic syndrome and broader issues of food security as well as cultural and social well-being; d) blood Hg measures are among the highest worldwide based on the results of human biomonitoring studies; e) Hg exposures are associated with adverse health outcomes across life stages (e.g., neurodevelopmental outcomes in young children to cardiovascular disease in adults); and f) risk communication needs to be balanced, targeted and clear, culturally appropriate, and be done collaboratively. These synthesized findings are particularly timely and policy-relevant given that the Minamata Convention entered into legal force worldwide in 2017 as a regulatory scheme to reduce the use and environmental release of Hg in order to protect human health and the environment. The Convention was influenced by health concerns raised by northern populations as indicated in the preamble text which makes reference to "the particular vulnerabilities of Arctic ecosystems and Indigenous communities".

Associations between time-weighted postnatal methylmercury exposure from fish consumption and neurodevelopmental outcomes through 24 years of age in the Seychelles Child Development Study Main Cohort

PURPOSE

Methylmercury (MeHg) is a known neurodevelopmental toxicant in sufficient dosage and is universally found in fish. Current fish advisories for children are based on epidemiology studies examining prenatal exposure with a premise that MeHg exposure resulting from children eating fish could also be neurotoxic and have long-term consequences. However, the evidence that this assumption is true is limited. We investigated postnatal MeHg exposure from regular fish consumption using time weighted Hg measurements to determine if there are neurotoxic consequences.

METHODS

We examined 85 neurodevelopmental outcomes measured from ages 9-24 years in the Seychelles Child Development Study Main Cohort (n = 312-550) and examined their association with time-weighted measures of postnatal MeHg exposure in childhood and early adulthood. Postnatal MeHg exposure measured in the first cm of participants' hair samples collected at seven evaluations were used to create two time-weighted (TW) average MeHg exposure metrics, one for childhood (TW-C) and the other for early adulthood (TW-A). TW-C was based on Hg measures at three ages between 6 months and 5.5 years, and TW-A was based on Hg measured at up to four ages between 17 and 24 years. We examined the association between each of these exposure metrics and the neurodevelopmental outcomes using linear regression with adjustment for covariates known to influence neurodevelopmental outcomes.

RESULTS

There were 14 statistically significant associations between a postnatal metric and an endpoint. Six were associated with the TW-C and eight with the TW-A. Thirteen were adverse. Only the TW-C association at 9 years with the Bender Gestalt error score showed improvement. TW-C was adversely associated at 9 years with the Continuous Performance Task risk score, at 22 years with the Boston Naming Test (BNT) total and no cues scores, and at 24 years with the Test of Variables of Attention (TOVA) auditory response time variability and visual response time mean on the logarithmic scale. TW-A was adversely associated at 17 years with the Wisconsin Card Sorting Test % total errors, the Woodcock-Johnson passage comprehension, and the CANTAB rapid visual information processing false alarms, and at 22 years with the BNT total and no cue scores, the CANTAB rapid visual information processing false alarms and the intra-extra dimensional shift total errors and trials.

CONCLUSION

These findings suggest that postnatal MeHg exposure may be adversely associated with neurodevelopmental outcomes in early adulthood. However, the associations are statistical and of unknown, if any, clinical significance. The results need confirmation in other cohorts.

DNA methylation changes associated with prenatal mercury exposure: A meta-analysis of prospective cohort studies from PACE consortium

Mercury (Hg) is a ubiquitous heavy metal that originates from both natural and anthropogenic sources and is transformed in the environment to its most toxicant form, methylmercury (MeHg). Recent studies suggest that MeHg exposure can alter epigenetic modifications during embryogenesis. In this study, we examined associations between prenatal MeHg exposure and levels of cord blood DNA methylation (DNAm) by meta-analysis in up to seven independent studies (n = 1462) as well as persistence of those relationships in blood from 7 to 8 year-old children (n = 794). In cord blood, we found limited evidence of differential DNAm at cg24184221 in MED31 (β = 2.28 × 10-4, p-value = 5.87 × 10-5) in relation to prenatal MeHg exposure. In child blood, we identified differential DNAm at cg15288800 (β = 0.004, p-value = 4.97 × 10-5), also located in MED31. This repeated link to MED31, a gene involved in lipid metabolism and RNA Polymerase II transcription function, may suggest a DNAm perturbation related to MeHg exposure that persists into early childhood. Further, we found evidence for association between prenatal MeHg exposure and child blood DNAm levels at two additional CpGs: cg12204245 (β = 0.002, p-value = 4.81 × 10-7) in GRK1 and cg02212000 (β = -0.001, p-value = 8.13 × 10-7) in GGH. Prenatal MeHg exposure was associated with DNAm modifications that may influence health outcomes, such as cognitive or anthropometric development, in different populations.

Associations between developmental exposure to environmental contaminants and spatial navigation in late adolescence

Inuit communities in Northern Quebec (Canada) are exposed to environmental contaminants, particularly to mercury, lead and polychlorinated biphenyls (PCBs). Previous studies reported adverse associations between these neurotoxicants and memory performance. Here we aimed to determine the associations of pre- and postnatal exposures to mercury, lead and PCB-153 on spatial navigation memory in 212 Inuit adolescents (mean age = 18.5 years) using a computer task which requires learning the location of a hidden platform based on allocentric spatial representation. Contaminant concentrations were measured in cord blood at birth and blood samples at 11 years of age and at time of testing. Multivariate regression models showed that adolescent mercury and prenatal PCB-153 exposures were associated with poorer spatial learning, whereas current exposure to PCB-153 was associated with altered spatial memory retrieval at the probe test trial. These findings suggest that contaminants might be linked to different aspects of spatial navigation processing at different stages.

Exposure to mercury among 9-year-old children and neurobehavioural function

Mercury (Hg) is an environmental neurotoxicant whose main route of exposure in humans is the consumption of seafood. The aim of this study was to explore the relationship between Hg exposure at 9 years old and behaviour assessed at 9 and 11 years old. Study subjects were mother-child pairs participating in the INMA (Environment and Childhood) Project in Valencia (Spain). Total Hg (THg) was measured in hair samples from the children at 9 years old. Behaviour and emotions were assessed at 9 (n = 472) years and 11 (n = 385) years of age using the Child Behaviour Checklist test (CBCL) and the Conners Parents Rating Scale-Revised: Short Form (CPRS-R:S). Furthermore, the attention function was assessed by the Attention Network Test at 11 years old. Socio-demographic, lifestyle and dietary information was collected through questionnaires during pregnancy and childhood. Polymorphism in BDNF, APOE and GSTP1 were genotyped in cord blood DNA. Multivariable negative binomial regression models were built in order to study the association between THg concentrations and the scores obtained by the children at 9 and 11 years old. Effect modification by sex and genetic polymorphisms was assessed. The association between Hg levels and CBCL scores was positive (worse neurobehavioural development) for the CBCL internalizing and total problem scales (Incidence Rate Ratio [95% confidence interval] = 1.07 [1.01, 1.13] and 1.05 [0.99, 1.11], respectively). The association between Hg and the externalizing and total problems CBCL scales and the Attention Deficit Hyperactivity Disorder (ADHD) index of the CPRS-R:S was different according to sex, with boys obtaining worse scores with increasing Hg, compared to girls. Statistically significant interactions were also observed for genetic polymorphisms affecting the association between early exposure to Hg and both CBCL and CPRS-R:S scores. In conclusion, postnatal Hg exposure is associated with poorer neurobehavioural development in 9- and 11-year-old children. Sex and the presence of certain genetic polymorphisms modified this association.

Human Health and Ocean Pollution

Background

Pollution - unwanted waste released to air, water, and land by human activity - is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems. Ocean pollution is an important, but insufficiently recognized and inadequately controlled component of global pollution. It poses serious threats to human health and well-being. The nature and magnitude of these impacts are only beginning to be understood.

Goals

(1) Broadly examine the known and potential impacts of ocean pollution on human health. (2) Inform policy makers, government leaders, international organizations, civil society, and the global public of these threats. (3) Propose priorities for interventions to control and prevent pollution of the seas and safeguard human health.

Methods

Topic-focused reviews that examine the effects of ocean pollution on human health, identify gaps in knowledge, project future trends, and offer evidence-based guidance for effective intervention.

Environmental Findings

Pollution of the oceans is widespread, worsening, and in most countries poorly controlled. It is a complex mixture of toxic metals, plastics, manufactured chemicals, petroleum, urban and industrial wastes, pesticides, fertilizers, pharmaceutical chemicals, agricultural runoff, and sewage. More than 80% arises from land-based sources. It reaches the oceans through rivers, runoff, atmospheric deposition and direct discharges. It is often heaviest near the coasts and most highly concentrated along the coasts of low- and middle-income countries. Plastic is a rapidly increasing and highly visible component of ocean pollution, and an estimated 10 million metric tons of plastic waste enter the seas each year. Mercury is the metal pollutant of greatest concern in the oceans; it is released from two main sources - coal combustion and small-scale gold mining. Global spread of industrialized agriculture with increasing use of chemical fertilizer leads to extension of Harmful Algal Blooms (HABs) to previously unaffected regions. Chemical pollutants are ubiquitous and contaminate seas and marine organisms from the high Arctic to the abyssal depths.

Ecosystem Findings

Ocean pollution has multiple negative impacts on marine ecosystems, and these impacts are exacerbated by global climate change. Petroleum-based pollutants reduce photosynthesis in marine microorganisms that generate oxygen. Increasing absorption of carbon dioxide into the seas causes ocean acidification, which destroys coral reefs, impairs shellfish development, dissolves calcium-containing microorganisms at the base of the marine food web, and increases the toxicity of some pollutants. Plastic pollution threatens marine mammals, fish, and seabirds and accumulates in large mid-ocean gyres. It breaks down into microplastic and nanoplastic particles containing multiple manufactured chemicals that can enter the tissues of marine organisms, including species consumed by humans. Industrial releases, runoff, and sewage increase frequency and severity of HABs, bacterial pollution, and anti-microbial resistance. Pollution and sea surface warming are triggering poleward migration of dangerous pathogens such as the Vibrio species. Industrial discharges, pharmaceutical wastes, pesticides, and sewage contribute to global declines in fish stocks.

Human Health Findings

Methylmercury and PCBs are the ocean pollutants whose human health effects are best understood. Exposures of infants in utero to these pollutants through maternal consumption of contaminated seafood can damage developing brains, reduce IQ and increase children's risks for autism, ADHD and learning disorders. Adult exposures to methylmercury increase risks for cardiovascular disease and dementia. Manufactured chemicals - phthalates, bisphenol A, flame retardants, and perfluorinated chemicals, many of them released into the seas from plastic waste - can disrupt endocrine signaling, reduce male fertility, damage the nervous system, and increase risk of cancer. HABs produce potent toxins that accumulate in fish and shellfish. When ingested, these toxins can cause severe neurological impairment and rapid death. HAB toxins can also become airborne and cause respiratory disease. Pathogenic marine bacteria cause gastrointestinal diseases and deep wound infections. With climate change and increasing pollution, risk is high that Vibrio infections, including cholera, will increase in frequency and extend to new areas. All of the health impacts of ocean pollution fall disproportionately on vulnerable populations in the Global South - environmental injustice on a planetary scale.

Conclusions

Ocean pollution is a global problem. It arises from multiple sources and crosses national boundaries. It is the consequence of reckless, shortsighted, and unsustainable exploitation of the earth's resources. It endangers marine ecosystems. It impedes the production of atmospheric oxygen. Its threats to human health are great and growing, but still incompletely understood. Its economic costs are only beginning to be counted.Ocean pollution can be prevented. Like all forms of pollution, ocean pollution can be controlled by deploying data-driven strategies based on law, policy, technology, and enforcement that target priority pollution sources. Many countries have used these tools to control air and water pollution and are now applying them to ocean pollution. Successes achieved to date demonstrate that broader control is feasible. Heavily polluted harbors have been cleaned, estuaries rejuvenated, and coral reefs restored.Prevention of ocean pollution creates many benefits. It boosts economies, increases tourism, helps restore fisheries, and improves human health and well-being. It advances the Sustainable Development Goals (SDG). These benefits will last for centuries.

Recommendations

World leaders who recognize the gravity of ocean pollution, acknowledge its growing dangers, engage civil society and the global public, and take bold, evidence-based action to stop pollution at source will be critical to preventing ocean pollution and safeguarding human health.Prevention of pollution from land-based sources is key. Eliminating coal combustion and banning all uses of mercury will reduce mercury pollution. Bans on single-use plastic and better management of plastic waste reduce plastic pollution. Bans on persistent organic pollutants (POPs) have reduced pollution by PCBs and DDT. Control of industrial discharges, treatment of sewage, and reduced applications of fertilizers have mitigated coastal pollution and are reducing frequency of HABs. National, regional and international marine pollution control programs that are adequately funded and backed by strong enforcement have been shown to be effective. Robust monitoring is essential to track progress.Further interventions that hold great promise include wide-scale transition to renewable fuels; transition to a circular economy that creates little waste and focuses on equity rather than on endless growth; embracing the principles of green chemistry; and building scientific capacity in all countries.Designation of Marine Protected Areas (MPAs) will safeguard critical ecosystems, protect vulnerable fish stocks, and enhance human health and well-being. Creation of MPAs is an important manifestation of national and international commitment to protecting the health of the seas.

Blood mercury and plasma polychlorinated biphenyls concentrations in pregnant Inuit women from Nunavik: Temporal trends, 1992-2017

The Inuit of Nunavik (Northern Quebec, Canada) are exposed to polychlorinated biphenyls (PCBs) and mercury (Hg) through their consumption of marine country foods. A temporal trend study was initiated in 1992 to monitor circulating levels of PCBs and Hg in pregnant Inuit women, since the fetus is most at risk of adverse health effects. We set out (1) to describe temporal trends of PCBs and Hg levels in pregnant Nunavik women between 1992 and 2017; (2) to determine the prevalence of participants exceeding the guidance values in 2017; (3) to investigate relations between marine country food intake and contaminant levels over the study period. A total of 559 pregnant women provided a blood sample for contaminant analysis from 1992 to 2017. PCB congeners were quantified in plasma (serum) by gas chromatography (GC) coupled to electron capture detection or mass spectrometry (MS). We determined whole blood mercury concentration by cold vapor atomic absorption or inductively-coupled plasma MS. We performed multilevel modeling to assess temporal trends in contaminant levels and relations with marine country food consumption. Concentrations of total PCBs and Hg decreased by 84% and 65% between 1992 and 2017, respectively. Nevertheless, 10% and 22% of women in 2017 exceeded guidance values for PCBs and Hg, respectively. While the decline in marine country food intake is the only factor associated with decreasing Hg levels, other factors may explain the decline in PCB levels. Despite the significant decline in PCBs and Hg levels from 1992 to 2017, exposure to these contaminants is still quite prevalent among pregnant Nunavik women. Most of the decline in Hg exposure is likely due to a shift away from marine country foods to store-bought foods, which is a concern given the cultural and nutritional importance of country foods and the high food insecurity that prevails in Nunavik.

Flame retardants and neurodevelopment: An updated review of epidemiological literature

Purpose of Review

Flame retardant (FR) compounds can adversely impact neurodevelopment. This updated literature review summarizes epidemiological studies of FRs and neurotoxicity published since 2015, covering historical (polybrominated biphenyls [PBBs], polychlorinated biphenyls [PCBs]), contemporary (polybrominated diphenyl ethers [PBDEs], hexabromocyclododecane [HBCD], and tetrabromobisphenol A [TBBPA]), and current-use organophosphate FRs (OPFRs) and brominated FRs (2-ethylhexyl 2,3,4,5-tetrabromobezoate [EH-TBB] TBB), bis(2-ethylhexyl) tetrabromophthalate [BEH-TEBP]), focusing on prenatal and postnatal periods of exposure.

Recent Findings

Continuing studies on PCBs still reveal adverse associations on child cognition and behavior. Recent studies indicate PBDEs are neurotoxic, particularly for gestational exposures with decreased cognition and increased externalizing behaviors. Findings were suggestive for PBDEs and other behavioral domains and neuroimaging. OPFR studies provide suggestive evidence of reduced cognition and more behavioral problems.

Summary

Despite a lack of studies of PBBs, TBBPA, EH-TBB, and BEH-TEBP, and only two studies of HBCD, recent literature of PCBs, PBDEs, and OPFRs are suggestive of developmental neurotoxicity, calling for more studies of OPFRs.

Towards a better understanding of the benefits and risks of country food consumption using the case of walruses in Nunavik (Northern Quebec, Canada)

Food insecurity affects Inuit communities. One solution is to consume locally harvested foods, named country foods. However, some country foods are not eaten as often as before, and pressures including contaminants and environmental changes threaten the health of Arctic fauna, thus its suitability for local consumption. By combining Inuit Knowledge with laboratory data, our study assessed the benefits and risks of walrus consumption by Inuit in Nunavik, Québec, Canada. It aimed to increase understanding of: 1) the hunt of healthy Atlantic walruses (Odobenus rosmarus rosmarus); 2) the safe preparation of walruses; 3) the nutritional benefits and risks of consuming walruses. To do so, we interviewed 34 hunters and Elders from Nunavik. Levels of mercury, omega-3 polyunsaturated fatty acids and selenium were evaluated from locally harvested walruses. Through the Nunavik Trichinellosis Prevention Program, a total of 755 Atlantic walrus samples, collected between 1994 and 2013, were tested for Trichinella nativa. Information on botulism was reviewed. While interviews informed on how to select healthy walruses and prepare them for consumption, laboratory analyses revealed that walruses had elevated levels of omega-3 fatty acids and selenium but low levels of mercury compared to some other wildlife. Only 3% of the 755 walruses were infected with T. nativa. Most walruses' infections were found within individuals from the South East Hudson Bay stock, where Inuit have thus decided to stop hunting since mid-2000s. Finally, although the number of outbreaks of trichinellosis related to the consumption of walruses has significantly reduced in Nunavik, botulism could continue to be an issue when igunaq (i.e. aged walrus) is not properly prepared. With the support of the Nunavik Trichinellosis Prevention Program and transmission of Inuit knowledge on igunaq preparation, the consumption of Atlantic walruses has the potential to help address issues related to food insecurity in Nunavik in the future.

Prenatal exposure to legacy contaminants and visual acuity in Canadian infants: a maternal-infant research on environmental chemicals study (MIREC-ID)

BACKGROUND

Prenatal exposure to environmental contaminants can have deleterious effects on child development. While psychomotor, cognitive and behavioural outcomes have been investigated in relation to chronic exposure, the associations with visual functions remains unclear. The present study's aim was to assess the associations of prenatal exposure to legacy persistent organic pollutants and heavy metals with visual acuity in Canadian infants. The potential protective effects of selenium against mercury toxicity were also examined.

METHODS

Participants (mean corrected age = 6.6 months) were part of the Maternal-Infant Research on Environmental Chemicals (MIREC) study. Concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), lead and mercury were measured in maternal blood during pregnancy, as well as in the cord blood. The Teller acuity card test (TAC) (n = 429) and the visual evoked potentials in a sub-group (n = 63) were used to estimate behavioural and electrophysiological visual acuity, respectively. Multivariable linear regression models were used to investigate the relationship between exposure to each contaminant and visual acuity measures, while controlling for potential confounders. Breastmilk selenium, which was available for about half of the TAC and VEP samples, was also taken into account in the mercury models as exploratory analyses.

RESULTS

We observed no significant associations between exposure to any contaminants and TAC. Analyses revealed a negative trend (p values < 0.1) between cord blood lead and mercury and electrophysiological visual acuity, whereas PCB and PBDE showed no association. When adding breastmilk selenium concentration to the mercury models, this association became statistically significant for cord concentrations (β = - 3.41, 95% CI = - 5.96,-0.86), but also for blood levels at 1st and 3rd trimesters of pregnancy (β = - 3.29, 95% CI = - 5.69,-0.88). However, further regression models suggested that this change in estimates might not be due to adjustment for selenium, but instead to a change in the study sample.

CONCLUSIONS

Our results suggest that subtle, but detectable alterations of infant electrophysiological visual acuity can be identified in a population prenatally exposed to low mercury concentrations. Compared to behavioural visual acuity testing, electrophysiological assessment may more sensitive in detecting visual neurotoxicity in relation with prenatal exposure to mercury.

Determinants of selenoneine concentration in red blood cells of Inuit from Nunavik (Northern Québec, Canada)

Selenium (Se) is a trace mineral essential to human health, and is especially abundant in marine foods consumed by Inuit populations in Nunavik (northern Quebec, Canada), leading to exceptionally high whole blood Se levels. While most epidemiological studies to date examine plasma or whole blood Se, little is known about the health implications of specific Se biomarkers (e.g. selenoproteins and small Se compounds). Selenoneine, a novel Se compound, is found in high concentrations in marine foods (and particularly beluga mattaaq) and the red blood cells (RBCs) of populations that consume them. We report here RBC selenoneine concentrations in a population of Inuit adults (n = 885) who participated in the Qanuippitaa? 2004 survey. Simple associations between RBC selenoneine and other Se and mercury (Hg) biomarkers were assessed using Spearman correlations and linear regressions. Wilcoxon ranksum tests were used to examine differences in biomarkers and characteristics between tertiles of RBC selenoneine concentration. A multiple linear regression analysis was used to determine factors (sociodemographic, lifestyle, and dietary) associated with RBC selenoneine concentrations. Selenoneine comprised a large proportion of whole blood Se and RBC Se in this population. Age and sex-adjusted geometric mean RBC selenoneine concentration was 118 μg/L (range: 1-3226 μg/L) and was much higher (p = 0.001) among women (150.3 μg/L) than men (87.6 μg/L) across all regions of Nunavik after controlling for age, region, and diet. RBC selenoneine was highly correlated with RBC Se (r_s = 0.96, p < 0.001) and whole blood Se (r_s = 0.89, p < 0.001), but only weakly correlated with plasma Se (r_s = 0.13, p < 0.001). Overall, increasing age (standardized β = 0.24), higher body-mass index (BMI; β = 0.08), female sex (β = 0.10), living in a Hudson Strait community (compared to Hudson Bay and Ungava Bay; β = 0.38), and consuming beluga mattaaq (g/day; β = 0.19) were positively associated with RBC selenoneine. Meanwhile, consumption of market meats (g/day; β = -0.07) was negatively associated with RBC selenoneine. RBC selenoneine is an important biomarker of Se dietary intake from local marine foods in Inuit populations. Further studies are needed to examine the health effects of selenoneine intake and the underlying mechanisms for sex differences among Inuit populations.

Blood and hair mercury concentrations among Cree First Nations of Eeyou Istchee (Quebec, Canada): time trends, prenatal exposure and links to local fish consumption

To describe exposure to methylmercury among Cree, focusing on women of childbearing age, we used data from 2 studies. Multiple regression was employed to examine associations between blood and hair mercury concentrations and consumption of locally harvested fish. Approximately 9.9% of non-pregnant women aged 15-44 y and 3.9% of pregnant women required follow-up according to Health Canada's blood mercury guidance value of 40 nmol/L. 8% of hair mercury observations in the non-pregnant women and 2.5% among pregnant women exceeded the equivalent threshold of 10 nmol/g. The geometric mean blood mercury concentration was 12.7 nmol/L in 1,429 persons aged 8 and over, and 17.7 nmol/L in adults aged 18 and older. The proportion of hair mercury concentrations greater than 12.5 nmol/g decreased in all age-sex groups when comparing the 2002-2009 data to published values for 1993-1994. Among women of childbearing age, local fish consumption was associated with increased blood and hair mercury concentrations. While over 90% of women of childbearing age in this population have acceptable levels of mercury, ongoing intake of mercury suggests that their consumption of fish with known high mercury content be minimised. Reducing consumption of fish known to be high in mercury content needs to be balanced with promoting ongoing connection to Cree culture and land-based activities that are also important determinants of health.

Temporal trends of contaminants in Arctic human populations

The first Arctic Monitoring and Assessment Programme (AMAP) report was published in 1998 and followed by three assessment reports of human health (AMAP 2003, 2009 and 2015). The focus area of the AMAP reports was to monitor levels of environmental contaminants in the Arctic and to assess the health effects connected with detected levels in Arctic countries. This review gives an overview of temporal trends of contaminants and their health effects in humans of the Arctic based on data published by AMAP, as well as Russian scientific literature. Several time series of 31 contaminants in humans of the Arctic from different cohorts are reported. The lengths of time series and periods covered differ from each other. International restrictions have decreased the levels of most persistent organic pollutants in humans and food webs. Percentage changes for contaminants in human biological matrices (blood samples from children, mothers and males and breast milk samples) for the period of sampling showed declining trends in most of the monitored Arctic locations, with the exception of oxychlordane, hexachlorobenzene (HCB), 2,2',4,4',5,5'-hexabromodiphenyl ether (PBDE153) and perfluorinated compounds (PFCs).

Polychlorinated biphenyls (PCBs) as sentinels for the elucidation of Arctic environmental change processes: a comprehensive review combined with ArcRisk project results

Polychlorinated biphenyls (PCBs) can be used as chemical sentinels for the assessment of anthropogenic influences on Arctic environmental change. We present an overview of studies on PCBs in the Arctic and combine these with the findings from ArcRisk-a major European Union-funded project aimed at examining the effects of climate change on the transport of contaminants to and their behaviour of in the Arctic-to provide a case study on the behaviour and impact of PCBs over time in the Arctic. PCBs in the Arctic have shown declining trends in the environment over the last few decades. Atmospheric long-range transport from secondary and primary sources is the major input of PCBs to the Arctic region. Modelling of the atmospheric PCB composition and behaviour showed some increases in environmental concentrations in a warmer Arctic, but the general decline in PCB levels is still the most prominent feature. 'Within-Arctic' processing of PCBs will be affected by climate change-related processes such as changing wet deposition. These in turn will influence biological exposure and uptake of PCBs. The pan-Arctic rivers draining large Arctic/sub-Arctic catchments provide a significant source of PCBs to the Arctic Ocean, although changes in hydrology/sediment transport combined with a changing marine environment remain areas of uncertainty with regard to PCB fate. Indirect effects of climate change on human exposure, such as a changing diet will influence and possibly reduce PCB exposure for indigenous peoples. Body burdens of PCBs have declined since the 1980s and are predicted to decline further.

Prenatal mercury exposure and child neurodevelopment outcomes at 18 months: Results from the Mediterranean PHIME cohort

INTRODUCTION

Neurotoxicity due to acute prenatal exposure to high-dose of mercury (Hg) is well documented. However, the effect of prenatal exposure to low Hg levels on child neurodevelopment and the question about "safety" of fish-eating during pregnancy remain controversial. International comparisons of Hg concentrations in mother-child biological samples and neurodevelopmental scores embedded in birth cohort studies may provide useful evidence to explore this issue.

MATERIALS AND METHODS

The Mediterranean (Italy, Slovenia, Croatia, and Greece) cohort study included 1308 mother-child pairs enrolled in the Public Health Impact of long-term, low-level, Mixed Element exposure in a susceptible population EU Sixth Framework Programme (PHIME). Maternal hair and venous blood, cord blood and breast milk samples were collected, and total Hg (THg) levels were measured. Demographic and socioeconomic information, lifestyles and nutritional habits were collected through questionnaires at different phases of follow-up. Children at 18 months of age underwent neurodevelopmental testing using the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III). Multivariate linear and logistic regressions were performed, for each country, to assess the association between THg and BSID-III scores, obtaining adjusted β coefficients and odds ratios (ORs). These values were used to conduct a meta-analysis, to explore possible heterogeneity among countries and to obtain combined estimates of the association between THg exposure and BSID-III scores.

RESULTS

Median THg (ng/g) was: 704 in maternal hair, 2.4 in maternal blood, 3.6 in cord blood, and 0.6 in breast milk. THg concentrations were highest in Greece and lowest in Slovenia. BSID-III neurodevelopmental scores were higher in Croatia and Slovenia. The meta-analysis of multivariate linear models found an overall positive association between language composite score and receptive communication scaled score and increasing THg in maternal hair (n = 1086; β = 0.55; 95%CI: 0.05-1.05 and n = 1075; β = 0.12; 95%CI: 0.02-0.22, respectively). The meta-analysis of logistic regression models showed that the overall adjusted OR between THg in cord blood and suboptimal gross motor score was borderline significant (n = 882; OR = 1.03; 95%CI: 1.00-1.07). Heterogeneity was found across the four sub-cohorts for language composite score in maternal blood, and for fine motor scaled score in cord blood and breast milk. Language composite score and THg concentrations in maternal venous blood were positively related (n = 58; β = 4.29; CI95% (-0.02, 8.60)) in Croatia and an increase of 1 ng/g of THg in maternal venous blood was associated with a reduced risk for children to fall in the lowest quintile of language score by 31% (n = 58; OR = 0.69; CI 95%: 0.37, 1.01). The comparison of β coefficients obtained by multiple linear regression model showed an inverse association between fine motor score and THg concentrations in cord blood for Croatia (n = 54; β = -0.53; CI 95%: -1.10, 0.04) and Slovenia (n = 225; β = -0.25; CI 95%: -0.49, -0.01). In Slovenia THg level in breast milk was associated with suboptimal fine motor performance (n = 195; OR = 5.25; CI 95%: 1.36, 21.10).

CONCLUSIONS

This study showed an inverse relation between THg levels and developmental motor scores at 18 months, although the evidence was weak and partially internally and externally inconsistent. No evidence of detrimental effects of THg was found for cognitive and language outcomes at these concentrations and age.

Ambient Air Exposure to PCBs: Regulation and Monitoring at Five Contaminated Sites in EPA Regions 1, 2, 4, and 5

Existing regulations seek to protect the public from exposure to polychlorinated biphenyls (PCBs) in food, water, and soil. Exposure to PCBs in ambient air has recently been given explicit consideration in the human health risk assessments that form the basis of risk management decisions at contaminated sites. The objective of this paper is to examine how ambient air exposure to PCBs is regulated and monitored at five contaminated sites in the United States. We reviewed online accessible materials (including Environmental Protection Agency-site specific websites, data repositories, and other agency websites). Results indicate that the five sites vary in regard to the measured PCB concentrations in air, the sampling and monitoring methodologies, and the established site-specific guidelines/standards and their basis. We conclude that current practices may not adequately protect those living or working near these sites from airborne PCB exposure and that regulations should include recognition of exposure to indoor sources.

Health effects associated with measured levels of contaminants in the Arctic

The Human Health Assessment Group has over the past decade recommended that effect studies be conducted in the circumpolar area. Such studies examine the association between contaminant exposure in the Arctic populations and health effects. Because foetuses and young children are the most vulnerable, effect studies are often prospective child cohort studies. The emphasis in this article is on a description of the effects associated with contaminant exposure in the Arctic. The main topics addressed are neurobehavioural, immunological, reproductive, cardiovascular, endocrine and carcinogenic effect. For each topic, the association between exposure and effects is described, and some results are reported for similar studies outside the Arctic.

Plasma levels of selenium-containing proteins in Inuit adults from Nunavik

Selenium (Se) is highly abundant in marine foods traditionally consumed by Inuit of Nunavik (Northern Quebec, Canada) and accordingly, their Se intake is among the highest in the world. However, little is known regarding the biological implications of this high Se status in this Arctic indigenous population. We used a method combining affinity chromatography and inductively coupled plasma-mass spectrometry with quantification by post-column isotope dilution to determine total Se levels and concentrations of Se-containing proteins in archived plasma samples of Inuit adults who participated to the 2004 Nunavik Inuit Health Survey (N = 852). Amounts of mercury (Hg) associated with Se-containing proteins were also quantified. Results show that glutathione peroxidase 3 (GPx3), selenoprotein P (SelP) and selenoalbumin (SeAlb) represented respectively 25%, 52% and 23% of total plasma Se concentrations. In addition, small amounts of Hg co-eluted with each Se-containing protein and up to 50% of plasma Hg was associated to SelP. Total plasma Se concentrations (median = 139 μg L− 1; interquartile range (IQR) = 22.7 μg L− 1) were markedly lower and less variable than whole blood Se concentration (median = 261 μg L− 1, IQR = 166 μg L− 1). A non linear relation was observed between whole blood Se and plasma Se levels, with plasma Se concentrations leveling off at approximately 200 μg L− 1, whereas 16% and 3% of individuals exhibited whole blood concentrations higher than 500 μg L− 1 and 1000 μg L− 1, respectively. In contrast, a linear relationship was previously reported in communities consuming Brazil nuts which are rich Se, mainly present as selenomethionine. This suggests that a different selenocompound, possibly selenoneine, is present in the Arctic marine food chain and accumulates in the blood cellular fraction of Inuit.

Altered fine motor function at school age in Inuit children exposed to PCBs, methylmercury, and lead

BACKGROUND

Motor deficits have frequently been reported in methylmercury (MeHg) poisoning in adults. However, whether exposure to neurotoxic contaminants from environmental sources early in life is associated with neuromotor impairments has received relatively little attention. This study examines the relation of developmental exposure to MeHg, polychlorinated biphenyls (PCBs), and lead to motor function in school-age Inuit children exposed through their traditional diet.

METHODS

In a prospective study in Nunavik, children (mean age=11.3years) were assessed on a battery of fine motor tasks, namely the Stanford-Binet Copying subtest (N=262), the Santa Ana Form Board, and the Finger Tapping Test (N=215). The relation of mercury (Hg; as an index of MeHg exposure), PCB congener 153 (PCB153), and lead concentrations in cord and current blood samples to task performance was examined using linear regression analyses.

RESULTS

After adjustment for potential confounders and control for the other contaminants, higher current PCB concentrations were associated with poorer Santa Ana Form Board and Finger Tapping performance. Results were virtually identical when PCB153 was replaced by other PCB congeners. Higher current Hg levels were independently associated with poorer Finger Tapping performance.

CONCLUSIONS

This is the first prospective longitudinal study in children to provide evidence of neuromotor impairments associated with postnatal exposure to seafood contaminants from environmental sources. Fine motor speed appears particularly sensitive to the effects of postnatal PCB exposure, which is unusually high in this population. Results with postnatal MeHg are concordant with previous cross-sectional studies with children and adults.

Mechanistic polychlorinated biphenyl exposure modeling of mothers in the Canadian Arctic: the challenge of reliably establishing dietary composition

BACKGROUND

Traditional food (TF) consumption represents the main route of persistent organic pollutant (POP) exposure for indigenous Arctic Canadians. Ongoing dietary transitions away from TFs and toward imported foods (IFs) may contribute to decreasing POP exposures observed in these groups.

METHODS

To explore this issue, we combined the global fate and transport model GloboPOP and the human food chain bioaccumulation model ACC-Human Arctic to simulate polychlorinated biphenyl (PCB) exposure in two indigenous Arctic Canadian communities from the Inuvik region, Northwest Territories and Baffin region, Nunavut. Using dietary survey information from initial (1996-98) and follow-up (2005-07) biomonitoring campaigns in Inuvik and Baffin, we simulated PCB exposures (PCB-118, -138, -153, and -180) for each individual study participant and also whole study populations.

RESULTS

TF intake rates, particularly of marine mammals (MMs), were the most important predictors of modeled PCB exposure, while TF consumption did not associate consistently with measured PCB exposures. Further, reported mean TF intake increased from baseline to follow-up in both Inuvik (from 8 to 183gd(-1)) and Baffin (from 60 to 134gd(-1)), opposing both the expected dietary transition direction and the observed decrease in human PCB exposures in these communities (ΣPCB Inuvik: from 43 to 29ngglipid(-1), ΣPCB Baffin: from 213 to 82ngglipid(-1)). However dietary questionnaire data are frequently subject to numerous biases (e.g., recall, recency, confirmation), and thus casts doubt on the usefulness of these data.

CONCLUSIONS

Ultimately, our model's capability to reproduce historic PCB exposure data in these two groups was highly sensitive to TF intake, further underscoring the importance of accurate TF consumption reporting, and clarification of the role of dietary transitions in future POP biomonitoring of indigenous Arctic populations.

Early Developmental Low-Dose Methylmercury Exposure Alters Learning and Memory in Periadolescent but Not Young Adult Rats

Few studies have assessed the effects of developmental methylmercury (MeHg) exposure on learning and memory at different ages. The possibility of the amelioration or worsening of the effects has not been sufficiently investigated. This study aimed to assess whether low-dose MeHg exposure in utero and during suckling induces differential disturbances in learning and memory of periadolescent and young adult rats. Four experimental groups of pregnant Sprague-Dawley rats were orally exposed to MeHg or vehicle from gestational day 5 to weaning: (1) control (vehicle), (2) 250 μg/kg/day MeHg, (3) 500 μg/kg/day MeHg, and (4) vehicle, and treated on the test day with MK-801 (0.15 mg/kg i.p.), an antagonist of the N-methyl D-aspartate receptor. The effects were evaluated in male offspring through the open field test, object recognition test, Morris water maze, and conditioned taste aversion. For each test and stage assessed, different groups of animals were used. MeHg exposure, in a dose-dependent manner, disrupted exploratory behaviour, recognition memory, spatial learning, and acquisition of aversive memories in periadolescent rats, but alterations were not observed in littermates tested in young adulthood. These results suggest that developmental low-dose exposure to MeHg induces age-dependent detrimental effects. The relevance of decreasing exposure to MeHg in humans remains to be determined.

Assessing determinants of maternal blood concentrations for persistent organic pollutants and metals in the eastern and western Canadian Arctic

Aboriginal peoples in the Canadian Arctic are exposed to persistent organic pollutants (POPs) and metals mainly through their consumption of a traditional diet of wildlife items. Recent studies indicate that many human chemical levels have decreased in the north, likely due to a combination of reduced global chemical emissions, dietary shifts, and risk mitigation efforts by local health authorities. Body burdens for chemicals in mothers can be further offset by breastfeeding, parity, and other maternal characteristics. We have assessed the impact of several dietary and maternal covariates following a decade of awareness of the contaminant issue in northern Canada, by performing multiple stepwise linear regression analyses from blood concentrations and demographic variables for 176 mothers recruited from Nunavut and the Northwest Territories during the period 2005-2007. A significant aboriginal group effect was observed for the modeled chemicals, except for lead and cadmium, after adjusting for covariates. Further, blood concentrations for POPs and metals were significantly associated with at least one covariate of older age, fewer months spent breastfeeding, more frequent eating of traditional foods, or smoking during pregnancy. Cadmium had the highest explained variance (72.5%) from just two significant covariates (current smoking status and parity). Although Inuit participants from the Northwest Territories consumed more traditional foods in general, Inuit participants from coastal communities in Nunavut continued to demonstrate higher adjusted blood concentrations for POPs and metals examined here. While this is due in part to a higher prevalence of marine mammals in the eastern Arctic diet, it is possible that other aboriginal group effects unrelated to diet may also contribute to elevated chemical body burdens in Canadian Arctic populations.

Are ASD and ADHD a Continuum? A Comparison of Pathophysiological Similarities Between the Disorders

OBJECTIVE

The objective of this study was to review and compare the similarities between autism spectrum disorder (ASD) and ADHD with regard to symptomatology, neurological deficits, metabolic and endocrine-related conditions, and brain pathology.

METHOD

A comprehensive review of the relevant research literature was carried out.

RESULTS

A number of important similarities between ASD and ADHD were identified, including recent increases in prevalence, male-biased incidence, shared involvement of sensory processing, motor and impulse control, abnormal patterns of neural connectivity, and sleep disturbances. Studies suggest involvement of androgen metabolism, impaired methylation, and heavy metal toxicity as possible contributing factors for both disorders.

CONCLUSION

ASD and ADHD share a number of features and pathophysiological conditions, which suggests that the two disorders may be a continuum and have a common origin.

Neurotoxicant exposure during pregnancy is a confounder for assessment of iodine supplementation on neurodevelopment outcome

CONTEXT

The developing brain is vulnerable to iodine deficiency (ID) and environmental neuro-toxicants.

OBJECTIVES

To assess neurocognitive development of children whose mothers have received (or not) iodine supplementation during pregnancy, in an area of borderline ID, while assessing in utero exposure to environmental neuro-toxicants.

DESIGN/PATIENTS

Among 86 children born from normal euthyroid women who participated in our prospective interventional study on iodine supplementation (150 μg/day) started early in pregnancy, 44 (19 with iodine supplementation, 25 controls) were assessed at two years using the Bayley test. Information on parents' education and habits (smoking), and on child development was recorded. Thyroid tests at each trimester of pregnancy and on cord blood (CB) were available, as well as milk concentrations of selected environmental compounds known for their neurotoxicity, including heavy metals and PCBs.

RESULTS

There was no difference in Bayley tests for children born to mothers with and without iodine supplementation, but sample size was small. Language and Social-Emotional Scales were negatively correlated with TBG at all times tested, while PCB 118 correlated negatively with all Language scales. Among maternal and CB thyroid tests, only CB thyroglobulin, the best marker of iodine status, correlated (negatively) with neurodevelopment scales (Motor and Expressive Language).

CONCLUSIONS

This pilot study suggests that PCB118 has a negative impact on neurocognitive development, possibly mitigating the benefit of iodine supplementation in an area of borderline ID. We propose that exposure to environmental neurotoxicants should be taken into account when designing studies on the benefit of iodine supplementation in pregnancy. The potential interactions between TBG, environmental neurotoxicants and brain development warrant further studies.

Local country food sources of methylmercury, selenium and omega-3 fatty acids in Nunavik, Northern Quebec

Country foods are central to Inuit culture and replete in selenium (Se) and long-chain omega-3 polyunsaturated fatty acids (n-3 PUFA). However, some marine country foods bioaccumulate high concentrations of methylmercury (MeHg). Se and n-3 are associated with several health benefits in Nunavik, Northern Quebec, but, recent studies show that prenatal MeHg exposure is associated with visual, cognitive and behavioral deficit later in childhood. The study objectives are to identify contemporary country food sources of MeHg, Se and long-chain n-3 PUFA in Nunavik, particularly among childbearing-age women, taking into account regional differences in consumption profiles. The contribution of different country foods to daily MeHg, Se, long-chain n-3 PUFA intake (μg/kg body weight/day) was estimated using: (i) country food consumption and blood biomarkers data from the 2004 Nunavik Health Survey (387 women, 315 men), and (ii) data on MeHg, Se, long-chain n-3 PUFA concentrations found in Nunavik wildlife species. In the region where most traditional beluga hunting takes place in Nunavik, the prevalence of at-risk blood Hg (≥ 8 μg/L) in childbearing-age women was 78.4%. While most country foods presently consumed contain low MeHg, beluga meat, not a staple of the Inuit diet, is the most important contributor to MeHg: up to two-thirds of MeHg intake in the beluga-hunting region (0.66 of MeHg intake) and to about one-third in other regions. In contrast, seal liver and beluga mattaaq - beluga skin and blubber - only mildly contributed to MeHg (between 0.06 and 0.15 of MeHg intake), depending on the region. Beluga mattaaq also highly contributed to Se intake (0.30 of Se intake). Arctic char, beluga blubber and mattaaq, and seal blubber contributed to most long-chain n-3 PUFA intake. This study highlights the importance of considering interconnections between local ecosystems and dietary habits to develop recommendations and interventions promoting country foods' benefits, while minimizing the risk of MeHg from beluga meat, especially for childbearing-age women.

Gestational exposure to polychlorinated biphenyls and dibenzofurans induced asymmetric hearing loss: Yucheng children study

INTRODUCTION

In 1979, approximately 2000 people in central Taiwan were exposed to polychlorinated biphenyls and dibenzofurans (PCBs/PCDFs) due to ingestion of contaminated rice oil. The children born to mothers exposed to PCBs/PCDFs were called Yucheng children. We conducted a follow-up study to examine the association between gestational PCBs/PCDFS exposure and auditory function in Yucheng children's early adulthood.

METHODS

In 1985 and early 1992, Yucheng children and their age, gender, socio-economic matched unexposed referent children were recruited for physical examination and long-term follow-ups. In 2007, Yucheng children and referent children were invited to participate in a health examination, including assessment of pure-tone air-conduction thresholds and distortion product otoacoustic emissions (DPOAEs) test. Gestational exposure to PCBs/PCDFs in Yucheng children were estimated by back-extrapolation of their mother's serum concentration to the time of childbirth.

RESULTS

A total of 86 Yucheng children (51.2% males) and 97 referent children (50.5% males) were included for analysis. No difference was found in demographic characteristics between two groups. Among the Yucheng children, 53 had estimated PCBs/PCDFs concentrations. We found that Yucheng children were at higher risk of having elevated hearing threshold at low frequencies in the right ear. Estimated maternal concentrations of 2,3,4,7,8-pnCDF at the time of birth were associated with increased hearing thresholds and decreased DPOAEs amplitudes at low frequencies in the right ear.

CONCLUSION

Gestational exposure to PCBs/PCDFs caused adverse asymmetrical hearing effects detectable even in early adulthood.

Association between environmental contaminants and health outcomes in indigenous populations of the Circumpolar North

Background

Since the 1990s, research has been carried out to monitor environmental contaminants and their effects on human health in the Arctic. Although evidence shows that Arctic indigenous peoples are exposed to higher levels of contaminants and do worse on several dimensions of health compared with other populations, the contribution of such exposures on adverse outcomes is unclear.

Objective

The purpose of this review is to provide a synopsis of the published epidemiological literature that has examined association between environmental contaminants and health outcomes in Arctic indigenous populations.

Design

A literature search was conducted in OVID Medline (1946-January 2014) using search terms that combined concepts of contaminant and indigenous populations in the Arctic. No language or date restrictions were applied. The reference lists of review articles were hand-searched.

Results

Of 559 citations, 60 studies were relevant. The studies fell under the following categories: paediatric (n=18), reproductive health (n=18), obstetrics and gynaecology (n=9), cardiology (n=7), bone health (n=2), oncology (n=2), endocrinology (n=2) and other (n=2). All studies, except one from Arctic Finland, were either from Nunavik or Greenland. Most studies assessed polychlorinated biphenyls (n=43) and organochlorine pesticides (n=29). Fewer studies examined heavy metals, perfluorinated compounds, or polybrominated diphenyl ethers. Details of study results for each health category are provided.

Conclusions

It is difficult to make conclusive statements about the effects of environmental contaminants on health due to mixed results, small number of studies and studies being restricted to a small number of regions. Meta-analytical synthesis of the evidence should be considered for priority contaminants and health outcomes. The following research gaps should be addressed in future studies: association of contaminants and health in other Arctic regions (i.e. Inuvialuit Settlement Region, Nunavut, Nunatsiavut, Alaska, European North and Russian North); assessment of contaminants on chronic diseases; inclusion of clinical endpoints in assessments; and assessment of the emerging contaminants of perfluorinated compounds and polybrominated diphenyl ethers.

Comparing plasma concentrations of persistent organic pollutants and metals in primiparous women from northern and southern Canada

The exposure of Aboriginal peoples in the Canadian Arctic to persistent organic pollutants (POPs) and metals through the consumption of traditional food items is well recognized; however, less information is available for Canadian immigrants. The direct comparison of blood chemical concentrations for expectant primiparous women sampled in the Inuvik and Baffin regions of the Canadian Arctic, as well as Canadian- and foreign-born women from five southern Canadian centers (Halifax, Vancouver, Hamilton, Ottawa, and Calgary), provides relative exposure information for samples of northern and southern mothers in Canada. Based on our analyses, Canadian mothers are exposed to a similar suite of contaminants; however, Inuit first birth mothers residing in the Canadian Arctic had higher age-adjusted geometric mean concentrations for several legacy POPs regulated under the Stockholm Convention, along with lead and total mercury. Significant differences in exposure were observed for Inuit mothers from Baffin who tended to demonstrate higher blood concentrations of POPs and total mercury compared with Inuit mothers from Inuvik. Conversely, northern mothers showed a significantly lower age-adjusted geometric mean concentration for a polybrominated diphenyl ether (PBDE-153) compared to southern mothers. Furthermore, southern Canadian mothers born outside of Canada showed the highest individual concentrations measured in the study: 1700 μg/kg lipids for p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and 990 μg/kg lipids for β-hexachlorocyclohexane (β-HCH). Data from Cycle 1 (2007-2009) of the nationally-representative Canadian Health Measures Survey (CHMS) places these results in a national biomonitoring context and affirms that foreign-born women of child-bearing age experience higher exposures to many POPs and metals than their Canadian-born counterparts in the general population.

Neurotoxicity from prenatal and postnatal exposure to methylmercury

The extent to which postnatal methylmercury exposure contributes to neurobehavioral delays is uncertain. Confounding may occur because the child's dietary exposure likely correlates with the mother's. This conundrum was examined in the Faroese birth cohort 1 born in 1986-1987. Exposure parameters included mercury concentrations in maternal hair at parturition, cord blood, and child blood and hair at the age-7 clinical examination (N=923). In regression analyses, the child's current blood-mercury at age 7 (N=694) showed only weak associations with the neuropsychological test variables, but visuospatial memory revealed a significant negative association. Mutual adjustment caused decreases of the apparent effect of the prenatal exposure. However, such adjustment may lead to underestimations due to the presence of correlated, error-prone exposure variables. In structural equation models, all methylmercury exposure parameters were instead entered into a latent exposure variable that reflected the total methylmercury load. This latent exposure showed significant associations with neurodevelopmental deficits, with prenatal exposure providing the main information. However, postnatal methylmercury exposure appeared to contribute to neurotoxic effects, in particular in regard to visuospatial processing and memory. Thus, addition in the regression analysis of exposure information obtained at a different point in time was not informative and should be avoided. Further studies with better information on exposure profiles are needed to characterize the effects of postnatal methylmercury exposure.

Domain-specific effects of prenatal exposure to PCBs, mercury, and lead on infant cognition: results from the Environmental Contaminants and Child Development Study in Nunavik

BACKGROUND

Polychlorinated biphenyls (PCBs), methylmercury (MeHg), and lead (Pb) are environmental contaminants known for their adverse effects on cognitive development.

OBJECTIVES

In this study we examined the effects of prenatal exposure to PCBs, MeHg, and Pb on cognitive development in a sample of Inuit infants from Arctic Québec.

METHODS

Mothers were recruited at local prenatal clinics. PCBs, mercury (Hg), Pb, and two seafood nutrients-docosahexaenoic acid (DHA) and selenium (Se)-were measured in umbilical cord blood. Infants (n = 94) were assessed at 6.5 and 11 months of age on the Fagan Test of Infant Intelligence (FTII), A-not-B test, and Bayley Scales of Infant Development-2nd Edition (BSID-II).

RESULTS

Multiple regression analyses revealed that higher prenatal PCB exposure was associated with decreased FTII novelty preference, indicating impaired visual recognition memory. Prenatal Hg was associated with poorer performance on A-not-B, which depends on working memory and is believed to be a precursor of executive function. Prenatal Pb was related to longer FTII fixation durations, indicating slower speed of information processing.

CONCLUSIONS

PCBs, MeHg, and Pb each showed specific and distinct patterns of adverse associations with the outcomes measured during infancy. By contrast, none of these exposures was associated with performance on the BSID-II, a global developmental measure. The more focused, narrow band measures of cognitive function that appeared to be sensitive to these exposures also provide early indications of long-term impairment in specific domains that would otherwise not likely be evident until school age.

CITATION

Boucher O, Muckle G, Jacobson JL, Carter RC, Kaplan-Estrin M, Ayotte P, Dewailly É, Jacobson SW. 2014. Domain-specific effects of prenatal exposure to PCBs, mercury, and lead on infant cognition: results from the Environmental Contaminants and Child Development Study in Nunavik. Environ Health Perspect 122:310-316; http://dx.doi.org/10.1289/ehp.1206323.

Postnatal toxic and acquired disorders

To develop and function optimally, the brain requires a balanced environment of electrolytes, amino acids, neurotransmitters, and metabolic substrates. As a consequence, organ dysfunction has the potential to induce brain disorders and toxic-metabolic encephalopathies, particularly when occurring during early stages of cerebral maturation. Induced toxicity of three different organ systems that are commonly associated with brain complications are discussed. First, thyroid hormone deficiency caused by intrinsic or extrinsic factors (e.g., environmental toxins) may induce severe adverse effects on child neurological development from reversible impairments to permanent mental retardation. Second, inadequate removal of wastes due to chronic renal failure leads to the accumulation of endogenous toxins that are harmful to brain function. In uremic pediatric patients, the brain becomes more vulnerable to exogenous substances such as aluminum, which can induce aluminum encephalopathy. Following surgical procedures, neurological troubles including focal defects and severe epileptic seizures may result from hypertensive encephalopathy combined with toxicity of immunomodulating substances, or from the delayed consequences of cardiovascular defect. Taken together, this illustrates that organ disorders clearly have an impact on child brain function in various ways.

Prenatal methylmercury, postnatal lead exposure, and evidence of attention deficit/hyperactivity disorder among Inuit children in Arctic Québec

BACKGROUND

Prenatal exposure to methylmercury (MeHg) and polychlorinated biphenyls (PCBs) has been associated with impaired performance on attention tasks in previous studies, but the extent to which these cognitive deficits translate into behavioral problems in the classroom and attention deficit/hyperactivity disorder (ADHD) remains unknown. By contrast, lead (Pb) exposure in childhood has been associated with ADHD and disruptive behaviors in several studies.

OBJECTIVES

In this study we examined the relation of developmental exposure to MeHg, PCBs, and Pb to behavioral problems at school age in Inuit children exposed through their traditional diet.

METHODS

In a prospective longitudinal study conducted in the Canadian Arctic, exposure to contaminants was measured at birth and at school age. An assessment of child behavior (n = 279; mean age = 11.3 years) was obtained from the child's classroom teacher on the Teacher Report Form (TRF) from the Child Behavior Checklist, and the Disruptive Behavior Disorders Rating Scale (DBD).

RESULTS

Cord blood mercury concentrations were associated with higher TRF symptom scores for attention problems and DBD scores consistent with ADHD. Current blood Pb concentrations were associated with higher TRF symptom scores for externalizing problems and with symptoms of ADHD (hyperactive-impulsive type) based on the DBD.

CONCLUSIONS

To our knowledge, this study is the first to identify an association between prenatal MeHg and ADHD symptomatology in childhood and the first to replicate previously reported associations between low-level childhood Pb exposure and ADHD in a population exposed to Pb primarily from dietary sources.