Cognitive deficits at age 22 years associated with prenatal exposure to methylmercury

Influence of Prenatal Exposure to Mercury, Perceived Stress, and Depression on Birth Outcomes in Suriname: Results from the MeKiTamara Study

Prenatal exposure to mercury, stress, and depression may have adverse effects on birth outcomes. Little is known on the influence of chemical and non-chemical stressors on birth outcomes in the country of Suriname. We assessed the influence of prenatal exposure to mercury, perceived stress, and depression on adverse birth outcomes in 1143 pregnant Surinamese women who participated in the Caribbean Consortium for Research in Environmental and Occupational Health-MeKiTamara prospective cohort study. Associations between mercury (≥1.1 μg/g hair, USEPA action level/top versus bottom quartile), probable depression (Edinburgh Depression Scale ≥12), high perceived stress (Cohen's Perceived Stress Scale ≥20), and adverse birth outcomes (low birthweight (<2500 g), preterm birth (<37 completed weeks of gestation), and low Apgar score (<7 at 5 min)) were assessed using bivariate and multivariate logistic regressions. Prevalence of elevated mercury levels, high perceived stress, and probable depression were 37.5%, 27.2%, and 22.4%, respectively. Mercury exposure was significantly associated with preterm birth in the overall study cohort (OR 2.47; 95% CI 1.05-5.83) and perceived stress with a low Apgar score (OR 9.73; 95% CI 2.03-46.70). Depression was not associated with any birth outcomes. These findings can inform policy- and practice-oriented solutions to improve maternal and child health in Suriname.

Methylmercury in Predatory and Non-predatory Fish Species Marketed in the Amazon Triple Frontier

This study assessed if the concentrations of methylmercury (MeHg) in predatory and non-predatory fish caught in the Upper Solimões River are safe for human consumption, according to the reference values established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). MeHg concentrations were evaluated in muscle of 5 predatory and 4 non-predatory fish species by gas chromatography with electron capture detector (GC-ECD). MeHg concentrations in predatory (0.09 mg kg^-1) and non-predatory (0.04 mg kg^-1) fish were under the safe upper limit for human consumption. The general average concentration of MeHg in these fish were 0.05 mg kg^-1. The Estimated Weekly Intake of MeHg was higher than the provisional tolerable weekly intake in both predatory and non-predatory fish, especially for women. Due to the high rates of fish consumption in the Amazon, the risk assessment based only on the concentration of MeHg in fish may not be accurate.

Mercury in fish marketed in the Amazon Triple Frontier and Health Risk Assessment

Fish has great socioeconomic, cultural, and nutritional importance for Amazonian populations. Despite all health benefits, fish can accumulate great amounts of mercury (Hg). The entry of Hg in aquatic trophic chains is an issue of concern to animal and human health. Higher risks of human exposure are strongly related to fish consumption. Upper Solimões population has one of the highest fish consumption rates of the Amazon. This study aimed to access the concentration of total Hg (THg) in muscle, liver, and gills of 17 species of fishes marketed in the Upper Solimões Region and Health Risk Assessment. Higher concentrations were observed in Carnivores/Piscivores. The highest THg concentration was found in liver of Cichla ocellaris (4.549 μg/g) and the lowest in gills of Hoplosternum littorale (0.002 μg/g). Most species had higher THg concentrations in muscle>liver>gills, in the Ebb period, and liver>muscle>gills, in the Flood period. Hoplias malabaricus, Pseudoplatystoma fasciatum, Plagioscion squamosissimus, Ageneiosus inermis, and C. ocellaris presented average THg concentrations above the safe limit stablished by WHO. THg levels in C. ocellaris, H. malabaricus, P. squamosissimus, P. fasciatum, and Semaprochilodus insignis were higher than those found in fish of heavily impacted areas. Signs of bioaccumulation and biomagnifications of Hg can already be observed in this region. The Western Amazon Region urgently needs government actions to inhibit Hg release in aquatic ecosystems and to advise this population on the safe amount of fish to be eaten according to species and period of the year.

Characterization of performance on an automated visual recognition memory task in 7.5-month-old infants

Infant looking behaviors measured during visual assessment paradigms may be more reliable predictors of long-term cognitive outcomes than standard measures such as the Bayley Scales of Infant Development typically used in environmental epidemiology. Infrared eye tracking technology offers an innovative approach to automate collection and processing of looking behavior data, making it possible to efficiently assess large numbers of infants. The goals of this study were to characterize infant looking behavior measures including side preference, fixation duration, and novelty preference using eye tracking and an automated version of an established visual recognition memory paradigm that includes both human faces and geometric figures as stimuli. An ancillary goal was to assess the feasibility of obtaining a precise measure of looking to the eye region of faces from the eye-tracking data. In this study, 309 7.5-month-old infants from a prospective birth cohort were assessed using a visual recognition memory (VRM) paradigm. Infrared eye tracking was used to record looking time as infants were shown nine blocks of trials with a pair of identical faces or shapes followed by two trials in which the familiar stimulus was paired with a novel one. Infants were assessed in one of four conditions: in conditions A and B, stimulus set 1 were the familiar stimuli and set 2 were novel; in conditions C and D, set 2 were familiar and set 1 novel. The novel stimuli were presented on the right first in conditions A and C and on the left first in conditions B and D. We observed a significant right side preference, which has not been reported before (57% of looking time spent looking at right side stimulus, p-value < 0.0001). Infants showed a preference for the novel stimuli similar to that published in prior studies (57-60% of looking time spent looking at the novel stimulus, p-value < 0.0001), as well as average fixation durations similar to previous studies. Infants also showed a strong preference for the eyes versus the rest of the face (p-value < 0.0001). Novelty preference was significantly higher when set 2 stimuli were novel (p-value < 0.0001), suggesting a preference among infants for set 2 stimuli compared to set 1 stimuli. The pattern of novelty preference across trials was significantly different between infants who saw the novel stimuli on the left first and those who saw them on the right first (p-value < 0.0001) but the overall mean novelty preference was not significantly different between these groups. There were also significant differences in average fixation duration and eyes preference measures across stimuli (p-values < 0.05). These findings show that VRM assessment can be automated for use in large-scale epidemiological studies using infrared eye tracking with looking behavior measure results similar to those obtained with standard non-automated methods, and that side and stimulus preferences are important modifiers of looking behavior that are critical to consider in this type of assessment.

Proteomic approach underlying the hippocampal neurodegeneration caused by low doses of methylmercury after long-term exposure in adult rats

Methylmercury (MeHg) is an important toxicant that causes cognitive dysfunctions in humans. This study aimed to investigate the proteomic and biochemical alterations of the hippocampus associated with behavioural consequences of low doses of MeHg in a long-term exposure model, and to realistically mimic in vivo the result of human exposure to this toxicant. Adult Wistar male rats were exposed to a dose of MeHg at 0.04 mg kg-1 day-1 by gavage for 60 days. Total mercury (Hg) content was significantly increased in the hippocampal parenchyma. The increase in the Hg levels was capable of reducing neuron and astrocyte cell density in the CA1, CA3, hilus and dentate gyrus regions, increasing both malondialdehyde and nitrite levels and decreasing antioxidant capacity against peroxyl radicals. The proteomic analysis detected 1041 proteins with altered expression due to MeHg exposure, including 364 proteins with no expression, 295 proteins with de novo expression and 382 proteins with up- or down-regulated expression. This proteomic approach revealed alterations in pathways related to chemical synapses, metabolism, amino acid transport, cell energy, neurodegenerative processes and myelin maintenance. Therefore, even at low doses of MeHg exposure, it is possible to cause hippocampal damage in adult rats at many organisational levels, triggering oxidative stress and proteome misbalance, featuring a neurodegenerative process and culminating in long- and short-term memory and learning deficits.

Neuropsychological Effects of Mercury Exposure in Children and Adolescents of the Amazon Region, Brazil

BACKGROUND

Studies with children exposed to methylmercury (MeHg) through fish consumption in the Brazilian Amazon region report that the high levels of hair Hg are associated with significant decreases in intelligence, memory, attention, and visuospatial processing.

OBJECTIVE

To investigate the relationship between mercury exposure and neuropsychological functions in riverside communities of the Brazilian Amazon.

METHOD

263 participants aged 6 to 14 years old were assessed, from resettlement regions, near the Madeira river, Rondônia, Brazil. To assess the neuropsychological functions we used the following instruments: intelligence (WASI), working memory (Corsi Block-Tapping Task and Digit Span), verbal fluency (Word Generation - NEPSY II), inhibitory control (Inhibition Errors - NEPSY II), shifting (Trail Making Test) and manual motor dexterity (Grooved PegBoard Test). Socioeconomic status was obtained through household surveys. Total Hg levels were quantified hair samples (Total HgH) collected from the occipital region of the scalp and analyzed by Cold Vapor Atomic Absorption Spectrometry.

RESULTS

The group in the upper quartile of Total HgH levels presented lower scores on the tasks that assessed estimated IQ, visuospatial working memory, semantic knowledge and phonological verbal fluency, when compared to the group in the lower quartile level. A regression analysis controlled for age, sex, and maternal education showed that for each increase of 10 μg/g of Total HgH, there was a decrease around half standard deviation in Verbal IQ, estimated IQ scores, semantic knowledge, phonological verbal fluency and for verbal and visuospatial working memory.

CONCLUSIONS

High concentrations of Total Hg in hair were associated with a lower performance in neuropsychological functions tests. The results show that environmental exposure to Hg is associated to children and adolescents' lower neuropsychological performance in the riverine and resettled areas of the Brazilian Amazon region.

Hepatic and neurobiological effects of foetal and breastfeeding and adulthood exposure to methylmercury in Wistar rats

Methylmercury (MeHg) is an organic bioaccumulated mercury derivative that strongly affects the environment and represents a public health problem primarily to riparian communities in South America. Our objective was to investigate the hepatic and neurological effects of MeHg exposure during the phases foetal and breast-feeding and adult in Wistar rats. Wistar rats (n = 10) were divided into 3 groups. Control group received mineral oil; The simple exposure (SE) group was exposed only in adulthood (0.5 mg/kg/day); and double exposure (DE) was pre-exposed to MeHg 0.5 mg/kg/day during pregnancy and breastfeeding (±40 days) and re-exposed to MeHg for 45 days from day 100. After, we evaluated possible abnormalities. Behavioral and biochemical parameters in liver and occipital cortex (CO), markers of liver injury, redox and AKT/GSK3β/mTOR signaling pathway. Our results showed that both groups treated with MeHg presented significant alterations, such as decreased locomotion and exploration and impaired visuospatial perception. The rats exposed to MeHg showed severe liver damage and increased hepatic glycogen concentration. The MeHg groups showed significant impairment in redox balance and oxidative damage to liver macromolecules and CO. MeHg upregulated the AKT/GSK3β/mTOR pathway and the phosphorylated form of the Tau protein. In addition, we found a reduction in NeuN and GFAP immunocontent. These results represent the first approach to the hepatotoxic and neural effects of foetal and adult MeHg exposure.

Prenatal exposure to glycol ethers and response inhibition in 6-year-old children: The PELAGIE cohort study

BACKGROUND

Exposure to glycol ethers (GEs) is suspected of impairing neurodevelopment in children, but the specific impact on their inhibitory capacity, a central deficit of ADHD, has never been studied. We aimed to assess the impact of prenatal exposure to GEs on the response inhibition of children aged six years.

METHODS

In total, 169 mother-child pairs from the French cohort PELAGIE (2002-2006) were studied. Maternal urinary concentrations of six GE metabolites (alkoxycarboxylic acids) were measured during pregnancy. Multiple imputation by quantile regression was used to handle non-detected values and the data were then classified into quartiles. Inhibition of children was evaluated by the Rhythmic Continuous Performance Test 90 (R-CPT90). The inhibition score (percentage of correct responses to non-target stimuli) was corrected for compliance with the instructions (percentage of correct responses to target stimuli). The analysis used a multiple linear regression model, adjusting for confounding factors for each metabolite.

RESULTS

Median concentrations of metabolites ranged from 0.02 mg/L (Ethoxyacetic acid, EAA) to 0.39 mg/L (Phenoxyacetic acid, PhAA). The median corrected inhibition score was 37.9% [first quartile: 29.8 - third quartile: 47.9]. We found a negative and statistically significant association between the inhibition score and prenatal urinary EAA concentration (p-trend = 0.03), with a significant β coefficient for the third quartile (β = -0.064; 95% confidence interval: -0.121, -0.007). There were no statistically significant associations for the other five metabolites.

CONCLUSION

These results are consistent with the hypothesis of possible impact of prenatal environmental exposure on inhibitory capacity among children. Data about the GEs metabolized to EAA (history of exposure sources and toxicokinetics) should be gathered to further interpret these results and guide precautionary measures.

Significant elevation of human methylmercury exposure induced by the food trade in Beijing, a developing megacity

Methylmercury (MeHg) poses health risks to humans worldwide. The investigation of a longer chain of biogeochemical MeHg transport from production to consumption than that addressed in previous studies could provide additional scientific foundation for the reduction of risks. The main objective of this study is to identify the impacts of the interregional food trade along with the age, gender and socioeconomic status of people on human MeHg exposure in a developing megacity. Based on a field investigation, sampling and measurements, we provide experimental evidence regarding the substantial displacement of human MeHg exposure from production areas to consumption areas induced by the food trade. In 2018, 20% and 64% of the exposure in Beijing originated from the international and interprovincial food trade, respectively. Meanwhile, the ingestion of fish contributed 79% to the total exposure, followed by rice (4.4%), crab (3.8%) and shrimp (2.7%), and the exposure risk in urban districts was higher than that in rural areas by a factor of 2.2. A significantly higher contribution of imported deep-sea species to exposure among young people than among older people was observed (P < 0.01**), and a larger contribution of the international food trade to the MeHg exposure risk for women of childbearing age (average: 27%) than that among other groups (average: 10%) was found. Overall, our efforts demonstrate the dramatic impact of the food trade on MeHg exposure in a developing megacity, and we suggest that MeHg-susceptible populations in China should choose indigenous fish species (e.g., hairtail, yellow croaker and carp species) rather than imported deep-sea species as their dietary protein source.

Environmental toxic agents: The impact of heavy metals and organochlorides on brain development

Exposure to environmental toxicants can have deleterious effects on the development of physical, cognitive, and mental health. Extensive laboratory and clinical studies have demonstrated how the developing brain is uniquely sensitive to toxic agents. This chapter focuses on the main neurologic impairments linked to prenatal and postnatal exposure to lead, methylmercury, and polychlorinated biphenyls, three legacy environmental contaminants whose neurotoxic effects have been extensively studied with respect to cognitive and behavioral development. The main cognitive, emotion regulation, sensory, and motor impairments in association with these contaminants are briefly reviewed, including the underlying neural mechanisms such as neuropathologic damages, brain neurotransmission, and endocrine system alterations. The use of neuroimaging as a novel tool to better understand how the brain is affected by exposure to environmental contaminants is also discussed.

Mercury Exposure, Fish Consumption, and Perceived Risk among Pregnant Women in Coastal Florida

Seafood consumption is the primary source of mercury (Hg) exposure, particularly among coastal populations. Hg exposure during pregnancy has been associated with cognitive impairment, as well as decrements in memory, attention, fine motor skills, and other markers of delayed neurodevelopment, although results are conflicting. High Hg hair concentrations in persons from coastal Florida, USA, have been previously reported. The purpose of the current study was to determine the concentrations of total Hg (THg) in the hair of pregnant women from this area and to assess the relationships between THg concentration, knowledge of the risks of mercury exposure, and dietary patterns among participants. Participants (n = 229) were recruited at prenatal clinics. Their mean total hair Hg concentration was 0.31 + 0.54 µg/g, lower or similar to US data for women of child-bearing age. Hair THg concentration was associated with consumption of locally caught fish and all seafood, a higher level of education, and first pregnancy. Eighty-five percent of women were aware of the risks of mercury exposure during pregnancy; over half reported a decrease in seafood consumption during pregnancy. Awareness of Hg in fish was marginally associated with lower hair THg concentration (p = 0.06) but reduction in seafood consumption during pregnancy was not.

Rice life cycle-based global mercury biotransport and human methylmercury exposure

Protecting the environment and enhancing food security are among the world’s greatest challenges. Fish consumption is widely considered to be the single significant dietary source of methylmercury. Nevertheless, by synthesizing data from the past six decades and using a variety of models, we find that rice could be a significant global dietary source of human methylmercury exposure, especially in South and Southeast Asia. In 2013, globalization caused 9.9% of human methylmercury exposure via the international rice trade and significantly aggravated rice-derived exposure in Africa (62%), Central Asia (98%) and Europe (42%). In 2016, 180 metric tons of mercury were generated in rice plants, 14-fold greater than that exported from oceans via global fisheries. We suggest that future research should consider both the joint ingestion of rice with fish and the food trade in methylmercury exposure assessments, and anthropogenic biovectors such as crops should be considered in the global mercury cycle.

Fish consumption is considered to be the only significant dietary source of MeHg. Here the authors show that rice could also be a significant global dietary source, especially in South and Southeast Asia. International rice trade and joint ingestion of fish and rice could aggravate the MeHg exposure levels in many areas.

Methylmercury Epigenetics

Methylmercury (MeHg) has conventionally been investigated for effects on nervous system development. As such, epigenetic modifications have become an attractive mechanistic target, and research on MeHg and epigenetics has rapidly expanded in the past decade. Although, these inquiries are a recent advance in the field, much has been learned in regards to MeHg-induced epigenetic modifications, particularly in the brain. In vitro and in vivo controlled exposure studies illustrate that MeHg effects microRNA (miRNA) expression, histone modifications, and DNA methylation both globally and at individual genes. Moreover, some effects are transgenerationally inherited, as organisms not directly exposed to MeHg exhibited biological and behavioral alterations. miRNA expression generally appears to be downregulated consequent to exposure. Further, global histone acetylation also seems to be reduced, persist at distinct gene promoters, and is contemporaneous with enhanced histone methylation. Moreover, global DNA methylation appears to decrease in brain-derived tissues, but not in the liver; however, selected individual genes in the brain are hypermethylated. Human epidemiological studies have also identified hypo- or hypermethylated individual genes, which correlated with MeHg exposure in distinct populations. Intriguingly, several observed epigenetic modifications can be correlated with known mechanisms of MeHg toxicity. Despite this knowledge, however, the functional consequences of these modifications are not entirely evident. Additional research will be necessary to fully comprehend MeHg-induced epigenetic modifications and the impact on the toxic response.

Methylmercury modifies temporally expressed myogenic regulatory factors to inhibit myoblast differentiation

Methylmercury (MeHg) is a pervasive environmental toxicant, with known detrimental effects on neurodevelopment. Despite a longstanding paradigm of neurotoxicity, where motor deficits are prevalent among those developmentally exposed, consideration of muscle as a MeHg target has received minimal investigation. Recent evidence has identified muscle-specific gene networks that modulate developmental sensitivity to MeHg toxicity. One such network is muscle cell differentiation. Muscle cell differentiation is a coordinated process regulated by the myogenic regulatory factors (MRFs): Myf5, MyoD, MyoG, and MRF4. A previous study demonstrated that MeHg inhibits muscle cell differentiation in vitro, concurrent with reduced MyoG expression. The potential for MeHg to modify the temporal expression of the MRFs to alter differentiation, however, has yet to be fully explored. Using the C2C12 mouse myoblast model, we examined MRF expression profiles at various stages subsequent to MeHg exposure to proliferating myoblasts. MeHg was seen to persistently alter myoblast differentiation capacity, as myod, myog, and mrf4 gene expression were all affected. Myog exhibited the most robust changes in expression across the various culture conditions, while myf5 was unaffected. Following MeHg exposure to myoblasts, where elevated p21 expression indicated departure from proliferation, cells failed to subsequently differentiate, even in the absence of MeHg, as reflected by a concurrent reduction in MRF4 and myosin heavy chain (MHC), markers of terminal differentiation. Our results indicate that within a brief window of exposure MeHg can disrupt the intrinsic myogenic differentiation program of proliferative myoblasts.

A Birth Cohort Study on the Genetic Modification of the Association of Prenatal Methylmercury With Child Cognitive Development

Genetic predisposition might affect neurodevelopmental outcomes of prenatal methylmercury exposure. We examined suspected heterogeneities for modification of exposure-related neurodevelopment in children from the Avon Longitudinal Study of Parents and Children (1991–2000), Bristol, United Kingdom. A subgroup (n = 1,127 from a pilot study and 1,045 from the present study) was identified based on the availability of the mercury concentration of cord tissue as a measure of prenatal methylmercury exposure, data on 247 single-nucleotide polymorphisms (SNPs), and Wechsler Intelligence Scale for Children intelligence quotient (IQ) scores. Log₁₀-transformed mercury concentration was positively associated with IQ, but adjustment for confounding cofactors attenuated this association. A finding of enhanced interaction with methylmercury was replicated in this study for the minor allele of rs1042838 (progesterone receptor) (β = −11.8, 95% confidence interval: −23.0, −0.6; P for interaction = 0.004) and weakly for rs662 (paraoxonase 1) (β = −3.6, 95% confidence interval: −11.4, 4.3; P = 0.117). In the joint sample, new interacting single-nucleotide polymorphisms were discovered in relation to superoxide dismutase 2, ATP binding cassette subfamily A member 1, and metallothionein 1M genes. While the low-level prenatal exposure to methylmercury was not associated with child cognition, progesterone receptor rs1042838 minor alleles revealed a negative association of mercury exposure with IQ.

Joint and independent neurotoxic effects of early life exposures to a chemical mixture: A multi-pollutant approach combining ensemble learning and g-computation

BACKGROUND

Exposure to mercury (Hg) is associated with adverse developmental effects. However, Hg occurs with a multitude of chemicals. We assessed the associations of developmental exposure to multiple pollutants with children's neurodevelopment using a novel approach.

METHODS

Hg, polychlorinated biphenyls (PCBs), and perfluoroalkyl substances were measured in maternal and children's blood at 5-years (n=449 and 419). At 7-years, children were administered Boston Naming Test (BNT) and the Strengths and Difficulties Questionnaire (SDQ). We used the G-formula combined with SuperLearner to estimate independent and joint effects of chemicals at both ages. We constructed flexible exposure-response relationships and assessed interactions.

RESULTS

Most chemicals showed negative relationships with BNT scores. An inter-quartile range (IQR) increase in maternal Hg and perfluorooctanoic acid (PFOA) was associated with 0.15 standard deviation [SD] (95% Confidence Interval [CI]: -0.29,-0.03) and 0.14 SD (95%CI: -0.26,-0.05) lower scores in BNT, whereas a joint IQR increase in the mixture of chemicals was associated with 0.48 SD (95%CI: -0.69,-0.25) lower scores in BNT. An IQR increase in PFOA was associated with 0.11 SD (95%CI: 0.02,0.26) higher total SDQ difficulties scores. Maternal ∑PCBs concentrations were associated with lower SDQ scores (β=-0.09 SD; 95%CI: -0.19,0), whereas 5-years ∑PCBs showed a negative association (β=-0.09 SD; 95%CI: -0.21,0). Finally, a joint IQR increase in the mixture was associated with 0.22 SD (95%CI: 0.04,0.4) higher SDQ scores.

CONCLUSIONS

Using a novel statistical approach, we confirmed associations between prenatal mercury exposure and lower cognitive function. The potential developmental effects of PFASs need additional attention.

Is breast feeding associated with offspring IQ at age 5? Findings from prospective cohort: Lifestyle During Pregnancy Study

OBJECTIVES

Breast feeding is associated with health benefits for both mother and child, but many studies focusing on neurodevelopment have lacked information on important confounders and few randomised trials exist. Our objective was to examine the influence of breast feeding on child IQ at 5 years of age while taking maternal IQ and other relevant factors into account.

DESIGN

Prospective observational study.

SETTING

Population-based birth cohort in Denmark.

PARTICIPANTS

We used data from The Lifestyle During Pregnancy Study 1782 mother-child pairs sampled from the Danish National Birth Cohort (n=101 042).

OUTCOME MEASURES

Child IQ was assessed at age 5 years by the Wechsler Primary and Preschool Scales of Intelligence-Revised. On the same occasion maternal intelligence was assessed by Wechsler Adult Intelligence Scale and Raven's Standard Progressive Matrices. Exposure data on duration of breast feeding (n=1385) were extracted from telephone interviews conducted when the child was 6 and 18 months, and analyses were weighted by relevant sampling fractions.

RESULTS

In multivariable linear regression analyses adjusted for potential confounders breast feeding was associated with child IQ at 5 years (categorical χ2 test for overall association p=0.03). Compared with children who were breast fed ≤1 month, children breast fed for 2-3, 4-6, 7-9 and 10 or more months had 3.06 (95% CI 0.39 to 5.72), 2.03 (95% CI -0.38 to 4.44), 3.53 (95% CI 1.18 to 5.87) and 3.28 (95% CI 0.88 to 5.67) points higher IQ after adjustment for core confounders, respectively. There was no dose-response relation and further analyses indicated that the main difference in IQ was between breast feeding ≤1 month versus >1 month.

CONCLUSIONS

Breastfeeding duration of 1 month or shorter compared with longer periods was associated with approximately three points lower IQ, but there was no evidence of a dose-response relation in this prospective birth cohort, where we were able to adjust for some of the most critical confounders, including maternal intelligence.

Trans-provincial health impacts of atmospheric mercury emissions in China

Mercury (Hg) exposure poses substantial risks to human health. Investigating a longer chain from economic activities to human health can reveal the sources and critical processes of Hg-related health risks. Thus, we develop a more comprehensive assessment method which is applied to mainland China-the largest global Hg emitter. We present a map of Hg-related health risks in China and estimate that 0.14 points of per-foetus intelligence quotient (IQ) decrements and 7,360 deaths from fatal heart attacks are related to the intake of methylmercury in 2010. This study, for the first time, reveals the significant impacts of interprovincial trade on Hg-related health risks across the whole country. For instance, interprovincial trade induced by final consumption prevents 0.39 × 10^-2 points for per-foetus IQ decrements and 194 deaths from fatal heart attacks. These findings highlight the importance of policy decisions in different stages of economic supply chains to reduce Hg-related health risks.

Risk tradeoffs associated with traditional food advisories for Labrador Inuit

The traditional Inuit diet includes wild birds, fish and marine mammals, which can contain high concentrations of the neurotoxicant methylmercury (MeHg). Hydroelectric development may increase MeHg concentrations in traditional foods. Consumption advisories are often used to mitigate such risks and can result in reduced intake of traditional foods. Data from a dietary survey, MeHg exposure assessment and risk analysis for individuals in three Inuit communities in Labrador, Canada (n = 1145) in 2014 indicate reducing traditional food intake is likely to exacerbate deficiencies in n-3 polyunsaturated fatty acids and vitamins B12 and B2. Traditional foods accounted for < 5% of per-capita calories but up to 70% of nutrients consumed. Although consumption advisories could lower neurodevelopmental risks associated with an increase in MeHg exposure (90th-percentile ∆IQ = - 0.12 vs. - 0.34), they may lead to greater risks of cardiovascular mortality (90th-percentile increase: + 58% to + 116% vs. + 25%) and cancer mortality (90th-percentile increase + 2% to + 4% vs. no increase). Conversely, greater consumption of locally caught salmon mostly unaffected by hydroelectric flooding would lower all these risks (90th-percentile ∆IQ = + 0.4; cardiovascular risk: - 45%; cancer risk: - 1.4%). We thus conclude that continued consumption of traditional foods is essential for Inuit health in these communities.

Fetal toxicology

Toxic chemicals, either from natural sources or man-made, are ubiquitous in our environment. Many of the synthetic chemicals make life more comfortable and therefore production continues to grow. Simultaneously with the increase in production, an increase in neurodevelopmental disorders has been observed. Some chemicals are not biodegradable or have a very long half-life time and, despite the fact that production of a number of those chemicals has been severely reduced, they are still ubiquitous in the environment. Fetal exposure to toxic chemicals is dependent on maternal exposure to those chemicals and the developing stage of the fetus. Human evidence from epidemiologic studies is described with regard to the effect of prenatal exposure to various groups of neurotoxicants (alcohol, particulate fine matter, metals, and endocrine disrupting chemicals) on neurobehavior development. Data indicate that prenatal exposure to alcohol, polycyclic aromatic hydrocarbons, lead, methylmercury (MeHg), organophosphate pesticides (OPPs), and polychlorinated biphenyl ethers (PBDEs) impair cognitive development, whereas exposure to alcohol, MeHg, organochlorine pesticides and OPPs, polychlorinated biphenyls, PBDEs, and bisphenol A increases the risk of developing either attention deficit/hyperactivity and/or autism spectrum disorders. Psychomotor development appears to be less affected. However, data are not conclusive, which may depend on the assessment of exposure and the exposure level, among other factors.

Prenatal, concurrent, and sex-specific associations between blood lead concentrations and IQ in preschool Canadian children

BACKGROUND

Lead exposure predicts altered neurodevelopment and lower intelligence quotient (IQ) in children, but few studies have examined this association in children who have relatively low blood lead concentrations.

OBJECTIVES

To test the associations between blood lead concentrations and cognitive function in Canadian preschoolers, with a possible moderation by sex.

METHODS

The data were gathered from 609 mother-child pairs from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. Lead was measured in umbilical and maternal blood, and in children's venous blood at age 3-4 years. Cognitive function was measured with the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III) at 3-4 years. We tested the relationship between WPPSI-III scores and blood lead concentrations with multiple linear regression, adding child sex as a moderator.

RESULTS

Median blood lead concentrations for the mother at 1st trimester and 3rd trimester of pregnancy, and for cord and child blood were 0.60 μg/dL, 0.58 μg/dL, 0.79 μg/dL and 0.67 μg/dL, respectively. We found no association between cord blood lead concentrations and WPPSI-III scores in multivariable analyses. However, cord blood lead concentrations showed a negative association with Performance IQ in boys but not in girls (B = 3.44; SE = 1.62; 95% CI: 0.82, 5.98). No associations were found between WPPSI-III scores and prenatal maternal blood or concurrent child blood lead concentrations.

CONCLUSIONS

Prenatal blood lead concentrations below 5 μg/dL were still associated with a decline in cognitive function in this Canadian cohort, but only for boys.

Eurasian river spring flood observations support net Arctic Ocean mercury export to the atmosphere and Atlantic Ocean

Midlatitude anthropogenic mercury (Hg) emissions and discharge reach the Arctic Ocean (AO) by atmospheric and oceanic transport. Recent studies suggest that Arctic river Hg inputs have been a potentially overlooked source of Hg to the AO. Observations on Hg in Eurasian rivers, which represent 80% of freshwater inputs to the AO, are quasi-inexistent, however, putting firm understanding of the Arctic Hg cycle on hold. Here, we present comprehensive seasonal observations on dissolved Hg (DHg) and particulate Hg (PHg) concentrations and fluxes for two large Eurasian rivers, the Yenisei and the Severnaya Dvina. We find large DHg and PHg fluxes during the spring flood, followed by a second pulse during the fall flood. We observe well-defined water vs. Hg runoff relationships for Eurasian and North American Hg fluxes to the AO and for Canadian Hg fluxes into the larger Hudson Bay area. Extrapolation to pan-Arctic rivers and watersheds gives a total Hg river flux to the AO of 44 ± 4 Mg per year (1σ), in agreement with the recent model-based estimates of 16 to 46 Mg per year and Hg/dissolved organic carbon (DOC) observation-based estimate of 50 Mg per year. The river Hg budget, together with recent observations on tundra Hg uptake and AO Hg dynamics, provide a consistent view of the Arctic Hg cycle in which continental ecosystems traffic anthropogenic Hg emissions to the AO via rivers, and the AO exports Hg to the atmosphere, to the Atlantic Ocean, and to AO marine sediments.

Effects of methylmercury and retinol palmitate co-administration in rats during pregnancy and breastfeeding: Metabolic and redox parameters in dams and their offspring

Ubiquitous low-dose methylmercury (MeHg) exposure through an increased fish consumption represents a global public health problem, especially among pregnant women. A plethora of micronutrients presented in fish affects MeHg uptake/distribution, but limited data is available. Vitamin A (VitA), another fish micronutrient is used in nutritional supplementation, especially during pregnancy. However, there is no information about the health effects arising from their combined exposure. Therefore, the present study aimed to examine the effects of both MeHg and retinyl palmitate administered on pregnant and lactating rats in metabolic and redox parameters from dams and their offspring. Thirty Wistar female rats were orally supplemented with MeHg (0,5 mg/kg/day) and retinyl palmitate (7500 µg RAE/kg/day) via gavage, either individually or in combination from the gestational day 0 to weaning. For dams (150 days old) and their offspring (31 days old), glycogen accumulation (hepatic and cardiac) and retinoid contents (plasma and liver) were analyzed. Hg deposition in liver tissue was quantified. Redox parameters (liver, kidney, and heart) were evaluated for both animals. Cytogenetic damage was analyzed with micronucleus test. Our results showed no general toxic or metabolic alterations in dams and their offspring by MeHg-VitA co-administration during pregnancy and lactation. However, increased lipoperoxidation in maternal liver and a disrupted pro-oxidant response in the heart of male pups was encountered, with apparently no particular effects in the antioxidant response in female offspring. GST activity in dam kidney was altered leading to possible redox disruption of this tissue with no alterations in offspring. Finally, the genomic damage was exacerbated in both male and female pups. In conclusion, low-dose MeHg exposure and retinyl palmitate supplementation during gestation and lactation produced a potentiated pro-oxidant effect, which was tissue-specific. Although this is a pre-clinical approach, we recommend precaution for pregnant women regarding food consumption, and we encourage more epidemiological studies to assess possible modulations effects of MeHg-VitA co-administration at safe or inadvertently used doses in humans, which may be related to specific pathologies in mothers and their children.

[Mercury as a Global Pollutant and Mercury Exposure Assessment and Health Effects]

Mercury and its compounds are classified into three main groups: metallic mercury (Hg⁰), inorganic mercury (Hg²⁺), and organic mercury (methyl mercury: CH₃Hg⁺, etc.). Metallic mercury is the only metal that is liquid at ambient temperature and normal pressure, which readily forms an amalgam with other metals. Therefore, mercury has long been used for refining various metals, and mercury amalgam has been used for dental treatment. Mercury has also been used in measuring instruments such as thermometers, barometers and blood pressure monitors, as well as electric appliances such as lighting equipment and dry batteries. Large amounts of metallic mercury are still used in other countries as a catalyst in the production of caustic soda by electrolysis. In addition, mercury compounds have been used in various chemicals such as mercurochrome, agricultural chemicals, and mildew-proofing agents. However, the use of mercury has also caused health problems for people. Minamata disease in Japan is a typical example. Also, since mercury is highly volatile, it is discharged as a product of industrial activities or derived from volcanoes, and it has been concluded on the basis of the findings of the United Nations Environment Program (UNEP) that it is circulating globally. Therefore, with the aim of establishing an internationally legally binding treaty for the regulation of mercury use to reduce risk, an intergovernmental negotiating committee was established in 2009. Japan actively contributed to this negotiation owing to its experience with Minamata disease, which led to the Convention on the regulation of mercury use being discharged as the "Minamata Convention on Mercury" and the treaty came into force on August 16, 2017. In this review, we introduce 1) the Global Mercury Assessment by UNEP; 2) mercury kinetics, exposure assessment and toxicity of different chemical forms; 3) large-scale epidemics of methylmercury poisoning; 4) methylmercury exposure assessment and health survey in whale-eating populations; 5) elemental mercury exposure assessment and health survey of mercury mine workers in China.

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).

Methylmercury Exposure and Developmental Outcomes in Tohoku Study of Child Development at 18 Months of Age

Seafood is an important component in a healthy diet and may contain methylmercury or other contaminants. It is important to recognize the risks and benefits of consuming seafood. A longitudinal prospective birth cohort study has been conducted to clarify the effects of neurotoxicants on child development—the Tohoku Study of Child Development (TSCD) in Japan. TSCD comprises two cohorts; a polychlorinated biphenyls (PCB) cohort (urban area) and a methylmercury cohort (coastal area). Our previous results from the coastal area showed prenatal methylmercury exposure affected psychomotor development in 18-month-olds, and boys appear to be more vulnerable to the exposure than girls. In this report, we have added the urban area cohort and we reanalyzed the impact of prenatal exposure to methylmercury, which gave the same results as before. These findings suggest prenatal exposure to low levels methylmercury may have adverse effects on child development, especially in boys.

Assessing mercury intoxication in isolated/remote populations: Increased S100B mRNA in blood in exposed riverine inhabitants of the Amazon

Mercury is a heavy metal responsible for human intoxication worldwide and especially in the Amazon, where both natural and anthropogenic sources are responsible for exposure in riverine populations. Methylmercury is the most toxic specie of mercury with recognized neurotoxicity due to its affinity for the central nervous system. S100B protein is a well-established biomarker of brain damage and it was recently associated with mercury-related neurotoxicity. Accurate measurement is especially challenging in isolated/remote populations due to the difficulty of adequate sample conservation, therefore here we use S100B mRNA levels in blood as a way to assay mercury neurotoxicity. We hypothesized that individuals from chronically exposed populations showing mercury levels above the limit of 10 μg/g in hair would present increased levels of S100B mRNA, likely due to early brain damage. A total of 224 riverine individuals were evaluated for anthropometric data (age, body mass index), self-reported symptoms of mercury intoxication, c-reactive protein in blood, and mercury speciation in hair. Approximately 20% of participants showed mercury levels above the limit, and prevalence for most symptoms was not different between individuals exposed to high or low mercury levels. Rigorous exclusion criteria were applied to avoid confounding factors and S100B mRNA in blood was tested by RT-qPCR. Participants with ≥10 μg/g of mercury had S100B mRNA levels over two times higher than that of individuals with lower exposure. A significant correlation was also detected between mercury content in hair and S100B mRNA levels in blood, supporting the use of the latter as a possible candidate to predict mercury-induced neurotoxicity. This is the first report of an association between S100B mRNA and mercury exposure in humans. The combination of both exposure and intoxication biomarkers could provide additional support for the screening and early identification of high-risk individuals in isolated populations and subsequent referral to specialized centers.

Unravelling motor behaviour hallmarks in intoxicated adolescents: methylmercury subtoxic-dose exposure and binge ethanol intake paradigm in rats

Methylmercury (MeHg) is a hazardous environmental pollutant, affecting Amazon basin communities by anthropogenic activities. The exact safe level of MeHg exposure is unclear, despite the efforts of health international societies to avoid mercury (Hg) poisoning. Central nervous system is severely impacted by Hg intoxication, reflecting on motor impairment. In addition, alcohol has been associated to an overall brain damage. According to lifestyle of Amazon riverside communities, alcohol intake occurs frequently. Thus, we investigated if continuous MeHg exposure at low doses during adolescence displays motor deficits (experiment 1). In the experiment 2, we examine if the co-intoxication (i.e. MeHg plus ethanol exposure) during adolescence intensify motor damage. In the experiment 1, Wistar adolescent rats (31 days old) received chronic exposure to low dose (CELD) of MeHg (40 μg/kg/day) for 35 days. For the experiment 2, five sessions of alcohol binge drinking paradigm (3ON-4OFF; 3.0 g/kg/day) were employed associated to MeHg intoxication. Motor behaviour was evaluated by the open field, pole test, beam walking and rotarod paradigms. CELDS of MeHg display motor function damage, related to hypoactivity, bradykinesia-like behaviour, coordination deficits and motor learning impairment. Co-intoxication of MeHg plus ethanol reduced cerebellar Hg content, however also resulted in motor behavioural impairment, as well as additive effects on bradykinesia and fine motor evaluation.

Neurotransmitter amines and antioxidant agents in neuronal protection against methylmercury-induced cytotoxicity in primary cultures of mice cortical neurons

Methylmercury (MeHg) is an environmental toxicant with detrimental effects on the developing brain and adult nervous system. The main mechanisms identified include oxidative stress, changes in intracellular calcium, mitochondrial changes, inhibition of glutamate uptake, of protein synthesis and disruption of microtubules. However, little is known about mechanisms of protection against MeHg neurotoxicity. We found that resveratrol (10 μM) and ascorbic acid (200 μM) protected MeHg-induced cell death in primary cultures of cortical neurons. In this work, we aimed at finding additional targets that may be related to MeHg mode of action in cell toxicity with special emphasis in cell protection. We wonder whether neurotransmitters may affect the MeHg effects on neuronal death. Our findings show that neurons exposed to low MeHg concentrations exhibit less mortality if co-exposed to 10 μM dopamine (DA). However, DA metabolites, HVA (homovanillic acid) and DOPAC (3,4-dihydroxyphenylacetic acid) are not responsible for such protection. Furthermore, both DA D1 and D2 receptors agonists showed a protective effect against MeHg toxicity. It is striking though that DA receptor antagonists SKF83566 (10 μM) and haloperidol (10 μM) did not inhibit DA protection against MeHg. In addition, the protective effect of 10 μM DA against MeHg-induced toxicity was not affected by additional organochlorine pollutants exposure. Our results also demonstrate that cells exposed to MeHg in presence of 100 μM acetylcholine (ACh), show an increase in cell mortality at the "threshold value" of 100 nM MeHg. Finally, norepinephrine (10 μM) and serotonin (20 μM) also had an effect on cell protection. Altogether, we propose to further investigate the additional mechanisms that may be playing an important role in MeHg-induced cytotoxicity.

Retention and distribution of methylmercury administered in the food in marine invertebrates: Effect of dietary selenium

Methylmercury is transported along aquatic food chains from the lower trophic levels and selenium modulates the biokinetics of mercury in organisms in complex ways. We investigated the retention of orally administered methylmercury in various marine invertebrates and the effect of selenium hereon. Shrimps (Palaemon adpersus and P. elegans), blue mussels (Mytilus edulis), shore crabs (Carcinus maenas) and sea stars (Asterias rubens) eliminated methylmercury slowly (t_½ = ½ to >1 year) and the copepod (Acartia tonsa) faster (t_½ ∼ 12-24 h). Orally administered selenite augmented elimination of methylmercury in the copepod (in one of two experiments) and blue mussels, but not in shrimps, crabs and sea stars. Selenium generally alters the distribution of the body burden of mercury, leaving more mercury in muscle and less mercury in digestive glands or rest of the body - also in the species where total body retention is not affected.

Methylmercury causes epigenetic suppression of the tyrosine hydroxylase gene in an in vitro neuronal differentiation model

Methylmercury (MeHg) is the causative substance of Minamata disease, which is associated with various neurological disorders such as sensory disturbance and ataxia. It has been suggested low-level dietary intake of MeHg from MeHg-containing fish during gestation adversely affects the fetus. In our study, we investigated the toxicological effects of MeHg exposure on neuronal differentiation focusing on epigenetics. We used human fetal brain-derived immortalized cells (LUHMES cells) as a human neuronal differentiation model. Cell viability, neuronal, and catecholamine markers in LUHMES cells were assessed after exposure to MeHg (0-1000 nM) for 6 days (from day 2 to day 8 of neuronal differentiation). Cell viability on day 8 was not affected by exposure to 1 nM MeHg for 6 days. mRNA levels of AADC, DBH, TUJ1, and SYN1 also were unaffected by MeHg exposure. In contrast, levels of TH, the rate-limiting enzyme for dopamine synthesis, were significantly decreased after MeHg exposure. Acetylated histone H3, acetylated histone H3 lysine 9, and tri-methyl histone H3 lysine 9 levels at the TH gene promoter were not altered by MeHg exposure. However, tri-methylation of histone H3 lysine 27 levels, related to transcriptional repression, were significantly increased at the TH gene promotor after MeHg exposure. In summary, MeHg exposure during neuronal differentiation led to epigenetic changes that repressed TH gene expression. This study provides useful insights into the toxicological mechanisms underlying the effects of developmental MeHg exposure during neuronal differentiation.

Neurodevelopmental Effects of Mercury

The toxicology of mercury (Hg) is of concern since this metal is ubiquitously distributed in the environment, and living organisms are routinely exposed to Hg at low to high levels. The toxic effects of Hg are well studied and it is known that they may differ depending on the Hg chemical species. In this chapter, we emphasize the neurotoxic effects of Hg during brain development. The immature brain is more susceptible to Hg exposure, since all the Hg chemical forms, not only the organic ones, can harm it. The possible consequences of Hg exposure during the early stages of development, the additive effects with other co-occurring neurotoxicants, and the known mechanisms of action and targets will be addressed in this chapter.

Endocrine active metals, prenatal stress and enhanced neurobehavioral disruption

Metals, including lead (Pb), methylmercury (MeHg) and arsenic (As), are long-known developmental neurotoxicants. More recently, environmental context has been recognized to modulate metals toxicity, including nutritional state and stress exposure. Modulation of metal toxicity by stress exposure can occur through shared targeting of endocrine systems, such as the hypothalamic-pituitary-adrenal axis (HPA). Our previous rodent research has identified that prenatal stress (PS) modulates neurotoxicity of two endocrine active metals (EAMs), Pb and MeHg, by altering HPA and CNS systems disrupting behavior. Here, we review this research and further test the hypothesis that prenatal stress modulates metals neurotoxicity by expanding to test the effect of developmental As ± PS exposure. Serum corticosterone and behavior was assessed in offspring of dams exposed to As ± PS. PS increased female offspring serum corticosterone at birth, while developmental As exposure decreased adult serum corticosterone in both sexes. As + PS induced reductions in locomotor activity in females and reduced response rates on a Fixed Interval schedule of reinforcement in males, with the latter suggesting unique learning deficits only in the combined exposure. As-exposed males showed increased time in the open arms of an elevated plus maze and decreased novel object recognition whereas females did not. These data further confirm the hypothesis that combined exposure to chemical (EAMs) and non-chemical (PS) stressors results in enhanced neurobehavioral toxicity. Given that humans are exposed to multiple environmental risk factors that alter endocrine function in development, such models are critical for risk assessment and public health protection, particularly for children.

Analysis of Nonlinear Associations between Prenatal Methylmercury Exposure from Fish Consumption and Neurodevelopmental Outcomes in the Seychelles Main Cohort at 17 Years

BACKGROUND

The Seychelles Child Development Study has been examining the relationship between prenatal methylmercury (MeHg) exposure from consuming fish during pregnancy and child development. This study re-analyzes seven outcomes in the 17 year Main Cohort data to determine if there are nonlinear or non-homogeneous (subgroup) associations that were not identified in the linear analysis.

METHODS

We adopted two statistical approaches. First, we carried out an additive nonlinear analysis assuming homogeneous prenatal MeHg-outcome relationships to explore overall associations. Second, we applied the regression tree to the Woodcock-Johnson Calculation subtest (it was significantly associated in earlier analyses) and identified 4 clusters based on covariates. Then we used additive models to assess the prenatal MeHg association in each of the four clusters for all seven outcomes. This approach assumes nonlinear associations in each cluster and non-homogeneous associations between clusters.

RESULTS

The additive nonlinear analysis yielded prenatal MeHg curves similar to the linear analysis. For the regression tree analysis, the curves relating prenatal MeHg to outcomes between the 4 clusters differed and some crossed at higher prenatal MeHg levels, suggesting non-homogeneity in the upper range of exposure. Additionally, some of the curves suggested a possible non-linear relationship within the range of exposure we studied.

CONCLUSION

This non-linear analysis supports the findings from the linear analysis. It shows little evidence to support an adverse association of prenatal MeHg exposure through maternal consumption of fish contaminated with natural background levels. However, the tree analysis suggests that the prenatal exposure/outcome relationship may not be homogeneous across all individuals and that some subpopulations may have an adverse association in the upper range of the exposures studied. More robust data in the higher levels of exposure in this cohort are needed to confirm this finding.

Oil extraction in the Amazon basin and exposure to metals in indigenous populations

Most oil extraction areas in the Peruvian Amazon are within indigenous territories. Poor environmental practices have exposed the indigenous population to metals. We conducted a survey in two indigenous Kukama communities to assess body burdens of metals after the occurrence of two major oil spills in 2014. Urine levels above those recommended by the Peruvian Ministry of Health were observed in 50% and 17% of the study population for mercury and cadmium, respectively.

A better approach to in vivo developmental neurotoxicity assessment: Alignment of rodent testing with effects seen in children after neurotoxic exposures

High throughput screens for developmental neurotoxicity (DN) will facilitate evaluation of chemicals and can be used to prioritize those designated for follow-up. DN is evaluated under different guidelines. Those for drugs generally include peri- and postnatal studies and juvenile toxicity studies. For pesticides and commercial chemicals, when triggered, include developmental neurotoxicity studies (DNT) and extended one-generation reproductive toxicity studies. Raffaele et al. (2010) reviewed 69 pesticide DNT studies and found two of the four behavioral tests underperformed. There are now many epidemiological studies on children showing adverse neurocognitive effects, yet guideline DN studies fail to assess most of the functions affected in children; nor do DN guidelines reflect the advances in brain structure-function relationships from neuroscience. By reducing the number of test ages, removing underperforming tests and replacing them with tests that assess cognitive abilities relevant to children, the value of DN protocols can be improved. Testing for the brain networks that mediate higher cognitive functions need to include assessments of working memory, attention, long-term memory (explicit, implicit, and emotional), and executive functions such as cognitive flexibility. The current DNT focus on what can be measured should be replaced with what should be measured. With the wealth of data available from human studies and neuroscience, the recommendation is made for changes to make DN studies better focused on human-relevant functions using tests of proven validity that assess comparable functions to tests used in children. Such changes will provide regulatory authorities with more relevant data.

Placental transfer and levels of mercury, selenium, vitamin E, and docosahexaenoic acid in maternal and umbilical cord blood

Methylmercury (MeHg) is a neurotoxicant known to affect the developing fetal brain as a sensitive target organ. As most mercury (Hg) in blood is MeHg, total mercury (THg) levels in blood are used to estimate the body burden of MeHg. The nutrients selenium (Se), vitamin E, and docosahexaenoic acid (DHA) are protective against MeHg toxicity. We compared maternal and cord blood concentrations of biochemical substances, THg and Se, vitamin E, DHA, and other elements, fatty acids, and amino acids in 54 Japanese mother-newborn pairs to elucidate the fetal risk of MeHg toxicity. Cord blood had higher hematocrit and amino acid values and lower concentrations of lipid components, including fatty acids compared with maternal blood. THg levels in cord blood (7.26ng/g) were 1.9 times higher than levels in maternal blood (3.79ng/g). Se concentrations in cord blood (176ng/g) were slightly higher than concentrations in maternal blood (156ng/g). Levels of vitamin E (0.31mg/dL) and DHA (58.8μg/mL) in cord blood were much lower than levels in maternal blood (1.38mg/dL and 147μg/mL, respectively). The ratios of Se/THg, vitamin E/THg, and DHA/THg in cord blood were lower than ratios in maternal blood. These results suggest that fetuses are at higher risk to MeHg toxicity.

Decadal Changes in the Edible Supply of Seafood and Methylmercury Exposure in the United States

BACKGROUND

Methylmercury (MeHg) exposure is associated with adverse effects on neurodevelopment and cardiovascular health. Previous work indicates most MeHg is from marine fish sold in the commercial market, but does not fully resolve supply regions globally. This information is critical for linking changes in environmental MeHg levels to human exposure in the U.S. population.

OBJECTIVES

We used available data to estimate the geographic origins of seafood consumed in the United States (major ocean basins, coastal fisheries, aquaculture, freshwater) and how shifts in edible supply affected MeHg exposures between 2000-2002 and 2010-2012.

METHODS

Source regions for edible seafood and MeHg exposure in the United States were characterized from national and international landing, export and import data from the Food and Agricultural Organization of the United Nations and the U.S. National Marine Fisheries Service.

RESULTS

Our analysis suggests 37% of U.S. population-wide MeHg exposure is from mainly domestic coastal systems and 45% from open ocean ecosystems. We estimate that the Pacific Ocean alone supplies more than half of total MeHg exposure. Aquaculture and freshwater fisheries together account for an estimated 18% of total MeHg intake. Shifts in seafood types and supply regions between 2000-2002 and 2010-2012 reflect changes in consumer preferences (e.g., away from canned light meat tuna), global ecosystem shifts (e.g., northern migration of cod stocks), and increasing supply from aquaculture (e.g., shrimp and salmon).

CONCLUSION

Our findings indicate global actions that reduce anthropogenic Hg emissions will be beneficial for U.S. seafood consumers because open ocean ecosystems supply a large fraction of their MeHg exposure. However, our estimates suggest that domestic actions can provide the greatest benefit for coastal seafood consumers. https://doi.org/10.1289/EHP2644.

Spatial, Temporal, and Dietary Variables Associated with Elevated Mercury Exposure in Peruvian Riverine Communities Upstream and Downstream of Artisanal and Small-Scale Gold Mining

Artisanal and small-scale gold mining (ASGM) is a primary contributor to global mercury and its rapid expansion raises concern for human exposure. Non-occupational exposure risks are presumed to be strongly tied to environmental contamination; however, the relationship between environmental and human mercury exposure, how exposure has changed over time, and risk factors beyond fish consumption are not well understood in ASGM settings. In Peruvian riverine communities (n = 12), where ASGM has increased 4–6 fold over the past decade, we provide a large-scale assessment of the connection between environmental and human mercury exposure by comparing total mercury contents in human hair (2-cm segment, n = 231) to locally caught fish tissue, analyzing temporal exposure in women of child bearing age (WCBA, 15–49 years, n = 46) over one year, and evaluating general mercury exposure risks including fish and non-fish dietary items through household surveys and linear mixed models. Calculations of an individual’s oral reference dose using the total mercury content in locally-sourced fish underestimated the observed mercury exposure for individuals in many communities. This discrepancy was particularly evident in communities upstream of ASGM, where mercury levels in river fish, water, and sediment measurements from a previous study were low, yet hair mercury was chronically elevated. Hair from 86% of individuals and 77% of children exceeded a USEPA (U.S. Environmental Protection Agency) provisional level (1.2 µg/g) that could result in child developmental impairment. Chronically elevated mercury exposure was observed in the temporal analysis in WCBA. If the most recent exposure exceeded the USEPA level, there was a 97% probability that the individual exceeded that level 8–10 months of the previous year. Frequent household consumption of some fruits (tomato, banana) and grains (quinoa) was significantly associated with 29–75% reductions in hair mercury. Collectively, these data demonstrate that communities located hundreds of kilometers from ASGM are vulnerable to chronically elevated mercury exposure. Furthermore, unexpected associations with fish mercury contents and non-fish dietary intake highlight the need for more in-depth analyses of exposure regimes to identify the most vulnerable populations and to establish potential interventions.

The Metal Neurotoxins: An Important Role in Current Human Neural Epidemics?

Many published studies have illustrated that several of the present day neurological epidemics (autism, attention deficit disorder, Alzheimer's) cannot be correlated to any single neurotoxicant. However, the present scientific examination of the numerous global blood monitoring databases for adults that include the concentrations of the neurotoxic elements, aluminum (Al), arsenic (As), lead (Pb), manganese (Mn), mercury (Hg), and selenium (Se) clearly indicate that, when considered in combination, for some, the human body may become easily over-burdened. This can be explained by changes in modern lifestyles. Similar data, solely for pregnant women, have been examined confirming this. All these elements are seen to be present in the human body and at not insignificant magnitudes. Currently suggested minimum risk levels (MRL) for humans are discussed and listed together with averages of the reported distributions, together with their spread and maximum values. One observation is that many distributions for pregnant women are not too dissimilar from those of general populations. Women obviously have their individual baseline of neurotoxin values before pregnancy and any efforts to modify this to any significant degree is not yet clearly apparent. For any element, distribution shapes are reasonably similar showing broad distributions with extended tails with numerous outlier values. There are a certain fraction of people that lie well above the MRL values and may be at risk, especially if genetically susceptible. Additionally, synergistic effects between neurotoxins and with other trace metals are now also being reported. It appears prudent for women of child-bearing age to establish their baseline values well before pregnancy. Those at risk then can be better identified. Adequate instrumental testing now is commercially available for this. In addition, directives are necessary for vaccination programs to use only non-neurotoxic adjuvants, especially for young children and all women of child-bearing ages. Additionally, clearer directives concerning fish consumption must now be reappraised.

Trends in and factors affecting the observed levels of urinary inorganic and total blood mercury among US children, adolescents, adults, and senior citizens over 2005-2012

Data from National Health and Nutrition Examination Survey (NHANES) for 2005-2012 were used to (i) study adjusted and unadjusted trends in the levels of urinary inorganic mercury (UIHG) and total blood mercury (TBHG) and (ii) factors that affect the observed levels of UIHG and TBHG among children aged 1-5 (CHLD15) and 6-11 (CHLD611) years, adolescents aged 12-19 years (ADOL), adults aged 20-64 years (ADLT), and senior citizens aged >=65 years (SNR). Decrease in adjusted levels of UIHG for each 2-year NHANES cycle for CHLD611 was 0.08114ng/L, 0.08379ng/L for ADOLs, and 0.12ng/L for ADLTs. Decreases in adjusted levels (AGM) of TBHG for each 2-year NHANES cycle were: 0.0632ng/L for CHLD15, 0.10239ng/L for CHLD611, 0.06424ng/L for ADOLs, and 0.056088ng/L for ADLTs. Among CHLD15 (0.34 vs. 0.39μg/L, p<0.01) and CHLD611 (0.42 vs. 0.44μg/L, p=0.04), males had lower AGMs for TBHG than females but among ADLTs (0.84 vs. 0.80μg/L, p<0.01) and SNRs (0.82 vs. 0.71μg/L, p<0.01) the reverse was true. For UIHG, for ADLTs (0.33 vs. 0.45μg/L, p<0.01) and SNRs (0.27 vs. 0.35μg/L, p<0.01) males had lower AGMs than females. Irrespective of age, those who were in unclassified race/ethnic group had the highest AGMs when compared with non-Hispanic whites, non-Hispanic blacks, and Mexican Americans and the differences, more often than not, were statistically significant (p<0.01). Irrespective of age, fish and shellfish consumption during the last 30days was associated with higher AGMs for both UIHG and TBHG than when fish and shellfish were not consumed and the differences were always statistically significant (p<0.01). Nonsmoker ADLTs (0.86 vs. 0.78μg/L, p<0.01) and SNRs (0.83 vs. 0.71μg/L, p<0.01) were found to have higher adjusted levels of TBHG than smokers. It is hypothesized that constituents in tobacco smoke may accelerate excretion of mercury from the body.

Aerobic Fitness and Neurocognitive Function Scores in Young Faroese Adults and Potential Modification by Prenatal Methylmercury Exposure

BACKGROUND

Exposure to methylmercury was shown to decrease neural stem cell populations, whereas aerobic fitness has beneficial effects on the adult brain that relies on improved neurogenesis in the hippocampus.

OBJECTIVES

We examined the association between aerobic fitness and neurocognitive outcomes at young adult age, along with the potential moderating effect of prenatal exposure to methylmercury.

METHODS

At age 22 years, 262 members of a Faroese birth cohort, established in 1986-1987, underwent a graded exercise test of aerobic fitness to measure maximal oxygen uptake (VO_2Max). Their prenatal methylmercury exposure had been assessed from the mercury concentration in cord blood. We estimated cross-sectional associations between VO_2Max and multiple measures of neurocognitive function. In addition, we compared groups with low and high prenatal methylmercury exposure.

RESULTS

A 1 standard deviation (SD) increase in VO_2Max was associated with better scores on short-term memory and cognitive processing speed by 0.21 SD (95% CI: -0.04, 0.46) and 0.28 SD (95% CI: 0.02, 0.54), respectively. In the group with lower prenatal methylmercury exposure, a 1 SD increase in VO_2Max was associated with increased scores on cognitive processing speed by 0.45 SD (95% CI: 0.08, 0.81) and with a slightly lesser benefit in short-term memory. No such association was observed in the group with high prenatal methylmercury exposure.

CONCLUSIONS

Higher aerobic capacity was associated with better performance in short-term memory and processing speed. However, prenatal methylmercury exposure seemed to attenuate these positive associations.

Neurological Deficits After Long-term Pyrethroid Exposure

Pyrethroid pesticides have been suggested to be a cause of Parkinson disease and other neurodegenerative diseases. To investigate this, a cross-sectional study was conducted among 120 Bolivian public health vector program spray men, primarily exposed to pyrethroids. Pesticide exposure and central nervous system (CNS) symptoms were determined by a structured interview, whereas neuromotor and neurocognitive performance was assessed using the computerized Behavioral Assessment and Research System and CATSYS system. Individuals exposed to higher levels reported significantly more CNS symptoms (adjusted odds ratio per quintile of cumulative exposure = 2.01 [1.22-3.31]). There was no association seen between pyrethroid exposure and neuromotor performance. Higher spraying intensity was associated with significantly worse neurocognitive performance in structural equation models (adjusted β per quintile = -0.405 [-0.660 to -0.150]), and workers only exposed to pyrethroids performed worse than workers also exposed to other pesticides (adjusted β = -1.344 [-2.224 to -0.464]). Chronic pyrethroid exposure may cause deterioration in neurocognitive performance, and exposure control is recommended.

Current progress on understanding the impact of mercury on human health

Mercury pollution and its impacts on human health is of global concern. The authors of this paper were members of the Plenary Panel on Human Health in the 12th International Conference on Mercury as a Global Pollutant held in Korea in June 2015. The Panel was asked by the conference organizers to address two questions: what is the current understanding of the impacts of mercury exposure on human health and what information is needed to evaluate the effectiveness of the Minamata Convention in lowering exposure and preventing adverse effects. The authors conducted a critical review of the literature published since January 2012 and discussed the current state-of-knowledge in the following areas: environmental exposure and/or risk assessment; kinetics and biomonitoring; effects on children development; effects on adult general populations; effects on artisanal and small-scale gold miners (ASGM); effects on dental workers; risk of ethylmercury in thimerosal-containing vaccines; interactions with nutrients; genetic determinants and; risk communication and management. Knowledge gaps in each area were identified and recommendations for future research were made. The Panel concluded that more knowledge synthesis efforts are needed to translate the research results into management tools for health professionals and policy makers.

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.

Characteristics of hand tremor and postural sway in patients with fetal-type Minamata disease

About forty certified patients aged around 50 years old existed as living witnesses to fetal-type Minamata disease (methylmercury poisoning due to in utero exposure) in Minamata, Japan in 2006. Computerized hand tremor and postural sway tests with spectral analysis were conducted for 24 of them and in matched control subjects to examine the pathophysiological feature of neuromotor function. The tremor intensities of the patients with fetal-type Minamata disease were significantly larger than those of the 67 controls at every frequency band for both hands. In the patients, proportions for intensity at 1-6 Hz of both hands were larger, but those of the intensity at 6-10 Hz were smaller compared with the controls. The center frequency of a tremor was significantly lower in the patients than in the controls. Only eight males of the 24 patients were examined to evaluate postural sway because of extremely low scores in activities of daily living in the remaining. Most of the postural sway parameters obtained with eyes open and closed were significantly larger in the patients than in the male controls. Likewise, Romberg quotients of postural sway in anterior-posterior direction were significantly higher in the patients. In conclusion, the patients with fetal-type Minamata disease of our study showed a larger tremor of low frequency at less than 6 Hz and postural instability. Spectral analyses of computerized hand tremor and postural sway are suggested to be useful for assessing the pathophysiological change, related to a lesion of the cerebellum, resulting from prenatal methylmercury exposure.

Mercury Exposure in Children of the Wanshan Mercury Mining Area, Guizhou, China

To evaluate the mercury (Hg) exposure level of children located in a Hg mining area, total Hg concentrations and speciation were determined in hair and urine samples of children in the Wanshan Hg mining area, Guizhou Province, China. Rice samples consumed by these same children were also collected for total mercury (THg) and methyl-mercury (MeHg) analysis. The geometric mean concentrations of THg and MeHg in the hair samples were 1.4 (range 0.50-6.0) μg/g and 1.1 (range 0.35-4.2) μg/g, respectively, while the geometric mean concentration of urine Hg (UHg) was 1.4 (range 0.09-26) μg/g Creatinine (Cr). The average of the probable daily intake (PDI) of MeHg via rice consumption was 0.052 (0.0033-0.39) µg/kg/day, which significantly correlated with the hair MeHg concentrations (r = 0.55, p < 0.01), indicating that ingestion of rice is the main pathway of MeHg exposure for children in this area. Furthermore, 18% (26/141) of the PDIs of MeHg exceeded the USEPA Reference Dose (RfD) of 0.10 µg/kg/day, indicating that children in this area are at a high MeHg exposure level. This paper for the first time evaluates the co-exposure levels of IHg and MeHg of children living in Wanshan mining area, and revealed the difference in exposure patterns between children and adults in this area.