Prenatal exposure to polychlorinated biphenyls: a neuropsychologic analysis

Serum polychlorinated biphenyls as a risk factor for MASLD: Exploring the association and underlying mechanisms

BACKGROUND

Fatty liver disease, a growing global health issue, is closely tied to metabolic disorders. The 2023 definition of metabolic-associated steatotic liver disease (MASLD) incorporates cardiometabolic risk factors, but the potential role of persistent organic pollutants (POPs) like polychlorinated biphenyls (PCBs), remains underexplored. Investigating the impact of environmental toxins on liver health is crucial for understanding emerging public health risks.

METHODS

1080 participants were included from the 1999-2018 National Health and Nutrition Examination Survey (NHANES). We employed weighted generalized linear models, weighted quantile sum regression, and Bayesian kernel machine regression to assess the relationship between serum PCB levels and MASLD, with NAFLD included for comparison. Protein interaction and enrichment analyses were also conducted to explore the underlying mechanisms.

RESULTS

PCB146, PCB156, PCB187, PCB174, and PCB180 were significantly associated with an increased MASLD risk in the GLM. Significant positive associations were found between serum PCB mixtures and MASLD in the WQS model (β: 0.411, p: 0.0056) and BKMR model (p < 0.05), with PCB180 contributing the most (β: 0.644, PIP: 0.903). NAFLD did not show significant associations. Network pharmacological analysis demonstrated enrichment in the regulation of lipolysis of adipocytes and the cAMP signaling pathway, and PPAR-γ and MAOA show significant importance in the protein-protein interaction networks.

CONCLUSION

This study underscores the epidemiological and mechanical link between MASLD and PCB exposure, highlighting the superiority of MASLD in identifying the impact of POPs on liver disease risk and particularly identifying PCB180 as a sentinel marker for PCB surveillance.

Early-life exposure to PCBs and PFAS exerts negative effects on the developing central nervous system

Persistent organic pollutants (POPs) are ubiquitous in the environment and display the capacity to bioaccumulate in living organisms, constituting a hazard to both wildlife and humans. Although restrictions have been applied to prohibit the production of several POPs since the 1960s, high levels of these compounds can still be detected in many environmental and biological matrices, due to their chemical properties and significantly long half-lives. Some POPs can be passed from mother to the fetus and can gain entry to the central nervous system (CNS), by crossing the blood-brain barrier (BBB), resulting in significant deleterious effects, including neurocognitive and psychiatric abnormalities, which may lead to long-term socio-economic burdens. A growing body of evidence obtained from clinical and experimental studies has increasingly indicated that these POPs may influence neurodevelopment through several cellular and molecular mechanisms. However, studies assessing their mechanisms of action are still incipient, requiring further research. Polychlorinated biphenyls (PCBs) and per- and polyfluoroalkyl substances (PFAS) are two of the main classes of POPs associated with disturbances in different human systems, mainly the nervous and endocrine systems. This narrative review discusses the main PCB and PFAS effects on the CNS, focusing on neuroinflammation and oxidative stress and their consequences for neural development and BBB integrity. Moreover, we propose which mechanisms could be involved in POP-induced neurodevelopmental defects. In this sense, we highlight potential cellular and molecular pathways by which these POPs can affect neurodevelopment and could be further explored to propose preventive therapies and formulate public health policies.

Developmental exposure to legacy environmental contaminants, medial temporal lobe volumes and spatial navigation memory in late adolescents

Exposure to lead, mercury, and polychlorinated biphenyls (PCBs) has been causally linked to spatial memory deficits and hippocampal changes in animal models. The Inuit community in Northern Canada is exposed to higher concentrations of these contaminants compared to the general population. This study aimed to 1) investigate associations between prenatal and current contaminant exposures and medial temporal brain volumes in Inuit late adolescents; 2) examine the relationship between these brain structures and spatial memory; and 3) assess the mediating role of brain structures in the association between contaminant exposure and spatial memory. Prenatal and current exposures were assessed from blood samples collected at birth and at the time of testing in 71 participants aged 16-22. Volumetric measurements of the hippocampi, entorhinal, and parahippocampal cortices from T1-weighted images were obtained using the Automatic Segmentation of Hippocampal Subfields method. Spatial navigation memory was evaluated using a computerized Morris Water Maze task. Prenatal lead exposure was associated with a smaller left hippocampal volume (β = -0.30, 95% CI = -0.56, -0.05), while current mercury (β = -0.34, 95% CI = -0.62, -0.06) and PCB-153 (β = -0.36, 95% CI = -0.70, -0.01) exposures were linked to a smaller left entorhinal cortex. The volume of the left entorhinal cortex positively correlated with spatial navigation memory performance (β = 0.26, 95% CI = 0.01, 0.51). These findings suggest specific windows of brain vulnerability to these contaminants, with the entorhinal cortex playing a key role in spatial navigation memory and potentially mediating the effects of exposure.

E-waste: mechanisms of toxicity and safety testing

Currently, information on the toxicity profile of the majority of the identified e-waste chemicals, while extensive and growing, is admittedly fragmentary, particularly at the cellular and molecular levels. Furthermore, the toxicity of the chemical mixtures likely to be encountered by humans during and after informal e-waste recycling, as well as their underlying mechanisms of action, is largely unknown. This review paper summarizes state-of-the-art knowledge of the potential underlying toxicity mechanisms associated with e-waste exposures, with a focus on toxic responses connected to specific organs, organ systems, and overall effects on the organism. To overcome the complexities associated with assessing the possible adverse outcomes from exposure to chemicals, a growing number of new approach methodologies have emerged in recent years, with the long-term objective of providing a human-based and animal-free system that is scientifically superior to animal testing, more effective, and acceptable. This encompasses a variety of techniques, typically regarded as alternative approaches for determining chemical-induced toxicities and holds greater promise for a better understanding of key events in the metabolic pathways that mediate known adverse health outcomes in e-waste exposure scenarios. This is crucial to establishing accurate scientific knowledge on mixed e-waste chemical exposures in shorter time frames and with greater efficacy, as well as supporting the need for safe management of hazardous chemicals. The present review paper discusses important gaps in knowledge and shows promising directions for mechanistically anchored effect-based monitoring strategies that will contribute to the advancement of the methods currently used in characterizing and monitoring e-waste-impacted ecosystems.

Developmental exposure to the Fox River PCB mixture modulates behavior in juvenile mice

Developmental exposures to PCBs are implicated in the etiology of neurodevelopmental disorders (NDDs). This observation is concerning given the continued presence of PCBs in the human environment and the increasing incidence of NDDs. Previous studies reported that developmental exposure to legacy commercial PCB mixtures (Aroclors) or single PCB congeners found in Aroclors caused NDD-relevant behavioral phenotypes in animal models. However, the PCB congener profile in contemporary human samples is dissimilar to that of the legacy Aroclors, raising the question of whether human-relevant PCB mixtures similarly interfere with normal brain development. To address this question, we assessed the developmental neurotoxicity of the Fox River Mixture (FRM), which was designed to mimic the congener profile identified in fish from the PCB-contaminated Fox River that constitute a primary protein source in the diet of surrounding communities. Adult female C57BL/6 J mouse dams (8-10 weeks old) were exposed to vehicle (peanut oil) or FRM at 0.1, 1.0, or 6.0 mg/kg/d in their diet throughout gestation and lactation, and neurodevelopmental outcomes were assessed in their pups. Ultrasonic vocalizations (USVs) and measures of general development were quantified at postnatal day (P) 7, while performance in the spontaneous alternation task and the 3-chambered social approach/social novelty task was assessed on P35. Triiodothyronine (T3) and thyroxine (T4) were quantified in serum collected from the dams when pups were weaned and from pups on P28 and P35. Developmental exposure to FRM did not alter pup weight or body temperature on P7, but USVs were significantly decreased in litters exposed to FRM at 0.1 or 6.0 mg/kg/d in the maternal diet. FRM also impaired male and female pups' performance in the social novelty task. Compared to sex-matched vehicles, significantly decreased social novelty was observed in male and female pups in the 0.1 and 6.0 mg/kg/d dose groups. FRM did not alter performance in the spontaneous alternation or social approach tasks. FRM increased serum T3 levels but decreased serum T4 levels in P28 male pups in the 1.0 and 6.0 mg/kg/d dose groups. In P35 female pups and dams, serum T3 levels decreased in the 6.0 mg/kg/d dose group while T4 levels were not altered. Collectively, these findings suggest that FRM interferes with the development of social communication and social novelty, but not memory, supporting the hypothesis that contemporary PCB exposures pose a risk to the developing brain. FRM had sex, age, and dose-dependent effects on serum thyroid hormone levels that overlapped but did not perfectly align with the FRM effects on behavioral outcomes. These observations suggest that changes in thyroid hormone levels are not likely the major factor underlying the behavioral deficits observed in FRM-exposed animals.

Prenatal exposure to mixtures of per- and polyfluoroalkyl substances and organochlorines affects cognition in adolescence independent of postnatal exposure

BACKGROUND

Studies on cognitive and neurodevelopmental outcomes have shown inconsistent results regarding the association with prenatal exposure to perfluoroalkyl substance (PFAS) and organochlorines. Assessment of mixture effects of correlated chemical exposures that persist in later life may contribute to the unbiased evaluation and understanding of dose-response associations in real-life exposures.

METHODS

For a subset of the 4th Flemish Environment and Health Study (FLEHS), concentrations of four PFAS and six organochlorines were measured in respectively 99 and 153-160 cord plasma samples and 15 years later in adolescents' peripheral serum by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). Sustained and selective attention were measured at 14-15 years with the Continuous Performance Test (CPT) and Stroop Test as indicators of potential neurodevelopmental deficits. Quantile g-computation was applied to assess the joint associations between prenatal exposure to separate and combined groups of PFAS and organochlorines and performance in the CPT and Stroop Test at adolescence. Subsequently, individual effects of each chemical compound were analyzed in mixed effects models with two sets of covariates. Analytical data at birth and at the time of cognitive assessment allowed for off-setting postnatal exposure.

RESULTS

In mixtures analysis, a simultaneous one-quantile increase in the natural log-transformed values of PFAS and organochlorines combined was associated with a decrease in the mean reaction time (RT) and the reaction time variability (RTV) in the CPT (β = -15.54, 95% CI:-29.64, -1.45, and β = -7.82, 95% CI: -14.97, -0.67 respectively) and for the mixture of PFAS alone with RT (β = -11.94, 95% CI: -23.29, -0.60). In the single pollutant models, these results were confirmed for the association between perfluorohexanesulfonate (PFHxS) with RT (β = -17.95, 95% CI = -33.35, -2.69) and hexachlorobenzene with RTV in the CPT (β = -5.78, 95% CI: -10.39, -0.76). Furthermore, the participants with prenatal exposure above the limit of quantification for perfluorononanoic acid (PFNA) had a significantly shorter RT and RTV in the CPT (β = -23.38, 95% CI: -41.55, -5.94, and β = -9.54, 95% CI: -19.75, -0.43, respectively).

CONCLUSION

Higher prenatal exposure to a PFAS mixture and a mixture of PFAS and organochlorines combined was associated with better sustained and selective attention during adolescence. The associations seemed to be driven by PFHxS and were not linked to exposure levels at the time of assessment.

Assessing Metabolic Differences Associated with Exposure to Polybrominated Biphenyl and Polychlorinated Biphenyls in the Michigan PBB Registry

BACKGROUND

Polybrominated biphenyls (PBB) and polychlorinated biphenyls (PCB) are persistent organic pollutants with potential endocrine-disrupting effects linked to adverse health outcomes.

OBJECTIVES

In this study, we utilize high-resolution metabolomics (HRM) to identify internal exposure and biological responses underlying PCB and multigenerational PBB exposure for participants enrolled in the Michigan PBB Registry.

METHODS

HRM profiling was conducted on plasma samples collected from 2013 to 2014 from a subset of participants enrolled in the Michigan PBB Registry, including 369 directly exposed individuals (F0) who were alive when PBB mixtures were accidentally introduced into the food chain and 129 participants exposed to PBB in utero or through breastfeeding, if applicable (F1). Metabolome-wide association studies were performed for PBB-153 separately for each generation and Σ PCB (PCB-118, PCB-138, PCB-153, and PCB-180) in the two generations combined, as both had direct PCB exposure. Metabolite and metabolic pathway alterations were evaluated following a well-established untargeted HRM workflow.

RESULTS

Mean levels were 1.75  ng / mL [standard deviation (SD): 13.9] for PBB-153 and 1.04  ng / mL (SD: 0.788) for Σ PCB . Sixty-two and 26 metabolic features were significantly associated with PBB-153 in F0 and F1 [false discovery rate (FDR) p < 0.2 ], respectively. There were 2,861 features associated with Σ PCB (FDR p < 0.2 ). Metabolic pathway enrichment analysis using a bioinformatics tool revealed perturbations associated with Σ PCB in numerous oxidative stress and inflammation pathways (e.g., carnitine shuttle, glycosphingolipid, and vitamin B9 metabolism). Metabolic perturbations associated with PBB-153 in F0 were related to oxidative stress (e.g., pentose phosphate and vitamin C metabolism) and in F1 were related to energy production (e.g., pyrimidine, amino sugars, and lysine metabolism). Using authentic chemical standards, we confirmed the chemical identity of 29 metabolites associated with Σ PCB levels (level 1 evidence).

CONCLUSIONS

Our results demonstrate that serum PBB-153 is associated with alterations in inflammation and oxidative stress-related pathways, which differed when stratified by generation. We also found that Σ PCB was associated with the downregulation of important neurotransmitters, serotonin, and 4-aminobutanoate. These findings provide novel insights for future investigations of molecular mechanisms underlying PBB and PCB exposure on health. https://doi.org/10.1289/EHP12657.

Influence of e-waste exposure on DNA damage and DNA methylation in people living near recycling sites

The association between long-term exposure to e-waste and poor health is well established, but how e-waste exposure affects DNA methylation is understudied. In this study, we measured the DNA damage levels and the alternation of DNA methylation in peripheral blood mononuclear cells (PBMCs) collected from a population exposed to e-waste. The concentration of 28 PCB congeners in the blood samples of e-waste recycling workers was elevated than those of the reference group. DNA damage levels were significantly higher than that of samples from the reference group by detecting the SCGE, CA, and CBMN assays. Eventually, we found that the methylation level of 1233 gene loci was changed in the exposure group. Bioinformatic analysis of differential genes revealed that the hypermethylated genes were enriched in cell component movement and regulation of cell function, and hypomethylated genes were involved in the cellular metabolic process. Among the 30 genes we tested, 14 genes showed a negative correlation between methylation level and expression level. Therefore, e-waste exposure potentially increased the levels of DNA damage and alters DNA methylation, which would likely impact human health.

Causal effects of prenatal and chronic PM2.5 exposures on cognitive function

Growing evidence indicated an association between PM_2.5 exposure and cognitive function, but the causal effect and the cognitive effect of prenatal PM_2.5 exposure remain elusive. We obtained 15,099 subjects from a nationally representative sample of China and measured their cognitive performance. We ascertained subjects' prenatal PM_2.5 exposure and chronic PM_2.5 exposure of the recent two years. Using this national sample, we found that PM_2.5 exposure during the mid- to late-pregnancy was significantly associated with declined cognition and income; chronic PM_2.5 exposure was also independently associated with cognition and income measured at adulthood with greater magnitude. Negative effect modification was observed between prenatal and chronic PM_2.5 exposure. Instrumental variable approach and difference-in-difference study verified causal effects: every 1 μg/m³ increase in prenatal and chronic PM_2.5 exposures were causally associated with -0.22% (-0.38%, -0.06%) and -0.17% (-0.31%, -0.03%) changes in cognitive function, respectively. People with low cognition and low income were more vulnerable to PM_2.5 exposure with greater cognitive and income decline. In the future, although China's improved air quality continues to benefit people and reduce cognitive decline induced by chronic PM_2.5 exposure, high prenatal PM_2.5 exposure will continue to hurt the overall cognition of Chinese population, since in total 360 million people were born during the 2000-2020 polluted era. Prenatal PM_2.5-induced cognitive decline would remain largely unchanged before 2050 and gradually reduce after 2065, regardless of environmental policy scenarios. The long-lasting cognitive impact of PM_2.5 is worth considering while enacting environmental policies.

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.

Polychlorinated Biphenyls (PCBs) in the Environment: Occupational and Exposure Events, Effects on Human Health and Fertility

In the last decade or so, polychlorinated biphenyls (PCBs) garnered renewed attention in the scientific community due to new evidence pointing at their continued presence in the environment and workplaces and the potential human risks related to their presence. PCBs move from the environment to humans through different routes; the dominant pathway is the ingestion of contaminated foods (fish, seafood and dairy products), followed by inhalation (both indoor and outdoor air), and, to a lesser extent, dust ingestion and dermal contact. Numerous studies reported the environmental and occupational exposure to these pollutants, deriving from building materials (flame-retardants, plasticizers, paints, caulking compounds, sealants, fluorescent light ballasts, etc.) and electrical equipment. The highest PCBs contaminations were detected in e-waste recycling sites, suggesting the need for the implementation of remediation strategies of such polluted areas to safeguard the health of workers and local populations. Furthermore, a significant correlation between PCB exposure and increased blood PCB concentrations was observed in people working in PCB-contaminated workplaces. Several epidemiological studies suggest that environmental and occupational exposure to high concentrations of PCBs is associated with different health outcomes, such as neuropsychological and neurobehavioral deficits, dementia, immune system dysfunctions, cardiovascular diseases and cancer. In addition, recent studies indicate that PCBs bioaccumulation can reduce fertility, with harmful effects on the reproductive system that can be passed to offspring. In the near future, further studies are needed to assess the real effects of PCBs exposure at low concentrations for prolonged exposure in workplaces and specific indoor environments.

Neurotoxicants, the Developing Brain, and Mental Health

While life in urban environments may confer a number of benefits, it may also result in a variety of exposures, with toxic consequences for neurodevelopment and neuropsychological health. Neurotoxicants are any of a large number of chemicals or substances that interfere with normal function and/or compromise adaptation in the central and/or peripheral nervous system. Evidence suggests that neurotoxicant effects have a greater effect when occurring in utero and during early childhood. Recent findings exploring neural-level mechanisms provide a crucial opportunity to explore the ways in which environmental conditions may get "under the skin" to impact a number of psychological behaviors and cognitive processes, ultimately allowing for greater synergy between macro- and microlevel efforts to improve mental health in the presence of neurotoxicant exposures. In this review, we provide an overview of 3 types of neurotoxicants related to the built environment and relevant to brain development during childhood and adolescence: lead exposure, outdoor particulate matter pollution, and endocrine-disrupting chemicals. We also discuss mechanisms through which these neurotoxicants affect central nervous system function, including recent evidence from neuroimaging literature. Furthermore, we discuss neurotoxicants and mental health during development in the context of social determinants and how differences in the spatial distribution of neurotoxicant exposures result in health disparities that disproportionately affect low-income and minority populations. Multifaceted approaches incorporating social systems and their effect on neurotoxicant exposures and downstream mental health will be key to reduce societal costs and improve quality of life for children, adolescents, and adults.

Developmental Exposure to a Human-Relevant Polychlorinated Biphenyl Mixture Causes Behavioral Phenotypes That Vary by Sex and Genotype in Juvenile Mice Expressing Human Mutations That Modulate Neuronal Calcium

Polychlorinated biphenyls (PCBs) are putative environmental risks for neurodevelopmental disorders. Here, we tested two hypotheses: (1) developmental exposure to a human-relevant PCB mixture causes behavioral phenotypes relevant to neurodevelopmental disorders; and (2) expression of human mutations that dysregulate neuronal Ca2+ homeostasis influence sensitivity to behavioral effects of developmental PCB exposures. To test these hypotheses, we used mice that expressed a gain-of-function mutation (T4826I) in ryanodine receptor 1 (RYR1), the X-linked fragile X mental retardation 1 (FMR1) CGG repeat expansion or both mutations (double mutant; DM). Transgenic mice and wildtype (WT) mice were exposed to the MARBLES PCB mix at 0, 0.1, 1, and 6 mg/kg/day in the maternal diet throughout gestation and lactation. The MARBLES PCB mix simulates the relative proportions of the 12 most abundant PCB congeners found in the serum of pregnant women at increased risk for having a child with a neurodevelopmental disorder. We assessed ultrasonic vocalizations at postnatal day 7 (P7), spontaneous repetitive behaviors at P25-P30, and sociability at P27-P32. Developmental PCB exposure reduced ultrasonic vocalizations in WT litters in all dose groups, but had no effect on ultrasonic vocalizations in transgenic litters. Developmental PCB exposure significantly increased self-grooming and decreased sociability in WT males in the 0.1 mg/kg dose group, but had no effect on WT females in any dose group. Genotype alone influenced ultrasonic vocalizations, self-grooming and to a lesser extent sociability. Genotype alone also influenced effects of PCBs on sociability. PCB levels in the brain tissue of pups increased in a dose-dependent manner, but within any dose group did not differ between genotypes. In summary, developmental PCB exposure phenocopied social behavior phenotypes observed in mice expressing human mutations that modify intracellular Ca2+ dynamics, and expression of these mutations alleviated PCB effects on ultrasonic vocalizations and repetitive behavior, and modified the dose-response relationships and sex-dependent effects of PCB effects on social behavior. These findings suggest that: (1) developmental PCB exposure causes behavioral phenotypes that vary by sex and genotype; and (2) sex-specific responses to environmental factors may contribute to sex biases in the prevalence and/or severity of neurodevelopmental disorders.

Converging Effects of Three Different Endocrine Disrupters on Sox and Pou Gene Expression in Developing Rat Hippocampus: Possible Role of microRNA in Sex Differences

Endocrine disrupting chemicals (EDCs) can impair hippocampus-dependent behaviors in rat offspring and in children. In search for key processes underlying this effect, we compared the transcriptomes of rat hippocampus on postnatal day 6 after gestational and lactational exposure to three different EDCs at doses known to impair development of learning and memory. Aroclor 1254, a commercial PCB mixture (5 mg/kg or 0.5 mg/kg), or bisphenol A (5 mg/kg or 0.5 mg/kg) were administered in chow, chlorpyrifos (3 mg/kg or 1 mg/kg) was injected subcutaneously. Male hippocampus exhibited a common effect of all three chemicals on genes involved in cell-autonomous processes, Sox6, Sox11, Pou2f2/Oct2, and Pou3f2/Brn2, all upregulated at the high dose. Additional genes of the Sox and Pou families were affected by only one or two of the chemicals. Real time RT PCR showed a comparable expression change for bisphenol A also at the lower dose. Female hippocampus exhibited much fewer genes with expression changes (almost none with false discovery rate <0.05), and none of the genes of the Sox and Pou families was affected. Since gene network analyses in male hippocampus suggested a link between Sox6 and miR-24, known to be repressed by activation of ER-alpha and to repress Sox6 in other tissues, this microRNA was measured. miR-24 was downregulated by all chemicals at the high dose in males. Values of Sox6 mRNA and miR-24 were inversely correlated in individual male hippocampus samples, supporting the hypothesis that the change in Sox6 expression resulted from an action of miR-24. In contrast, miR-24 levels remained unchanged in hippocampus of females. A sexually dimorphic response of miR-24 may thus be at the basis of the sex difference in Sox6 expression changes following exposure to the three chemicals. ER-alpha expression was also sex-dependent, but the expression changes did not parallel those of potential downstream genes such as Sox6. Sox6 is known to suppress differentiation of Parvalbumin (Pvalb)-expressing interneurons. Individual Sox6 levels (FPKM) were inversely correlated with levels of Pvalb, but not with markers of Sox6-independent interneuron subpopulations, Nos1 and 5HT3aR. Effects on interneuron development are further suggested, in males, by expression changes of Nrg1 and its receptor Erbb4, controlling interneuron migration. Our study disclosed new types of EDC-responsive morphogenetic genes, and illustrated the potential relevance of microRNAs in sexually dimorphic EDC actions.

Developmental exposure to non-dioxin-like polychlorinated biphenyls promotes sensory deficits and disrupts dopaminergic and GABAergic signaling in zebrafish

The most abundant polychlorinated biphenyl (PCB) congeners found in the environment and in humans are neurotoxic. This is of particular concern for early life stages because the exposure of the more vulnerable developing nervous system to neurotoxic chemicals can result in neurobehavioral disorders. In this study, we uncover currently unknown links between PCB target mechanisms and neurobehavioral deficits using zebrafish as a vertebrate model. We investigated the effects of the abundant non-dioxin-like (NDL) congener PCB153 on neuronal morphology and synaptic transmission linked to the proper execution of a sensorimotor response. Zebrafish that were exposed during development to concentrations similar to those found in human cord blood and PCB contaminated sites showed a delay in startle response. Morphological and biochemical data demonstrate that even though PCB153-induced swelling of afferent sensory neurons, the disruption of dopaminergic and GABAergic signaling appears to contribute to PCB-induced motor deficits. A similar delay was observed for other NDL congeners but not for the potent dioxin-like congener PCB126. The effects on important and broadly conserved signaling mechanisms in vertebrates suggest that NDL PCBs may contribute to neurodevelopmental abnormalities in humans and increased selection pressures in vertebrate wildlife.

Persistent organic pollutants at the synapse: Shared phenotypes and converging mechanisms of developmental neurotoxicity

The developing nervous system is sensitive to environmental and physiological perturbations in part due to its protracted period of prenatal and postnatal development. Epidemiological and experimental studies link developmental exposures to persistent organic pollutants (POPs) including polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polybrominated diphenyl ethers, and benzo(a)pyrene to increased risk for neurodevelopmental disorders in children. Mechanistic studies reveal that many of the complex cellular processes that occur during sensitive periods of rapid brain development are cellular targets for developmental neurotoxicants. One area of research interest has focused on synapse formation and plasticity, processes that involve the growth and retraction of dendrites and dendritic spines. For each chemical discussed in this review, we summarize the morphological and electrophysiological data that provide evidence that developmental POP exposure produces long-lasting effects on dendritic morphology, spine formation, glutamatergic and GABAergic signaling systems, and synaptic transmission. We also discuss shared intracellular mechanisms, with a focus on calcium and thyroid hormone homeostasis, by which these chemicals act to modify synapses. We conclude our review highlighting research gaps that merit consideration when characterizing synaptic pathology elicited by chemical exposure. These gaps include low-dose and nonmonotonic dose-response effects, the temporal relationship between dendritic growth, spine formation, and synaptic activity, excitation-inhibition balance, hormonal effects, and the need for more studies in females to identify sex differences. By identifying converging pathological mechanisms elicited by POP exposure at the synapse, we can define future research directions that will advance our understanding of these chemicals on synapse structure and function.

Exposure to prenatal PCBs shifts the timing of neurogenesis in the hypothalamus of developing rats

The developing brain is highly sensitive to the hormonal milieu, with gonadal steroid hormones involved in neurogenesis, neural survival, and brain organization. Limited available evidence suggests that endocrine-disrupting chemicals (EDCs) may perturb these developmental processes. In this study, we tested the hypothesis that prenatal exposure to a mixture of polychlorinated biphenyls (PCBs), Aroclor 1221, would disrupt the normal timing of neurogenesis in two hypothalamic regions: the ventromedial nucleus (VMN) and the preoptic area (POA). These regions were selected because of their important roles in the control of sociosexual behaviors that are perturbed in adulthood by prenatal EDC exposure. Pregnant Sprague-Dawley rats were exposed to PCBs from Embryonic Day 8 (E8) to E18, encompassing the period of neurogenesis of all hypothalamic neurons. To determine the birth dates of neurons, bromo-2-deoxy-5-uridine (BrdU) was administered to dams on E12, E14, or E16. On the day after birth, male and female pups were perfused, brains immunolabeled for BrdU, and numbers of cells counted. In the VMN, exposure to PCBs significantly advanced the timing of neurogenesis compared to vehicle-treated pups, without changing the total number of BrdU+ cells. In the POA, PCBs did not change the timing of neurogenesis nor the total number of cells born. This is the first study to show that PCBs can shift the timing of neurogenesis in the hypothalamus, specifically in the VMN but not the POA. This result has implications for functions controlled by the VMN, especially sociosexual behaviors, as well as for sexual selection more generally.

The ENDpoiNTs Project: Novel Testing Strategies for Endocrine Disruptors Linked to Developmental Neurotoxicity

Ubiquitous exposure to endocrine-disrupting chemicals (EDCs) has caused serious concerns about the ability of these chemicals to affect neurodevelopment, among others. Since endocrine disruption (ED)-induced developmental neurotoxicity (DNT) is hardly covered by the chemical testing tools that are currently in regulatory use, the Horizon 2020 research and innovation action ENDpoiNTs has been launched to fill the scientific and methodological gaps related to the assessment of this type of chemical toxicity. The ENDpoiNTs project will generate new knowledge about ED-induced DNT and aims to develop and improve in vitro, in vivo, and in silico models pertaining to ED-linked DNT outcomes for chemical testing. This will be achieved by establishing correlative and causal links between known and novel neurodevelopmental endpoints and endocrine pathways through integration of molecular, cellular, and organismal data from in vitro and in vivo models. Based on this knowledge, the project aims to provide adverse outcome pathways (AOPs) for ED-induced DNT and to develop and integrate new testing tools with high relevance for human health into European and international regulatory frameworks.

Evidence Implicating Non-Dioxin-Like Congeners as the Key Mediators of Polychlorinated Biphenyl (PCB) Developmental Neurotoxicity

Despite being banned from production for decades, polychlorinated biphenyls (PCBs) continue to pose a significant risk to human health. This is due to not only the continued release of legacy PCBs from PCB-containing equipment and materials manufactured prior to the ban on PCB production, but also the inadvertent production of PCBs as byproducts of contemporary pigment and dye production. Evidence from human and animal studies clearly identifies developmental neurotoxicity as a primary endpoint of concern associated with PCB exposures. However, the relative role(s) of specific PCB congeners in mediating the adverse effects of PCBs on the developing nervous system, and the mechanism(s) by which PCBs disrupt typical neurodevelopment remain outstanding questions. New questions are also emerging regarding the potential developmental neurotoxicity of lower chlorinated PCBs that were not present in the legacy commercial PCB mixtures, but constitute a significant proportion of contemporary human PCB exposures. Here, we review behavioral and mechanistic data obtained from experimental models as well as recent epidemiological studies that suggest the non-dioxin-like (NDL) PCBs are primarily responsible for the developmental neurotoxicity associated with PCBs. We also discuss emerging data demonstrating the potential for non-legacy, lower chlorinated PCBs to cause adverse neurodevelopmental outcomes. Molecular targets, the relevance of PCB interactions with these targets to neurodevelopmental disorders, and critical data gaps are addressed as well.

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.

Endocrine-disrupting chemicals alter the neuromolecular phenotype in F2 generation adult male rats

Endocrine-disrupting chemical (EDC) exposures to the fetus have long-lasting effects on health and disease in adulthood. Such EDC exposure to the F1 fetuses also reaches the germ cells that become the F2 generation. Previously, we demonstrated that adult social and communicative behaviors such as ultrasonic vocalizations and mating behaviors were altered by EDCs in F2 rats, especially males. In the current study, we used the brains of these F2 males to ascertain the underlying molecular changes in the hypothalamus related to these behavioral outcomes. Their progenitors were Sprague-Dawley rat dams, treated on pregnancy days 8 to 18 with one of three treatments: a polychlorinated biphenyl (PCB) mixture, Aroclor 1221, selected because it is weakly estrogenic; the anti-androgenic fungicide vinclozolin (VIN); or the vehicle, 6% dimethylsulfoxide in sesame oil (VEH). In adulthood, F1 male and female offspring were bred with untreated partners to generate paternal or maternal lineages of the F2 offspring, the subjects of molecular work. Quantitative real-time PCR was conducted in the medial preoptic area (POA) and the ventromedial nucleus (VMN) of the hypothalamus, selected for their roles in social and sexual behaviors. Of the genes assessed, steroid hormone receptors (estrogen receptor α, androgen receptor, progesterone receptor) but not dopamine receptors 1 and 2 or DNA methyltransferase 3a expression were altered, particularly in the VIN males. Several significant correlations between behavior and gene expression were also detected. These results suggest that preconceptional exposure of male rats to EDCs at the germ cell stage alters the neuromolecular phenotype in adulthood in a lineage-dependent manner.

Benefits of cooperation among large-scale cohort studies and human biomonitoring projects in environmental health research: An exercise in blood lead analysis of the Environment and Child Health International Birth Cohort Group

A number of prospective cohort studies are ongoing worldwide to investigate the impact of foetal and neonatal exposures to chemical substances on child health. To assess multiple exposure (mixture) effects and low prevalence health outcomes it is useful to pool data from several studies and conduct mega-data-analysis. To discuss a path towards data harmonization, representatives from several large-scale birth cohort studies and a biomonitoring programme formed a collaborative group, the Environment and Child Health International Birth Cohort Group (ECHIBCG). In this study, an intra-laboratory trial was performed to harmonize existing blood lead measurements within the groups' studies. Then, decentralized analyses were conducted in individual countries' laboratories to evaluate blood lead levels (BLL) in each study. The measurements of pooled BLL samples in French, German and three Japanese laboratories resulted in an overall mean blood lead concentration of 8.66 μg l-1 (95% confidence interval: 8.59-8.72 μg l-1) with 3.0% relative standard deviation. Except for China's samples, BLL from each study were comparable with mean concentrations below or close to 10 μg l-1. The decentralized multivariate analyses revealed that all models had coefficients of determination below 0.1. Determinants of BLL were current smoking, age >35 years and overweight or obese status. The three variables were associated with an increase in BLL in each of the five studies, most strongly in France by almost 80% and the weakest effect being in Norway with only 15%; for Japan, with the far largest sample (~18,000), the difference was 36%. This study successfully demonstrated that the laboratory analytical methods were sufficiently similar to allow direct comparison of data and showed that it is possible to harmonize the epidemiological data for joint analysis. This exercise showed the challenges in decentralized data analyses and reinforces the need for data harmonization among studies.

Neurotoxicity of polychlorinated biphenyls and related organohalogens

Halogenated organic compounds are pervasive in natural and built environments. Despite restrictions on the production of many of these compounds in most parts of the world through the Stockholm Convention on Persistent Organic Pollutants (POPs), many "legacy" compounds, including polychlorinated biphenyls (PCBs), are routinely detected in human tissues where they continue to pose significant health risks to highly exposed and susceptible populations. A major concern is developmental neurotoxicity, although impacts on neurodegenerative outcomes have also been noted. Here, we review human studies of prenatal and adult exposures to PCBs and describe the state of knowledge regarding outcomes across domains related to cognition (e.g., IQ, language, memory, learning), attention, behavioral regulation and executive function, and social behavior, including traits related to attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASD). We also review current understanding of molecular mechanisms underpinning these associations, with a focus on dopaminergic neurotransmission, thyroid hormone disruption, calcium dyshomeostasis, and oxidative stress. Finally, we briefly consider contemporary sources of organohalogens that may pose human health risks via mechanisms of neurotoxicity common to those ascribed to PCBs.

Association between Early Life Exposure to Air Pollution and Working Memory and Attention

BACKGROUND

Although previous studies have reported negative associations between exposure to air pollution and cognition, studies of the effects of prenatal and postnatal exposures in early childhood have been limited.

OBJECTIVES

We sought to assess the role exposure to fine particulate matter ([Formula: see text]) during different prenatal and postnatal windows may play in children's cognitive development at school age.

METHODS

Within the Brain Development and Air Pollution Ultrafine Particles in School Children (BREATHE) Project, we estimated residential [Formula: see text] exposures by land use regression for the prenatal period and first seven postnatal years of 2,221 children from Barcelona, Spain. The participants ([Formula: see text]) completed computerized tests assessing working memory, attentiveness, and conflict network during four visits in 2012–2013. We used linear mixed effects and distributed lag models to assess the period of exposure to [Formula: see text] in association with cognitive development.

RESULTS

Inverse associations were identified between [Formula: see text] exposure during the fifth and sixth postnatal years and working memory, with boys showing much higher vulnerability. Regarding attention functions, exposure to higher [Formula: see text] levels during the prenatal period and from the fourth postnatal year were associated with a reduction in conflict network performance, though we found no association with attentiveness. The overall estimated cumulative effect of a [Formula: see text] increase in [Formula: see text] resulted in a reduction in the working memory [Formula: see text] score of [Formula: see text] [95% confidence interval (CI): [Formula: see text], [Formula: see text]] points and an increase in the conflict attentional network of 11.31 (95% CI: 6.05, 16.57) milliseconds, indicating a poorer performance.

CONCLUSIONS

Early life exposure to [Formula: see text] was associated with a reduction in fundamental cognitive abilities, including working memory and conflict attentional network. https://doi.org/10.1289/EHP3169.

Comparative Analyses of the 12 Most Abundant PCB Congeners Detected in Human Maternal Serum for Activity at the Thyroid Hormone Receptor and Ryanodine Receptor

Polychlorinated biphenyls (PCBs) pose significant risk to the developing human brain; however, mechanisms of PCB developmental neurotoxicity (DNT) remain controversial. Two widely posited mechanisms are tested here using PCBs identified in pregnant women in the MARBLES cohort who are at increased risk for having a child with a neurodevelopmental disorder (NDD). As determined by gas chromatography-triple quadruple mass spectrometry, the mean PCB level in maternal serum was 2.22 ng/mL. The 12 most abundant PCBs were tested singly and as a mixture mimicking the congener profile in maternal serum for activity at the thyroid hormone receptor (THR) and ryanodine receptor (RyR). Neither the mixture nor the individual congeners (2 fM to 2 μM) exhibited agonistic or antagonistic activity in a THR reporter cell line. However, as determined by equilibrium binding of [3H]ryanodine to RyR1-enriched microsomes, the mixture and the individual congeners (50 nM to 50 μM) increased RyR activity by 2.4-19.2-fold. 4-Hydroxy (OH) and 4-sulfate metabolites of PCBs 11 and 52 had no TH activity; but 4-OH PCB 52 had higher potency than the parent congener toward RyR. These data support evidence implicating RyRs as targets in environmentally triggered NDDs and suggest that PCB effects on the THR are not a predominant mechanism driving PCB DNT. These findings provide scientific rationale regarding a point of departure for quantitative risk assessment of PCB DNT, and identify in vitro assays for screening other environmental pollutants for DNT potential.

Polychlorinated biphenyls influence on autism spectrum disorder risk in the MARBLES cohort

BACKGROUND

Autism spectrum disorder (ASD) is suspected to have environmental and genetic contributions. Polychlorinated biphenyls (PCBs) are environmental risk factors of interest due to their potential as neurodevelopmental toxicants and environmental persistence despite a US production ban in the 1970s.

METHODS

Participants were mother-child pairs from MARBLES, a high-risk pregnancy cohort that enrolls families who have one child diagnosed with ASD and are planning to have another child. PCB concentrations were measured in maternal blood at each trimester of pregnancy using gas chromatography coupled with triple quadruple mass spectrometry. Concentrations were summed into total PCB and two categories based on function/mechanisms of action: dioxin-like (DL), and ryanodine receptor (RyR)-activating PCBs. Multinomial logistic regression assessed risk of clinical outcome classification of ASD and non-typical development (Non-TD) compared to typically developing (TD) in the children at 3 years old.

RESULTS

A total of 104 mother-child pairs were included. There were no significant associations for total PCB; however, there were borderline significant associations between DL-PCBs and decreased risk for Non-TD outcome classification (adjusted OR: 0.41 (95% CI 0.15-1.14)) and between RyR-activating PCBs and increased risk for ASD outcome classification (adjusted OR: 2.63 (95% CI 0.87-7.97)).

CONCLUSION

This study does not provide strong supporting evidence that PCBs are risk factors for ASD or Non-TD. However, these analyses suggest the need to explore more deeply into subsets of PCBs as risk factors based on their function and structure in larger cohort studies where non-monotonic dose-response patterns can be better evaluated.

Persistent organic pollutants in fish: biomonitoring and cocktail effect with implications for food safety

The impact of anthropogenic wastes of persistent organic pollutants (POPs) on the marine environment has increased in the last decades. POPs include polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs). To assess the levels of these POPs in the wild fish population, pelagic and benthopelagic predator fish species were selected as biomonitors. For detection and quantification of POPs in muscular tissues, a simple extraction through Accelerated-Solvent-Extraction (ASE) with an 'in-line' clean up purification approach was applied, followed by a GC-MS/MS analysis. Concentrations of sum DDT, sum HCH and endrin correlated with all PCB concentrations. Significant differences among fish species were found for all OCs and all PCBs except PCB 31 and 101. Blackspot seabream had the highest PCB concentrations; OCs were highest in tuna. Due to major concerns regarding fish population losses and the possible human chronic exposure to contaminated fish, studies addressing combined effects of multiple POPs ('cocktail effect') should be implemented. Our data motivate further experimental and observational studies in fish to define adequate baseline levels for cumulative human exposure and potential role of these contaminants for food safety.

Air pollution and body burden of persistent organic pollutants at an electronic waste recycling area of China

This paper reviews the concentrations of persistent organic pollutants (POPs) in atmosphere of an electronic waste (e-waste) recycling town, Guiyu, in Southeast China, focusing on polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). We assess the evidence for the association between air pollution and human body burden, to provide an indication of the severity of respiratory exposure. Compared with standards and available existing data for other areas, it clearly shows that four typical POPs, derived from recycling processes, lead to serious atmospheric pollution and heavy body burden. From published data, the estimated respiratory exposure doses of Guiyu adults and children, varied between 2.48-10.37 and 3.25-13.6 ng kg^-1 body weight (bw) day^-1 for PBDEs, 2.31-7.6 and 4.09-13.58 pg World Health Organization-Toxic Equivalent Quantity (WHO-TEQ) kg^-1 bw day^-1 for PCDD/Fs, 5.57 and 20.52 ng kg^-1 bw day^-1 for PCBs, and 8.59-50.01 and 31.64-184.14 ng kg^-1 bw day^-1 for PAHs, respectively. These results show that air pollution is more harmful to children. Furthermore, except for PBDEs, the hazard quotient (HQ) of the other three pollutants was rated more than 1 by respiratory exposure only, and all of them are at risk of carcinogenesis. So we speculate these pollutants enter the body mainly through air inhalation, making respiratory exposure may be more important than dietary exposure in the Guiyu e-waste recycling area. Effective management policies and remediation techniques are urgently needed to prevent the deterioration of ambient air quality in the e-waste recycling area.

3,3'-Dichlorobiphenyl (PCB 11) promotes dendritic arborization in primary rat cortical neurons via a CREB-dependent mechanism

PCB 11 (3,3'-dichlorobiphenyl), a contemporary congener produced as a byproduct of current pigment production processes, has recently emerged as a prevalent worldwide pollutant. We recently demonstrated that exposure to PCB 11 increases dendritic arborization in vitro, but the mechanism(s) mediating this effect remain unknown. To address this data gap, primary cortical neuron-glia co-cultures derived from neonatal Sprague-Dawley rats were exposed for 48 h to either vehicle (0.1% DMSO) or PCB 11 at concentrations ranging from 1 fM to 1 nM in the absence or presence of pharmacologic antagonists of established molecular targets of higher chlorinated PCBs. Reporter cell lines were used to test activity of PCB 11 at the aryl hydrocarbon receptor (AhR) and thyroid hormone receptor (THR). PCB 11 lacked activity at the AhR and THR, and antagonism of these receptors had no effect on the dendrite-promoting activity of PCB 11. Pharmacologic antagonism of various calcium channels or treatment with antioxidants also did not alter PCB 11-induced dendritic arborization. In contrast, pharmacologic blockade or shRNA knockdown of cAMP response element-binding protein (CREB) significantly decreased dendritic growth in PCB 11-exposed cultures, suggesting PCB 11 promotes dendritic growth via CREB-mediated mechanisms. Since CREB signaling is crucial for normal neurodevelopment, and perturbations of CREB signaling have been associated with neurodevelopmental disorders, our findings suggest that this contemporary pollutant poses a threat to the developing brain, particularly in individuals with heritable mutations that promote CREB signaling.

Perinatal exposure to endocrine disrupting compounds and the control of feeding behavior-An overview

Endocrine disrupting compounds (EDC) are ubiquitous environmental contaminants that can interact with steroid and nuclear receptors or alter hormone production. Many studies have reported that perinatal exposure to EDC including bisphenol A, PCB, dioxins, and DDT disrupt energy balance, body weight, adiposity, or glucose homeostasis in rodent offspring. However, little information exists on the effects of perinatal EDC exposure on the control of feeding behaviors and meal pattern (size, frequency, duration), which may contribute to their obesogenic properties. Feeding behaviors are controlled centrally through communication between the hindbrain and hypothalamus with inputs from the emotion and reward centers of the brain and modulated by peripheral hormones like ghrelin and leptin. Discrete hypothalamic nuclei (arcuate nucleus, paraventricular nucleus, lateral and dorsomedial hypothalamus, and ventromedial nucleus) project numerous reciprocal neural connections between each other and to other brain regions including the hindbrain (nucleus tractus solitarius and parabrachial nucleus). Most studies on the effects of perinatal EDC exposure examine simple crude food intake over the course of the experiment or for a short period in adult models. In addition, these studies do not examine EDC's impacts on the feeding neurocircuitry of the hypothalamus-hindbrain, the response to peripheral hormones (leptin, ghrelin, cholecystokinin, etc.) after refeeding, or other feeding behavior paradigms. The purpose of this review is to discuss those few studies that report crude food or energy intake after perinatal EDC exposure and to explore the need for deeper investigations in the hypothalamic-hindbrain neurocircuitry and discrete feeding behaviors.

Endocrine disruption and differential gene expression in sentinel fish on St. Lawrence Island, Alaska: Health implications for indigenous residents

People living a subsistence lifestyle in the Arctic are highly exposed to persistent organic pollutants, including polychlorinated biphenyls (PCBs). Formerly Used Defense (FUD) sites are point sources of PCB pollution; the Arctic contains thousands of FUD sites, many co-located with indigenous villages. We investigated PCB profiles and biological effects in freshwater fish (Alaska blackfish [Dallia pectoralis] and ninespine stickleback [Pungitius pungitius]) living upstream and downstream of the Northeast Cape FUD site on St. Lawrence Island in the Bering Sea. Despite extensive site remediation, fish remained contaminated with PCBs. Vitellogenin concentrations in males indicated exposure to estrogenic contaminants, and some fish were hypothyroid. Downstream fish showed altered DNA methylation in gonads and altered gene expression related to DNA replication, response to DNA damage, and cell signaling. This study demonstrates that, even after site remediation, contaminants from Cold War FUD sites in remote regions of the Arctic remain a potential health threat to local residents - in this case, Yupik people who had no influence over site selection and use by the United States military.

Impact of commuting exposure to traffic-related air pollution on cognitive development in children walking to school

A few studies have found associations between the exposure to traffic-related air pollution at school and/or home and cognitive development. The impact on cognitive development of the exposure to air pollutants during commuting has not been explored. We aimed to assess the role of the exposure to traffic-related air pollutants during walking commute to school on cognitive development of children. We performed a longitudinal study of children (n = 1,234, aged 7-10 y) from 39 schools in Barcelona (Catalonia, Spain) who commuted by foot to school. Children were tested four times during a 12-month follow-up to characterize their developmental trajectories of working memory (d' of the three-back numbers test) and inattentiveness (hit reaction time standard error of the Attention Network Test). Average particulate matter ≤2.5 μm (PM_2.5), Black Carbon (BC) and NO₂ concentrations were estimated using Land Use Regression for the shortest walking route to school. Differences in cognitive growth were evaluated by linear mixed effects models with age-by-pollutant interaction terms. Exposure to PM_2.5 and BC from the commutes by foot was associated with a reduction in the growth of working memory (an interquartile range increase in PM_2.5 and BC concentrations decreased the annual growth of working memory by 5.4 (95% CI [-10.2, -0.6]) and 4.6 (95% CI [-9.0, -0.1]) points, respectively). The findings for NO₂ were not conclusive and none of the pollutants were associated with inattentiveness. Efforts should be made to implement pedestrian school pathways through low traffic streets in order to increase security and minimize children's exposure to air pollutants.

PCBs and measures of attention and impulsivity on a continuous performance task of young adults

The present study examines the relationship between current body burden of persistent PCBs and attention and impulsivity in 140 Akwesasne Mohawk young adults aged 17 to 21 whose environment has been contaminated by industrial effluent. Attention and impulsivity were measured by errors of omission, errors of commission, and patterns of reaction time responses on the Conners Continuous Performance Test. The PCB measure was the sum of those persistent PCB congeners detected in 50% of the participants. After adjusting for multiple covariates, regression analyses showed a significant positive relationship between PCB levels and omission scores, but only for males.

CDC42 expression is altered by dioxin exposure and mediated by multilevel regulations via AhR in human neuroblastoma cells

Emerging evidence has shown that dioxin causes dysregulation of microRNAs (miRs) in a variety of tissues or cells. However, little is known about dioxin effects on neuronal miRs expression. In the present study, 277 differentially expressed miRs were identified by miRs microarray analysis in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, at 10⁻¹⁰ M) treated SK-N-SH neuroblastoma cells. Among them, 53 miRs exhibited changes of more than 0.4-fold. Consistent with the microarray data, we verified the induction effect of TCDD on hsa-miR-608 expression, which is a primate-specific miR associated with brain functions. Bioinformatics analysis showed involvement of hsa-miR-608 in cytoskeleton organization, in which one of the hsa-miR-608 target genes, Cell Division Cycle 42 (CDC42), might play a role. We also confirmed induction of CDC42 expression by TCDD in SK-N-SH cells. TCDD induced the expression of CDC42 mRNA in hsa-miR-608 inhibitor transfected cells more obviously than in control cells, suggesting involvement of both transcriptional and post-transcriptional mechanisms in the TCDD-induced CDC42 regulation. Furthermore, CH223191, an antagonist of the aryl hydrocarbon receptor (AhR), counteracted TCDD-induced hsa-miR-608 and CDC42 expression. These results indicated that AhR not only mediates transcriptional induction of CDC42, but also hsa-miR-608-induced post-transcriptional regulation of CDC42 in dioxin treated neuroblastoma cells.

Relative toxicity for indoor semi volatile organic compounds based on neuronal death

BACKGROUND

Semi Volatile Organic Compounds (SVOCs) are contaminants commonly found in dwellings as a result of their use as plasticizers, flame retardants, or pesticides in building materials and consumer products. Many SVOCs are suspected of being neurotoxic, based on mammal experimentation (impairment of locomotor activity, spatial learning/memory or behavioral changes), raising the question of cumulative risk assessment. The aim of this work is to estimate the relative toxicity of such SVOCs, based on neuronal death.

METHOD

SVOCs fulfilling the following conditions were included: detection frequency >10% in dwellings, availability of data on effects or mechanism of action for neurotoxicity, and availability of dose-response relationships based on cell viability assays as a proxy of neuronal death. Benchmark concentration values (BMC) were estimated using a Hill model, and compared to assess relative toxicity.

RESULTS

Of the 58 SVOCs selected, 28 were suspected of being neurotoxic in mammals, and 21 have been documented as inducing a decrease in cell viability in vitro. 13 have at least one dose-response relationship that can be used to derive a BMC based on a 10% fall in neuronal viability. Based on this in vitro endpoint, PCB-153 appeared to be the most toxic compound, having the lowest BMC₁₀ (0.072μM) and diazinon the least toxic compound, having the highest BMC₁₀ (94.35μM). We showed that experimental designs (in particular choice of cell lines) had a significant influence on BMC calculation.

CONCLUSION

For the first time, the relative in vitro toxicity of 13 indoor contaminants belonging to different chemical families has been assessed on the basis of neuronal cell viability. Lack of comparable toxicity datasets limits the number of SVOCs that can be included. More standardized protocols in terms of cell lines, species and exposure duration should be developed with a view to cumulative risk assessment.

Exploration of potential biomarkers and related biological pathways for PCB exposure in maternal and cord serum: A pilot birth cohort study in Chiba, Japan

Polychlorinated biphenyls (PCBs) have been associated with adverse human reproductive and fetal developmental measures or outcomes because of their endocrine-disrupting effects; however, the biological mechanisms of adverse effects of PCB exposure in humans are not currently well established. In this study, we aimed to identify the biological pathways and potential biomarkers of PCB exposure in maternal and umbilical cord serum using a hydrophilic interaction chromatography-tandem mass spectrometry (HILIC-MS/MS) metabolomics platform. The median concentration of total PCBs in maternal (n=93) and cord serum (n=93) were 350 and 70pgg^-1 wet wt, respectively. PCB levels in maternal and fetal serum from the Chiba Study of Mother and Children's Health (C-MACH) cohort are comparable to those of earlier cohort studies conducted in Japan, the USA, and European countries. We used the random forest model with the metabolome profile to predict exposure levels of PCB (first quartile [Q1] and fourth quartile [Q4]) for pregnant women and fetuses. In the prediction model for classification of Q1 versus Q4 (area-under-curve [AUC]: pregnant women=0.812 and fetuses=0.919), citraconic acid level in maternal serum and ethanolamine, p-hydroxybenzoate, and purine levels in cord serum had >0.70 AUC values. These candidate biomarkers and metabolite included in composited models were related to glutathione and amino acid metabolism in maternal serum and the amino acid metabolism and ubiquinone and other terpenoid-quinone biosynthesis in cord serum (FDR <0.10), indicating disruption of metabolic pathways by PCB exposure in pregnant women and fetuses. These results showed that metabolome analysis might be useful to explore potential biomarkers and related biological pathways for PCB exposure. Thus, more detailed studies are needed to verify sensitivity of the biomarkers and clarify the biochemical changes resulting from PCB exposure.

Prenatal PBDE and PCB Exposures and Reading, Cognition, and Externalizing Behavior in Children

BACKGROUND

Prenatal polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) exposures may influence children's neurodevelopment.

OBJECTIVE

We examined the association of prenatal PBDE and PCB exposures with children's reading skills at ages 5 and 8 years, Full-Scale Intelligence Quotient (FSIQ), and externalizing behavior problems at age 8 years.

METHODS

From 239 mother-child pairs recruited (2003-2006) in Cincinnati, Ohio, we measured maternal serum PBDE and PCB concentrations, assessed child's reading skills using the Woodcock-Johnson Tests of Achievement III (WJ-III) at age 5 years and the Wide Range Achievement Test-4 (WRAT-4) at age 8 years, tested FSIQ using the Wechsler Intelligence Scale for Children-IV (WISC-IV), and externalizing behavior problems using the Behavioral Assessment System for Children-2 (BASC-2) at age 8 years. We used multiple linear regression to examine the association of prenatal PBDE and PCB concentrations and reading, FSIQ, and externalizing behavior problems after adjusting for covariates.

RESULTS

An increase of Sum4PBDEs (BDE-47, BDE-99, BDE-100, and BDE-153) by 10 times was not significantly associated with reading scores at age 5 years at the p = 0.05 level but was inversely associated with Reading Composite scores (β: -6.2, 95% CI: -11.7, -0.6) and FSIQ (β: -5.3, 95% CI: -10.6, -0.02) at age 8 years; it was positively associated with the score for externalizing behavior problems (β: 3.5, 95% CI: -0.1, 7.2) at age 8 years. Prenatal Sum4PCBs (PCB-118, -153, -138-158, and -180) was not significantly associated with a child's reading skills, FSIQ, and externalizing behavior problems.

CONCLUSION

Prenatal PBDE concentration was inversely associated with reading skills and FSIQ and positively associated with externalizing behavior problems at age 8 years. No significant associations were found in prenatal PCB concentration.

Avoid the PCB mistakes: A more sustainable future for ionic liquids

Based on our original knowledge and experience on both polychlorinated biphenyls (PCBs) identification in aquatic ecosystems, and use of ionic liquids (ILs) as solvents and/or co-catalysts in green chemistry, we drawn a dared comparison between these two families. Indeed, PCBs has been used during several decades for their new properties, but are now considered as prevalent and persistent pollutants; some toxic effects on environment or human are still revealed. ILs, often designated as "green solvents" are increasingly used in numerous applications, but few studies reported about their environmental impact are still controversial. Through a parallel between properties and applications of PCBs and ILs, we wondered if history could not repeat itself, and how to provide a better future for ILs. Here, we provide some interesting comparisons and we discuss which tracks it could be important to follow for ILs applications in order to avoid the errors done with PCBs.

Epigenetic impacts of endocrine disruptors in the brain

The acquisition of reproductive competence is organized and activated by steroid hormones acting upon the hypothalamus during critical windows of development. This review describes the potential role of epigenetic processes, particularly DNA methylation, in the regulation of sexual differentiation of the hypothalamus by hormones. We examine disruption of these processes by endocrine-disrupting chemicals (EDCs) in an age-, sex-, and region-specific manner, focusing on how perinatal EDCs act through epigenetic mechanisms to reprogram DNA methylation and sex steroid hormone receptor expression throughout life. These receptors are necessary for brain sexual differentiation and their altered expression may underlie disrupted reproductive physiology and behavior. Finally, we review the literature on histone modifications and non-coding RNA involvement in brain sexual differentiation and their perturbation by EDCs. By putting these data into a sex and developmental context we conclude that perinatal EDC exposure alters the developmental trajectory of reproductive neuroendocrine systems in a sex-specific manner.

Review of reviews on exposures to synthetic organic chemicals and children's neurodevelopment: Methodological and interpretation challenges

Environmental epidemiology data are becoming increasingly important in public health decision making, which commonly incorporates a systematic review of multiple studies. This review addresses two fundamental questions: What is the quality of available reviews on associations between exposure to synthetic organic chemicals and neurodevelopmental outcomes? What is the value (e.g., quality and consistency) of the underlying literature? Published reviews on associations between synthetic organic environmental chemical exposures and neurodevelopmental outcomes in children were systematically evaluated. Seventy-four relevant reviews were identified, and these were evaluated with respect to four methodological characteristics: (1) systematic inclusion/exclusion criteria and reproducible methods for search and retrieval of studies; (2) structured evaluation of underlying data quality; (3) systematic assessment of consistency across specific exposure-outcome associations; and (4) evaluation of reporting/publication bias. None of the 74 reviews fully met the criteria for all four methodological characteristics. Only four reviews met two criteria, and six reviews fulfilled only one criterion. Perhaps more importantly, the higher quality reviews were not able to meet all of the criteria owing to the shortcomings of underlying studies, which lacked comparability in terms of specific research question of interest, overall design, exposure assessment, outcome ascertainment, and analytic methods. Thus, even the most thoughtful and rigorous review may be of limited value if the underlying literature includes investigations that address different hypotheses and are beset by methodological inconsistencies and limitations. Issues identified in this review of reviews illustrate considerable challenges that are facing assessments of epidemiological evidence.

Prenatal exposure to persistent organic pollutants in association with offspring neuropsychological development at 4years of age: The Rhea mother-child cohort, Crete, Greece

BACKGROUND

Persistent Organic Pollutants (POPs) are highly-resistant compounds to environmental degradation and due to fat solubility they bioaccumulate through the food chain. As they cross the placenta, in utero exposure to POPs could disrupt child neurodevelopment as they are considered to be neurotoxic.

AIMS

We examined whether in utero exposure to levels of different POPs is associated with offspring cognitive and behavioral outcomes at 4years of age in a mother-child cohort in Crete, Greece (Rhea study).

METHODS

We included 689 mother-child pairs. Concentrations of several polychlorinated biphenyls (PCBs) and other organochlorine compounds (dichlorodiphenyl dichloroethene [DDE], hexachlorobenzene [HCB]) were determined in maternal serum collected in the first trimester of pregnancy by triple quadrupole mass spectrometry. Neurodevelopment at 4years was assessed by means of the McCarthy Scales of Children's Abilities. Behavioral difficulties were assessed by Strengths and Difficulties Questionnaire and Attention Deficit Hyperactivity Disorder Test. Linear regression analyses were used to estimate the associations between the exposures and outcomes of interest after adjustment for potential confounders.

RESULTS

Children with "high" HCB concentrations (≥90th percentile) in maternal serum, demonstrated decreased scores in perceptual performance (adjusted β=-6.07; 95% CI: -10.17, -1.97), general cognitive (adjusted β=-4.97; 95% CI: -8.99, -0.96), executive function (adjusted β=-6.24; 95% CI: -10.36, -2.11) and working memory (adjusted β=-4.71; 95% CI: -9.05, -0.36) scales at 4years of age. High exposure to PCBs (≥90th percentile) during pregnancy was associated with a 4.62 points reduction in working memory score at 4years of age (95% CI: -9.10, -0.14). Prenatal exposure to DDE, HCB and PCBs was not associated with child behavioral difficulties.

CONCLUSIONS

The findings suggest that prenatal exposure to HCB and PCBs may contribute to reduced cognitive development at preschool age. Our results raise the possibility that exposure to HCB may play a more important role in child cognition than previously considered.

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.

The influence of maternal dietary exposure to dioxins and PCBs during pregnancy on ADHD symptoms and cognitive functions in Norwegian preschool children

BACKGROUND

Polychlorinated dibenzo-p-dioxins/dibenzofurans (dioxins) and polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) with potentially adverse impact on child neurodevelopment. Whether the potential detrimental effects of dioxins and PCBs on neurodevelopment are of specific or unspecific character is not clear.

OBJECTIVES

The purpose of the current study was to examine the influence of maternal dietary exposure to dioxins and PCBs on ADHD symptoms and cognitive functioning in preschoolers. We aimed to investigate a range of functions, in particular IQ, expressive language, and executive functions.

MATERIAL AND METHODS

This study includes n=1024 children enrolled in a longitudinal prospective study of ADHD (the ADHD Study), with participants recruited from The Norwegian Mother and Child Cohort Study (MoBa). Boys and girls aged 3.5years participated in extensive clinical assessments using well-validated tools; The Preschool Age Psychiatric Assessment interview (PAPA), Stanford-Binet 5th revision (SB-5), Child Development Inventory (CDI), and Behavior Rating Inventory of Executive Function, Preschool version (BRIEF-P). Maternal dietary exposure to dioxins and PCBs was estimated based on a validated food frequency questionnaire (FFQ) answered mid-pregnancy and a database of dioxin and PCB concentrations in Norwegian foods. Exposure to dioxins and dioxin-like PCBs (dl-compounds) was expressed in total toxic equivalents (TEQ), and PCB-153 was used as marker for non-dioxin-like PCBs (ndl-PCBs). Generalized linear and additive models adjusted for confounders were used to examine exposure-outcome associations.

RESULTS

Exposure to PCB-153 or dl-compound was not significantly associated with any of the outcome measures when analyses were performed for boys and girls together. After stratifying by sex, adjusted analyses indicated a small inverse association with language in girls. An increase in the exposure variables of 1 SD was associated with a reduction in language score of -0.2 [CI -0.4, -0.1] for PCB-153 and -0.2 [CI -0.5, -0.1] for dl-compounds in girls. For boys, exposure to PCB-153 or dl-compounds was not associated with language skills. The difference between sex-specific associations was not statistically significant (p-value=0.13). No sex-specific effects were observed for ADHD-symptoms, IQ scores, or executive functions.

CONCLUSIONS

We found no indications that variation in current low-level exposure to PCB-153 or dl-compounds in Norway is associated with variation ADHD-symptoms, verbal/non-verbal IQ, or executive functions including working memory in preschoolers. However, our findings indicated that maternal dietary exposure to PCB-153 or dl-compounds during pregnancy was significantly associated with poorer expressive language skills in preschool girls, although the sex-specific associations were not significantly different.

Dietary and Socio-Demographic Determinants of Serum Persistent Organic Pollutants (POPs) Levels in Pregnant Women in Tehran

Objective: To determine the levels of Polychlorinated biphenyls (PCBs) and Polybrominateddiphenyl ethers (PBDEs) as persistent organic pollutants (POPs) in serum of primiparous women at the third trimester of pregnancy and identify the main determinants of POPs levels such as socio-demographic, lifestyle, and diet in Tehran. Materials and methods: One- hundred eighty five serum samples from two simultaneous case-control studies were collected from September 2013 until August 2015.Ten most abundant PCB congeners (International Union of Pure and Applied Chemistry (IUPAC) congeners 28, 52, 74, 99, 101, 118, 138, 153, 180 and 187) as well as eight PBDE congeners (IUPAC congeners 28, 47, 99, 100, 153, 154, 183 and 209)were analyzed by Gas Chromatography Mass Spectrometry (GC/MS). Multiple linear regression analysis was conducted to explain the relationship between total PCBs and total BPDEs and most detected congeners and some determinants, separately. Results: The mean (SD) age of the participating women was 27.82 ± 5.24 years. The geometric mean (SD) of total PCBs was 2.42 ± 2.26 and total PBDEs was 1.28 ± 1.41 ng/g lipid. Only the PCB 138, PCB 153 and PBDE 153 were detected in 100% of samples. We observed a significant relationship between the time of being indoors and total PBDEs (P = 0.03). Passive smoking was significantly associated with PCB 153 (P = 0.049). The results of the linear regression analysis showed the negative and weak association (P-value < 0.05) between diet (egg and fat and oil consumption) and POPs in this population. Conclusion: It seems the most common route of exposure to PBDEs in our population is indoor pollutants. Meanwhile inhalation of smoke from environment is a route of exposure to PCB 153. Further study is needed to evaluate the effects of socio-demographics and especially dietary intake on POPs level.

Chaotic time series prediction for prenatal exposure to polychlorinated biphenyls in umbilical cord blood using the least squares SEATR model

Chaotic time series prediction based on nonlinear systems showed a superior performance in prediction field. We studied prenatal exposure to polychlorinated biphenyls (PCBs) by chaotic time series prediction using the least squares self-exciting threshold autoregressive (SEATR) model in umbilical cord blood in an electronic waste (e-waste) contaminated area. The specific prediction steps basing on the proposal methods for prenatal PCB exposure were put forward, and the proposed scheme's validity was further verified by numerical simulation experiments. Experiment results show: 1) seven kinds of PCB congeners negatively correlate with five different indices for birth status: newborn weight, height, gestational age, Apgar score and anogenital distance; 2) prenatal PCB exposed group at greater risks compared to the reference group; 3) PCBs increasingly accumulated with time in newborns; and 4) the possibility of newborns suffering from related diseases in the future was greater. The desirable numerical simulation experiments results demonstrated the feasibility of applying mathematical model in the environmental toxicology field.

Determinants of plasma PCB, brominated flame retardants, and organochlorine pesticides in pregnant women and 3 year old children in The Norwegian Mother and Child Cohort Study

BACKGROUND

Exposure to persistent organic pollutants (POPs) during prenatal and postnatal life has been extensively studied in relation to adverse health effects in children.

OBJECTIVES

The aim was to identify determinants of the concentrations of polychlorinated biphenyls (PCBs), brominated flame retardants (polybrominated diphenyl ethers, PBDEs; polybrominated biphenyl, PBB), and organochlorine pesticides (OCPs) in blood samples from pregnant women and children in The Norwegian Mother and Child Cohort Study (MoBa).

METHODS

Blood samples were collected from two independent subsamples within MoBa; a group of women (n=96) enrolled in mid-pregnancy during the years 2002-2008 and a group of 3 year old children (n=99) participating during 2010-2011. PCB congeners (74, 99, 138, 153, 180, 170, 194, 209, 105, 114, 118, 156, 157, 167, and 189), brominated flame retardants (PBDE-28, 47, 99, 100, 153, 154, and PBB-153), as well as the OCPs hexachlorobenzene (HCB), oxychlordane, 4,4'dichlorodiphenyltrichloroethane (DDT), and 4,4'dichlorodiphenyldichloroethylene (DDE) were measured in both pregnant women and children.

RESULTS

Age, low parity, and low pre-pregnant BMI were the most important determinants of increased plasma concentrations of POPs in pregnant women. In 3 year old children, prolonged breastfeeding duration was a major determinant of increased POP concentrations. Estimated dietary exposure to PCBs during pregnancy was positively associated with plasma concentrations in 3 year old children, but not in pregnant women. Plasma concentrations were approximately 40% higher in children compared to pregnant women.

CONCLUSIONS

Several factors associated with exposure and toxicokinetics, i.e. accumulation, excretion and transfer via breastmilk of POPs were the main predictors of POP levels in pregnant women and children. Diet, which is the main exposure source for these compounds in the general population, was found to predict PCB levels only among children. For the PBDEs, for which non-dietary sources are more important, toxicokinetic factors appeared to have less predictive impact.