Neonatal Exposure to Higher Brominated Diphenyl Ethers, Hepta-, Octa-, or Nonabromodiphenyl Ether, Impairs Spontaneous Behavior and Learning and Memory Functions of Adult Mice

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Metabolomic insights into neurological effects of BDE-47 exposure in the sea cucumber Apostichopus japonicus

The persistent organic pollutant 2,2',4,4'-Tetrabromodiphenyl ether (BDE-47), a prevalent congener among polybrominated diphenyl ethers (PBDEs), exhibits potent bioaccumulation and toxicity. Despite extensive research into the adverse effects of BDE-47, its neurotoxicity in sea cucumbers remains unexplored. Given the crucial role of the sea cucumber's nervous system in survival and adaptation, evaluating the impacts of BDE-47 is vital for sustainable aquaculture and consumption. In this study, we employed ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Triple-TOF-MS) to analyze metabolomic changes in neuro-related tissues of Apostichopus japonicus exposed to low (0.1 µg/L), medium (1.0 µg/L), and high (10.0 µg/L) BDE-47 concentrations. We identified significantly changed metabolites in each exposure group (87 in low, 79 in medium, and 102 in high), affecting a variety of physiological processes such as steroid hormone balance, nucleotide metabolism, energy metabolism, neurotransmitter levels, and neuroprotection. In addition, we identified concentration-dependent, common, and some other metabolic responses in the neuro-related tissues. Our findings reveal critical insights into the neurotoxic effects of BDE-47 in sea cucumbers and contribute to risk assessment related to BDE-47 exposure in the sea cucumber industry, paving the way for future neurotoxicological research in invertebrates.

Perfluorinated chemicals (PFOA) can, by interacting with highly brominated diphenyl ethers (PBDE 209) during a defined period of neonatal brain development, exacerbate neurobehavioural defects

Perfluorinated compounds (PFCs) and polybrominated diphenyl ethers (PBDEs) are ubiquitous persistent environmental compounds, present in humans and at higher levels in infants/children than in adults. This study shows that co-exposure to pentadecafluorooctanoic acid (PFOA) and 2,2',3,3',4,4',5,5',6,6'-decaBDE (PBDE 209) can significantly exacerbate developmental neurobehavioural defects. Neonatal male NMRI mice, 3 and 10 days old, were exposed perorally to PBDE 209 (1.4 or 8.0 μmol/kg bw), PFOA (1.4 or 14 μmol/kg bw), co-exposed to PBDE 209 and PFOA (at the given doses), or a vehicle (20% fat emulsion) and observed for spontaneous behaviour in a novel home environment when 2 and 4 months old. The behavioural defects observed included hyperactivity and reduced habituation indicating cognitive defects. This interaction appears most likely dependent on the presence of PBDE 209 and/or its metabolites together with PFOA, during a defined critical period of neonatal brain development, corresponding to the perinatal and newborn period in humans.

Impact of Chemical Endocrine Disruptors and Hormone Modulators on the Endocrine System

There is growing concern regarding the health and safety issues of endocrine-disrupting chemicals (EDCs). Long-term exposure to EDCs has alarming adverse health effects through both hormone-direct and hormone-indirect pathways. Non-chemical agents, including physical agents such as artificial light, radiation, temperature, and stress exposure, are currently poorly investigated, even though they can seriously affect the endocrine system, by modulation of hormonal action. Several mechanisms have been suggested to explain the interference of EDCs with hormonal activity. However, difficulty in quantifying the exposure, low standardization of studies, and the presence of confounding factors do not allow the establishment of a causal relationship between endocrine disorders and exposure to specific toxic agents. In this review, we focus on recent findings on the effects of EDCs and hormone system modulators on the endocrine system, including the thyroid, parathyroid glands, adrenal steroidogenesis, beta-cell function, and male and female reproductive function.

The association between prenatal concentrations of polybrominated diphenyl ether and child cognitive and psychomotor function

Previous studies suggest a negative association between prenatal polybrominated diphenyl ethers (PBDEs) exposure and child cognitive and psychomotor development. However, the timing of the relationship between PBDE exposure and neurodevelopment is still unclear. We examined the association between PBDE concentration at two different prenatal times (early and late pregnancy) and cognitive function in children 6-8 years of age.

Methods

Eight hundred pregnant women were recruited between 2007 and 2009 from Sherbrooke, Canada. Four PBDE congeners (BDE-47, -99, -100, and -153) were measured in maternal plasma samples collected during early pregnancy (12 weeks of gestation) and at delivery. At 6-8 years of age, 355 children completed a series of subtests spanning multiple neuropsychologic domains: verbal and memory skills were measured using the Wechsler Intelligence Scale for Children, Fourth Edition; visuospatial processing using both Wechsler Intelligence Scale for Children, Fourth Edition and Neuropsychological Assessment second edition; and attention was assessed through the Test of Everyday Attention for Children. Additionally, parents completed subtests from the Developmental Coordination Disorder Questionnaire to measure child motor control. We used linear regression and quantile g-computation models to estimate associations of PBDE congener concentrations and psychologic test scores.

Results

In our models, no significant associations were detected between PBDE mixture and any of the child psychologic scores. BDE-99 concentration at delivery was nominally associated with higher scores on short-term and working memory while a decrease in spatial perception and reasoning was nominally associated with higher BDE-100 concentration at delivery.

Conclusion

Overall, our results did not show a significant association between PBDEs and child cognitive and motor development.

Polybrominated diphenyl ethers in soils from Tianjin, North China: distribution, health risk, and temporal trends

Available information is still insufficient for a comprehensive understanding of the global distribution of polybrominated diphenyl ethers (PBDEs) in the environment. In particular, little is known about the changing trend of their distribution in urban soils. We conducted a survey of 21 PBDEs in urban soils from Tianjin, China. The chemicals were widely present in the area and summed concentrations ranged from 0.65 to 108 ng/g in soil, indicating low to moderate levels of pollution relative to other areas. BDE-209 was the predominant congener, contributing 88.9% of the concentrations of total soil PBDEs. Source assessment indicated that soil PBDEs in the area were mainly derived from the release of commercial deca-BDE from local industrial production processes and consumer products. We found that the soil concentrations of PBDEs appear to have declined in recent years, compared with other previous reports in this region. However, more studies are needed on this possible change trend of PBDE pollution, especially its impact on human health, although their calculated non-carcinogenic health risks in this study were low.

Occurrence of chemical pollutants in major e-waste sites in West Africa and usefulness of cytotoxicity and induction of ethoxyresorufin-O-deethylase (EROD) in determining the effects of some detected brominated flame retardants and e-waste soil-derived extracts

We investigated the occurrence of chemical pollutants in major e-waste sites in West Africa and usefulness of cytotoxicity and induction of ethoxyresorufin-O-deethylase (EROD) in determining the effects of some detected brominated flame retardants (BFRs) and e-waste soil-derived extracts. Analysis of the e-waste site samples using AAS and GC-MS techniques revealed the presence of a range of toxic metals as well as persistent and toxic organic pollutants, respectively, in the vicinity of the e-waste sites. As expected, the occurrence (%) of all the detected chemical pollutants in experimental soils significantly (P < 0.05) differs from occurrence (%) in control soil. The calculated LC₅₀ values on RBL-2H3 cells of the detected tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) were 3.75 μM and 4.2 μM, respectively. Tribromophenol (TBP), dibromobiphenyl (DBB), and decabromodiphenyl ether (DBDE) were remarkably less toxic on RBL-2H3 cells compared with TBBPA and HBCD as they did not reduce RBL-2H3 cell viability below 50% in the tested concentration range (0-20 μM). The study revealed that TBBPA and HBCD could induce significant RBL-2H3 cell death through caspase-dependent apoptosis. The study further shows that the cytotoxicity of some of these BFRs could increase synergistically when in mixtures and potentially activate inflammation through the stimulation of mast cell degranulation. The e-waste soil-derived extracts induced a concentration-dependent increase in EROD activity in the exposed RTG-W1 cells. Ultimately, nonpolar extracts had higher EROD-inducing potency compared with polar extracts and hence suggesting the presence in higher amounts of AhR agonists in nonpolar e-waste soil-derived extracts than polar extracts. Overall, there is urgent need for actions in order to improve the environmental quality of the e-waste sites.

Perinatal exposure to octabromodiphenyl ether mixture, DE-79, alters the vasopressinergic system in adult rats

Polybrominated diphenyl ethers (PBDEs) are persistent environmental pollutants considered as neurotoxicants and endocrine disruptors with important biological effects ranging from alterations in growth, reproduction, and effects on the hypothalamus-pituitary-adrenal axis. The vasopressinergic (AVPergic) system is a known target for pentaBDEs mixture (DE-71) and the structurally similar chemicals, polychlorinated biphenyls. However, the potential adverse effects of mixtures containing octaBDE compounds, like DE-79, on the AVPergic system are still unknown. The present study aims to examine the effects of perinatal DE-79 exposure on the AVPergic system. Dams were dosed from gestational day 6 to postnatal day 21 at doses of 0 (control), 1.7 (low) or 10.2 (high) mg/kg/day, and male offspring from all doses at 3-months-old were subjected to normosmotic and hyperosmotic challenge. Male offspring where later assessed for alterations in osmoregulation (i.e. serum osmolality and systemic vasopressin release), and both vasopressin immunoreactivity (AVP-IR) and gene expression in the hypothalamic paraventricular and supraoptic nuclei. Additionally, to elucidate a possible mechanism for the effects of DE-79 on the AVPergic system, both neuronal nitric oxide synthase immunoreactivity (nNOS-IR) and mRNA expression were investigated in the same hypothalamic nuclei. The results showed that perinatal DE-79 exposure AVP-IR, mRNA expression and systemic release in adulthood under normosmotic conditions and more evidently under hyperosmotic stimulation. nNOS-IR and mRNA expression were also affected in the same nuclei. Since NO is an AVP regulator, we propose that disturbances in NO could be a mechanism underlying the AVPergic system disruption following perinatal DE-79 exposure leading to osmoregulation deficits.

Brain Bromine Levels Associated with Alzheimer's Disease Neuropathology

BACKGROUND

Bromine is a naturally occurring element that is widely present in the human environment in various chemical forms primarily as flame retardants, pesticides, and water treatments.

OBJECTIVE

In this exploratory study, we investigated the association of brain bromine concentrations on Alzheimer's disease (AD) neuropathology, cerebral infarcts, and Lewy bodies.

METHODS

The study was conducted in 215 deceased participants of the Memory and Aging Project, a clinical-pathologic cohort study. Brain bromine levels were measured using instrumental neutron activation analysis. Multiple brain regions were assessed for diffuse and neuritic plaques, neurofibrillary tangles, cerebral macro-and microinfarcts, and Lewy bodies. Standardized measures of AD pathology (Braak, CERAD, NIA-Reagan, global AD pathology) were computed.

RESULTS

In linear regression models, the higher brain bromine levels were associated with more AD neuropathology (Braak (p trend = 0.01); CERAD (p trend = 0.02); NIA-Reagan (p trend = 0.02).

CONCLUSION

Bromine accumulation in the brain is associated with higher level of AD neuropathology. The potential deleterious effects of this element on AD need further exploration.

Functional connectivity of the reading network is associated with prenatal polybrominated diphenyl ether concentrations in a community sample of 5 year-old children: A preliminary study

Genetic factors explain 60 percent of variance in reading disorder. Exposure to neurotoxicants, including polybrominated diphenyl ethers (PBDEs), may be overlooked risk factors for reading problems. We used resting-state functional magnetic resonance imaging (rs-fMRI) to examine associations between prenatal PBDE concentrations and functional connectivity of a reading-related network (RN) in a community sample of 5-year-old children (N = 33). Maternal serum PBDE concentrations (∑PBDE) were measured at 12.2 ± 2.8 weeks gestation (mean ± SD). The RN was defined by 12 regions identified in prior task-based fMRI meta-analyses; global efficiency (GE) was used to measure network integration. Linear regression evaluated associations between ∑PBDE, word reading, and GE of the RN and the default mode network (DMN); the latter to establish specificity of findings. Weighted quantile sum regression analyses evaluated the contributions of specific PBDE congeners to observed associations. Greater RN efficiency was associated with better word reading in these novice readers. Children with higher ∑PBDE showed reduced GE of the RN; ∑PBDE was not associated with DMN efficiency, demonstrating specificity of our results. Consistent with prior findings, ∑PBDE was not associated word reading at 5-years-old. Altered efficiency and integration of the RN may underlie associations between ∑PBDE concentrations and reading problems observed previously in older children.

Oxidative and nitrosative stress in the neurotoxicity of polybrominated diphenyl ether-153: possible mechanism and potential targeted intervention

Polybrominated diphenyl ethers (PBDEs) have been known to exhibit neurotoxicity in rats; however, the underlying mechanism remains unknown and there is no available intervention. In this study, we aimed to investigate the role of oxidative and nitrosative stress in the neurotoxicity in the cerebral cortex and primary neurons in rats following the BDE-153 treatment. Compared to the untreated group, BDE-153 treatment significantly induced the neurotoxic effects in rats, as manifested by the increased lactate dehydrogenase (LDH) activities and cell apoptosis rates, and the decreased neurotrophic factor contents and cholinergic enzyme activities in rats' cerebral cortices and primary neurons. When compared to the untreated group, the oxidative and nitrosative stress had occurred in the cerebral cortex or primary neurons in rats following the BDE-153 treatment, as manifested by the increments in levels of reactive oxygenspecies (ROS), malondialdehyde (MDA), nitric oxide (NO), and neuronal nitric oxide synthase (nNOS) mRNA and protein expressions, along with the decline in levels of superoxide dismutase (SOD) activity, glutathione (GSH) content, and peroxiredoxin I (Prx I) and Prx II mRNA and protein expressions. In addition, the ROS scavenger N-acetyl-l-cysteine (NAC) or NO scavenger NG-Nitro-l-arginine (L-NNA) significantly rescued the LDH leakage and cell survival, reversed the neurotrophin contents and cholinergic enzymes, mainly via regaining balance between oxidation/nitrosation and antioxidation. Overall, our findings suggested that oxidative and nitrosative stresses are involved in the neurotoxicity induced by BDE-153, and that the antioxidation is a potential targeted intervention.

Sex-specific effects of perinatal FireMaster® 550 (FM 550) exposure on socioemotional behavior in prairie voles

The rapidly rising incidence of neurodevelopmental disorders with social deficits is raising concern that developmental exposure to environmental contaminants may be contributory. Firemaster 550 (FM 550) is one of the most prevalent flame-retardant (FR) mixtures used in foam-based furniture and baby products and contains both brominated and organophosphate components. We and others have published evidence of developmental neurotoxicity and sex specific effects of FM 550 on anxiety-like and exploratory behaviors. Using a prosocial animal model, we investigated the impact of perinatal FM 550 exposure on a range of socioemotional behaviors including anxiety, attachment, and memory. Virtually unknown to toxicologists, but widely used in the behavioral neurosciences, the prairie vole (Microtus ochrogaster) is a uniquely valuable model organism for examining environmental factors on sociality because this species is spontaneously prosocial, biparental, and displays attachment behaviors including pair bonding. Dams were exposed to 0, 500, 1000, or 2000 μg of FM 550 via subcutaneous (sc) injections throughout gestation, and pups were directly exposed beginning the day after birth until weaning. Adult offspring of both sexes were then subjected to multiple tasks including open field, novel object recognition, and partner preference. Effects were dose responsive and sex-specific, with females more greatly affected. Exposure-related outcomes in females included elevated anxiety, decreased social interaction, decreased exploratory motivation, and aversion to novelty. Exposed males also had social deficits, with males in all three dose groups failing to show a partner preference. Our studies demonstrate the utility of the prairie vole for investigating the impact of chemical exposures on social behavior and support the hypothesis that developmental FR exposure impacts the social brain. Future studies will probe the possible mechanisms by which these effects arise.

Childhood polybrominated diphenyl ether (PBDE) serum concentration and reading ability at ages 5 and 8 years: The HOME Study

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) exist extensively in the environment and human beings. PBDE concentrations are higher in children than adults. A previous study found that prenatal PBDE exposure was associated with decreased reading skills in children; however, evidence is limited on the potential impact of childhood exposure to PBDEs. The study examined the association between childhood PBDE exposures and reading ability in children at ages 5 and 8 years.

METHODS

The study included 230 children from an ongoing prospective pregnancy and birth cohort study, the Health Outcomes and Measures of Environment (HOME) Study, conducted in Cincinnati, Ohio. Children's serum concentrations of eleven PBDE congeners were measured at 1, 2, 3, 5, and 8 years. The Woodcock-Johnson Tests of Achievement - III and the Wide Range Achievement Test - 4 were administered to assess children's reading skills at ages 5 and 8 years, respectively. We used multiple informant models to examine the associations between repeated measures of PBDEs and reading scores at ages 5 and 8 years. We also estimated the βs and 95% CIs of the association of PBDE measure at each age by including interaction terms between PBDE concentrations and child age in the models.

RESULTS

All childhood BDE-153 concentrations were inversely associated with reading scores at 5 and 8 years, but associations were not statistically significant after covariate adjustment. For example, a 10-fold increase in BDE-153 concentrations at ages 3 and 5 years was associated with a -5.0 (95% confidence interval (CI): -11.0, 1.0) and -5.5 (95% CI: -12.5, 1.4) point change in Basic Reading score at age 5 years, respectively. Similarly, the estimates for Brief Reading score at age 5 years were -4.5 (95% CI: -10.5, 1.5) and -5.2 (95% CI: -12.2, 1.7) point changes, respectively. Serum concentration of BDE-47, -99, -100, and Sum₄PBDEs (sum of BDE-47, 99, 100, and 153) at every age were inversely associated with reading scores at ages 5 and 8 years in unadjusted analyses. While the adjusted estimates were much attenuated and became non-significant, the direction of most of the associations was not altered.

CONCLUSION

Our study has shown a suggestive but non-significant trend of inverse associations between childhood PBDE serum concentrations, particularly BDE-153, and children's reading skills. Future studies with a larger sample size are needed to examine these associations.

Polybrominated diphenyl ether (PBDE) neurotoxicity: a systematic review and meta-analysis of animal evidence

A recent systematic review (SR) and meta-analysis of human studies found an association between prenatal serum polybrominated diphenyl ethers (PBDE) concentrations and a decrease in the IQ of children. A SR of experimental developmental animal PBDE-mediated neurotoxicity studies was performed in the present study. Outcomes assessed included measures related to learning, memory, and attention, which parallel the intelligence-related outcomes evaluated in the human studies SR. PubMed, Embase, and Toxline were searched for relevant experimental non-human mammalian studies. Evaluation of risk of bias (RoB) and overall body of evidence followed guidance developed by the National Toxicology Program. Animal studies using varying designs and outcomes were available for BDEs 47, 99, 153, 203, 206, and 209 and the technical mixture DE-71. Study reporting of methods and results was often incomplete leading to concerns regarding RoB. A meta-analysis of 6 Morris water maze studies showed evidence of a significant increase in last trial latency (effect size of 25.8 [CI, 20.3 to 31.2]) in PBDE-exposed animals with low heterogeneity. For most endpoints, there were unexplained inconsistencies across studies and no consistent evidence of a dose-response relationship. There is a "moderate" level of evidence that exposure to BDEs 47, 99, and 209 affects learning. For other PBDEs and other endpoints, the level of evidence was "low" or "very low". The meta-analysis led to stronger conclusions than that based upon a qualitative review of the evidence. The SR also identified RoB concerns that might be remedied by better study reporting.

Prenatal exposure to polybrominated diphenyl ethers and predisposition to frustration at 7 months: Results from the MIREC study

BACKGROUND

Prenatal exposure to polybrominated diphenyl ethers (PBDEs) has been associated with cognitive deficits and behavioral problems in children. To date, no study has examined this exposure in association with neurobehavioral development in infants younger than 12 months assessed with observational tasks.

OBJECTIVES

This study examined the relation between prenatal PBDE concentrations and predisposition to frustration, assessed by the arm restraint task (ART), in Canadian infants.

METHODS

In a prospective longitudinal study conducted in Canada, exposure to nine PBDE congeners was measured in maternal plasma during the first trimester of pregnancy. The ART was used to measure predisposition to frustration in infancy (N = 333; mean age = 6.9 months), as assessed by negative vocalizations (crying and screaming) and physical reactivity (discomfort movements).

RESULTS

Maternal plasma PBDE-47 concentrations collected during pregnancy were associated with negative vocalizations using the ART (adjusted Relative Risk [aRR] = 1.04, 95% CI: 1.00, 1.09). Prenatal PBDE-99 concentrations during pregnancy were also related to a shift to the left in the tail of the distribution of onset of negative vocalizations as measured by a decrease of 38 s (95% CI: -78.1, 1.3) in the 75th quantile of the distribution for infants whose mothers had detectable levels of PBDE-99 compared to infants of mothers with undetectable levels. Similarly, infants whose mothers had detectable levels of PBDE-100 showed an increase of 24.1 s (95% CI: 4.1, 44.1) in the 75th quantile of the distribution of proportion of time in negative vocalizations compared with infants of mothers with undetectable levels. Finally, the association between PBDE-47 and PBDE-153, and physical reactivity was significantly modified by sex (p < 0.1), with opposite patterns in girls and boys.

CONCLUSIONS

Prenatal exposure to PBDEs was associated with increased incidence of crying and screaming with delayed onset of discomfort movement, which may indicate a predisposition to frustration and lack of habituation in infants younger than 12 months from the general population.

Associations between prenatal and childhood PBDE exposure and early adolescent visual, verbal and working memory

BACKGROUND

Prenatal and childhood exposure to polybrominated diphenyl ether (PBDE) flame retardants has been inversely associated with cognitive performance, however, few studies have measured PBDE concentrations in samples collected during both prenatal and postnatal periods.

METHODS

We examined prenatal (cord) and childhood (ages 2, 3, 5, 7 and 9 years) plasma PBDE concentrations in relation to memory outcomes assessed between the ages of 9 and 14 years. The study sample includes a subset (n = 212) of the African American and Dominican children enrolled in the Columbia Center for Children's Environmental Health Mothers and Newborns birth cohort. We used multivariable linear regression to examine associations between continuous log₁₀-transformed PBDE concentrations and performance on tests of visual, verbal and working memory in age-stratified models. We additionally used latent class growth analysis to estimate trajectories of exposure across early life, which we analyzed as a categorical variable in relation to memory outcomes. We examined interactions between PBDE exposure and sex using cross-product terms.

RESULTS

Associations between prenatal exposure and working memory significantly varied by sex (p-interaction = 0.02), with inverse relations observed only among girls (i.e. β_BDE-47 = -7.55, 95% CI: -13.84, -1.24). Children with sustained high concentrations of BDEs-47, 99 or 100 across childhood scored approximately 5-8 standard score points lower on tests of visual memory. Children with PBDE plasma concentrations that peaked during toddler years performed better on verbal domains, however, these associations were not statistically significant.

CONCLUSIONS

Exposure to PBDEs during both prenatal and postnatal periods may disrupt memory domains in early adolescence. These findings contribute to a substantial body of evidence supporting the developmental neurotoxicity of PBDEs and underscore the need to reduce exposure among pregnant women and children.

Mechanisms of Action Point Towards Combined PBDE/NDL-PCB Risk Assessment

At present, human risk assessment of the structurally similar non-dioxin-like (NDL) PCBs and polybrominated diphenylethers (PBDEs) is done independently for both groups of compounds. There are however obvious similarities between NDL-PCBs and PBDEs with regard to modulation of the intracellular calcium homeostasis (basal calcium levels, voltage-gated calcium channels, calcium uptake, ryanodine receptor) and thyroid hormone (TH) homeostasis (TH levels and transport). which are mechanisms of action related to neurobehavioral effects (spontaneous activity, habituation and learning ability). There also similarities in agonistic interactions with the hepatic nuclear receptors PXR and CAR. Several effects on developmental (reproductive) processes have also been observed, but results were more dispersed and insufficient to compare both groups of compounds. The available mechanistic information is sufficient to warrant a dose addition model for NDL-PCBs and PBDEs, including their hydroxylated metabolites.Although many of the observed effects are similar from a qualitative point of view for both groups, congener or tissue specific differences have also been found. As this is a source of uncertainty in the combined hazard and risk assessment of these compounds, molecular entities involved in the observed mechanisms and adverse outcomes associated with these compounds need to be identified. The systematical generation of (quantitative) structure-activity information for NDL-PCBs and PBDEs on these targets (including potential non-additive effects) will allow a more realistic risk estimation associated with combined exposure to both groups of compounds during early life. Additional validation studies are needed to quantify these uncertainties for risk assessment of NDL-PCBs and PBDEs.

Predictors of human PBDE body burdens for a UK cohort

Human exposure to polybrominated diphenyl ethers (PBDEs) was investigated in a cohort of 20 UK adults along with their anthropometric covariates and relevant properties such as room surveys, lifestyle, diet and activity details. Selected PBDE congeners were measured in matched samples of indoor dust (n = 41), vehicles (n = 8), duplicate diet (n = 24), serum (n = 24) and breast milk (n = 6). Combined exposure estimates via dust and diet revealed total PBDE intakes of 104 to 1,440 pg kg^-1 bw d^-1 for ΣBDEs_3-7 and 1,170 to 17,000 pg kg^-1 bw d^-1 for BDE-209. These adult intakes are well within health reference doses suggested by the European Food Safety Authority (EFSA) and the US EPA. Diet was the primary source of intake of BDE_3-7 congeners for the majority of the cohort, with dust the primary source of BDE-209. Primary sources of PBDE exposure vary between countries and regions with differing fire prevention regulations. Estimated infant exposures (ages 1.5-4.5 years) showed that BDE-99 intake for one of the households did not meet EFSA's recommended margin of exposure, a further two households had borderline PBDE exposures for high level dust and diet intake. Males and those having a lower body fat mass had higher serum BDE-153. Higher meat consumption was significantly correlated with higher BDEs_3-7 in serum. A reduction in dietary BDEs_3-7 would therefore result in the greatest reduction in BDE-99 exposure. Rooms containing PUF sofas or armchairs over 20 years old had more BDEs_3-7 in their dust, and rooms with carpets or rugs of that age had higher dust BDE-209. Dusting rooms more frequently resulted in significantly lower concentrations of all major congeners in their dust. Correlation between BDE-209 body burden and dust or diet exposure was limited by its low bioaccessibility. Although vehicle dust contained the highest concentrations of BDEs_3-7 and BDE-209, serum BDEs_3-7 correlated most strongly with bedroom dust.

A Human Mixture Risk Assessment for Neurodevelopmental Toxicity Associated with Polybrominated Diphenyl Ethers Used as Flame Retardants

BACKGROUND

The European Food Safety Authority recently concluded that the exposure of small children (1-3 y old) to brominated diphenyl ether (BDE)-99 may exceed acceptable levels defined in relation to neurodevelopmental toxicity in rodents. The flame retardant BDE-209 may release BDE-99 and other lower brominated BDEs through biotic and abiotic degradation, and all age groups are exposed not only to BDE-209 and -99 but also to a cocktail of BDE congeners with evidence of neurodevelopmental toxicity. The possible risks from combined exposures to these substances have not been evaluated.

OBJECTIVES

We performed a congener-specific mixture risk assessment (MRA) of human exposure to combinations of BDE-209 and other BDEs based on estimated exposures via diet and dust intake and on measured levels in biologic samples.

METHODS

We employed the Hazard Index (HI) method by using BDE congener-specific reference doses for neurodevelopmental toxicity.

RESULTS

Our HI analysis suggests that combined exposures to polybrominated diphenyl ethers (PBDEs) may exceed acceptable levels in breastfeeding infants (0-3 mo old) and in small children (1-3 y old), even for moderate (vs. high) exposure scenarios. Our estimates also suggest that acceptable levels of combined PBDEs may be exceeded in adults whose diets are high in fish. Small children had the highest combined exposures, with some estimated body burdens that were similar to body burdens associated with developmental neurotoxicity in rodents.

CONCLUSIONS

Our estimates corroborate reports from several recent epidemiological studies of associations between PBDE exposures and neurobehavioral outcomes, and they support the inclusion of BDE-209 in the persistent organic pollutant (POP) convention as well as the need for strategies to reduce exposures to PBDE mixtures, including maximum residue limits for PBDEs in food and measures for limiting the release of PBDEs from consumer waste. https://doi.org/10.1289/EHP826.

Perinatal exposure to organohalogen pollutants decreases vasopressin content and its mRNA expression in magnocellular neuroendocrine cells activated by osmotic stress in adult rats

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are environmental pollutants that produce neurotoxicity and neuroendocrine disruption. They affect the vasopressinergic system but their disruptive mechanisms are not well understood. Our group reported that rats perinatally exposed to Aroclor-1254 (A1254) and DE-71 (commercial mixtures of PCBs and PBDEs) decrease somatodendritic vasopressin (AVP) release while increasing plasma AVP responses to osmotic activation, potentially emptying AVP reserves required for body-water balance. The aim of this research was to evaluate the effects of perinatal exposure to A1254 or DE-71 (30mgkg/day) on AVP transcription and protein content in the paraventricular and supraoptic hypothalamic nuclei, of male and female rats, by in situ hybridization and immunohistochemistry. cFOS mRNA expression was evaluated in order to determine neuroendocrine cells activation due to osmotic stimulation. Animal groups were: vehicle (control); exposed to either A1254 or DE-71; both, control and exposed, subjected to osmotic challenge. The results confirmed a physiological increase in AVP-immunoreactivity (AVP-IR) and gene expression in response to osmotic challenge as reported elsewhere. In contrast, the exposed groups did not show this response to osmotic activation, they showed significant reduction in AVP-IR neurons, and AVP mRNA expression as compared to the hyperosmotic controls. cFOS mRNA expression increased in A1254 dehydrated groups, suggesting that the AVP-IR decrease was not due to a lack of the response to the osmotic activation. Therefore, A1254 may interfere with the activation of AVP mRNA transcript levels and protein, causing a central dysfunction of vasopressinergic system.

The ROS-mediated pathway coupled with the MAPK-p38 signalling pathway and antioxidant system plays roles in the responses of Mytilus edulis haemocytes induced by BDE-47

Our previous study found that BDE-47 could change the immune function of haemocytes in Mytilus edulis, and reactive oxygen species (ROS) might be involved in the process of physiological alteration. Here, we aimed to better understand this relationship. To accomplish this, we analysed changes in different ROS as well as various antioxidant system components. Additionally, the expression of MAPK-p38, a signalling protein regulated by ROS that helps to regulate numerous cellular processes, was also analysed. BDE-47 was given at low, medium, and high amounts. The results showed that (1) BDE-47 significantly affected ROS component levels in haemocytes. O₂^- content was increased under all conditions. H₂O₂ content was also increased under all conditions, except in the middle concentration group. In contrast, OH content was increased in the low and middle concentration groups and decreased in the high concentration group. (2) Estimations of the antioxidant systems revealed concentration-dependent changes. Catalase activity was increased throughout the experiment, while superoxide dismutase (SOD) exhibited a decreasing trend in the tested groups with an increase of exposure time. On day 21, only the high concentration group showed a slight increase in SOD activity compared to the control. Furthermore, glutathione peroxidase and glutathione reductase activity increased in the low and middle concentration groups but decreased in the high concentration group. The GSH/GSSG ratio increased for all treatments over time, indicating that changes in redox status occurred. (3) MAPK-p38 was activated following BDE-47 exposure. Based on our previous study, we speculate that BDE-47 exposure induces ROS production and affects the ROS-mediated pathway, which may explain the resultant functional damage observed in haemocytes. Furthermore, BDE-47 also affected the antioxidant system and altered redox status, although these changes did not ameliorate the damage caused by ROS.

Calpain-2/p35-p25/Cdk5 pathway is involved in the neuronal apoptosis induced by polybrominated diphenyl ether-153

Polybrominated diphenyl ethers (PBDEs) have been demonstrated to induce neurotoxicity in experimental rats and mice, with neuronal apoptosis as one of the major mechanisms, however, the mechanisms underlying PBDEs-induced neuronal apoptosis remain unclear. In this study, we aimed to investigate the role of calpain/p35-p25/Cdk5 pathway in BDE-153-induced neuronal apoptosis in the hippocampus and primary neurons in rats. Results showed that compared to the controls, neuronal apoptosis was significantly increased in vivo and ex vivo, as manifested by the increased hippocampus TUNEL-positive cell rates, apoptotic neurons in Hoechst and AO/EB staining, and the increased LDH activity and percentage of Annexin V-positive cells in rat hippocampus and primary neurons. Calpain activity was significantly increased in all the BDE-153-treated groups in vivo and ex vivo when compared to non-treatment controls. In addition, we showed that calpain-2 accounted for the calpain activation instead of calpain-1, as demonstrated by the up-regulated mRNA and protein expressions in calpain-2 but not calpain-1. Activated calpain truncated p35 into p25, which resulted in the p25/Cdk5 formation and activation. Calpain inhibitor PD150606 or p25/Cdk5 inhibitor Roscovitine relieved neuronal apoptosis mainly via inhibiting the p25/Cdk5 activation. Overall, the findings suggested that calpain-2/p35-p25/Cdk5 pathway was involved in BDE-153-induced neuronal apoptosis, which provides novel insight into the mechanisms of PBDE neurotoxicity.

Metabolite profiling study on the toxicological effects of polybrominated diphenyl ether in a rat model

Polybrominated diphenyl ethers (PBDEs) are commonly used to retard the combustion of materials such as foam padding, textiles, or plastics, and numerous studies have confirmed the accumulation thereof in the environment and in fish, mammals, and humans. In this study, we used metabolomics to conduct an environmental risk assessment of the PBDE-209. We profiled the urinary metabolites of control and PBDE-treated rats (exposed to PBDE-209) using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Global metabolic profiling indicated that the effects of PBDE-209 on the urinary metabolic profile were not significant. However, targeted metabolic profiling revealed progressive effects of PBDE-209 over a 7-day PBDE-209 treatment. Moreover, despite the weak PBDE-209 effects, we observed that choline, acetylcholine, 3-indoxylsulfate, creatinine, urea, and dimethyl sulfone levels were decreased, whereas that of pyruvate was significantly increased. Furthermore, we suggest that the increased pyruvate level and decreased levels of choline, acetylcholine, and uremic toxins were suggestive of endocrine disruption and neurodevelopmental toxicity caused by PBDEs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1262-1272, 2017.

Prenatal and postnatal polybrominated diphenyl ether exposure and visual spatial abilities in children

Polybrominated diphenyl ethers (PBDEs) are associated with impaired visual spatial abilities in toxicological studies, but no epidemiologic study has investigated PBDEs and visual spatial abilities in children. The Health Outcomes and Measures of the Environment Study, a prospective birth cohort (2003-2006, Cincinnati, OH), was used to examine prenatal and childhood PBDEs and visual spatial abilities in 199 children. PBDEs were measured at 16±3 weeks gestation and at 1, 2, 3, 5, and 8 years using gas chromatography/isotope dilution high-resolution mass spectrometry. We used the Virtual Morris Water Maze to measure visual spatial abilities at 8 years. In covariate-adjusted models, 10-fold increases in BDE-47, -99, and -100 at 5 years were associated with shorter completion times by 5.2s (95% Confidence Interval [CI] -9.3, -1.1), 4.5s (95% CI -8.1, -0.9), and 4.7s (95% CI -9.0, -0.3), respectively. However, children with higher BDE-153 at 3 years had longer completion times (β=5.4s, 95% CI -0.3, 11.1). Prenatal PBDEs were associated with improved visual spatial memory retention, with children spending a higher percentage of their search path in the correct quadrant. Child sex modified some associations between PBDEs and visual spatial learning. Longer path lengths were observed among males with increased BDE-47 at 2 and 3 years, while females had shorter paths. In conclusion, prenatal and postnatal BDE-28, -47, -99, and -100 at 5 and 8 years were associated with improved visual spatial abilities, whereas a pattern of impairments in visual spatial learning was noted with early childhood BDE-153 concentrations.

Neonatal exposure to BDE 209 impaired learning and memory, decreased expression of hippocampal core SNAREs and synaptophysin in adult rats

Polybrominated diphenyl ethers (PBDEs) are a class of flame retardants. While the mechanism remains unknown, the potential neurotoxic effects of PBDEs remain a relevant issue. In the present study, neonatal Sprague-Dawley rats of both sexes were administered BDE 209 (1, 10, or 20mg/kg body weight) or peanut oil once daily from postnatal day (PND) 5 to PND 10. We examined the spatial learning and memory by Morris water maze and the working and reference memory by eight-arm radial maze in the stage of adulthood. Compared with controls, significantly longer escape latencies and fewer platform-crossings in the Morris water maze were observed in rats exposed to 1, 10, and 20mg/kg BDE 209, and these effects were dose-dependent. Significantly higher working and reference memory error rates in the eight-arm radial maze were also observed in rats exposed to 10 and 20mg/kg BDE 209. Furthermore, we detected the mRNA and protein expressions of hippocampal synaptobrevin 2, syntaxin 1A, Synaptosome Associated Protein 25 (SNAP-25), and synaptophysin using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and western blot methods. Compared with controls, the mRNA expressions of synaptobrevin 2, syntaxin 1A, SNAP-25, and synaptophysin were significantly decreased in the hippocampi of rats exposed to 1, 10, and 20 mg/kg BDE 209, and the protein expressions of synaptobrevin 2 and SNAP-25 were significantly decreased in the hippocampi of rats exposed to 10 and 20 mg/kg BDE 209, while syntaxin 1A and synaptophysin were significantly decreased in rats exposed to 1, 10, and 20 mg/kg BDE 209. Alterations that may be involved in the learning and memory deficits induced by BDE 209 reveal the possibility of synapse loss.

Levels and Profiles of Polybrominated Diphenyl Ethers in Breast Milk During Different Nursing Durations

Eight PBDE congeners, BDE-28, 47, 99, 100, 153, 154, 183 and 209, were measured using gas chromatography coupled to mass spectrometry. The concentrations of Σ8PBDEs ranged from 0.04 to 19.93 ng g(-1) lipid weight (lw), with median and mean value of 1.21 and 2.72 ng g(-1) lw. PBDE congeners were detected in approximately 90 % of samples with BDE-209 as the dominant one. No significant correlations were found between the mothers' age, body mass index and PBDEs concentrations. We estimated the infant's dietary intake of the studied PBDEs via human milk during different nursing durations, and found that babies younger than 1 month might take a relatively higher body burden of PBDEs. The median levels of Σ8PBDEs were 0.74, 2.80, 2.43 and 0.90 ng g(-1) lw in colostrum, milk sampled at 1, 3 and 6 months after birth, respectively. High consumption of animal-origin food after birth may lead to the elevated ΣPBDEs concentrations in breast milk. A rational nutrition deployment is essential for postpartum mother.

Exposure to endocrine disrupting chemicals and neurodevelopmental alterations

The developing brain is remarkably malleable as neural circuits are formed and these circuits are strongly dependent on hormones for their development. For those reasons, the brain is very vulnerable to the effects of endocrine-disrupting chemicals (EDCs) during critical periods of development. This review focuses on three ubiquitous endocrine disruptors that are known to disrupt the thyroid function and are associated with neurobehavioral deficits: polychlorinated biphenyls, polybrominated diphenyl ethers, and bisphenol A. The human and rodent data suggesting effects of those EDCs on memory, cognition, and social behavior are discussed. Their mechanisms of action go beyond relative hypothyroidism with effects on neurotransmitter release and calcium signaling.

Oral administration of potassium bromate induces neurobehavioral changes, alters cerebral neurotransmitters level and impairs brain tissue of swiss mice

Background

Potassium bromate (KBrO₃) is widely used as a food additive and is a major water disinfection by-product. The present study reports the side effects of KBrO₃ administration on the brain functions and behaviour of albino mice.

Methods

Animals were divided into three groups: control, low dose KBrO₃ (100 mg/kg/day) and high dose KBrO₃ (200 mg/kg/day) groups.

Results

Administration of KBrO₃ led to a significant change in the body weight in the animals of the high dose group in the first, second and the last weeks while water consumption was not significantly changed. Neurobehavioral changes and a reduced Neurotransmitters levels were observed in both KBrO₃ groups of mice. Also, the brain level of reduced glutathione (GSH) in KBrO₃ receiving animals was decreased. Histological studies favoured these biochemical results showing extensive damage in the histological sections of brain of KBrO₃-treated animals.

Conclusions

These results show that KBrO₃ has serious damaging effects on the central nervous system and therefore, its use should be avoided.

Multiparameter toxicity assessment of novel DOPO-derived organophosphorus flame retardants

Halogen-free organophosphorus flame retardants are considered as replacements for the phased-out class of polybrominated diphenyl ethers (PBDEs). However, toxicological information on new flame retardants is still limited. Based on their excellent flame retardation potential, we have selected three novel 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives and assessed their toxicological profile using a battery of in vitro test systems in order to provide toxicological information before their large-scale production and use. PBDE-99, applied as a reference compound, exhibited distinct neuro-selective cytotoxicity at concentrations ≥10 µM. 6-(2-((6-oxido-6H-dibenzo[c,e][1,2]oxaphosphinin-6-yl)amino)ethoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide (ETA-DOPO) and 6,6′-(ethane-1,2-diylbis(oxy))bis(6H-dibenzo[c,e][1,2]oxaphosphinine-6-oxide) (EG-DOPO) displayed adverse effects at concentrations >10 µM in test systems reflecting the properties of human central and peripheral nervous system neurons, as well as in a set of non-neuronal cell types. DOPO and its derivative 6,6′-(ethane-1,2-diylbis(azanediyl))bis(6H-dibenzo[c,e][1,2]oxaphosphinine-6-oxide) (EDA-DOPO) were neither neurotoxic, nor did they exhibit an influence on neural crest cell migration, or on the integrity of human skin equivalents. The two compounds furthermore displayed no inflammatory activation potential, nor did they affect algae growth or daphnia viability at concentrations ≤400 µM. Based on the superior flame retardation properties, biophysical features suited for use in polyurethane foams, and low cytotoxicity of EDA-DOPO, our results suggest that it is a candidate for the replacement of currently applied flame retardants.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Expanding the test set: Chemicals with potential to disrupt mammalian brain development

High-throughput test methods including molecular, cellular, and alternative species-based assays that examine critical events of normal brain development are being developed for detection of developmental neurotoxicants. As new assays are developed, a "training set" of chemicals is used to evaluate the relevance of individual assays for specific endpoints. Different training sets are necessary for each assay that would comprise a developmental neurotoxicity test battery. In contrast, evaluation of the predictive ability of a comprehensive test battery requires a set of chemicals that have been shown to alter brain development after in vivo exposure ("test set"). Because only a small number of substances have been well documented to alter human neurodevelopment, we have proposed an expanded test set that includes chemicals demonstrated to adversely affect neurodevelopment in animals. To compile a list of potential developmental neurotoxicants, a literature review of compounds that have been examined for effects on the developing nervous system was conducted. The search was limited to mammalian studies published in the peer-reviewed literature and regulatory studies submitted to the U.S. EPA. The definition of developmental neurotoxicity encompassed changes in behavior, brain morphology, and neurochemistry after gestational or lactational exposure. Reports that indicated developmental neurotoxicity was observed only at doses that resulted in significant maternal toxicity or were lethal to the fetus or offspring were not considered. As a basic indication of reproducibility, we only included a chemical if data on its developmental neurotoxicity were available from more than one laboratory (defined as studies originating from laboratories with a different senior investigator). Evidence from human studies was included when available. Approximately 100 developmental neurotoxicity test set chemicals were identified, with 22% having evidence in humans.

Selective damage to dopaminergic transporters following exposure to the brominated flame retardant, HBCDD

Over the last several decades, the use of halogenated organic compounds has become the cause of environmental and human health concerns. Of particular notoriety has been the establishment of the neurotoxicity of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The subsequent banning of PBDEs has led to greatly increased use of 1,2,5,6,9,10-hexabromocyclododecane (HBCDD, also known as HBCD) as a flame retardant in consumer products. The physiochemical similarities between HBCDD and PBDEs suggest that HBCDD may also be neurotoxic to the dopamine system, which is specifically damaged in Parkinson disease (PD). The purpose of this study was to assess the neurotoxicity of HBCDD on the nigrostriatal dopamine system using an in vitro and in vivo approach. We demonstrate that exposure to HBCDD (0-25 μM) for 24 h causes significant cell death in the SK-N-SH catecholaminergic cell line, as well as reductions in the growth and viability of TH+ primary cultured neurons at lower concentrations (0-10 μM) after 72 h of treatment. Assessment of the in vivo neurotoxicity of HBCDD (25 mg/kg for 30 days) resulted in significant reductions in the expression of the striatal dopamine transporter and vesicular monoamine transporter 2, both of which are integral in mediating dopamine homeostasis and neurotransmission in the dopamine circuit. However, no changes were seen in the expression of tyrosine hydroxylase in the dopamine terminal, or striatal levels of dopamine. To date, these are the first data to demonstrate that exposure to HBCDD disrupts the nigrostriatal dopamine system. Given these results and the ubiquitous nature of HBCDD in the environment, its possible role as an environmental risk factor for PD should be further investigated.

Human health risk associated with brominated flame-retardants (BFRs)

The purposes of this review are to assess the human exposure and human and experimental evidence for adverse effects of brominated flame-retardants (BFRs) with specific focus on intake from seafood. The leakage of BFRs from consumer products leads to exposure of humans from fetal life to adulthood. Fish and fish products contain the highest levels of BFRs and dominate the dietary intake of frequent fish eaters in Europe, while meat, followed by seafood and dairy products accounted for the highest US dietary intake. House dust is also reported as an important source of exposure for children as well as adults. The levels of BFRs in the general North American populations are higher than those in Europe and Japan and the highest levels are detected in infants and toddlers. The daily intake via breast milk exceeds the RfD in 10% of US infants. BFRs including PBDEs, HBCDs and TBBP-A have induced endocrine-, reproductive- and behavior effects in laboratory animals. Furthermore, recent human epidemiological data demonstrated association between exposure to BFRs and similar adverse effects as observed in animal studies. Fish including farmed fish and crude fish oil for human consumption may contain substantial levels of BFRs and infants and toddlers consuming these products on a daily basis may exceed the tolerable daily intake suggesting that fish and fish oil alone represent a risk to human health. This intake comes in addition to exposure from other sources (breast milk, other food, house dust). Because potential harmful concentrations of BFRs and other toxicants occur in fish and fish products, research on a wider range of products is warranted, to assess health hazard related to the contamination of fish and fish products for human consumption.

Selected oxidative stress parameters after single and repeated administration of octabromodiphenyl ether to rats

OBJECTIVES

Octabromodiphenyl ether (OctaBDE) was used as a flame retardant applied mostly in the manufacture of plastics utilized in the electrical and electronic industries. Owing to its long half-life and being regarded as an environmental pollutant, OctaBDE, like other polybrominated diphenyl ethers, has been classified as a persistent organic pollutant (POP). This study was carried out to assess the effects of oxidative stress (redox homeostasis) induced in rats by OctaBDE.

MATERIAL AND METHODS

Female Wistar rats exposed intragastrically to OctaBDE at single (25, 200 or 2000 mg/kg b.w.), or repeated (0.4, 2, 8, 40 or 200 mg/kg/day) doses during 7-28 days were used in the experiment. Selected oxidative stress parameters were determined in the liver and blood serum.

RESULTS

Administration (single or repeated) of OctaBDE to rats resulted in the impaired redox homeostasis, as evidenced by the increased levels of reduced (GSH) and oxidized (GSSG) glutathione in the liver, the reduced total antioxidant status (TAS) in serum and the increased concentration of malondialdehyde (MDA) in the liver. After multiple doses of OctaBDE, elevated activity of glutathione transferase (GST) in the liver was also noted.

CONCLUSIONS

After repeated administration of OctaBDE at the lowest dose (0.4 mg/kg/day), changes were observed in the parameters (MDA, TAS, GSSG) indicative of oxidative stress.

Developmental exposure to the polybrominated diphenyl ether PBDE 209: Neurobehavioural and neuroprotein analysis in adult male and female mice

Polybrominated diphenyl ethers (PBDEs), used as flame retardants in polymer products, are reported to cause developmental neurotoxic effects in mammals. The present study have investigated neurotoxic effects arising from neonatal exposure to PBDE 209, including alterations in sex differences, spontaneous behaviour, learning and memory, neuroproteins and altered susceptibility of the cholinergic system in adults. Three-day-old NMRI mice, of both sexes, were exposed to PBDE 209 (2,2',3,3',4,4',5,5',6,6'-decaBDE at 0, 1.4, 6.0 and 14.0μmol/kg b.w.). At adult age (2-7 months) a similar developmental neurotoxic effects in both male and female mice were seen, including lack of or reduced habituation to a novel home environment, learning and memory defects, modified response to the cholinergic agent's paraoxon (males) and nicotine (females) indicating increased susceptibility of the cholinergic system. The behavioural defects were dose-response related and persistent. In mice of both sexes and showing behavioural defects, neuroprotein tau was increased.

Developmental Exposure to Polybrominated Diphenyl Ethers and Neurodevelopment

Exposure to polybrominated diphenyl ethers (PBDE) during sensitive developmental windows can interfere with cognitive function and behavior, which are critical components of neurodevelopment. The association between developmental exposure to PBDEs and neurodevelopment has been extensively studied using animal models. In this review, we focus on the accumulating evidence in humans. Despite methodological, geographical, and temporal differences between studies, the majority of the epidemiologic evidence supports that early life exposure to PBDEs measured during pregnancy and/or during childhood is detrimental to child neurodevelopment in domains related to child behavior, cognition, and motor skills. While the precise mechanism of action of PBDEs on neurodevelopment is unknown, PBDE-induced neurotoxicity via thyroid hormone disruption and direct action of PBDEs on the developing brain have been proposed and tested. Additional studies are suggested to better understand how early life and/or childhood PBDE exposures, including exposure to specific PBDE congeners, impact neurodevelopmental indices.

A rapid throughput approach identifies cognitive deficits in adult zebrafish from developmental exposure to polybrominated flame retardants

A substantial body of evidence has correlated the human body burdens of some polybrominated diphenyl ether (PBDE) flame retardants with cognitive and other behavioral deficits. Adult zebrafish exhibit testable learning and memory, making them an increasingly attractive model for neurotoxicology. Our goal was to develop a rapid throughput means of identifying the cognitive impact of developmental exposure to flame retardants in the zebrafish model. We exposed embryos from 6h post fertilization to 5 days post fertilization to either PBDE 47 (0.1μM), PBDE 99 (0.1μM) or PBDE 153 (0.1μM), vehicle (0.1% DMSO), or embryo medium (EM). The larvae were grown to adulthood and evaluated for the rate at which they learned an active-avoidance response in an automated shuttle box array. Zebrafish developmentally exposed to PBDE 47 learned the active avoidance paradigm significantly faster than the 0.1% DMSO control fish (P<0.0001), but exhibited significantly poorer performance when retested suggestive of impaired memory retention or altered neuromotor activity. Learning in the PBDE 153 group was not significantly different from the DMSO group. Developmental exposure to 0.1% DMSO impaired adult active avoidance learning relative to the sham group (n=39; P<0.0001). PBDE 99 prevented the DMSO effect, yielding a learning rate not significantly different from the sham group (n=36; P>0.9). Our results underscore the importance of vehicle choice in accurately assessing chemical effects on behavior. Active avoidance response in zebrafish is an effective model of learning that, combined with automated shuttle box testing, will provide a highly efficient platform for evaluating persistent neurotoxic hazard from many chemicals.

Prenatal exposure to decabrominated diphenyl ether impairs learning ability by altering neural stem cell viability, apoptosis, and differentiation in rat hippocampus

Background:Polybrominated diphenyl ether (PBDE) levels in children and teenagers were higher than those of the adults and the highest levels were found in infants and toddlers. 2,2',3,3',4,4',5,5',6,6'-Decabrominated diphenyl ether (BDE-209) readily crosses the placental barrier and produces toxicity in the developing fetus, particularly to the developing brain.Objectives:This present study aims to investigate the potential effects of prenatal BDE-209 exposure on regulation of neurogenesis and learning function in an experimental rat model.Methods:Pregnant rats received BDE-209 (10, 30, or 50 mg kg-1 day-1) or vehicle (arachis oil) through gastric gavage from gestation day 1 to 14 (n = 10 per group). The embryonic hippocampal neural stem cells (NSCs) from five pregnant rats in each group were collected on day 14 and cultured in vitro to determine the cell viability, apoptosis, and differentiation of NSCs using cell counting kit 8 assay, flow cytometry, and immunofluorescence staining, respectively. In total, 20 male offspring on postnatal day 25 from each group were chosen to evaluate learning ability using a Morris water navigation task assay.Results:The data showed that prenatal exposure to BDE-209 decreased cell viability and differentiation of NSCs but promoted apoptosis in a dose-dependent manner. Prenatal BDE-209 exposure also impaired rat-learning acquisition in a dose-dependent manner.Conclusions:Prenatal BDE-209 exposure impairs rat-learning acquisition, possibly by affecting neurogenesis in the hippocampus during embryonic development.

Alterations to the circuitry of the frontal cortex following exposure to the polybrominated diphenyl ether mixture, DE-71

Recent studies have identified exposure to polybrominated diphenyl ethers (PBDEs) as a risk factor for deficits in cognitive functioning seen in children as well as adults. Additionally, similar alterations in learning and memory have also been observed in animal models of PBDE exposure. However, given these findings, the molecular alterations that may underlie these neurobehavioral endpoints have not been identified. As the frontal cortex is involved in modulating several cognitive functions, the purpose of our study was to investigate the possible changes to the GABAergic and glutamatergic neurotransmitter systems located in the frontal cortex following exposure to the PBDE mixture, DE-71. Primary cultured neurons isolated from the frontal cortex showed a dose-dependent reduction in neurons as well as neurite outgrowth. Furthermore, evaluation of DE-71 neurotoxicity in the frontal cortex using an in vivo model showed alterations to specific proteins involved in mediating GABA and glutamate neurotransmission, including GAD67, vGAT, vGlut, and GABA(A) 2α receptor subunit. Interestingly, these alterations appeared to be preferential for the GABA and glutamate systems located in the frontal cortex. These findings identify specific targets of PBDE neurotoxicity and provide a possible molecular mechanism for PBDE-mediated neurobehavioral deficits that arise from the frontal cortex.

Polybrominated diphenyl ethers (PBDEs) in aborted human fetuses and placental transfer during the first trimester of pregnancy

Data on early human fetal exposure to polybrominated diphenyl ethers (PBDEs) is limited. However, early pregnancy, in particular the first trimester, is critical for fetal development. We investigated exposure to PBDEs and placental transfer during early pregnancy by analyzing PBDEs in paired aborted fetuses (n = 65), placentas (n = 65), and maternal blood samples (n = 31) at 10-13 weeks gestation, which were collected in a hospital near electronic wastes (e-wastes) recycling sites in Taizhou, China. Mean total PBDE (∑PBDE) concentrations were 4.46, 7.90, and 15.7 ng/g of lipid weight (lw) in the fetuses, placentas, and blood, respectively. The three matrices had roughly similar PBDE congener profiles, dominated by BDE-209, BDE-197, BDE-153, BDE-47, and BDE-28. Significant correlations were found between ∑PBDE concentrations in the paired matrices. Comparing the concentration ratios between the paired samples, we observed significantly higher fetus/blood and fetus/placenta ratios for BDE-28, BDE-99, and BDE-47 than for BDE-197, BDE-209, and BDE-153, while opposite results were found in placenta/blood ratios. Our results indicate that PBDEs can enter the fetus during the first trimester and low-brominated congeners cross the placenta more easily than high-brominated congeners, which tend to remain in the placenta. This phenomenon is consistent with findings at the end of pregnancy.