Polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and neuropsychological status among older adults in New York

Neurotransmitter Systems Affected by PBDE Exposure: Insights from In Vivo and In Vitro Neurotoxicity Studies

Polybrominated diphenyl ethers (PBDEs) are synthetic halogen compounds, industrially used as flame retardants in many flammable products. PBDEs are environmentally persistent and bioaccumulative substances that were used from the 1970s and discontinued in the 1990s. PBDEs are present in air, soil, water, and food, where they remain stable for a long time. Chronic exposure to PBDEs is associated with adverse human health effects, including cancer, immunotoxicity, hepatotoxicity, reproductive and metabolic disorders, motor and hormonal impairments, and neurotoxicity, especially in children. It has been demonstrated that PBDE exposure can cause mitochondrial and DNA damage, apoptosis, oxidative stress, epigenetic modifications, and changes in calcium and neurotransmitter levels. Here, we conduct a comprehensive review of the molecular mechanisms of the neurotoxicity of PBDEs using different approaches. We discuss the main neurotransmitter pathways affected by exposure to PBDEs in vitro and in vivo in different mammalian models. Excitatory and inhibitory signaling pathways are the putative target where PBDEs carry out their neurotoxicity. Based on this evidence, environmental PBDEs are considered a risk to human public health and a hazard to biota, underscoring the need for environmental monitoring to mitigate exposure to PBDEs.

Assessing the contribution of the chemical exposome to neurodegenerative disease

Over the past few decades, numerous environmental chemicals from solvents to pesticides have been suggested to be involved in the development and progression of neurodegenerative diseases. Most of the evidence has accumulated from occupational or cohort studies in humans or laboratory research in animal models, with a range of chemicals being implicated. What has been missing is a systematic approach analogous to genome-wide association studies, which have identified dozens of genes involved in Alzheimer's disease, Parkinson's disease and other neurodegenerative diseases. Fortunately, it is now possible to study hundreds to thousands of chemical features under the exposome framework. This Perspective explores how advances in mass spectrometry make it possible to generate exposomic data to complement genomic data and thereby better understand neurodegenerative diseases.

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.

Endocrine disrupting chemicals: effects on pituitary, thyroid and adrenal glands

BACKGROUND

In recent years, scientific research has increasingly focused on Endocrine Disrupting Chemicals (EDCs) and demonstrated their relevant role in the functional impairment of endocrine glands. This induced regulatory authorities to ban some of these compounds and to carefully investigate others in order to prevent EDCs-related conditions. As a result, we witnessed a growing awareness and interest on this topic.

AIMS

This paper aims to summarize current evidence regarding the detrimental effects of EDCs on pivotal endocrine glands like pituitary, thyroid and adrenal ones. Particularly, we directed our attention on the known and the hypothesized mechanisms of endocrine dysfunction brought by EDCs. We also gave a glimpse on recent findings from pioneering studies that could in the future shed a light on the pathophysiology of well-known, but poorly understood, endocrine diseases like hormone-producing adenomas.

CONCLUSIONS

Although intriguing, studies on endocrine dysfunctions brought by EDCs are challenging, in particular when investigating long-term effects of EDCs on humans. However, undoubtedly, it represents a new intriguing field of science research.

Association between mixed exposure of phthalates and cognitive function among the U.S. elderly from NHANES 2011-2014: Three statistical models

BACKGROUND

Studies on the relationship between phthalate exposure and cognition in adults are sparse and inconsistent. These studies only assessed their association of single phthalates for one-time and the tools for assessing cognitive function were different.

OBJECTIVE

We aimed to examine the association between mixed phthalates and cognition in the U.S elderly using three statistical models.

METHODS

The generalized linear (GLM), weighted quantile sum (WQS), and Bayesian kernel machine regression (BKMR) models were used to evaluate the associations between mixed phthalates and the standardized z-scores of four cognitive tests [Immediate Recall test (IRT), Delayed Recall test (DRT), Animal Fluency test (AFT), and Digit Symbol Substitution test (DSST)] in participants aged over 60 years from NHANES 2011-2014.

RESULTS

835 individuals were included and the median raw scores of IRT, DRT, AFT, and DSST were 19 (IQR: 16-23), 6 (IQR: 5-8), 16 (IQR: 13-20), 46 (IQR: 35-59). In adjusted GLM, negative associations were observed between MECPP, MnBP, MCOP, MCPP, and the IRT z-scores; MCPP, MBzP, and the DRT z-scores. Positive relationships were found between MCOP, MCPP, and the AFT z-scores; MCPP and the DSST z-scores. The WQS index was associated with the IRT z-scores (β(95%CI): -0.069(-0.118, -0.020)), where MCPP weighted the highest. In the BKMR, negative overall trends between the mixture and the IRT, DRT z-scores were observed when the mixture was at 40th to 65th percentile, 65th percentile or above it, respectively, where MnBP and MBzP drove the main effect of the mixture.

CONCLUSION

This study is an academic exploration of the association between phthalates exposure and cognitive function, suggesting that exposure to phthalates might be associated with bad performance in IRT and DRT in the U.S. elderly.

Association between social determinants of health and olfactory function: a scoping review

BACKGROUND

Social determinants of health (SDoH) include the socioeconomic, demographic, and social conditions that influence differences in health status among individuals and groups. The impact of these conditions on olfactory function remains poorly understood. In this scoping review, we systematically review the available literature to synthesize the association between SDoH and olfactory function.

METHODS

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Review (PRISMA-ScR) guidelines, we performed systematic search queries in PubMed, Embase, and Ovid databases and categorized articles according to themes that emerged regarding SDoH. The primary outcomes included self-reported and objective measurements of smell.

RESULTS

We identified 722 unique references that underwent title and abstract review by two independent reviewers, with 70 articles undergoing full-text review and 57 relevant for data extraction. Six themes emerged in our review, under which we categorized the studies and synthesized respective associations with olfactory function. These include studies exploring socioeconomic status (n = 19, 33%), education status (n = 27, 47%), occupational exposures (n = 26, 46%), racial/ethnic disparities (n = 12, 21%), and lifestyle/behavioral factors (n = 33, 58%).

CONCLUSIONS

Within the context of this scoping review, olfactory dysfunction is significantly more prevalent in patients with lower socioeconomic status, exposure to environmental and occupational toxins, and of minority race/ethnicity, whereas the associations between olfactory dysfunction and education level and lifestyle factors such as smoking and drinking seem to be much more elusive. This review highlights the importance of accounting for SDoH in observational studies examining olfactory outcomes. Given the increased awareness of olfactory loss, special consideration should be given to understanding olfactory dysfunction in the context of these factors.

Chemosensory Dysfunction Induced by Environmental Pollutants and Its Potential As a Novel Neurotoxicological Indicator: A Review

Air pollution composed of the complex interactions among particular matter, chemicals, and pathogens is an emerging and global environmental issue that closely correlates with a variety of diseases and adverse health effects, especially increasing incidences of neurodegenerative diseases. However, as one of the prevalent health outcomes of air pollution, chemosensory dysfunction has not attracted enough concern until recently. During the COVID-19 pandemic, multiple scientific studies emphasized the plausibly essential roles of the chemosensory system in the airborne transmission airway of viruses into the human body, which can also be utilized by pollutants. In this Review, in addition to summarizing current progress regarding the contributions of traditional air pollutants to chemosensory dysfunction, we highlight the roles of emerging contaminants. We not only sum up clarified mechanisms, such as inflammation and apoptosis but also discuss some not yet completely identified mechanisms, e.g., disruption of olfactory signal transduction. Although the existing evidence is not overwhelming, the chemosensory system is expected to be a useful indicator in neurotoxicology and neural diseases based on accumulating studies that continually excavate the deep link between chemosensory dysfunction and neurodegenerative diseases. Finally, we argue the importance of studies concerning chemosensory dysfunction in understanding the health effects of air pollution and provide comments for some future directions of relevant research.

Contamination status, emission sources, and human health risk of brominated flame retardants in urban indoor dust from Hanoi, Vietnam: the replacement of legacy polybrominated diphenyl ether mixtures by alternative formulations

This study investigated the occurrence, distribution of several additive brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) and some novel brominated flame retardants (NBFRs) in urban indoor dust collected from ten inner districts of Hanoi, Vietnam to assess the contamination status, emission sources, as well as their associated human exposure through indoor dust ingestion and health risks. Total concentrations of PBDEs and NBFRs in indoor dust samples ranged from 43 to 480 ng g^-1 (median 170 ng g^-1) and from 56 to 2200 ng g^-1 (median 180 ng g^-1), respectively. The most abundant PBDE congener in these dust samples was BDE-209 with concentrations ranging from 29 to 360 ng g^-1, accounting for 62.6-86.5% of total PBDE levels. Among the NBFRs analyzed, decabromodiphenyl ethane (DBDPE) was the predominant compound with a mean contribution of 98.6% total NBFR amounts. Significant concentrations of DBDPE were detected in all dust samples (median 180 ng g^-1, range 54-2200 ng g^-1), due to DBDPE as a substitute for deca-BDE. Other NBFRs such as 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), pentabromoethylbenzene (PBEB) and 2,2',4,4',5,5'-hexabromobiphenyl (BB-153) were found at very low levels. Based on the measured BFR concentrations, daily intake doses (IDs) of PBDEs and NBFRs via dust ingestion at exposure scenarios using the median and 95^th percentile levels for both adults and children were calculated for risk assessment. The results showed that the daily exposure doses via dust ingestion of all compounds, even in the high-exposure scenarios were also lower than their reference dose (RfD) values. The lifetime cancer risks (LTCR) were much lower than the threshold level (10^-6), which indicated the acceptable health risks resulting from indoor BFRs exposure for urban residents in Hanoi.

Polybrominated Diphenyl Ether Serum Concentrations and Depressive Symptomatology in Pregnant African American Women

(1) Polybrominated diphenyl ethers (PBDEs) were widely produced in the United States until 2004 but remain highly persistent in the environment. The potential for PBDEs to disrupt normal neuroendocrine pathways resulting in depression and other neurological symptoms is largely understudied. This study examined whether PBDE exposure in pregnant women was associated with antenatal depressive symptomatology. (2) Data were collected from 193 African American pregnant women at 8–14 weeks gestation. Serum PBDEs and depressive symptoms were analyzed and a mixture effect was calculated. (3) Urban pregnant African American women in the Southeastern United States had a high risk of depression (27%) compared to the National average. Increased levels of PBDEs were found. BDE-47 and -99 exposures are significantly associated with depressive symptomatology in the pregnant cohort. The weighted body burden estimate of the PBDE mixture was associated with a higher risk of mild to moderate depression using an Edinburgh Depression Scale cutoff score of ≥10 (OR = 2.93; CI 1.18, 7.82). (4) Since antenatal depression may worsen in postpartum, reducing PBDE exposure may have significant clinical implications.

Global distribution and trends of polybrominated diphenyl ethers in human blood and breast milk: A quantitative meta-analysis of studies published in the period 2000-2019

Polybrominated diphenyl ethers (PBDEs) are a class of flame-retardants that are found throughout the human body. However, global trends and diversity of the concentrations in human body and the potential risks remain largely unresolved. Based on published data during 2000-2019, we conducted a systematic meta-analysis to understand the burden and risks of PBDEs in humans and their spatiotemporal variations. The report provides a global picture of PBDE concentrations in human blood and breast milk. We found the levels of body PBDE burden in the North American population were higher than those from Asia and Europe. However, high concentrations of blood PBDEs in occupational population from Asia were observed, largely because of poorly controlled e-waste recycling operations. Penta- and deca-BDE were the main contributors in North America and Asia, respectively, reflecting the difference in the production and use of these chemicals. On a global scale, no substantial decreases in the concentrations of PBDEs in the blood and breast milk were observed, although most of the chemicals have been phased out. The results suggested that humans will be exposed to PBDEs with relatively high concentrations in a certain period because of the legacy in products and the environmental media. And the potential health risks necessitate careful study in the future. Our results also remind that the uses of degradation-resistant chemicals should be attached great importance to their safety.

Biomarkers of metabolic disorders and neurobehavioral diseases in a PCB- exposed population: What we learned and the implications for future research

Polychlorinated biphenyls (PCBs) are one of the original twelve classes of toxic chemicals covered by the Stockholm Convention on Persistent Organic Pollutants (POP), an international environmental treaty signed in 2001. PCBs are present in the environment as mixtures of multiple isomers at different degree of chlorination. These compounds are manmade and possess useful industrial properties including extreme longevity under harsh conditions, heat absorbance, and the ability to form an oily liquid at room temperature that is useful for electrical utilities and in other industrial applications. They have been widely used for a wide range of industrial purposes over the decades. Despite a ban in production in 1979 in the US and many other countries, they remain persistent and ubiquitous in environment as contaminants due to their improper disposal. Humans, independent of where they live, are therefore exposed to PCBs, which are routinely found in random surveys of human and animal tissues. The prolonged exposures to PCBs have been associated with the development of different diseases and disorders, and they are classified as endocrine disruptors. Due to its ability to interact with thyroid hormone, metabolism and function, they are thought to be implicated in the global rise of obesity diabetes, and their potential toxicity for neurodevelopment and disorders, an example of gene by environmental interaction (GxE). The current review is primarily intended to summarize the evidence for the association of PCB exposures with increased risks for metabolic dysfunctions and neurobehavioral disorders. In particular, we present evidence of gene expression alterations in PCB-exposed populations to construct the underlying pathways that may lead to those diseases and disorders in course of life. We conclude the review with future perspectives on biomarker-based research to identify susceptible individuals and populations.

Environmental Endocrine-Disrupting Chemical Exposure: Role in Non-Communicable Diseases

The exponential growth of pollutant discharges into the environment due to increasing industrial and agricultural activities is a rising threat for human health and a biggest concern for environmental health globally. Several synthetic chemicals, categorized as potential environmental endocrine-disrupting chemicals (EDCs), are evident to affect the health of not only livestock and wildlife but also humankind. In recent years, human exposure to environmental EDCs has received increased awareness due to their association with altered human health as documented by several epidemiological and experimental studies. EDCs are associated with deleterious effects on male and female reproductive health; causes diabetes, obesity, metabolic disorders, thyroid homeostasis and increase the risk of hormone-sensitive cancers. Sewage effluents are a major source of several EDCs, which eventually reach large water bodies and potentially contaminate the drinking water supply. Similarly, water storage material such as different types of plastics also leaches out EDCs in drinking Water. Domestic wastewater containing pharmaceutical ingredients, metals, pesticides and personal care product additives also influences endocrine activity. These EDCs act via various receptors through a variety of known and unknown mechanisms including epigenetic modification. They differ from classic toxins in several ways such as low-dose effect, non-monotonic dose and trans-generational effects. This review aims to highlight the hidden burden of EDCs on human health and discusses the non-classical toxic properties of EDCs in an attempt to understand the magnitude of the exposome on human health. Present data on the environmental EDCs advocate that there may be associations between human exposure to EDCs and several undesirable health outcomes that warrants further human bio-monitoring of EDCs.

Dose-response assessment for impaired memory from chronic exposure to domoic acid among native American consumers of razor clams

Domoic acid (DA) is a marine neurotoxin that accumulates in filtering shellfish during harmful algal blooms. A health protection limit of 20 ppm DA in razor clams (RC) has been set based principally upon an episode of acute DA toxicity in humans that included Amnesic Shellfish Poisoning among survivors. The objective of this study was to determine the dose-response relationship between estimated DA exposure through RC consumption and memory loss in Washington state Native Americans from 2005 to 2015. Results from total learning recall (TLR) memory scores were compared before and after the highest DA exposures. A decrease in TLR was related to DA dose (p < 0.01) regardless whether the effect was assumed to be transient or lasting, and whether the dose was expressed as an average daily dose or an average dose per meal. Benchmark dose modeling identified BMDL₁₀ values of 167 ng/kg-day and 2740 ng/kg-meal assuming a transient effect, and 196 ng/kg-day and 2980 ng/kg-meal assuming no recovery of function occurs. These DA dose thresholds for a measurable memory function reduction observed in this study of clam consumers are well below the safe acute dose underpinning the current regulatory DA limit of 20 ppm (ca. 60 μg/kg).

Indoor polybrominated diphenyl ethers in urban China: An exposure and risk assessment based on settled dust from selected urban regions

In this study, measurements of seven typical polybrominated diphenyl ethers (PBDEs) in indoor settled dust were summarized in selected urban regions of China. BDE-209 was the most dominant congener in settled dust (1.4-101 μg/g), with a mean contribution of 95%. Indoor exposures to PBDEs were estimated via inhalation, dust ingestion, and dermal absorption. The average daily intake of ΣPBDE was 4.9 to 19.1 ng/day/kg for all the population groups, with >80% of the total exposures from dust ingestion. Exposures in commuting environments (contributing 60%-80% of the total exposures) were higher than those in other microenvironments. The means of hazard indexes ranged from 1.66 × 10^-3 to 5.26 × 10^-3, which were mainly as a result of exposure to BDE-209, BDE-47, and BDE-99. The average lifetime cancer risks were from 0.03 × 10^-9 to 2.37 × 10^-9, which indicated the acceptable health risks resulting from indoor PBDE exposure for the Chinese population. The present study could provide valuable information that could be helpful for decision-makers, analysts and researchers to develop, implement and evaluate the effectiveness of interventions for the reduction of exposures to semi-volatile organic compounds (SVOCs) for large population groups in China.

A longitudinal study of polychlorinated biphenyls and neuropsychological function among older adults from New York State

BACKGROUND

Cross-sectional studies have linked greater polychlorinated biphenyl (PCB) exposure to adverse neuropsychological effects in older adults, including learning, memory, and depressive symptoms. However, no studies among older adults have evaluated the association over time.

OBJECTIVES

To assess the effect of serum PCB levels on neuropsychological function over a 14-year period in a cohort of older men and women from a PCB-contaminated area of New York State.

METHODS

In 2000-2002, we assessed serum PCB levels and neuropsychological function (including the California Verbal Learning Test Trial 1 (CVLTT1) for verbal memory and learning, and the Beck Depression Index (BDI) for depressive symptoms) in 253 men and women, ages 55-74 years. A total of 116 (46%) persons repeated the PCB and neuropsychological assessment 14 years later. To assess the association over time, we used generalized estimating equations with clustering variables time, total PCB (∑PCB), and ∑PCB × time, and adjusted for baseline age, sex, smoking, and total serum-lipids. For statistically significant ∑PCB × time interactions, we evaluated the association between PCBs and either verbal memory and learning or depressive symptoms while holding ∑PCB constant at the 10th and 90th percentiles to clarify the direction of the interaction.

RESULTS

Over the study period, serum ∑PCB levels (wet-weight) declined by 22%, and were associated with different patterns of change over time for memory (∑PCB × Time β = 0.08 p = 0.009) and depressive symptoms (∑PCB × Time β = -0.16 p = 0.013). Specifically, verbal memory and learning decreased (β = -0.08 p = 0.008) and depressive symptoms increased (β = 0.17 p = 0.008) among persons with low exposure (∑PCB levels at the 10th percentile), while persons with high exposure (90th percentile) showed non-significant improvements.

DISCUSSION

In this cohort, declining ∑PCB levels were likely due at least in part to low rates of local fish consumption in recent decades, given the ban since 1976. The decreased verbal memory and learning and increased depressive symptoms over time among persons with low serum ∑PCB levels is consistent with studies of normative aging. However, the small improvements in those outcomes among those with high serum ∑PCB levels was unexpected. Healthy survivor selection bias or uncontrolled confounding may explain this result. It may also indicate that the neurotoxic impacts of PCBs in older adults are not permanent, but future studies are needed to confirm this possibility.

Factors influencing risk assessments of brominated flame-retardants; evidence based on seafood from the North East Atlantic Ocean

Brominated flame-retardants (BFRs) such as polybrominated diphenyl ethers (PBDE) and hexabromocyclododecane (HBCD) are considered hazardous to human health. Due to their persistence, they are still present in the environment and in biota and seafood is major contributor of BFRs to human exposure. Here, we used data from >9700 samples of wild and farmed fish, fish feed and fish feed ingredients collected from the North Atlantic between 2006 and 2016 aiming to investigate factors influencing the risk assessments of BFRs. Due to most representative number of analyses, PBDEs were the main focus of investigation. Mean ∑PBDE in fillet samples ranged from below quantification in Atlantic cod fillet to 2.0 μg kg^-1 in Atlantic halibut. The main congener contributing to the ∑PBDE in all species was BDE 47. Factors affecting the level of BFR in seafood were multifaceted, and the levels were within species mainly determined by fish age, geographical origin and time of sampling. BDE 47, 99, 153 and HBCD were selected for margin of exposure (MOE) evaluation. When other sources of BFR than seafood were excluded, our risk assessment showed low risk at the current dietary intake of seafood. However, the dietary intake of BDE 99 may be of concern for toddlers when all sources are considered. The choice of fish species, dietary studies, choice of statistics, as well as exposure from other sources than seafood, were all factors that influenced the final MOE of BFRs. We propose the use of regression on order statistics as a tool for risk assessment, to illustrate means and spreads in large surveillance datasets to avoid the issue of measurements below the limit of quantification. A harmonized, updated evaluation of the risk associated with exposure to BFRs from diet, air and dust is warranted, where the fish species most commonly consumed also is taken into consideration.

Estrogenic Endocrine Disrupting Chemicals Influencing NRF1 Regulated Gene Networks in the Development of Complex Human Brain Diseases

During the development of an individual from a single cell to prenatal stages to adolescence to adulthood and through the complete life span, humans are exposed to countless environmental and stochastic factors, including estrogenic endocrine disrupting chemicals. Brain cells and neural circuits are likely to be influenced by estrogenic endocrine disruptors (EEDs) because they strongly dependent on estrogens. In this review, we discuss both environmental, epidemiological, and experimental evidence on brain health with exposure to oral contraceptives, hormonal therapy, and EEDs such as bisphenol-A (BPA), polychlorinated biphenyls (PCBs), phthalates, and metalloestrogens, such as, arsenic, cadmium, and manganese. Also we discuss the brain health effects associated from exposure to EEDs including the promotion of neurodegeneration, protection against neurodegeneration, and involvement in various neurological deficits; changes in rearing behavior, locomotion, anxiety, learning difficulties, memory issues, and neuronal abnormalities. The effects of EEDs on the brain are varied during the entire life span and far-reaching with many different mechanisms. To understand endocrine disrupting chemicals mechanisms, we use bioinformatics, molecular, and epidemiologic approaches. Through those approaches, we learn how the effects of EEDs on the brain go beyond known mechanism to disrupt the circulatory and neural estrogen function and estrogen-mediated signaling. Effects on EEDs-modified estrogen and nuclear respiratory factor 1 (NRF1) signaling genes with exposure to natural estrogen, pharmacological estrogen-ethinyl estradiol, PCBs, phthalates, BPA, and metalloestrogens are presented here. Bioinformatics analysis of gene-EEDs interactions and brain disease associations identified hundreds of genes that were altered by exposure to estrogen, phthalate, PCBs, BPA or metalloestrogens. Many genes modified by EEDs are common targets of both 17 β-estradiol (E2) and NRF1. Some of these genes are involved with brain diseases, such as Alzheimer's Disease (AD), Parkinson's Disease, Huntington's Disease, Amyotrophic Lateral Sclerosis, Autism Spectrum Disorder, and Brain Neoplasms. For example, the search of enriched pathways showed that top ten E2 interacting genes in AD-APOE, APP, ATP5A1, CALM1, CASP3, GSK3B, IL1B, MAPT, PSEN2 and TNF-underlie the enrichment of the Kyoto Encyclopedia of Genes and Genomes (KEGG) AD pathway. With AD, the six E2-responsive genes are NRF1 target genes: APBB2, DPYSL2, EIF2S1, ENO1, MAPT, and PAXIP1. These genes are also responsive to the following EEDs: ethinyl estradiol (APBB2, DPYSL2, EIF2S1, ENO1, MAPT, and PAXIP1), BPA (APBB2, EIF2S1, ENO1, MAPT, and PAXIP1), dibutyl phthalate (DPYSL2, EIF2S1, and ENO1), diethylhexyl phthalate (DPYSL2 and MAPT). To validate findings from Comparative Toxicogenomics Database (CTD) curated data, we used Bayesian network (BN) analysis on microarray data of AD patients. We observed that both gender and NRF1 were associated with AD. The female NRF1 gene network is completely different from male human AD patients. AD-associated NRF1 target genes-APLP1, APP, GRIN1, GRIN2B, MAPT, PSEN2, PEN2, and IDE-are also regulated by E2. NRF1 regulates targets genes with diverse functions, including cell growth, apoptosis/autophagy, mitochondrial biogenesis, genomic instability, neurogenesis, neuroplasticity, synaptogenesis, and senescence. By activating or repressing the genes involved in cell proliferation, growth suppression, DNA damage/repair, apoptosis/autophagy, angiogenesis, estrogen signaling, neurogenesis, synaptogenesis, and senescence, and inducing a wide range of DNA damage, genomic instability and DNA methylation and transcriptional repression, NRF1 may act as a major regulator of EEDs-induced brain health deficits. In summary, estrogenic endocrine disrupting chemicals-modified genes in brain health deficits are part of both estrogen and NRF1 signaling pathways. Our findings suggest that in addition to estrogen signaling, EEDs influencing NRF1 regulated communities of genes across genomic and epigenomic multiple networks may contribute in the development of complex chronic human brain health disorders.

Effects of Ambient Air Pollution Exposure on Olfaction: A Review

BACKGROUND

Olfactory dysfunction affects millions of people worldwide. This sensory impairment is associated with neurodegenerative disease and significantly decreased quality of life. Exposure to airborne pollutants has been implicated in olfactory decline, likely due to the anatomic susceptibility of the olfactory nerve to the environment. Historically, studies have focused on occupational exposures, but more recent studies have considered effects from exposure to ambient air pollutants.

OBJECTIVES

To examine all relevant human data evaluating a link between ambient pollution exposure and olfaction and to review supporting animal data in order to examine potential mechanisms for pollution-associated olfactory loss.

METHODS

We identified and reviewed relevant articles from 1950 to 2015 using PubMed and Web of Science and focusing on human epidemiologic and pathophysiologic studies. Animal studies were included only to support pertinent data on humans. We reviewed findings from these studies evaluating a relationship between environmental pollutant exposure and olfactory function.

RESULTS

We identified and reviewed 17 articles, with 1 additional article added from a bibliography search, for a total of 18 human studies. There is evidence in human epidemiologic and pathologic studies that increased exposure to ambient air pollutants is associated with olfactory dysfunction. However, most studies have used proxies for pollution exposure in small samples of convenience. Human pathologic studies, with supporting animal work, have also shown that air pollution can contact the olfactory epithelium, translocate to the olfactory bulb, and migrate to the olfactory cortex. Pollutants can deposit at each location, causing direct damage and disruption of tissue morphology or inducing local inflammation and cellular stress responses.

CONCLUSIONS

Ambient air pollution may impact human olfactory function. Additional studies are needed to examine air pollution-related olfactory impacts on the general population using measured pollution exposures and to link pollution exposure with olfactory dysfunction and related pathology. Citation: Ajmani GS, Suh HH, Pinto JM. 2016. Effects of ambient air pollution exposure on olfaction: a review. Environ Health Perspect 124:1683-1693; http://dx.doi.org/10.1289/EHP136.

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.

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.

Polybrominated diphenyl ethers in atmosphere from three different typical industrial areas in Beijing, China

Three common industries that cause polybrominated diphenyl ethers (PBDEs) pollution in Beijing, China, are solid waste incineration, chemical manufacturing, and coal-fired thermal power generation. This study was conducted to determine both the concentrations and profiles of 42 PBDEs in gaseous and particulate matter (including PM2.5, PM2.5-10, and total suspended particulate (TSP)) from the major industries listed above at three sites in Beijing. The total concentration of PBDEs (defined as the sum of 42 congeners in gas and TSP) were 60.5-216 pg m(-3) at the solid waste incineration plant, 71.8-7500 pg m(-3) at the chemical plant, and 34.4-454 pg m(-3) at the coal-fired thermal power plant. The results indicate that the components of PBDE in gas were similar between three industrial sites, and the dominant congener was tri-BDEs. However, in particulate matter, the dominant BDEs were different between the three sites, possibly because they originated from different sources. In particulate matter, the dominant PBDEs were penta-BDEs at the solid waste incineration plant, deca-BDE at the coal-fired thermal power plant, and tetra-BDEs and deca-BDE at the chemical plant. Source analysis revealed that PBDE contamination might be associated with the use of different commercial PBDE flame-retardant mixtures. Results from a previous risk assessment indicated that the risk to human health was low. However, results from this study suggest that there is a potential threat associated with human exposure to PBDEs for the residents near these industrial sites.

Perfluoroalkyl substances and thyroid function in older adults

Current understanding of the thyroid disruptive properties of perfluoroalkyl substances (PFASs), particularly in aging populations, is limited. The objectives of this study were to (i) assess associations between thyroid function, as measured by serum thyrotropin (thyroid stimulating hormone, TSH), free thyroxine (fT4), total thyroxine (T4), and total triiodothyronine (T3), and serum perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in an aging population and (ii) determine if other persistent organic pollutants with thyroid disruptive properties including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) modify such associations. We conducted a cross-sectional study of 87 men and women 55 to 74years of age, without clinically-diagnosed thyroid disease, who resided in upper Hudson River communities in New York. Geometric means (standard deviations) of serum PFOS and PFOA were 31.6 (1.7) ng/mL and 9.17 (1.72) ng/mL, respectively. Multivariable linear regression analyses indicated that one interquartile range difference in PFOS corresponded to 4% and 9% increases in fT4 and T4 respectively. We detected statistical interactions between PFOA and age for effects on fT4 and T4; joint increases in PFOA and age were associated with increases in fT4 and T4, of 3% and 7%, respectively. We also detected statistical interactions between PFOS and total PCBs for the effect on T3 and between PFOA and total PBDEs for the effect on TSH. Our results suggest that PFASs are associated with subtle alterations in thyroid hormone levels in this population, and that these associations are likely to vary by age, and levels of PCBs and PBDEs.

Polychlorinated biphenyls and selected organochlorine pesticides in serum of Slovak population from industrial and non-industrial areas

The concentrations of indicator polychlorinated biphenyls (PCBs No. 28, 52, 101, 138, 153 and 180) and organochlorine pesticides (HCB, p,p'-DDE and p,p'-DDT) in 121 blood serum specimens collected from non-occupationally exposed adults living in contaminated and comparison areas were determined using high-resolution gas chromatography/electron capture detection (HRGC/ECD). The sum of the serum concentrations of the three most abundant PCB congeners (No. 138, 153 and 180) found in participants (N = 81) living in industrial areas near incinerators, metallurgical and chemical plants (Krompachy, Kosice, Nemecka and Sala) was significantly higher (p < 0.001) than in participants living in villages and towns without known sources causing persistent organic pollutant (POP) contamination (N = 40). Similarly, significant differences were observed for p,p'-DDE (p < 0.0001) and p,p'-DDT (p < 0.002). However, a Mann-Whitney U test between groups showed that the difference for HCB was not statistically significant (p = 0.089). Age was positively correlated with the sum of PCBs (No. 138, 153 and 180), HCB and the sum of p,p'-DDE and p,p'-DDT (p < 0.01 for all).

Impact of endocrine-disrupting chemicals on thyroid function and brain development

Endocrine disrupting chemicals (EDCs) are synthetic or natural substances in the environment. EDCs have been shown to disrupt reproductive, developmental and other homeostatic systems by interfering with the synthesis, secretion, transport, metabolism and action of endogenous hormones including the thyroid hormone (TH) system. Since TH plays a critical role in brain development, the exposure to TH-system disrupting EDCs during development may have serious consequences. In this article, representative previous studies showing the effect of representative EDCs on the TH system are summarized. Then, the molecular mechanisms of action of polychlorinated biphenyls and polybrominated diphenyl ethers on the TH system are discussed further. Particularly, the effect of polychlorinated biphenyls and polybrominated diphenyl ethers on TH-mediated brain development is discussed. Our recent studies may provide a novel idea regarding the effect of EDCs on the TH system.

Health consequences of exposure to brominated flame retardants: a systematic review

BACKGROUND

Brominated flame retardants (BFRs), are chemicals widely used in consumer products including electronics, vehicles, plastics and textiles to reduce flammability. Experimental animal studies have confirmed that these compounds may interfere with thyroid hormone homeostasis and neurodevelopment but to date health effects in humans have not been systematically examined.

OBJECTIVES

To conduct a systematic review of studies on the health impacts of exposure to BFRs in humans, with a particular focus on children.

METHODS

A systematic review was conducted using the MEDLINE and EMBASE electronic databases up to 1 February 2012. Published cohort, cross-sectional, and case-control studies exploring the relationship between BFR exposure and various health outcomes were included.

RESULTS

In total, 36 epidemiological studies meeting the pre-determined inclusion criteria were included. Plausible outcomes associated with BFR exposure include diabetes, neurobehavioral and developmental disorders, cancer, reproductive health effects and alteration in thyroid function. Evidence for a causal relationship between exposure to BFRs and health outcomes was evaluated within the Bradford Hill framework.

CONCLUSION

Although there is suggestive evidence that exposure to BFRs is harmful to health, further epidemiological investigations particularly among children, and long-term monitoring and surveillance of chemical impacts on humans are required to confirm these relationships.

Prenatal exposure to the brominated flame retardant hexabromocyclododecane (HBCD) impairs measures of sustained attention and increases age-related morbidity in the Long-Evans rat

Hexabromocyclododecane (HBCD) is a brominated flame retardant that is widely-used in foam building materials and to a lesser extent, furniture and electronic equipment. After decades of use, HBCD and its metabolites have become globally-distributed environmental contaminants that can be measured in the atmosphere, water bodies, wildlife, food staples and human breastmilk. Emerging evidence suggests that HBCD can affect early brain development and produce behavioral consequences for exposed organisms. The current study examined some of the developmental and lifelong neurobehavioral effects of prenatal HBCD exposure in a rat model. Pregnant rats were gavaged with 0, 3, 10, or 30mg/kg HBCD from gestation day 1 to parturition. A functional observation battery was used to assess sensorimotor behaviors in neonates. Locomotor and operant responding under random ratio and Go/no-go schedules of food reinforcement were examined in cohorts of young adult and aged rats. HBCD exposure was associated with increased reactivity to a tailpinch in neonates, decreased forelimb grip strength in juveniles, and impaired sustained attention indicated by Go/no-go responding in aged rats. In addition, HBCD exposure was associated with a significant increase in morbidity in the aged cohort. One health complication, a progressive loss of hindleg function, was observed only in the aged, 3mg/kg HBCD animals. These effects suggest that HBCD is a developmental neurotoxicant that can produce long-term behavioral impairments that emerge at different points in the lifespan following prenatal exposure.

Polybrominated diphenyl ether (PBDE) exposure in children: possible associations with cardiovascular and psychological functions

BACKGROUND

Polybrominated diphenyl ethers (PBDE) have been used widely in consumer products and are currently found at detectable levels in the blood of humans and animals across the globe. In stark contrast to this widespread exposure to PBDEs, there is relatively little research on potential adverse health effects of exposure of children to these chemicals.

OBJECTIVES

We performed this cross-sectional study to determine if blood PBDE levels (for 4 congeners) are associated with cardiovascular stress responses and psychological states in children.

METHODS

Levels of 4 PBDE congeners (BDE-28, -47, -99, and -100) in whole blood were measured in children (N=43). These levels were analyzed in relation to cardiovascular disease risk factors, including cardiovascular responses to acute stress and relevant psychological variables, namely, hostility and depression.

RESULTS

Higher levels of blood PBDEs were associated with significantly greater sympathetic activation during acute psychological stress and greater anger, as evidenced by significant associations with 3 different measures of this psychological variable.

CONCLUSIONS

This study suggests an association between PBDE exposure and children's cardiovascular responses to stress as well as parental and self-reported anger in the child. These variables are particularly important as they may be of potential relevance to the future development of cardiovascular disease (CVD). Although intriguing, there is a need for further investigation and replication with a larger sample of children.

Levels and trends of PBDEs and HBCDs in the global environment: status at the end of 2012

In this paper, we have compiled and reviewed the most recent literature, published in print or online from January 2010 to December 2012, relating to the human exposure, environmental distribution, behaviour, fate and concentration time trends of polybrominated diphenyl ether (PBDE) and hexabromocyclododecane (HBCD) flame retardants, in order to establish their current trends and priorities for future study. More data are now becoming available for remote areas not previously studied, Indian Ocean islands, for example. Decreasing time trends for penta-mix PBDE congeners were seen for soils in northern Europe, sewage sludge in Sweden and the USA, carp from a US river, trout from three of the Great Lakes and in Arctic and UK marine mammals and many birds, but increasing time trends continue in polar bears and some birds at high trophic levels in northern Europe. This may be partially a result of the time delay inherent in long-range atmospheric transport processes. In general, concentrations of BDE209 (the major component of the deca-mix PBDE product) are continuing to increase. Of major concern is the possible/likely debromination of the large reservoir of BDE209 in soils and sediments worldwide, to yield lower brominated congeners which are both more mobile and more toxic, and we have compiled the most recent evidence for the occurrence of this degradation process. Numerous studies reported here reinforce the importance of this future concern. Time trends for HBCDs are mixed, with both increases and decreases evident in different matrices and locations and, notably, with increasing occurrence in birds of prey. Temporal trends for both PBDEs and HBCD in Asia are unclear currently. A knowledge gap has been noted in relation to metabolism and/or debromination of BDE209 and HBCD in birds. Further monitoring of human exposure and environmental contamination in areas of e-waste recycling, particularly in Asia and Africa, is warranted. More data on temporal trends of BDE and HBCD concentrations in a variety of matrices and locations are needed before the current status of these compounds can be fully assessed, and the impact of regulation and changing usage patterns among different flame retardants determined.

Thyroid hormones are associated with exposure to persistent organic pollutants in aging residents of upper Hudson River communities

The aim of this study was to evaluate the association between persistent organic pollutants (POPs) and thyroid hormones in an aging population. Forty-eight women and 66 men, aged 55-74 years and living in upper Hudson River communities completed a questionnaire and provided blood specimens. Serum was analyzed for thyrotropin (thyroid stimulating hormone, TSH), free (fT4) and total thyroxine (T4), total triiodothyronine (T3), and for POPs. POPs included 39 polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) determined by gas chromatography with electron capture detection (GC-ECD), and nine polybrominated diphenyl ethers (PBDEs) determined by high-resolution gas chromatography with high-resolution mass spectrometry detection (HRGC-HRMS). Multivariable linear regression analysis was used to evaluate associations between thyroid hormones and sums of POPs, adjusted for covariates and stratified by sex. Effects were expressed as differences in thyroid hormone levels associated with a doubling in the level of exposure. Among women, DDT+DDE increased T4 by 0.34μg/dL (P=0.04) and T3 by 2.78ng/dL (P=0.05). Also in women, sums of PCBs in conjunction with PBDEs elicited increases of 24.39-80.85ng/dL T3 (P<0.05), and sums of PCBs in conjunction with DDT+DDE elicited increases of 0.18-0.31μg/dL T4 (P<0.05). For men estrogenic PCBs were associated with a 19.82ng/dL T3 decrease (P=0.003), and the sum of estrogenic PCBs in conjunction with DDT+DDE elicited an 18.02ng/dL T3 decrease (P=0.04). Given age-related declines in physiologic reserve, the influence of POPs on thyroid hormones in aging populations may have clinical implications and merits further investigation.

Serum concentrations of polychlorinated biphenyls (PCBs) in participants of the Anniston Community Health Survey

Serum concentrations of 35 ortho-substituted polychlorinated biphenyl congeners (PCBs) were measured in 765 adults from Anniston, Alabama, where PCBs were manufactured between 1929 and 1971. As part of the Anniston Community Health Survey (ACHS), demographic data, questionnaire information, and blood samples were collected from participants in 2005-2007. Forty-six percent of study participants were African-American, 70% were female, and the median age was 56 years. The median concentration of the sum of 35 PCB congeners (ΣPCBs) was 528 ng/g lipid, with a 90th percentile of 2,600 ng/g lipid, minimum of 17.0 ng/g lipid, and maximum of 27,337 ng/g lipid. The least square geometric mean ΣPCBs was more than 2.5 times higher for African-American participants than for White participants (866 ng/g lipid vs. 331 ng/g lipid); this difference did not change materially after adjustment for age, sex, body mass index (BMI) and current smoking. In spite of large differences in absolute PCB levels, relative contributions of individual congeners to ΣPCBs were quite similar between race groups. Nevertheless, while percent contributions to ΣPCBs for most of the most abundant penta- to heptachlorobiphenyls were higher among African-Americans, the percentages were higher in Whites for the lower-chlorinated PCBs 28 and 74 and for octa- to decachlorinated PCBs. No major differences were observed in geometric mean ΣPCBs between women and men when adjusted for age, race, BMI and current smoking (516 ng/g lipid vs. 526 ng/g lipid). Principal component analysis revealed groups of co-varying congeners that appear to be determined by chlorine substitution patterns. These congener groupings were similar between ACHS participants and the National Health and Nutrition Examination Survey (NHANES) 2003-04 sample of the general United States population, despite ACHS participants having serum concentrations of ΣPCBs two to three times higher than those in comparable age and race groups from NHANES.

Concentrations of persistent organic pollutants (POPs) in human blood samples from Mexico City, Mexico

Studies in Mexico have demonstrated exposure to persistent organic pollutants (POPs) in people living in different sites through the country. However, studies evaluating exposure to POPs in people living in Mexico City (one of most contaminated places in the world) are scarce. Therefore, the aim of this study was to assess the levels of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and its metabolite dichlorodiphenyldichloroethylene (DDE) in the blood as exposure biomarkers in people living in Mexico City. A total of 123 participants (blood donors aged 20-60 years) were recruited during 2010 in Mexico City. Quantitative analyses of blood samples were performed using gas chromatography coupled with mass spectrometry. Levels of the assessed compounds ranged from non-detectable (<LOD) to 350 ng/g lipid; from 8.20 to 91.0 ng/g lipid and from <LOD to 34.0 ng/g lipid for total PBDEs, total PCBs and total DDT, respectively. The current study indicates POP exposure in the people assessed and highlights the need for further biomonitoring studies of these POPs in the region. In this regard, biomonitoring of toxins on a global scale may be the first step towards the prevention of toxin-induced illnesses in the population.

Proposed mechanistic description of dose-dependent BDE-47 urinary elimination in mice using a physiologically based pharmacokinetic model

Polybrominated diphenyl ethers (PBDEs) have been used in a wide variety of consumer applications as additive flame retardants. In North America, scientists have noted continuing increases in the levels of PBDE congeners measured in human serum. Some recent studies have found that PBDEs are associated with adverse health effects in humans, in experimental animals, and wildlife. This laboratory previously demonstrated that urinary elimination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is saturable at high doses in mice; however, this dose-dependent urinary elimination has not been observed in adult rats or immature mice. Thus, the primary objective of this study was to examine the mechanism of urinary elimination of BDE-47 in adult mice using a physiologically based pharmacokinetic (PBPK) model. To support this objective, additional laboratory data were collected to evaluate the predictions of the PBPK model using novel information from adult multi-drug resistance 1a/b knockout mice. Using the PBPK model, the roles of mouse major urinary protein (a blood protein carrier) and P-glycoprotein (an apical membrane transporter in proximal tubule cells in the kidneys, brain, intestines, and liver) were investigated in BDE-47 elimination. The resulting model and new data supported the major role of m-MUP in excretion of BDE-47 in the urine of adult mice, and a lesser role of P-gp as a transporter of BDE-47 in mice. This work expands the knowledge of BDE-47 kinetics between species and provides information for determining the relevancy of these data for human risk assessment purposes.

Polybrominated diphenyl ethers and polychlorinated biphenyls in cord blood from women in Poland

The purpose of this study was to assess human exposure in the prenatal period to selected PBDEs (BDE-47, BDE-99, BDE-153) and PCBs (CB-77, CB-101, CB-118, CB-126, CB-138, CB-153, CB-170, CB-180) basing on the analysis of these compounds in cord blood. The experimental material consisted of 89 cord blood samples taken from women resident in Warsaw and its vicinity. In over 90% of all tested samples the presence of congeners CB-153, CB-138, CB-180 and BDE-47 was identified. The least frequently found were CB-126 and BDE-153, which were present at relatively low concentration levels. Among all analysed PCBs, the highest average concentrations were found in the case of congeners CB-138 (11.8 ng/g of fat) and CB-153 (43.4 ng/g of fat), whereas the lowest was in the case of CB-170 (0.4 ng/g of fat) and CB-126 (0.1 ng/g of fat). In the case of PBDEs the greatest share in the total concentration was that of the congeners BDE-47 and BDE-99, whereas the smallest share was that of the higher brominated congener BDE-153. These results suggest that human exposure to the examined compounds begins already in the period of intrauterine life. The comparison of our own results with the findings of other authors indicates that the PCBs and PBDEs levels in cord blood of women living in Poland do not differ from the respective concentrations in cord blood of other female inhabitants of Europe.

Exposure to lipophilic chemicals as a cause of neurological impairments, neurodevelopmental disorders and neurodegenerative diseases

Many studies have associated environmental exposure to chemicals with neurological impairments (NIs) including neuropathies, cognitive, motor and sensory impairments; neurodevelopmental disorders (NDDs) including autism and attention deficit hyperactivity disorder (ADHD); neurodegenerative diseases (NDGs) including Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (ALS). The environmental chemicals shown to induce all these diseases include persistent organic pollutants (POPs), the plastic exudates bisphenol A and phthalates, low molecular weight hydrocarbons (LMWHCs) and polynuclear aromatic hydrocarbons (PAHs). It is reported here that though these chemicals differ widely in their chemical properties, reactivities and known points of attack in humans, a common link does exist between them. All are lipophilic species found in serum and they promote the sequential absorption of otherwise non-absorbed toxic hydrophilic species causing these diseases.

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.

A hydroxylated metabolite of flame-retardant PBDE-47 decreases the survival, proliferation, and neuronal differentiation of primary cultured adult neural stem cells and interferes with signaling of ERK5 MAP kinase and neurotrophin 3

Polybrominated diphenyl ethers (PBDEs) are a group of organobromine compounds widely used as flame retardants. PBDE-47 is one of the most prominent PBDE congeners found in human tissues, and it can be transformed into several metabolites, including 6-OH-PBDE-47. Recent studies have shown that PBDE-47 is neurotoxic to animals and possibly humans. However, the basis for the neurotoxicity of PBDEs and their metabolites is unclear. For example, it is not known whether PBDEs affect adult neurogenesis, a process implicated in learning and memory and in olfactory behavior. In this study, we examined the toxicity of PBDEs for primary adult neural stem/progenitor cells (aNSCs) isolated from the subventricular zone (SVZ) of adult mice. We discovered that 6-OH-PBDE-47, but not its parent compound PBDE-47, is cytotoxic for aNCSs using MTS metabolism and cell number as a measure of cytotoxicity. Interestingly, 6-OH-PBDE-47 induced apoptosis at concentrations above 7.5μM inhibited proliferation at 2.5-5μM while suppressing neuronal and oligodendrocyte differentiation at submicromolar concentrations (≤ 1μM). The effect on proliferation was reversed upon removal of 6-OH-PBDE-47 and correlated with selective but reversible inhibition of ERK5 activation by mitogenic growth factors EGF and bFGF. 6-OH-PBDE-47 also inhibited the proneuronal differentiation effect of neurotrophin 3 (NT3) and NT3 activation of ERK5. Together, these data show that 6-OH-PBDE-47 is more toxic than its parent compound for SVZ-derived aNSCs and that it inhibits multiple aspects of adult neurogenesis. Furthermore, inhibition of ERK5 signaling may underlie the adverse effect of 6-OH-PBDE-47 on proliferation and neuronal differentiation. Our data suggest that exposure to PBDE-based flame retardants could cause neurotoxicity in the adult brain by interfering with adult neurogenesis.

Neurobehavioral function and low-level exposure to brominated flame retardants in adolescents: a cross-sectional study

BACKGROUND

Animal and in vitro studies demonstrated a neurotoxic potential of brominated flame retardants, a group of chemicals used in many household and commercial products to prevent fire. Although the first reports of detrimental neurobehavioral effects in rodents appeared more than ten years ago, human data are sparse.

METHODS

As a part of a biomonitoring program for environmental health surveillance in Flanders, Belgium, we assessed the neurobehavioral function with the Neurobehavioral Evaluation System (NES-3), and collected blood samples in a group of high school students. Cross-sectional data on 515 adolescents (13.6-17 years of age) was available for the analysis. Multiple regression models accounting for potential confounders were used to investigate the associations between biomarkers of internal exposure to brominated flame retardants [serum levels of polybrominated diphenyl ether (PBDE) congeners 47, 99, 100, 153, 209, hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA)] and cognitive performance. In addition, we investigated the association between brominated flame retardants and serum levels of FT3, FT4, and TSH.

RESULTS

A two-fold increase of the sum of serum PBDE's was associated with a decrease of the number of taps with the preferred-hand in the Finger Tapping test by 5.31 (95% CI: 0.56 to 10.05, p = 0.029). The effects of the individual PBDE congeners on the motor speed were consistent. Serum levels above the level of quantification were associated with an average decrease of FT3 level by 0.18 pg/mL (95% CI: 0.03 to 0.34, p = 0.020) for PBDE-99 and by 0.15 pg/mL (95% CI: 0.004 to 0.29, p = 0.045) for PBDE-100, compared with concentrations below the level of quantification. PBDE-47 level above the level of quantification was associated with an average increase of TSH levels by 10.1% (95% CI: 0.8% to 20.2%, p = 0.033), compared with concentrations below the level of quantification. We did not observe effects of PBDE's on neurobehavioral domains other than the motor function. HBCD and TBBPA did not show consistent associations with performance in the neurobehavioral tests.

CONCLUSIONS

This study is one of few studies and so far the largest one investigating the neurobehavioral effects of brominated flame retardants in humans. Consistently with experimental animal data, PBDE exposure was associated with changes in the motor function and the serum levels of the thyroid hormones.