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

Identification of polychlorinated biphenyls (PCBs) and PCB metabolites associated with changes in the gut microbiome of female mice exposed to an environmental PCB mixture

Polychlorinated biphenyls (PCBs) are neurotoxic hazardous materials that may cause toxicity via the gut-liver-brain axis. This study investigated PCB × microbiome interactions in adult female mice exposed orally to an environmental PCB mixture. Female mice (6-week-old) were exposed daily for 7 weeks to peanut butter containing 0, 0.1, 1, or 6 mg/kg/day of PCBs. Twenty hours after the final exposure, the cecal content was collected to characterize the microbiome composition and predicted function. PCB and its metabolites in feces were analyzed using gas chromatography-tandem mass spectrometry (GC-MS/MS), while cecal content was assessed with liquid chromatography-high resolution mass spectrometry (LC-HRMS). PCB exposure influenced the abundance of microbial taxa and predicted functions within the cecal content. Complex PCB and metabolite mixtures were detected in the gastrointestinal tract. Network analysis revealed associations between specific parent PCBs and metabolites with changes in the abundance of bacteria in the gastrointestinal tract. These findings demonstrate that individual PCBs and their metabolites significantly influence the abundance of specific bacteria in the gastrointestinal tract following oral PCB exposure. These findings inform further research targeting the microbiome to attenuate the adverse health outcomes of PCB exposure.

Developmental polychlorinated biphenyl (PCB) exposure impacts on voiding physiology persist into adulthood and influence sensitivity to bladder stimuli in mice

Polychlorinated biphenyls (PCBs) are toxicants present in the environment, foodstuff, animal and human tissues. PCBs are linked to numerous adverse health effects; however, impacts of developmental PCB exposure on lower urinary tract function are a comparatively newer area of interest. We have previously found developmental exposure (in utero and lactational) to a human-relevant PCB mixture in mice leads to sex- and dose- dependent changes to urinary voiding physiology at 6 weeks of age. This study expands upon previous findings to investigate if developmental PCB-induced urinary voiding phenotypes persist or shift as mice age to 12 weeks of age. Urinary voiding physiology testing through void spot assays, uroflowmetry, and cystometry demonstrated several sex- and dose- dependent effects of PCB exposure at 12 weeks of age. Further, patterns of dysfunction were either maintained, newly acquired, or reversed compared to those from younger adult mice in a previous study. Here, developmental PCB exposure decreased number of small urine spots in adult male and female mice in a dose dependent manner, and female mice had more frequent voiding events assessed by anesthetized cystometry. Mice also had PCB dose-dependent changes to urinary voiding physiology when challenged with intravesical capsaicin infusion to target transient receptor potential cation channel subfamily V member 1 (TRPV1)-mediated pathways. PCBs either blocked or exacerbated capsaicin induced responses depending on the endpoint examined, suggesting this pathway may play a role in PCB-dependent changes in voiding. PCBs also had subtle impacts on prostate wet weight, with high PCB doses reducing tissue mass compared to low PCB doses, while none differed from vehicle. This study demonstrates developmental exposure to PCBs continues to impact lower urinary tract function in adulthood to at least 12 weeks of age both during homeostatic conditions and upon challenge of capsaicin. Better understanding of how early life stressors like PCBs contribute to aging-associated voiding dysfunction are imperative as these findings may help mitigate risk or improve treatment strategies for patients suffering from lower urinary tract symptoms.

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

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

Elucidating the Metabolism of Chiral PCB95 in Wildtype and Transgenic Mouse Models with Altered Cytochrome P450 Enzymes Using Intestinal Content Screening

Polychlorinated biphenyls (PCBs), such as 2,2',3,5',6-pentachlorobiphenyl (PCB95), are persistent organic pollutants associated with adverse health outcomes, including developmental neurotoxicity. PCB95 is a chiral neurotoxic PCB congener atropselectively metabolized to potentially neurotoxic metabolites in vivo. However, the metabolic pathways of most PCB congeners, including PCB95, remain unknown. To address this knowledge gap, we analyzed the intestinal contents of mice exposed to PCB95 to elucidate the PCB95 metabolism pathway and assess if genetic manipulation of hepatic drug-metabolizing enzymes affects PCB95 metabolism. Our study exposed male and female wildtype (WT), Cyp2abfgs-null (KO), and CYP2A6-transgenic/Cyp2abfgs-null (KI) mice orally to 1.0 mg/kg body weight of PCB95. Intestinal content was collected 24 h after PCB administration. aS-PCB95 was enriched in all intestinal content samples, irrespective of sex and genotype. Gas chromatography-tandem mass spectrometry (GC-MS/MS) analyses identified 5 mono- (OH-PCB95) and 4 dihydroxylated PCB (diOH-PCB95) metabolites. Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) identified 15 polar hydroxylated, methoxylated, and sulfated PCB95 metabolites, including 3 dechlorinated metabolites. A sex difference in the relative OH-PCB95 levels was observed only for KO in the LC-HRMS analysis. Genotype-dependent differences were observed for female, but not male, mice, with OH-PCB95 levels in female KO (FKO) mice tending to be lower than those in female WT (FWT) and KI (FKI) mice. Based on the GC-MS/MS analysis, these differences are due to the unknown PCB95 metabolites, X1-95 and Y1-95. These findings demonstrate that combining GC-MS/MS analyses and LC-HRMS subject screening of the intestinal content of PCB95-exposed mice can significantly advance our understanding of PCB95 metabolism in vivo.

Inhalation of 2,2',5,5'-tetrachlorobiphenyl (PCB52) causes changes to the gut microbiome throughout the gastrointestinal tract

Polychlorinated biphenyls (PCBs), such as PCB52, are hazardous environmental contaminants present in indoor and outdoor environments. Oral PCB exposure affects the colon microbiome; however, it is unknown if inhalation of PCBs alters the intestinal microbiome. We hypothesize that sub-acute inhalation of PCB52 affects microbial communities depending on the location in the (GI) gastrointestinal tract and the local profiles of PCB52 and its metabolites present in the GI tract following mucociliary clearance and biliary or intestinal excretion. Sprague-Dawley rats were exposed via nose-only inhalation 4 h per day, 7 days per week, for 4 weeks to either filtered air or PCB52. After 28 days, differences in the microbiome and levels of PCB52 and its metabolites were characterized throughout the GI tract. PCB52 inhalation altered taxa abundances and predicted functions altered throughout the gut, with most alterations occurring in the large intestine. PCB52 and metabolite levels varied across the GI tract, resulting in differing PCB × microbiome networks. Thus, the presence of different levels of PCB52 and its metabolites in different parts of the GI tract has varying effects on the composition and predicted function of microbial communities. Future studies need to investigate whether these changes lead to adverse outcomes.

Cytosolic sulfotransferases in endocrine disruption

The mammalian cytosolic sulfotransferases (SULTs) catalyze the sulfation of endocrine hormones as well as a broad array of drugs, environmental chemicals, and other xenobiotics. Many endocrine-disrupting chemicals (EDCs) interact with these SULTs as substrates and inhibitors, and thereby alter sulfation reactions responsible for metabolism and regulation of endocrine hormones such as estrogens and thyroid hormones. EDCs or their metabolites may also regulate expression of SULTs through direct interaction with nuclear receptors and other transcription factors. Moreover, some sulfate esters derived from EDCs (EDC-sulfates) may serve as ligands for endocrine hormone receptors. While the sulfation of an EDC can lead to its excretion in the urine or bile, it may also result in retention of the EDC-sulfate through its reversible binding to serum proteins and thereby enable transport to other tissues for intracellular hydrolysis and subsequent endocrine disruption. This mini-review outlines the potential roles of SULTs and sulfation in the effects of EDCs and our evolving understanding of these processes.

Effects of 28-day nose-only inhalation of PCB52 (2,2',5,5'-Tetrachlorobiphenyl) on the brain transcriptome

A semi-volatile polychlorinated biphenyl (PCB) congener, PCB52, is present in the indoor air of schools; however, the effects of inhaled PCB52 on the brain have not been investigated. This study exposed male Sprague-Dawley rats at 39 days of age and female rats at 42 days of age to PCB52 for 4 hours per day over 28 consecutive days through nose-only inhalation. Neurobehavioral tests were conducted during the last 5 days of exposure. The total estimated PCB52 exposures after 28 days were 1080±20 µg/kg BW for male rats and 1140±10 µg/kg BW for female rats. PCB52 and its metabolites were detected by gas chromatography-tandem mass spectrometry in the brain, lung, and serum, with the lung showing the highest concentrations. PCB52 levels were higher in the brains of females than males. Males showed increased exploratory behavior compared to controls, whereas females exhibited decreased exploratory behavior compared to controls in the same tests. PCB52 exposure did not impact locomotor activity or working memory. Gene expression and pathway analysis in the striatum and cerebellum suggest that PCB52 inhalation causes mitochondrial dysfunction. No significant differences were observed by immunohistochemical evaluation in the density and percent area of total cells, astrocytes, or microglia in the striatum and cerebellar cortex. Our results indicate multilevel effects of inhaled PCB52 on the rat brain, from gene expression to behavioral effects.

Interactions of Polychlorinated Biphenyls and Their Metabolites with the Brain and Liver Transcriptome of Female Mice

Exposure to polychlorinated biphenyls (PCBs) is linked to neurotoxic effects. This study aims to close knowledge gaps regarding the specific modes of action of PCBs in female C57BL/6J mice (>6 weeks) orally exposed for 7 weeks to a human-relevant PCB mixture (MARBLES mix) at 0, 0.1, 1, and 6 mg/kg body weight/day. PCB and hydroxylated PCB (OH-PCBs) levels were quantified in the brain, liver, and serum; RNA sequencing was performed in the striatum, prefrontal cortex, and liver, and metabolomic analyses were performed in the striatum. Profiles of PCBs but not their hydroxylated metabolites were similar in all tissues. In the prefrontal cortex, PCB exposure activated the oxidative phosphorylation respiration pathways, while suppressing the axon guidance pathway. PCB exposure significantly changed the expression of genes associated with neurodevelopmental and neurodegenerative diseases in the striatum, impacting pathways like growth hormone synthesis and dendrite development. PCBs did not affect the striatal metabolome. In contrast to the liver, which showed activation of metabolic processes following PCB exposure and the induction of cytochrome P450 enzymes, the expression of xenobiotic processing genes was not altered by PCB exposure in either brain region. Network analysis revealed complex interactions between individual PCBs (e.g., PCB28 [2,4,4'-trichlorobiphenyl]) and their hydroxylated metabolites and specific differentially expressed genes (DEGs), underscoring the need to characterize the association between specific PCBs and DEGs. These findings enhance the understanding of PCB neurotoxic mechanisms and their potential implications for human health.

Upregulation of fatty acid synthesis genes in the livers of adolescent female rats caused by inhalation exposure to PCB52 (2,2',5,5'-Tetrachlorobiphenyl)

Elevated airborne PCB levels in older schools are concerning due to their health impacts, including cancer, metabolic dysfunction-associated steatotic liver disease (MASLD), cardiovascular issues, neurodevelopmental diseases, and diabetes. During a four-week inhalation exposure to PCB52, an air pollutant commonly found in school environments, adolescent rats exhibited notable presence of PCB52 and its hydroxylated forms in their livers, alongside changes in gene expression. Female rats exhibited more pronounced changes in gene expression compared to males, particularly in fatty acid synthesis genes regulated by the transcription factor SREBP1. In vitro studies with human liver cells showed that the hydroxylated metabolite of PCB52, 4-OH-PCB52, but not the parent compound, upregulated genes involved in fatty acid biosynthesis similar to in vivo exposure. These findings highlight the sex-specific effects of PCB52 exposure on livers, particularly in females, suggesting a potential pathway for increased MASLD susceptibility.

Microglial responses to inflammatory challenge in adult rats altered by developmental exposure to polychlorinated biphenyls in a sex-specific manner

Polychlorinated biphenyls are ubiquitous environmental contaminants linkedc with peripheral immune and neural dysfunction. Neuroimmune signaling is critical to brain development and later health; however, effects of PCBs on neuroimmune processes are largely undescribed. This study extends our previous work in neonatal or adolescent rats by investigating longer-term effects of perinatal PCB exposure on later neuroimmune responses to an inflammatory challenge in adulthood. Male and female Sprague-Dawley rats were exposed to a low-dose, environmentally relevant, mixture of PCBs (Aroclors 1242, 1248, and 1254, 1:1:1, 20 μg / kg dam BW per gestational day) or oil control during gestation and via lactation. Upon reaching adulthood, rats were given a mild inflammatory challenge with lipopolysaccharide (LPS, 50 μg / kg BW, ip) or saline control and then euthanized 3 hours later for gene expression analysis or 24 hours later for immunohistochemical labeling of Iba1+ microglia. PCB exposure did not alter gene expression or microglial morphology independently, but instead interacted with the LPS challenge in brain region- and sex-specific ways. In the female hypothalamus, PCB exposure blunted LPS responses of neuroimmune and neuromodulatory genes without changing microglial morphology. In the female prefrontal cortex, PCBs shifted Iba1+ cells from reactive to hyperramified morphology in response to LPS. Conversely, in the male hypothalamus, PCBs shifted cell phenotypes from hyperramified to reactive morphologies in response to LPS. The results highlight the potential for long-lasting effects of environmental contaminants that are differentially revealed over a lifetime, sometimes only after a secondary challenge. These neuroimmune endpoints are possible mechanisms for PCB effects on a range of neural dysfunction in adulthood, including mental health and neurodegenerative disorders. The findings suggest possible interactions with other environmental challenges that also influence neuroimmune systems.

Environmental remediation of emerging contaminants using subcritical water: A review

The continuous rise of emerging contaminants (ECs) in the environment has been a growing concern due to their potentially harmful effects on humans, animals, plants, and aquatic life, even at low concentrations. ECs include human and veterinary pharmaceuticals, hormones, personal care products, pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organic dyes, heavy metals (HMs), and others. The world's growing population contributes to the release of many kinds of chemicals into the environment, which is estimated to be more than 200 billion metric tons annually and results in over 9 million deaths. The removal of these contaminants using conventional physical, chemical, and biological treatments has proven to be ineffective, highlighting the need for simple, effective, inexpesive, practical, and eco-friendly alternatives. Thus, this article discusses the utilization of subcritical water oxidation (SBWO) and subcritical water extraction (SBWE) techniques to remove ECS from the environment. Subcritical water (water below the critical temperature of 374.15 °C and critical pressure of 22.1 Mpa) has emerged as one of the most promising methods for remediation of ECs from the environment due to its non-toxic properties, simplicity and efficiency of application. Furthermore, the impact of temperature, pressure, treatment time, and utilization of chelating agents, organic modifiers, and oxidizing agents in the static and dynamic modes was investigated to establish the best conditions for high ECs removal efficiencies.

Placental-brain axis in females detected within broadly impacted metabolic gene networks protects against prenatal PCB exposure

Background

Neurodevelopmental disorders have a strong male bias that is poorly understood. Placenta is a rich source of molecular information about environmental interactions with genetics (including biological sex), that affect the developing brain. We investigated placental-brain transcriptional responses in an established mouse model of prenatal exposure to a human-relevant mixture of polychlorinated biphenyls (PCBs).

Results

To understand sex, tissue, and dosage effects in embryonic (E18) brain and placenta by RNAseq, we used weighted gene correlation network analysis (WGCNA) to create correlated gene networks that could be compared across sex or tissue. WGCNA revealed that expression within most correlated gene networks was significantly and strongly associated with PCB exposures, but frequently in opposite directions between male-female and placenta-brain comparisons. In both WGCNA and differentially expressed gene analyses, male brain showed more PCB-induced transcriptional changes than male placenta, but the reverse pattern was seen in females. Furthermore, non-monotonic dose responses to PCBs were observed in most gene networks but were most prominent in male brain. The transcriptomic effects of low dose PCB exposure were significantly reversed by dietary folic acid supplementation across both sexes, but these effects were strongest in female placenta. PCB-dysregulated and folic acid-reversed gene networks were commonly enriched in functions in metabolic pathways involved in energy usage and translation, with female-specific protective effects enriched in PPAR, thermogenesis, glycerolipids, and O-glycan biosynthesis, as opposed to toxicant responses in male brain.

Conclusions

The female protective effect in prenatal PCB exposures appears to be mediated by dose-dependent sex differences in transcriptional modulation of metabolism in placenta.

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

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

Distribution of 2,2',5,5'-Tetrachlorobiphenyl (PCB52) Metabolites in Adolescent Rats after Acute Nose-Only Inhalation Exposure

Inhalation of PCB-contaminated air is increasingly recognized as a route for PCB exposure. Because limited information about the disposition of PCBs following inhalation exposure is available, this study investigated the disposition of 2,2',5,5'-tetrachlorobiphenyl (PCB52) and its metabolites in rats following acute, nose-only inhalation of PCB52. Male and female Sprague-Dawley rats (50-58 days of age, 210 ± 27 g; n = 6) were exposed for 4 h by inhalation to approximately 14 or 23 μg/kg body weight of PCB52 using a nose-only exposure system. Sham animals (n = 6) were exposed to filtered lab air. Based on gas chromatography-tandem mass spectrometry (GC-MS/MS), PCB52 was present in adipose, brain, intestinal content, lung, liver, and serum. 2,2',5,5'-Tetrachlorobiphenyl-4-ol (4-OH-PCB52) and one unknown monohydroxylated metabolite were detected in these compartments except for the brain. Liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis identified several metabolites, including sulfated, methoxylated, and dechlorinated PCB52 metabolites. These metabolites were primarily found in the liver (7 metabolites), lung (9 metabolites), and serum (9 metabolites) due to the short exposure time. These results demonstrate for the first time that complex mixtures of sulfated, methoxylated, and dechlorinated PCB52 metabolites are formed in adolescent rats following PCB52 inhalation, laying the groundwork for future animal studies of the adverse effects of inhaled PCB52.

Complex roles for sulfation in the toxicities of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic toxicants derived from legacy pollution sources and their formation as inadvertent byproducts of some current manufacturing processes. Metabolism of PCBs is often a critical component in their toxicity, and relevant metabolic pathways usually include their initial oxidation to form hydroxylated polychlorinated biphenyls (OH-PCBs). Subsequent sulfation of OH-PCBs was originally thought to be primarily a means of detoxication; however, there is strong evidence that it may also contribute to toxicities associated with PCBs and OH-PCBs. These contributions include either the direct interaction of PCB sulfates with receptors or their serving as a localized precursor for OH-PCBs. The formation of PCB sulfates is catalyzed by cytosolic sulfotransferases, and, when transported into the serum, these metabolites may be retained, taken up by other tissues, and subjected to hydrolysis catalyzed by intracellular sulfatase(s) to regenerate OH-PCBs. Dynamic cycling between PCB sulfates and OH-PCBs may lead to further metabolic activation of the resulting OH-PCBs. Ultimate toxic endpoints of such processes may include endocrine disruption, neurotoxicities, and many others that are associated with exposures to PCBs and OH-PCBs. This review highlights the current understanding of the complex roles that PCB sulfates can have in the toxicities of PCBs and OH-PCBs and research on the varied mechanisms that control these roles.

A Review: Subcritical Water Extraction of Organic Pollutants from Environmental Matrices

Most organic pollutants are serious environmental concerns globally due to their resistance to biological, chemical, and photolytic degradation. The vast array of uses of organic compounds in daily life causes a massive annual release of these substances into the air, water, and soil. Typical examples of these substances include pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). Since they are persistent and hazardous in the environment, as well as bio-accumulative, sensitive and efficient extraction and detection techniques are required to estimate the level of pollution and assess the ecological consequences. A wide variety of extraction methods, including pressurized liquid extraction, microwave-assisted extraction, supercritical fluid extraction, and subcritical water extraction, have been recently used for the extraction of organic pollutants from the environment. However, subcritical water has proven to be the most effective approach for the extraction of a wide range of organic pollutants from the environment. In this review article, we provide a brief overview of the subcritical water extraction technique and its application to the extraction of PAHs, PCBs, pesticides, pharmaceuticals, and others form environmental matrices. Furthermore, we briefly discuss the influence of key extraction parameters, such as extraction time, pressure, and temperature, on extraction efficiency and recovery.

Predicted versus observed activity of PCB mixtures toward the ryanodine receptor

Non-dioxin-like polychlorinated biphenyls (NDL PCBs) alter the activity of the ryanodine receptor (RyR), and this activity is linked to developmental neurotoxicity. Most work to date has focused on the activity of single congeners rather than relevant mixtures. The current study assessed the RyR activity of single congeners or binary, tertiary, and complex PCB mixtures. Observed mixture activity was then compared to the expected activity calculated using the concentration addition (CA) model or a RyR-specific neurotoxic equivalency scheme (rNEQ). The predictions of the CA model were consistent with the observed activity of binary mixtures at the lower portion of the concentration-response curve, supporting the additivity of RyR1 active PCBs. Findings also show that minimally active congeners can compete for the RyR1 binding site, and congeners that do not activate the RyR1 do not interfere with the activity of a full agonist. Complex PCB mixtures that mimic PCB profiles detected in indoor air, fish tissue, and the serum of mothers and children activated the RyR1 and displayed similar efficacy and potency regardless of varying congener profiles. Neither the CA model nor the rNEQ perfectly predicted the observed activity of complex mixtures, but predictions were often within one magnitude of change from the observed response. Importantly, PCB mixtures approximating profiles found in environmental samples or human serum displayed RyR1 activity at concentrations reported in published research. The work presented will aid in the development of risk assessment platforms for NDL PCBs and similar compounds toward RyR1 activation and related neurotoxicity.

Use of a polymeric implant system to assess the neurotoxicity of subacute exposure to 2,2',5,5'-tetrachlorobiphenyl-4-ol, a human metabolite of PCB 52, in male adolescent rats

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that ubiquitously exist in the environment. PCB exposure has been linked to cancer and multi-system toxicity, including endocrine disruption, immune inhibition, and reproductive and neurotoxicity. 2,2',5,5'-Tetrachlorobiphenyl (PCB 52) is one of the most frequently detected congeners in the environment and human blood. The hydroxylated metabolites of PCB 52 may also be neurotoxic, especially for children whose brains are still developing. However, it is challenging to discern the contribution of these metabolites to PCB neurotoxicity because the metabolism of PCB is species-dependent. In this study, we evaluated the subacute neurotoxicity of a human-relevant metabolite, 2,2',5,5'-tetrachlorobiphenyl-4-ol (4-52), on male adolescent Sprague Dawley rats, via a novel polymeric implant drug delivery system grafted subcutaneously, at total loading concentrations ranging from 0%, 1%, 5%, and 10% of the implant (w/w) for 28 days. Y-maze, hole board test, open field test, and elevated plus maze were performed on exposure days 24-28 to assess their locomotor activity, and exploratory and anxiety-like behavior. 4-52 and other possible hydroxylated metabolites in serum and vital tissues were quantified using gas chromatography with tandem mass spectrometry (GC-MS/MS). Our results demonstrate the sustained release of 4-52 from the polymeric implants into the systemic circulation in serum and tissues. Dihydroxylated and dechlorinated metabolites were detected in serum and tissues, depending on the dose and tissue type. No statistically significant changes were observed in the neurobehavioral tasks across all exposure groups. The results demonstrate that subcutaneous polymeric implants provide a straightforward method to expose rats to phenolic PCB metabolites to study neurotoxic outcomes, e.g., in memory, anxiety, and exploratory behaviors.

Polychlorinated biphenyl (PCB) exposure in adult female mice can influence bladder contractility

Lower urinary tract symptoms (LUTS) greatly reduce quality of life. While LUTS etiology is not completely understood, it is plausible that environmental contaminants could play a role. Polychlorinated biphenyls (PCBs), are a group of persistent environmental toxicants frequently documented in animal and human tissues. PCBs are capable of influencing voiding function in mouse offspring exposed developmentally, however whether PCB exposure during adulthood can also influence voiding dynamics is unknown. Therefore, the purpose of this study was to determine whether PCB exposure in adult female mice can impact voiding function. As part of a larger study to generate developmentally exposed offspring, adult female C57Bl/6J mice were dosed orally with the MARBLES PCB mixture (0.1, 1, or 6 mg/kg/day) or vehicle control beginning two weeks before mating and throughout gestation and lactation (9 weeks). Adult dosed female dams then underwent void spot assay, uroflowmetry, and anesthetized cystometry to assess voiding function. Bladder contractility was assessed in ex vivo bladder bath assays, and bladders were collected for morphology and histology assessments. While voiding behavior endpoints were minimally impacted, alterations to bladder contractility dynamics were more pronounced. Adult female mice dosed with 1 mg/kg/d PCB showed an increase in urine spots 2-3 cm2 in size, increased bladder contractility in response to electrical field stimulation, and decreased bladder wall thickness compared to vehicle control. PCBs also altered contractile response to cholinergic agonist in a dose-dependent manner. Overall, these results indicate that exposure to PCBs in adult female mice is sufficient to produce changes in bladder physiology. These results also highlight the critical role of timing of exposure in influencing voiding function.

Disposition and metabolomic effects of 2,2',5,5'-tetrachlorobiphenyl in female rats following intraperitoneal exposure

The disposition and toxicity of lower chlorinated PCBs (LC-PCBs) with less than five chlorine substituents have received little attention. This study characterizes the distribution and metabolomic effects of PCB 52, an LC-PCB found in indoor and outdoor air, three weeks after intraperitoneal exposure of female Sprague Dawley rats to 0, 1, 10, or 100 mg/kg BW. PCB 52 exposure did not affect overall body weight. Gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis identified PCB 52 in all tissues investigated. Hydroxylated, sulfated, and methylated PCB metabolites, identified using GC-MS/MS and nontarget liquid chromatography-high resolution mass spectrometry (Nt-LCMS), were primarily found in the serum and liver of rats exposed to 100 mg/kg BW. Metabolomic analysis revealed minor effects on L-cysteine, glycine, cytosine, sphingosine, thymine, linoleic acid, orotic acid, L-histidine, and erythrose serum levels. Thus, the metabolism of PCB 52 and its effects on the metabolome must be considered in toxicity studies.

Predicted Versus Observed Activity of PCB Mixtures Toward the Ryanodine Receptor

Non-dioxin-like polychlorinated biphenyls (NDL PCBs) alter the activity of the ryanodine receptor (RyR), and this activity is linked to developmental neurotoxicity. Most work to date has focused on the activity of single congeners rather than relevant mixtures. The current study assessed the RyR activity of single congeners or binary, tertiary, and complex PCB mixtures. Observed mixture activity was then compared to the expected activity calculated using the concentration addition (CA) model or a RyR-specific neurotoxic equivalency scheme (rNEQ). The predictions of the CA model were consistent with the observed activity of binary mixtures at the lower portion of the concentration-response curve, supporting the additivity of RyR1 active PCBs. Findings also show that minimally active congeners can compete for the RyR1 binding site, and congeners that do not activate the RyR1 do not interfere with the activity of a full agonist. Complex PCB mixtures that mimic PCB profiles detected in indoor air, fish tissue, and the serum of mothers and children activated the RyR1 and displayed similar efficacy and potency regardless of varying congener profiles. Neither the CA model nor the rNEQ perfectly predicted the observed activity of complex mixtures, but predictions were often within one magnitude of change from the observed response. Importantly, PCB mixtures approximating profiles found in environmental samples or human serum displayed RyR1 activity at concentrations reported in published research. The work presented will aid in the development of risk assessment platforms for NDL PCBs, and similar compounds, towards RyR1 activation and related neurotoxicity.

Enantiomeric Fractions Reveal Differences in the Atropselective Disposition of 2,2',3,5',6-Pentachlorobiphenyl (PCB 95) in Wildtype, Cyp2abfgs-Null, and CYP2A6-Humanized Mice

Polychlorinated biphenyls (PCBs) are environmental contaminants that can cause neurotoxicity. PCBs, such as PCB 95 (2,2',3,5',6-pentachlorobiphenyl), can be metabolized by cytochrome P450 enzymes into neurotoxic metabolites. To better understand how the metabolism of PCB 95 affects neurotoxic outcomes, we conducted a study on the disposition of PCB 95 in transgenic mouse models. The mice were given a single oral dose of PCB 95 (1.0 mg/kg) and were euthanized 24 h later for analysis. PCB 95 levels were highest in adipose tissue, followed by the liver, brain, and blood. Adipose tissue levels were significantly higher in wild-type (WT) mice than in Cyp2abfgs-null (KO) or CYP2A6-transgenic (KI) mice. We also observed genotype-dependent differences in the enrichment of aS-PCB 95 in female mice, with a less pronounced enrichment in KO than WT and KI mice. Ten hydroxylated PCB 95 metabolites were detected in blood and tissue across all exposure groups. The metabolite profiles differed across tissues, while sex and genotype-dependent differences were less pronounced. Total OH-PCB levels were highest in the blood, followed by the liver, adipose tissue, and brain. Total OH-PCB blood levels were lower in KO than in WT mice, while the opposite trend was observed in the liver. In male mice, total OH-PCB metabolite levels were significantly lower in KI than in WT mice in blood and the liver, while the opposite trend was observed in female mice. In conclusion, the study highlights the differences in the atropselective disposition of PCB 95 and its metabolites in different types of mice, demonstrating the usefulness of these transgenic mouse models for characterizing the role of PCB metabolism in PCB neurotoxicity.

Disposition and Metabolomic Effects of 2,2',5,5'-Tetrachlorobiphenyl in Female Rats Following Intraperitoneal Exposure

The disposition and toxicity of lower chlorinated PCBs (LC-PCBs) with less than five chlorine substituents have received little attention. This study characterizes the distribution and metabolomic effects of PCB 52, an LC-PCB found in indoor and outdoor air, three weeks after intraperitoneal exposure of female Sprague Dawley rats to 0, 1, 10, or 100 mg/kg BW. PCB 52 exposure did not affect overall body weight. Gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis identified PCB 52 in all tissues investigated. Hydroxylated, sulfated, and methylated PCB metabolites, identified using GC-MS/MS and nontarget liquid chromatography-high resolution mass spectrometry (Nt-LCMS), were primarily found in the serum and liver of rats exposed to 100 mg/kg BW. Metabolomic analysis revealed minor effects on L-cysteine, glycine, cytosine, sphingosine, thymine, linoleic acid, orotic acid, L-histidine, and erythrose serum levels. Thus, the metabolism of PCB 52 and its effects on the metabolome must be considered in toxicity studies.

Highlights

PCB 52 was present in adipose, brain, liver, and serum 3 weeks after PCB exposureLiver and serum contained hydroxylated, sulfated, and methylated PCB 52 metabolitesMetabolomics analysis revealed minor changes in endogenous serum metabolitesLevels of dopamine and its metabolites in the brain were not affected by PCB 52.

Updating "Dataset of transcriptomic changes that occur in human preadipocytes over a 3-day course of exposure to 3,3',4,4',5-Pentachlorobiphenyl (PCB126)" with additional data on exposure to 2,2',5,5'-tetrachlorobiphenyl (PCB52) or its 4-hydroxy metabolite (4-OH-PCB52)

Polychlorinated biphenyls (PCBs) were used extensively in building materials, including those used in schools. PCBs accumulate in fat, and exposure to PCBs is associated with the development of cancer, neurodevelopmental disorders, cardiovascular disease, obesity, and diabetes. The non-dioxin-like PCB congener, PCB52 (2,2',5,5'-tetrachlorobiphenyl), is found at one of the highest levels of any congener in school air. PCB52 is oxidized in the liver to hydroxylated forms, mainly 4-OH-PCB52 (2,2',5,5'-tetrachlorobiphenyl-4-ol). In a previous study, we reported on RNAseq data generated from exposure of human preadipocytes to the dioxin-like PCB congener, PCB126. In this new dataset, we used identical techniques to examine alterations in gene transcript levels in human preadipocytes exposed to PCB52 or 4-OH-PCB52 over a time course. This updated set of data provides a comprehensive transcriptional profile of changes that occur in preadipocytes exposed to PCB52 or 4-OH-PCB52 over time and allows for comparison of these changes between the parent compound and its hydroxy metabolite. The datasets will allow others to explore how PCB52 and 4-OH-PCB52 impact biological pathways in preadipocytes. Further studies can be performed to determine how these changes might lead to disease.

Polychlorinated Biphenyls (PCBs) Impact Prostatic Collagen Density and Bladder Volume in Young Adult Mice Exposed during in Utero and Lactational Development

Polychlorinated biphenyls (PCBs) are persistent organic pollutants linked to deleterious health outcomes, including voiding dysfunction in developmentally exposed mice. Changes in prostate volume and/or extracellular matrix composition are associated with voiding dysfunction in men and animal models. Whether PCB-induced changes in voiding function in male mice occur in part via alterations to the prostate or an alternate mechanism is unclear. Therefore, we tested whether developmental exposure to the MARBLES PCB mixture altered prostate morphology in young adult offspring. C57Bl/6J female mice were dosed daily with the MARBLES PCB mixture at 0, 0.1, 1 or 6 mg/kg/d for two weeks prior to mating and through gestation and lactation, offspring were collected at 6 weeks of age. Ventral prostate mass was decreased in the 1 mg/kg/d PCB group compared to other PCB groups. There were no PCB-induced changes in prostate smooth muscle thickness, apoptosis, proliferation, or testes mass. PCBs impacted the prostate extracellular matrix; anterior prostate collagen density was decreased in the 1 mg/kg/d PCB group compared to all other groups. Normalized bladder volume was increased in male and female offspring in the 6 mg/kg/d PCB group compared to control. No change in water consumption, bladder mass or bladder smooth muscle thickness accompanied changes in bladder volume. Urine and serum creatinine concentrations were elevated but only in male mice. Together, these results suggest that developmental exposure to PCBs can influence prostate wet weight and prostate/bladder morphology, but PCBs do not promote prostate enlargement. Whether these changes persist throughout adult life and how they contribute to voiding function in animal models and humans is of future interest.

Altered MANF and RYR2 concentrations associated with hypolipidemia in the serum of patients with schizophrenia

Schizophrenia (SCZ) is associated with abnormal serum lipid profiles, but their relationship is poorly understood. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an important regulator of lipid metabolism. Previous studies have shown its involvement in the pathogenesis of numerous neuropsychiatric disorders, while its role in SCZ is still unknown. Therefore, this study was conducted to examine serum MANF levels in patients with SCZ, and to investigate the potential relationship between MANF, serum lipid levels and SCZ. The results showed that total cholesterol (TC) levels were significantly lower in 225 patients with SCZ than in 233 healthy controls (HCs). According to Ingenuity Pathway Analysis, hypolipidemia is associated with SCZ via MANF/ryanodine receptor 2 (RYR2) pathway. This theory was supported by another sample set, which showed significantly lower MANF levels and higher RYR2 levels in the serum of 170 SCZ patients compared to 80 HCs. Moreover, MANF and RYR2 levels both were significantly correlated with the severity of psychotic symptoms and TC levels. In addition, a model consisting of MANF and RYR2 was found to be effective in distinguishing SCZ patients from HCs. These findings suggested that the MANF/RYR2 pathway might serve as a bridge between hypolipidemia and SCZ, and MANF and RYR2 held promise as biomarkers for SCZ.

Hydroxylation markedly alters how the polychlorinated biphenyl (PCB) congener, PCB52, affects gene expression in human preadipocytes

Polychlorinated biphenyls (PCBs) accumulate in adipose tissue and are linked to obesity and diabetes. The congener, PCB52 (2,2',5,5'-tetrachorobiphenyl), is found at high levels in school air. Hydroxylation of PCB52 to 4-OH-PCB52 (4-hydroxy-2,2',5,5'-tetrachorobiphenyl) may increase its toxicity. To understand PCB52's role in causing adipose dysfunction, we exposed human preadipocytes to PCB52 or 4-OH-PCB52 across a time course and assessed transcript changes using RNAseq. 4-OH-PCB52 caused considerably more changes in the number of differentially expressed genes as compared to PCB52. Both PCB52 and 4-OH-PCB52 upregulated transcript levels of the sulfotransferase SULT1E1 at early time points, but cytochrome P450 genes were generally not affected. A set of genes known to be transcriptionally regulated by PPARα were consistently downregulated by PCB52 at all time points. In contrast, 4-OH-PCB52 affected a variety of pathways, including those involving cytokine responses, hormone responses, focal adhesion, Hippo, and Wnt signaling. Sets of genes known to be transcriptionally regulated by IL17A or parathyroid hormone (PTH) were found to be consistently downregulated by 4-OH-PCB52. Most of the genes affected by PCB52 and 4-OH-PCB52 were different and, of those that were the same, many were changed in an opposite direction. These studies provide insight into how PCB52 or its metabolites may cause adipose dysfunction to cause disease.

Networks of placental DNA methylation correlate with maternal serum PCB concentrations and child neurodevelopment

BACKGROUND

Gestational exposure to polychlorinated biphenyls (PCBs) has been associated with elevated risk for neurodevelopmental disorders. Placental epigenetics may serve as a potential mechanism of risk or marker of altered placental function. Prior studies have associated differential placental DNA methylation with maternal PCB exposure or with increased risk of autism spectrum disorder (ASD). However, sequencing-based placental methylomes have not previously been tested for simultaneous associations with maternal PCB levels and child neurodevelopmental outcomes.

OBJECTIVES

We aimed to identify placental DNA methylation patterns associated with maternal PCB levels and child neurodevelopmental outcomes in the high-risk ASD MARBLES cohort.

METHODS

We measured 209 PCB congeners in 104 maternal serum samples collected at delivery. We identified networks of DNA methylation from 147 placenta samples using the Comethyl R package, which performs weighted gene correlation network analysis for whole genome bisulfite sequencing data. We tested placental DNA methylation modules for association with maternal serum PCB levels, child neurodevelopment, and other participant traits.

RESULTS

PCBs 153 + 168, 170, 180 + 193, and 187 were detected in over 50% of maternal serum samples and were highly correlated with one another. Consistent with previous findings, maternal age was the strongest predictor of serum PCB levels, alongside year of sample collection, pre-pregnancy BMI, and polyunsaturated fatty acid levels. Twenty seven modules of placental DNA methylation were identified, including five which significantly correlated with one or more PCBs, and four which correlated with child neurodevelopment. Two modules associated with maternal PCB levels as well as child neurodevelopment, and mapped to CSMD1 and AUTS2, genes previously implicated in ASD and identified as differentially methylated regions in mouse brain and placenta following gestational PCB exposure.

CONCLUSIONS

Placental DNA co-methylation modules were associated with maternal PCBs and child neurodevelopment. Methylation of CSMD1 and AUTS2 could be markers of altered placental function and/or ASD risk following maternal PCB exposure.

Probing the Role of CYP2 Enzymes in the Atropselective Metabolism of Polychlorinated Biphenyls Using Liver Microsomes from Transgenic Mouse Models

Chiral polychlorinated biphenyls (PCB) are environmentally relevant developmental neurotoxicants. Because their hydroxylated metabolites (OH-PCBs) are also neurotoxic, it is necessary to determine how PCB metabolism affects the developing brain, for example, in mouse models. Because the cytochrome P450 isoforms involved in the metabolism of chiral PCBs remain unexplored, we investigated the metabolism of PCB 91 (2,2',3,4',6-pentachlorobiphenyl), PCB 95 (2,2',3,5',6-pentachlorobiphenyl), PCB 132 (2,2',3,3',4,6'-hexachlorobiphenyl), and PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl) using liver microsomes from male and female Cyp2a(4/5)bgs-null, Cyp2f2-null, and wild-type mice. Microsomes, pooled by sex, were incubated with 50 μM PCB for 30 min, and the levels and enantiomeric fractions of the OH-PCBs were determined gas chromatographically. All four PCB congeners appear to be atropselectively metabolized by CYP2A(4/5)BGS and CYP2F2 enzymes in a congener- and sex-dependent manner. The OH-PCB metabolite profiles of PCB 91 and PCB 132, PCB congeners with one para-chlorine substituent, differed between null and wild-type mice. No differences in the metabolite profiles were observed for PCB 95 and PCB 136, PCB congeners without a para-chlorine group. These findings suggest that Cyp2a(4/5)bgs-null and Cyp2f2-null mice can be used to study how a loss of a specific metabolic function (e.g., deletion of Cyp2a(4/5)bgs or Cyp2f2) affects the toxicity of chiral PCB congeners.

Gene×environment interactions in autism spectrum disorders

There is credible evidence that environmental factors influence individual risk and/or severity of autism spectrum disorders (hereafter referred to as autism). While it is likely that environmental chemicals contribute to the etiology of autism via multiple mechanisms, identifying specific environmental factors that confer risk for autism and understanding how they contribute to the etiology of autism has been challenging, in part because the influence of environmental chemicals likely varies depending on the genetic substrate of the exposed individual. Current research efforts are focused on elucidating the mechanisms by which environmental chemicals interact with autism genetic susceptibilities to adversely impact neurodevelopment. The goal is to not only generate insights regarding the pathophysiology of autism, but also inform the development of screening platforms to identify specific environmental factors and gene×environment (G×E) interactions that modify autism risk. Data from such studies are needed to support development of intervention strategies for mitigating the burden of this neurodevelopmental condition on individuals, their families and society. In this review, we discuss environmental chemicals identified as putative autism risk factors and proposed mechanisms by which G×E interactions influence autism risk and/or severity using polychlorinated biphenyls (PCBs) as an example.

Aerobic Bioaugmentation to Decrease Polychlorinated Biphenyl (PCB) Emissions from Contaminated Sediments to Air

We conducted experiments to determine whether bioaugmentation with aerobic, polychlorinated biphenyl (PCB)-degrading microorganisms can mitigate polychlorinated biphenyl (PCB) emissions from contaminated sediment to air. Paraburkholderia xenovorans strain LB400 was added to bioreactors containing PCB-contaminated site sediment. PCB mass in both the headspace and aqueous bioreactor compartments was measured using passive samplers over 35 days. Time-series measurements of all 209 PCB congeners revealed a 57% decrease in total PCB mass accumulated in the vapor phase of bioaugmented treatments relative to non-bioaugmented controls, on average. A comparative congener-specific analysis revealed preferential biodegradation of lower-chlorinated PCBs (LC-PCBs) by LB400. Release of the most abundant congener (PCB 4 [2,2'-dichlorobiphenyl]) decreased by over 90%. Simulations with a PCB reactive transport model closely aligned with experimental observations. We also evaluated the effect of the phytogenic biosurfactant, saponin, on PCB bioavailability and biodegradation by LB400. Time-series qPCR measurements of biphenyl dioxygenase (bphA) genes showed that saponin better maintained bphA abundance, compared to the saponin-free treatment. These findings indicate that an active population of bioaugmented, aerobic PCB-degrading microorganisms can effectively lower PCB emissions and may therefore contribute to minimizing PCB inhalation exposure in communities surrounding PCB-contaminated sites.

Ryanodine receptor-active non-dioxin-like polychlorinated biphenyls cause neurobehavioral deficits in larval zebrafish

Although their production was banned in the United States in 1977, polychlorinated biphenyls (PCBs) continue to pose significant risks to the developing nervous system. Perinatal exposure to PCBs is associated with increased risk of neuropsychiatric disorders, perhaps due to altered patterns of dendritic arborization of central neurons. Non-dioxin-like (NDL) PCB congeners enhance dendritic arborization of developing mammalian neurons via sensitization of ryanodine receptors (RYR). Structure-activity relationships (SAR) of RYR sensitization by PCBs have been demonstrated using mammalian and rainbow trout (Oncorhynchus mykiss) tissue homogenates. The purpose of this study is to determine whether this SAR translates to developmental neurotoxicity (DNT) of PCBs in vivo, a question that has yet to be tested. To address this gap, we leveraged a zebrafish model to evaluate the developmental neurotoxicity potential of PCBs 28, 66, 84, 95, 138, and 153, congeners previously shown to have broadly different potencies towards sensitizing RYR. We first confirmed that these PCB congeners exhibited differing potency in sensitizing RYR in zebrafish muscle ranging from negligible (PCB 66) to moderate (PCB 153) to high (PCB 95) RYR activity. Next, enzymatically dechorionated embryos were statically exposed to varying concentrations (0.1-10 μM) of each PCB congener from 6 h post-fertilization to 5 days post-fertilization (dpf). Embryos were observed daily using stereomicroscopy to assess mortality and gross malformations and photomotor behavior was assessed in larval zebrafish at 3, 4, and 5 dpf. The body burden of each PCB was measured by gas chromatography. The key findings are: 1) None of these PCBs caused death or overt teratology at the concentrations tested; 2) A subset of these PCB congeners altered photomotor behavior in larval zebrafish and the SAR for PCB behavioral effects mirrored the SAR for RYR sensitization; and 3) Quantification of PCB levels in larval zebrafish ruled out the possibility that congener-specific effects on behavior were due to differential uptake of PCB congeners. Collectively, the findings from this study provide in vivo evidence in support of the hypothesis that RYR sensitization contributes to the DNT of PCBs.

Inadvertently Generated PCBs in Consumer Products: Concentrations, Fate and Transport, and Preliminary Exposure Assessment

Although commercial polychlorinated biphenyl (PCB) production was banned in 1979 under the Toxics Substance Control Act, inadvertent generation of PCBs through a variety of chemical production processes continues to contaminate products and waste streams. In this research, a total of 39 consumer products purchased from local and online retailer stores were analyzed for 209 PCB congeners. Inadvertent PCBs (iPCBs) were detected from seven products, and PCB-11 was the only congener detected in most of the samples, with a maximum concentration exceeding 800 ng/g. Emission of PCB-11 to air was studied from one craft foam sheet product using dynamic microchambers at 40 °C for about 120 days. PCB-11 migration from the product to house dust was also investigated. The IAQX program was then employed to estimate the emissions of PCB-11 from 10 craft foam sheets to indoor air in a 30 m3 room at 0.5 h-1 air change rate for 30 days. The predicted maximum PCB-11 concentration in the room air (156.8 ng/m3) and the measured concentration in dust (20 ng/g) were applied for the preliminary exposure assessment. The generated data from multipathway investigation in this work should be informative for further risk assessment and management for iPCBs.

Environmental Toxicants and NAFLD: A Neglected yet Significant Relationship

The liver is an organ of vital importance in the body; it is the center of metabolic activities and acts as the primary line of defense against toxic compounds. Exposure to environmental toxicants is an unavoidable fallout from rapid industrialization across the world and is even higher in developing countries. Technological development and industrialization have led to the release of toxicants such as pollutant toxic gases, chemical discharge, industrial effluents, pesticides and solvents, into the environment. In the last few years, a growing body of evidence has shed light on the potential impact of environmental toxicants on liver health, in particular, on non-alcoholic fatty liver disease (NAFLD) incidence and progression. NAFLD is a multifactorial disease linked to metabolic derangement including diabetes and other complications. Environmental toxicants including xenobiotics and pollutants may have a direct or indirect steatogenic/fibrogenic impact on the liver and should be considered as risk factors associated with NAFLD. This review discusses the contribution of environmental toxicants toward the increasing disease burden of NAFLD.

Assessment of Polychlorinated Biphenyls and Their Hydroxylated Metabolites in Postmortem Human Brain Samples: Age and Brain Region Differences

Exposure to polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) has been implicated in neurodevelopmental disorders. However, the distribution of PCBs and OH-PCBs in the human brain has not been characterized. This study investigated the age-, sex-, and brain region-specific distribution of all 209 PCBs using gaschromatography-tandem mass spectrometry (GC-MS/MS) in neonatal (N = 7) and adult (N = 7) postmortem brain samples. OH-PCB analyses were performed by GC-MS/MS (as methylated derivatives) and, in a subset of samples, by nontarget liquid chromatography high-resolution mass spectrometry (Nt-LCMS). Fourteen higher chlorinated PCB congeners were observed with a detection frequency >50%. Six lower chlorinated PCBs were detected with a detection frequency >10%. Higher chlorinated PCBs were observed with higher levels in samples from adult versus younger donors. PCB congener profiles from adult donors showed more similarities across brain regions and donors than younger donors. We also assess the potential neurotoxicity of the PCB residues in the human brain with neurotoxic equivalency (NEQ) approaches. The median ΣNEQs, calculated for the PCB homologues, were 40-fold higher in older versus younger donors. Importantly, lower chlorinated PCBs made considerable contributions to the neurotoxic potential of PCB residues in some donors. OH-PCBs were identified for the first time in a small number of human brain samples by GC-MS/MS and Nt-LCMS analyses, and all contained four or fewer chlorine.

Developmental polychlorinated biphenyl (PCB) exposure alters voiding physiology in young adult male and female mice

The impact of developmental exposure to environmental chemicals on lower urinary tract function is not well understood, despite the fact that these chemicals could contribute to etiologically complex lower urinary tract symptoms (LUTS). Polychlorinated biphenyls (PCBs) are environmental toxicants known to be detrimental to the central nervous system, but their impact on voiding function in mouse models is not known. Therefore, we test whether developmental exposure to PCBs is capable of altering voiding physiology in young adult mice. C57Bl/6J female mice received a daily oral dose of the MARBLES PCB mixture for two weeks prior to mating and through gestation and lactation. The mixture mimics the profile of PCBs found in a contemporary population of pregnant women. Voiding function was then tested in young adult offspring using void spot assay, uroflowmetry and anesthetized cystometry. PCB effects were sex and dose dependent. Overall, PCBs led to increases in small size urine spots in both sexes with males producing more drop-like voids and greater peak pressure during a voiding cycle while females displayed decreases in void duration and intervoid interval. Together, these results indicate that developmental exposure to PCBs are capable of altering voiding physiology in young adult mice. Further work to identify the underlying mechanisms driving these changes may help develop more effective preventative or therapeutic strategies for LUTS.

Placenta and fetal brain share a neurodevelopmental disorder DNA methylation profile in a mouse model of prenatal PCB exposure

Polychlorinated biphenyls (PCBs) are developmental neurotoxicants implicated as environmental risk factors for neurodevelopmental disorders (NDDs). Here, we report the effects of prenatal exposure to a human-relevant mixture of PCBs on the DNA methylation profiles of mouse placenta and fetal brain. Thousands of differentially methylated regions (DMRs) distinguish placenta and fetal brain from PCB-exposed mice from sex-matched vehicle controls. In both placenta and fetal brain, PCB-associated DMRs are enriched for functions related to neurodevelopment and cellular signaling and enriched within regions of bivalent chromatin. The placenta and brain PCB DMRs overlap significantly and map to a shared subset of genes enriched for Wnt signaling, Slit/Robo signaling, and genes differentially expressed in NDD models. The consensus PCB DMRs also significantly overlap with DMRs from human NDD brain and placenta. These results demonstrate that PCB-exposed placenta contains a subset of DMRs that overlap fetal brain DMRs relevant to an NDD.

Triiodothyronine or Antioxidants Block the Inhibitory Effects of BDE-47 and BDE-49 on Axonal Growth in Rat Hippocampal Neuron-Glia Co-Cultures

We previously demonstrated that polybrominated diphenyl ethers (PBDEs) inhibit the growth of axons in primary rat hippocampal neurons. Here, we test the hypothesis that PBDE effects on axonal morphogenesis are mediated by thyroid hormone and/or reactive oxygen species (ROS)-dependent mechanisms. Axonal growth and ROS were quantified in primary neuronal-glial co-cultures dissociated from neonatal rat hippocampi exposed to nM concentrations of BDE-47 or BDE-49 in the absence or presence of triiodothyronine (T3; 3-30 nM), N-acetyl-cysteine (NAC; 100 µM), or α-tocopherol (100 µM). Co-exposure to T3 or either antioxidant prevented inhibition of axonal growth in hippocampal cultures exposed to BDE-47 or BDE-49. T3 supplementation in cultures not exposed to PBDEs did not alter axonal growth. T3 did, however, prevent PBDE-induced ROS generation and alterations in mitochondrial metabolism. Collectively, our data indicate that PBDEs inhibit axonal growth via ROS-dependent mechanisms, and that T3 protects axonal growth by inhibiting PBDE-induced ROS. These observations suggest that co-exposure to endocrine disruptors that decrease TH signaling in the brain may increase vulnerability to the adverse effects of developmental PBDE exposure on axonal morphogenesis.

Male Lower Urinary Tract Dysfunction: An Underrepresented Endpoint in Toxicology Research

Lower urinary tract dysfunction (LUTD) is nearly ubiquitous in men of advancing age and exerts substantial physical, mental, social, and financial costs to society. While a large body of research is focused on the molecular, genetic, and epigenetic underpinnings of the disease, little research has been dedicated to the influence of environmental chemicals on disease initiation, progression, or severity. Despite a few recent studies indicating a potential developmental origin of male LUTD linked to chemical exposures in the womb, it remains a grossly understudied endpoint in toxicology research. Therefore, we direct this review to toxicologists who are considering male LUTD as a new aspect of chemical toxicity studies. We focus on the LUTD disease process in men, as well as in the male mouse as a leading research model. To introduce the disease process, we describe the physiology of the male lower urinary tract and the cellular composition of lower urinary tract tissues. We discuss known and suspected mechanisms of male LUTD and examples of environmental chemicals acting through these mechanisms to contribute to LUTD. We also describe mouse models of LUTD and endpoints to diagnose, characterize, and quantify LUTD in men and mice.

Hydroxylated Polychlorinated Biphenyls Are Emerging Legacy Pollutants in Contaminated Sediments

We measured the concentrations of 837 hydroxylated polychlorinated biphenyls (OH-PCBs, in 275 chromatographic peaks) and 209 polychlorinated biphenyls (PCBs, in 174 chromatographic peaks) in sediments from New Bedford Harbor in Massachusetts, Altavista wastewater lagoon in Virginia, and the Indiana Harbor and Ship Canal in Indiana, USA and in the original commercial PCB mixtures Aroclors 1016, 1242, 1248, and 1254. We used the correlation between homologues and the peak responses to quantify the full suite of OH-PCBs including those without authentic standards available. We found that OH-PCB levels are approximately 0.4% of the PCB levels in sediments and less than 0.0025% in Aroclors. The OH-PCB congener distributions of sediments are different from those of Aroclors and are different according to sites. We also identified a previously unknown compound, 4-OH-PCB52, which together with 4'-OH-PCB18 made up almost 30% of the OH-PCBs in New Bedford Harbor sediments but less than 1.2% in the Aroclors and 3.3% in any other sediments. This indicates site-specific environmental transformations of PCBs to OH-PCBs. We conclude that the majority of OH-PCBs in these sediments are generated in the environment. Our findings suggest that these toxic breakdown products of PCBs are prevalent in PCB-contaminated sediments and present an emerging concern for humans and ecosystems.

Sex and Genotype Modulate the Dendritic Effects of Developmental Exposure to a Human-Relevant Polychlorinated Biphenyls Mixture in the Juvenile Mouse

While many neurodevelopmental disorders (NDDs) are thought to result from interactions between environmental and genetic risk factors, the identification of specific gene-environment interactions that influence NDD risk remains a critical data gap. We tested the hypothesis that polychlorinated biphenyls (PCBs) interact with human mutations that alter the fidelity of neuronal Ca²⁺ signaling to confer NDD risk. To test this, we used three transgenic mouse lines that expressed human mutations known to alter Ca²⁺ signals in neurons: (1) gain-of-function mutation in ryanodine receptor-1 (T4826I-RYR1); (2) CGG-repeat expansion in the 5′ non-coding portion of the fragile X mental retardation gene 1 (FMR1); and (3) a double mutant (DM) that expressed both mutations. Transgenic and wildtype (WT) mice were exposed throughout gestation and lactation to the MARBLES PCB mix at 0.1, 1, or 6 mg/kg in the maternal diet. The MARBLES mix simulates the relative proportions of the twelve most abundant PCB congeners found in serum from pregnant women at increased risk for having a child with an NDD. Using Golgi staining, the effect of developmental PCB exposure on dendritic arborization of pyramidal neurons in the CA1 hippocampus and somatosensory cortex of male and female WT mice was compared to pyramidal neurons from transgenic mice. A multilevel linear mixed-effects model identified a main effect of dose driven by increased dendritic arborization of cortical neurons in the 1 mg/kg PCB dose group. Subsequent analyses with genotypes indicated that the MARBLES PCB mixture had no effect on the dendritic arborization of hippocampal neurons in WT mice of either sex, but significantly increased dendritic arborization of cortical neurons of WT males in the 6 mg/kg PCB dose group. Transgene expression increased sensitivity to the impact of developmental PCB exposure on dendritic arborization in a sex-, and brain region-dependent manner. In conclusion, developmental exposure to PCBs present in the gestational environment of at-risk humans interfered with normal dendritic morphogenesis in the developing mouse brain in a sex-, genotype- and brain region-dependent manner. Overall, these observations provide proof-of-principle evidence that PCBs interact with heritable mutations to modulate a neurodevelopmental outcome of relevance to NDDs.

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

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

The Bladder Is a Novel Target of Developmental Polychlorinated Biphenyl Exposure Linked to Increased Inflammatory Cells in the Bladder of Young Mice

Bladder inflammation is associated with several lower urinary tract symptoms that greatly reduce quality of life, yet contributing factors are not completely understood. Environmental chemicals are plausible mediators of inflammatory reactions within the bladder. Here, we examine whether developmental exposure to polychlorinated biphenyls (PCBs) leads to changes in immune cells within the bladder of young mice. Female mice were exposed to an environmentally relevant mixture of PCBs through gestation and lactation, and bladders were collected from offspring at postnatal day (P) 28-31. We identify several dose- and sex-dependent PCB effects in the bladder. The lowest concentration of PCB (0.1 mg/kg/d) increased CD45+ hematolymphoid immune cells in both sexes. While PCBs had no effect on CD79b+ B cells or CD3+ T cells, PCBs (0.1 mg/kg/d) did increase F4/80+ macrophages particularly in female bladder. Collagen density was also examined to determine whether inflammatory events coincide with changes in the stromal extracellular matrix. PCBs (0.1 mg/kg/d) decreased collagen density in female bladder compared to control. PCBs also increased the number of cells undergoing cell division predominantly in male bladder. These results implicate perturbations to the immune system in relation to PCB effects on the bladder. Future study to define the underlying mechanisms could help understand how environmental factors can be risk factors for lower urinary tract symptoms.

Endocrine disrupting chemicals and thyroid hormone action

Thyroid hormones (predominantly thyroxine, T4, and triiodothyronine, T3) are essential for normal development and for adult physiology. There are several challenges, however, that make identifying chemicals that produce adverse effects by interfering with the thyroid system difficult. First, individual variability in serum concentrations of thyroid hormones represent only about 10% of the population reference range that is considered to be "normal." This means that populations studies evaluating the relationship between chemical exposure and serum thyroid hormones must be large enough to overcome this internal variance. In addition, we know that there are chemicals that do not produce changes in thyroid hormone levels, but nevertheless impact thyroid signaling in target tissues. A good example is that of polychlorinated biphenyls (PCBs). PCB exposure during development are clearly associated with cognitive deficits in humans. But PCB exposure isn't uniformly associated with a reduction in serum thyroid hormone in human populations despite mechanistic studies showing that PCBs reduce serum T4 in animals. In contrast, perchlorate is a chemical that inhibits iodide uptake, thereby reducing thyroid hormone synthesis and serum hormone levels. Human studies have been variable in identifying a relationship between thyroid hormone and perchlorate exposure, but studies also show that dietary iodine, cigarette smoking and other factors can modify this relationship. The conclusion is that identifying chemicals that interfere with thyroid hormone could depend on in vitro analysis of chemicals that interact with different proteins important for thyroid hormone to function properly.

Perspective on prenatal polychlorinated biphenyl exposure and the development of the progeny nervous system (Review)

The developmental origins of health and disease concept illustrates that exposure in early life to various factors may affect the offspring's long-term susceptibility to disease. During development, the nervous system is sensitive and vulnerable to the environmental insults. Polychlorinated biphenyls (PCBs), which are divided into dioxin-like (DL-PCBs) and non-dioxin-like PCBs (NDL-PCBs), are synthetic persistent environmental endocrine-disrupting chemicals. The toxicological mechanisms of DL-PCBs have been associated with the activation of the aryl hydrocarbon receptor and NDL-PCBs have been associated with ryanodine receptor-mediated calcium ion channels, which affect neuronal migration, promote dendritic growth and alter neuronal connectivity. In addition, PCB accumulation in the placenta destroys the fetal placental unit and affects endocrine function, particularly thyroid hormones and the dopaminergic system, leading to neuroendocrine disorders. However, epidemiological investigations have not achieved a consistent result in different study cohorts. The present review summarizes the epidemiological differences and possible mechanisms of the effects of intrauterine PCB exposure on neurological development.

Non-dioxin-like polychlorinated biphenyl neurotoxic equivalents found in environmental and human samples

Non-dioxin like polychlorinated biphenyls (NDL PCB) are recognized neurotoxicants with implications on altered neurodevelopment and neurodegeneration in exposed organisms. NDL PCB neurotoxic relative potency schemes have been developed for a single mechanism, namely activity toward the ryanodine receptor (RyR), or combined mechanisms including, but not limited to, alterations of RyR and dopaminergic pathways. We compared the applicability of the two neurotoxic equivalency (NEQ) schemes and applied each scheme to PCB mixtures found in environmental and human serum samples. A multiple mechanistic NEQ predicts higher neurotoxic exposure concentrations as compared to a scheme based on the RyR alone. Predictions based on PCB ortho categorization, versus homologue categorization, lead to a higher prediction of neurotoxic exposure concentrations, especially for the mMOA. The application of the NEQ schemes to PCB concentration data suggests that PCBs found in fish from US lakes represent a considerable NEQ exposure to fish consuming individuals, that indoor air of schools contained high NEQ concentrations representing an exposure concern when inhaled by children, and that levels already detected in the serum of adults and children may contribute to neurotoxicity. With further validation and in vivo exposure data the NEQ scheme would help provide a more inclusive measure of risk presented by PCB mixtures.

Unintentionally produced polychlorinated biphenyls in pigments: An updated review on their formation, emission sources, contamination status, and toxic effects

The formation, emission, environmental occurrence, and potential adverse effects of unintentionally produced polychlorinated biphenyls (PCBs) in pigments are reviewed, providing a comprehensive and up-to-date picture on these pollutants. PCBs are typically formed during manufacturing of organic pigments that involve chlorinated intermediates and reaction solvents, rather than those of inorganic pigments. Concentrations and profiles of PCBs vary greatly among pigment types and producers, with total PCB levels ranging from lower than detection limits to several hundred ppm; major components can be low-chlorinated (e.g., CB-11) or high-chlorinated congeners (e.g., CB-209). Pigment-derived PCBs can be released into the environment through different steps including pigment production, application, and disposal. They can contaminate atmospheric, terrestrial, and aquatic ecosystems, and then affect organisms living there. This situation garners scientific and public attention to nonlegacy emissions of PCBs and suggests the need for appropriate monitoring, management, and abatement strategies regarding these pollutants.

In utero and lactational PCB exposure drives anatomic changes in the juvenile mouse bladder

Bladder dysfunction, including incontinence, difficulty emptying the bladder, or urgency to urinate is a pervasive health and quality of life concern. However, risk factors for developing these symptoms are not completely understood, and the influence of exposure to environmental chemicals, especially during development, on the formation and function of the bladder is understudied. Environmental contaminants such as polychlorinated biphenyls (PCBs) are known to pose a risk to the developing brain; however, their influence on the development of peripheral target organs, such as bladder, are unknown. To address this data gap, C57Bl/6J mouse dams were exposed to an environmentally-relevant PCB mixture at 0, 0.1, 1 or 6 mg/kg daily beginning two weeks prior to mating and continuing through gestation and lactation. Bladders were collected from offspring at postnatal days (P) 28-31. PCB concentrations were detected in bladders in a dose-dependent manner. PCB effects on the bladder were sex- and dose-dependent. Overall, PCB effects were observed in male, but not female, bladders. PCBs increased bladder volume and suburothelial βIII-tubulin-positive nerve density compared to vehicle control. A subset of these nerves were sensory peptidergic axons indicated by increased calcitonin gene-related protein (CGRP) positive nerve fibers in mice exposed to the highest PCB dose compared to the lowest PCB dose. PCB-induced increased nerve density was also positively correlated with the number of mast cells in the bladder, suggesting inflammation may be involved. There were no detectable changes in epithelial composition or apoptosis as indicated by expression of cleaved caspase 3, suggesting PCBs do not cause overt toxicity. Bladder volume changes were not accompanied by changes in bladder mass or epithelial thickness, indicating that obstruction was not likely involved. Together, these results are the first to suggest that following developmental exposure, PCBs can distribute to the bladder and alter neuroanatomic development and bladder volume in male mice.

A two-step gas chromatography-tandem mass spectrometry method for measurement of multiple environmental pollutants in human plasma

Individuals are exposed to a wide variety of chemicals over their lifetime, yet current understanding of mixture toxicology is still limited. We present a two-step analytical method using a gas chromatograph-triple quadrupole mass spectrometer that requires less than 1 mL of sample. The method is applied to 183 plasma samples from a study population of children with autism spectrum disorder, their parents, and unrelated neurotypical children. We selected 156 environmental chemical compounds and ruled out chemicals with detection rates less than 20% of our study cohort (n = 61), as well as ones not amenable to the selected extraction and analytical methods (n = 34). The targeted method then focused on remaining chemicals (n = 61) plus 8 additional polychlorinated biphenyls (PCBs). Persistent pollutants, such as p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and PCB congeners 118 and 180, were detected at high frequencies and several previously unreported chemicals, including 2,4,6-trichlorophenol, isosafrole, and hexachlorobutadiene, were frequently detected in our study cohort. This work highlights the benefits of employing a multi-step analytical method in exposure studies and demonstrates the efficacy of such methods for reporting novel information on previously unstudied pollutant exposures.

Infant dietary exposure to dioxin-like polychlorinated biphenyls (dlPCBs), polybrominated and mixed halogenated dibenzo-p-dioxins and furans (PBDD/Fs and PXDD/Fs) in milk samples of lactating mothers in Accra, Ghana

In this study, polybrominated and mixed halogenated dibenzo-p-dioxins and furans (PBDD/Fs and PXDD/Fs), and dioxin-like polychlorinated biphenyls (dlPCBs) were quantified in 24 human milk samples of first-time lactating mothers from Greater Accra region in Ghana. The aims of the study were to determine the concentrations and toxic equivalent concentrations of PBDD/F, PXDD/F and dlPCBs in human milk, and to estimate an infant's daily intake. The samples were analysed for 12 dioxin-like PCBs, 7 congeners of 2,3,7,8-polybrominated dibenzo-p-dioxins and furans (PBDD/Fs), and 7 congeners of 2,3,7,8-mixed halogenated dioxins and furans (PXDD/Fs, where X = Br/Cl). The mean concentrations in human milk ranged from 0.15 to 212.9 pg/g lipid for dlPCB congeners (mean TEQ: 1.67 pg WHO₂₀₀₅-TEQ/g lipid). Lesser concentrations for 2,3,7,8-PXDD/Fs (and PBDD/Fs congeners) ranged between <0.01-1.67 pg/g lipid, with a total mean tentative TEQ of 0.56 pg WHO₂₀₀₅-TEQ/g lipid. For an infant of average weight 7 kg, consuming an estimated volume of 600 mL human milk, the estimated average daily intake of dlPCBs in 21 human milk samples was 4.95 pg TEQ/kg bw/day; contributions from dlPCBs, PXDD/Fs and PBDD/Fs resulted in an average estimated daily intake of 6.56 pg TEQ/kg bw/day. The results obtained in this study, although lower than infant dietary intake estimates in human milk from industrialized countries, exceeded the recommended safety standards of 1 pg TEQ/kg bw/day and 1-4 pg TEQ/kg bw/day from the Agency for Toxic Substances and Disease Registry (ATSDR) and the World Health Organization (WHO), respectively.