Flame retardants and neurodevelopment: An updated review of epidemiological literature

Critical review on unveiling the toxic and recalcitrant effects of microplastics in aquatic ecosystems and their degradation by microbes

Production of synthetic plastic obtained from fossil fuels are considered as a constantly growing problem and lack in the management of plastic waste has led to severe microplastic pollution in the aquatic ecosystem. Plastic particles less than 5mm are termed as microplastics (MPs), these are pervasive in water and soil, it can also withstand longer period of time with high durability. It can be broken down into smaller particles and can be adsorbed by various life-forms. Most marine organisms tend to consume plastic debris that can be accumulated easily into the vertebrates, invertebrates and planktonic entities. Often these plastic particles surpass the food chain, resulting in the damage of various organs and inhibiting the uptake of food due to the accumulation of microplastics. In this review, the physical and chemical properties of microplastics, as well as their effects on the environment and toxicity of their chemical constituents are discussed. In addition, the paper also sheds light on the potential of microorganisms such as bacteria, fungi, and algae which play a pivotal role in the process of microplastics degradation. The mechanism of microbial degradation, the factors that affect degradation, and the current advancements in genetic and metabolic engineering of microbes to promote degradation are also summarized. The paper also provides information on the bacterial, algal and fungal degradation mechanism including the possible enzymes involved in microplastic degradation. It also investigates the difficulties, limitations, and potential developments that may occur in the field of microbial microplastic degradation.

Sex-specific effects on elements of the social brain neural network in Wistar rats from perinatal exposure to FireMaster 550 or its components

Developmental exposure to chemical flame retardants (FRs) has been linked to a variety of neurodevelopmental disorders and abnormal socioemotional behaviors in human and laboratory animal studies. We have previously shown in Wistar rats that gestational and lactational exposure to the FR mixture Firemaster 550 (FM 550) or its brominated or organophosphate ester (OPFR) components (at 2,000µg, 1,000µg, and 1,000µg oral to the dam respectively) results in increased anxiety-like behaviors in females and decreased sociality in both sexes. Using their siblings, this study characterized sex and chemical specific targets of disruption in brain regions underlying each behavioral phenotype. Offspring were exposed across gestation and lactation then prepared for either immunohistochemistry or autoradiography at postnatal day 90 to quantify expression of serotonin, estrogen receptor α (ERα), and oxytocin receptor (OTR) in multiple brain regions. No effect of exposure was found in males for any biological target. In females, serotonin innervation was increased in the medial amygdala of FM 550 exposed animals while ERα expression in the bed nucleus of the stria terminalis (BNST) was reduced by FM 550 and OPFR. Evidence of disrupted OTR was observed in males, particularly the BNST but considered an exploratory finding given the small sample size. These results begin to shed light on the mechanisms by which developmental FR exposure alters socioemotional behaviors of relevance to neurodevelopmental disorders.

Polybrominated diphenyl ethers in paired dust-breast milk samples: Levels, predictors of contamination, and health risk assessment for infants and mothers

An integrated study on the levels of 7 polybrominated diphenyl ethers (PBDEs) in house dust and breast milk samples from women (N = 30) living in these households was conducted. ∑PBDEs ranged from Collapse

Key Words

• Biomonitoring
• Flame retardants
• House dust
• PBDEs
• Risk assessment

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Affiliation(s)

Karla Jagić Division of Environmental Hygiene, Institute for Medical Research and Occupational Health, Ksaverska cesta 2, Zagreb 10001, Croatia
Marija Dvoršćak Division of Environmental Hygiene, Institute for Medical Research and Occupational Health, Ksaverska cesta 2, Zagreb 10001, Croatia
Blanka Tariba Lovaković Division of Toxicology, Institute for Medical Research and Occupational Health, Ksaverska cesta 2, Zagreb 10001, Croatia
Darija Klinčić Division of Environmental Hygiene, Institute for Medical Research and Occupational Health, Ksaverska cesta 2, Zagreb 10001, Croatia.

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Children's exposure to brominated flame retardants in the home: The TESIE study

Due to differences in chemical properties and half-lives, best practices for exposure assessment may differ for legacy versus novel brominated flame retardants (BFRs). Our objective was to identify the environment matrix that best predicted biomarkers of children's BFR exposures. Paired samples were collected from children aged 3-6 years and their homes, including dust, a small piece of polyurethane foam from the furniture, and a handwipe and wristband from each child. Biological samples collected included serum, which was analyzed for 11 polybrominated diphenyl ethers (PBDEs), and urine, which was analyzed for tetrabromobenzoic acid (TBBA), a metabolite of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB). Significant positive correlations were typically observed between BFRs measured in dust, handwipes and wristbands, though wristbands and handwipes tended to be more strongly correlated with one another than with dust. PBDEs, EH-TBB and BEH-TEBP were detected in 30% of the sofa foam samples, suggesting that the foam was treated with PentaBDE or Firemaster® 550/600 (FM 550/600). PBDEs were detected in all serum samples and TBBA was detected in 43% of urine samples. Statistically significant positive correlations were observed between the environmental samples and serum for PBDEs. Urinary TBBA was 6.86 and 6.58 times more likely to be detected among children in the highest tertile of EH-TBB exposure for handwipes and wristbands, respectively (95 % CI: 2.61, 18.06 and 1.43, 30.05 with p < 0.001 and 0.02, respectively). The presence of either PentaBDE or FM 550/600 in furniture was also associated with significantly higher levels of these chemicals in dust, handwipes and serum (for PBDEs) and more frequent detection of TBBA in urine (p = 0.13). Our results suggest that children are exposed to a range of BFRs in the home, some of which likely originate from residential furniture, and that silicone wristbands are a practical tool for evaluating external exposure to both legacy and novel BFRs.

House dust-derived mixtures of organophosphate esters alter the phenotype, function, transcriptome, and lipidome of KGN human ovarian granulosa cells

Organophosphate esters (OPEs), used as flame retardants and plasticizers, are present ubiquitously in the environment. Previous studies suggest that exposure to OPEs is detrimental to female fertility in humans. However, no experimental information is available on the effects of OPE mixtures on ovarian granulosa cells, which play essential roles in female reproduction. We used high-content imaging to investigate the effects of environmentally relevant OPE mixtures on KGN human granulosa cell phenotypes. Perturbations to steroidogenesis were assessed using ELISA and qRT-PCR. A high-throughput transcriptomic approach, TempO-Seq, was used to identify transcriptional changes in a targeted panel of genes. Effects on lipid homeostasis were explored using a cholesterol assay and global lipidomic profiling. OPE mixtures altered multiple phenotypic features of KGN cells, with triaryl OPEs in the mixture showing higher potencies than other mixture components. The mixtures increased basal production of steroid hormones; this was mediated by significant changes in the expression of critical transcripts involved in steroidogenesis. Further, the total-OPE mixture disrupted cholesterol homeostasis and the composition of intracellular lipid droplets. Exposure to complex mixtures of OPEs, similar to those found in house dust, may adversely affect female reproductive health by altering a multitude of phenotypic and functional endpoints in granulosa cells. This study provides novel insights into the mechanisms of actions underlying the toxicity induced by OPEs and highlights the need to examine the effects of human relevant chemical mixtures.

The association between brominated flame retardants exposure with bone mineral density in US adults: A cross-sectional study of the national health and nutrition examination survey (NHANES) 2005-2014

BACKGROUND AND AIMS

Exposure to brominated flame retardants (BFRs) has been widely confirmed to impair the normal functioning of the human body system. However, there is a paucity of study on the effects of serum BFRs on bone mineral density (BMD). This study aims to investigate the relationship between exposure to BFRs and BMD in a nationally representative sample of U.S. adults.

METHODS

3079 participants aged between 20 and 80 years with complete data were included in the study. Serum levels of BFRs were measured using automated liquid-liquid extraction and subsequent sample clean-up. The BMD of all participants were assessed by DXA examinations. Generalize linear model, Restricted cubic spline (RCS), subgroup, weighted quantile sum (WQS) and bayesian kernel machine regression (BKMR) were used to estimate the association between serum BFRs and BMD.

RESULTS

Multivariate linear regression analyses revealed that, after adjusting for covariates, PBB153 was significantly associated with TF-BMD (β = 0.0177, 95%CI: 0.0103-0.0252), FN-BMD (β = 0.009, 95%CI: 0.0036-0.0145), TS-BMD (β = 0.0081, 95%CI: 0.0013-0.015) and L1-BMD (β = 0.0144, 95%CI: 0.0075-0.0213). However, the associations lose their statistical significance after further adjustment for sex. BFRs exhibited S-shaped or line-plateau dose-response curves with BMD. In subgroup analyses, BFRs were significantly associated with BMD in participants who were younger than 55 years, female, overweight (BMI >25 kg/m2), and less alcohol consumption. In WQS and BKMR analyses, the effects of BFRs mixtures on BMD differed by sex, and PBDE153, PBDE209 and PBB153 had the highest weights in the WQS regression model.

CONCLUSION

This study showed that serum BFRs negatively predicted BMD in men, but not in women or the general population. PBDE153, PBDE209, and PBB153 were significant BMD factors, especially in younger, overweight, and less alcohol consumption individuals.

ZLN005 alleviates PBDE-47 induced impairment of mitochondrial translation and neurotoxicity through PGC-1α/ERRα axis

Recent studies are identified the mitochondria as critical targets of 2, 2', 4, 4'-tetrabromodiphenyl ether (PBDE-47) induced neurotoxicity. This study aimed at examining the impact of PBDE-47 exposure on mitochondrial translation, and its subsequent effect on PBDE-47 neurotoxicity. The Sprague-Dawley (SD) rat model and neuroendocrine pheochromocytoma (PC12) cells were adopted for the measurements of mitochondrial ATP levels, mitochondrial translation products, and expressions of important mitochondrial regulators, such as required meiotic nuclear division 1 (RMND1), estrogen-related receptor α (ERRα), and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α). To delve into the role of PGC-1α/ERRα axis in mitochondrial translation, 2-(4-tert-butylphenyl) benzimidazole (ZLN005) was employed. Both cellular and animal model results shown that PBDE-47 impeded PGC-1α/ERRα axis and mitochondrial translation. PBDE-47 suppressed mitochondrial function in rat hippocampus and PC12 cells by decreasing relative mitochondrial DNA (mtDNA) content, mitochondrial translation products, and mitochondrial ATP levels. Particularly, ZLN005 reversed PBDE-47 neurotoxicity by enhancing mitochondrial translation through activation of PGC-1α/ERRα axis, yet suppressing PGC-1α with siRNA attenuates its neuroprotective effect in vitro. In conclusion, this work highlights the importance of mitochondrial translation in PBDE-47 neurotoxicity by presenting results from cellular and animal models and suggests a potential therapeutic approach through activation of PGC-1α/ERRα axis. ENVIRONMENTAL IMPLICATION: PBDEs have attracted extensive attention because of their high lipophilicity, persistence, and detection levels in various environmental media. Increasing evidence has shown that neurodevelopmental disorders in children are associated with PBDE exposure. Several studies have also found that perinatal PBDE exposure can cause long-lasting neurobehavioral abnormalities in experimental animals. Our recent studies have also demonstrated the impact of PBDE-47 exposure on mitochondrial biogenesis and dynamics, leading to memory and neurobehavioral deficits. Therefore, we explore whether the pathological mechanism of PBDE-47-induced neurotoxicity involves the regulation of mitochondrial translation through the PGC-1α/ERRα axis.

Prenatal exposure to a mixture of organophosphate flame retardants and infant neurodevelopment: A prospective cohort study in Shandong, China

BACKGROUND

Previous studies have suggested that prenatal exposure to organophosphate flame retardants (OPFRs) may have adverse effect on early neurodevelopment, but limited data are available in China, and the overall effects of OPFRs mixture are still unclear.

OBJECTIVE

This study aimed to investigate the association between prenatal exposure to OPFR metabolites mixture and the neurodevelopment of 1-year-old infants.

METHODS

A total of 270 mother-infant pairs were recruited from the Laizhou Wan (Bay) Birth Cohort in China. Ten OPFR metabolites were measured in maternal urine. Neurodevelopment of 1-year-old infants was assessed using the Gesell Developmental Schedules (GDS) and presented by the developmental quotient (DQ) score. Multivariate linear regression and weighted quantile sum (WQS) regression models were conducted to estimate the association of prenatal exposure to seven individual OPFR metabolites and their mixture with infant neurodevelopment.

RESULTS

The positive rates of seven OPFR metabolites in the urine of pregnant women were greater than 70% with the median concentration ranged within 0.13-3.53 μg/g creatinine. The multivariate linear regression model showed significant negative associations between bis (1-chloro-2-propyl) phosphate (BCIPP), din-butyl phosphate (DnBP), and total OPFR metabolites exposure and neurodevelopment in all infants. Results from the WQS model consistently revealed that the OPFR metabolites mixture was inversely associated with infant neurodevelopment. Each quartile increased in the seven OPFR metabolites mixture was associated with a 1.59 decrease (95% CI: 2.96, -0.21) in gross motor DQ scores, a 1.41 decrease (95% CI: 2.38, -0.43) in adaptive DQ scores, and a 1.08 decrease (95% CI: 2.15, -0.02) in social DQ scores, among which BCIPP, bis (1, 3-dichloro-2-propyl) phosphate (BDCIPP) and DnBP were the main contributors.

CONCLUSION

Prenatal exposure to a mixture of OPFRs was negatively associated with early infant neurodevelopment, particularly in gross motor, adaptive, and social domains.

How neurobehavior and brain development in alternative whole-organism models can contribute to prediction of developmental neurotoxicity

Developmental neurotoxicity (DNT) is not routinely evaluated in chemical risk assessment because current test paradigms for DNT require the use of mammalian models which are ethically controversial, expensive, and resource demanding. Consequently, efforts have focused on revolutionizing DNT testing through affordable novel alternative methods for risk assessment. The goal is to develop a DNT in vitro test battery amenable to high-throughput screening (HTS). Currently, the DNT in vitro test battery consists primarily of human cell-based assays because of their immediate relevance to human health. However, such cell-based assays alone are unable to capture the complexity of a developing nervous system. Whole organismal systems that qualify as 3 R (Replace, Reduce and Refine) models are urgently needed to complement cell-based DNT testing. These models can provide the necessary organismal context and be used to explore the impact of chemicals on brain function by linking molecular and/or cellular changes to behavioural readouts. The nematode Caenorhabditis elegans, the planarian Dugesia japonica, and embryos of the zebrafish Danio rerio are all suited to low-cost HTS and each has unique strengths for DNT testing. Here, we review the strengths and the complementarity of these organisms in a novel, integrative context and highlight how they can augment current cell-based assays for more comprehensive and robust DNT screening of chemicals. Considering the limitations of all in vitro test systems, we discuss how a smart combinatory use of these systems will contribute to a better human relevant risk assessment of chemicals that considers the complexity of the developing brain.

Exposure of children to brominated flame retardants and heavy metals in Morocco: Urine and blood levels in association with global cytosine and adenine methylation

Persistent pollutants, namely brominated flame retardants (BFRs) and heavy metals, are compounds that are added to a wide range of products and materials for preventing ignition, increasing the functionality of materials or improving their performance, e.g. electric conductivity. The exposure of children might consequently be inferred, through indoor dust and hand-to-mouth or toy-chewing behaviors. The current study is aimed at assessing the exposure of Moroccan children to BFRs and heavy metal elements, and evaluating their associations with global DNA methylation. First, parents responded to a questionnaire pertaining to children's lifestyle, then blood and urine samples were collected from (n = 93) children aged between 5 and 11 years for biomonitoring and DNA methylation analysis. BFRs were detected in 54.84% of samples with a median concentration of 0.01 nmol/mL (range: 0.004-0.051 nmol/mL) while metal elements were detected in more than 90% of samples. BFRs showed no variations with global DNA methylation, unlike metal elements, which revealed significant associations with global DNA methylation markers, namely 5-mC, 5-hmC and N⁶-mA levels. Moroccan children may be exposed to flame retardants and heavy metals through several routes. Further research is required to assess the exposure and the health impacts of environmental pollutants and ultimately protect the Moroccan population by the prevention of adverse health effects.

Uncovering the common factors of chemical exposure and behavior: Evaluating behavioral effects across a testing battery using factor analysis

Although specific environmental chemical exposures, including flame retardants, are known risk factors for neurodevelopmental disorders (NDDs), direct experimental evidence linking specific chemicals to NDDs is limited. Studies focusing on the mechanisms by which the social processing systems are vulnerable to chemical exposure are underrepresented in the literature, even though social impairments are defining characteristics of many NDDs. We have repeatedly demonstrated that exposure to Firemaster 550 (FM 550), a prevalent flame retardant mixture used in foam-based furniture and infant products, can adversely impact a variety of behavioral endpoints. Our recent work in prairie voles (Microtus ochrogaster), a prosocial animal model, demonstrated that perinatal exposure to FM 550 sex specifically impacts socioemotional behavior. Here, we utilized a factor analysis approach on a battery of behavioral data from our prior study to extract underlying factors that potentially explain patterns within the FM 550 behavior data. This approach identified which aspects of the behavioral battery are most robust and informative, an outcome critical for future study designs. Pearson's correlation identified behavioral endpoints associated with distance and stranger interactions that were highly correlated across 5 behavioral tests. Using these behavioral endpoints, exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) extracted 2 factors that could explain the data: Activity (distance traveled endpoints) and Sociability (time spent with a novel conspecific). Exposure to FM 550 significantly decreased Activity and decreased Sociability. This factor analysis approach to behavioral data offers the advantages of modeling numerous measured variables and simplifying the data set by presenting the data in terms of common, overarching factors in terms of behavioral function.

Prenatal exposures to organophosphate ester metabolite mixtures and children's neurobehavioral outcomes in the MADRES pregnancy cohort

BACKGROUND

Evidence suggests organophosphate esters (OPEs) are neurotoxic; however, the epidemiological literature remains scarce. We investigated whether prenatal exposures to OPEs were associated with child neurobehavior in the MADRES cohort.

METHODS

We measured nine OPE metabolites in 204 maternal urine samples (gestational age at collection: 31.4 ± 1.8 weeks). Neurobehavior problems were assessed among 36-month-old children using the Child Behavior Checklist's (CBCL) three composite scales [internalizing, externalizing, and total problems]. We examined associations between tertiles of prenatal OPE metabolites (> 50% detection) and detect/non-detect categories (< 50% detection) and CBCL composite scales using linear regression and generalized additive models. We also examined mixtures for widely detected OPEs (n = 5) using Bayesian kernel machine regression.

RESULTS

Maternal participants with detectable versus non-detectable levels of bis(2-methylphenyl) phosphate (BMPP) had children with 42% (95% CI: 4%, 96%) higher externalizing, 45% (-2%, 114%) higher internalizing, and 35% (3%, 78%) higher total problems. Participants in the second versus first tertile of bis(butoxethyl) phosphate (BBOEP) had children with 43% (-1%, 109%) higher externalizing scores. Bis(1-chloro-2-propyl) phosphate (BCIPP) and child sex had a statistically significant interaction in internalizing (p = 0.02) and total problems (p = 0.03) models, with 120% (23%, 295%) and 57% (6%, 134%) higher scores in the third versus first BCIPP tertile among males. Among females, detectable vs non-detectable levels of prenatal BMPP were associated with 69% higher externalizing scores (5%, 170%) while the third versus first tertile of prenatal BBOEP was associated with 45% lower total problems (-68%, -6%). Although the metabolite mixture and each CBCL outcome had null associations, we observed marginal associations between di-n-butyl phosphate and di-isobutyl phosphate (DNBP + DIBP) and higher internalizing scores (0.15; 95% CrI: -0.02, 0.32), holding other metabolites at their median.

CONCLUSIONS

Our results generally suggest adverse and sex-specific effects of prenatal exposure to previously understudied OPEs on neurobehavioral outcomes in 36-month children, providing evidence of potential OPE neurotoxicity.

Machine learning reveals common transcriptomic signatures across rat brain and placenta following developmental organophosphate ester exposure

Toxicogenomics is a critical area of inquiry for hazard identification and to identify both mechanisms of action and potential markers of exposure to toxic compounds. However, data generated by these experiments are highly dimensional and present challenges to standard statistical approaches, requiring strict correction for multiple comparisons. This stringency often fails to detect meaningful changes to low expression genes and/or eliminate genes with small but consistent changes particularly in tissues where slight changes in expression can have important functional differences, such as brain. Machine learning offers an alternative analytical approach for "omics" data that effectively sidesteps the challenges of analyzing highly dimensional data. Using 3 rat RNA transcriptome sets, we utilized an ensemble machine learning approach to predict developmental exposure to a mixture of organophosphate esters (OPEs) in brain (newborn cortex and day 10 hippocampus) and late gestation placenta of male and female rats, and identified genes that informed predictor performance. OPE exposure had sex specific effects on hippocampal transcriptome, and significantly impacted genes associated with mitochondrial transcriptional regulation and cation transport in females, including voltage-gated potassium and calcium channels and subunits. To establish if this holds for other tissues, RNAseq data from cortex and placenta, both previously published and analyzed via a more traditional pipeline, were reanalyzed with the ensemble machine learning methodology. Significant enrichment for pathways of oxidative phosphorylation and electron transport chain was found, suggesting a transcriptomic signature of OPE exposure impacting mitochondrial metabolism across tissue types and developmental epoch. Here we show how machine learning can complement more traditional analytical approaches to identify vulnerable "signature" pathways disrupted by chemical exposures and biomarkers of exposure.

BDE-47 Causes Depression-like Effects in Zebrafish Larvae via a Non-Image-Forming Visual Mechanism

Depression is a high-incidence mood disorder that is frequently accompanied by sleep disturbances, which can be triggered by the non-image-forming (NIF) visual system. Therefore, we hypothesize that polybrominated diphenyl ethers are known to induce visual impairment that could promote depression by disrupting the NIF visual pathway. In this study, zebrafish larvae were exposed to BDE-47 at environmentally relevant concentrations (2.5 and 25 μg/L). BDE-47 caused melanopsin genes that dominate the NIF visual system that fell at night (p < 0.05) but rose in the morning (p < 0.05). Such bidirectional difference transmitted to clock genes and neuropeptides in the suprachiasmatic nucleus and impacted the adjacent serotonin system. However, indicative factors of depression, including serta, htr1aa, and aanat2, were unidirectionally increased 1.3- to 1.6-fold (p < 0.05). They were consistent with the increase in nighttime thigmotaxis (p < 0.05) and circadian hypoactivity (p < 0.05). The results of melanopsin antagonism also indicated that these consequences were possibly due to the combination of direct photoentrainment by melanopsin and circadian disruption originating from melanopsin. Collectively, our findings revealed that BDE-47 exposure disrupted the NIF visual pathway and resulted in depression-like effects, which may further exert profound health effects like mood disorders.

Organophosphate Esters Disrupt Steroidogenesis in KGN Human Ovarian Granulosa Cells

Organophosphate esters (OPEs) are used extensively as flame retardants and plasticizers and are found ubiquitously in the environment and human matrices. Previous studies suggested that exposure to some of these chemicals may disrupt the homeostasis of female sex hormones and have detrimental effects on female fertility. Here, we determined the effects of OPEs on the function of KGN ovarian granulosa cells. We hypothesized that OPEs alter the steroidogenic ability of these cells by dysregulating the expression of transcripts involved in steroid and cholesterol biosynthesis. KGN cells were exposed for 48 hours to 1 of 5 OPEs (1-50μM): triphenyl phosphate (TPHP), tris(methylphenyl) phosphate (TMPP), isopropylated triphenyl phosphate (IPPP), tert-butylphenyl diphenyl phosphate (BPDP), and tributoxyethyl phosphate (TBOEP), or to a polybrominated diphenyl ether flame retardant, 2,2',4,4' tetrabromodiphenyl ether (BDE-47), in the presence or absence of Bu2cAMP. OPEs increased the basal production of progesterone (P4) and 17β-estradiol (E2) and had either no effect or inhibited Bu2cAMP-stimulated P4 and E2 synthesis; exposure to BDE-47 had no effect. Quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed that OPEs (≥5μM) increased the basal expression of critical genes (STAR, CYP11A1, CYP19A1, HSD3B2, and NR5A1) involved in steroidogenesis; upon stimulation, the expression of all genes tested was downregulated. An overall inhibition in cholesterol biosynthesis was induced by OPEs, characterized by a downregulation in HMGCR and SREBF2 expression. TBOEP consistently showed the least effect. Therefore, OPEs perturbed steroidogenesis in KGN granulosa cells by targeting the expression of steroidogenic enzymes and cholesterol transporters; these effects may have an adverse impact on female reproduction.

The association of prenatal phthalates, organophosphorous pesticides, and organophosphate esters with early child language ability in Norway

BACKGROUND

Prenatal exposure to phthalates, organophosphate esters, and organophosphorous pesticides have been associated with neurodevelopmental deficits including language ability, however, few studies consider the effect of exposure mixtures and the potential longitudinal detriments over time.

OBJECTIVE

This study examines the influence of prenatal exposure to phthalates, organophosphate esters, and organophosphorous pesticides, on children's language ability from toddlerhood to the preschool period.

METHODS

This study includes 299 mother-child dyads from Norway in the Norwegian Mother, Father and Child Cohort Study (MoBa). Prenatal exposure to chemicals were assessed at 17 weeks' gestation, and child language skills were assessed at 18 months using the Ages and Stages Questionnaire communication subscale and at preschool age using the Child Development Inventory. We ran two structural equation models to examine the simultaneous influences of chemical exposures on parent-reported and teacher-reported child language ability.

RESULTS

Prenatal organophosphorous pesticides were negatively associated with preschool language ability through language ability at 18 months. Additionally, there was a negative association between low molecular weight phthalates and teacher-reported preschool language ability. There was no effect of prenatal organophosphate esters on child language ability at either 18 months or preschool age.

CONCLUSIONS

This study adds to the literature on prenatal exposure to chemicals and neurodevelopment and highlights the importance of developmental pathways in early childhood.

Descriptive analysis of organophosphate ester metabolites in a pan-Canadian pregnancy cohort

Organophosphate esters (OPEs) are widely used in numerous consumer products for their flame retardant and plasticizing properties. Despite potential widespread exposure, biomonitoring data during critical windows of development are scarce and limited to the most widely studied metabolites. We quantified urinary concentrations of multiple OPE metabolites in a vulnerable Canadian population. Using data and biobanked specimens from the Maternal-Infant Research on Environmental Chemicals (MIREC) study (2008-2011), we measured first trimester urinary concentrations of 15 OPE metabolites as well as one flame retardant metabolite and quantified associations with sociodemographic and sample collection characteristics in 1865 pregnant participants. We applied 2 different analytical methods to quantify OPEs, one using UItra-Performance Liquid Chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) and the other using Atmospheric Pressure Gas Chromatography coupled to mass spectrometry (APGC-MS/MS) with sensitive limits of detection (0.008-0.1 μg/L). We modelled associations between sociodemographic and sample collection characteristics and specific gravity-standardized chemical concentrations. Six OPE metabolites were detected in the majority (68.1-97.4 %) of participants. Bis-(2-chloroethyl) hydrogen phosphate had the highest detection rate (97.4 %). Diphenyl phosphate had the highest geometric mean concentration (0.657 μg/L). Metabolites of tricresyl phosphate were detected in few participants. Associations between sociodemographic characteristics varied according to each OPE metabolite. Pre-pregnancy body mass index tended to be positively associated with OPE metabolite concentrations whereas age tended to be inversely associated with OPE concentrations. OPE concentrations were, on average, higher in urine samples collected in the summer than other seasons the winter. We present the largest biomonitoring study of OPE metabolites in pregnant people to date. These findings demonstrate widespread exposure to OPEs and their metabolites and identify subpopulations who may experience heightened exposure.

Armour G, Horman BM, Rock KD, Witchey SK, Greenbaum A, Patisaul HB. Maternal organophosphate flame retardant exposure alters the developing mesencephalic dopamine system in fetal rat

Organophosphate flame retardants (OPFRs) have become the predominant substitution for legacy brominated flame retardants but there is concern about their potential developmental neurotoxicity (DNT). OPFRs readily dissociate from the fireproofed substrate to the environment, and they (or their metabolites) have been detected in diverse matrices including air, water, soil, and biota, including human urine and breastmilk. Given this ubiquitous contamination, it becomes increasingly important to understand the potential effects of OPFRs on the developing nervous system. We have previously shown that maternal exposure to OPFRs results in neuroendocrine disruption, alterations to developmental metabolism of serotonin (5-HT) and axonal extension in male fetal rats, and potentiates adult anxiety-like behaviors. The development of the serotonin and dopamine systems occur in parallel and interact, therefore, we first sought to enhance our prior 5-HT work by first examining the ascending 5-HT system on embryonic day 14 using whole mount clearing of fetal heads and 3-dimensional (3D) brain imaging. We also investigated the effects of maternal OPFR exposure on the development of the mesocortical dopamine system in the same animals through 2-dimensional and 3D analysis following immunohistochemistry for tyrosine hydroxylase (TH). Maternal OPFR exposure induced morphological changes to the putative ventral tegmental area and substantia nigra in both sexes and reduced the overall volume of this structure in males, whereas 5-HT nuclei were unchanged. Additionally, dopaminergic axogenesis was disrupted in OPFR exposed animals, as the dorsoventral spread of ventral telencephalic TH afferents were greater at embryonic day 14, while sparing 5-HT fibers. These results indicate maternal exposure to OPFRs alters the development trajectory of the embryonic dopaminergic system and adds to growing evidence of OPFR DNT.

Seasonal and source characteristics of organophosphorus flame retardants in air and house dust in Taiwan residential microenvironments: Implications for young children's exposure and risk assessment using a probabilistic approach

Organophosphate flame retardants (OPFRs) are prevalent in multiple industries. They have gradually replaced brominated flame retardants in recent years. Eleven OPFRs were collected from indoor air and house dust in two primary activity spaces--bedrooms and living rooms. The aim of the present study was to explore the potential sources of, and health risks associated with, OPFR exposure in young children using integrated and probabilistic approaches. The level of 11 indoor air OPFRs (466 ng/m³) in the bedroom was greater than that measured in the living room (379 ng/m³), and these values contrasted with those detected in dust. The air OPFRs in the warmer season were higher than those measured in the cold season; the inverse was true for those detected in house dust. In both activity spaces, the composition profiles indicated that tris(1-chloro-2-propyl)phosphate in indoor air (39%) and tris(2-butoxyethyl)phosphate in house dust (67%) were the dominant congeners. The average daily exposure dose (ADD) of OPFRs via air inhalation and dust ingestion did not differ significantly between preschool and school-aged children or based on sex. The Monte-Carlo-simulated 95th percentile ADD of the OPFRs in dust ingested by preschool children was 1.4 times higher. The OPFR exposure from air inhalation and dust ingestion in Taiwanese children is currently an acceptable non-carcinogenic risk and a negligible carcinogenic risk to Taiwan residents.

Hormone receptor activities of complex mixtures of known and suspect chemicals in personal silicone wristband samplers worn in office buildings

Humans are exposed to increasingly complex mixtures of hormone-disrupting chemicals from a variety of sources, yet, traditional research methods only evaluate a small number of chemicals at a time. We aimed to advance novel methods to investigate exposures to complex chemical mixtures. Silicone wristbands were worn by 243 office workers in the USA, UK, China, and India during four work shifts. We analyzed extracts of the wristbands for: 1) 99 known (targeted) chemicals; 2) 1000+ unknown chemical features, tentatively identified through suspect screening; and 3) total hormonal activities towards estrogen (ER), androgen (AR), and thyroid hormone (TR) receptors in human cell assays. We evaluated associations of chemicals with hormonal activities using Bayesian kernel machine regression models, separately for targeted versus suspect chemicals (with detection ≥50%). Every wristband exhibited hormonal activity towards at least one receptor: 99% antagonized TR, 96% antagonized AR, and 58% agonized ER. Compared to men, women were exposed to mixtures that were more estrogenic (180% higher, adjusted for country, age, and skin oil abundance in wristband), anti-androgenic (110% higher), and complex (median 836 detected chemical features versus 780). Adjusted models showed strong associations of jointly increasing chemical concentrations with higher hormonal activities. Several targeted and suspect chemicals were important co-drivers of overall mixture effects, including chemicals used as plasticizers, fragrance, sunscreen, pesticides, and from other or unknown sources. This study highlights the role of personal care products and building microenvironments in hormone-disrupting exposures, and the substantial contribution of chemicals not often identifiable or well-understood to those exposures.

Does Using Corsi-Rosenthal Boxes to Mitigate COVID-19 Transmission Also Reduce Indoor Air Concentrations of PFAS and Phthalates?

The COVID-19 pandemic brought new emphasis on indoor air quality. However, few studies have investigated the impact of air filtration, a COVID-mitigation approach, on indoor air concentrations of semivolatile organic compounds (SVOCs). Using a quasi-experimental design, we quantified the impact of a relatively low-cost "do-it-yourself" air filter (Corsi-Rosenthal Box; CR Box) on indoor air concentrations of 42 PFAS and 24 other SVOCs. We sampled air before (October-November 2021) and during (February-March 2022) deployment of CR Boxes in 17 rooms located in an occupied Providence, Rhode Island office building. We measured sound levels in rooms with CR Boxes operating and not operating. While CR Boxes were deployed, concentrations of seven PFAS (N-EtFOSE, N-EtFOSA, FBSA, PFBS, PFHxS, PFOS, PFNA) were 28-61% lower and concentrations of five phthalates (DMP, DEP, DiBP, BBzP, DCHP) were 29-62% lower. Concentrations of five PFAS and one phthalate increased 23-44% during the intervention period, but the 95% CI of most of these estimates included the null. Daytime sound levels increased 5.0 dB when CR Boxes were operating. These results indicate that CR Boxes reduced exposure to several lower-volatility phthalates and sulfonated PFAS previously reported to be found in office building materials and products, with potentially distracting increases in sound levels.

Ubiquitin proteasomal system is a potential target of the toxic effects of organophosphorus flame retardant triphenyl phosphate

The consumption of the widely used flame retardant Triphenyl phosphate (TPP) is increasing. It is now frequently detected in the environment and also domestically. Although the possibility of dermal exposure to TPP is quite high, little is known about its potential molecular toxicity mechanisms. In this study, we found that TPP caused cytotoxicity on human skin keratinocytes (HaCaT) and significantly inhibited the proliferation and cell migration in a concentration-dependent manner. Additionally, HaCaT cells were sensitive to TPP-induced apoptosis. Reactive oxygen species production was induced with TPP, which increased the protein carbonylation and lipid peroxidation levels. Moreover, TPP inhibited proteasome activity and increased the accumulation of ubiquitinated proteins. Exposure to TPP significantly increased the HSP90, HSP70, GRP94 and GRP78 protein levels. Overall, our findings indicate that TPP may pose a risk to human health and contribute to the current understanding of the risks of TPP at the molecular level.

A systematic scoping review of epidemiological studies on the association between organophosphate flame retardants and neurotoxicity

Organophosphate flame retardants (OPFRs) are increasingly and widely used as substitutes for brominated flame retardants in daily life. The chemical structure of OPFRs is very similar to that of organophosphorus pesticides, leading to concerns about their neurotoxicity. A few epidemiological studies have been published with inconsistent results on this topic, and a systematic scoping review is needed to provide an overview or map of the current evidence on the relationship of OPFRs with neurodevelopmental toxicity. Therefore, MEDLINE (accessed through PubMed), Web of Science, and CNKI (Chinese National Knowledge Infrastructure) were systematically searched for articles published in the last two decades. Nine eligible articles were included in the present systematic scoping review for adherence to the predefined PECOS (population, exposure, comparison, outcome, study design) statement. Six studies were conducted in the USA, and the remaining three studies were conducted in Austria, Norway and China. A total of 2 581 children (1 203 females and 1 378 males) were included. Half of the included studies focused on the adverse effects of OPFR exposure on cognition in children, while others primarily focused on the behaviors of children. In summary, the current evidence suggests inverse associations between early-life exposure to OPFRs and the childhood intelligence quotient and internalizing behavior and positive relationships of OPFR exposure with externalizing behavior. However, some differences in the timing of sample collection for exposure measurements, in the individual OPFR metabolites available, in the neurodevelopmental scales for outcome measurement, and in the statistical methods used to analyze the data are noted. In addition, further studies are warranted to evaluate some important issues, such as sex differences in the association, exposure-sensitive periods, and cumulative exposure risk assessment.

Impacts of Gestational FireMaster 550 Exposure on the Neonatal Cortex Are Sex Specific and Largely Attributable to the Organophosphate Esters

INTRODUCTION

Flame retardants (FRs) are common bodily and environmental pollutants, creating concern about their potential toxicity. We and others have found that the commercial mixture FireMaster® 550 (FM 550) or its individual brominated (BFR) and organophosphate ester (OPFR) components are potential developmental neurotoxicants. Using Wistar rats, we previously reported that developmental exposure to FM 550 or its component classes produced sex- and compound-specific effects on adult socioemotional behaviors. The underlying mechanisms driving the behavioral phenotypes are unknown.

METHODS

To further mechanistic understanding, here we conducted transcriptomics in parallel with a novel lipidomics approach using cortical tissues from newborn siblings of the rats in the published behavioral study. Inclusion of lipid composition is significant because it is rarely examined in developmental neurotoxicity studies. Pups were gestationally exposed via oral dosing to the dam to FM 550 or the BFR or OPFR components at environmentally relevant doses.

RESULTS

The neonatal cortex was highly sexually dimorphic in lipid and transcriptome composition, and males were more significantly impacted by FR exposure. Multiple adverse modes of action for the BFRs and OPFRs on neurodevelopment were identified, with the OPFRs being more disruptive than the BFRs via multiple mechanisms including dysregulation of mitochondrial function and disruption of cholinergic and glutamatergic systems. Disrupted mitochondrial function by environmental factors has been linked to a higher risk of autism spectrum disorders and neurodegenerative disorders. Impacted lipid classes included ceramides, sphingomyelins, and triacylglycerides. Robust ceramide upregulation in the OPFR females could suggest a heightened risk of brain metabolic disease.

CONCLUSIONS

This study reveals multiple mechanisms by which the components of a common FR mixture are developmentally neurotoxic and that the OPFRs may be the compounds of greatest concern.

Hierarchy of contamination control in the fire service: Review of exposure control options to reduce cancer risk

The international fire service community is actively engaged in a wide range of activities focused on development, testing, and implementation of effective approaches to reduce exposure to contaminants and the related cancer risk. However, these activities are often viewed independent of each other and in the absence of the larger overall effort of occupational health risk mitigation. This narrative review synthesizes the current research on fire service contamination control in the context of the National Institute for Occupational Safety and Health (NIOSH) Hierarchy of Controls, a framework that supports decision making around implementing feasible and effective control solutions in occupational settings. Using this approach, we identify evidence-based measures that have been investigated and that can be implemented to protect firefighters during an emergency response, in the fire apparatus and at the fire station, and identify several knowledge gaps that remain. While a great deal of research and development has been focused on improving personal protective equipment for the various risks faced by the fire service, these measures are considered less effective. Administrative and engineering controls that can be used during and after the firefight have also received increased research interest in recent years. However, less research and development have been focused on higher level control measures such as engineering, substitution, and elimination, which may be the most effective, but are challenging to implement. A comprehensive approach that considers each level of control and how it can be implemented, and that is mindful of the need to balance contamination risk reduction against the fire service mission to save lives and protect property, is likely to be the most effective.

Individual and Combined Effects of Paternal Deprivation and Developmental Exposure to Firemaster 550 on Socio-Emotional Behavior in Prairie Voles

The prevalence of neurodevelopmental disorders (NDDs) is rapidly rising, suggesting a confluence of environmental factors that are likely contributing, including developmental exposure to environmental contaminants. Unfortunately, chemical exposures and social stressors frequently occur simultaneously in many communities, yet very few studies have sought to establish the combined effects on neurodevelopment or behavior. Social deficits are common to many NDDs, and we and others have shown that exposure to the chemical flame retardant mixture, Firemaster 550 (FM 550), or paternal deprivation impairs social behavior and neural function. Here, we used a spontaneously prosocial animal model, the prairie vole (Microtus ochrogaster), to explore the effects of perinatal chemical (FM 550) exposure alone or in combination with an early life stressor (paternal absence) on prosocial behavior. Dams were exposed to vehicle (sesame oil) or 1000 µg FM 550 orally via food treats from conception through weaning and the paternal absence groups were generated by removing the sires the day after birth. Adult offspring of both sexes were then subjected to open-field, sociability, and a partner preference test. Paternal deprivation (PD)-related effects included increased anxiety, decreased sociability, and impaired pair-bonding in both sexes. FM 550 effects include heightened anxiety and partner preference in females but reduced partner preference in males. The combination of FM 550 exposure and PD did not exacerbate any behaviors in either sex except for distance traveled by females in the partner preference test and, to a lesser extent, time spent with, and the number of visits to the non-social stimulus by males in the sociability test. FM 550 ameliorated the impacts of parental deprivation on partner preference behaviors in both sexes. This study is significant because it provides evidence that chemical and social stressors can have unique behavioral effects that differ by sex but may not produce worse outcomes in combination.

Comprehensive analysis based in silico study of organophosphate flame retardants - environmental explanation of bladder cancer progression

Brominated flame retardants are associated with increased toxicity and high concerns for environmental pollution. Therefore, organophosphate flame retardants (OPFRs) are considered safer alternatives and are widely used in building materials and electronics. This study aimed to determine whether organophosphate flame retardants are implicated in bladder cancer development and progression. Data of interactive genes associated with OPFRs was obtained from the CTD database (http://ctdbase.org/) in July 2021. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that organophosphate flame retardants were closely linked to bladder cancer. Furthermore, the immune-related genes showed a strong correlation with bladder cancer. Further analysis revealed that the immune-related genes were associated with the prognosis, clinical characteristics, and response to immunotherapies in bladder cancer. In conclusion, OPFRs and their metabolites could promote the progression of bladder cancer by affecting the expression of immune genes.

Beyond Cholinesterase Inhibition: Developmental Neurotoxicity of Organophosphate Ester Flame Retardants and Plasticizers

BACKGROUND

To date, the toxicity of organophosphate esters has primarily been studied regarding their use as pesticides and their effects on the neurotransmitter acetylcholinesterase (AChE). Currently, flame retardants and plasticizers are the two largest market segments for organophosphate esters and they are found in a wide variety of products, including electronics, building materials, vehicles, furniture, car seats, plastics, and textiles. As a result, organophosphate esters and their metabolites are routinely found in human urine, blood, placental tissue, and breast milk across the globe. It has been asserted that their neurological effects are minimal given that they do not act on AChE in precisely the same way as organophosphate ester pesticides.

OBJECTIVES

This commentary describes research on the non-AChE neurodevelopmental toxicity of organophosphate esters used as flame retardants and plasticizers (OPEs). Studies in humans, mammalian, nonmammalian, and in vitro models are presented, and relevant neurodevelopmental pathways, including adverse outcome pathways, are described. By highlighting this scientific evidence, we hope to elevate the level of concern for widespread human exposure to these OPEs and to provide recommendations for how to better protect public health.

DISCUSSION

Collectively, the findings presented demonstrate that OPEs can alter neurodevelopmental processes by interfering with noncholinergic pathways at environmentally relevant doses. Application of a pathways framework indicates several specific mechanisms of action, including perturbation of glutamate and gamma-aminobutyric acid and disruption of the endocrine system. The effects may have implications for the development of cognitive and social skills in children. Our conclusion is that concern is warranted for the developmental neurotoxicity of OPE exposure. We thus describe important considerations for reducing harm and to provide recommendations for government and industry decision makers. https://doi.org/10.1289/EHP9285.

Sex-specific Disruption of the Prairie Vole Hypothalamus by Developmental Exposure to a Flame Retardant Mixture

Prevalence of neurodevelopmental disorders (NDDs) with social deficits is conspicuously rising, particularly in boys. Flame retardants (FRs) have long been associated with increased risk, and prior work by us and others in multiple species has shown that developmental exposure to the common FR mixture Firemaster 550 (FM 550) sex-specifically alters socioemotional behaviors including anxiety and pair bond formation. In rats, FRs have also been shown to impair aspects of osmoregulation. Because vasopressin (AVP) plays a role in both socioemotional behavior and osmotic balance we hypothesized that AVP and its related nonapeptide oxytocin (OT) would be vulnerable to developmental FM 550 exposure. We used the prairie vole (Microtus ochrogaste) to test this because it is spontaneously prosocial. Using siblings of prairie voles used in a prior study that assessed behavioral deficits resulting from developmental FM 550 exposure across 3 doses, here we tested the hypothesis that FM 550 sex-specifically alters AVP and OT neuronal populations in critical nuclei, such as the paraventricular nucleus (PVN), that coordinate those behaviors, as well as related dopaminergic (determined by tyrosine hydroxylase (TH) immunolabeling) populations. Exposed females had fewer AVP neurons in the anterior PVN and more A13 TH neurons in the zona incerta than controls. By contrast, in FM 550 males, A13 TH neuron numbers in the zona incerta were decreased but only in 1 dose group. These results expand on previous work showing evidence of endocrine disruption of OT/AVP pathways, including to subpopulations of PVN AVP neurons that coordinate osmoregulatory functions in the periphery.