Assessing in-vitro estrogenic effects of currently-used flame retardants

Safety Assessment of Triphenyl Phosphate as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) assessed the safety of Triphenyl Phosphate, which is reported to function as a plasticizer in manicuring products. The Panel reviewed the available data to determine the safety of this ingredient. The Panel concluded that Triphenyl Phosphate is safe in cosmetics in the present practices of use and concentration described in this safety assessment.

Weight of evidence evaluation of the metabolism disrupting effects of triphenyl phosphate using an expert knowledge elicitation approach

Identification of Endocrine-Disrupting Chemicals (EDCs) in a regulatory context requires a high level of evidence. However, lines of evidence (e.g. human, in vivo, in vitro or in silico) are heterogeneous and incomplete for quantifying evidence of the adverse effects and mechanisms involved. To date, for the regulatory appraisal of metabolism-disrupting chemicals (MDCs), no harmonised guidance to assess the weight of evidence has been developed at the EU or international level. To explore how to develop this, we applied a formal Expert Knowledge Elicitation (EKE) approach within the European GOLIATH project. EKE captures expert judgment in a quantitative manner and provides an estimate of uncertainty of the final opinion. As a proof of principle, we selected one suspected MDC -triphenyl phosphate (TPP) - based on its related adverse endpoints (obesity/adipogenicity) relevant to metabolic disruption and a putative Molecular Initiating Event (MIE): activation of peroxisome proliferator activated receptor gamma (PPARγ). We conducted a systematic literature review and assessed the quality of the lines of evidence with two independent groups of experts within GOLIATH, with the objective of categorising the metabolic disruption properties of TPP, by applying an EKE approach. Having followed the entire process separately, both groups arrived at the same conclusion, designating TPP as a "suspected MDC" with an overall quantitative agreement exceeding 85%, indicating robust reproducibility. The EKE method provides to be an important way to bring together scientists with diverse expertise and is recommended for future work in this area.

The flame retardant triphenyl phosphate alters the epigenome of embryonic cells in an aquatic in vitro model

Triphenyl phosphate (TPhP) is an organophosphate flame retardant and plasticizer that is added to a wide variety of consumer and industrial products. It is also a ubiquitous environmental pollutant. Exposure to TPhP has been shown to alter gene expression in metabolic and estrogenic signaling pathways in in vitro and in vivo models of a variety of species, and as such, is considered to be an endocrine disrupting chemical. Exposure to endocrine disrupting chemicals is increasingly being associated with changes to the epigenome, especially during embryonic development. The aim of this study was to evaluate whether TPhP exposure in aquatic ecosystems has the ability to alter the epigenome in two immortal cell lines derived from trout (Oncorhynchus mykiss). This study assessed whether 24 h exposure to TPhP resulted in changes to histone modification and DNA methylation profiles in steelhead trout embryonic cells and rainbow trout gill epithelial cells. Results show that several epigenetic modifications on histone H3 and DNA methylation are altered in the embryonic cells following TPhP exposure, but not in the gill epithelial cells. Specifically, histone H3 acetylation, histone H3 mono-methylation and global DNA methylation were found to be reduced. The alterations of these epigenetic modification profiles in the embryonic cells suggest that exposure to TPhP during fetal development may alter gene expression in the developing embryo, likely in metabolic and estrogenic pathways. The impacts to the epigenome determined in this study may even carry multigenerational detrimental effects on human and ecosystem health, which requires further investigation.

Disruption of neurosteroid synthesis and release by tris(2,3-dibromopropyl)isocyanurate in primary mouse cortical astrocytes in vitro

Neurosteroidogenesis in astrocytes is crucial for the proper development and functioning of the brain. During this process, key neurohormones such as progesterone (P4 ), testosterone (T), and estradiol (E2 ) are produced. Proper production and release of neurosteroids can be affected by substances referred to as endocrine-disrupting compounds (EDCs). Tris-(2,3-dibromopropyl)isocyanurate (TBC) is a representative of novel brominated flame retardants used to stop ignition or reduce fire-related property damage to plastics, polyolefin, polyphenyl alkene, unsaturated polyester, synthetic rubber, and fibers. Interestingly, previous studies have shown that TBC can enhance the proliferation of estradiol-sensitive breast cancers in vitro, which suggests that TBC has EDC properties. Therefore, given the suspected endocrine-disrupting properties of TBC, the aim of the present study was to determine the impact of TBC on the neurosteroid (P4 , T, and E2 ) production and secretion as well as the mRNA expression of key enzymes involved in its production in mouse astrocytes in vitro. Our paper shows that TBC increases P4 production with a strong decrease in T production, which is accompanied by a decrease in Cyp17a1 mRNA expression, that is, the main enzyme metabolizing P4 to T. Moreover, TBC in both studied concentrations increases P4 secretion in the culture medium. Finally, our studies have demonstrated an increase in the expression of Cyp19a1 mRNA, an enzyme metabolizing T to E2 , with a simultaneous increase in the amount of E2 in cells. Our data clearly show that TBC in an in vitro environment acts as EDCs, which may lead to serious consequences for the proper development and functioning of the brain.

Anti-androgenic activity of novel flame retardants in mixtures: Newly identified contribution from tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO)

In recent decades, male infertility has been on the rise, largely attributed to exposure to chemicals with endocrine-disrupting properties. The adverse effects of disrupting androgen actions on the development and reproductive health of children and adolescents have been extensively studied. Flame retardants (FRs), used in consumer products to delay flammability, have been identified as antagonists of the androgen receptor (AR), potentially leading to adverse outcomes in male reproductive health later in life. This study examined the interaction of eight novel FRs with the AR, employing an in vitro AR-dependent luciferase reporter gene assay utilizing MDA-kb2 cells. The investigation revealed the anti-androgenic activity of tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO), a frequently detected FR in the environment. Furthermore, TDBP-TAZTO contributed to anti-androgenic activity when combined with six other anti-androgenic FRs. The mixture effects were predicted by three commonly employed models: concentration addition (CA), generalized CA, and independent action, with the CA model showcasing the highest accuracy. This suggests that all FRs act through a similar mechanism, as further confirmed by in silico molecular docking, indicating limited synergy or antagonism. Importantly, in the mixtures, each FR contributed to the induction of anti-androgenic effects at concentrations below their individual effective concentrations in single exposures. This raises concern for public health, especially considering the co-detection of these FRs and their potential co-occurrence with other anti-androgenic chemicals like bisphenols. Therefore, our findings, along with previous research, strongly support the incorporation of combined effects of mixtures in risk assessment to efficiently safeguard population health.

Exposure to environmentally relevant concentrations of TnBP results in tissue-specific bio-accumulation and inhibits growth of silver carp (Hypophthalmichthys molitrix)

Tri-n-butyl phosphate (TnBP) is commonly used as flame retardant and rubber plasticizer, and has been widely detected in aquatic organisms and natural waters. However, the potential toxicity of TnBP in fish remains unclear. In the present study, silver carp (Hypophthalmichthys molitrix) larvae were treated with environmentally relevant concentrations (100 or 1000 ng/L) of TnBP for 60 d and then they were depurated in clean water for 15 d, and the accumulation and depuration of the chemical in six tissues of silver carp were measured. Furthermore, effects on growth were evaluated and potential molecular mechanisms were explored. Results indicated that TnBP could be rapidly accumulated and depurated in silver carp tissues. In addition, the bio-accumulation of TnBP displayed tissue-specificity, where intestine contained the greatest and vertebra had the smallest level of TnBP. Furthermore, exposure to environmentally relevant concentrations of TnBP led to time- and concentration-dependent growth inhibition of silver carp, even though TnBP was completely depurated in tissues. Mechanistic studies suggested that exposure to TnBP up- and down-regulated the expression of ghr and igf1 in liver, respectively, and increased GH contents in plasma of silver carp. TnBP exposure also up-regulated the expression of ugt1ab and dio2 in liver, as well as decreased T4 contents in plasma of silver carp. Our findings provide direct evidence of health hazards of TnBP to fish in natural waters, calling for more attention of environmental risks of TnBP in aquatic environment.

Occurrence and Health Effects of Hexabromocyclododecane: An Updated Review

Hexabromocyclododecane (HBCD) is a non-aromatic compound belonging to the bromine flame retardant family and is a known persistent organic pollutant (POP). This compound accumulates easily in the environment and has a high half-life in water. With a variety of uses, the HBCD is found in house dust, electronics, insulation, and construction. There are several isomers and the most studied are α-, β-, and γ-HBCD. Initially used as a substitute for other flame retardants, the polybrominated diphenyl ethers (PBDEs), the discovery of its role as a POP made HBCD use and manufacturing restricted in Europe and other countries. The adverse effects on the environment and human health have been piling, either as a result from its accumulation or considering its power as an endocrine disruptor (ED). Furthermore, it has also been proven that it has detrimental effects on the neuronal system, endocrine system, cardiovascular system, liver, and the reproductive system. HBCD has also been linked to cytokine production, DNA damage, increased cell apoptosis, increased oxidative stress, and reactive oxygen species (ROS) production. Therefore, this review aims to compile the most recent studies regarding the negative effects of this compound on the environment and human health, describing the possible mechanisms by which this compound acts and its possible toxic effects.

Reprotoxic Effect of Tris(2,3-Dibromopropyl) Isocyanurate (TBC) on Spermatogenic Cells In Vitro

Tris(2,3-dibromopropyl) isocyanurate (TBC) belongs to the class of novel brominated flame retardants (NFBRs) that are widely used in industry. It has commonly been found in the environment, and its presence has been discovered in living organisms as well. TBC is also described as an endocrine disruptor that is able to affect male reproductive processes through the estrogen receptors (ERs) engaged in the male reproductive processes. With the worsening problem of male infertility in humans, a mechanism is being sought to explain such reproductive difficulties. However, so far, little is known about the mechanism of action of TBC in male reproductive models in vitro. Therefore, the aim of the study was to evaluate the effect of TBC alone and in cotreatment with BHPI (estrogen receptor antagonist), 17β-estradiol (E₂), and letrozole on the basic metabolic parameters in mouse spermatogenic cells (GC-1 spg) in vitro, as well as the effect of TBC on mRNA expression (Ki67, p53, Pparγ, Ahr, and Esr1). The presented results show the cytotoxic and apoptotic effects of high micromolar concentrations of TBC on mouse spermatogenic cells. Moreover, an increase in Pparγ mRNA levels and a decrease in Ahr and Esr1 gene expression were observed in GS-1spg cells cotreated with E₂. These results suggest the significant involvement of TBC in the dysregulation of the steroid-based pathway in the male reproductive cell models in vitro and may be the cause of the currently observed deterioration of male fertility. However, more research is needed to reveal the full mechanism of TBC engagement in this phenomenon.

Gestational exposure to triphenyl phosphate induces epigenetic modifications in C57Bl/6 fetal liver

INTRODUCTION

Triphenyl phosphate (TPHP) is a chemical flame retardant and plasticizer which is added to consumer and industrial products. The developmental origins of health and disease hypothesis postulate that in utero exposures can have later-in-life effects on the developing fetus and can alter fetal gene expression. This study aimed to determine whether epigenetic modifications occurred following in utero TPHP exposure in mice and whether these changes were dose and/or sex-dependent.

METHODS

Pregnant C57Bl/6 mice were treated with 0, 5, 25, or 50 mg/kg of TPHP on gestational days (GD) 8, 10, 12, and 14 via intraperitoneal injection and fetal livers were collected on GD 19. Changes in the levels of acetylation of H3 and H4, as well as methylation of H3K9 and global DNA methylation were assessed in the fetal livers by western blot.

RESULTS

Results showed that there was a significant decrease in fetal DNA methylation following in utero exposure to 50 mg/kg TPHP compared to the control (0 mg/kg) independent of the sex of the fetus. While there were no significant alterations compared to controls in any histone modifications at any dose or sex following in utero TPHP exposure, we did note a decrease (t test, p = .025) in the levels of acetylated H3 in males versus females following a maternal dose of 25 mg/kg. The monomethylated H3K9 levels were also increased in females versus males following exposure to TPHP at 5 mg/kg (p = .018) and 25 mg/kg (p = .027) when analyzed via unpaired t tests, although not significantly different from controls.

DISCUSSION

The results suggest that gestational TPHP exposure can induce epigenetic modifications in murine fetal tissue. Specifically, global DNA methylation levels were downregulated in response to TPHP. Additionally, males appear to be more sensitive to TPHP-induced histone modifications than females. These data support the need for further studies investigating the impacts of gestational TPHP exposure on the developing fetus.

Early life organophosphate ester exposures and bone health at age 12 years: The Health Outcomes and Measures of the Environment (HOME) Study

BACKGROUND

No human studies have evaluated early life organophosphate ester (OPE) exposures with bone health outcomes, despite evidence of osteotoxicity.

OBJECTIVES

We assessed associations of urinary OPE metabolites measured across early life with areal bone mineral density (aBMD) and bone mineral content (BMC) at age 12 years.

METHODS

Among 223 mother-child dyads enrolled in the Health Outcomes and Measures of the Environment (HOME) Study, we quantified concentrations of bis-2-chloroethyl phosphate (BCEP), bis-(1,3-dichloro-2-propyl) (BDCIPP), di-n-butyl phosphate (DnBP), and diphenyl phosphate (DPHP) in urine collected from mothers during pregnancy and children at ages 1, 2, 3, 5, and 8 years. At age 12 years, we performed dual energy x-ray absorptiometry and calculated aBMD and BMC z-scores at six skeletal sites. We estimated overall and sex-stratified BMD/BMC z-score differences per interquartile range (IQR) increase in OPE concentrations at multiple exposure timepoints: gestation (average) and 1-3 (average), 5, and 8 years.

RESULTS

In adjusted models, overall associations of BCEP and BDCIPP with total hip and 1/3rd distal radius aBMD and BMC varied significantly by exposure timepoint, as did BDCIPP with whole body aBMD. For example, differences (95 % CI) in total hip aBMD z-score per IQR increase in BDCIPP were 0.33 (0.01, 0.64), -0.10 (-0.34, 0.14), -0.18 (-0.40, 0.05), and 0.14 (-0.09, 0.38) for concentrations during gestation and at 1-3, 5, and 8 years, respectively. Overall DnBP and DPHP associations were generally null at all timepoints. We observed sex-specific associations for some timepoints and skeletal sites. For example, an IQR increase in 8-year DPHP was associated with a 0.21 (0.05, 0.38) greater total hip aBMD z-score among females but -0.19 (-0.43, 0.05) lower z-score among males.

DISCUSSION

Early life OPE exposures may be associated with sex- and exposure period-dependent alterations in early adolescent bone mineral accrual and strength.

Liver immune and lipid metabolism disorders in mice induced by triphenyl phosphate with or without high fructose and high fat diet

Organophosphorus flame retardants (OPFRs) are frequently detected in food and human samples, and epidemiological studies have found that human exposure to aryl-OPFRs (triphenyl phosphate, TPP) is associated with lipid metabolism. Although toxicity studies suggest a potential obesity risk from TPP exposure, the molecular mechanism remains unclear. This study investigated the subchronic dietary effects on mouse liver significantly changed proteins (SCPs) and elucidated the underlying molecular mechanisms of TPP with or without a high-fructose and high-fat (HFF) diet. Male C57BL/6J mice were exposed to low-dose TPP (corresponding to the oral reference dose, 10 μg/kg body weight (bw)/day) and high-dose TPP (1000 μg/kg bw/day) for 12 weeks. The results showed that exposure to TPP generated changes of liver function and organelle damage as well as increases in total cholesterol and triglyceride levels. TPP exposure at a low dose damaged the liver immune system via major histocompatibility complex-related proteins involved in antigen processing and presentation. TPP exposure at a high dose caused disorders of the biosynthesis of unsaturated fatty acids and steroid hormones, thereby inducing lipid accumulation in the liver. Although 10 μg/kg TPP did not cause serious lipid metabolism disorders in the liver, significant overexpression of fatty acid-binding protein 5, malic enzyme 1, and other related SCPs was observed, which led to disorders of cholesterol metabolism and lipogenesis to activate the proliferator-activated receptor signaling pathway and thus induced potential obesity risks. In addition, lipid metabolism disorders related to TPP were aggravated under the HFF diet, impairing liver mitochondrial and endoplasmic reticulum function in mice by altering the activity of cytochrome P450 enzyme subfamilies. These findings provide an in-depth understanding of the molecular toxicity mechanisms and health risks associated with subchronic exposure to TPP under different dietary regimes.

Comprehensive review of the impact of tris(2,3-dibromopropyl) isocyanurate (TBC or TDBP-TAZTO) on living organisms and the environment

Tris(2,3-dibromopropyl) isocyanurate (TBC or TDBP-TAZTO) belongs to the group of brominated flame retardants (BFRs). The production of this compound is increasing due to the growing demand and wide application in electrical, electronic, musical instrument, and automotive component industries. The properties of TBC, e.g., the high octanol-air partition coefficient (Koa), high octanol-water partition coefficient (Kow), and high bioconcentration factor (BCF), indicate a possibility of its spread in aquatic and terrestrial ecosystems and bioaccumulation in living organisms. The presence of TBC has been confirmed in soil, sediments, river water, and such materials as microplastic, curtains, and e-waste devices. The compound has potential to bioaccumulate in the food chain of living organisms. TBC has been demonstrated to exert a harmful effect mainly on the nervous and endocrine systems, lungs, and liver. The possible mechanism of toxicity of the compound in the nervous system is based on the generation of oxidative stress by TBC leading to apoptosis of neuronal cells, while mitochondrial damage is considered to be responsible for changes in the respiratory organ. Moreover, the potential of mussels and earthworms to be bioindicators of TBC has been proven. Therefore, the literature review is focused on TBC properties and analysis of the identification and impact of the compound on the environment, living organisms, and human cell lines. Given the many toxic effects of TBC highlighted in the literature, there is a need for more profound research on the safety of TBC and methods for identification and degradation of this compound.

Brominated flame retardants effect in MCF-7 cells: Impact on vitamin D pathway

Brominated flame retardants (BFRs) are persistent environmental pollutants, allowing a constant human exposure which carries several health risks, including the occurrence of breast cancer and vitamin D deficiency. Vitamin D inhibits cell growth and is negatively associated with breast cancer risk. The effect of BFRs in breast cancer and vitamin D pathway is still poorly understood. MCF-7 cells were treated with hexabromocyclododecane (HBCD), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), hexabromobenzene (HBB) and pentabromotoluene (PBT) using short and long-term exposure protocols. Viability, proliferation, migration, cell cycle and gene expression were assessed. Gene expression of hVDBP and hCYP2R1 was also evaluated in hepatocytes. Long-term exposure of MCF-7 cells to HBB increased cell proliferation and migration, consequently increasing MMP-9 expression. The vitamin D pathway was also altered by BFRs: cells appeared less prepared to activate and transport vitamin D and the signaling, action and inactivation mechanisms were diminished in the presence of BFRs. Untreated MCF-7 cells showed cell cycle arrest in phase G0/G1 in the presence of activated vitamin D. However, when MCF-7 cells were exposed to BFRs, cell cycle was arrested in phase G2/M, possibly due to DNA damage. Nonetheless, calcitriol seems to be able to mitigate the effect of some BFRs exposure, e.g. PBT.

The adverse outcome pathway (AOP) of estrogen interference effect induced by triphenyl phosphate (TPP): Integrated multi-omics and molecular dynamics approaches

Triphenyl phosphate (TPP) has been detected with increasing frequency in various biota and environmental media, and it has been confirmed that G protein-coupled estrogen receptor (GPER) was involved in the estrogenic activity of TPP. Therefore, it is necessary to link the estrogen-interfering effects and possible mechanisms of action of TPP with the molecular initiation event (MIE) to improve its adverse outcome pathway framework. In this study, transcriptomic and proteomic methods were used to analyze the estrogen interference effect of TPP mediated by GPER, and the causal relationship was supplemented by molecular dynamics simulation and fluorescence analysis. The omics results showed that TPP could regulate the response of key GPER signaling factors and the activation of downstream pathways including PI3K-Akt signaling pathway, MAPK signaling pathway, and estrogen signaling pathway. The similar activation effect of TPP and agonist G1 change of GPER was proved by molecular dynamics simulation. After TPP binding, the conformation of GPER will change from the inactive to active state. Therefore, TPP may affect cell proliferation, metastasis, and apoptosis and regulate gene transcription and kinase activity, leading to abnormal immune function and other estrogen-dependent cell processes and cancer through GPER, ultimately causing the estrogen interference effect.

Study on the reproductive toxicity and mechanism of tri-n-butyl phosphate (TnBP) in Caenorhabditis elegans

Tri-n-butyl phosphate (TnBP), a typical alkyl organophosphate ester is widely used as an emerging flame retardant for polybrominated diphenyl ethers alternatives, but the potential toxicity and mechanism are unclear. In this study, the reproductive toxicity of TnBP and its related mechanisms were explored using the Caenorhabditis elegans (C. elegans) model. After TnBP (100-1000 μg/L) exposure, brood size and the number of fertilized eggs in the uterus in C. elegans were significantly reduced, the relative area of gonad arm and the number of total germline cells in C. elegans were significantly reduced, germ cell apoptosis and germ cell DNA damage in C. elegans were significantly increased, the level of ROS in C. elegans was significantly increased. Furthermore, TnBP exposure caused abnormal gene expressions of cell apoptosis (ced-9, ced-4 and ced-3), DNA damage (hus-1, clk-2, cep-1 and egl-1) and oxidative stress (mev-1 and gas-1). TnBP exposure can lead to reproductive ability decreased and gonad development impaired in C. elegans, the mechanism of TnBP reduced reproductive ability may be related to germ cell apoptosis, germ cell DNA damage and oxidative stress. Environmental exposure to TnBP may have potential reproductive toxicity.

In situ localization of tris(2,3-dibromopropyl) isocyanurate in mouse organs by MALDI-IMS with auxiliary matrix strategy

Tris(2,3-dibromopropyl) isocyanurate (TBC) is one of the novel brominated flame retardants that has been widely used in consumer goods. Humans may be exposed to TBC daily. Studies showed that TBC can induce significant toxicity. However, there is currently no report on its in situ localization in organs. In this study, we aimed to develop a reliable and reproductive method to determine the in situ localization of TBC in mouse organs by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). As commercially available matrices were not able to detect TBC in tissue section, we then developed a novel MALDI-IMS method based on 1,5-diaminonaphthalene hydrochloride and silver trifluoromethanesulfonate (NDA/AgOTf) as the matrix for the in situ localization of TBC. AgOTf used as the auxiliary matrix in the negative-ion mode showed an excellent MS signal of TBC. The detection limit of [2AgOTf + Br]^- was at the μg/mL level. The developed MALDI-IMS method was successfully employed to obtain the TBC spatial distribution in the mouse organs collected from mice exposed to 160 mg/kg/day of TBC for 30 days. High-pressure liquid chromatography-tandem mass spectroscopy (HPLC-MS/MS) was also used to evaluate the accumulation of TBC in liver, kidney, heart, and brain. The combination of MALDI-IMS and HPLC-MS/MS showed that TBC can accumulate in mice organs and it is mainly distributed in the renal parenchyma. In summary, an innovative method was developed for the analysis of TBC spatial distribution by MALDI-IMS using a novel NDA/AgOTf matrix, extending the application of MALDI-IMS in environmental pollutants.

Transcriptomic Analysis of the Differential Nephrotoxicity of Diverse Brominated Flame Retardants in Rat and Human Renal Cells

Brominated flame retardants (BFRs) are environmentally persistent, are detected in humans, and some have been banned due to their potential toxicity. BFRs are developmental neurotoxicants and endocrine disruptors; however, few studies have explored their potential nephrotoxicity. We addressed this gap in the literature by determining the toxicity of three different BFRs (tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and tetrabromodiphenyl ether (BDE-47)) in rat (NRK 52E) and human (HK-2 and RPTEC) tubular epithelial cells. All compounds induced time- and concentration-dependent toxicity based on decreases in MTT staining and changes in cell and nuclear morphology. The toxicity of BFRs was chemical- and cell-dependent, and human cells were more susceptible to all three BFRs based on IC₅₀s after 48 h exposure. BFRs also had chemical- and cell-dependent effects on apoptosis as measured by increases in annexin V and PI staining. The molecular mechanisms mediating this toxicity were investigated using RNA sequencing. Principal components analysis supported the hypothesis that BFRs induce different transcriptional changes in rat and human cells. Furthermore, BFRs only shared nine differentially expressed genes in rat cells and five in human cells. Gene set enrichment analysis demonstrated chemical- and cell-dependent effects; however, some commonalities were also observed. Namely, gene sets associated with extracellular matrix turnover, the coagulation cascade, and the SNS-related adrenal cortex response were enriched across all cell lines and BFR treatments. Taken together, these data support the hypothesis that BFRs induce differential toxicity in rat and human renal cell lines that is mediated by differential changes in gene expression.

Endocrine disrupting potential of replacement flame retardants - Review of current knowledge for nuclear receptors associated with reproductive outcomes

BACKGROUND AND AIM

Endocrine disrupting chemicals (EDCs) constitute a major public health concern because they can induce a large spectrum of adverse effects by interfering with the hormonal system. Rapid identification of potential EDCs using in vitro screenings is therefore critical, particularly for chemicals of emerging concerns such as replacement flame retardants (FRs). The review aimed at identifying (1) data gaps and research needs regarding endocrine disrupting (ED) properties of replacement FRs and (2) potential EDCs among these emerging chemicals.

METHODS

A systematic search was performed from open literature and ToxCast/Tox21 programs, and results from in vitro tests on the activities of 52 replacement FRs towards five hormone nuclear receptors (NRs) associated with reproductive outcomes (estrogen, androgen, glucocorticoid, progesterone, and aryl hydrocarbon receptors) were compiled and organized into tables. Findings were complemented with information from structure-based in silico model predictions and in vivo information when relevant.

RESULTS

For the majority of the 52 replacement FRs, experimental in vitro data on activities towards these five NRs were either incomplete (15 FRs) or not found (24 FRs). Within the replacement FRs for which effect data were found, some appeared as candidate EDCs, such as triphenyl phosphate (TPhP) and tris(1,3-dichloropropyl)phosphate (TDCIPP). The search also revealed shared ED profiles. For example, anti-androgenic activity was reported for 19 FRs and predicted for another 21 FRs.

DISCUSSION

This comprehensive review points to critical gaps in knowledge on ED potential for many replacement FRs, including chemicals to which the general population is likely exposed. Although this review does not cover all possible characteristics of ED, it allowed the identification of potential EDCs associated with reproductive outcomes, calling for deeper evaluation and possibly future regulation of these chemicals. By identifying shared ED profiles, this work also raises concerns for mixture effects since the population is co-exposed to several FRs and other chemicals.

Update of the risk assessment of hexabromocyclododecanes (HBCDDs) in food

The European Commission asked EFSA to update its 2011 risk assessment on hexabromocyclododecanes (HBCDDs) in food. HBCDDs, predominantly mixtures of the stereoisomers α-, β- and γ-HBCDD, were widely used additive flame retardants. Concern has been raised because of the occurrence of HBCDDs in the environment, food and in humans. Main targets for toxicity are neurodevelopment, the liver, thyroid hormone homeostasis and the reproductive and immune systems. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour in mice can be considered the critical effects. Based on effects on spontaneous behaviour in mice, the Panel identified a lowest observed adverse effect level (LOAEL) of 0.9 mg/kg body weight (bw) as the Reference Point, corresponding to a body burden of 0.75 mg/kg bw. The chronic intake that would lead to the same body burden in humans was calculated to be 2.35 μg/kg bw per day. The derivation of a health-based guidance value (HBGV) was not considered appropriate. Instead, the margin of exposure (MOE) approach was applied to assess possible health concerns. Over 6,000 analytical results for HBCDDs in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary LB exposure to HBCDDs were fish meat, eggs, livestock meat and poultry. The CONTAM Panel concluded that the resulting MOE values support the conclusion that current dietary exposure to HBCDDs across European countries does not raise a health concern. An exception is breastfed infants with high milk consumption, for which the lowest MOE values may raise a health concern.

New understanding of novel brominated flame retardants (NBFRs): Neuro(endocrine) toxicity

Traditional brominated flame retardants (BFRs) negatively affect the environment and human health, especially in the sensitive (developing) nervous system. Considering the physicochemical similarities between novel brominated flame retardants (NBFRs) and BFRs, more and more evidence reveals the neurotoxic effects of NBFRs. We reviewed the neuro(endocrine) toxic effects of NBFRs in vivo and in vitro and discussed their action mechanisms based on the available information. The neurotoxic potential of NBFRs has been demonstrated through direct neurotoxicity and disruption of the neuroendocrine system, with adverse effects on neurobehavioral and reproductive development. Mechanistic studies have shown that the impact of NBFRs is related to the complex interaction of neural and endocrine signals. From disrupting the gender differentiation of the brain, altering serum thyroid/sex hormone levels, gene/protein expression, and so on, to interfere with the feedback effect between different levels of the HPG/HPT axis. In this paper, the mechanism of neurotoxic effects of NBFRs is explored from a new perspective-neuro and endocrine interactions. Gaps in the toxicity data of NBFRs in the neuroendocrine system are supplemented and provide a broader dataset for a complete risk assessment.

Tetrabromobisphenol A (TBBPA): A controversial environmental pollutant

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants and is extensively used in electronic equipment, furniture, plastics, and textiles. It is frequently detected in water, soil, air, and organisms, including humans, and has raised concerns in the scientific community regarding its potential adverse health effects. Human exposure to TBBPA is mainly via diet, respiration, and skin contact. Various in vivo and in vitro studies based on animal and cell models have demonstrated that TBBPA can induce multifaceted effects in cells and animals, and potentially exert hepatic, renal, neural, cardiac, and reproductive toxicities. Nevertheless, other reports have claimed that TBBPA might be a safe chemical. In this review, we re-evaluated most of the published TBBPA toxicological assessments with the goal of reaching a conclusion about its potential toxicity. We concluded that, although low TBBPA exposure levels and rapid metabolism in humans may signify that TBBPA is a safe chemical for the general population, particular attention should be paid to the potential effects of TBBPA on early developmental stages.

In vitro estrogen-disrupting effects of organophosphate flame retardants

Organophosphate flame retardants (OPFRs), as substitutes for polybrominated diphenyl ethers (PBDEs), are frequently detected in the environment and biota due to their widespread use. Thus, there is a need to investigate their potential estrogen-disrupting effects and possible mechanisms of action in an effort to obtain a better risk assessment. In this study, we characterized the activities on estrogen receptor α (ERα) and the estrogen-disrupting potential of fourteen OPFRs, TMP, TEP, TPP, TnBP, TiBP, THP, TPhP, TCP, DPK, MDPP, IDPP, CDP, IPPDP and MPhP, using three in vitro assays representing different specific modes of action (MoAs). In the yeast two-hybrid assay, no OPFRs induced agonistic activity, but TiBP, DPK, TPhP, MDPP, CDP and IPPDP were shown to be hydrophobicity-dependent antagonists and to compete with E₂ for binding to ERα. In the MVLN cell assay, TPhP was the only OPFR among the 14 tested that was able to activate ERα-estrogen responsive element (ERE) pathways. The results from the E-SCREEN assay showed that all tested OPFRs except TMP had estrogenic properties, and G protein-coupled receptor 30 (GPR30) was involved in the estrogenicity of eight OPFRs, TiBP, THP, TPhP, TCP, MDPP, IPPDP, CDP and MPhP. It was also found that in the E-SCREEN assay, the estrogenicity of alkyl-OPFRs but not aryl-OPFRs was closely correlated to hydrophobicity. Our research suggested that most OPFRs were estrogen disruptors, but their related mechanisms were complex and might involve ERα-mediated and/or ERα-independent pathways. Further in vitro studies concerning the estrogenic effects and involved mechanisms of OPFRs, as well as comprehensive evaluations of OPFRs including health and ecological assessments are needed to determine whether they are safe substitutes for PBDEs.

Predictors and reproducibility of urinary organophosphate ester metabolite concentrations during pregnancy and associations with birth outcomes in an urban population

BACKGROUND

Organophosphate esters (OPEs) are synthetic chemicals used as flame retardants and plasticizers in a variety of goods. Despite ubiquitous human exposures and laboratory evidence that prenatal OPE exposures may disrupt offspring metabolism, perinatal studies of OPE health effects are limited. The objectives of this study were to: 1) Determine predictors and reproducibility of urinary OPE biomarker concentrations during pregnancy, and 2) Estimate the relation of prenatal OPE exposures with birth outcomes and cord blood adipokine and insulin concentrations.

METHODS

We analyzed five OPE metabolites in urine samples collected at up to three visits during pregnancy from 90 women enrolled in the ORigins of Child Health And Resilience in Development (ORCHARD) pregnancy cohort in Baltimore, MD from 2017 to 2019. To quantify the variability of metabolite concentrations during pregnancy, we calculated intraclass correlation coefficients (ICCs) for each metabolite using mixed effects regression models. Using self-reported questionnaire data collected during gestation, we assessed possible sociodemographic and environmental/behavioral predictors of each OPE metabolite using generalized estimating equations to account for repeated exposure measures. We ascertained birth outcomes of 76 offspring from medical records, including weight-for-gestational age, length, ponderal index, and gestational age. In a subset of 37 infants, we measured cord blood concentrations of leptin, adiponectin, and insulin. To account for repeated exposure measures, we used linear structural equation models to assess the relations of standard deviation (SD) increases in prenatal OPE metabolite factor scores with continuous birth outcomes and cord blood biomarker concentrations.

RESULTS

ICCs ranged from 0.09 for isopropylphenyl-phenyl phosphate (ip-PPP) to 0.59 for bis(1,3-dichloro-2-propyl) phosphate (BDCIPP). We observed little consistency in environmental or behavioral predictors of OPE exposures, although concentrations were generally lower for samples collected in the afternoon compared to morning and winter compared to other seasons. In adjusted analyses, a SD increase in BDCIPP concentration was associated with a 0.06 g/cm3 (95% CI: 0.00, 0.12) greater ponderal index. A SD increase in BDCIPP was associated with a 0.37 (95% CI: - 0.62, - 0.13) SD lower insulin concentration and 0.24 (95% CI: - 0.39, - 0.08) SD lower leptin concentration. Other OPEs were not associated with infant outcomes.

CONCLUSIONS

These findings suggest some OPEs may be metabolic disruptors warranting investigation in larger studies.

The steroid receptor coactivator 1 (SRC1) and 3 (SRC3) recruitment as a novel molecular initiating event of 4-n-nonylphenol in estrogen receptor α-mediated pathways

Recently, the action of steroid receptor coactivators (SRCs) has been recognized to be an important molecular initiating event (MIE) in estrogenic adverse outcome pathways (AOPs). However, the role of SRCs in the molecular mechanisms of many highly concerned environmental estrogens remains poorly understood. In this study, the widely studied environmental estrogen, 4-n-nonylphenol (4-n-NP), was used as a typical pollutant to study SRCs recruitment in its estrogenic effects. In MCF7 cell proliferation (E-SCREEN) assay and MVLN cell assay, 4-n-NP showed significant estrogenic potency that involved an increase in estrogen receptor α (ERα), SRC1 and SRC3 transcript levels. Moreover, 4-n-NP was found to induce estrogen response element (ERE)-mediated activity via ERα in MVLN cells. To investigate the mechanism by which SRCs recruitment is induced by 4-n-NP-ERα, a coactivators recruitment assay was performed, and the results showed that 4-n-NP-ERα recruited both SRC1 and SRC3, whereas it failed to recruit SRC2. Similarly, it had no interaction with SRC2 in the ERα-SRC2 two-hybrid yeast assay. This is the first report to investigate the novel MIE of SRCs recruitment in 4-n-NP-ERα-induced estrogenicity. Overall, our results suggest that the action of 4-n-NP on estrogenic effects involves the following MIEs: the activation of ERα, the recruitment of SRC1 and SRC3, and the induction of ERE-mediated activity. The findings also provide valuable insights into the MIE associated with the different SRCs that are recruited in the adverse outcome pathways of environmental estrogens.

In Vitro Effects of Bisphenol A and Tetrabromobisphenol A on Cell Viability and Reproduction-Related Gene Expression in Pituitaries from Sexually Maturing Atlantic Cod (Gadus morhua L.)

Bisphenol A (BPA) and tetrabromobisphenol A (TBBPA) are widely used industrial chemicals, ubiquitously present in the environment. While BPA is a well-known endocrine disruptor and able to affect all levels of the teleost reproductive axis, information regarding TBBPA on this subject is very limited. Using primary cultures from Atlantic cod (Gadus morhua), the present study was aimed at investigating potential direct effects of acute (72 h) BPA and TBBPA exposure on cell viability and the expression of reproductive-relevant genes in the pituitary. The results revealed that both bisphenols stimulate cell viability in terms of metabolic activity and membrane integrity at environmentally relevant concentrations. BPA had no direct effects on gonadotropin gene expression, but enhanced the expression of gonadotropin-releasing hormone (GnRH) receptor 2a, the main gonadotropin modulator in Atlantic cod. In contrast, TBBPA increased gonadotropin transcript levels but had no effect on GnRH receptor mRNA. In conclusion, both anthropogenic compounds display endocrine disruptive properties and are able to directly interfere with gene expression related to reproductive function in cod pituitary cells at environmentally relevant concentrations in vitro.

Associations between urinary organophosphate ester metabolites and measures of adiposity among U.S. children and adults: NHANES 2013-2014

BACKGROUND

Organophosphate esters (OPEs) are synthetic chemicals found in many consumer products, including furniture, electronics, processed foods, and building materials. Emerging in vitro and in vivo studies suggest that OPEs are metabolism disrupting compounds; however, epidemiologic studies investigating their associations with adiposity markers are sparse.

OBJECTIVE

We examined cross-sectional associations between OPE biomarkers and adiposity measures among U.S. children and adults participating in the National Health and Nutrition Examination Survey (NHANES: 2013-2014).

METHODS

Concentrations of five OPE metabolites were quantified in urine: diphenyl phosphate (DPHP), bis(1,3-dichloro-2-propyl) phosphate (BDCPP), bis(2-chloroethyl) phosphate (BCEP), dibutyl phosphate (DBUP), and bis(1-chloro-2-propyl) phosphate (BCPP). We conducted covariate-adjusted logistic and linear regressions to examine associations between log2-transformed and dichotomized OPE metabolite concentrations and obesity, body mass index (BMI), and waist circumference (WC), separately among 784 children (6-19 years) and 1672 adults (≥20 years). We also assessed heterogeneity of associations by sex.

RESULTS

DBUP concentrations were inversely associated with the prevalence odds of being obese vs. normal weight in children (adjusted Prevalence Odds Ratio, aPOR: 0.82, 95% Confidence Interval, 95% CI: 0.70, 0.95) and adults (aPOR: 0.83, 95% CI: 0.72, 0.96). DBUP was also significantly associated with lower BMI z-scores (β:-0.08, 95% CI:-0.17, 0.01) and WC (β:-0.71, 95% CI: -1.49, 0.07) in children. BCEP concentrations were associated with increased prevalence odds of being overweight vs. normal weight (aPOR: 1.15, 95% CI: 1.01, 1.32) among children; similar, albeit not statistically significant, relationships were observed with other child adiposity outcomes. Among adults, detectable BCPP concentrations were associated with increased prevalence odds of being obese vs. normal weight (aPOR: 1.70, 95% CI: 1.21, 2.38) and having a high vs. normal WC (aPOR: 1.51, 95% CI: 1.11, 2.07) as well as higher BMI (β: 1.31, 95% CI: 0.30, 2.33). Other OPE metabolites were not consistently associated with adiposity measures among adults. Although associations of BCPP exposure with adiposity outcomes were generally inverse among boys, but not girls, we did not observe consistent evidence of sexually-dimorphic associations for other OPE metabolites.

CONCLUSIONS

Exposure to select OPEs may be differentially associated with body size among children and adults. Given the cross-sectional design of the present study, future prospective studies are needed to confirm these findings.

Prenatal exposure to organophosphate esters and behavioral development in young children in the Pregnancy, Infection, and Nutrition Study

Organophosphate esters (OPEs) are commonly used as plasticizers and flame retardants in consumer products, and exposure is relatively ubiquitous in most populations studied. This may be of concern as some OPEs may be neurotoxic, endocrine-disrupting, and interfere with behavioral development; however, observational evidence is limited. We used data from the Pregnancy, Infection, and Nutrition Study, a prospective birth cohort study, to investigate associations between maternal OPE metabolite concentrations during pregnancy and behavioral development in offspring. Women provided a urine sample during pregnancy that was analyzed for concentrations of OPE metabolites, including diphenyl phosphate (DPHP), bis(1,3-dichloro-2-propyl phosphate) (BDCIPP), isopropyl-phenyl phenyl phosphate (ip-PPP), and 1-hydroxyl-2-propyl bis(1-chloro-2-propyl) phosphate (BCIPHIPP). Offspring's behavioral development was assessed by the Behavioral Assessment System for Children (2nd Edition) (BASC-2) at approximately 36 months. Linear regression was used to estimate associations between tertiles in specific gravity-corrected OPE metabolite concentrations and children's scores on the BASC-2, adjusted for maternal age, maternal BMI, maternal race, maternal education, familial income, maternal depression, quality of the home environment, and sex. Higher BDCIPP concentrations were associated with higher scores on the Behavioral Symptoms Index (1st vs. 3rd tertile: β = 3.03; 95% CI = 0.40, 5.67) and Externalizing Problems (1st vs. 3rd tertile: β = 2.49; 95% CI: -0.12, 5.10) composites. Among BASC-2 scales, BDCIPP was most strongly associated with Withdrawal, Attention Problems, Depression, Hyperactivity, and Aggression. DPHP concentrations were also associated with higher scores on the Externalizing Problems and Behavioral Symptoms Index composites, but not as strongly as BDCIPP. Conversely, higher concentrations of ip-PPP were associated with fewer adverse behavioral symptoms, including an inverse association with the Internalizing Problems composite (1st vs. 3rd tertile: β = -3.74; 95% CI = -6.75, -0.74) and constituent scales. BCIPHIPP was not strongly associated with any measured behavioral outcomes. Our results suggest that greater maternal exposure to tris(1,3-dichloro-2-propyl phosphate) (TDCIPP, parent compound of BDCIPP) and, to a lesser degree, triphenyl phosphate (TPHP, parent compound of DPHP) during pregnancy is associated with adverse behavioral development in children. Our study contributes to the growing body of evidence pertaining to adverse developmental effects of prenatal OPE exposure and highlights the need for further research to characterize risks associated with this ubiquitous family of chemicals.

Characterization of the Fundulus heteroclitus embryo transcriptional response and development of a gene expression-based fingerprint of exposure for the alternative flame retardant, TBPH (bis (2-ethylhexyl)-tetrabromophthalate)

Although alternative Flame Retardant (FR) chemicals are expected to be safer than the legacy FRs they replace, their risks to human health and the environment are often poorly characterized. This study used a small volume, fish embryo system to reveal potential mechanisms of action and diagnostic exposure patterns for TBPH (bis (2-ethylhexyl)-tetrabromophthalate), a component of several widely-used commercial products. Two different concentration of TBPH were applied to sensitive early life stages of an ecologically important test species, Fundulus heteroclitus (Atlantic killifish), with a well-annotated genome. Exposed fish embryos were sampled for transcriptomics or chemical analysis of parent compound and primary metabolite or observed for development and survival through larval stage. Global transcript profiling using RNA-seq was conducted (n = 16 per treatment) to provide a non-targeted and statistically robust approach to characterize TBPH gene expression patterns. Transcriptomic analysis revealed a dose-response in the expression of genes associated with a surprisingly limited number of biological pathways, but included the aryl hydrocarbon receptor signal transduction pathway, which is known to respond to several toxicologically-important chemical classes. A transcriptional fingerprint using Random Forests was developed that was able to perfectly discriminate exposed vs. non-exposed individuals in test sets. These results suggest that TBPH has a relatively low potential for developmental toxicity (at least in fishes), despite concerns related to its structural similarities to endocrine disrupting chemicals and that the early life stage Fundulus system may provide a convenient test system for exposure characterization. More broadly, this study advances the usefulness of a biological testing and analysis system utilizing non-targeted transcriptomics profiling and early developmental endpoints that complements current screening methods to characterize chemicals of ecological and human health concern.

DNA damage and methylation induced by organophosphate flame retardants: Tris(2-chloroethyl) phosphate and tris(1-chloro-2-propyl) phosphate in human peripheral blood mononuclear cells

Phosphorus flame retardants are a group of chemicals that are used to slow or prevent the spread of fire. These compounds have been detected in different environments including human organism. In the present study, we have investigated DNA-damaging potential and effect on DNA methylation of tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCPP) in human peripheral blood mononuclear cells (PBMCs). In order to determine DNA damage and repair, the alkaline and neutral versions of the comet assay were used. The level of DNA methylation was determined with specific antibodies against methylated DNA. PBMCs were exposed to TCEP and TCPP at the concentrations in the range of 1-1000 µM for 24 h. We have observed that TCEP and TCPP induced DNA damage-DNA breaks and alkali-labile sites. All DNA damages were effectively repaired during 120-min repair incubation. The results have also shown that TCEP and TCPP decreased the level of DNA methylation in PBMCs. In the case of TCEP, this effect was observed at a very low concentration of 1 µM.

Electronics, interior decoration and cleaning patterns affect flame retardant levels in the dust from Dutch residences

Consumer products such as furniture foam and electronic device casings are treated with flame retardant chemicals (FRs) to prevent the spread of fire. Many FRs are able to leach out of a product and end up in house dust. FRs in house dust can be taken up by humans through inhalation, ingestion or dermal adsorption. This study aims to identify factors in the home environment that are associated with FR levels in house dust. House dust and a wide range of data on characteristics of electronics, including age and use, interior decoration, domestic house and cleaning patterns, were collected from 50 households in the Netherlands. Decabromodiphenyl ether (BDE209) and several organophosphate flame retardants were measured in dust at detection percentages ranging from 58 to 94%, with median concentrations ranging from 32 ng/g (resorcinol-bis(diphenyl)phosphate (PBDPP)) to 825 ng/g (tris(chloropropyl)phosphate (TCIPP)). For the first time, age, hours of operation and use of the standby function of electronic devices were found to affect FR levels in dust. We found that if the total number of electronic devices purchased before 2008 increased by 1 device, BDE209 levels in house dust significantly increased by 66%. In addition, house dust from homes with carpeted floors was significantly associated with a 70-80% lower concentration of several FRs compared to homes with smooth floors (e.g., laminate). Less frequent vacuum cleaning and dusting were significantly associated with 41 to 88% higher concentrations of several FRs in dust. These associations suggest that actions such as frequent vacuum cleaning and dusting as well as different FR regulations for electronic devices affect indoor exposure levels.

Neonatal triphenyl phosphate and its metabolite diphenyl phosphate exposure induce sex- and dose-dependent metabolic disruptions in adult mice

The widespread application of organophosphorous flame retardants (OPFRs) has led to considerable human exposure, with major concerns regarding their health risks. Herein, we investigate the effects of triphenyl phosphate (TPP), one of the most widely used OPFRs, and one of its main metabolite diphenyl phosphate (DPP) on the endocrine systems and metabolic profiles after neonatal exposure from postnatal days 1-10 at two dosages (2 and 200 μg per day). Both TPP and DPP had no negative effect on uterine weight, glucose tolerance, and estradiol. ¹H-NMR-based metabolomics revealed a sex-specific metabolic disturbance of TPP. Specifically, low dose of TPP altered the metabolic profiles of male mice while exerting no significant effects on female ones. Furthermore, a dose-dependent effect of TPP in male mice was observed, where a low toxicity dose up-regulated lipid-related metabolites, while a high toxicity dose down-regulated the pyruvate metabolism and TCA cycles. These results highlight the importance of carefully assessing the health impact of TPP on infants.

The association between urinary concentrations of phosphorous-containing flame retardant metabolites and semen parameters among men from a fertility clinic

BACKGROUND

The use of PFRs has steadily increased as brominated compounds have been or are being phased out. Human exposure is widespread and animal studies have shown adverse impacts on male reproduction, but human data are lacking.

OBJECTIVE

To study the associations between urinary concentrations of phosphorous-containing flame retardant (PFR) metabolites and semen parameters.

METHODS

A subset of 220 men from an existing longitudinal cohort of couples were recruited from Massachusetts General Hospital fertility clinic between 2005 and 2015. Semen parameters included sperm count, concentration, motility, and morphology; some men had samples measured from multiple clinic visits (up to five visits; n = 269 semen samples). Metabolites [bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), diphenyl phosphate (DPHP), isopropylphenyl phenyl phosphate (ip-PPP), tert-butylphenyl phenyl phosphate (tb-PPP) and bis(1-chloro-2-propyl) phosphate (BCIPP)] were measured in urine samples (between one and five urine samples per participant; n = 355 urine samples). Semen parameters were evaluated continuously and dichotomized for models. Metabolites were assessed for associations with semen parameters as continuous and categorized into quartiles using multivariable generalized mixed models, adjusted for specific gravity, age, BMI, smoking, and abstinence period.

RESULTS

Metabolites BDCIPP, DPHP, and ip-PPP were detected in a high proportion of urine samples (85%, 86%, and 65% respectively). Concentrations varied by season of collection, particularly for BDCIPP where samples collected in the summer were approximately 2-fold higher than concentrations of other seasons (p < 0.0001). The odds of having a sperm count less than 39 mil/ejaculate decreased by 20% for increasing BDCIPP concentrations (p = 0.04). When regressing semen parameters on PFR metabolite quartiles, some negative associations were observed for individual quartiles among sample volume and morphology, but overall associations were weak and inconsistent.

CONCLUSION

Detection rates were high for BDCIPP, DPHP, and ip-PPP. We did not observe consistent associations between PFR metabolites and semen parameters. Due to the high prevalence of exposure, further investigation of other potential health effects should be conducted.

Transcriptome profiling of HepG2 cells exposed to the flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)

The flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), has been receiving great interest given its superior fire protection properties, and its predicted low level of persistence, bioaccumulation, and toxicity. However, empirical toxicological data that are essential for a complete hazard assessment are severely lacking. In this study, we attempted to identify the potential toxicological modes of action by transcriptome (RNA-seq) profiling of the human liver hepatocellular carcinoma cell line, HepG2. Such insight may help in identifying compounds of concern and potential toxicological phenotypes. DOPO was found to have little cytotoxic potential, with lower effective concentrations compared to other flame retardants studied in the same cell line. Differentially expressed genes revealed a wide range of molecular effects including changes in protein, energy, DNA, and lipid metabolism, along with changes in cellular stress response pathways. In response to 250 μM DOPO, the most perturbed biological processes were fatty acid metabolism, androgen metabolism, glucose transport, and renal function and development, which is in agreement with other studies that observed similar effects of other flame retardants in other species. However, treatment with 2.5 μM DOPO resulted in very few differentially expressed genes and failed to indicate any potential effects on biology, despite such concentrations likely being orders of magnitude greater than would be encountered in the environment. This, together with the low levels of cytotoxicity, supports the potential replacement of the current flame retardants by DOPO, although further studies are needed to establish the nephrotoxicity and endocrine disruption of DOPO.

Current-use flame retardants: Maternal exposure and neurodevelopment in children of the CHAMACOS cohort

Flame retardants are commonly used in consumer products found in U.S. households. Restrictions on the use of polybrominated diphenyl ether flame retardants have resulted in increased use of replacement chemicals, including Firemaster 550^® (FM 550^®) and organophosphate flame retardants (PFRs): tris(1,3- dichloro-2-propyl) phosphate (TDCIPP); tris(chloropropyl) phosphate (TCIPP); tris(2-chloroethyl) phosphate (TCEP); and triphenyl phosphate (TPHP). Animal research suggests that PFRs may affect neurodevelopment through noncholinergic mechanisms similar to some organophosphate (OP) pesticides. Despite the widespread presence of these compounds in home environments, and their structural similarity to neurotoxic OP pesticides, understanding of human exposure and health effects of PFRs is limited. We measured four urinary PFR metabolites from pregnant women in the CHAMACOS birth cohort study (n = 310) and assessed neurodevelopment of their children at age 7. Metabolites of TDCIPP (BDCIPP: bis(1,3-dichloro-2-propyl) phosphate) and TPHP (DPHP: diphenyl phosphate) were detected in >75% of urine samples, and isopropylphenyl phenyl phosphate (ip-PPP), a metabolite of one component of FM 550^®, was detected in 72% of urine samples. We observed decreases of 2.9 points (95% Confidence Interval (CI): -6.3, 0.5) and 3.9 points (95% CI: -7.3,-0.5) in Full-Scale intelligence quotient and Working Memory, respectively, for each ten-fold increase in DPHP in adjusted regression models (n = 248). Decreases in Full-Scale IQ and Working Memory were greater in models of the molar sum of the PFR metabolites compared to the DPHP models. This is the first study to examine PFR and FM 550^® exposures and potential neurodevelopmental outcomes in pregnant women and children. Additional research is warranted.

Parallel in vivo and in vitro transcriptomics analysis reveals calcium and zinc signalling in the brain as sensitive targets of HBCD neurotoxicity

Hexabromocyclododecane (HBCD) is a brominated flame retardant (BFR) that accumulates in humans and affects the nervous system. To elucidate the mechanisms of HBCD neurotoxicity, we used transcriptomic profiling in brains of female mice exposed through their diet to HBCD (199 mg/kg body weight per day) for 28 days and compared with those of neuronal N2A and NSC-19 cell lines exposed to 1 or 2 µM HBCD. Similar pathways and functions were affected both in vivo and in vitro, including Ca²⁺ and Zn²⁺ signalling, glutamatergic neuron activity, apoptosis, and oxidative stress. Release of cytosolic free Zn²⁺ by HBCD was confirmed in N2A cells. This Zn²⁺ release was partially quenched by the antioxidant N-acetyl cysteine indicating that, in accordance with transcriptomic analysis, free radical formation is involved in HBCD toxicity. To investigate the effects of HBCD in excitable cells, we isolated mouse hippocampal neurons and monitored Ca²⁺ signalling triggered by extracellular glutamate or zinc, which are co-released pre-synaptically to trigger postsynaptic signalling. In control cells application of zinc or glutamate triggered a rapid rise of intracellular [Ca²⁺]. Treatment of the cultures with 1 µM of HBCD was sufficient to reduce the glutamate-dependent Ca²⁺ signal by 50%. The effect of HBCD on zinc-dependent Ca²⁺ signalling was even more pronounced, resulting in the reduction of the Ca²⁺ signal with 86% inhibition at 1 µM HBCD. Our results show that low concentrations of HBCD affect neural signalling in mouse brain acting through dysregulation of Ca²⁺ and Zn²⁺ homeostasis.

Estrogenicity assessment of membrane concentrates from landfill leachate treated by the UV-Fenton process using a human breast carcinoma cell line

Membrane concentrates (MCs) are generated when membranes are used to concentrate landfill leachate. It contains high concentrations of inorganic and organic environmental pollutants, which are highly toxic and carcinogenic. In this paper, the proliferation effect (PE) from MC before and after treatment with the UV-Fenton process was assessed using the human breast carcinoma cell line MCF-7. The highest value of 116% was found at 5% (v/v) concentration after a 10 min reaction. Phthalic acid esters (PAEs) play an important role in the MC estrogenicity. Estrogen simulation solutions (ESS) of PAEs were prepared to simulate the changes in estrogenic active substances during the UV-Fenton process. The ESS degradation conformed to the first-order kinetics model. The estrogenicity decreased after an initial increase until it acted in a non-estrogenic manner. Convincingly, the intermediates were determined by GC/MS, and the estrogenicity was assessed during the degradation process. The estrogenicity was highly related to the generation of intermediates and the PAE concentration. The results provide guidance for UV-Fenton application in MC estrogenicity reduction.

Flame retardants and their metabolites in the homes and urine of pregnant women residing in California (the CHAMACOS cohort)

Organophosphate flame retardants (PFRs), used in consumer products since the 1970s, persist in the environment. Restrictions on penta-polybrominated diphenyl ether (PBDE) flame retardants resulted in increased use of Firemaster^® 550 (FM^® 550), and the organophosphate triesters: tris(1,3- dichloro-2-propyl) phosphate (TDCIPP); tris(chloropropyl) phosphate (TCIPP); tris(2-chloroethyl) phosphate (TCEP); and triphenyl phosphate (TPHP). The objectives of this study were to (1) identify determinants of flame retardants (4 PFRs, PentaBDEs and FM^® 550) in house dust, (2) measure urinary PFR metabolites in pregnant women, and (3) estimate health risks from PFR exposure. We measured flame retardants in house dust (n = 125) and metabolites in urine (n = 310) collected in 2000-2001 from Mexican American women participating in the CHAMACOS birth cohort study in California. We detected FM^® 550 and PFRs, including two (TCEP and TDCIPP) known to the state of California to cause cancer, in most dust samples. The maximum TCEP and TDCIPP dust levels were among the highest ever reported although the median levels were generally lower compared to other U.S. cohorts. Metabolites of TDCIPP (BDCIPP: bis(1,3-dichloro-2-propyl) phosphate) and TPHP (DPHP: diphenyl phosphate) were detected in 78% and 79% of prenatal urine samples, respectively. We found a weak but positive correlation between TPHP in dust and DPHP in 124 paired prenatal urine samples (Spearman rho = 0.17; p = 0.06). These results provide information on PFR exposure and risk in pregnant women from the early 2000's and are also valuable to assess trends in exposure and risk given changing fire safety regulations and concomitant changes in chemical flame retardant use.