Effects of primary metabolites of organophosphate flame retardants on transcriptional activity via human nuclear receptors

Estimated daily intake and cumulative risk assessment of organophosphate esters and associations with DNA damage among e-waste workers in Hong Kong

Organophosphate esters (OPEs) are extensively used as additives in various products, including electronic equipment, which becomes e-waste when obsolete. Nevertheless, no study has evaluated OPEs exposure levels and the related health risks among e-waste workers in Hong Kong. Therefore, 201 first-spot morning urine samples were collected from 101 e-waste workers and 100 office workers to compare eight urinary OPE metabolites (mOPEs) levels in these groups. The concentrations of six mOPEs were similar in e-waste workers and office workers, except for significantly higher levels of diphenyl phosphate (DPHP) in e-waste workers and bis(1-chloro-2propyl) phosphate (BCIPP) in office workers. Spearman correlation analysis showed that most non-chlorinated mOPEs were correlated with each other in e-waste workers (i.e., nine out of ten pairs, including di-p-cresyl phosphate (DpCP) and di-o-cresyl phosphate (DoCP), DpCP and bis(2-butoxyethyl) phosphate (BBOEP), DpCP and DPHP, DpCP and dibutyl phosphate (DBP), DoCP and BBOEP, DoCP and DPHP, DoCP and DBP, BBOEP and DPHP, DPHP and DBP), indicating that handling e-waste could be the exposure source of specific OPEs. The median values of estimated daily intake (EDI) and hazard quotient (HQ) suggested that the health risks from OPEs exposures were under the recommended thresholds. However, linear regression models, Quantile g-computation, and Bayesian kernel machine regression found that urinary mOPEs elevated 8-hydroxy-2-deoxyguanosine (8-OhdG) levels individually or as a mixture, in which DPHP contributed prominently. In conclusion, although e-waste might not elevate the internal OPEs levels among the participating Hong Kong e-waste workers, attention should be paid to the potential DNA damage stimulated by OPEs under the currently recommended thresholds.

OPFR removal by white rot fungi: screening of removers and approach to the removal mechanism

The persistent presence of organophosphate flame retardants (OPFRs) in wastewater (WW) effluents raises significant environmental and health concerns, highlighting the limitations of conventional treatments for their remotion. Fungi, especially white rot fungi (WRF), offer a promising alternative for OPFR removal. This study sought to identify fungal candidates (from a selection of four WRF and two Ascomycota fungi) capable of effectively removing five frequently detected OPFRs in WW: tributyl phosphate (TnBP), tributoxy ethyl phosphate (TBEP), trichloroethyl phosphate (TCEP), trichloro propyl phosphate (TCPP) and triethyl phosphate (TEP). The objective was to develop a co-culture approach for WW treatment, while also addressing the utilization of less assimilable carbon sources present in WW. Research was conducted on carbon source uptake and OPFR removal by all fungal candidates, while the top degraders were analyzed for biomass sorption contribution. Additionally, the enzymatic systems involved in OPFR degradation were identified, along with toxicity of samples after fungal contact. Acetate (1.4 g·L-1), simulating less assimilable organic matter in the carbon source uptake study, was eliminated by all tested fungi in 4 days. However, during the initial screening where the removal of four OPFRs (excluding TCPP) was tested, WRF outperformed Ascomycota fungi. Ganoderma lucidum and Trametes versicolor removed over 90% of TnBP and TBEP within 4 days, with Pleorotus ostreatus and Pycnoporus sanguineus also displaying effective removal. TCEP removal was challenging, with only G. lucidum achieving partial removal (47%). A subsequent screening with selected WRF and the addition of TCPP revealed TCPP's greater susceptibility to degradation compared to TCEP, with T. versicolor exhibiting the highest removal efficiency (77%). This observation, plus the poor degradation of TEP by all fungal candidates suggests that polarity of an OPFR inversely correlates with its susceptibility to fungal degradation. Sorption studies confirmed the ability of top-performing fungi of each selected OPFR to predominantly degrade them. Enzymatic system tests identified the CYP450 intracellular system responsible for OPFR degradation, so reactions of hydroxylation, dealkylation and dehalogenation are possibly involved in the degradation pathway. Finally, toxicity tests revealed transformation products obtained by fungal degradation to be more toxic than the parent compounds, emphasizing the need to identify them and their toxicity contributions. Overall, this study provides valuable insights into OPFR degradation by WRF, with implications for future WW treatment using mixed consortia, emphasizing the importance of reducing generated toxicity.

Organophosphate triesters and their diester degradation products in the atmosphere-A critical review

Organophosphate triesters (tri-OPEs) have found substantial use as plasticizers and flame retardants in commercial and industrial products. Despite upcoming potential restrictions on use of OPEs, widespread environmental contamination is likely for the foreseeable future. Organophosphate diesters (di-OPEs) are known biotic or abiotic degradation products of tri-OPEs. In addition, direct use of di-OPEs as commercial products also contributes to their presence in the atmosphere. We review the available data on contamination with tri-OPEs and di-OPEs in both indoor and outdoor air. Concentrations of tri-OPEs in indoor air exceed those in outdoor air. The widespread discovery of tri-OPE traces in polar regions and oceans is noteworthy and is evidence that they undergo long-range transport. There are only two studies on di-OPEs in outdoor air and no studies on di-OPEs in indoor air until now. Current research on di-OPEs in indoor and outdoor air is urgently needed, especially in countries with potentially high exposure to di-OPEs such as the UK and the US. Di-OPE concentrations are higher at e-waste dismantling areas than at surrounding area. We also summarise the methods employed for sampling and analysis of OPEs in the atmosphere and assess the relative contribution to atmospheric concentrations of di-OPEs made by environmental degradation of triesters, compared to the presence of diesters as by-products in commercial triester products. Finally, we identify shortcomings of current research and provide suggestions for future research.

Applying a modified systematic review and integrated assessment framework (SYRINA) - a case study on triphenyl phosphate

This work presents a case study in applying a systematic review framework (SYRINA) to the identification of chemicals as endocrine disruptors. The suitability and performance of the framework is tested with regard to the widely accepted World Health Organization definition of an endocrine disruptor (ED). The endocrine disrupting potential of triphenyl phosphate (TPP), a well-studied flame retardant reported to exhibit various endocrine related effects was assessed. We followed the 7 steps of the SYRINA framework, articulating the research objective via Populations, Exposures, Comparators, Outcomes (PECO) statements, performed literature search and screening, conducted study evaluation, performed data extraction and summarized and integrated the evidence. Overall, 66 studies, consisting of in vivo, in vitro and epidemiological data, were included. We concluded that triphenyl phosphate could be identified as an ED based on metabolic disruption and reproductive function. We found that the tools used in this case study and the optimizations performed on the framework were suitable to assess properties of EDs. A number of challenges and areas for methodological development in systematic appraisal of evidence relating to endocrine disrupting potential were identified; significant time and effort were needed for the analysis of in vitro mechanistic data in this case study, thus increasing the workload and time needed to perform the systematic review process. Further research and development of this framework with regards to grey literature (non-peer-reviewed literature) search, harmonization of study evaluation methods, more consistent evidence integration approaches and a pre-defined method to assess links between adverse effect and endocrine activity are recommended. It would also be advantageous to conduct more case studies for a chemical with less data than TPP.

Developmental organophosphate flame retardant exposure disrupts adult hippocampal neurogenesis in Wistar rats

Organophosphate flame retardant (OPFR) contamination is ubiquitous and bio-monitoring studies have shown that human exposure is widespread and may be unavoidable. OPFRs bear structural similarities to known neurotoxicants such as organophosphate insecticides and have been shown to have both endocrine disrupting and developmental neurotoxic effects. The perinatal period in rodents represents a critical period in the organization of the developing nervous system and insults during this time can impart profound changes on the trajectory of neural development and function, lasting into adulthood. Adult hippocampal neurogenesis (AHN) facilitates dentate gyrus function and broader hippocampal circuit activity in adults; however, the neurogenic potential of this process in adulthood is vulnerable to disruption by exogenous factors during early life. We sought to assess the impact of OPFRs on AHN in offspring of dams exposed during gestation and lactation. Results indicate that developmental OPFR exposure has significant, sex specific impacts on multiple markers of AHN in the dentate gyrus of rats. In males, OPFR exposure significantly reduced the number of neural progenitors the number of new/immature neurons and reduced dentate gyrus volume. In females, exposure increased the number of neural progenitors, decreased the number of new/immature neurons, but had no significant effect on dentate gyrus volume. These results further elucidate the developmental neurotoxic properties of OPFRs, emphasize the long-term impact of early life OPFR exposure on neural processes, and highlight the importance of including sex as a biological variable in neurotoxicology research.

Emerging organophosphate ester resorcinol bis(diphenyl phosphate) exerts estrogenic effects via estrogen receptor pathways

Environmental occurrence and human exposure of emerging organophosphate esters (eOPEs) have increased significantly in recent years. Resorcinol bis(diphenyl) phosphate (RDP) is one of the major eOPEs detected in indoor dust, but the knowledge on its toxicities and health risks is rather limited. In this study, we investigated the in vitro estrogenic effects and underlying mechanism of RDP in comparison with a legacy OPE triphenyl phosphate (TPHP). Our results showed that RDP promoted MCF-7 cell proliferation with the lowest effect concentration of 2.5 μM, and the maximum enhancement of 1.6 folds is greater than that of TPHP (1.3 folds). The effect was inhibited completely by an estrogen receptor (ER) antagonist, suggesting that ER activation was responsible for the enhancement. In luciferase reporter gene assays both RDP and TPHP activated ER transcriptional activity at 2.5 μM, but RDP activity was higher than TPHP. Competitive fluorescence binding assays showed that RDP bound to ER with an IC10 of 0.26 μM, which is 20 folds lower than TPHP (5.6 μM). Molecular docking simulation revealed that both RDP and TPHP interacted with ER at the binding pocket of estradiol, although the hydrogen bonds were different. Taken together, RDP exerted stronger estrogenic effects than TPHP through ER-mediated pathways and may pose more health risks.

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.

A critical review on sources and environmental behavior of organophosphorus flame retardants in the soil: Current knowledge and future perspectives

Organophosphorus flame retardants (OPFRs) have been widely used in industrial and commercial applications. Unfortunately, the chemical constituents of OPFRs, organophosphate esters (OPEs), which have been proven to be carcinogenic and biotoxic, can release into the environment and pose potential risks to human health. This paper reviews the research progress of OPEs in the soil through bibliometric analysis and comprehensively elaborates on their pollution status, potential sources, and environmental behaviors. The OPE pollution is widely distributed in the soil at concentrations ranging from several to tens of thousands of ng/g dw. Some novel OPEs, newly discovered OPEs in the environment in recent years, are also detected. OPE concentrations vary substantially among landuses, and waste processing areas are important point sources of OPE pollution in the soil. Emission source intensity, physicochemical properties of compounds, and soil properties play important roles in the transfer process of OPEs in the soil. Biodegradation, especially microbial degradation, has potential application prospects in the remediation of OPE-contaminated soil. Brevibacillus brevis, Sphingomonas, Sphingopyxis, Rhodococcus, and other microorganisms can degrade some OPEs. This review helps clarify the pollution status of OPEs in the soil and highlights perspectives for future research.

Sex-specific effects of prenatal organophosphate ester (OPE) metabolite mixtures and adverse infant birth outcomes in the maternal and developmental risks from environmental and social stressors (MADRES) pregnancy cohort

BACKGROUND

Organophosphate esters (OPEs) are used as flame retardants and plasticizers in various consumer products. Limited prior research suggests sex-specific effects of prenatal OPE exposures on fetal development. We evaluated overall and sex-specific associations between prenatal OPE exposures and gestational age (GA) at birth and birthweight for gestational age (BW for GA) z-scores among the predominately low-income, Hispanic MADRES cohort.

METHODS

Nine OPE metabolite concentrations were measured in 421 maternal urine samples collected during a third trimester visit (GA = 31.5 ± 2.0 weeks). We examined associations between single urinary OPE metabolites and GA at birth and BW for GA z-scores using linear regression models and Generalized Additive Models (GAMs) and effects from OPE mixtures using Bayesian Kernel Machine Regression (BKMR). We also assessed sex-specific differences in single metabolite analyses by evaluating statistical interactions and stratifying by sex.

RESULTS

We did not find significant associations between individual OPE metabolites and birth outcomes in the full infant sample; however, we found that higher bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) was associated with earlier GA at birth among male infants (p = 0.04), and a nonlinear, inverted U-shape association between the sum of dibutyl phosphate and di-isobutyl phosphate (DNBP + DIBP) and GA at birth among female infants (p = 0.03). In mixtures analysis, higher OPE metabolite mixture exposures was associated with lower GA at birth, which was primarily driven by female infants. No associations were observed between OPE mixtures and BW for GA z-scores.

CONCLUSION

Higher BDCIPP and DNBP + DIBP concentrations were associated with earlier GA at birth among male and female infants, respectively. Higher exposure to OPE mixtures was associated with earlier GA at birth, particularly among female infants. However, we saw no associations between prenatal OPEs and BW for GA. Our results suggest sex-specific impacts of prenatal OPE exposures on GA at birth.

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.

Organophosphate tri- and diesters in source water supply and drinking water treatment systems of a metropolitan city in China

The water contaminations with organophosphate triesters (tri-OPEs) and diesters (di-OPEs) have recently provoked concern. However, the distributions of these compounds in natural water sources and artificial water treatment facilities are poorly characterized. A comprehensive study was therefore performed to measure their concentrations in a water source, a long-distance water pipeline, and a drinking water treatment plant (DWTP). Eight tri-OPEs and 3 di-OPEs were found to be widely distributed, with total concentrations in source water and pipelines ranging from 290.6 to 843.9 ng/L. The most abundant pollutants were tris(1-chloro-2-propyl) phosphate (TCPP), triethyl phosphate, tri-n-butyl phosphate (TnBP), and diphenyl phosphate (DPhP). Di-OPEs appeared to be removed less efficiently in the DWTP than the parent tri-OPEs, and the elimination efficiencies of tri-OPEs were structure-dependent. Long-distance pipeline transportation had no significant effect on the distributions of tri- and di-OPEs. Statistical analysis suggested that the sources of di-OPEs and the corresponding tri-OPEs differed, as did those of DPhP and di-n-butyl phosphate. A risk analysis indicated that tri-OPEs present limited ecological risks that are mainly due to TnBP and TCPP, and that the human health risks of tri-OPEs are negligible. However, di-OPEs (especially DPhP) may increase these risks. Further studies on the risks posed by di-OPEs in aquatic environments are therefore needed.

Association between Organophosphate Ester Exposure and Insulin Resistance with Glycometabolic Disorders among Older Chinese Adults 60-69 Years of Age: Evidence from the China BAPE Study

BACKGROUND

Organophosphate esters (OPEs) are common endocrine-disrupting chemicals, and OPE exposure may be associated with type 2 diabetes (T2D). However, greater knowledge regarding the biomolecular intermediators underlying the impact of OPEs on T2D in humans are needed to understand biological etiology.

OBJECTIVES

We explored the associations between OPE exposure and glycometabolic markers among older Chinese adults 60-69 years of age to elucidate the underlying mechanisms using a multi-omics approach.

METHODS

This was a longitudinal panel study comprising 76 healthy participants 60-69 years of age who lived in Jinan city of northern China. The study was conducted once every month for 5 months, from September 2018 to January 2019. We measured a total of 17 OPEs in the blood, 11 OPE metabolites in urine, and 4 glycometabolic markers (fasting plasma glucose, glycated serum protein, fasting insulin, and homeostatic model assessment for insulin resistance). The blood transcriptome and serum/urine metabolome were also evaluated. The associations between individual OPEs and glycometabolic markers were explored. An adverse outcome pathway (AOP) was established to determine the biomolecules mediating the associations.

RESULTS

Exposure to five OPEs and OPE metabolites (trimethylolpropane phosphate, triphenyl phosphate, tri-iso-butyl phosphate, dibutyl phosphate, and diphenyl phosphate) was associated with increased levels of glycometabolic markers. The mixture effect analysis further indicated the adverse effect of OPE mixtures. Multi-omics analyses revealed that the endogenous changes in the transcriptional and metabolic levels were associated with OPE exposure. The putative AOPs model suggested that triggers of molecular initiation events (e.g., insulin receptor and glucose transporter type 4) with subsequent key events, including disruptions in signal transduction pathways (e.g., phosphatidylinositol 3-kinase/protein kinase B and insulin secretion signaling) and biological functions (glucose uptake and insulin secretion), may constitute the diabetogenic effects of OPEs.

DISCUSSION

OPEs are associated with the elevated risk of T2D among older Chinese adults 60-69 years of age. Implementing OPE exposure reduction strategies may help reduce the T2D burden among these individuals, if the relationship is causal. https://doi.org/10.1289/EHP11896.

Gestational organophosphate ester exposure and preschool attention-deficit/hyperactivity disorder in the Norwegian Mother, Father, and Child cohort study

BACKGROUND

Attention-deficit/hyperactivity-disorder (ADHD) is a leading neurodevelopmental disorder in children worldwide; however, few modifiable risk factors have been identified. Organophosphate esters (OPEs) are ubiquitous chemical compounds that are increasingly prevalent as a replacement for other regulated chemicals. Current research has linked OPEs to neurodevelopmental deficits. The purpose of this study was to assess gestational OPE exposure on clinically-assessed ADHD in children at age 3 years.

METHODS

In this nested case-control study within the Norwegian Mother, Father, and Child Cohort study, we evaluated the impact of OPE exposure at 17 weeks' gestation on preschool-age ADHD. Between 2007 and 2011, 260 ADHD cases were identified using the Preschool Age Psychiatric Assessment and compared to a birth-year-stratified control group of 549 children. We categorized bis(2-butoxyethyl) phosphate (BBOEP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) as values < limit of detection (LOD) (BBOEP N = 386, BDCIPP N = 632), ≥LOD but < limit of quantification (LOQ) (BBOEP N = 413; BDCIPP N = 75), or above LOQ (BBOEP N = 70; BDCIPP N = 102). Diphenyl phosphate (DPhP) and di-n-butyl phosphate (DnBP) were categorized as quartiles and also modeled with a log10 linear term. We estimated multivariable adjusted odds ratios (ORs) using logistic regression and examined modification by sex using an augmented product term approach.

RESULTS

Mothers in the 3rd DnBP quartile had 1.71 times the odds of having a child with ADHD compared to the 1st quartile (95%CI: 1.13, 2.58); a similar trend was observed for log10 DnBP and ADHD. Mothers with BDCIPP ≥ LOD but < LOQ had 1.39 times the odds of having a child with ADHD compared to those with BDCIPP < LOD (95%CI: 0.83, 2.31). Girls had lower odds of ADHD with increasing BBOEP exposure (log10 OR: 0.55 (95%CI: 0.37, 0.93), however boys had a weakly increased odds (log10 OR: 1.25 (95%CI: 0.74, 2.11) p-interaction = 0.01].

CONCLUSIONS

We found modest increased odds of preschool ADHD with higher DnBP and BDCIPP exposure.

Tris(1,3-dichloro-2-propyl) phosphate is a metabolism-disrupting chemical in male mice

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate flame retardant. The primary TDCPP metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP), is detectable in the urine of over 90 % of Americans. Epidemiological studies show sex-specific associations between urinary BDCPP levels and metabolic syndrome, which is an established risk factor for type 2 diabetes, heart disease, and stroke. We used a mouse model to determine whether TDCPP exposure disrupts glucose homeostasis. Six-week old male and female C57BL/6J mice were given ad libitum access to diets containing vehicle (0.1 % DMSO) and TDCPP resulting in the following treatment groups: 0 mg/kg/day, 0.02 mg/kg/day, 1 mg/kg/day, or 100 mg/kg/day. After being on the experimental diet for five weeks without interruption, body composition was analyzed, glucose and insulin tolerance tests were performed, and fasting glucose and insulin levels were quantified. TDCPP at 100 mg/kg/day caused male sex-specific adiposity, fasting hyperglycemia, and insulin resistance. TDCPP-induced modulation of nuclear receptor activation was investigated using an in vitro screen to identify potential mechanisms of metabolic disruption. TDCPP activated farnesoid X receptor (FXR) and pregnane X receptor (PXR), and inhibited the androgen receptor (AR). PXR target genes, but not FXR target genes, were upregulated in livers from mice exposed to 100 mg TDCPP/kg/day. Interestingly, PXR target genes were differentially expressed in livers from both males and females. It remains to be determined whether TDCPP-induced metabolic disruption occurs via modulation of nuclear receptor activity. Taken together, these studies build upon the association of TDCPP exposure and metabolic syndrome in humans by identifying sex-specific effects of TDCPP on glucose homeostasis in mice.

Triphenyl phosphate proved more potent than its metabolite diphenyl phosphate in inducing hepatic insulin resistance through endoplasmic reticulum stress

Triphenyl phosphate (TPHP) is a widely used flame retardant and plasticizer and has been detected extensively in environmental media, wildlife and human bodies. Several epidemiological and animal studies have revealed that TPHP exposure is positively associated with glucose homeostasis disruption and diabetes. However, the effects of TPHP on hepatic glucose homeostasis and the underlying mechanisms remain unclear. The present work aimed to investigate the cytotoxicity and glucose metabolism disruption of TPHP and its metabolite diphenyl phosphate (DPHP) within hepatocytes. The cell viability assay undertaken on human normal liver (L02) cells showed that TPHP exhibited more potent hepatotoxicity than DPHP. RNA sequencing (RNA-seq) data showed that TPHP and DPHP presented different modes of toxic action. Insulin resistance is one of the predominant toxicities for TPHP, but not for DPHP. The insulin-stimulated glucose uptake and glycogen synthesis were impaired by TPHP, while DPHP exhibited no significant impairment on these factors. TPHP exposure induced endoplasmic reticulum (ER) stress, and the ER stress antagonist 4-PBA restored the impairment of insulin-stimulated glucose uptake and glycogen synthesis induced by TPHP. TPHP could also induce liver ER stress and insulin resistance in mice. Taken together, the results suggested that TPHP induces more potent insulin resistance through ER stress than its metabolite DPHP.

Organophosphate tri-esters and di-esters in drinking water and surface water from the Pearl River Delta, South China: Implications for human exposure

Some organophosphate di-esters (di-OPEs) have been found to be more toxic than their respective tri-esters. The environmental occurrence of di-OPEs remains largely unclear. A total of 106 water samples, including 56 drinking water (bottled, barreled, and tap water) and 50 surface water (lake and river) samples were collected and analyzed for 10 organophosphate tri-esters (tri-OPEs) and 7 di-OPEs. The concentrations (range (median)) of ∑₇di-OPE were 2.8-22 (9.7), 1.1-5.8 (2.6), 3.7-250 (120), 13-410 (220), and 92-930 (210) ng/L in bottled water, barreled water, tap water, lake water, and river water, respectively. In all types of water samples, tris(1-chloro-2-propyl) phosphate was the dominant tri-OPE compound. Diphenyl phosphate was the predominant di-OPE compound in tap water and surface water, while di-n-butyl phosphate and bis(2-ethylhexyl) phosphate was the dominant compound in bottled water and barreled water, respectively. Source analysis suggested diverse sources of di-OPEs, including industrial applications, effluents of municipal wastewater treatment plants, degradation from tri-OPEs during production/usage and under natural environmental conditions. The non-carcinogenic and carcinogenic risks of OPEs were lower than the theoretical threshold of risk, indicating the human health risks to OPEs via drinking water consumption were negligible. More studies are needed to explore environmental behaviors of di-OPEs in the aquatic environment and to investigate ecological risks.

Tox21-Based Comparative Analyses for the Identification of Potential Toxic Effects of Environmental Pollutants

Chemical pollution has become a prominent environmental problem. In recent years, quantitative high-throughput screening (qHTS) assays have been developed for the fast assessment of chemicals' toxic effects. Toxicology in the 21st Century (Tox21) is a well-known and continuously developing qHTS project. Recent reports utilizing Tox21 data have mainly focused on setting up mathematical models for in vivo toxicity predictions, with less attention to intuitive qHTS data visualization. In this study, we attempted to reveal and summarize the toxic effects of environmental pollutants by analyzing and visualizing Tox21 qHTS data. Via PubMed text mining, toxicity/structure clustering, and manual classification, we detected a total of 158 chemicals of environmental concern (COECs) from the Tox21 library that we classified into 13 COEC groups based on structure and activity similarities. By visualizing these COEC groups' bioactivities, we demonstrated that COECs frequently displayed androgen and progesterone antagonistic effects, xenobiotic receptor agonistic roles, and mitochondrial toxicity. We also revealed many other potential targets of the 13 COEC groups, which were not well illustrated yet, and that current Tox21 assays may not correctly classify known teratogens. In conclusion, we provide a feasible method to intuitively understand qHTS data.

Exposure of men living in the greater Montreal area to organophosphate esters: Association with hormonal balance and semen quality

Exposure to organophosphate esters (OPEs) is extensive, yet few studies have investigated their association with hormone levels or semen quality. Here, we studied the association between urinary concentrations of OPEs and their metabolites with hormone levels and semen parameters in men (n = 117) predominantly in the 20-29 years age range who were recruited from the greater Montreal area between 2009 and 2012. Urine, serum, and semen samples were analyzed for OPEs, hormones, and semen quality, respectively. Bis(2-ethylhexyl) phosphate (BEHP), bis(2,4-di-tert-butylphenyl) hydrogen phosphate (B2,4DtBPP), tris(2-chloroisopropyl) phosphate (TCIPP), diphenyl phosphate (DPHP), bis (2-butoxyethyl) phosphate (BBOEP) and di-cresyl phosphate (DCPs) were detected in urine at a frequency ≥ 95%. The highest geometric mean concentration was observed for DPHP (18.54 ng/mL) and the second highest was B2,4DtBPP (6.23 ng/mL). Associations between a doubling in analyte concentrations in urine and hormone levels and semen quality parameters were estimated using multivariable linear regression. B2,4DtBPP levels were positively associated with total T3 (β = 0.09; 95% CI: 0.01, 0.17). DPHP was inversely associated with estradiol (β = -2.56; 95% CI: -5.00, -0.17), and TCIPP was inversely associated with testosterone (β = -0.78; 95% CI: -1.40, -0.17). Concentrations of BCIPP were inversely associated with sperm concentrations (β = -7.76; 95% CI: -14.40, -0.61), progressive motility (β = - 4.98; 95% CI: -8.71, -1.09), and the sperm motility index (β = -9.72; 95% CI: -17.71, -0.96). In contrast, urinary DPHP concentrations were positively associated with the sperm motility (β = 4.37; 95% CI: 0.76, 8.12) and fertility indices (β = 6.64; 95% CI: 1.96, 11.53). Thus, OPE detection rates were high and exposure to several OPEs was associated with altered hormone levels and semen parameters. The possibility that OPEs affect male reproduction warrants further investigation.

Occupational exposure to organophosphate esters in e-waste dismantling workers: Risk assessment and influencing factors screening

Organophosphate esters (OPEs) are increasingly added in electronic products as alternative flame retardants, which may result in high occupational exposure of electronic waste recycling employees. This study investigated occupational exposure to OPEs in an e-waste recycling site in northern China, with intent to explore the impacts of occupational exposure and dismantling manipulation mode. Human urine samples from three sites with different distances from the core dismantling area, including employees from family workshops and plants with centralized management and residents from nearby areas, were collected and analyzed for OPEs' metabolites (mOPEs). The urinary ∑mOPEs' median concentrations (0.910 ng/mL) of all employees were significantly higher than those of residents in Ziya Town (0.526 ng/mL) and Jinghai downtown (0.600 ng/mL), suggesting the risk of occupational OPEs' exposure associated with e-waste dismantling. However, the spatial variation was insignificant for residents with different distances from the e-waste recycling site. Besides, OPEs' exposure levels were significantly affected by manipulation modes and the urinary ∑mOPEs' median concentrations in the employees of family workshops (1.05 ng/mL) were significantly higher than those in plants with centralized management (0.667 ng/mL). The result suggests that mechanical dismantling and active ventilating measures can reduce the OPEs' occupational exposure risk. Moreover, ∑mOPEs were higher in volunteers with age above 50 years old and in the underweight subgroup. Finally, different categories of mOPEs in human urine showed associations with corresponding OPEs in dust samples in the same area.

Estrogenic and growth inhibitory responses to organophosphorus flame retardant metabolites in zebrafish embryos

Recent evidence has revealed that organophosphorus flame retardants (OPFRs) elicit a variety of toxic effects, including endocrine disruption. The present study examined estrogenic and growth inhibitory responses to OPFR metabolites in comparison to their parent compounds using zebrafish eleutheroembryos.¹ Exposure to 4-hydroxylphenyl diphenyl phosphate (HO-p-TPHP) but not its parent compound triphenyl phosphate (TPHP) elicited upregulation of a marker gene of estrogenic responses, cytochrome P450 19A1b (CYP19A1b), and this upregulation was reversed by co-exposure to an estrogen receptor antagonist. Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), as well as 3-hydroxylphenyl diphenyl phosphate (HO-m-TPHP) and diphenyl phosphate (DPHP), did not elicit significant changes in the CYP19A1b expression. Reduction in body length was induced by TPHP and to a lesser extent by its hydroxylated metabolites. Altered expression of genes involved in the synthesis and action of thyroid hormones, including iodothyronine deiodinases 1 and 2, thyroid hormone receptor alpha, and transthyretin, were commonly observed for TPHP and its hydroxylated metabolites. Reduction in the body length was also seen in embryos exposed to TDCIPP but not BDCIPP. The transcriptional effect of TDCIPP was largely different from that of TPHP, with decreased expression of growth hormone and prolactin observed only in TDCIPP-exposed embryos. Considering the concentration-response relationships for the growth retardation and gene expression changes, together with existing evidence from other researchers, it is likely that prolactin is in part involved in the growth inhibition caused by TDCIPP. The present study showed similarities and differences in the endocrine disruptive effects of OPFRs and their metabolites.

Maternal urinary OPE metabolite concentrations and blood pressure during pregnancy: The HOME study

BACKGROUND

Few studies have examined the association between maternal exposure to organophosphate esters (OPEs) and systolic/diastolic blood pressure (SBP/DBP) during pregnancy.

METHODS

We analyzed data from 346 women with a singleton live birth in the HOME Study, a prospective birth cohort in Cincinnati, Ohio, USA. We quantified four OPE metabolites in maternal spot urine samples collected at 16 and 26 weeks pregnancy, standardized by specific gravity. We calculated intraclass correlation coefficients (ICCs). We extracted the first two recorded BP measurements (<20 weeks), the two highest recorded BP measurements (≥20 weeks), and diagnoses of hypertensive disorders of pregnancy (HDP) via chart review. Women with two BP measurements ≥140/90 mmHg or HDP noted in the chart at ≥20 weeks pregnancy were defined as HDP cases. We used linear mixed models and modified Poisson regression with covariate adjustment to estimate associations between OPE concentrations as continuous variables or in tertiles with maternal BP and HDP.

RESULTS

ICCs of OPEs were 0.17-0.45. Diphenyl phosphate (DPHP) had the highest geometric mean concentration among OPE metabolites. Increasing the average bis(2-chloroethyl) phosphate (BCEP) concentrations were positively associated with two highest recorded DBP ≥20 weeks pregnancy. Compared with women in the 1st DPHP tertile, women in the 3rd tertile at 16 weeks pregnancy had 1.72 mmHg (95% CI: -0.01, 3.46) higher DBP <20 weeks pregnancy, and women in the 3rd tertile of the average DPHP concentrations had 2.25 mmHg (95% CI: 0.25, 4.25) higher DBP ≥20 weeks pregnancy. 33 women (9.5%) were identified with HDP. Di-n-butyl phosphate (DNBP) concentrations at 16 weeks were positively associated with HDP, with borderline significance (RR = 2.98, 95% CI 0.97-9.15). Other OPE metabolites were not significantly associated with HDP.

CONCLUSION

Maternal urinary BCEP and DPHP concentrations were associated with increased BP during pregnancy. Maternal urinary DNBP concentrations were associated with HDP, with borderline significance.

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.

Tricresyl phosphate inhibits fertilization in Japanese medaka (Oryzias latipes): Emphasizing metabolic toxicity

As tricresyl phosphate (TCrP) is commonly found in global water sources, its potential reproductive toxicity to fish is of increasing concern. Japanese medaka larvae were exposed to TCrP at 657.9, 1,511, and 4042 ng/L for 100 days. We identified significant fertilization inhibition (6.9%-12.8%) in all exposure groups. Intersex was significantly induced at 4042 ng/L, with an incidence of 22.0%. TCrP exposure also caused dilation of the efferent duct in the testes with maximum duct widths of 83.3, 93.2, and 149.7 μm in the 657.9, 1,511, and 4042 ng/L exposure groups, respectively. These widths were all significantly larger than that observed in the control group (37.7 μm) and likely contributed substantially to fertilization inhibition. The TCrP metabolites 4-OH-MDTP and 3-OH-MDTP, were detected at high concentrations in the liver and elicited 5.8-fold and 5.3-fold greater androgen receptor antagonistic activity than that elicited by TCrP (39.8 μM), which may explain the intersex observed in low exposure groups. 4-OH-MDTP and 3-OH-MDTP elicited anti-estrogenic activities by blocking the estrogen receptor, and the concentrations at which its responses were equal to the IC₂₀ of tamoxifen were 16.1 μM and 18.9 μM, respectively, as detected using the yeast two-hybrid assay. Such anti-estrogenic activities were likely the main driver of dilation of the efferent duct. Observed adverse outcomes after exposure to TCrP all occurred under environmentally relevant concentrations, suggesting considerable ecological risk to wild fish.

Triphenyl phosphate delayed pubertal timing and induced decline of ovarian reserve in mice as an estrogen receptor antagonist

Although concerns have been raised about the adverse effects of triphenyl phosphate (TPhP) on female fertility, its risk to ovarian functioning remains unknown. In this study, female C57BL/6 mice at postnatal day 21 were exposed on a daily basis to TPhP dose of 2, 10, and 50 mg/kg for 40 days. A significant delay in pubertal timing was observed in the mice exposed to 50 mg/kg of TPhP. An estrogen-responsive reporter transgenic mice assay demonstrated that TPhP significantly downregulated the estrogen receptor (ER) signaling by 45.1% in the whole body in the 50 mg/kg group, and by 14.7-43.7% in the uterus for all exposure groups compared with the control. This strong antagonistic activity of TPhP toward ER explained the delay in pubertal timing. A significant reduction in the number of follicles in all stages was observed in mice after being exposed to TPhP for 40 days at concentrations of 10 and 50 mg/kg, resulting in a decline of the ovarian reserve. The elevation of the follicle-stimulating hormone concentration may have contributed to this phenomenon, as controlled by the antagonistic activity of TPhP toward ER in the brain. The toxic effects of TPhP on ovarian functioning highlight this chemical as a potential risk factor for female fertility.

A review on organophosphate flame retardants in the environment: Occurrence, accumulation, metabolism and toxicity

Organophosphate flame retardants (OPFRs), as a substitute for brominated flame retardants (BFRs), are widely used in industrial production and life. The presence of OPFRs in the environment has an adverse effect on the ecological environment system. This review provides comprehensive data for the occurrence of OPFRs and their diester metabolites (OP diesters) in wastewater treatment plants, surface water, drinking water, sediment, soil, air and dust in the environment. In particular, the accumulation and metabolism of OPFRs in organisms and the types of metabolites and metabolic pathways are discussed for animals and plants. In addition, the toxicity of OP triesters and OP diesters in organisms is discussed. Although research on OPFRs has gradually increased in recent years, there are still many gaps to be filled, especially for metabolic and toxicity mechanisms that need in-depth study. This review also highlights the shortcomings of current research and provides suggestions for a basis for future research on OPFRs.

Organophosphate (OP) diesters and a review of sources, chemical properties, environmental occurrence, adverse effects, and future directions

Over the course of the continual phase-outs of toxic halogenated flame retardants (HFRs), there has been an increasing demand for organophosphate esters (OPEs) in global FR markets. OPE-FRs have largely been identified as OP triesters, which have a basic chemical structure of O = P(OR)₃. In addition to OP triesters, OPEs can refer to another class of related substances, namely, OP diesters that have a typical chemical structure of O = P(OR)₂(OH)). OP diesters are known as biotic or abiotic degradation products of OP triesters. In recent years, environmental scientists have proven that OP diesters widely exist in a variety of environmental matrices and biotic samples around the world, implying the potential risks from OP diester exposure to biota and humans in the environment. Here, we have reviewed the scientific literature for studies involving OP diesters and up to the end of 2020. The aim of the present review is to assess the present understanding of the physicochemical properties, sources (industrial production and degradation), environmental occurrence of OP diesters, and adverse effects to exposed organisms. Based on the literature in the Web of Science core collection, we found that at least 23 OP diesters have been reported as contaminants in various environments or as degradation products of OP triesters. The physicochemical properties of OP diesters vary depending on their specific chemical structures. OP diesters containing halogen atoms and aryl groups seem to be more persistent (with greater estimated half-life (t_1/2) values) in environmental matrices. There were multiple sources of OP diesters, including industrial production and biotic or abiotic degradation from OP triesters. Specifically, we found that ten OP diesters are produced somewhere in the world, and the total annual output was estimated to be 17,050 metric tons (this number is underestimated due to the limitation of the available information). In addition, the wide application of OP triesters worldwide makes the degradation of OP triesters another critical source of OP diesters to the environment and to organisms. Current monitoring studies have demonstrated that some OP diesters were detectable in the human body (via both blood and urine samples), indoor dust, wastewater, or sewage sludge worldwide. The highest concentrations of diphenyl phosphate (DPHP) in human urine have been reported as high as 727 ng/mL (children (aged 0-5 years) urine samples from Australia). In addition, adverse effects following direct or indirect exposure to 11 OP diesters in organisms (including animals, bacteria, and algae) have been reported, and the recorded adverse outcomes following exposure to OP diesters included developmental toxicity, alteration of gene expression, and disturbance of nuclear receptor activity. Biomonitoring studies regarding human samples have frequently reported statistically significant associations between the concentrations of OP diesters and markers of human health (mainly related to reproductive toxicity). Finally, on the basis of current knowledge on OP diesters, we propose prospects for related research directions in future studies.

Health toxicity effects of brominated flame retardants: From environmental to human exposure

Hexabromocyclododecane (HBCD) and Tetrabromobisphenol A (TBBP-A) are brominated flame retardants widely used in variety of industrial and consumer products (e.g., automobiles, electronics, furniture, textiles and plastics) to reduce flammability. HBCD and TBBPA can also contaminate the environment, mainly water, dust, air and soil, from which human exposure occurs. This constant exposure has raised some concerns against human health. These compounds can act as endocrine disruptors, a property that gives them the ability to interfere with hormonal function and quantity, when HBCD and TBBPA bind target tissues in the body. Studies in human and animals suggest a correlation between HBCD and TBBPA exposure and adverse health outcomes, namely thyroid disorders, neurobehavior and development disorders, reproductive health, immunological, oncological and cardiovascular diseases. However, in humans these effects are still poorly understood, once only a few data evaluated the human health effects. Thus, the purpose of this review is to present the toxicity effects of HBCD and TBBPA and how these compounds affect the environment and health, resorting to data and knowledge of 255 published papers from 1979 to 2020.

A review of environmental occurrence, analysis, bioaccumulation, and toxicity of organophosphate esters

The ban and restriction of polychlorinated biphenyls (PCBs) and major brominated flame retardants (BFRs), including hexabromocyclododecane (HBCD) and polybrominated diphenyl ethers (PBDEs), due to their confirmed detrimental effects on wildlife and humans have paved the way for the wide application of organophosphate esters (OPEs). OPEs have been extensively used as alternative flame retardants, plasticizer, and antifoaming agents in various industrial and consumer products, which leads to an increase in production, usage, and discharge in the environment. We compile recent information on the production/usage and physicochemical properties of OPEs and discussed and compared the available sample treatment and analysis techniques of OPEs, including extraction, clean-up, and instrumental analysis. The occurrence of OPEs in sediment, aquatic biota, surface, and drinking water is documented. Toxicity, human exposure, and ecological risks of OPEs were summarized; toxicological data of several OPEs shows different adverse health effects on aquatic organisms and humans. Much attention was given to document evidence regarding the bioaccumulation and biomagnification potential of OPEs in aquatic organisms. Finally, identified research gaps and avenues for future studies are forwarded.

Pregnancy exposure to organophosphate esters and the risk of attention-deficit hyperactivity disorder in the Norwegian mother, father and child cohort study

BACKGROUND

Organophosphate esters (OPEs) are a class of flame retardants in common use. OPEs can easily leach from materials, resulting in human exposure. Increasing concentrations have been reported in human populations over the past decade. Recent studies have linked prenatal OPE exposure to hyperactivity and attention problems in children. Such behaviors are often found among children with attention-deficit hyperactivity disorder (ADHD), however, no study has investigated OPEs in relation to clinically assessed ADHD.

OBJECTIVE

To evaluate prenatal exposure to OPEs as risk factors for clinically assessed ADHD using a case-cohort study nested within the Norwegian Mother, Father, and Child Cohort Study (MoBa).

METHODS

We included in the case group 295 ADHD cases obtained via linkage with the Norwegian Patient Registry, and the sub-cohort group 555 children sampled at baseline, irrespective of their ADHD case status. Prenatal concentrations of OPE metabolites were measured in maternal urine collected at 17 weeks of gestation, and included diphenyl phosphate (DPHP), di-n-butyl phosphate (DNBP), bis(2-butoxyethyl) hydrogen phosphate (BBOEP), and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP). We estimated risk ratios and the corresponding 95% confidence intervals [95% CI] using logistic regression, adjusting for season of urine collection, child sex, birth year, and maternal depression, education, and sum of urinary di(2-ethylhexyl) phthalate metabolites (∑DEHP) concentration during pregnancy. To assess the overall impact of simultaneously decreasing exposure to all chemical constituents of an OPE-phthalate mixture, quantile based g-computation was implemented. The mixture constituents included OPE and phthalate metabolites commonly detected in our study. In all models, we considered effect measure modification by child sex and polymorphisms in genes encoding paraoxonase 1 (PON1) and cytochrome P450 (P450) enzymes. Mediation analysis was conducted using thyroid function biomarkers estimated from maternal blood collected at 17 weeks of gestation.

RESULTS

DPHP was detected in nearly all samples (97.2%), with a higher geometric mean among the case group (0.70 µg/L) as compared to the sub-cohort (0.52 µg/L). DNBP was commonly detected as well (93.8%), while BBOEP (52.9%) and BDCIPP (22.9%) were detected less frequently. A higher risk of ADHD was observed in children with greater than median exposure to DPHP during pregnancy (risk ratio: 1.38 [95% CI: 0.96, 1.99]), which was slightly higher among girls (2.04 [1.03, 4.02]) and children of mothers with PON1 Q192R genotype QR (1.69 [0.89, 3.19]) or PON1 Q192R genotype RR (4.59 [1.38, 15.29]). The relationship between DPHP and ADHD (total risk ratio: 1.34 [0.90, 2.02]) was partially mediated through total triiodothyronine to total thyroxine ratio (natural direct effect: 1.29 [0.87, 1.94]; natural indirect effect: 1.04 [1.00, 1.10]; 12.48% mediated). We also observed an elevated risk of ADHD in relation to BDCIPP detection during pregnancy (1.50 [0.98, 2.28]). We did not observe notable differences in ADHD by DNBP (0.88 [0.62, 1.26]) or BBOEP (1.03 [0.73, 1.46]) during pregnancy. Simultaneously decreasing all constituents of common-detect OPE-phthalate mixture, specifically DPHP, DNBP, and 6 phthalate metabolites, by a quartile resulted in an ADHD risk ratio of 0.68 [0.64, 0.72].

CONCLUSION

Prenatal exposure to DPHP and BDCIPP may increase the risk of ADHD. For DPHP, we observed potential modification by child sex and maternal PON1 Q192R genotype and partial mediation through maternal thyroid hormone imbalance at 17 weeks gestation.

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.

Phosphorus Deficiency Promoted Hydrolysis of Organophosphate Esters in Plants: Mechanisms and Transformation Pathways

The biotransformation of organophosphate esters (OPEs) in white lupin (Lupinus albus) and wheat (Triticum aestivum L.) was investigated in hydroponic experiments with different phosphorus (P)-containing conditions. The hydrolysis rates of OPEs followed the order of triphenyl phosphate (TPHP) > tri-n-butyl phosphate (TnBP) > tris(1,3-dichloro-2-propyl) phosphate (TDCPP). Hydrolysis of OPEs was accelerated at P-deficient conditions, and faster hydrolysis took place in white lupin than in wheat. Coincidingly, the production of acid phosphatase (ACP) in both plants was promoted, and much higher intracellular and extracellular ACPs were observed in white lupin under P-deficient conditions. In vitro experiments revealed that ACP was a key enzyme to hydrolyze OPEs. The hydrolysis rates of OPEs were significantly correlated with the Hirshfeld charges, calculated by density functional theory, of the oxygen atom in the single P-O bond. Using ultra-high-performance liquid chromatography coupled with Orbitrap Fusion mass spectrometer, 30 metabolites were successfully identified. Some of these metabolites, such as sulfate-conjugated products, hydration of cysteine-conjugated products of TPHP, and reductively dechlorinated metabolites of TDCPP, were observed for the first time in plants. It is noteworthy that OPEs may transform into many hydroxylated metabolites, and special attention should be paid to their potential environmental effects.

Identification of biotransformation products of organophosphate ester from various aquatic species by suspect and non-target screening approach

Organic pollutants that are introduced into the aquatic ecosystem can transform by various mechanisms. Biotransformation is an important process for predicting the remaining structures of pollutants in the ecosystem, and their toxicity. This study focused on triphenyl phosphate (TPHP), which is a commonly used organophosphate flame retardant and plasticizer. Since TPHP is particularly toxic to aquatic organisms, it is essential to understand its biotransformation in the aquatic environment. In the aquatic ecosystem, based on consideration of the producer-consumer-decomposer relationship, the biotransformation products of TPHP were identified, and their toxicity was predicted. Liquid chromatography-high resolution mass spectrometry was used for target, suspect, and non-target analysis. The obtained biotransformation products were estimated for toxicity based on the prediction model. As a result, 29 kinds of TPHP biotransformation products were identified in the aquatic ecosystem. Diphenyl phosphate was detected as a common biotransformation product through a hydrolysis reaction. In addition, products were identified by the biotransformation mechanisms of green algae, daphnid, fish, and microorganism. Most of the biotransformation products were observed to be less toxic than the parent compound due to detoxification except some products (hydroquinone, beta-lyase products, palmitoyl/stearyl conjugated products). Since various species exist in a close relationship with each other in an ecosystem, an integrated approach for not only single species but also various connected species is essential.

Establishment of a Target, Suspect, and Functional Group-Dependent Screening Strategy for Organophosphate Esters (OPEs): "Into the Unknown" of OPEs in the Sediment of Taihu Lake, China

Current environmental monitoring studies are generally confined to several target organophosphate esters (OPEs), and there is a lack of strategies for comprehensively screening all potential OPEs in environmental samples. Here, an effective and accurate strategy was developed for the target, suspect, and functional group-dependent screening of OPEs by the use of ultrahigh-performance liquid chromatography-Q Exactive hybrid quadrupole-Orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS), and this strategy was applied for the analysis of n = 74 sediment samples (including 23 surface sediment samples and 51 sediment core samples) collected from Taihu Lake (eastern China) in 2019. In these analyzed samples, we successfully identified n = 35 OPEs, and 23 of them were reported in this region for the first time. In addition, this strategy also presented other interesting findings, i.e., (1) OPE concentrations decreased with increasing distance from the coast of the lake; (2) the newly identified 3-hydroxyphenyl diphenyl phosphate (meta-OH-TPHP) was not statistically significantly correlated with triphenyl phosphate (TPHP; r = 0.02494, p = 0.9101) but with resorcinol bis(diphenyl phosphate) (RDP) (r = 0.9271, p < 0.0001) and three other OPEs; and (3) the summed concentrations of aryl OPEs (∑_arylOPEs) in sediment core samples exhibited significantly increasing trends as the depth decreased. Collectively, this study provided an effective strategy that was successfully applied for comprehensive screening of OPEs in the sediments of Taihu Lake, and this strategy could have promising potential to be extended to other environmental matrices or samples.

Flame Retardants-Mediated Interferon Signaling in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a growing concern worldwide, affecting 25% of the global population. NAFLD is a multifactorial disease with a broad spectrum of pathology includes steatosis, which gradually progresses to a more severe condition such as nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and eventually leads to hepatic cancer. Several risk factors, including exposure to environmental toxicants, are involved in the development and progression of NAFLD. Environmental factors may promote the development and progression of NAFLD by various biological alterations, including mitochondrial dysfunction, reactive oxygen species production, nuclear receptors dysregulation, and interference in inflammatory and immune-mediated signaling. Moreover, environmental contaminants can influence immune responses by impairing the immune system’s components and, ultimately, disease susceptibility. Flame retardants (FRs) are anthropogenic chemicals or mixtures that are being used to inhibit or delay the spread of fire. FRs have been employed in several household and outdoor products; therefore, human exposure is unavoidable. In this review, we summarized the potential mechanisms of FRs-associated immune and inflammatory signaling and their possible contribution to the development and progression of NAFLD, with an emphasis on FRs-mediated interferon signaling. Knowledge gaps are identified, and emerging pharmacotherapeutic molecules targeting the immune and inflammatory signaling for NAFLD are also discussed.

Aerobic degradation of nonhalogenated organophosphate flame esters (OPEs) by enriched cultures from sludge: Kinetics, pathways, bacterial community evolution, and toxicity evaluation

The degradation by bacteria has been considered the main process for eliminating nonhalogenated organophosphate esters (OPEs) from wastewater treatment plants (WWTPs), but limited research has reported the biodegradation processes and clarified the microbial-mediated mechanisms for nonhalogenated OPE degradation in WWTPs. The aim of this study was to monitor the biodegradation of the most common nonhalogenated OPEs, namely, tris(2-butoxyethyl) phosphate (TBOEP), tris (n-butyl) phosphate (TNBP) and trisphenyl phosphate (TPHP), under aerobic conditions by sludge cultures from a conventional sewage plant. The microbial cultures were enriched separately with each OPE from activated sludge cultures, and the presence of glucose significantly enhanced degradation of the OPEs during the enrichment. The removal ratios for the three OPEs reached 29.3-89.9% after 5 cycles (25 days) of cultivation, and the first-order degradation kinetics followed the order of TPHP > TBOEP > TNBP, with their half-lives ranging between 12.8 and 99.0 h. Pathways of hydrolysis, hydroxylation, methoxylation, and substitution were confirmed for the aerobic biodegradation of these nonhalogenated OPEs, but only di-alkyl phosphates (DAPs) largely accumulated in culture medium as the most predominant transformation products. Phylotypes in Klebsiella were significantly more abundant during OPE biodegradation than in the initial sludge, which indicated that these microorganisms are associated with the biodegradation of nonhalogenated OPEs in sludge culture. Biodegradation of all investigated nonhalogenated OPEs was associated with a significant reduction in the residual toxicity to Vibrio fischeri, indicating a rather positive ecotoxicological outcome of the aerobic biotransformation processes achieved by the enriched sludge culture.

Organophosphate ester flame retardants have antiandrogenic potential and affect other endocrine related endpoints in vitro and in silico

Organophosphate ester flame retardants (OPFRs) are used to prevent ignition and spreading of fire. They are present in various human matrices suggesting adult, fetal, and neonate exposure. Endocrine related effects have been observed in vivo, but information at the molecular level is lacking for some OPFRs. Also, a better understanding of potential contribution from chemical substructures is needed. The aim of this study was to screen OPFRs for endocrine disruptive potential in vitro and in silico. We selected eleven substances to represent some OPFRs with 1) little information on endocrine activity and others to represent 2) varied chemical substructures. We used in vitro assays for androgen receptor (AR), aryl hydrocarbon receptor (AhR), and Nrf2 activity, effects on steroidogenesis, and transthyretin (TTR) binding, as well as in silico models covering estrogen, thyroid, and CYP3A4 induction related endpoints. Ten OPFRs affected AR and AhR activity, seven affected TTR binding, and five affected 17β-estradiol levels. Several substances had IC₅₀-values below 10 μM and exhibited efficacious effects. These included TPHP, CDP, TMPP, TIPPP, and EHDPP for AR antagonism, suggesting that the degree of arylation and the size of the substance can play a role for the activity. Chlorinated OPFRs had low/no effect on TTR binding. No clear trend was observed for AhR and steroidogenesis, but all arylated OPFRs were predicted to have alert for estrogen receptor binding in an in silico model with metabolism simulator included. Collectively, our data suggest that OPFRs have endocrine disruptive potential warranting further studies to enable human risk assessment.

Beyond Traditional Organophosphate Triesters: Prevalence of Emerging Organophosphate Triesters and Organophosphate Diesters in Indoor Dust from a Mega E-waste Recycling Industrial Park in South China

Numerous studies have reported the environmental contamination with traditional organophosphate triesters (tri-OPEs), but there is very little information on emerging tri-OPEs and organophosphate diesters (di-OPEs), especially in e-waste recycling areas. In this study, we conducted a comprehensive survey to monitor a broad suite of 11 traditional tri-OPEs, 12 emerging OPEs, and 10 di-OPEs in indoor dust collected from the workshops of (n = 42) and residential homes adjacent to (n = 24) a mega e-waste recycling industrial park in South China. In addition to traditional tri-OPEs, all of the emerging OPEs and di-OPEs were frequently detected in the dust samples. Total concentrations of emerging tri-OPEs and di-OPEs were in the range of 1210-62 900 and 2010-55 600 ng/g in the workshop dust and 435-23 700 and 186-4350 ng/g in the local home dust, respectively, which were comparable to those of traditional tri-OPEs (1160-61 500 and 370-13 900 ng/g, respectively). Most OPEs exhibited significantly higher concentrations in workshop dust versus local home dust (p < 0.05), indicating that e-waste dismantling activities contributed to the high residues of OPEs in indoor dust. Correlation analysis revealed that tri-OPEs have some common emission sources, i.e., e-waste and household products, while di-OPEs could originate from different sources, e.g., tri-OPE degradation, direct commercial application, and impurities in tri-OPE formulas. For both occupational workers and local adults, the median estimated daily intake values of emerging tri-OPEs (7.5 and 1.7 ng/kg bw/day, respectively) and di-OPEs (3.9 and 0.2 ng/kg bw/day, respectively) were comparable to that of traditional tri-OPEs (4.3 and 1.0 ng/kg bw/day, respectively), which suggests the important contribution of the emerging tri-OPEs and di-OPEs to the overall risks of human external exposure to OPE chemicals.

2-Ethylhexyl Diphenyl Phosphate and Its Hydroxylated Metabolites are Anti-androgenic and Cause Adverse Reproductive Outcomes in Male Japanese Medaka (Oryzias latipes)

Although high concentrations of 2-ethylhexyl diphenyl phosphate (EHDPP) have been detected in wild fish, its reproductive toxicity in fish remains unclear. In this study, we for the first time observed that EHDPP elicited androgen receptor (AR) antagonistic activity with a 50% inhibitory concentration of 37.5 μM. 2-Ethyl-5-hydroxyhexyl diphenyl phosphate was proved to be the dominant metabolite of EHDPP in Japanese medaka and elicited 3.1-fold stronger AR antagonistic activity than that of EHDPP. Medaka larvae (0-day post hatching) were exposed to EHDPP for 100 days, and intersex was observed in males from all exposure groups with significantly increased incidence (13.5-48.6%). 17β-E₂ was promoted at 104 ng/L, and androgens were suppressed at 434 ng/L, which account for the intersex incidence in the high-exposure groups but do not explain the significant incidence of intersex in the 29.9 ng/L exposure group. The AR antagonistic activity of EHDPP and its metabolites must therefore play a key role in intersex incidence. EHDPP also significantly (p < 0.05) repressed reproductive behaviors of males in the 434 ng/L group and decreased fertility in high-exposure groups compared with the control. All the adverse outcomes were observed under environmentally relevant concentrations, implying that EHDPP poses an ecological risk for wild fish populations.

Inhibitory effects of organophosphate esters on carboxylesterase activity of rat liver microsomes

We investigated the inhibitory effects of 13 organophosphate esters (OPEs) and hydrolytic metabolites on the carboxylesterase activity of rat liver microsomes in vitro in order to examine whether there might be a potential impact on human health, and to elucidate the structure activity relationship. Among the test compounds, 2-ethylhexyl diphenyl phosphate (EDPhP) was the most potent inhibitor of carboxylesterase activity, as measured in terms of 4-nitrophenol acetate hydrolase activity, followed by tri-m-cresyl phosphate (TmCP), cresyl diphenyl phosphate (CDPhP) and triphenyl phosphate (TPhP). The IC₅₀ values were as follows: EDPhP (IC₅₀: 0.03 μM) > TmCP (0.4 μM) > CDPhP (0.8 μM) > TPhP (14 μM) > tris(1,3-dichloro-2-propyl) phosphate (17 μM) > tris(2-ethylhexyl) phosphate (77 μM) > tri-n-propyl phosphate (84 μM) > tris(2-chloroethyl) phosphate (104 μM) > tris(2-butoxyethyl) phosphate (124 μM) > tri-n-butyl phosphate (230 μM). The IC₅₀ value of EDPhP was three orders of magnitude lower than that of bis(4-nitrophenyl) phosphate, which is widely used as an inhibitor of carboxylesterase. Trimethyl phosphate, triethyl phosphate and tris(2-chloroisopropyl) phosphate slightly inhibited the carboxylesterase activity; their IC₅₀ values were above 300 μM. Lineweaver-Burk plots indicated that the inhibition by several OPEs was non-competitive. Diphenyl and monophenyl phosphates, which are metabolites of TPhP, showed weaker inhibitory effects than that of TPhP.

The impact of oral exposure to low-dose tris(2-butoxyethyl) phosphate in allergic asthmatic mice

Tris(2-butoxyethyl) phosphate (TBEP) is a major organophosphorus flame retardant and has been widely increasing as a substitute for brominated flame retardants. TBEP may have adverse effects on human health; however, its impact on immune and allergic responses remains largely uncharacterized. In this study, the effects of low-dose TBEP comparable with the level of actual human exposure to that of human tolerable daily intake on allergic asthmatic mice were explored. Five-week-old C3H/HeJSlc male mice consumed a diet containing approximately 0.02, 0.2 or 2 μg/kg/day TBEP and were intratracheally administrated ovalbumin (OVA) (1 μg/mouse every 2 weeks from 5 to 11 weeks of age). Exposure to 2 μg/kg/day TBEP with OVA tended to enhance allergic pulmonary inflammation and significantly elevated mRNA levels of interleukin-5, eotaxin-1 and estrogen receptor alpha (ERα) compared with OVA alone. In mediastinal lymph nodes (MLNs), TBEP (0.2 or 2 μg/kg/day) with OVA significantly increased in total cell number and promoted conventional dendritic cell activation than OVA alone; MLN cell proliferation by OVA restimulation was also enhanced in these groups. In the bone marrow (BM), TBEP (0.02 or 0.2 μg/kg/day) with OVA resulted in a net decrease in total cell number and fraction of CCR2⁺ Gr-1⁺ cells; the fraction of Gr-1⁺ cells increased. In conclusion, oral exposure to low-dose TBEP levels equivalent to tolerable daily intake may exacerbate allergic pulmonary inflammation by promoting a skewed T-helper 2 cell response, upregulation of ERα and dysregulation of both MLN and BM microenvironments.

Developmental circulatory failure caused by metabolites of organophosphorus flame retardants in zebrafish, Danio rerio

Organophosphate triesters are used worldwide as additives in flame retardants and plasticizer as a replacement of polybrominated diphenyl ethers. Increasing evidence on human exposure to and environmental contamination with organophosphorus flame retardants (OPFRs) requires an adequate toxicity assessment for this class of chemicals. While developmental toxicity of several OPFRs has been reported, developmental effects of OPFR metabolites have still to be understood. The present study aimed at characterizing developmental effects of OPFR metabolites using zebrafish embryos (Danio rerio). Triphenyl phosphate (TPHP) and two of its metabolites, 3-hydroxylphenyl diphenyl phosphate and 4-hydroxylphenyl diphenyl phosphate, were most potent for inducing pericardial edema and reduction in blood flow in trunk vessels. Other TPHP metabolites, such as diphenyl phosphate and 4-hydroxylphenyl phenyl phosphate, showed no substantial increase in circulatory failure at concentrations up to 30 μM. Tris (1,3-dichloro-2-propyl) phosphate showed circulatory failure at 30 μM, but its metabolite bis(1,3-dichloro-2-propyl) phosphate did not. Neither tris(2-chloroethyl) phosphate nor its metabolite bis(2-chloroethyl) phosphate, induced circulatory failure. The circulatory failure appeared to be enhanced with the increase in the octanol-water partition coefficients of OPFRs and their metabolites, suggesting that developmental circulatory failure posed by these chemicals could be estimated by their bioaccumulative potential. The present study demonstrated developmental circulatory failure of hydroxylated TPHP metabolites, which was almost equipotent to TPHP. Diester OPFR metabolites showed no major developmental toxicity at the concentrations used in this study. The current results establish the foundation for further understanding the similarities and differences in the toxic mechanisms between OPFRs and their metabolites.

New Insights in the Endocrine Disrupting Effects of Three Primary Metabolites of Organophosphate Flame Retardants

Despite the ubiquity of organophosphate flame retardants (OPFRs) metabolites in the biota, the endocrine disrupting potency has not been well examined. Herein, we chose three primary metabolites of OPFRs (BCIPP, BDCIPP, and DPHP) to investigate their potential endocrine disrupting effects by in vitro, in vivo, and in silico assays. Three metabolites were agonistic to rat estrogenic receptor alpha (ERα) and antagonists to human mineralocorticoid receptor (MR). BCIPP exerted endocrine disrupting effect contrasting to the negative response of its parental compound. It also poses the strongest binding capacity to ERα among the tested compounds. Both BCIPP and BDCIPP upregulated the genes encoded for estrogenic synthesis enzymes in H295R cells, including 17βHSD and CYP19. All three compounds stimulated the transcription of CYP11B1, whereas BCIPP and DPHP also triggered CYP11B2, encoding for corticoid production. BDCIPP inhibits genes for progesterone synthesis including CYP11A1, STAR, and 3-βHSD. The induction of mortality and low hatchability of zebrafish embryo were ranked as BCIPP ≥ BDCIPP > DPHP. All compounds lead to malformation of zebrafish larvae. Both of the hypothalamic-pituitary-adrenocortical and hypothalamic-pituitary-gonadal axes were disrupted, with the highest impact by BCIPP. Altogether, the data clarified OPFRs metabolites may produce comparable or even higher endocrine disrupting effects than OPFRs.

Combined exposure to phthalate esters and phosphate flame retardants and plasticizers and their associations with wheeze and allergy symptoms among school children

BACKGROUND

Phthalate esters and phosphate flame retardants and plasticizers (PFRs) are both used as plasticizers and are commonly detected in indoor environments. Although both phthalates and PFRs are known to be associated with children's wheeze and allergic symptoms, there have been no previous studies examining the effects of mixtures of these exposures.

OBJECTIVES

To investigate the association between exposure to mixtures of phthalate esters and PFRs, and wheeze and allergic symptoms among school-aged children.

METHODS

A total of 128 elementary school-aged children were enrolled. Metabolites of 3 phthalate esters and 7 PFRs were measured in urine samples. Parent-reported symptoms of wheeze, rhinoconjunctivitis, and eczema were evaluated using the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. In the primary model, we created a phthalate ester and PFR mixture exposure index, and estimated odds ratios (ORs) using weighted quantile sum (WQS) regression and quantile g (qg)-computation. The two highest chemicals according to qg-computation weight %s were combined to create a combination high × high exposure estimate, with ORs calculated using the "low × low" exposure group as the reference category. Concentrations of each metabolite were corrected by multiplying this value by the sex- and body size-Standardised creatinine concentration and dividing by the observed creatinine value. All models were adjusted for sex, grade, dampness index and annual house income.

RESULTS

The odds ratio of rhinoconjunctivitis for the association between exposure to chemical mixtures according to the WQS index positive models was; OR = 2.60 (95% confidence interval [CI]: 1.38-5.14). However, wheeze and eczema of the WQS index positive model, none of the WQS index negative models or qg-computation result yielded statistically significant results. Combined exposure to the two highest WQS weight %s of "high-high" ΣTCIPP and ΣTPHP was associated with an increased prevalence of rhino-conjunctivitis, OR = 5.78 (1.81-18.43) to the "low × low" group.

CONCLUSIONS

Significant associations of mixed exposures to phthalates and PFRs and increased prevalence of rhinoconjunctivitis was found among elementary school-aged children in the WQS positive model. Mixed exposures were not associated with any of allergic symptoms in the WQS negative model or qg-computation approach. However, the combined effects of exposure to two PFRs suggested an additive and/or multiplicative interaction, potentially increasing the prevalence of rhinoconjunctivitis. A further study with a larger sample size is needed to confirm these results.

Characterizing biotransformation products and pathways of the flame retardant triphenyl phosphate in Daphnia magna using non-target screening

Triphenyl phosphate (TPHP), one of the organophosphate flame retardants, has been widely used in manufacturing, thereby causing a gradual increase in TPHP concentrations in aquatic environments. However, the information on the biotransformation mechanism of TPHP in invertebrates is lacking. The study identified the biotransformation products of TPHP in Daphnia magna, which showed particularly high toxicity in aquatic organisms, and determined the rates of depuration. Daphnia magna, a standard species for toxicity studies, was exposed to triphenyl phosphate and transferred to the pure medium. The biotransformation products of TPHP and its depuration rates were determined by liquid chromatography-high resolution mass spectrometry. Nine biotransformation products (five in the positive mode and four in the negative mode) of triphenyl phosphate were identified in D. magna. Based on the depuration ratio, the major biotransformation mechanism is estimated to be cysteine conjugation and sulfation. Certain biotransformation products (diphenyl phosphate, hydroxylated triphenyl phosphate, and thiol triphenyl phosphate) might induce toxicity in biota. The results could be used to predict main biotransformation processes and toxic products of organophosphate flame retardants in aquatic invertebrates.

Sorption and desorption behaviors of triphenyl phosphate (TPhP) and its degradation intermediates on aquatic sediments

As triphenyl phosphate (TPhP) can biodegrade extensively in sediments, researches should further the understanding of the fate and transport of TPhP and its degradation intermediates in the environment. Therefore, the sorption/desorption behaviors of TPhP, diphenyl phosphate (DPhP) and phenyl phosphate (PhP) on sediments were investigated. The kinetic process was well-fitted by pseudo-second-order model, suggesting that chemisorption was involved. And the Langmuir model could describe the sorption isotherms of TPhP and DPhP well except for PhP. The redundancy analysis revealed that the sorption amount had a positive correlation with sediment organic matter, zeta potential and C/H of sediments. Besides the sorption/desorption behaviors were greatly influenced by the physicochemical properties of the sorbates. PhP with high molecular electrostatic potential (0.132 e⁰) was prone to protonation and formed hydrogen bonds, leading to higher sorption. Furthermore, hydrophobicity, π-π interactions, Lewis acid-base interaction and hydrogen bonding were involved in the sorption process and resulted in nonlinear sorption isotherms. TPhP, DPhP and PhP exhibited apparent desorption hysteresis on the sediments. Sediments with organic matter removed, which have complex pore distributions, exhibited more hysteresis. These results may contribute to the risk assessment and fate modeling of TPhP and its degradation products in sediments.

Photochemical reaction of tricresyl phosphate (TCP) in aqueous solution: Influencing factors and photolysis products

Organophosphate triesters (OPEs) have caused great concern as a class of emerging environmental contaminants due to their widespread use and their toxicity to organisms. However, the phototransformation behavior of OPE is still not fully understood, which is important for understanding their environmental fate. In the present study, the photodegradation of tricresyl phosphate (TCP), one of the most widely detected OPEs in aqueous environments, was investigated including the direct photolysis and in the presence of several natural water factors, NO₂^-, Fe³⁺ and humic acid. The degradation process followed the pseudo-first-order kinetics, with rate constant increasing slightly with increasing initial TCP concentration. The presence of NO₂^- and Fe³⁺ was observed to promote the photochemical loss of TCP, while humic acid played a negative role on TCP transformation. Electron spin resonance (EPR) analysis showed that carbon-centered radical was produced in the photolysis process of TCP, and hydroxyl radical contributed to the promotion of rate constant for Fe³⁺ and NO₂^-. Four photolysis products were tentatively identified by HPLC-LTQ-Orbitrap MS analysis, and the possible degradation pathways of TCP were proposed. These findings provide a meaningful reference for the fate and transformation of OPEs in natural water.

Triphenyl Phosphate at Environmental Levels Retarded Ovary Development and Reduced Egg Production in Japanese Medaka (Oryzias latipes)

Since triphenyl phosphate (TPhP) elicits both antiestrogenic activities via blocking the estrogen receptor (ER) and estrogenic activity by elevating 17β-estradiol (17β-E2) synthesis, its adverse effect on female reproduction is uncertain. In this study, we exposed Japanese medaka to TPhP at 131, 363, and 1773 ng/L for 100 days following hatching. TPhP significantly induced ovary retardation in all exposure groups (incidence: from 11.9 to 37.8%) and reduced egg production by 38.9 and 50.9% in the 363 and 1773 ng/L exposure groups, respectively. Vitellogenin (vtg) transcription was significantly downregulated by 35.4-57.4% after TPhP exposure, explaining the ovary retardation. Considering that 17β-E2 was only significantly decreased in the 1773 ng/L exposure group, ER antagonism could be the dominant contributor to the inhibition of vtg transcription and female reproductive toxicity of TPhP. As 4-hydroxyphenyl diphenyl phosphate, a metabolite of TPhP, was detected in livers with similar concentration [68.4-1237 ng/g lipid weight (lw)] to that of TPhP (485-1594 ng/g lw) and elicited medaka ER antagonistic activity (50% inhibitory concentration = 78.1 μM), TPhP and its metabolite should both contribute to the reproductive inhibition. We demonstrate that TPhP at environmentally relevant concentrations is toxic to female reproduction, which poses an ecological risk to wild fish at the population level.

Glucocorticoid and mineralocorticoid receptors and corticosteroid homeostasis are potential targets for endocrine-disrupting chemicals

Endocrine-disrupting chemicals (EDCs) have received significant concern, since they ubiquitously exist in the environment and are able to induce adverse health effects on human and wildlife. Increasing evidence shows that the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR), members of the steroid receptor subfamily, are potential targets for EDCs. GR and MR mediate the actions of glucocorticoids and mineralocorticoids, respectively, which are two main classes of corticosteroids involved in many physiological processes. The effects of EDCs on the homeostasis of these two classes of corticosteroids have also gained more attention recently. This review summarized the effects of environmental GR/MR ligands on receptor activity, and disruption of corticosteroid homeostasis. More than 130 chemicals classified into 7 main categories were reviewed, including metals, metalloids, pesticides, bisphenol analogues, flame retardants, other industrial chemicals and pharmaceuticals. The mechanisms by which EDCs interfere with GR/MR activity are primarily involved in ligand-receptor binding, nuclear translocation of the receptor complex, DNA-receptor binding, and changes in the expression of endogenous GR/MR genes. Besides directly interfering with receptors, enzyme-catalyzed synthesis and prereceptor regulation pathways of corticosteroids are also important targets for EDCs. The collected evidence suggests that corticosteroids and their receptors should be considered as potential targets for safety assessment of EDCs. The recognition of relevant xenobiotics and their underlying mechanisms of action is still a challenge in this emerging field of research.