In ovo transformation of two emerging flame retardants in Japanese quail (Coturnix japonica)

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and Dechlorane Plus (DP) are two chlorinated, alternative flame retardants that have been found in wild birds and bird eggs. Little is known about the fate and effect of these compounds in birds, especially during the vulnerable stages of embryonic development. To investigate the ability of birds to biotransform these compounds, an in ovo exposure experiment with Japanese quail eggs was performed. Quail eggs were injected in the yolk sac with 1000ng/g egg of TDCIPP (2.3 nmol/g ww), DP (1.5 nmol/g ww) or a mixture of both and were then incubated at 37.5°C for 17 days. To get a time-integrated understanding of the in ovo transformation of the compounds, one egg per treatment was removed from the incubator every day and analyzed for TDCIPP and its metabolite bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) and/or for DP. By the end of the incubation period, TDCIPP was completely metabolized, while simultaneously BDCIPP was formed. The conversion of the parent compound into the metabolite did not occur proportionally and the concentration of BDCIPP showed a tendency to decrease when TDCIPP became depleted, both indicating that BDCIPP was further transformed into compounds not targeted for analysis. Further untargeted investigations did not show the presence of other metabolites, possibly due to the volatility of the metabolites. On the other hand, the DP concentration did not decrease during egg incubation. This study indicates that within the incubation period, avian embryos are able to biotransform TDCIPP, but not DP.

Novel aspects of uptake patterns, metabolite formation and toxicological responses in Salmon exposed to the organophosphate esters-Tris(2-butoxyethyl)- and tris(2-chloroethyl) phosphate

Given the compound differences between tris(2-butoxyethyl)- and tris(2-cloroethyl) phosphate (TBOEP and TCEP, respectively), we hypothesized that exposure of juvenile salmon to TBOEP and TCEP will produce compound-specific differences in uptake and bioaccumulation patterns, resulting in potential formation of OH-metabolites. Juvenile salmon were exposed to waterborne TCEP or TBOEP (0.04, 0.2 and 1 mg/L) for 7 days. The muscle accumulation was measured and bioconcentration factor (BCF) was calculated, showing that TCEP was less accumulative and resistant to metabolism in salmon than TBOEP. Metabolite formations were only detected in TBOEP-exposed fish, showing seven phase I biotransformation metabolites with hydroxylation, ether cleavage or combination of both reactions as important metabolic pathways. In vitro incubation of trout S9 liver fraction with TBOEP was performed showing that the generated metabolite patterns were similar to those found in muscle tissue exposed in vivo. However, another OH-TBOEP isomer and an unidentified metabolite not present in in vivo exposure were observed with the trout S9 incubation. Overall, some of the observed metabolic products were similar to those in a previous in vitro report using human liver microsomes and some metabolites were identified for the first time in the present study. Toxicological analysis indicated that TBOEP produced less effect, although it was taken up faster and accumulated more in fish muscle than TCEP. TCEP produced more severe toxicological responses in multiple fish organs. However, liver biotransformation responses did not parallel the metabolite formation observed in TBOEP-exposed fish.

In Vitro and in Silico Competitive Binding of Brominated Polyphenyl Ether Contaminants with Human and Gull Thyroid Hormone Transport Proteins

Tetradecabromo-1,4-diphenoxybenzene (TeDB-DiPhOBz) is a highly brominated additive flame retardant (FR). Debrominated photodegradates of TeDB-DiPhOBz are hydroxylated in vitro in liver microsomal assays based on herring gulls (Larus argentatus), including one metabolite identified as 4″-OH-2,2',2″,4-tetrabromo-DiPhOBz. Chemically related methoxylated tetra- to hexabromo-DiPhOBzs are known contaminants in herring gulls. Collectively, nothing is currently known about biological effects of these polybrominated (PB) DiPhOBz-based compounds. The present study investigated the potential thyroidogenicity of 2,2',2″,4-tetrabromo-(TB)-DiPhOBz along with its para-methoxy (MeO)- and hydroxy-(OH)-analogues, using an in vitro competitive protein binding assay with the human thyroid hormone (TH) transport proteins transthyretin (hTTR) and albumin (hALB). This model para-OH-TB-DiPhOBz was found to be capable of competing with thyroxine (T4) for the binding site on hTTR and hALB. In silico analyses were also conducted using a 3D homology model for gull TTR, to predict whether these TB-DiPhOBz-based compounds may also act as ligands for an avian TH transport protein despite evolutionary differences with hTTR. This analysis found all three TB-DiPhOBz analogues to be potential ligands for gull TTR and have similar binding efficacies to THs. Results indicate structure-related differences in binding affinities of these ligands and suggest there is potential for these contaminants to interact with both mammalian and avian thyroid function.

Paternal urinary concentrations of organophosphate flame retardant metabolites, fertility measures, and pregnancy outcomes among couples undergoing in vitro fertilization

BACKGROUND

Use of organophosphate flame retardants (PFRs) has increased over the past decade following the phase out of some brominated flame retardants, leading to increased human exposure. We recently reported that increasing maternal PFR exposure is associated with poorer pregnancy outcomes among women from a fertility clinic. Because a small epidemiologic study previously reported an inverse association between male PFR exposures and sperm motility, we sought to examine associations of paternal urinary concentrations of PFR metabolites and their partner's pregnancy outcomes.

METHODS

This analysis included 201 couples enrolled in the Environment and Reproductive Health (EARTH) prospective cohort study (2005-2015) who provided one or two urine samples per IVF cycle. In both the male and female partner, we measured five urinary PFR 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)] using negative electrospray ionization liquid chromatography tandem mass spectrometry (LC-MS/MS). The sum of the molar concentrations of the urinary PFR metabolites was calculated. We used multivariable generalized linear mixed models to evaluate the association of urinary concentrations of paternal PFR metabolites with IVF outcomes, accounting for multiple in vitro fertilization (IVF) cycles per couple. Models were adjusted for year of IVF treatment cycle, primary infertility diagnosis, and maternal urinary PFR metabolites as well as paternal and maternal age, body mass index, and race/ethnicity.

RESULTS

Detection rates were high for paternal urinary concentrations of BDCIPP (84%), DPHP (87%) and ip-PPP (76%) but low for tb-PPP (12%) and zero for BCIPP (0%). We observed a significant 12% decline in the proportion of fertilized oocytes from the first to second quartile of male urinary ΣPFR and a 47% decline in the number of best quality embryos from the first to third quartile of male urinary BDCIPP in our adjusted models. An 8% decline in fertilization was observed for the highest compared to lowest quartile of urinary BDCIPP concentrations (95% CI: 0.01, 0.12, p-trend=0.06).

CONCLUSIONS

Using IVF as a model to investigate human reproduction and pregnancy outcomes, we found that paternal urinary concentrations of BDCIPP were associated with reduced fertilization. In contrast to previously reported findings for the female partners, the paternal urinary PFR metabolites were not associated with the proportion of cycles resulting in successful implantation, clinical pregnancy, and live birth. These results indicate that paternal preconception exposure to TDCIPP may adversely impact successful oocyte fertilization, whereas female preconception exposure to ΣPFRs may be more relevant to adverse pregnancy outcomes.

Bis-(3-allyl-4-hydroxyphenyl) sulfone decreases embryonic viability and alters hepatic mRNA expression at two distinct developmental stages in chicken embryos exposed via egg injection

Concerns surrounding the toxicological effects and environmental prevalence of bisphenol A (BPA) have increased efforts to identify suitable safer replacement alternatives. Bis-(3-allyl-4-hydroxyphenyl) sulfone (TGSH) represents a potential BPA alternative; however, exposure and ecotoxicological data are scarce. To determine effects on embryonic viability, development, and hepatic mRNA expression at 2 distinct developmental periods (midincubation [day 11] and pipping [days 20-21]), TGSH was injected into the air cell of unincubated, fertilized chicken embryos at 4 concentrations ranging from 0 to 180 μg/g egg. Concentrations of TGSH increased in a dose-dependent manner in whole-embryo homogenates, and the estimated median lethal dose (LD50) based on embryonic viability at midincubation was 66 µg/g (95% confidence interval = 31-142 µg/g), which is similar to the BPA LD50 (∼ 67 μg/g) reported in a previous study. Modulation of hepatic gene targets from a chicken ToxChip polymerase chain reaction (PCR) array was observed at both developmental stages. At midincubation, 21/43 genes on the PCR array were significantly altered (by >1.5-fold) in the 180 μg/g dose group, whereas 9 and 6/43 were altered at pipping in the 9.2 and 48 μg/g groups, respectively. Predominant toxicity pathways included xenobiotic metabolism, lipid homeostasis, bile acid synthesis, and cell cycle regulation. The estrogen-responsive gene apolipoprotein II was significantly up-regulated in liver tissue of midincubation embryos at 180 μg/g; however, neither apolipoprotein II nor vitellogenin II were altered at the other concentrations or developmental time points. Given the importance of identifying suitable BPA replacement alternatives, the present study provides novel, whole-animal toxicological data for a BPA replacement alternative that has an effect on embryonic viability similar to that of the compound it could replace. Environ Toxicol Chem 2018;37:530-537. © 2017 SETAC.

Organophosphate triesters and selected metabolites enhance binding of thyroxine to human transthyretin in vitro

The toxicological properties of organophosphate (OP) triesters that are used as flame retardants and plasticizers are currently not well understood, though increasing evidence suggests they can affect the thyroid system. Perturbation of thyroid hormone (TH) transport is one mechanism of action that may affect thyroid function. The present study applied an in vitro competitive protein binding assay with thyroxine (T4) and human transthyretin (hTTR) transport protein to determine the potential for the OP triesters, TDCIPP (tris(1,3-dichloro-2-propyl) phosphate), TBOEP (tris(butoxyethyl) phosphate), TEP (triethyl phosphate), TPHP (triphenyl phosphate), p-OH-TPHP (para-hydroxy triphenyl phosphate), and the OP diester DPHP (diphenyl phosphate), to competitively displace T4 from hTTR. Enhancement of T4 binding to hTTR, rather than the hypothesized competition, was observed for the six OP esters and in a concentration-dependent manner. For example, T4-hTTR binding was significantly increased at concentrations of TBOEP as low as 64 nM, and up to 184% of controls at 5000 nM. A plausible explanation of these results, which to our knowledge has not been previously reported, may be allosteric interactions of the OP esters with hTTR allowing T4 to access the second site of the TH binding pocket. These in vitro results suggest a novel mechanism of OP ester toxicity via T4 binding enhancement, and possible dysregulation of T4-hTTR interactions.

Whole-Life-Stage Characterization in the Basic Biology of Daphnia magna and Effects of TDCIPP on Growth, Reproduction, Survival, and Transcription of Genes

Toxicity tests of chemicals have mainly focused on the partial life-cycle evaluation of model animals. Limited information is available for the evaluation of effects of chemicals from a whole-life-stage exposure perspective. The objective of this study was to perform a whole-life-stage characterization in the basic biology of Daphnia magna (D. magna) and evaluate the effects of a known organophosphate ester (OPE) contaminant, tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), on growth, reproduction, survival, and transcription of genes. The whole-life-stage characterization in growth, reproduction, and survival of D. magna was conducted, and representative sampling time points for the three developmental stages were identified (day 6, day 32, and day 62). Transcriptomic profiles for these three stages were compared, and stage-specific PCR arrays of D. magna were developed. The whole-life-stage exposure to environmentally relevant or greater concentrations of TDCIPP significantly inhibited growth and reproduction of D. magna and decreased survival at the later stage of the exposure experiment (≥32 days). Such adverse effects were not observed in the early stage of the exposure (<32 days), suggesting that short-term toxicity tests, such as the standard 21-day test, might underestimate the environmental risk of TDCIPP. Furthermore, expressions of genes selected at day 6, day 32, and day 62 were significantly changed after TDCIPP exposure, and the changes in the expressions of partial genes were correlated to the inhibitory effects on growth, reproduction, and survival.

Determination and prediction of octanol-air partition coefficients for organophosphate flame retardants

Organophosphate flame retardants (OPFRs) have attracted wide concerns due to their toxicities and ubiquitous occurrence in the environment. In this work, Octanol-air partition coefficient (K_OA) for 14 OPFRs including 4 halogenated alkyl-, 5 aryl- and 5 alkyl-OPFRs, were estimated as a function of temperature using a gas chromatographic retention time (GC-RT) method. Their log K_OA-GC values and internal energies of phase transfer (Δ_OAU/kJmol^-1) ranged from 8.03 to 13.0 and from 69.7 to 149, respectively. Substitution pattern and molar volume (V_M) were found to be capable of influencing log K_OA-GC values of OPFRs. The halogenated alkyl-OPFRs had higher log K_OA-GC values than aryl- or alkyl-OPFRs. The bigger the molar volume was, the greater the log K_OA-GC values increased. In addition, a predicted model of log K_OA-GC versus different relative retention times (RRTs) was developed with a high cross-validated value (Q²_(cum)) of 0.951, indicating a good predictive ability and stability. Therefore, the log K_OA-GC values of the remaining OPFRs can be predicted by using their RRTs on different GC columns.

Associations between flame retardant applications in furniture foam, house dust levels, and residents' serum levels

Polyurethane foam (PUF) in upholstered furniture frequently is treated with flame retardant chemicals (FRs) to reduce its flammability and adhere to rigorous flammability standards. For decades, a commercial mixture of polybrominated diphenyl ethers (PBDEs) called PentaBDE was commonly applied to foam to fulfill these regulations; however, concerns over toxicity, bioaccumulation, and persistence led to a global phase-out in the mid-2000s. Although PentaBDE is still detected in older furniture, other FR compounds such as tris(1,3-dichloroisopropyl) phosphate (TDCIPP) and Firemaster® 550 (FM550) have been increasingly used as replacements. While biomonitoring studies suggest exposure is widespread, the primary sources of exposure are not clearly known. Here, we investigated the relationships between specific FR applications in furniture foam and human exposure. Paired samples of furniture foam, house dust and serum samples were collected from a cohort in North Carolina, USA and analyzed for FRs typically used in PUF. In general, the presence of a specific FR in the sofa of a home was associated with an increase in the concentration of that FR in house dust. For example, the presence of PentaBDE in sofas was associated with significantly higher levels of BDE-47, a major component of PentaBDE, in house dust (10^β=6.4, p<0.001). A similar association was observed with a component of FM550, 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), with levels that were approximately 3 times higher in house dust when FM550 was identified in the sofa foam (p<0.01). These relationships were modified by dust loading rates in the living room and the ratio of sofa size to room size. Interestingly, levels of TDCIPP and tris(1-chloro-2-isopropyl) phosphate (TCIPP) were also higher in dust with detections in sofa foam; however, these associations were not statistically significant and may suggest there are other prominent sources of these compounds in the home. In addition, the presence of PentaBDE in sofa foam was associated with significantly higher levels of BDE-47 in serum (p<0.01). These results suggest that FR applications in sofas are likely major sources of exposure to these compounds in the home.

Demographic and dietary risk factors in relation to urinary metabolites of organophosphate flame retardants in toddlers

Organophosphate flame retardants (OPFRs), including Tris (1,3-dichloro-isopropyl) phosphate (TDCPP), triphenyl phosphate (TPP), and isopropylated triphenyl phosphate (ITP), are increasingly used in consumer products because of the recent phase out of polybrominated diphenyl ether (PBDE) flame retardants. OPFRs have been widely detected in adults and have been linked to reproductive and endocrine changes in adult males. Carcinogenicity and damage to immunologic, neurologic and developmental systems have been observed in human cell lines. Young children are especially vulnerable to OPFR exposure, but little is known about exposure levels or exposure risk factors in this population. We examined parent-reported demographic and dietary survey data in relation to OPFR urinary metabolite concentrations in 15- to 18-month old toddlers (n = 41). OPFR metabolites were detected in 100% of subjects. The metabolite of TPP, diphenyl phosphate (DPP) was detected most commonly (100%), with TDCPP metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP), detected in 85-95% of samples, and ITP metabolite, monoisopropylphenyl phenyl phosphate (ip-DPP), detected in 81% of samples (n = 21). Toddlers of mothers earning <$10,000 annually had geometric mean DPP concentrations 66% higher (p = 0.05) than toddlers of mothers earning >$10,000/year (7.8 ng/mL, 95% CI 5.03, 12.11 and 4.69 ng/mL, 95% CI 3.65-6.04, respectively). While no dietary factors were significantly associated with OPFR metabolite concentrations, results suggested meat and fish consumption may be associated with higher DPP and BDCPP levels while increased dairy and fresh food consumption may be associated with lower DPP, BDCPP, and ip-DPP levels. Research with larger sample sizes and more detailed dietary data is required to confirm these preliminary findings.

Volatile Methylsiloxanes and Organophosphate Esters in the Eggs of European Starlings (Sturnus vulgaris) and Congeneric Gull Species from Locations across Canada

Volatile methylsiloxanes (VMSs) and organophosphate esters (OPEs) are two suites of chemicals that are of environmental concern as organic contaminants, but little is known about the exposure of wildlife to these contaminants, particularly in birds, in terrestrial and aquatic ecosystems. The present study investigates the spatial distributions of nine cyclic and linear VMSs and 17 OPEs in the eggs of European starlings (Sturnus vulgaris) and three congeneric gull species (i.e., herring gull (Larus argentatus), glaucous-winged gull (L. glaucescens), and California gull (L. californicus)) from nesting sites across Canada. ∑VMS concentrations for all bird eggs were dominated by decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), and octamethylcyclotetrasiloxane (D4). With European starlings, birds breeding adjacent to landfill sites had eggs containing significantly greater ∑VMS concentrations (median: 178 ng g^-1 wet weight (ww)) compared with those from the urban industrial (20 ng g^-1 ww) and rural sites (1.3 ng g^-1 ww), indicating that the landfills are important sources of VMSs to Canadian terrestrial environments. In gull eggs, the median ∑VMS concentrations were up to 254 ng g^-1 ww and suggested greater detection frequencies and levels of VMSs in aquatic- versus terrestrial-feeding birds in Canada. In contrast, the detection frequency of OPEs in all European starling and gull eggs was lower than 16%. This suggested that low dietary exposure or rapid metabolism of accumulated OPEs occurs in aquatic feeding birds and may warrant further investigation for the elucidation of the reasons for these differences.

Assessment of tris (1, 3-dichloro-2-propyl) phosphate toxicology in PC12 cells by using digital gene expression profiling

Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP), one of the most universally used organophosphate flame retardants (OPFRs), is an environmental pollutant. However, limited information is available regarding its toxicity and environmental health risk. In the present study, PC12 cells provided a useful model for the evaluation of the toxic effects of TDCIPP. Exposure to 7.5, 15, 30, or 60 μM TDCIPP for 72 h inhibited cell viability, and enhanced cellular apoptosis and oxidative stress. To further explore the underlying mechanisms, digital gene expression (DGE) technology was used to identify early transcriptional changes following TDCIPP exposure. Expression of the transcripts of 161 genes was significantly altered upon treatment with TDCIPP. Functional and pathway analysis of the transcriptional profile demonstrated that genes showing significant TDCIPP-associated changes in expression were involved in the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway, extracellular matrix-receptor interactions, protein digestion and absorption, and microRNAs in cancer. Using quantitative real-time PCR, we validated the differential expression of selected genes. These results showed that the expression profiles of cells exposed to 60 μM TDCIPP were consistent with the DGE data. Furthermore, western blotting showed that treatment with TDCIPP reduced the Bcl-2/Bax ratio and attenuated PI3K/Akt/Myc signaling. Taken together, these data suggest that TDCIPP exposure can reduce cell viability and induce apoptosis in PC12 cells by inhibiting activation of the PI3K/Akt/Myc signaling pathway. These observations provide valuable preliminary information regarding the mechanisms of TDCIPP-induced toxicity in PC12 cells and indicate that further study of the toxicity of other environmental OPFRs is warranted.

Tributylphosphate (TBP) and tris (2-butoxyethyl) phosphate (TBEP) induced apoptosis and cell cycle arrest in HepG2 cells

The purpose of this study was to investigate the cytotoxic effects of tributylphosphate (TBP) and tris (2-butoxyethyl) phosphate (TBEP) and to explore the underlying molecular mechanism focusing on oxidative stress, apoptosis, and cell cycle arrest. The results showed that TBP and TBEP could inhibit cell proliferation, induce cellular reactive oxidative stress, and suppress the mitochondrial membrane potential in HepG2 cells. TBP and TBEP could induce both mitochondrial and p53 mediated apoptosis through different mitogen-activated protein kinase (MAPK) signal pathways. TBP activated the c-Jun N-terminal kinase (JNK) and extracellular regulated protein kinase (ERK1/2) pathways, while TBEP activated the JNK pathway. Furthermore, TBP and TBEP caused a concentration-dependent decrease of cyclin D1 expression and an increase of cyclin-dependent kinase (CDK) inhibitor proteins such as p21 and p27, resulting in significant cell cycle arrest in the G0/G1 phase. Taken together, the toxicity of TBP and TBEP on the HepG2 cells was associated with apoptosis and cell cycle arrest induced by oxidative stress.

Urinary Concentrations of Organophosphate Flame Retardant Metabolites and Pregnancy Outcomes among Women Undergoing in Vitro Fertilization

BACKGROUND

Evidence from animal studies suggests that exposure to organophosphate flame retardants (PFRs) can disrupt endocrine function and impair embryo development. However, no epidemiologic studies have been conducted to evaluate effects on fertility and pregnancy outcomes.

OBJECTIVES

We evaluated associations between urinary concentrations of PFR metabolites and outcomes of in vitro fertilization (IVF) treatment among couples recruited from an academic fertility clinic.

METHODS

This analysis included 211 women enrolled in the Environment And Reproductive Health (EARTH) prospective cohort study (2005-2015) who provided one or two urine samples per IVF cycle. We measured five urinary PFR 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)] using negative electrospray ionization liquid chromatography tandem mass spectrometry (LC-MS/MS). Molar concentrations of the urinary PFR metabolites were summed. We used multivariable generalized linear mixed models to evaluate the association of the PFR metabolites with IVF outcomes, accounting for multiple IVF cycles per woman.

RESULTS

Detection frequencies were high for BDCIPP (87%), DPHP (94%), and ip-PPP (80%), but low for tb-PPP (14%) and BCIPP (0%). We observed decreased success for several IVF outcomes across increasing quartiles of both summed and individual PFR metabolites (DPHP and ip-PPP) in our adjusted multivariable models. Significant declines in adjusted means from the lowest to highest quartile of ΣPFR were observed for the proportion of cycles resulting in successful fertilization (10% decrease), implantation (31%), clinical pregnancy (41%), and live birth (38%).

CONCLUSIONS

Using IVF to investigate human reproduction and pregnancy outcomes, we found that concentrations of some urinary PFR metabolites were negatively associated with proportions of successful fertilization, implantation, clinical pregnancy, and live birth. https://doi.org/10.1289/EHP1021.

Estimated tris(1,3-dichloro-2-propyl) phosphate exposure levels for US infants suggest potential health risks

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been widely used as a flame retardant and is commonly detected in environmental samples. Biomonitoring studies relying on urinary metabolite levels (i.e. bis(1,3-dichloro-2-propyl) phosphate (BDCIPP)) demonstrate widespread exposure, but TDCIPP intake is unknown. Intake data area critical component of meaningful risk assessments and are needed to elucidate the potential health impacts of TDCIPP exposure. Using biomonitoring data, we estimated TDCIPP intake for infants. Infants aged 2-18 months were recruited from central, North Carolina (n=43, recruited 2014-2015), and spot urine samples were analyzed for BDCIPP. TDCIPP intake rates were estimated using daily urine excretion and the fraction of TDCIPP excreted as BDCIPP in urine. Daily TDCIPP intake estimates ranged from 0.01-15.03 μg/kg-day for children included in our assessment, with some variation depending on model assumptions. The U.S. Consumer Products Safety Commission (CPSC) previously established an acceptable daily intake of 5μg/kg-day for non-cancer health risks. Depending on modeling assumptions, we found that 2-9% percent of infants had TDCIPP intake estimates above this threshold. Our results indicate that current TDCIPP exposure levels could pose health risks for highly exposed infants.

Influence of storage vial material on measurement of organophosphate flame retardant metabolites in urine

Use of organophosphate flame retardants (PFRs) has increased over the past decade with the phase out of polybrominated diphenyl ethers. Urinary metabolites of PFRs are used as biomarkers of exposure in epidemiologic research, which typically uses samples collected and stored in polypropylene plastic cryovials. However, a small study suggested that the storage vial material may influence reported concentrations. Therefore, we aimed to examine the influence of the storage vial material on analytical measurement of PFR urinary metabolites. Using urine samples collected from participants in the Environment and Reproductive Health (EARTH) Study, we analyzed the PFR metabolites in duplicate aliquots that were stored in glass and plastic vials (n = 31 pairs). Bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), diphenyl phosphate (DPHP) and isopropyl-phenyl phenyl phosphate (ip-PPP) were detected in 98%, 97% and 87% of duplicates. We observed high correlations between glass-plastic duplicates for BDCIPP (rs = 0.95), DPHP (rs = 0.79) and ip-PPP (rs = 0.82) (p < 0.0001). Urinary ip-PPP was an average of 0.04 ng/ml (p = 0.04) higher among samples stored in glass, with a mean relative difference of 14%. While this difference is statistically significant, it is small in magnitude. No differences were observed for BDCIPP or DPHP, however future research should seek to reduce the potential for type II error (false negatives). We conclude that storing urine samples in polypropylene plastic cryovials may result in slightly reduced concentrations of urinary ip-PPP relative to storage in glass vials and future research should seek to increase the sample size, reduce background variability and consider the material of the urine collection cup.

Japanese quail (Coturnix japonica) liver and thyroid gland histopathology as a result of in ovo exposure to the flame retardants tris(1,3-dichloro-2-propyl) phosphate and Dechlorane Plus

Japanese quails (Coturnix japonica) were exposed in ovo to tris(1,3-dichloro-2-propyl) phosphate (TDCIPP; 500 ng/µl), Dechlorane Plus (DP; 500 ng/µl), or a 1:1 mixture of these two to investigate the effects on liver and thyroid gland morphology. Histological examination of 14-day-old quails showed that exposure to TDCIPP or the mixture induced hepatic sinusoidal dilatation. No marked effects were seen for DP alone. In addition, the mixture produced divergence of thyroid gland follicles and proliferation of follicular cells. Our study is the first demonstrating histopathological alterations as a result of exposure during early development to the flame retardants TDCIPP or a TDCIPP-DP mixture suggesting the need for further research efforts to investigate potential adverse health effects associated with exposure to these environmental chemicals in wild birds.

Organophosphorus Flame Retardants in Pregnant Women and Their Transfer to Chorionic Villi

The potential for prenatal exposure has recently raised concerns over the health risks of endocrine disruptors; however, knowledge about human prenatal exposure to organophosphorus flame retardants (OPFRs) is lacking. In this study, 2-ethylhexyl diphenyl phosphate (EHDPP), tributyl phosphate (TBP), triphenyl phosphate (TPHP), and tris(2-chloroethyl) phosphate (TCEP) were detected in the majority of chorionic villus samples, with median concentrations of 13.6, 18.8, 11.1, and 0.51 ng/g of dry weight (dw), respectively, significantly higher than those in the matching maternal decidua samples (5.96, 10.8, 1.44, and 0.26 ng/g of dw, respectively). The ratios of concentrations in chorionic villi (containing embryos) to those in maternal deciduae (CMRs) were 4.17, 3.82, 2.81, and 2.00 for EHDPP, TPHP, TBP, and TCEP, respectively, which correlated with their log K_ow values (p = 0.003). The results of transthyretin (TTR) binding assays indicated that the stronger the binding ability to TTR, the higher the CMRs. The median concentrations of the metabolites diphenyl phosphate (DPHP), dibutyl phosphate (DBP), and bis(2-chloroethyl) phosphate (BCEP) were 4.11, 429, and 157 ng/g of dw in chorionic villi, higher than those in deciduae (1.64, 181, and 25.4 ng/g of dw, respectively). The ratios of DPHP/TPHP and DPHP/EHDPP were 0.20 and 0.43 in chorionic villi and 1.24 and 2.03 in deciduae, respectively, much lower than those of DBP/TBP and BCEP/TCEP (20.9 and 165.6 in chorionic villi and 13.1 and 35.3 in deciduae, respectively), suggesting that the difference in metabolism between the deciduae and chorionic villi would affect their maternal transfer.

Halogen-free organophosphorus flame retardants caused oxidative stress and multixenobiotic resistance in Asian freshwater clams (Corbicula fluminea)

Halogen-free organophosphorus flame retardants are widespread in aquatic environments. Although it has been documented that they affect the behavior and reproduction of aquatic species, researches investigating cellular detoxification and the defense system in bivalves are scarce. In this study, adult Asian clams (C. fluminea) were exposed to tris (2-butoxyethyl) phosphate (TBEP) and tributyl phosphate (TBP) at 20, 200, and 2000 μg/L for 28 d. The results showed no noticeable difference in siphoning behavior. However, the siphoning behavior displayed a trend toward a slight decrease in the treatment groups. GR activity was markedly reduced compared with the control groups, whereas the levels of cyp4 significantly increased following the 2000 μg/L TBP treatments (p < 0.05). Moreover, the levels of gsts1 and gstm1 significantly decreased following all TBEP treatments and were significantly inhibited by 20 μg/L TBP (p < 0.05). The adverse effects on antioxidant enzymes suggested that C. fluminea mainly relies on the antioxidant system to reduce damage without an increase in MDA levels following exposure to a low concentration. Moreover, mRNA expression levels of heat shock proteins (hsp 22, 40, 60, 70, and 90) were significantly down-regulated with TBEP and TBP treatments lower than 200 μg/L (p < 0.05), whereas significant up-regulations were observed for hsp 22 and hsp 70 in response to 2000 μg/L TBP treatment (p < 0.05). Up-regulation of ATP-binding cassette (ABC) transporter genes (abcb1 and abcc1) showed that TBEP and TBP could activate the multixenobiotic resistance (MXR) system to discharge xenobiotics in C. fluminea, which kept its shell closed at high concentrations to prevent xenobiotic entry. Our results provide a new insight into the different mechanisms of cellular detoxification and the MXR system of C. fluminea in response to low and high concentrations of TBEP and TBP.

Birds and flame retardants: A review of the toxic effects on birds of historical and novel flame retardants

Flame retardants (FRs) are a diverse group of chemicals, many of which persist in the environment and bioaccumulate in biota. Although some FRs have been withdrawn from manufacturing and commerce (e.g., legacy FRs), many continue to be detected in the environment; moreover, their replacements and/or other novel FRs are also detected in biota. Here, we review and summarize the literature on the toxic effects of various FRs on birds. Birds integrate chemical information (exposure, effects) across space and time, making them ideal sentinels of environmental contamination. Following an adverse outcome pathway (AOP) approach, we synthesized information on 8 of the most commonly reported endpoints in avian FR toxicity research: molecular measures, thyroid-related measures, steroids, retinol, brain anatomy, behaviour, growth and development, and reproduction. We then identified which of these endpoints appear more/most sensitive to FR exposure, as determined by the frequency of significant effects across avian studies. The avian thyroid system, largely characterized by inconsistent changes in circulating thyroid hormones that were the only measure in many such studies, appears to be moderately sensitive to FR exposure relative to the other endpoints; circulating thyroid hormones, after reproductive measures, being the most frequently examined endpoint. A more comprehensive examination with concurrent measurements of multiple thyroid endpoints (e.g., thyroid gland, deiodinase enzymes) is recommended for future studies to more fully understand potential avian thyroid toxicity of FRs. More research is required to determine the effects of various FRs on avian retinol concentrations, inconsistently sensitive across species, and to concurrently assess multiple steroid hormones. Behaviour related to courtship and reproduction was the most sensitive of all selected endpoints, with significant effects recorded in every study. Among domesticated species (Galliformes), raptors (Accipitriformes and Falconiformes), songbirds (Passeriformes), and other species of birds (e.g. gulls), raptors seem to be the most sensitive to FR exposure across these measurements. We recommend that future avian research connect biochemical disruptions and changes in the brain to ecologically relevant endpoints, such as behaviour and reproduction. Moreover, connecting in vivo endpoints with molecular endpoints for non-domesticated avian species is also highly important, and essential to linking FR exposure with reduced fitness and population-level effects.

Predictors of urinary flame retardant concentration among pregnant women

BACKGROUND

Organophosphate compounds are commonly used in residential furniture, electronics, and baby products as flame retardants and are also used in other consumer products as plasticizers. Although the levels of exposure biomarkers are generally higher among children and decrease with age, relatively little is known about the individual characteristics associated with higher levels of exposure. Here, we investigate urinary metabolites of several organophosphate flame retardants (PFRs) in a cohort of pregnant women to evaluate patterns of exposure.

METHODS

Pregnant North Carolina women (n=349) provided information on their individual characteristics (e.g. age and body mass index (BMI)) as a part of the Pregnancy Infection and Nutrition Study (2002-2005). Women also provided second trimester urine samples in which six PFR metabolites were measured using mass spectrometry methods.

RESULTS

PFR metabolites were detected in every urine sample, with BDCIPP, DHPH, ip-PPP and BCIPHIPP detected in >80% of samples. Geometric mean concentrations were higher than what has been reported previously for similarly-timed cohorts. Women with higher pre-pregnancy BMI tended to have higher levels of urinary metabolites. For example, those classified as obese at the start of pregnancy had ip-PPP levels that were 1.52 times as high as normal weight range women (95% confidence interval: 1.23, 1.89). Women without previous children also tended to have higher urinary levels of DPHP, but lower levels of ip-PPP. In addition, we saw strong evidence of seasonal trends in metabolite concentrations (e.g. higher DPHP, BDCIPP, and BCIPHIPP in summer, and evidence of increasing ip-PPP between 2002 and 2005).

CONCLUSIONS

Our results indicate ubiquitous exposure to PFRs among NC women in the early 2000s. Additionally, our work suggests that individual characteristics are related to exposure and that temporal variation, both seasonal and annual, may exist.

A Review of Organophosphate Esters in the Environment from Biological Effects to Distribution and Fate

Organophosphate esters (OPEs) are synthetic phosphoric acid derivatives used in a wide variety of applications including as flame retardants and plasticizers. Their production and usage has increased in recent years, due to the phase-out of other flame retardant formulations (e.g., polybrominated diphenyl ethers). As such, there has been a recent push to understand the global distribution of OPEs and their behaviour in biota. Multiple studies have been published over the last few years pertaining to OPE concentrations in biotic and abiotic environmental compartments, as well as the metabolism of OPEs in biota. This paper aims to provide a brief review of the occurrence and levels of OPEs in the environment, as well as recent developments concerning the elucidation of OPE metabolism in biota.

Parental transfer of tris(1,3-dichloro-2-propyl) phosphate and transgenerational inhibition of growth of zebrafish exposed to environmentally relevant concentrations

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a re-emerging environmental contaminant that has been frequently detected at sub-ppb (<μg/L) concentrations in natural waters. The objective of this study was to evaluate effects of TDCIPP on growth in initial generation (F₀) zebrafish after chronic exposure to environmentally relevant concentrations, and to examine possible parental transfer of TDCIPP and transgenerational effects on growth of first generation (F₁) larvae. When zebrafish (1-month old) were exposed to 580 or 7500 ng TDCIPP/L for 240 days, bioconcentration resulted in significantly less growth as measured by body length, body mass, brain-somatic index (BSI) and hepatic-somatic index (HSI) in F₀ females but not F₀ males. These effects were possibly due to down-regulation of expression of genes along the growth hormone/insulin-like growth factor (GH/IGF) axis. Furthermore, residues of TDCIPP were detected in F₁ eggs after exposure of parents, which resulted in less survival, body length and heart rate in F₁ individuals. Down-regulation of genes in the GH/IGF axis (e.g., gh, igf1) might be responsible for transgenerational toxicity. This study provides the first known evidence that exposure of zebrafish to environmentally relevant concentrations of TDCIPP during development can inhibit growth of offspring, which were not exposed directly to TDCIPP.

Do flame retardant chemicals increase the risk for thyroid dysregulation and cancer?

PURPOSE OF REVIEW

Flame retardant chemicals are added to consumer products to reduce fire incidence and severity; approximately 1.5 million tons of these chemicals are used annually. However, their widespread use has led to their ubiquitous presence in the environment and chronic accumulation in human tissues. We summarize current trends in human flame retardant chemical exposure, and review recent data highlighting concerns for thyroid dysregulation and cancer risk in human populations.

RECENT FINDINGS

Polybrominated diphenyl ethers were once commonly used as flame retardant chemicals, but recently were phased out. Exposure is associated with thyroid dysregulation (mainly T4 reductions) in animals, with new work focusing on specific mechanisms of action. Polybrominated diphenyl ethers also impact human thyroid regulation and are related to clinical thyroid disease, but associations appear both dose and life-stage dependent. Emerging data suggest that common alternate flame retardant chemicals may be more potent thyroid disruptors than their predecessors, which is particularly concerning given increasing levels of exposure.

SUMMARY

Potential health impacts of flame retardant chemicals are only beginning to be understood for 'legacy flame retardant chemicals' (i.e., polybrominated diphenyl ethers), and are largely unevaluated for newer-use chemicals. Cumulatively, current data suggest impact on thyroid regulation is likely, potentially implicating flame retardant chemicals in thyroid disease and cancers for which thyroid dysregulation impacts risk or prognosis.

In ovo tris(2-butoxyethyl) phosphate concentrations significantly decrease in late incubation after a single exposure via injection, with no evidence of effects on hatching success or latent effects on growth or reproduction in zebra finches

Zebra finch (Taeniopygia guttata) eggs were injected with the organophosphate triester flame retardant tris(2-butoxyethyl) phosphate (TBOEP) at 0 μg/g, 0.01 μg/g, 1 μg/g, 10 μg/g, or 50 μg/g egg. Subsets of high-dose eggs were collected throughout incubation to measure TBOEP, which started declining in late incubation and then decreased rapidly to 28% of injected concentration by hatching. The authors found no effects of TBOEP on survival, growth, or reproduction even at very high doses. Environ Toxicol Chem 2017;36:83-88. © 2016 SETAC.

Rice ingestion is a major pathway for human exposure to organophosphate flame retardants (OPFRs) in China

Although organophosphate flame retardants (OPFRs) have been shown to accumulate in abiotic and biotic environmental compartments, data about OPFRs concentrations in various foods are limited and are none in humans through diets. In this work, the concentrations of 6 typical OPFRs were investigated in 50 rice samples, 75 commonly consumed foods and 45 human hair samples from China. The dietary intakes of OPFRs for adult people via food ingestion were estimated. The concentrations of ΣOPFRs in foods ranged from 0.004ng/g to 287ng/g. OPFRs were detected in 53.3% of the human hair samples. The highest OPFRs concentrations were found in rice and vegetables. Tri(2-chloroethyl)phosphate(TCEP), tris(2-chloroisopropyl)phosphate(TCIPP), and tri(2-ethyltexyl)phosphate(TEHP) were predominant in all food samples. OPFRs concentrations in foods were not significantly affected by the packaging materials. The mean dietary intakes of ΣOPFRs for adult males and females were 539 and 601ng/kg body weight/day, respectively. The greatest contribution to these values is from rice, accounting for approximately 60% of the total intake, particularly from rice protein. Rice ingestion was considered a potential major pathway for human exposure to OPFRs, and regional differences in the levels of OPFRs in foods and dietary differences should be given more attention in the future.

Multigenerational effects of tris(1,3-dichloro-2-propyl) phosphate on the free-living ciliate protozoa Tetrahymena thermophila exposed to environmentally relevant concentrations and after subsequent recovery

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is considered a re-emerging environmental pollutant, and exposure to environmentally relevant concentrations has been shown to cause individual developmental toxicity in zebrafish and the water flea (Daphnia magna). However, multigenerational effects during exposure to TDCIPP and after subsequent recovery were unknown. In the present study, individuals of a model aquatic organism, the ciliated protozoan, T. thermophila were exposed to environmentally-relevant concentrations of TDCIPP (0, 300 or 3000 ng/L) for 60 days (e.g., theoretically 372 generations) followed by a 60-day period of recovery, during which T. thermophila were not exposed to TDCIPP. During exposure and after exposure, effects at the molecular, histological, individual and population levels were examined. Multigenerational exposure to 300 or 3000 ng TDCIPP/L for 60 days significantly decreased numbers of individuals, sizes of individuals, expressed as length and width of bodies, number of cilia, and depth and diameter of basal bodies of cilia, and up-regulated expressions of genes related to assembly and maintenance of cilia. Complete or partial recoveries of theoretical sizes of populations as well as sizes of individuals and expressions of genes were observed during the 60-day recovery period. Effects on number of cilia and depth and diameter of basal body of cilia were not reversible and could still be observed long after cease of TDCIPP exposure. Collectedly, and shown for the first time, multigenerational effects to T. thermophila were caused by exposure to environmentally relevant concentrations of TDCIPP. Also, there were multi-generational effects at the population level that were not caused by carry-over exposure to TDCIPP. The "permanent" alterations and their potential significance are discussed.

Retrospective analysis of organophosphate flame retardants in herring gull eggs and relation to the aquatic food web in the Laurentian Great Lakes of North America

With the phase-out and regulation of some flame retardant chemicals, the production and usage of organophosphate triester flame retardants (OPFRs) has increased in recent years. In the present study, 14 OPFRs (either chlorinated, brominated or non-halogenated) were analyzed in egg pools of 10-13 individual herring gull eggs from five colonial nesting sites for 11 years spanning 1990-2010, (for a total of n=55 egg pools) in the Laurentian Great Lakes of North America (Chantry Island, Fighting Island, Agawa Rocks, Toronto Harbour and Gull Island). OPFR profiles varied slightly between colony sites and collection years. For all five sites tris(2-chloroisopropyl) phosphate (TCIPP), tris(2-chloroethyl) phosphate (TCEP) and tris(2-butoxyethyl) phosphate (TBOEP) were detected, while triphenyl phosphate (TPHP) was only quantifiable in eggs from Chantry Island and Gull Island collected in 2008 and 2010. For the 2010 egg pools, the ΣOPFR concentrations were generally low and ranged from 2.02 to 6.69 ng/g wet weight (ww). ΣOPFR concentrations in 2010 were significantly higher (p<0.05) than they were between 1990 and 2004 (4.06 vs. 1.55 ng/g ww, respectively). In a pilot examination of Great Lakes aquatic food webs, 2010-collected alewife and rainbow smelt (major herring gull fish prey) and lake trout from western Lake Erie and Ontario, only contained TBOEP at low to sub ng/g ww concentrations. These results demonstrate that low to sub-ppb concentrations of at least three OPFRs, TCIPP, TCEP and TBOEP, have been persistent in herring gull eggs from the Great Lakes for at least the past 20 years, probably bioaccumulate mainly via the fish diet, and are transferred to the eggs of exposed herring gulls.

Urinary biomarkers of flame retardant exposure among collegiate U.S. gymnasts

Flame retardants are widely used in polyurethane foam materials including gymnastics safety equipment such as pit cubes and landing mats. We previously reported elevated concentrations of flame retardants in the air and dust of a U.S. gymnastics training facility and elevated PentaBDE in the serum of collegiate gymnasts. Our objective in this pilot study was to compare urinary biomarkers of exposure to other flame retardants and additives of polyurethane foam including tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), triphenyl phosphate (TPHP) and 2-ethylhexyl- 2,3,4,5-tetrabromobenzoate (EH-TBB) in samples collected from 11 collegiate gymnasts before and after a gymnastics practice (n=53 urine samples total). We identified a 50% increase in the TPHP biomarker (p=0.03) from before to after practice, a non-significant 22% increase in the TDCIPP biomarker (p=0.14) and no change for the EH-TBB biomarker. These preliminary results indicate that the gymnastics training environment can be a source of recreational exposure to flame retardants. Such exposures are likely widespread, as we identified flame retardants in 89% of foam samples collected from gyms across the U.S.

Editor's Highlight: Comparative Toxicity of Organophosphate Flame Retardants and Polybrominated Diphenyl Ethers to Caenorhabditis elegans

With the phasing-out of the polybrominated diphenyl ether (PBDE) flame retardants due to concerns regarding their potential developmental toxicity, the use of replacement compounds such as organophosphate flame retardants (OPFRs) has increased. Limited toxicity data are currently available to estimate the potential adverse health effects of the OPFRs. The toxicological effects of 4 brominated flame retardants, including 3 PBDEs and 3,3',5,5'-tetrabromobisphenol A, were compared with 6 aromatic OPFRs and 2 aliphatic OPFRs. The effects of these chemicals were determined using 3 biological endpoints in the nematode Caenorhabditis elegans (feeding, larval development, and reproduction). Because C. elegans development was previously reported to be sensitive to mitochondrial function, results were compared with those from an in vitro mitochondrial membrane permeabilization (MMP) assay. Overall 11 of the 12 flame retardants were active in 1 or more C. elegans biological endpoints, with only tris(2-chloroethyl) phosphate inactive across all endpoints including the in vitro MMP assay. For 2 of the C. elegans endpoints, at least 1 OPFR had similar toxicity to the PBDEs: triphenyl phosphate (TPHP) inhibited larval development at levels comparable to the 3 PBDEs; whereas TPHP and isopropylated phenol phosphate (IPP) affected C. elegans reproduction at levels similar to the PBDE commercial mixture, DE-71. The PBDEs reduced C. elegans feeding at lower concentrations than any OPFR. In addition, 9 of the 11 chemicals that inhibited C. elegans larval development also caused significant mitochondrial toxicity. These results suggest that some of the replacement aromatic OPFRs may have levels of toxicity comparable to PBDEs.

Analysis of human hair to assess exposure to organophosphate flame retardants: Influence of hair segments and gender differences

Hair is a promising, non-invasive, human biomonitoring matrix that can provide insight into retrospective and integral exposure to organic pollutants. In the present study, we measured the concentrations of organophosphate flame retardants (PFRs) in hair and serum samples from university students in Guangzhou, China, and compared the PFR concentrations in the female hair segments using paired distal (5~10cm from the root) and proximal (0~5cm from the root) samples. PFRs were not detected in the serum samples. All PFRs except tricresyl phosphate (TMPP) and tri-n-propyl phosphate (TPP) were detected in more than half of all hair samples. The concentrations of total PFRs varied from 10.1 to 604ng/g, with a median of 148ng/g. Tris(chloroisopropyl) phosphate (TCIPP) and tri(2-ethylexyl) phosphate (TEHP) were the predominant PFRs in hair. The concentrations of most PFRs in the distal segments were 1.5~8.6 times higher than those in the proximal segments of the hair (t-test, p<0.05), which may be due to the longer exposure time of the distal segments to external sources. The values of log (PFR concentrations-distal/PFR concentrations-proximal) were positively and significantly correlated with log KOA of PFRs (p<0.05, r=0.68), indicating that PFRs with a higher log KOA tend to accumulate in hair at a higher rate than PFRs with a lower log KOA. Using combined segments of female hair, significantly higher PFR concentrations were observed in female hair than in male hair. In contrast, female hair exhibited significantly lower PFR concentrations than male hair when using the same hair position for both genders (0-5cm from the scalp). The controversial results regarding gender differences in PFRs in hair highlight the importance of segmental analysis when using hair as an indicator of human exposure to PFRs.

Endocrine disrupting activities of surface water associated with a West Virginia oil and gas industry wastewater disposal site

Currently, >95% of end disposal of hydraulic fracturing wastewater from unconventional oil and gas operations in the US occurs via injection wells. Key data gaps exist in understanding the potential impact of underground injection on surface water quality and environmental health. The goal of this study was to assess endocrine disrupting activity in surface water at a West Virginia injection well disposal site. Water samples were collected from a background site in the area and upstream, on, and downstream of the disposal facility. Samples were solid-phase extracted, and extracts assessed for agonist and antagonist hormonal activities for five hormone receptors in mammalian and yeast reporter gene assays. Compared to reference water extracts upstream and distal to the disposal well, samples collected adjacent and downstream exhibited considerably higher antagonist activity for the estrogen, androgen, progesterone, glucocorticoid and thyroid hormone receptors. In contrast, low levels of agonist activity were measured in upstream/distal sites, and were inhibited or absent at downstream sites with significant antagonism. Concurrent analyses by partner laboratories (published separately) describe the analytical and geochemical profiling of the water; elevated conductivity as well as high sodium, chloride, strontium, and barium concentrations indicate impacts due to handling of unconventional oil and gas wastewater. Notably, antagonist activities in downstream samples were at equivalent authentic standard concentrations known to disrupt reproduction and/or development in aquatic animals. Given the widespread use of injection wells for end-disposal of hydraulic fracturing wastewater, these data raise concerns for human and animal health nearby.

In vitro assessment of thyroid hormone receptor activity of four organophosphate esters

Previous animal experiments have implied that organophosphate esters (OPEs) have a disruption effect on the thyroid endocrine system. However, knowledge of the toxicological mechanism remains limited. In this study, the activities of four OPEs have been characterized against the thyroid hormone (TH) nuclear receptor (TR) using two in vitro models, with the aim of evaluating their toxicity mechanisms towards the TR. The results of a TH-dependent cell proliferation assay showed that tris(2-chloro-1-(chloromethyl)ethyl)phosphate (TDCPP) could induce cell growth, while the other three OPEs had no effect. The results of a luciferase reporter gene assay revealed that all four of the OPEs tested in the current study showed agonistic activity towards TRβ, with TDCPP being the most potent one. Moreover, molecular docking revealed that all the tested OPEs could fit into the ligand binding pocket of TRβ, with TDCPP binding more effectively than the other three OPEs. Taken together, these data suggest that OPEs might disrupt the thyroid endocrine system via a mechanism involving the activation of TR.

Bisphenol S alters embryonic viability, development, gallbladder size, and messenger RNA expression in chicken embryos exposed via egg injection

Amid concerns about the toxicological effects and environmental prevalence of bisphenol A (BPA), efforts to find suitable, safer replacement alternatives are essential. Bisphenol S (BPS) is a potential chemical substitute for BPA; however, few studies are available confirming that it has a more desirable ecotoxicological profile. In the present study, BPS was injected into the air cell of unincubated, fertilized chicken embryos at 6 concentrations ranging from 0 μg/g to 207 μg/g egg to determine effects on pipping success, development, hepatic messenger ribonucleic acid (mRNA) expression, thyroid hormone levels, and circulating bile acid concentrations. Concentrations of BPS increased in a dose-dependent manner in whole-embryo homogenates, and exposure to the highest dose, 207 μg/g, resulted in decreased pipping success (estimated median lethal dose  = 279 μg/g; 95% confidence interval = 161-486 μg/g). Exposure to BPS also reduced growth metrics including embryo mass and tarsus length, whereas the most pronounced phenotypic effect was the concentration-dependent, significant increase in gallbladder size at concentrations ≥52.8 μg/g. These adverse phenotypic outcomes were associated with the modulation of gene targets from a chicken ToxChip polymerase chain reaction array, which are involved with xenobiotic metabolism, lipid homeostasis, bile acid synthesis, and the thyroid hormone pathway. Expression levels of 2 estrogen-responsive genes, apolipoprotein II and vitellogenin, were too low at the sampling time point assessed (i.e., pipping embryos) to quantify changes, and no effects were observed on circulating free thyroxine or bile acid concentrations. The present study provides novel, whole-animal toxicological data for a BPA replacement alternative that is not well characterized. Environ Toxicol Chem 2016;35:1541-1549. © 2015 SETAC.

Effects of tris(1,3-dichloro-2-propyl)phosphate on pathomorphology and gene/protein expression related to thyroid disruption in rats

Previous studies demonstrated that tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) caused adverse effects on thyroid hormone (TH) imbalance in aquatic and avian organisms. This study focused on the effects of TDCIPP on thyroid function and hormone homeostasis in mammals. Pubertal female Sprague-Dawley rats were orally administered 50, 100, or 250 mg per kg per d of TDCIPP from postnatal day (PND) 22 to PND42 for 21 days. The serum triiodothyronine (T3) levels increased significantly at 250 mg per kg per d of TDCIPP. There were no significant differences in the body weight, serum thyroxine (T4) and free thyroxine (FT4) levels between the control and TDCIPP treated groups. There were significant dose-dependent increases in the mRNA and protein expression levels of genes related to drug metabolism (cytochrome-p450-3A1, CYP3A1) and TH clearance (udp-glucuronosyltransferase-1A6, UGT1A6) in the liver. Treatment with TDCIPP increased hepatic type 1 deiodinase (DIO1) mRNA at 250 mg per kg per d but down-regulated hepatic TH receptor beta (TRβ) mRNA expression. In addition, TDCIPP exposure induced slight thyroid follicular hyperplasia, and several genes involved in TH biosynthesis (NIS, TPO, Tg) were altered at 100 and 250 mg per kg per d of TDCIPP. Nevertheless, serum thyroid stimulating hormone (TSH) levels and the receptor (TSHr) mRNA significantly decreased at only the low dose group. Based on these results, we certified that TDCIPP disturbs the normal bioprocess on TH synthesis, biotransformation or clearance, and hepatic detoxification of pubertal female SD rats, causing thyroid function disorder.

Kinetics of tris (1-chloro-2-propyl) phosphate (TCIPP) metabolism in human liver microsomes and serum

Tris(1-chloro-2-propyl) phosphate (TCIPP) is an emerging contaminant which is ubiquitous in the indoor and outdoor environment. Moreover, its presence in human body fluids and biota has been evidenced. Since no quantitative data exist on the biotransformation or stability of TCIPP in the human body, we performed an in vitro incubation of TCIPP with human liver microsomes (HLM) and human serum (HS). Two metabolites, namely bis(2-chloro-isopropyl) phosphate (BCIPP) and bis(1-chloro-2-propyl) 1-hydroxy-2-propyl phosphate (BCIPHIPP), were quantified in a kinetic study using HLM or HS (only BCIPP, the hydrolysis product) and LC-MS. The Michaelis-Menten model fitted best the NADPH-dependent formation of BCIPHIPP and BCIPP in HLM, with respective V(MAX) of 154 ± 4 and 1470 ± 110 pmol/min/mg protein and respective apparent K(m) of 80.2 ± 4.4 and 96.1 ± 14.5 μM. Hydrolases, which are naturally present in HLM, were also involved in the production of BCIPP. A HS paraoxonase assay could not detect any BCIPP formation above 38.6 ± 10.8 pmol/min/μL serum. Our data indicate that BCIPP is the major metabolite of TCIPP formed in the liver. To our knowledge, this is the first quantitative assessment of the stability of TCIPP in tissues of humans or any other species. Further research is needed to confirm whether these biotransformation reactions are associated with a decrease or increase in toxicity.

Acute Exposure to Tris(1,3-dichloro-2-propyl) Phosphate (TDCIPP) Causes Hepatic Inflammation and Leads to Hepatotoxicity in Zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been frequently detected in environmental media and has adverse health effect on wildlife and humans. It has been implicated to have hepatotoxicity, but its molecular mechanisms remain unclear. In the present study, adult male zebrafish were exposed to TDCIPP and global hepatic gene expression was examined by RNA-Seq and RT-qPCR in order to understand the molecular mechanisms of TDCIPP-induced hepatotoxicity. Our results indicated that TDCIPP exposure significantly up-regulated the expression of genes involved in endoplasmic reticulum stress and Toll-like receptor (TLR) pathway, implying an inflammatory response, which was supported by up-regulation of inflammation-related biomaker genes. Hepatic inflammation was further confirmed by histological observation of increase of infiltrated neutrophils and direct observation of liver recruitment of neutrophils labeled with Ds-Red fluorescent protein of Tg(lysC:DsRed) zebrafish upon TDCIPP exposure. To further characterize the hepatotoxicity of TDCIPP, the expression of hepatotoxicity biomarker genes, liver histopathology and morphology were examined. The exposure to TDCIPP significantly up-regulated the expression of several biomarker genes for hepatotoxicity (gck, gsr and nqo1) and caused hepatic vacuolization and apoptosis as well as increase of the liver size. Collectively, our results suggest that exposure to TDCIPP induces hepatic inflammation and leads to hepatotoxicity in zebrafish.

Environmentally Relevant Concentrations of the Flame Retardant Tris(1,3-dichloro-2-propyl) Phosphate Inhibit Growth of Female Zebrafish and Decrease Fecundity

Bioconcentrations of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) in brain, gonad, and liver as well as effects on fecundity and development of zebrafish (Danio rerio) were determined. Zebrafish (1-month old) were exposed to environmentally relevant concentrations of 29 ± 2.1, 600 ± 21, or 6300 ± 130 ng TDCIPP/L. After 120 days of exposure, TDCIPP accumulated in the brain, gonad, and liver with bioconcentration factors of 460, 38, and 87 in females and 26, 55, and 110 in males, respectively. TDCIPP accumulated to a greater extent in brains of females than those of males. Exposure to 6300 ± 130 ng TDCIPP/L resulted in significantly (P < 0.05) fewer eggs being produced, but the histology of the gonad, plasma concentrations of estradiol and 11-ketotestosterone, and expression of genes involved in hypothalamic-pituitary-gonadal-liver axis were not significantly (P > 0.05) different between individuals exposed to TDCIPP and the unexposed control fish. Exposure to TDCIPP resulted in shorter body length, lighter body mass, and lower gonadal-somatic index in females. These effects were possibly due to down-regulation of expression of genes along the growth hormone/insulin-like growth factor (GH/IGF) axis. Correlations between the production of eggs and developmental parameters or expression of genes along the GH/IGF axis further suggested that environmentally relevant concentrations of TDCIPP could have adverse effects on reproduction, possibly due to the inhibition of the growth of females.

High Exposure to Organophosphate Flame Retardants in Infants: Associations with Baby Products

Infant products containing polyurethane foam are commonly treated with organophosphate flame retardants (PFRs), including tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and triphenyl phosphate (TPHP). Infants may have greater exposure due to greater contact with these products, yet little is known about levels of exposure or the factors contributing to higher exposure. We recruited children age 2-18 months from North Carolina to investigate PFR exposure (n = 43; recruited 2014-2015). Parents provided information on potential sources and modifiers of exposure, and reported whether they owned common infant products. We measured five PFR metabolites in urine samples collected from children. TDCIPP and TPHP metabolites (bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) and diphenyl phosphate (DPHP)) were most commonly detected (>93% detect). Other metabolites were detected infrequently (<35% detect). Although we did not observe a clear age trend for infants, BDCIPP levels were substantially higher than those reported for adults (geometric mean = 7.3 ng/mL). The number of infant products owned was strongly associated with BDCIPP; children with >16 products had BDCIPP levels that were 6.8 times those with <13 (p = 0.02). Infants attending daycare centers also had higher BDCIPP levels (3.7 times those of others; p = 0.07), suggesting time spent in this microenvironment contributes to higher exposure. In contrast, DPHP levels were not related to products owned, time in different microenvironments, or behavior.

Effects of Tris(1,3-dichloro-2-propyl) Phosphate on Growth, Reproduction, and Gene Transcription of Daphnia magna at Environmentally Relevant Concentrations

The synthetic flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been frequently detected in natural waters, and its maximum concentration ever reported is 377 ng/L. However, information on the adverse effects of environmentally relevant concentrations of TDCIPP on aquatic organisms are totally unknown. In this study, <12-h old water fleas, D. magna, were exposed to concentrations of 0, 65±7.1, 550±33, or 6500±1400 ng/L TDCIPP, and dose- and time-dependent effects on reproduction and development were evaluated. Sequences of genes of D. magna were obtained from the National Center for Biotechnology Information and were used to develop PCR arrays for D. magna. Arrays were then used to study transcriptional responses of D. magna to TDCIPP. Exposure to environmentally relevant concentrations of TDCIPP significantly decreased fecundity as well as length of F0 and F1 generations. Transcriptional responses showed that, of the 155 genes tested, expressions of 57 genes were significantly changed, and some changes occurred following exposure to environmentally relevant concentrations (i.e., 65±7.1 and 550±23 ng/L). Furthermore, pathways related to protein synthesis and metabolism and endocytosis were considered to be significantly affected in a dose- and time-dependent manner and might be responsible for TDCIPP-induced reproductive and developmental toxicities.

Spatial and temporal comparisons of legacy and emerging flame retardants in herring gull eggs from colonies spanning the Laurentian Great Lakes of Canada and United States

In the Laurentian Great Lakes basin of North America, an increasing number of chemicals of emerging concern (CECs) are being investigated, including legacy and replacement flame retardants (FRs). In the present study, 14 polybrominated diphenyl ethers (PBDEs), 23 non-PBDEs halogenated FRs (NPHFRs) and 16 organophosphate ester FRs (OPE-FRs) were analyzed in 100 individual eggs collected in 2012 and 2013 and in 15 egg pools of herring gulls collected in 2012 from 20 colonies across the entire Laurentian Great Lakes basin. For CEC-FRs in eggs from all colonies, 14 PBDEs, 12 NPHFRs and 9 OPE-FRs were quantifiable in at least one of the 115 analyzed samples. The mean sum PBDE (Σ14PBDE) concentrations ranged from 244 to 657 ng/g wet weight (ww), and on average were 1-2 orders of magnitude greater than the Σ12NPHFR concentrations (13.8-35.6 ng/g ww), and 2-3 orders of magnitude greater than Σ9OPE-FR concentrations (0.31-2.14 ng/g ww). Mean Σ14PBDE and sum of syn- and anti-Dechlorane Plus isomer (Σ2DDC-CO) concentrations in eggs from colonies within Laurentian Great Lakes Areas of Concern (AOCs) were in most cases greater than in eggs from nearby colonies outside of AOCs. Comparing CEC-FR concentrations in eggs collected in 2012-2013 to those previously measured in eggs collected approximately 7 years earlier (2006 and 2008) showed that Σ7PBDE (BDE-28, -47, -100, -99, -154,-153 and -183) mean concentrations in eggs from 6 colonies were approximately 30% less than they were in eggs from the same colonies from the earlier time period, whereas 3 current-use FR (BDE-209, HBCDD and Σ2DDC-CO) concentrations were significantly greater (p<0.05) than previously measured. Between 2006 and 2013 there were significant changes in individual PBDE patterns for BDE-71, -138, -153, -203, -206 and -207. Among all of the examined CEC-FRs, concentrations of Σ4PBDE (BDE-47, -99, -100 and -153) and HBCDD in gull eggs from all colonies were greater than or comparable to their lowest observed effect concentrations (LOECs) based on in ovo egg injection studies. Overall, the current profiles of a broad suite of FRs in Laurentian Great Lakes herring gull eggs highlights the need to better understand e.g., exposure-effect implications and metabolism of FRs, i.e. OPE-FRs, and emphasizes the importance of continued monitoring of CEC-FRs whose concentrations appear to be increasing, including BDE-209, HBCDD and DDC-COs.

Bioconcentration, metabolism and alterations of thyroid hormones of Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) in Zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate widely used as a flame retardant, and has frequently been detected in the environment and biota. The present study investigates the bioconcentration and metabolism of TDCPP in fish. Zebrafish embryos (from 2h post-fertilization) were exposed to TDCPP (0, 4, 20 and 100μg/L) for six months. Exposure to TDCPP significantly induced phase I metabolic enzymes 7-ethoxyresorufin O-deethylase (EROD) and 7-methoxyresorufin O-demethylase (MROD) in fish. The mRNA expression of genes related to Phase I and II metabolic enzymes, such as cyp1a1, cyp1b1, cyp1c1 and ugt1ab were also significantly upregulated. Exposure to TDCPP significantly reduced plasma thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels in females. Chemicals analysis indicated significant levels of TDCPP and its metabolite, bis (1,3-dichloro-2-propyl) phosphate (BDCPP), in the liver. The present study reveals that exposure to low concentrations of TDCPP can cause bioconcentration in fish, and TDCPP can be readily metabolized in liver.

Neurotoxicological and thyroid evaluations of rats developmentally exposed to tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and tris(2-chloro-2-ethyl)phosphate (TCEP)

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and tris(2-chloro-2-ethyl)phosphate (TCEP) are organophosphorous flame retardants with widespread usage and human exposures through food, inhalation, and dust ingestion. They have been detected in human tissues including urine and breast milk. Reports of disrupted neural growth in vitro, abnormal development in larval zebrafish, and altered thyroid hormones in several species have raised concern for neurodevelopmental toxicity. This is especially the case for TDCIPP, which is more potent and has more activity in those assays than does TCEP. We evaluated the potential for developmental neurotoxicity of TDCIPP and TCEP in a mammalian model. Pregnant Long-Evans rats were administered TDCIPP (15, 50, or 150 mg/kg/day) or TCEP (12, 40, 90 mg/kg/day) via oral gavage from gestational day 10 to weaning. Corn oil was the vehicle control in both studies. Body weight and righting reflex development were monitored in all pups. A subset of offspring at culling and weaning, and dams at weaning, were sacrificed for serum and organ collection for measurement of brain, liver, and thyroid weights, serum thyroid levels, and serum and brain acetylcholinesterase activities. Brain weights were also measured in a group of adult TDCIPP-treated offspring. One male and one female from each litter were allocated for behavioral testing at several ages: standard locomotor activity (preweaning, postweaning, adults), locomotor activity including a lighting change mid-way (postweaning, adults), elevated zero maze (postweaning, adults), functional observational battery (FOB; postweaning, adults), and Morris water maze (place learning, reference and working memory; adults). Neither chemical produced changes in maternal body weight or serum thyroid hormones, but relative liver weight was increased at the high doses of both TDCIPP and TCEP. In offspring, there were no effects on viability, litter size, or birth weight. With TDCIPP, absolute liver weights were lower at weaning and weight gain was lower in the high-dose offspring until about two months of age. Thyroid hormones and brain weights were not altered and acetylcholinesterase (both brain and serum) was not inhibited by either chemical. TDCIPP-treated offspring showed slight differences in floating in the water maze, hindlimb grip strength, and altered activity habituation, whereas TCEP-treated rats showed differences in quadrant time (probe) and middle-zone preference in the water maze. Regarding these few changes, the effects were minimal, mostly not related to dose, and did not appear treatment-related or biologically significant. Overall, these data do not support the potential for thyrotoxicity or developmental neurotoxicity produced by TDCIPP or TCEP.

Investigating endocrine and physiological parameters of captive American kestrels exposed by diet to selected organophosphate flame retardants

Organophosphate triesters are high production volume additive flame retardants (OPFRs) and plasticizers. Shown to accumulate in abiotic and biotic environmental compartments, little is known about the risks they pose. Captive adult male American kestrels (Falco sparverius) were fed the same dose (22 ng OPFR/g kestrel/d) daily (21 d) of tris(2-butoxyethyl) phosphate (TBOEP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), or tris(1,2-dichloro-2-propyl) phosphate (TDCIPP). Concentrations were undetected in tissues (renal, hepatic), suggesting rapid metabolism. There were no changes in glutathione status, indicators of hepatic oxidative status, or the cholinergic system (i.e., cerebrum, plasma cholinesterases; cerebrum muscarinic, nicotinic receptors). Modest changes occurred in hepatocyte integrity and function (clinical chemistry). Significant effects on plasma free triiodothyronine (FT3) concentrations occurred with exposure to TBOEP, TCEP, TCIPP, and TDCIPP; TBOEP and TCEP had additional overall effects on free thyroxine (FT4), whereas TDCIPP also influenced total thyroxine (TT4). Relative increases (32%-96%) in circulating FT3, TT3, FT4, and/or TT4 were variable with each OPFR at 7 d exposure, but limited thereafter, which was likely maintained through decreased thyroid gland activity and increased hepatic deiodinase activity. The observed physiological and endocrine effects occurred at environmentally relevant concentrations and suggest parent OPFRs or metabolites may have been present despite rapid degradation.

TPP and TCEP induce oxidative stress and alter steroidogenesis in TM3 Leydig cells

Effects of triphenyl phosphate (TPP) and tris-(2-chloroethyl) phosphate (TCEP) exposure on induction of oxidative stress and endocrine disruption were investigated in TM3 cells. After 24h exposure, cell growth declined and morphology changed in TPP and TCEP treated groups with high dosages. Significant increases in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione S-transferase (GST) activities and their respective gene expressions in a dose-dependent and/or time-dependent manner in TPP or TCEP groups. Moreover, the expression of main genes related to testosterone (T) synthesis including cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), cytochrome P450 17α-hydroxysteroid dehydrogenase (P450-17α), 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD) were dramatically reduced by TPP and TCEP treatments, especially with the high dosage for 24h. TPP and TCEP treatments for 24h caused significant decreases in T levels in the medium. Furthermore, co-treatments of hCG with TPP or TCEP could inhibit hCG-induced changes in the expression of P450scc, P450-17α and 17β-HSD and T levels. Taken together, TPP and TCEP could induce oxidative stress and endocrine disruption in TM3 cells.