Prenatal exposure to emerging and traditional organophosphate flame retardants: Regional comparison, transplacental transfer, and birth outcomes

During gestation, organophosphate flame retardants (OPFRs) have the potential to pose health risks to fetuses due to their ability to cross the placental barrier. However, data are scarce regarding the transplacental transfer of these compounds, particularly concerning emerging OPFRs and regional variations. In this study, we analyzed 14 traditional OPFRs and 5 emerging OPFRs in maternal and cord serum samples from Mianyang and Hangzhou, two cities in eastern and western China, respectively. The results revealed marked disparities in the overall levels of OPFRs between the two cities (p < 0.05), with the average concentration in maternal serum being higher in Hangzhou (14.55 ng/mL) than in Mianyang (8.28 ng/mL). The most abundant compounds found in both cities were tris (2-chloroethyl) phosphate (TCEP), Triphenyl phosphate (TPHP), and Tri-n-butyl phosphate (TnBP). Additionally, this study marked the first detection of novel OPFRs, including resorcinol bis (diphenyl phosphate) (RDP), isodecyl diphenyl phosphate (IDDPP), cresyl diphenyl phosphate (CDP), and bisphenol A bis (diphenyl phosphate) (BPA-BDPP) in maternal and cord serum simultaneously with the detection frequencies higher than 45%. This study also found that transplacental transfer efficiencies for OPFRs varied by ester group, with Aryl-OPFRs exhibiting the highest transfer rates (0.90-1.11) and Alkyl-OPFRs exhibiting the lowest (0.66-0.83). Transfer efficiencies exhibited a positive correlation with log Kow values (p < 0.05), suggesting that hydrophobic OPFRs with higher log Kow values are more likely to permeate the placental barrier. Moreover, the exposure levels of Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP), Tri (Chloropropyl) Phosphate (TCIPP), TPHP, and CDP in cord serum were negatively associated (p < 0.05) with birthweight of newborns. This research adds to our understanding of the transplacental transfer of OPFRs and the possible health risks associated with prenatal exposure.

Maternal transfer of resorcinol-bis(diphenyl)-phosphate perturbs gut microbiota development and gut metabolism of offspring in rats

Resorcinol-bis(diphenyl)-phosphate (RDP), an emerging organophosphate flame retardant, is increasingly used as a primary alternative for decabromodiphenyl ether and is frequently detected in global environmental matrices. However, the long-term effects of its exposure to humans remain largely unknown. To investigate its intergenerational transfer capacity and health risks, female Sprague Dawley rats were orally exposed to RDP from the beginning of pregnancy to the end of the lactation period. The RDP content, gut microbiota homeostasis, and metabolic levels were determined. RDP accumulation occurred in the livers of maternal rats and offspring and increased with exposure time. 16S rRNA gene sequencing showed that exposure to RDP during pregnancy and/or lactation significantly disrupted gut microbiota homeostasis, as evidenced by decreased abundance and diversity. In particular, the abundance of Turicibacter, Adlercreutzia, and YRC22 decreased, correlating significantly with glycollipic metabolism. This finding was consistent with the reduced levels of short-chain fatty acids, the crucial gut microbial metabolites. Meanwhile, RDP exposure resulted in changes in gut microbiome-related metabolism. Nine critical overlapping KEGG metabolic pathways were identified, and the levels of related differential metabolites decreased. Our results suggest that the significant adverse impacts of RDP on gut microbiota homeostasis and metabolic function may increase the long-term risks related to inflammation, obesity, and metabolic diseases.

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.

The associations between renal disease severity and exposure to organophosphate flame retardants in patients with chronic kidney disease

Organophosphate flame retardants (OPFRs) are emerging and widespread environmental pollutants with potential health hazards, including nephrotoxicity. However, the exposure patterns and nephrotoxic potential of OPFRs are yet to be investigated in patients with chronic kidney disease (CKD). We conducted a cross-sectional study involving 166 patients with CKD stratified by estimated glomerular filtration rate (eGFR) and severity of proteinuria. The urinary concentrations of 10 OPFR compounds were measured to evaluate the exposure patterns. Clinical and urinary OPFR profiles were compared among subgroups to identify whether the OPFR compounds were independently correlated with eGFR and proteinuria. Additionally, lifestyle factors were compared among subgroups stratified by median concentrations of urinary OPFR compounds associated with renal disease severity. This study revealed universal exposure to OPFRs in the CKD population, with an overall urinary detection rate of 98.80 %. Furthermore, after adjusting for covariates, the urinary concentration of bis(2-chloroethyl) phosphate (BCEP) was identified as an independent predictor of lower eGFR (low vs high eGFR, odds ratio (OR) (95 % confidence interval (CI)), 1.761 (1.032-3.005) per log μg/g creatinine, p = 0.038), and the urinary concentration of bis(2-butoxyethyl) phosphate (BBOEP) was independently correlated with overt proteinuria in CKD patients (with vs without overt proteinuria, OR (95 % CI), 1.813 (1.065-3.086) per log μg/g creatinine, p = 0.028). Moreover, frequent seafood consumption was negatively correlated with urinary BCEP concentration (high vs low BCEP, OR (95 % CI), 0.455 (0.228-0.908), p = 0.025), and age was inversely associated with urinary BBOEP concentration (high vs low BBOEP, OR (95 % CI), 0.968 (0.937-0.999) per year, p = 0.048). In conclusion, our investigation highlights the extensive exposure to OPFRs and the independent association between renal disease severity and urinary BCEP/BBOEP concentrations in the CKD population, indicating the nephrotoxic potential of these pollutants.

A QuEChERS-based UPLC-MS/MS method for rapid determination of organophosphate flame retardants and their metabolites in human urine

Organophosphate flame retardants (OPFRs) have been widely used in consumer products to prevent fire spread. However, once released into the atmospheric environment, they may accumulate in humans and undergo metabolic transformation and excretion by urine. In order to clarify the human exposure to OPFRs, a quick, easy, cheap, effective, rugged, and safe method for the simultaneous determination of urinary OPFRs and their metabolites by ultra-performance liquid chromatography-tandem triple quadrupole mass spectrometry was developed. After the optimization by a single-factor or orthogonal experiment, the satisfactory recovery (87.8-119%), matrix effect (-8.88-9.29%), method quantitation limit (3.66-159 ng/L), and inter-day repeatability (1.24 - 10.6%) of most analytes were achieved in artificial urine samples. Based on a monitoring test by the developed method, we propose that urinary bis(1-chloro-2-propyl) phosphate and di-p-cresyl phosphate could be used to trace human exposure to tris(1-chloro-2-propyl) phosphate and tricresyl phosphate, respectively. Most importantly, this is the first study to reveal that 4-hydroxyphenyl diphenyl phosphate (4-OH-TPHP) was dominantly presented in its conjugated form rather than its free form in urine (p = 0.037). Overall, the obtained results contribute a relatively rapid method to help conduct large-scale urine monitoring for revealing the human exposure and risk of OPFRs.

Quantitative fatty acid signature analysis (QFASA) in indoor dust: Implication for tracking indoor source accumulation of organic pollutant exposure

Indoor dust has been used as a proxy for estimating human indoor pollutant exposure risks, yet source identification remains challenging. This study tentatively investigated whether quantitative fatty acid signature analysis (QFASA) of dust, could be applied to indicate sources and their respective contributions for a major class of indoor organic pollutants organophosphate flame retardants (OPFRs). We observed significant correlations between OPFR concentrations and lipid content (p < 0.05) in house dusts. Using 15 signature fatty acids (FAs) in various indoor sources and the QFASA model, we found that clothing (39.1% in Australia and 36.5% in China) was the predominant contributing vector of dust OPFR followed by cooking oil and pet hair. Among these sources, clothing materials were proposed to be important vectors introducing organic pollutants to the indoor environment. Our QFASA contribution estimation analyses allowed for accurate prediction of most OPFR concentrations in clothing, validating our findings that clothing materials may serve as important carrier for OPFRs in indoor migration. This is the first study attempting to identify sources of organic pollutants using QFASA in an indoor setting and will provide important insight into the transfer of organic pollutants in indoor environment.

Preparation of magnetic powdered carbon/nano-Fe3O4 composite for efficient adsorption and degradation of trichloropropyl phosphate from water

Trichloropropyl phosphate (TCPP) as a widely used typical chlorinated organophosphate flame retardant has received significant attention because of its widespread presence in water and negative effects on human health. In this study, a ball-milling method was used to prepare a magnetic powdered carbon adsorbent (PC/nano-Fe₃O₄ composite) for TCPP removal via adsorption and catalytic degradation. The effect of Fe₃O₄ content on TCPP adsorption and degradation performance by PC/nano-Fe₃O₄ composite was investigated. The PC/nano-Fe₃O₄ composite prepared by high Fe₃O₄ content (25%) was not favorable for TCPP adsorption and degradation. However, the PC/Fe₃O₄ containing low Fe₃O₄ content (10%) had insufficient magnetic separation ability from water. The synthesized PC/nano-Fe₃O₄ composite with a Fe₃O₄/PC mass ratio of 1/5 exhibited a maximum adsorption capacity of 2682.1 μg/g as well as a complete TCPP degradation within 3 h in a Fenton-like system. Moreover, the possible break sites of TCPP and its degradation pathway were proposed based on theoretical calculation and experimental analysis. Regeneration studies showed that PC/nano-Fe₃O₄ composite had high reusability and adsorption capacity in six cycles, while its catalytic performance declined in the multiple reuse cycles. This strategy could be extended to prepare other magnetic powdered adsorbents for organic pollutant adsorption and degradation.

Temporal variability of organophosphate flame retardant metabolites in spot, first morning, and 24-h urine samples among healthy adults

A single measurement of organophosphate flame retardant (OPFR) metabolites in a spot sample is often used in epidemiological studies to estimate individual exposures. Over seven consecutive days, we collected 661 spot samples, including 127 first morning voids (FMVs) and 123 simulated 24-h collections, from 20 healthy adults and analyzed for eight OPFR metabolites. Intraclass correlation coefficients (ICCs) were calculated to evaluate the variability of the analyzed metabolites. In spot samples group, serial measurements of OPFR metabolites showed poor reproducibility (0.0422 ≤ ICC ≤ 0.349), and the within-day variability was the main contributor of the total variability. The estimated ICCs based on different correction methods for urine dilution (i.e., specific gravity-adjusted, creatinine-adjusted, and creatinine as a covariate) were similar, but varied according to gender and body mass index. Uniformly low sensitivities (0.417-0.633) were observed when using a single FMV or spot sample to predict the 1-week highly (top 33.0%) exposed volunteers. Therefore, using a single urinary measurement to predict chronic exposure to OPFRs can lead to a high degree of classification errors. When multiple urine samples are collected, considering the sampling type, the time of collection, and demographic characteristics may provide a more complete approach to assess exposure to diverse OPFRs.

The influence of an upgrade on the reduction of organophosphate flame retardants in a wastewater treatment plant

The appearance of an increased amount of organophosphate flame retardant (OPFRs) in natural water is related the treated effluents from wastewater treatment plants (WWTPs) and thus understanding the OPFRs concentration and reduction variation in WWTPs would provide valuable insight into OPFR management and reduction. In this study, we have analyzed OPFRs (10 kinds: tris(chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCPP), tris(1,3-dichloropropyl) phosphate (TDCP), tris(phenyl) phosphate (TPhP), tris(2-ethylhexyl) phosphate (TEHP), diphenylcresylphosphate (DCP), tris(methylphenyl) phosphate (TCP), tris(2-butoxyethyl) phosphate (TBEP), 2-ethylhexyl diphenyl phosphate (EHDP), and tris(butyl) phosphate (TBP)) in both water and sludge samples collected from different phases of a WWTP upgrading. The results show that TCPP and TCEP were mainly present in the aqueous phase, whereas TEHP dominated in the solid phase. The overall OPFR reduction efficiencies were above 40% through whole treatment processes by all the phases. More OPFRs reduction efficiency in primary sedimentation tanks was higher mainly because of bigger tank volume. The anaerobic zone in all cases could decrease OPFRs by over 13%. The removal of OPFRs in the oxic zone highly varied under the influence of the aeration pipe, water temperature, and aeration amount. Compared with chlorinated OPFRs, aryl and alkyl OPFRs were easier to reduce and less affected by the upgrading. Because OPFRs have been widely used in plastic materials such as pipes, WWTP upgrading - which usually requires more aeration and addition of reagents and instruments and the aim of which is normally to reduce more COD, N and P -- has introduced more OPFRs into the water within the WWTP.

Polybrominated Diphenyl Ether and Organophosphate Flame Retardants in Canadian Fire Station Dust

Fire fighters are at a high risk for exposure to toxic chemicals during and subsequent to fire suppression activities. In the Canadian Fire Station Dust Study (CFSDS) we measured 19 polybrominated diphenyl ether (PBDE) and six organophosphate flame retardant (OPFR) chemicals in dust collected in 2017-18 by vacuuming the living quarters of 24 Canadian fire stations from four provinces. The predominant flame retardant (FR) was BDE-209, with a median concentration of 7060 ng/g, which was a magnitude higher than medians of the major congeners of the pentaBDE formulation measured at 620 ng/g (Σ₅ BDE-47, 99, 100, 153 and 154). OPFR median concentrations exceeded those of pentaBDE and were on the same order of magnitude as BDE-209, with TCIPP, TDCIPP and TPHP as the dominant OPFRs with median concentrations ranging from 2350 to 4780 ng/g. Fire station age and carpeting were significantly correlated with select OPFRs and PBDEs. Furthermore, fire stations that also vacuumed equipment bays and fire truck interiors had median concentrations that were a magnitude higher (BDE-209: 81,700 ng/g) and two to three-fold higher (TCIPP, TDCIPP and TPHP) than fire stations that excluded those areas. FR concentrations in CFSDS dust were higher but on the same order of magnitude as Canadian residential dust and significantly lower than dust collected from Canadian WEEE dismantling. CFSDS FR concentrations were also significantly lower than those we reported in our 2015 U.S. fire station dust. Our data reflect the downward trend of PBDEs following their phase out and a shift toward OPFRs as replacements.

Metabolomics reveals that tris(1,3-dichloro-2-propyl)phosphate (TDCPP) causes disruption of membrane lipids in microalga Scenedesmus obliquus

Tris(1,3-dichloro-2-propyl)phosphate (TDCPP) is one of the most widely used organophosphate ester flame retardants. The presence of TDCPP in surface waters and aquatic organisms have been reported worldwide, yet the ecological risk of TDCPP on microalgae is rarely studied. We investigated the biotransformation of TDCPP and its toxicity on the microalga Scenedesmus obliquus using an untargeted metabolomics approach. Exposure to TDCPP resulted in a dose-response decrease of micoalgal biomass. In the presence of microalgae, TDCPP concentration in the media decreased by 25.3-40.6% after 5 days. TDCPP metabolites were identified in the media including hydrolysis and hydroxyl-substituted dechlorination products. A dose-response separation of metabolic profiles of microalgae was observed, with effect seen at the lowest concentration of 10 µg/L tested, which is slightly higher than environmentally relevant concentrations. Differentiated metabolites identified include 52 lipids and 6 polar metabolites. Analysis of altered lipid pathways suggests that microalgal cells reinforce thylakoid membranes (function to protect photosynthesis) by compromising the integrity of plasma membrane (function to protect cellular substances) and extraplastidial cellular membranes. Changes in the polar metabolites might indicate osmotic stress and improved NO signaling after TDCPP exposure. Consistent with perturbation of membrane lipids, further experiment confirmed that exposure to 10 mg/L TDCPP resulted in significant (p < 0.01) plasma membrane damage. This study indicates biotransformation and the membrane damage toxicity mechanism of TDCPP on S. obliquus, demonstrating the usefulness of metabolomics for the toxicity mechanism elucidation of emerging pollutants.

Effects of environmentally relevant concentrations of tris (2-butoxyethyl) phosphate on growth and transcription of genes involved in the GH/IGF and HPT axes in zebrafish (Danio rerio)

Tris (2-butoxyethyl) phosphate (TBOEP), as one of the most widely used organophosphate flame retardants (OPFRs), is applied in nearly all manufactured items and materials. It has been reported that TBOEP could cause developmental impairments and disrupt the endocrine regulation of fish growth during acute toxic experiments. However, concentrations to which fish were exposed in these studies were greater than environmentally relevant concentrations ever reported. This study examined effects on growth associated with exposure of zebrafish to 0, 0.1, 1 and 10 μg/L TBOEP during 20-90 days post fertilization (dpf). The changes in growth indicators and bioaccumulation of TBOEP were examined along with the transcription of related genes in the growth hormone/insulin-like growth factor (GH/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis. The average body contents of TBOEP were higher in females than in males in all the exposure groups. Exposure to environmentally relevant concentrations of TBOEP significantly decreased body length and body mass and down-regulated expression of several genes involved in the GH/IGF and HPT axes. Exposure to TBOEP decreased plasma thyroxine (T4) content accompanied by decreased mRNA level of thyrotropin β-subunit (tshβ) in females at 60 dpf, but no effects were observed at 90 dpf. These results suggested that bioaccumulation of TBOEP and down-regulation of genes involved in the GH/IGF axis might be responsible for the observed growth inhibition in zebrafish exposed to TBOEP.

Tissue-specific distribution and bioaccumulation potential of organophosphate flame retardants in crucian carp

The concentrations, distributions, and bioaccumulation of nine organophosphate flame retardants (OPFRs) were investigated in both abiotic and biotic media, comprising river water, sediment, and crucian carp. The highest concentrations were observed in liver (6.22-18.1 ng/g ww), and the levels in muscle (4.23-7.75 ng/g ww) and gonad (3.08-7.70 ng/g ww) were similar. In whole blood, tris(2-butoxyethyl) phosphate (TBOEP; 31.1-256 ng/mL) accounted for 90% of the total OPFR concentration. Distributions of OPFRs differed between biotic and abiotic media, as tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), and TBOEP were dominant in abiotic media, whereas triethyl phosphate (TEP), tri-n-butyl phosphate (TNBP), TCEP, and TBOEP dominated in crucian carp. The TNBP had remarkable accumulation potential among nine OPFRs, which the TNBP concentrations in muscle increased with increased total length and body weight. The higher perfusion rate of TNBP to female eggs were observed rather than to male gonads as the concentrations were higher in males than in females, while the opposite results were observed in gonad. Moreover, the concentration of TNBP in female muscle began to decrease near maximum growth as a sexually dimorphic difference in crucian carp. This is the first study to simultaneously investigate the fate of OPFRs in biotic and abiotic media and to show sex differences.

Organophosphate flame retardants and plasticizers in indoor dust, air and window wipes in newly built low-energy preschools

The construction of extremely airtight and energy efficient low-energy buildings is achieved by using functional building materials, such as age-resistant plastics, insulation, adhesives, and sealants. Additives such as organophosphate flame retardants (OPFRs) can be added to some of these building materials as flame retardants and plasticizers. Some OPFRs are considered persistent, bioaccumulative and toxic. Therefore, in this pilot study, the occurrence and distribution of nine OPFRs were determined for dust, air, and window wipe samples collected in newly built low-energy preschools with and without environmental certifications. Tris(1,3-dichloroisopropyl) phosphate (TDCIPP) and triphenyl phosphate (TPHP) were detected in all indoor dust samples at concentrations ranging from 0.014 to 10μg/g and 0.0069 to 79μg/g, respectively. Only six OPFRs (predominantly chlorinated OPFRs) were detected in the indoor air. All nine OPFRs were found on the window surfaces and the highest concentrations, which occurred in the reference preschool, were measured for 2-ethylhexyl diphenyl phosphate (EHDPP) (maximum concentration: 1500ng/m²). Interestingly, the OPFR levels in the environmental certified low-energy preschools were lower than those in the reference preschool and the non-certified low-energy preschool, probably attributed to the usage of environmental friendly and low-emitting building materials, interior decorations, and consumer products.

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.

Effects of tris (2-butoxyethyl) phosphate (TBOEP) on endocrine axes during development of early life stages of zebrafish (Danio rerio)

Due to phasing out of additive flame retardants such as polybrominated diphenyl ethers (PBDEs), Tris (2-butoxyethyl) phosphate (TBOEP) is widely used as a substitute. TBOEP is ubiquitous in the environment and has been measured at concentrations of micrograms per liter (μg L(-1)) in surface waters and wastewater. Information on potential adverse effects on development of aquatic organisms caused by exposure to environmentally relevant concentrations of TBOEP is limited, especially for effects that may be caused through impairment of endocrine-modulated homeostasis. Therefore, this study was conducted to determine effects of TBOEP on ontogeny and transcription profiles of genes along the hypothalamus-pituitary-thyroidal (HPT), hypothalamus-pituitary-adrenal (HPA), and hypothalamus-pituitary-gonadal (HPG) axes in embryos/larvae of zebrafish (Danio rerio). Exposure to TBOEP (2-5,000 μg L(-1)) from 3 h post-fertilization (hpf) to 120 hpf induced developmental malformations in zebrafish with a LC50 of 288.54 μg L(-1) at both 96 hpf and 120 hpf. The predicted no observed effect concentration (PNOEC) was 2.40 μg L(-1). Exposure to 2, 20, or 200 μg TBOEP L(-1) altered expression of genes involved in three major molecular pathways in a concentration-dependent manner after 120 hpf. TBOEP caused lesser expression of some genes involved in synthesis of hormones, such as (pomc and fshβ) as well as upregulating expression of some genes coding for receptors (thr, tshr, gr, mr, er and ar) in zebrafish larvae. These changes at the molecular level could result in alterations of endocrine function, which could result in edema or deformity and ultimately death.

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.

Developmental exposure to the organophosphorus flame retardant tris(1,3-dichloro-2-propyl) phosphate: estrogenic activity, endocrine disruption and reproductive effects on zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate flame retardant that is detectable in the environment and biota, prompting concern over its risk to wildlife and human health. Our objective was to investigate whether long-term exposure to low concentrations of TDCPP can affect fish reproduction. Zebrafish embryos were exposed to low concentrations (0, 4, 20 and 100μg/L) of TDCPP from 2h post-fertilization until sexual maturation. Exposure to TDCPP significantly increased plasma estradiol and testosterone levels in females, but had no effect in males. TDCPP exposure also caused a significant reduction in fecundity as indicated by decreased egg production. Real-time PCR was performed to examine selected genes in the hypothalamic-pituitary-gonadal (HPG) axis and liver. Principle component analysis (PCA) showed that sex hormone levels and fecundity were related to the mRNA level of several genes in the HPG axis. Furthermore, hepatic vitellogenin (vtg1 and vtg3) expression was upregulated in both females and males, suggesting TDCPP has estrogenic activity. Histological examination revealed promotion of oocyte maturation in the females, but retardation of spermiation in males. Reduced egg quality (e.g., egg diameter) and increased malformation rates were observed in the F1 generation. Chemical analysis showed significant levels of TDCPP and its metabolite bis(1,3-dichloro-2-propyl) phosphate in the gonads of males and females. In conclusion, long-term exposure to low concentrations of TDCPP impairs fish reproduction.

Time-dependent effects of the flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCPP) on mRNA expression, in vitro and in ovo, reveal optimal sampling times for rapidly metabolized compounds

The flame retardant, tris(1,3-dichloro-2-propyl) phosphate (TDCPP), was previously shown to affect chicken embryo growth, gallbladder size, and lipid homeostasis. A microarray study, however, revealed only modest transcriptional alterations in liver tissue of pipping embryos (days 20-21), which was attributed to the rapid metabolism of TDCPP throughout incubation. To identify the most appropriate sampling time for rapidly metabolized compounds, the present study assessed the time-dependent effects of TDCPP on 27 genes, in ovo (50 µg [116 nmol] TDCPP/g egg) and in vitro (10 µM), using a chicken ToxChip polymerase chain reaction array. The greatest magnitude in dysregulation (up to 362-fold) occurred on day 8 of incubation (in ovo) with alterations of genes involved in phase I, II, and III metabolism, among others. Gallbladder hypotrophy was observed by embryonic day 12, corroborating the finding in pipping embryos from our previous study. From days 12 to 19, genes involved in lipid homeostasis, steroid hormone metabolism, and oxidative stress were affected. In chicken embryonic hepatoctyes (CEHs), TDCPP was completely metabolized to bis(1,3-dichloro-2-propyl) phosphate (BDCPP) within 36 h, but transcriptional changes remained significant up to 36 h. These changes were not attributed to BDCPP exposure as it only altered 1 gene (CYP1A4). An 18-h exposure in CEHs altered the greatest number of genes, making it an appropriate time point for high-throughput chemical screening; however, depending on the biological pathways of interest, shorter or longer incubation times may be more informative. Overall, TDCPP elicits the transcriptional and phenotypic alterations observed in vitro and in ovo, whereas its major metabolite, BDCPP, is far less biologically active.

Tris(1,3-dichloro-2-propyl) phosphate perturbs the expression of genes involved in immune response and lipid and steroid metabolism in chicken embryos

We previously demonstrated that in ovo exposure to the flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCPP) decreased plasma thyroxine levels, reduced growth parameters, and decreased gallbladder size in chicken embryos. In the current study DNA microarrays were used to evaluate global mRNA expression in liver tissue of male chicken embryos that exhibited the above mentioned effects. Injected doses were dimethyl sulfoxide vehicle control, 7.6 or 45 μg TDCPP/g egg. TDCPP caused significant changes in the expression of five genes at the low dose and 47 genes at the high dose (False Discovery Rate p ≤ 0.1, fold change ≥ 1.5). The gene expression analysis suggested a compromised immune function, a state of cholestatic liver/biliary fibrosis, and disrupted lipid and steroid metabolism. Circulating bile acid levels were elevated, which is an indication of liver dysfunction, and plasma cholesterol levels were reduced; however, hepatic bile acid and cholesterol levels were unaltered. Interactome analyses identified apolipoprotein E, hepatocyte nuclear factor 4 alpha, and peroxisome proliferator-activated receptor alpha as key regulatory molecules involved in the effects of TDCPP. Our results demonstrate a targeted effect of TDCPP toxicity on lipid metabolism, including cholesterol, that helps explain the aforementioned phenotypic effects, as chicken embryos are highly dependent on yolk lipids for growth and maintenance throughout development. Finally, our results are in concordance with the literature that describes TDCPP as a cancer-causing agent, since the majority of dysregulated genes were involved in cancer pathways.

Priority and emerging flame retardants in rivers: occurrence in water and sediment, Daphnia magna toxicity and risk assessment

The occurrence, partitioning and risk of eight polybrominated diphenyl ethers (PBDEs), nine new brominated (NBFRs) and ten organophosphorus flame retardants (OPFRs) were evaluated in three Spanish rivers suffering different anthropogenic pressures (Nalón, Arga and Besòs). OPFRs were ubiquitous contaminants in water (ΣOPFRs ranging from 0.0076 to 7.2μgL(-1)) and sediments (ΣOPFRs ranging 3.8 to 824μgkg(-1)). Brominated flame retardants were not detected in waters, whereas ΣPBDEs ranged from 88 to 812μgkg(-1) and decabromodiphenyl ethane (DBDPE) reached 435μgkg(-1) in sediments from the River Besòs, the most impacted river. The occurrence of flame retardants in river water and sediment was clearly associated with human activities, since the highest levels occurred near urban and industrial zones and after wastewater treatment plants discharge. Daphnia magna toxicity was carried out for OPFRs, the most ubiquitous flame retardants, considering individual compounds and mixtures. Toxicity of nine tested OPFRs differed largely among compounds, with EC50 values ranging over three magnitude orders (0.31-381mgL(-1)). Results evidenced that these compounds act by non-polar narcosis, since their toxicity was proportional to their lipophilicity (Kow). Furthermore, their joint toxicity was additive, which means that single and joint toxicity can be predicted knowing their concentration levels in water using quantitative structure activity relationships (QSARs) and predictive mixture models. Based on these results, a risk assessment considering joint effect was performed calculating and summing risk quotients (RQs) for the water and sediment samples. No significant risk to D. magna (ΣRQs <1) was observed for any of the monitored rivers.