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

Semicarbazide disturbs the reproductive system of male zebrafish (Danio rerio) through the GABAergic system

Semicarbazide (SMC), an emerging water contaminant, exerts anti-estrogenic effects in female zebrafish. However, the exact influence of SMC on male reproduction remains unclear. In this study, adult male zebrafish were exposed to 1-1000μg/L SMC in a semi-static system for 28 d prior to examining the testicular somatic index (TSI), testis histology, plasma sex hormone levels, and the transcription of genes involved in reproduction. The results showed that testicular morphology was altered and TSI was down-regulated by high concentrations of SMC (≥100μg/L and 1000μg/L, respectively). Plasma testosterone and 17β-estradiol concentrations were significantly decreased by all of the SMC treatments, along with down-regulation of the corresponding steroidogenic gene transcripts. These changes were associated with the inhibition of gamma-aminobutyric acid synthesis and function, in addition to the decreased expression of reproductive regulators. Our results contribute to elucidating the mechanisms underlying the adverse reproductive effects of SMC in male zebrafish.

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.

Potential Glucocorticoid and Mineralocorticoid Effects of Nine Organophosphate Flame Retardants

Organophosphate flame retardants (OPFRs), as alternatives of polybrominated diphenyl ethers (PBDEs), have been frequently detected in the environment and biota, and could pose adverse effects on organisms. However, information on the potential endocrine disruption of OPFRs, especially their effects on steroid hormone receptors, such as glucocorticoid and mineralocorticoid receptors (GR/MR), is limited. In this study, the dual-luciferase reporter gene assay via GR/MR and a H295R steroidogenesis assay were employed to evaluate the endocrine disruption of nine OPFRs. We found TMPP, TPHP, and TDBPP exhibited both GR and MR antagonistic activities, while TNBP and TDCIPP only showed MR antagonistic property within a concentration range of 10^-8 to 10^-5 mol/L(M). In the H295R steroidogenesis assay, the fold changes of eight steroidogenic genes in response to OPFRs were further studied. We found CYP17,CYP21, and CYP11B1 expression were significantly down-regulated following TMPP, TPHP, or TDBPP exposure at a concentration of 2 × 10^-6 M. Meanwhile TMPP decreased the production of cortisol and TDBPP down-regulated the secretion of aldosterone. Our results indicate that some OPFRs can interact with GR and MR, and have the potential to disturb steroidogenesis. Data provided here will be helpful to comprehensively understand the potential endocrine disruption of OPFRs.

Multigenerational effects and DNA alterations of QDs-Indolicidin on Daphnia magna

The complex QDs-Indolicidin (QDs-Ind) has been previously shown to be a good antimicrobial system with a low acute toxicity on Daphnia magna (D. magna). However, multigenerational effects caused by exposure to QDs-Ind and after subsequent recovery are still unknown. In this study, we performed multigenerational exposure tests and we evaluated individual fitness, population growth, DNA alteration, expression of Dhb (haemoglobin), Vtg (vitellogenin), CYP4 (cytochrome P450s CYP4 family), and CYP314 (cytochrome P450s mitochondrial family 314) genes on three generation of D. magna. Results showed that the total amount of eggs produced per female and total number of brood per female and body lengths were significantly decreased, Dhb, CYP4 were upregulated while Vtg was down-regulated except at reproduction days when it was slightly up-regulated under QDs-Ind exposure. Random Amplification of Polymorphic DNA (RAPD) method has proven to be useful to qualitative assess of DNA damage during generation and to underline modification in somatic or germinal cells. The results of the study suggest that effects of chronic exposure cannot be ignored.

Effects of food-borne exposure of juvenile rainbow trout (Oncorhynchus mykiss) to emerging brominated flame retardants 1,2-bis(2,4,6-tribromophenoxy)ethane and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate

Brominated flame retardants (BFRs) represent a large group of chemicals used in a variety of household and commercial products to prevent fire propagation. The environmental persistence and toxicity of some of the most widely used BFRs has resulted in a progressive ban worldwide and the development of novel BFRs for which the knowledge on environmental health impacts remains limited. The objectives of this study were to evaluate the effects of two emerging BFRs, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), in diet exposed juvenile rainbow trout (Oncorhynchus mykiss). Both compounds were detected in fish carcasses at 76% and 2% of the daily dosage of BTBPE and EH-TBB, respectively, indicating accumulation of BTBPE and by contrast extensive depuration/metabolism of EH-TBB. Liver gene transcription analysis using RNA-sequencing indicated that the chronic 28-d dietary exposure of trout to EH-TBB down-regulated one single gene related to endocrine-mediated processes, whereas BTBPE impacted the transcription of 33 genes, including genes involved in the immune response, reproduction, and oxidative stress. Additional analysis using qRT-PCR after 48-h and 28-d of exposure confirmed the impact of BTBPE on immune related genes in the liver (apolipoprotein A-I, lysozyme) and the head-kidney (complement c3-4). However, the activity of lysozymes measured at the protein level did not reflect transcriptomic results. Overall, results suggested an impact on immune-related gene transcription in BTBPE exposed fish, as well as oxidative stress and endocrine disruption potentials.

Androgen signaling regulates the transcription of anti-Müllerian hormone via synergy with SRY-related protein SOX9A

Anti-Müllerian hormone (amh) is one of the earliest functional genes expressed during testicular differentiation. It has been suggested that androgen signaling regulates critical genes for the differentiation and development of the testis. To elucidate the exact regulatory mechanisms involved in amh transcription mediated by androgen signaling, androgen signaling was manipulated in zebrafish by cytochrome P450 17a1 (cyp17a1) knockout and Flutamide treatment. In cyp17a1-deficient and Flutamide-treated testes, up-regulated sry-box9a (sox9a) and down-regulated amh were observed. Moreover, a physical association of the zebrafish androgen receptor (AR) and SOX9A was found. The interaction between AR and SOX9A was mediated via the DNA binding domain (DBD) of AR and the transactivation domain (TA) of SOX9A, and was further enhanced by 5-alpha dihydrotestosterone (DHT), one of the most potent androgens. Intriguingly, together with SOX9A, androgen signaling synergistically promoted amh transcription, mainly through the proximal 1kb of the amh promoter region. Taken together, our data demonstrate a critical mechanism underlying the direct synergy of androgen signaling and SOX9A in the regulation of amh transcription.

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.

Gene Expression Profiling in Fish Toxicology: A Review

In this review, we present an overview of transcriptomic responses to chemical exposures in a variety of fish species. We have discussed the use of several molecular approaches such as northern blotting, differential display reverse transcription-polymerase chain reaction (DDRT-PCR), suppression subtractive hybridization (SSH), real time quantitative PCR (RT-qPCR), microarrays, and next-generation sequencing (NGS) for measuring gene expression. These techniques have been mainly used to measure the toxic effects of single compounds or simple mixtures in laboratory conditions. In addition, only few studies have been conducted to examine the biological significance of differentially expressed gene sets following chemical exposure. Therefore, future studies should focus more under field conditions using a multidisciplinary approach (genomics, proteomics and metabolomics) to understand the synergetic effects of multiple environmental stressors and to determine the functional significance of differentially expressed genes. Nevertheless, recent developments in NGS technologies and decreasing costs of sequencing holds the promise to uncover the complexity of anthropogenic impacts and biological effects in wild fish populations.

Reproduction impairment and endocrine disruption in adult zebrafish (Danio rerio) after waterborne exposure to TBOEP

Tris (2-butoxyethyl) phosphate (TBOEP) is widely used as a substitute of polybrominated diphenyl ethers (PBDEs). It has been frequently measured at concentrations of micrograms per liter (μg/L) in surface waters and waste water. However, limited information is available about the reproduction toxicology of TBOEP. In this study, adult zebrafish pairs were exposed to TBOEP at concentrations of 0, 5, 50, and 500μg/L for 21days. The effects on reproduction, hormone concentration, transcription of genes along the hypothalamic-pituitary-gonadal (HPG) axis, and gonadal development were investigated. After exposure to TBOEP, plasma concentrations of 17β-estradiol were significantly increased in both sexes of fish, while increase of testosterone was observed only in male fish. Transcription of genes along the HPG axis was significantly influenced by exposure to TBOEP in both male and female fish. Moreover, TBOEP decreases the average number of eggs production, as well as hatching success and survival rates in offspring. Histological examination shows inhibition of oocyte maturation in females and retardation spermiation in males, respectively. The results demonstrate that TBOEP could disturb the sex hormone balance by altering regulatory circuits of the HPG axis, affect gonadal development, eventually leading to disruption of reproductive performance and the development of progeny.

Levels of Urinary Metabolites of Organophosphate Flame Retardants, TDCIPP, and TPHP, in Pregnant Women in Shanghai

Flame retardants are widely used in consumer products to reduce their flammability. Previously used flame retardants have been sequentially banned due to their environmental and human toxicity. Currently, tris(1,3-dichloropropyl) phosphate (TDCIPP) and triphenyl phosphate (TPHP) are among the most commonly used flame retardants. TDCIPP and TPHP are reproductive toxins and have carcinogenic, neurotoxic, and endocrine-disrupting properties. Although high levels of TDCIPP and TPHP have been found in drinking water, seawater, and office air in China, data regarding human exposure are lacking. In this study, we assessed the level of urinary TPHP and TDCIPP metabolites (DPHP and BDCIPP, resp.) in a cohort of pregnant women (N = 23) from Shanghai, China, using liquid chromatography-tandem mass spectrometry. DPHP were detected in 100% urine samples, while only four urine samples had detectable level of BDCIPP in this cohort (17% detected). Geometric means of DPHP and BDCIPP concentrations were 1.1 ng/mL (interquartile range [IQR]: 0.6, 1.5 ng/mL) and 1.2 ng/mL (IQR: 0.6, 2.2 ng/mL), respectively. In this small cohort, urinary DPHP and BDCIPP levels were not significantly correlated with miscarriages, neonatal birthweight, gestational diabetes, or maternal age. These data suggest that exposure to TPHP is widespread, and they demonstrate the feasibility of using urinary biomarkers to measure exposures to modern flame-retardant chemicals.

Tris (1, 3-dichloro-2-propyl) phosphate induces apoptosis and autophagy in SH-SY5Y cells: Involvement of ROS-mediated AMPK/mTOR/ULK1 pathways

Tris (1, 3-dichloro-2-propyl) phosphate (TDCIPP), an extensively used organophosphorus flame retardant, is frequently detected in the environment and biota. Recent studies have shown that TDCIPP has neurotoxic effects. We hypothesized that the neurotoxicity might occur via the induction of the apoptosis and autophagy pathways. In the present study, we investigated TDCIPP-induced apoptotic death and autophagy in SH-SY5Y cells. Treatment with TDCIPP induced increased reactive oxygen species (ROS) generation and cell apoptosis, as well as autophagy. The autophagy inhibitor 3-methyladenine (3-MA) markedly decreased the expression of the autophagy marker beclin-1, microtubule-associated protein light chain 3-II (LC3II), p62/sequestosome 1 (SQSTM1) degradation, and promoted apoptosis. Conversely, the autophagy inducer rapamycin (Rapa) alleviated TDCIPP-induced apoptosis and markedly increased the expression of the autophagy markers. Pretreatment with N-acetyl cysteine (NAC) eliminated the increased ROS generation, resulting in increased cell viability. For further examination of the signaling pathways involved in TDCIPP-induced autophagy, compound C, a pharmacological inhibitor of adenosine monophosphate activated protein kinase (AMPK) was used. Western blotting showed that compound C markedly reduced the expression of phospho-AMPK (p-AMPK) and phospho-Unc-51-like kinase 1 (p-ULK1), increased phospho-mammalian target of rapamycin (p-mTOR) expression, and decreased beclin-1 and LC3II expression. These results suggested that the AMPK/mTOR/ULK1 signaling pathway was involved in TDCIPP-induced autophagy. The antioxidant NAC antagonized TDCIPP-induced activation of AMPK and autophagy. Taken together, our findings provide the first evidence that TDCIPP promotes apoptosis and autophagy simultaneously and that this process involves the ROS-mediated AMPK/mTOR/ULK1 pathways. Lastly, the induction of autophagy is a protective mechanism against TDCIPP-induced apoptosis.

Organophosphate Ester Flame Retardants and Plasticizers in the Global Oceanic Atmosphere

Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers and have been detected ubiquitously in the remote atmosphere. Fourteen OPEs were analyzed in 115 aerosol phase samples collected from the tropical and subtropical Atlantic, Pacific, and Indian Oceans during the MALASPINA circumnavigation campaign. OPEs were detected in all samples with concentrations ranging from 360 to 4400 pg m^-3 for the sum of compounds. No clear concentration trends were found between the Northern and Southern hemispheres. The pattern was generally dominated by tris(1-chloro-2-propyl) phosphate (TCPP), although tri-n-butyl phosphate (TnBP) had a predominant role in samples close to continents and in those influenced by air masses originating in continents. The dry deposition fluxes of aerosol phase ∑₁₄OPE ranged from 4 to 140 ng m^-2 d^-1. An estimation of the OPE gas phase concentration and gross absorption fluxes by using three different sets of physical chemical properties suggested that the atmosphere-ocean diffusive exchange of OPEs could be 2-3 orders of magnitude larger than dry deposition. The associated organic phosphorus inputs coming from diffusive OPE fluxes were estimated to potentially trigger up to 1.0% of the reported primary production in the most oligotrophic oceanic regions. However, the uncertainty associated with these calculations is high and mostly driven by the uncertainty of the physical chemical properties of OPEs. Further constraints of the physical chemical properties and fluxes of OPEs are urgently needed, in order to estimate their environmental fate and relevance as a diffusive source of new organic phosphorus to the ocean.

Impairment of reproduction of adult zebrafish (Danio rerio) by binary mixtures of environmentally relevant concentrations of triclocarban and inorganic mercury

Effects of chemical mixtures at environmentally relevant concentrations on endocrine systems of aquatic organisms are of concern. Triclocarban (TCC) and inorganic mercury (Hg²⁺) are ubiquitous in aquatic environments, and are known to interfere with endocrine pathways via different mechanisms of toxic action. However, effects of mixtures of the two pollutants on aquatic organisms and associated molecular mechanisms were unknown. This study examined effects of binary mixtures of TCC and Hg²⁺ on histopathological and biochemical alteration of reproductive organs in zebrafish (Danio rerio) after 21 d exposure. The results showed that: 1) At concentrations studied, TCC alone caused little effect on hepatic tissues, but it aggravated lesions in liver caused by Hg²⁺ via indirect mechanisms of disturbing homeostasis and altering concentrations of hormones; 2) Histological lesions were more severe in gonads of individuals, especially males, exposed to the binary mixture. Exposure to TCC alone (2.5 or 5μg/L) (measured concentration 140 or 310ng/L) or Hg²⁺ alone (5μg/L or 10μg/L (measured concentration 367 or 557ng/L) slightly retarded development of oocytes, whereas co-exposure to nominal concentrations of 5μg/L TCC and 10μg /L Hg²⁺ promoted maturation of oocytes. In males, maturation of sperm was slightly delayed by exposure to either TCC or Hg²⁺, while their combinations caused testes to be smaller and sperm to be fewer compared with fish exposed to either of the contaminants individually; 3) Lesions observed in fish exposed to binary mixtures might be due to altered transcription of genes involved in steroidogenesis, such as cyp19a, 3beta-HSD, cyp17, 17beta-HSD and modulated concentrations of testosterone and estradiol in blood plasma. The observed results further support the complexity of toxic responses of fish exposed to lesser concentrations of binary chemical mixtures. Since it is impossible to collect empirical information in controlled studies of all possible combinations of toxicants, the application of omics methods might improve the predictive capabilities of results of single classes of chemicals.

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.

Tris(1,3-dichloro-2-propyl)phosphate Induces Genome-Wide Hypomethylation within Early Zebrafish Embryos

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) is a high-production volume organophosphate-based plasticizer and flame retardant widely used within the United States. Using zebrafish as a model, the objectives of this study were to determine whether (1) TDCIPP inhibits DNA methyltransferase (DNMT) within embryonic nuclear extracts; (2) uptake of TDCIPP from 0.75 h postfertilization (hpf, 2-cell) to 2 hpf (64-cell) or 6 hpf (shield stage) leads to impacts on the early embryonic DNA methylome; and (3) TDCIPP-induced impacts on cytosine methylation are localized to CpG islands within intergenic regions. Within this study, 5-azacytidine (5-azaC, a DNMT inhibitor) was used as a positive control. Although 5-azaC significantly inhibited zebrafish DNMT, TDCIPP did not affect DNMT activity in vitro at concentrations as high as 500 μM. However, rapid embryonic uptake of 5-azaC and TDCIPP from 0.75 to 2 hpf resulted in chemical- and chromosome-specific alterations in cytosine methylation at 2 hpf. Moreover, TDCIPP exposure predominantly resulted in hypomethylation of positions outside of CpG islands and within intragenic (exon) regions of the zebrafish genome. Overall, these findings provide the foundation for monitoring DNA methylation dynamics within zebrafish as well as identifying potential associations among TDCIPP exposure, adverse health outcomes, and DNA methylation status within human populations.

Multimedia screening of contaminants of emerging concern (CECS) in coastal urban watersheds in southern California (USA)

To examine the occurrence and fate of contaminants of emerging concern (CECs) and inform future monitoring of CECs in coastal urban waterways, water, sediment, and fish tissue samples were collected and analyzed for a broad suite of pharmaceuticals and personal care products (PPCPs), commercial and/or household chemicals, current use pesticides, and hormones in an effluent-dominated river and multiple embayments in southern California (USA). In the Santa Clara River, which receives treated wastewater from several facilities, aqueous phase CECs were detectable at stations nearest discharges from municipal wastewater treatment plants but were attenuated downstream. Sucralose and the chlorinated phosphate flame retardants tris(1-chloro-2-propyl) phosphate (TCPP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), and tris(2-chloroethyl) phosphate (TCEP) were most abundant in water, with maximum concentrations of 35 μg/L, 3.3 μg/L, 1.4 μg/L, and 0.81 μg/L, respectively. Triclocarban, an antimicrobial agent in use for decades, was more prevalent in water than triclosan or nonylphenol. Maximum concentrations of bifenthrin, permethrin, polybrominated diphenyl ethers (PBDEs), and degradates of fipronil exceeded CEC-specific monitoring trigger levels recently established for freshwater and estuarine sediments by factors of 10 to 1000, respectively. Maximum fish tissue concentrations of PBDEs varied widely (370 ng/g and 7.0 ng/g for the Santa Clara River and coastal embayments, respectively), with most species exhibiting concentrations at the lower end of this range. These results suggest that continued monitoring of pyrethroids, PBDEs, and degradates of fipronil in sediment is warranted in these systems. In contrast, aqueous pharmaceutical concentrations in the Santa Clara River were not close to exceeding current monitoring trigger levels, suggesting a lower priority for targeted monitoring in this medium. Environ Toxicol Chem 2016;35:1986-1994. © 2016 SETAC.

Disruption of apoptosis pathways involved in zebrafish gonad differentiation by 17α-ethinylestradiol and fadrozole exposures

Zebrafish (Danio rerio) sex determination seems to involve genetic factors (GSD) but also environmental factors (ESD), such as endocrine disrupting chemicals (EDCs) that are known to mimic endogenous hormones and disrupt gonad differentiation. Apoptosis has also been proposed to play a crucial role in zebrafish gonad differentiation. Nevertheless, the interactions between EDCs and apoptosis have received little attention. Thus, this study aimed to assess if and which apoptotic pathways are involved in zebrafish gonad differentiation and how EDCs may interfere with this process. With these purposes, zebrafish were exposed to 17α-ethinylestradiol (EE2, 4ng/L) and fadrozole (Fad, 50μg/L) from 2h to 35days post-fertilization (dpf). Afterwards, a gene expression analysis by qRT-PCR and a stereological analysis, based on systematic sampling and protein immunohistochemistry, were performed. The death receptors (FAS; TRADD), anti-apoptotic (BCL-2; MDM2), pro-apoptotic (CASP-2 and -6) and cell proliferation (BIRC5/survivin; JUN) genes and proteins were evaluated. In general, apoptosis was inhibited in females through the involvement of anti-apoptotic pathways, while in males apoptosis seemed to be crucial to the failure of the "juvenile ovary" development and the induction of testes transformation. The JUN protein was shown to be necessary in juvenile ovaries, while the BIRC5 protein seemed to be involved in zebrafish spermatogenesis. Both EDCs, EE2 and Fad, increased the apoptosis stimulus in zebrafish gonad. It was noticed that the few females that were resistant to Fad-induced sex reversal had increased anti-apoptotic factor levels, while males exposed to EE2 showed increased pro-apoptotic genes/proteins and were more advanced in gonad differentiation. Overall, our findings show that apoptosis pathways are involved in zebrafish gonad differentiation and that EDCs can disrupt this process.

Effects of tris(2-butoxyethyl) phosphate exposure on endocrine systems and reproduction of zebrafish (Danio rerio)

Tris(2-butoxyethyl) phosphate (TBEOP), a widely used organophosphate flame retardant, has frequently been detected both in the environment and the biota. However, limited information is available on the effects of TBEOP on the endocrine system and its underlying mechanisms. We exposed adult zebrafish pairs to TBEOP at concentrations of 0, 2.1, 11, and 118 μg/L for 21 d, and investigated the effects on gene transcription and hormone production related to the hypothalamic-pituitary-gonadal (HPG) axis, and on reproduction. The adverse effects on the F1 generation were further examined. In male fish, plasma concentrations of 17β-estradiol were significantly increased along with up-regulation of cyp19a. Exposure to TBEOP at 118 μg/L led to a significant decrease in average egg production. Exposure of the F0 generation to TBEOP delayed hatching and lowered hatching rates in the F1 generation. The results demonstrate that exposure to TBEOP at environmentally relevant concentration levels could affect the sex hormone balance by altering regulatory circuits of the HPG axis, eventually leading to disruption of reproductive performance and the development of offspring.

The binary mixtures of megestrol acetate and 17α-ethynylestradiol adversely affect zebrafish reproduction

Synthetic progesterones and estrogens are broadly used bioactive pharmaceutical agents and have been detected in aquatic environments. In the present study, we investigated the combined reproductive effects of megestrol acetate (MTA) and 17α-ethinylestradiol (EE2) on zebrafish. Adult zebrafish were exposed to MTA (33, 100 or 333 ng/L), EE2 (10 ng/L) or a mixture of both (MTA + EE2: 33 + 10, 100 + 10 or 333 + 10 ng/L) for 21 days. Results demonstrated that egg production was significantly reduced by exposure to 10 ng/L EE2, but not MTA. However, a combined exposure to MTA and EE2 caused further reduction of fish fecundity compared to EE2 exposure alone, suggesting an additive effect on egg production when EE2 is supplemented with MTA. Plasma concentrations of 17β-estradiol and testosterone in the females and 11-ketotestosterone in the males were significantly decreased in the groups exposed to EE2 or MTA alone compared with the solvent control, and the plasma concentrations of the three hormones were further reduced in the co-exposure groups relative to the MTA exposure group, but not the EE2 exposure group. These data indicate that the inhibitory effects on plasma concentrations in the co-exposures were predominantly caused by EE2. Furthermore, exposure to MTA and EE2 (alone or in combination) led to histological alterations in the ovaries (decreased vitellogenic/mature oocytes), but not in the testes. This study has important implications for environmental risk assessment of synthetic hormones that are concurrently present in aquatic systems.

Thyroid hormone-disrupting activity and ecological risk assessment of phosphorus-containing flame retardants by in vitro, in vivo and in silico approaches

In recent years, phosphorus-containing flame retardants (PFRs) have been frequently detected in various environmental media and biota - and in humans - as the result of steady increase in global usage of PFRs. However, studies on the potential health and ecological risks of PFRs are still scarce. In this study, we investigated the thyroid hormone-disrupting activity and ecological risk of nine frequently detected PFRs by in vitro, in vivo and in silico approaches. Results from the dual-luciferase reporter gene assay showed that tributyl phosphate (TNBP), tricresyl phosphate (TMPP), tris(2-chloroisopropyl)phosphate (TCIPP) and tris(2-chloro-1-(chloromethyl)ethyl)phosphate (TDCIPP) exerted thyroid receptor β (TRβ) antagonistic activity, with the values of RIC20 of 5.2 × 10(-7), 2.7 × 10(-7), 1.2 × 10(-6) and 6.8 × 10(-6) M, respectively. Molecular docking platform simulations suggested that the observed effects may be attributed to direct binding of PFRs to TR. Results from the T-screen assay indicated that TNBP and TMPP showed T3 antagonistic activity and thus significantly decreased the viability of GH3 cell lines in the presence of T3. The exposure assay using Xenopus tropicalis embryos revealed the potential teratogenic effect of TNBP, TMPP, TCIPP and TDCIPP. In conclusion, our studies revealed that some PFRs were potential thyroid hormone disruptors and may cause health and ecological risks. However, the mode of action of PFRs on TR remains uncertain. The correlation between the predicted affinity and the amplitude of the effect observed in cell based assay is encouraging, but not decisive. Further in vitro binding experiments of TR and PFRs are required. At the same time, the results provided here also demonstrated that multi-model approaches are of great importance to comprehensively evaluate the potential risks of emerging contaminants.

Can activated sludge treatments and advanced oxidation processes remove organophosphorus flame retardants?

This study aims to determine the occurrence of 10 OPFRs (including chlorinated, nonchlorinated alkyl and aryl compounds) in influent, effluent wastewaters and partitioning into sludge of 5 wastewater treatment plants (WWTP) in Catalonia (Spain). All target OPFRs were detected in the WWTPs influents, and the total concentration ranged from 3.67 µg L(-1) to 150 µg L(-1). During activated sludge treatment, most OPFRs were accumulated in the sludge at concentrations from 35.3 to 9980 ng g(-1) dw. Chlorinated compounds tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP) and tris(2,3-dichloropropyl) phosphate (TDCPP) were not removed by the conventional activated sludge treatment and they were released by the effluents at approximately the same inlet concentration. On the contrary, aryl compounds tris(methylphenyl) phosphate (TMPP) and 2-ethylhexyl diphenyl phosphate (EHDP) together with alkyl tris(2-ethylhexyl) phosphate (TEHP) were not detected in any of the effluents. Advanced oxidation processes (UV/H2O2 and O3) were applied to investigate the degradability of recalcitrant OPFRs in WWTP effluents. Those detected in the effluent sample (TCEP, TCIPP, TDCPP, tributyl phosphate (TNBP), tri-iso-butyl phosphate (TIBP) and tris(2-butoxyethyl) phosphate (TBOEP)) had very low direct UV-C photolysis rates. TBOEP, TNBP and TIBP were degraded by UV/H2O2 and O3. Chlorinated compounds TCEP, TDCPP and TCIPP were the most recalcitrant OPFR to the advanced oxidation processes applied. The study provides information on the partitioning and degradability pathways of OPFR within conventional activated sludge WWTPs.

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.

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.