Mixtures of estrogenic chemicals enhance vitellogenic response in sea bass

Bisphenol A and its substitutes in the aquatic environment: Occurrence and toxicity assessment

Bisphenol A is classified as a high production volume chemical commonly used in the manufacture of polycarbonate plastics, epoxy resins and thermal paper. The endocrine disrupting properties of this xenobiotic have led to the restriction and prohibition of its use in many consumer products. To date, many chemical compounds with a chemical structure similar to bisphenol A have been used in consumer products as its replacement. The ubiquitous occurrence of bisphenol A and its substitutes in the environment and their endocrine activity as well as adverse effects on aquatic organisms is a global concern, especially because many available literature reports show that many substitutes (e.g. bisphenol AF, bisphenol AP, bisphenol B, bisphenol C, bisphenol F, bisphenol G, bisphenol FL, tetrabromobisphenol A) exert adverse effects on aquatic organisms, similar to, or even stronger than bisphenol A. Therefore, the objective of this paper is to provide a comprehensive overview of the production, sources, occurrence and associated toxicity, as well as the endocrine activity of bisphenol A and its substitutes on aquatic species. The environmental levels and ecotoxicological data presented in this review allowed for a preliminary assessment and prediction of the risk of bisphenol A and its substitutes for aquatic organisms. Furthermore, the data collected in this paper highlight that several compounds applied in bisphenol A-free products are not safe alternatives and regulations regarding their use should be introduced.

Endocrine-Disrupting Compounds in Fish Physiology, with Emphasis on their Effects on the Arginine Vasotocin/Isotocin System

The purposes of this review are to promote better use of existing knowledge of marine pollutants especially endocrine-disrupting compounds (EDCs) and to draw attention to the slow progression of the research on the influence of those compounds on arginine vasotocin/isotocin system (AVT/IT) in fish. EDCs are leading to the degradation of fish habitats, reducing their spawning potential and possibly their population parameters (e.g. growth, maturation), by preventing fish from breeding and rebuilding their populations. Therefore, searching for new welfare indicators such as AVT and IT and developing research procedures mimicking environmental conditions using a versatile fish model is extremely important. Fish species such as Zebrafish (Daniorerio) and round goby (Neogobiusmelanostomus) can be recommended as very suitable modelsfor studying estrogenic EDCs on the AVT/IT system and other hormones involved in the neuroendocrine regulation of physiological processes in fish.These studies would not only improve our understanding of the effects of EDCs on vertebrates but could also help safeguard the well-being of aquatic and terrestrial organisms from the harmful effects of these compounds.

In vitro estrogenic activity of binary and multicomponent mixtures with bisphenol A

Bisphenol A and its analogs are environmental contaminants with well known estrogenic and anti-androgenic activities. In studies of human biomonitoring, simultaneous exposure to multiple bisphenols was shown in different biological samples, at picomolar to low nanomolar concentrations. Evaluation of their combined toxicities will therefore be a more realistic and reliable predictor for estimation of health risks than evaluation of only the single chemicals. In the present study, estrogenic activities of individual bisphenols were evaluated, along with their binary and multicomponent mixtures including three- and four-component mixtures, using the Organisation for Economic Co-operation and Development validated transactivation assay with the hERα-Hela9903 cell line. Concentration-dependent estrogenic activity was confirmed for all of the tested bisphenols, in the nanomolar to micromolar range. Estrogenic activities of binary and multicomponent mixtures followed a concentration addition model. Although exposure to individual bisphenols remains below their effective doses, we demonstrate that as a mixture, they can contribute additively to toxicity. This study thus emphasizes the importance of mixture toxicity evaluation for risk assessment of compounds that act like the bisphenols.

Microplastic exposure and effects in aquatic organisms: A physiological perspective

The impact of microplastics (MPs) on aquatic life, given their ubiquitous presence in the water compartment, represents a growing concern. Consistently, scientific knowledge is advancing rapidly, although evidence on actual adverse effects is still highly fragmented. This paper summarizes the recent literature on MP impacts on aquatic organisms in an attempt to link routes of uptake, possible alterations of physiological processes, and outcomes at different levels of biological organization. Animal feeding strategies and MP biodistribution is discussed, alongside with relevant effects at molecular, cellular, and systemic level. Pathways from animal exposure to apical physiological responses are examined to define the relevance of MPs for animal health, and to point out open questions and research gaps. Emphasis is given to emerging threats posed by leaching of plastic additives, many of which have endocrine disruption potential. The potential role of MPs as substrates for microorganism growth and vehicle for pathogen spreading is also addressed.

The utility of vitellogenin as a biomarker of estrogenic endocrine disrupting chemicals in molluscs

Estrogenic endocrine disrupting chemicals (EDCs) are natural hormones, synthetic compounds or industrial chemicals that mimic estrogens due to their structural similarity with estrogen's functional moieties. They typically enter aquatic environments through wastewater treatment plant effluents or runoff from intensive livestock operations. Globally, most natural and synthetic estrogens in receiving aquatic environments are in the low ng/L range, while industrial chemicals (such as bisphenol A, nonylphenol and octylphenol) are present in the μg to low mg/L range. These environmental concentrations often exceed laboratory-based predicted no effect concentrations (PNECs) and have been evidenced to cause negative reproductive impacts on resident aquatic biota. In vertebrates, such as fish, a well-established indicator of estrogen-mediated endocrine disruption is overexpression of the egg yolk protein precursor vitellogenin (Vtg) in males. Although the vertebrate Vtg has high sensitivity and specificity to estrogens, and the molecular basis of its estrogen inducibility has been well studied, there is growing ethical concern over the use of vertebrate animals for contaminant monitoring. The potential utility of the invertebrate Vtg as a biomonitor for environmental estrogens has therefore gained increasing attention. Here we review evidence providing support that the molluscan Vtg holds promise as an invertebrate biomarker for exposure to estrogens. Unlike vertebrates, estrogen signalling in invertebrates remains largely unclarified and the classical genomic pathway only partially explains estrogen-mediated activation of Vtg. In light of this, in the latter part of this review, we summarise recent progress towards understanding the molecular mechanisms underlying the activation of the molluscan Vtg gene by estrogens and present a hypothetical model of the interplay between genomic and non-genomic pathways in the transcriptional regulation of the gene.

Comparisons of analytical chemistry and biological activities of extracts from North Pacific gyre plastics with UV-treated and untreated plastics using in vitro and in vivo models

Plastic debris is an emerging worldwide threat to marine biota. Marine species may face unique challenges in low-flow estuarine systems with a high abundance of "macro-sized" (>4.75 mm) plastic due to the leaching of constituents and adsorbed contaminants. To simulate this leaching process, plastic samples recovered from the North Pacific Gyre along with corresponding UV-irradiated virgin plastic and non-irradiated virgin plastic counterparts were incubated in saltwater for 30 days at ambient temperatures ranging from 17 to 25 °C. Following solid-phase extraction, water samples were fractionated with sequential methanol elution from 10 to 100% and evaluated using in vitro assays assessing estrogen receptor (ER) and aryl hydrocarbon receptor (AhR) activities. In vivo responses (vitellogenin [vtg] and cytochrome p450 1A [cyp1a] mRNA) were measured following 5-day exposures in Japanese medaka (Oryzias latipes) larvae (3 days post hatch). Estrogenic plasticizers, co-planar PCBs and PAHs were quantified in the extracts using targeted GC-MS/MS and UPLC-MS/MS. In vitro estrogenicity showed highest activity in the 70% methanol fraction for all plastic leachate exposures. Whole extract in vitro estradiol equivalent (EEQ) values were 4.34 ± 2.65, 8.79 ± 2.09 and 13.78 ± 3.64 ng/L, for virgin plastic, UV-irradiated virgin plastic and North Pacific Gyre-recovered plastic, respectively (mean ± SD). Significant vtg induction was observed in medaka larvae exposed to leachate extracts from North Pacific Gyre-recovered plastic and UV-irradiated virgin plastic (9.9-fold, p = 0.039 and 10.1-fold, p = 0.042, respectively). Chemically-determined EEQ values were also localized in the 70% methanol fraction. Whole leachate extract chemical EEQ values were 0.33 ± 0.07, 1.64 ± 0.62 and 11.4 ± 2.13 ng/L, for virgin plastic, UV-irradiated virgin plastic and North Pacific Gyre-recovered plastic, respectively. In-vitro AhR activity was highest in the 70% methanol elution with greater activity in North Pacific Gyre-recovered plastic than in virgin plastic and UV-irradiated virgin plastic (toxic equivalency [TEQ] = 1.06 ± 0.54, 0.38 ± 0.07 and 0.71 ± 0.47 ng/L, respectively). CYP1A mRNA was significantly induced in larval medaka exposed to North Pacific Gyre-recovered plastic leachates (17.8-fold, p = 0.02) while exposure to virgin plastic and UV-irradiated virgin plastic leachates caused no significant change. Chemically-determined TEQ analysis for AhR indicated highest activity in the 90% methanol fraction for all leachates, with whole extract in vitro TEQs being 1.47 ± 0.87, 0.03 ± 0.05 and 0.42 ± 0.38 ng/L for North Pacific Gyre-recovered plastic, virgin plastic and UV-irradiated virgin plastic, respectively. These results indicate that weathering and UV radiation release estrogenic plasticizers and demonstrate the ability for plastics to transport adsorbed persistent organic pollutants at eco-toxicologically relevant concentrations.

Prediction of the combined effects of multiple estrogenic chemicals on MCF-7 human breast cancer cells and a preliminary molecular exploration of the estrogenic proliferative effects and related gene expression

The environmental risks of environmental estrogens (EEs) are often assessed via the same mode of action in the concentration addition (CA) model, neglecting the complex combined mechanisms at the genetic level. In this study, the cell proliferation effects of estrone, 17α-ethinylestradiol, 17β-estradiol, estriol, diethylstilbestrol, estradiol valerate, bisphenol A, 4-tert-octylphenol and 4-nonylphenol were determined individually using the CCK-8 method, and the proliferation effects of a multicomponent mixture of estrogenic chemicals mixed at equipotent concentrations using a fixed-ratio design were studied using estrogen-sensitive MCF-7 cells. Furthermore, transcription factors related to cell proliferation were analyzed using RT-PCR assays to explore the potential molecular mechanisms related to the estrogenic proliferative effects. The results showed that the estrogenic chemicals act together in an additive mode, and the combined proliferative effects could be predicted more accurately by the response addition model than the CA model with regard to their adverse outcomes. Furthermore, different signaling pathways were involved depending on the different mixtures. The RT-PCR analyses showed that different estrogens have distinct avidities and preferences for different estrogen receptors at the gene level. Furthermore, the results indicated that estrogenic mixtures increased ERα, PIK3CA, GPER, and PTEN levels and reduced Akt1 level to display combined estrogenicity. These findings indicated that the potential combined environmental risks were greater than those found in some specific assessment procedures based on a similar mode of action due to the diversity of environmental pollutions and their multiple unknown modes of action. Thus, more efforts are needed for mode-of-action-driven analyses at the molecular level. Furthermore, to more accurately predict and assess the individual responses in vivo from the cellular effects in vitro, more parameters and correction factors should be taken into consideration in the addition model.

Short-term induction of vitellogenesis in the immature male yellowfin seabream (Acanthopagrus latus) exposed to bisphenol A and 17β-estradiol

Bisphenol A (BPA) is a known environmental endocrine-disrupting chemical that is widely used in plastics manufacturing. BPA enters in the aquatic environment mainly through urban and industrial sewage effluents, thereby posing a potential threat to organisms living in these ecosystems. This study was conducted to investigate the effect of BPA on VTG production with direct (sodium dodecyl sulfate-polyarylamide gel electrophoresis) and indirect (alkali-labile phosphate (ALP), total plasma calcium and protein) methods in immature male yellowfin seabream ( Acanthopagrus latus) as a marine fish model. Fish were randomly distributed into seven groups that were administered 1, 10, 50, and 100 µg g−1 week−1 of BPA and 2 µg g−1week−1 of 17β-estradiol (E2) over a period of 2 weeks. Solvent controls received olive oil, whereas controls were not injected. The fish were sampled on days 0, 7, and 14, and their blood plasma and liver were obtained. The results showed that the hepatosomatic index of all treated fish was elevated in comparison with controls. Direct and indirect indicators showed that fish VTG protein was induced by BPA and E2 exposure. The protein was found to have two bands with molecular weights around 210 and 190 KDa. ALP, total plasma calcium and protein levels were increased in dose- and time-dependent manners. The results of this study demonstrated that short-term exposure of yellowfin seabream to BPA induced adverse effects in the reproductive system of hermaphrodite fish.

Vitellogenin levels and others biomarkers show evidences of endocrine disruption in fish species from Iguaçu River - Southern Brazil

The adverse effects of endocrine disrupting chemicals (EDCs) on aquatic wildlife and human health represent a current issue of high public concern. Even so, they are still poorly studied in aquatic environments of South America. The aim of the present study was to investigate the impact of EDCs in five cascading reservoirs from the Iguaçu River, evaluating reproductive endpoints in three native fish species (Astyanax bifasciatus, Chrenicicla iguassuensis and Geophagus brasiliensis). Additionally, a polyclonal antiserum anti-vitellogenin from G. brasiliensis and a capture ELISA assay were developed for detection of estrogenic or anti-estrogenic activities in male and female fish, respectively. Vitellogenin (VTG) levels in male fish from the Iguacu River was observed, as well as decreased levels of vitellogenin and estradiol in the plasma of female fish. These findings were associated with immature gonads and lower gonadosomatic index in G. brasiliensis adult females from the Foz do Areia (FA) Reservoir. Additionally, both endemic species (Astyanax bifasciatus and Chrenicicla iguassuensis) displayed immature gonads and histological changes, such as degeneration of germ cells, in other studied reservoirs. The current results suggest that these reproductive responses may be associated with the bioavailability of EDCs in the Iguaçu River. These impacts are likely related to chemicals released by human activities, especially from sewage and industrial sources and agricultural production, detected in previous studies. Overall, the FA reservoir was potentially the most affected by chemicals with endocrine properties, and further studies are necessary to identify and quantify these chemicals.

Capturing ecology in modeling approaches applied to environmental risk assessment of endocrine active chemicals in fish

Endocrine active chemicals (EACs) are widespread in freshwater environments and both laboratory and field based studies have shown reproductive effects in fish at environmentally relevant exposures. Environmental risk assessment (ERA) seeks to protect wildlife populations and prospective assessments rely on extrapolation from individual-level effects established for laboratory fish species to populations of wild fish using arbitrary safety factors. Population susceptibility to chemical effects, however, depends on exposure risk, physiological susceptibility, and population resilience, each of which can differ widely between fish species. Population models have significant potential to address these shortfalls and to include individual variability relating to life-history traits, demographic and density-dependent vital rates, and behaviors which arise from inter-organism and organism-environment interactions. Confidence in population models has recently resulted in the EU Commission stating that results derived from reliable models may be considered when assessing the relevance of adverse effects of EACs at the population level. This review critically assesses the potential risks posed by EACs for fish populations, considers the ecological factors influencing these risks and explores the benefits and challenges of applying population modeling (including individual-based modeling) in ERA for EACs in fish. We conclude that population modeling offers a way forward for incorporating greater environmental relevance in assessing the risks of EACs for fishes and for identifying key risk factors through sensitivity analysis. Individual-based models (IBMs) allow for the incorporation of physiological and behavioral endpoints relevant to EAC exposure effects, thus capturing both direct and indirect population-level effects.

Characterizing cytotoxic and estrogenic activity of Arctic char tissue extracts in primary Arctic char hepatocytes

Contaminants from various anthropogenic activities are detected in the Arctic due to long-range atmospheric transport, ocean currents, and living organisms such as migrating fish or seabirds. Although levels of persistent organic pollutants (POPs) in Arctic fish are generally low, local hot spots of contamination were found in freshwater systems such as Lake Ellasjøen at Bjørnøya (Bear Island, Norway). Higher concentrations of organic halogenated compounds (OHC), and higher levels of cytochrome P450 and DNA-double strand breaks were reported in Arctic char (Salvelinus alpinus) from this lake compared to fish from other lakes on Bjørnøya. Although several of the measured contaminants are potential endocrine disrupters, few studies have investigated potential endocrine disruptive effects of the contaminant cocktail in this fish population. The aim of this study was to compare acutely toxic and estrogenic potency of the cocktail of pollutants as evidenced by cytotoxic and/or estrogenic effects in vitro using extracts of Arctic char livers from contaminated Lake Ellasjøen with those from less contaminated Lake Laksvatn at Bjørnøya. This was performed by in situ sampling and contaminant extraction from liver tissue, followed by chemical analysis and in vitro testing of the following contaminated tissue extracts: F1-nonpolar OHC, F2-polar pesticides and metabolites of OHC, and F3-polar OHC. Contaminant levels were highest in extracts from Ellasjøen fish. The F2 and F3 extracts from Lake Laksvatn and Lake Ellasjøen fish reduced in vitro cell viability at a concentration ratio of 0.03-1 relative to tissue concentration in Arctic char. Only the F3 liver extract from Ellasjøen fish increased in vitro vitellogenin protein expression. Although compounds such as estrogenic OH-PCBs were quantified in Ellasjøen F3 extracts, it remains to be determined which compounds were inducing estrogenic effects.

Molecular Mechanisms of Action of BPA

Bisphenol A (BPA) exposure has been associated with serious endocrine-disrupting effects in humans and wildlife. Toxicological and epidemiological studies evidenced that BPA increases body mass index and disrupts normal cardiovascular physiology by interfering with endogenous hormones in rodents, nonhuman primates, and cell culture test systems. The BPA concentration derived from these experiments were used by government regulatory agencies to determine the safe exposure levels of BPA in humans. However, accumulating literature in vivo and in vitro indicate that at concentrations lower than that reported in toxicological studies, BPA could elicit a different endocrine-disrupting capacity. To further complicate this picture, BPA effects rely on several and diverse mechanisms that converge upon endocrine and reproductive systems. If all or just few of these mechanisms concur to the endocrine-disrupting potential of low doses of BPA is at present still unclear. Thus, taking into account that the incidence and/or prevalence of health problems associated with endocrine disruption have increased worldwide, the goal of the present review is to give an overview of the many mechanisms of BPA action in order to decipher whether different mechanisms are at the root of the effect of low dose of BPA on endocrine system.

Bisphenol A accumulation in eggs disrupts the endocrine regulation of growth in rainbow trout larvae

Bisphenol A (BPA), a monomer used in the production of plastics and epoxy resins, is ubiquitously present in the aquatic environment. BPA is considered a weak estrogen in fish, but the effects of this chemical on early developmental events are far from clear. We tested the hypothesis that BPA accumulation in eggs, mimicking maternal transfer, disrupts growth hormone/insulin-like growth factor (GH/IGF) axis function, leading to defects in larval growth in rainbow trout. Trout oocytes were exposed to 0 (control), 0.3, 3, and 30 μg ml(-1) BPA for 3h, which led to an accumulation of around 0, 1, 4 and 40 ng BPA per egg, respectively. All treatment groups were fertilized with clean milt and reared in clean water for the rest of the experiment. The embryo BPA content declined over time in all groups and was completely eliminated by 42 days post-fertilization (dpf). Hatchlings from BPA accumulated eggs had higher water content and reduced total energy levels prior to first feed. There was an overall reduction in the specific growth rate and food conversion ratio in larvae reared from BPA-laden eggs. BPA accumulation disrupted the mRNA abundance of genes involved in GH/IGF axis function, including GH isoforms and their receptors, IGF-1 and -2 and IGF receptors, in a life stage-dependent manner. Also, there was a temporal disruption in the mRNA levels of thyroid hormone receptors in the larvae raised from BPA-laden eggs. Altogether, BPA accumulation in eggs, mimicking maternal transfer, affects larval growth and the mode of action involves disruption of genes involved in the GH/IGF and thyroid axes function in trout.

Exploring the impacts of two separate mixtures of pesticide and surfactants on estrogenic activity in male fathead minnows and rainbow trout

In this study, male fathead minnows (FHM) (Pimephales promelas) and juvenile rainbow trout (RT; Oncorhynchus mykiss) were exposed to two different surfactant mixtures of analytical-grade nonlyphenol, 4-tert octyphenol, octylphenol ethoxylates, nonylphenol ethoxylates, and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). After a 7-days exposure to environmentally relevant concentrations of these compounds, there was no difference in the relative mRNA expression of vitellogenin (VTG) in male juvenile RT exposed to individual compounds or the 2,4-D-surfactant mixture compared with the control. In male FHM, there was a significant increase in VTG mRNA expression in the high individual treatments of 2,4-D and the surfactants but not the 2,4-D-surfactant mixtures compared with the control. These results were compared with another study exposing male FHM to individual and a mixture of alkylphenols and alkylphenol ethoxylates in two different combinations with the herbicide diuron and the insecticide bifenthrin. There were no differences in the relative expression of VTG mRNA amongst individual exposures and the control. Interestingly, when the ethoxylate mixture was combined with diuron, there was a significant decrease in the relative mRNA expression of VTG compared with the control. However, when the ethoxylate mixture was combined with both diuron and bifenthrin, there was a significant increase in the relative mRNA expression of VTG in male compared with all other groups in the multichemical mixture. The results of this study highlight differences between species and measurements of VTG in assessing the risk of mixtures to aquatic organisms.

Effects of individual and binary mixtures of estrogens on male goldfish (Carassius auratus)

Adverse effects of five typical environmental estrogens, namely estrone (E1), 17β-estradiol (E2), 4-n-octylphenol (4-n-OP), 4-n-nonylphenol (4-n-NP) and bisphenol A (BPA) on adult male goldfish (Carassius auratus) were investigated both individually and in binary mixtures, using serum vitellogenin (VTG) induction and gonadosomatic index (GSI) as the endpoints. Doses of individual and binary mixtures of estrogens were chosen at broad ranges. Five individual estrogens induced common dose-dependent increases of serum VTG in the experimental fish when injection doses of the estrogen series were comparatively low. The levels of VTG induction in fish descended after peaked at a certain dose of the individual estrogen. Significant GSI decreases were observed in fish treated by all dose series of E1 and E2, and comparatively high doses of 4-n-OP, 4-n-NP and BPA when compared with that of solvent control (SC). Effects of binary mixtures of the five typical estrogens on VTG induction in male goldfish were in additive manner at low-effect doses, but divergences occurred at high dose levels, with the predicted effects by additive manner exceeding those were observed. All of GSI of fish treated by the binary mixtures were about or lower than 10(-3)%. Serious atrophy of gonads was observed in all the mixture treatment groups when compared with that of SC. These findings highlight the potential reproductive risk of fish resulted from existing mixtures of hormones in the aquatic environment, and they have important implications for environmental estrogen hazard assessment.

Combined effects of estrogenic chemicals with the same mode of action using an estrogen receptor binding bioassay

The increasing amounts of various estrogenic chemicals coexisting in the aquatic environment may pose environmental risks. While the concept of estradiol equivalent (EEQ) has been frequently applied in studying estrogenic mixtures, few experiments have been done to prove its reliability. In this study, the reliability of EEQ and the related model concentration addition (CA) was verified based on the two-hybrid recombinant yeast bioassay when all mixture components had the same mode of action and target of action. Our results showed that the measured estrogenic effects could be well predicted by CA and EEQ for all laboratory-made mixtures using two designs, despite the varying estrogenic activity, concentration levels and ratios of the test chemicals. This suggests that when an appropriate endpoint and its relevant bioassay are chosen, CA should be valid and the application of EEQ in predicting the effect of non-equi-effect mixtures is feasible.

Developmental exposure of zebrafish (Danio rerio) to bisphenol-S impairs subsequent reproduction potential and hormonal balance in adults

In the recent years, there has been a growing concern about the production and use of bisphenol-A substitute, namely bisphenol-S (BPS). Due to its novel nature, there have been few studies addressing the ability of BPS to disrupt the endocrine system of animals. In the present study, zebrafish (Danio rerio) embryos were exposed to and reared in various concentrations of BPS (0, 0.1, 1, 10 and 100 μg/l) for 75 days. Then adult males and females were paired in spawning tanks for 7 days in clean water and the consequent effects on fish development, reproduction, plasma vitellogenin (VTG), sex steroids and thyroid hormone levels were investigated as endpoints. After 75 days of exposure, there was a skewed sex ratio in favor of females. The results also showed that body length and weight significantly decreased in males exposed to 100 μg/l of BPS. Gonadosomatic index was significantly reduced in fish at ≥ 10 μg/l. Hepatosomatic index exhibited a significant increase in both male and female fish. At ≥ 1 μg/l of BPS, plasma 17β-estradiol levels were significantly increased in both males and females. However, plasma testosterone showed a significant reduction in males exposed to 10 and 100 μg/l of BPS. A significant induction in plasma VTG level was observed in both males and females at ≥ 10 μg/l of BPS. Plasma thyroxine and triiodothyronine levels were significantly decreased at 10 and 100 μg/l of BPS in males, and at 100 μg/l in females. Egg production and sperm count were also significantly decreased in groups received 10 and 100 μg/l of BPS. Moreover, once time to hatching and hatching rates were calculated for fertilized eggs the postponed and decreased rates of hatching were observed. Taken together, these results suggest that developmental exposure to low concentrations of BPS has adverse effects on different parts of the endocrine system in zebrafish.

Anti-androgens act jointly in suppressing spiggin concentrations in androgen-primed female three-spined sticklebacks - prediction of combined effects by concentration addition

Increasing attention is being directed at the role played by anti-androgenic chemicals in endocrine disruption of wildlife within the aquatic environment. The co-occurrence of multiple contaminants with anti-androgenic activity highlights a need for the predictive assessment of combined effects, but information about anti-androgen mixture effects on wildlife is lacking. This study evaluated the suitability of the androgenised female stickleback screen (AFSS), in which inhibition of androgen-induced spiggin production provides a quantitative assessment of anti-androgenic activity, for predicting the effect of a four component mixture of anti-androgens. The anti-androgenic activity of four known anti-androgens (vinclozolin, fenitrothion, flutamide, linuron) was evaluated from individual concentration-response data and used to design a mixture containing each chemical at equipotent concentrations. Across a 100-fold concentration range, a concentration addition approach was used to predict the response of fish to the mixture. Two studies were conducted independently at each of two laboratories. By using a novel method to adjust for differences between nominal and measured concentrations, good agreement was obtained between the actual outcome of the mixture exposure and the predicted outcome. This demonstrated for the first time that androgen receptor antagonists act in concert in an additive fashion in fish and that existing mixture methodology is effective in predicting the outcome, based on concentration-response data for individual chemicals. The sensitivity range of the AFSS assay lies within the range of anti-androgenicity reported in rivers across many locations internationally. The approach taken in our study lays the foundations for understanding how androgen receptor antagonists work together in fish and is essential in informing risk assessment methods for complex anti-androgenic mixtures in the aquatic environment.

Induction and recovery of estrogenic effects after short-term 17β-estradiol exposure in juvenile rainbow trout (Oncorhynchus mykiss)

Estrogenic compounds found in the aquatic environment include natural and synthetic estrogen hormones as well as other less potent estrogenic xenobiotics. In this study, a comprehensive approach was used to examine effects on fish endocrine system endpoints during a short-term xenoestrogen exposure as well as after post-exposure recovery. Rainbow trout (Oncorhynchus mykiss) were exposed to an aqueous 17β-estradiol (E2) concentration of 0.473 μg l(-1) for 2 and 7 days (d) followed by a 14-d recovery period. At d2 and d7, plasma E2 concentrations in treated fish were 458- and 205-fold higher than in control fish and 23- and 16-fold higher than the exposure water concentration. E2 treatment resulted in significant increases in hepatosomatic index (HSI), plasma vitellogenin (VTG) protein concentrations, and liver VTG and estrogen receptor alpha mRNA levels. All of these parameters, with the exception of plasma VTG protein, returned to baseline values during the recovery period. Plasma cortisol concentrations were unaffected by treatment. This research shows varied time frames of the estrogen-responsive molecular-, biochemical-, and tissue-level alterations, as well as their persistence, in juvenile rainbow trout treated with aqueous E2. These results have implications for feral rainbow trout exposed to xenoestrogens and indicate the importance of evaluating a comprehensive suite of endpoints in assessing the impact of this type of environmental contaminant.

Endocrine-disrupting chemicals: associated disorders and mechanisms of action

The incidence and/or prevalence of health problems associated with endocrine-disruption have increased. Many chemicals have endocrine-disrupting properties, including bisphenol A, some organochlorines, polybrominated flame retardants, perfluorinated substances, alkylphenols, phthalates, pesticides, polycyclic aromatic hydrocarbons, alkylphenols, solvents, and some household products including some cleaning products, air fresheners, hair dyes, cosmetics, and sunscreens. Even some metals were shown to have endocrine-disrupting properties. Many observations suggesting that endocrine disruptors do contribute to cancer, diabetes, obesity, the metabolic syndrome, and infertility are listed in this paper. An overview is presented of mechanisms contributing to endocrine disruption. Endocrine disruptors can act through classical nuclear receptors, but also through estrogen-related receptors, membrane-bound estrogen-receptors, and interaction with targets in the cytosol resulting in activation of the Src/Ras/Erk pathway or modulation of nitric oxide. In addition, changes in metabolism of endogenous hormones, cross-talk between genomic and nongenomic pathways, cross talk with estrogen receptors after binding on other receptors, interference with feedback regulation and neuroendocrine cells, changes in DNA methylation or histone modifications, and genomic instability by interference with the spindle figure can play a role. Also it was found that effects of receptor activation can differ in function of the ligand.

Bisphenol A exposure, effects, and policy: a wildlife perspective

Thousands of anthropogenic chemicals are present in the environment, and mounting evidence indicates that some have endocrine-disrupting effects in a variety of organisms. Of particular concern are chemicals that act as agonists or antagonists on vertebrate estrogen or androgen receptors. One such compound is bisphenol A (BPA), which appears to be both an estrogen receptor agonist and an androgen receptor antagonist. Used in the manufacture of plastic resins, BPA is found at low levels in surface-water, sediments, soils, and biota. Although it degrades quickly, it is pseudo-persistent in the environment because of continual inputs. Due to its environmental ubiquity, organisms may be exposed to BPA chronically or during sensitive life stages. While the impacts of BPA-related endocrine disruption in humans have been extensively studied, the endocrinal and systemic effects in wildlife are less well known. This article reviews the current state of knowledge of BPA inputs to the environment, routes of exposure, and effects on wildlife. We then critically examine the regulatory structure governing the environmental endpoints of BPA in the United States, European Union, and Canada, and discuss major challenges to the effective regulation of BPA. We conclude with a survey of treatment and mitigation options.

Effects of ethinylestradiol and of an environmentally relevant mixture of xenoestrogens on steroidogenic gene expression and specific transcription factors in zebrafish

In natural environments fish are exposed to endocrine disrupting compounds (EDCs) present at low concentrations and with different modes of actions. Here, adult zebrafish of both sexes were exposed for 21 days to an estrogenic mixture (Mix) of eleven EDCs previously quantified in Douro River estuary (Portugal) and to 100 ng/L 17α-ethinylestradiol (EE2) as positive control. Vitellogenin mRNA and HSI in males confirmed both exposure regimes as physiologically active. Potential candidates for estrogenic disturbance of steroidogenesis were identified (StAR, 17β-HSD1, cyp19a1), but Mix only affected cyp19a1 in females. Significant differences in the response of FSHβ, cypa19a2, 20β-HSD were observed between EE2 and Mix. Mtf-1 and tfap2c transcription factor binding sites were discovered in the putative promoter regions and corresponding transcription factors were found to be differentially expressed in response to Mix and EE2. The results suggest that "non-classical effects" of estrogenic EDC in fish are mediated via transcription factors.

A mixture of an environmentally realistic concentration of a phthalate and herbicide reduces testosterone in male fathead minnow (Pimephales promelas) through a novel mechanism of action

Several chemicals that are used by humans, such as pesticides and plastics, are released into the aquatic environment through wastewater and runoff and have been shown to be potent disruptors of androgen synthesis at high concentrations. Although many of these chemicals have been studied in isolation, a large amount of uncertainty remains over how fish respond to low concentrations of anti-androgenic mixtures, which more accurately reflects how such chemicals are present in the aquatic environment. In this study male fathead minnows (FHM) (Pimephales promelas) were exposed to environmentally relevant concentrations of two anti-androgens, the herbicide linuron, and the plasticizer di(2-ethylhexyl) phthalate (DEHP) individually and as part of a mixture of the two for a 28-day period. At the end of this period there was a reduction in plasma testosterone (T) concentrations in male FHM exposed to the mixture, but not in FHM exposed individually to linuron or DEHP or the control FHM. There was also a significant reduction in 17β-estradiol (E2) in the DEHP-only and mixture exposed groups as compared to the control. Contrary to what has been previously published for these two chemicals in mammals, the lower plasma T concentrations in male FHM exposed to the mixture was not a result of the inhibition of genes involved in steroidogenesis; nor due to an increase in the expression of genes associated with peroxisome proliferation. Rather, an increase in relative transcript abundance for CYP3A4 in the liver and androgen- and estrogen-specific SULT2A1 and SULT1st2 in the testes provides evidence that the decrease in plasma T and E2 may be linked to increased steroid catabolism. Feedback from the pituitary is not repressed as the relative expression of follicle stimulating hormone β-subunit mRNA transcript levels in the brain was significantly higher in both DEHP and mixture exposed FHM. In addition, luteinizing hormone β-subunit mRNA transcript levels increased but were not significant in the mixture as compared to the control. Hormone receptor mRNA transcript levels in the liver and testes were not significantly different across all four exposure groups. This study highlights the importance of assessing environmentally relevant concentrations of mixtures when determining risk to aquatic organisms.

Single and combined effects of selected pharmaceuticals at sublethal concentrations on multiple biomarkers in Carassius auratus

In this study, the sublethal effects of caffeine, sulfamethoxazole and their mixture on goldfish (Carassius auratus) were investigated, the biomarkers including acetylcholinesterase (AChE) in brain, 7-ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and superoxide dismutase (SOD) in liver and vitellogenin (VTG) in serum were determined after 1, 2, 4, and 7 days of exposure. AChE activity was significantly inhibited by caffeine (≥0.4 mg/l), sulfamethoxazole (≥0.4 mg/l) and their mixtures (≥0.048 mg/l) during all exposure periods, and obvious concentration-response and time-response relationships were obtained. EROD, GST and SOD activities were significantly increased by individual compounds and mixtures in most cases. GST induction exhibited bell-shaped concentration-response curves. Serum VTG was significantly induced by 2 mg/l of caffeine, 10 mg/l of sulfamethoxazole and the mixtures at concentrations ≥1.2 mg/l. In general, the two pharmaceuticals induced similar biological responses. The joint effect of caffeine/sulfamethoxazole was additive with regard to AChE and GST activity variation and was antagonistic with regard to EROD and SOD induction. The results indicated that multiple biomarker response method might be a useful tool for describing an integrated toxicological effect of chemicals. VTG induction suggested that caffeine and sulfamethoxazole may cause a slightly feminization effect.

Assessing combined toxicity of estrogen receptor agonists in a primary culture of rainbow trout (Oncorhynchus mykiss) hepatocytes

The presence of highly complex mixtures of chemicals in the environment challenges our ability to assess single chemical effects and the interaction that occurs with cellular receptor targets and regulation of endocrine processes. In this study concentration addition (CA) and independent action (IA) prediction models were used to assess the combined toxicity of mixtures of environmental relevant estrogen receptor (ER) agonists (hormones and anthropogenic pollutants) in a primary culture of rainbow trout (Oncorhynchus mykiss) hepatocytes using the ER-mediated production of vitellogenin (Vtg) as a biological marker (biomarker) for estrogenicity. Nine of the eleven tested chemicals induced the production of Vtg and the parameters from the fitted concentration-response curves were used to model four mixtures containing four (17β-estradiol, estrone, estriol and diethylstilbestrol), five (musk ketone, 4-tert-octylphenol, bisphenol A, o,p'-DDT and dibenzothiophene), seven (17β-estradiol, estrone, estriol, diethylstilbestrol, 4-tert-octylphenol, bisphenol A and o,p'-DDT) and nine compounds (17β-estradiol, estrone, estriol, diethylstilbestrol, musk ketone, 4-tert-octylphenol, bisphenol A, o,p'-DDT and dibenzothiophene). The CA and IA prediction model proved to be a good estimation for the combined effect of mixtures of ER agonists at low relative mixture concentration (e.g. relative to the maximum mixture concentrations used), but a deviation from the prediction models was observed when exposing hepatocytes to high relative mixture concentrations. The CA and IA prediction models' ability to predict the combined estrogenic effect of complex mixtures, especially in the low concentration-response range, is of ecological relevance since organisms in the environment generally encounter low concentrations of chemicals from a wide array of chemical groups that may not elicit estrogenic effects on their own.

Interactions between estrogenic chemicals in binary mixtures investigated using vitellogenin induction and factorial analysis

Considerable progress has been made in assessing the combined effects of chemicals, but the effect of mixtures remains one of the most daunting challenges in environmental toxicology. In this study, the effects of binary mixtures of estrogenic chemicals were investigated using plasma vitellogenin (VTG) induction in male adult Japanese medaka (Oryzias latipes) as the endpoint. We focused on whether or not the factorial design using rigorous statistical methods was appropriate for the identification of possible interactions. The estrogenic activities of 17beta-estradiol (E2), 4-tert-nonylphenol (NP) and bisphenol A (BPA) were investigated in medaka following 14 d of exposure. Although all chemicals induced concentration-dependent increases in plasma VTG, a complete concentration-response curve was obtained only for E2, while partial curves were obtained for NP and BPA. Therefore, a 3 x 3 factorial design was employed to identify both the individual and interactive effects. A significant difference in mean plasma VTG induction was found when any chemical was considered alone. However, no significant interactions between E2 and NP, E2 and BPA, and NP and BPA were demonstrated. These results suggest that these three model estrogenic chemicals share a common mechanism for inducing VTG synthesis, and that no interactions occur when they act in combination. We also demonstrated the ability of this experimental design to detect interactions between binary mixtures, which will allow the assessment of biological effects of more complex mixtures in future research.

Estrogenic activity of ternary UV filter mixtures in fish (Pimephales promelas) - an analysis with nonlinear isobolograms

Numerous estrogenic compounds are present in aquatic environments, but currently it is not well understood how compounds that differ in maxima and slope of their individual dose-response curves contribute to the overall mixture effect. In order to better understand such interactions we investigated 3 commonly used UV filters, for their estrogenic mixture activity and analysed their joint effects by using the concentration addition (CA) concept. Thereby, we extended the method of isoboles for analysis of 3 compounds that differ in maxima and slopes of their dose-response curves. 3-Benzylidene camphor (3BC), benzophenone-1 (BP1) and benzophenone-2 (BP2) are estrogenic in fish and act as pure- or partial estrogen receptor alpha agonists. First we exposed juvenile fathead minnows for 14 days to six concentrations of each UV filter alone to determine vitellogenin (VTG) induction curves, calculate equi-effective mixture concentrations and predict mixture effects. For 3BC, BP1 and BP2 significant VTG-induction occurred at 420, 2668, and 4715 microg/L, respectively. BP2 displayed a full dose-response curve, whereas 3BC and BP1 showed submaximal activity of 70 and 78%, respectively. Second, we exposed fish to 6 equi-effective mixtures (EC-NOEC, EC1, EC5, EC10, EC20, EC30) of these UV filters. Significant VTG-induction occurred at EC5 and higher. Submaximal activity of 67% as compared to the control EE2 (100 ng/L) was reached. The curves for the observed and predicted mixture activity agreed for mixture levels (EC10 to EC30), however, at EC-NOEC, EC1 and EC5, lower activity was observed than predicted by CA. Detailed isobolographic analysis indicate additivity at EC10 to EC30, and antagonism at low levels (EC-NOEC to EC5). Our data show for the first time, that for compounds with differences in maxima and slope, considerably more mixture combinations are additive than previously thought. This should be taken into account for hazard and risk assessment of UV filters and xenoestrogens.