Effects of estrogen exposure in mussels, Mytilus edulis, at different stages of gametogenesis

Exploring the mechanism of nonylphenol-induced ovarian developmental delay of manila clams, Ruditapes philippinarum: Applying RNAi to toxicological analysis

Nonylphenol (NP) contamination in the coastal environment of China poses ecological risks to aquatic organisms. However, the endocrine disruptive impacts of NP on bivalves, particularly on ovarian development, remain poorly understood. In this study, Manila clams Ruditapes philippinarum at the developing stage of gonad were exposed to 1.0 μg/L NP for 21 days. Utilizing RNA interference (RNAi) to suppress ER gene expression, we observed a delay in ovarian development as evidenced by histological observations under both NP and NPRi (NP with ER-RNAi) treatment, with Vtg elevation exclusive to the NP group. Comprehensive analyses encompassing transcriptomics, real-time quantitative PCR, and steroid hormone measurement revealed significant alterations in aldosterone synthesis, estrogen signaling, and thyroid hormone synthesis. These pathways showed similar perturbations in both NP and NPRi groups compared to controls. Notably, the NPRi group exhibited distinct enrichment in PPAR and insulin signaling pathways, may implicating these in ER function suppression. Steroid hormone biosynthesis was notably reduced in both treatments, pointing to a profound impact on hormone synthesis. The contrast between in vivo and in vitro findings suggests that NP's detrimental effects on ovarian development may primarily involve neuroendocrine regulation of steroidogenesis. This investigation highlights the complex dynamics of NP-induced endocrine disruption in bivalves, emphasizing the pivotal role of ER and associated pathways.

Exposure of Mytilus galloprovincialis to Microplastics: Accumulation, Depuration and Evaluation of the Expression Levels of a Selection of Molecular Biomarkers

Microplastic contamination is a growing marine environmental issue with possible consequences for seafood safety. Filter feeders are the target species for microplastic (MPs) pollution because they filter large quantities of seawater to feed. In the present study, an experimental contamination of Mytilus galloprovincialis was conducted using a mixture of the main types of MPs usually present in the seawater column (53% filaments, 30% fragments, 3% granules) in order to test the purification process as a potential method for removing these contaminants from bivalves intended for human consumption. A set of molecular biomarkers was also evaluated in order to detect any variations in the expression levels of some genes associated with biotransformation and detoxification, DNA repair, cellular response, and the immune system. Our results demonstrate that: (a) the purification process can significantly reduce MP contamination in M. galloprovincialis; (b) a differential expression level has been observed between mussels tested and in particular most of the differences were found in the gills, thus defining it as the target organ for the use of these biomarkers. Therefore, this study further suggests the potential use of molecular biomarkers as an innovative method, encouraging their use in next-generation marine monitoring programs.

The impact of pharmaceutical pollutants on daphnids - A metabolomic approach

Pharmaceuticals have been classified as emerging contaminants in the aquatic ecosystem, mainly due to their increased use and improper disposal. A significant range of pharmaceutical compounds and their metabolites have been globally detected in surface waters and pose detrimental effects to non-target organisms. Monitoring pharmaceutical water pollution relies on the analytical approaches for their detection, however, such approaches are limited by their sensitivity limit and coverage of the wide range pharmaceutical compounds. This lack of realism in risk assessment is bypassed with effect-based methods, which are complemented by chemical screening and impact modelling, and are able to provide mechanistic insight for pollution. Focusing on the freshwater ecosystem, in this study we evaluated the acute effects on daphnids for three distinct groups of pharmaceuticals; antibiotics, estrogens, and a range of commonly encountered environmentally relevant pharmaceutical pollutants. Combining several endpoints such as mortality, biochemical (enzyme activities) and holistic (metabolomics) we discovered distinct patterns in biological responses. In this study, changes in enzymes of metabolism e.g. phosphatases and lipase, as well as the detoxification enzyme, glutathione-S-transferase, were recorded following acute exposure to the selected pharmaceuticals. A targeted analysis of the hydrophilic profile of daphnids revealed mainly the up-regulation of metabolites following metformin, gabapentin, amoxicillin, trimethoprim and β-estradiol. Whereas gemfibrozil, sulfamethoxazole and oestrone exposure resulted in the down-regulation of majority of metabolites.

Does dietary exposure to 17α-ethinylestradiol alter biomarkers related with endocrine disruption and oxidative stress in the adult triploid of Danio rerio?

This study was conducted to investigate a comprehensive effect of 17α-ethinylestradiol (EE2) in zebrafish (Danio rerio) with the emphasis on endocrine disruption, oxidative stress and detoxification processes at different levels. Adult male triploid zebrafish were exposed to EE2 administered in feed at two concentrations - 10 and 1000 μg/kg for six weeks. The estrogenic potential of EE2 was evaluated using an analysis of vitellogenin, gene expression focused on reproductive disorders and gonad histological examination. The alterations in antioxidant and detoxification status were assessed using analyses of enzyme activities and changes in transcriptional levels of selected genes. The most significant changes were observed especially in fish exposed to a high concentration of EE2 (i.e., 1000 μg/kg). Such high concentration caused extensive mortality (25 %) mainly in the second half of the experiment followed by a highly significant decrease in the length and body weight. Similarly, highly significant induction of vitellogenin level and vtg1 mRNA expression (about 43,000-fold compared to the control) as well as a significant downregulation of gonad aromatase expression (cyp19a1a) and histological changes in testicular tissue were confirmed in this group. In the group exposed to environmentally relevant concentration of EE2 (i.e., 10 μg/kg), no significant differences in vitellogenin were observed, although all fish were positive in the detection of vitellogenin compared to control, where only 40 % of individuals were positive. In addition, the high concentration of EE2 resulted in significant alterations in most monitored antioxidant and detoxifying enzymes with the exception of catalase, followed by strongly significant upregulation in mRNA expression of gsr, gpx1a, cat and cyp1a genes. Furthermore, a significant decrease in the glutathione reductase activity was recorded in fish exposed to 10 μg EE2/kg. To our knowledge, this is the first study which reports the effects of subchronic per oral exposure to EE2 in adult triploid zebrafish.

Comparison and quantification of estrogen receptor-mediated responsiveness to endocrine disruptors in bivalves by using complementary model and a novel yeast assay approach

Endocrine disrupting chemicals (EDCs) in estuaries and coastal habitats have been widely detected over the world and caused global concern. Bivalves have been shown to be vulnerable to endocrine disruption. However, estrogen receptors (ERs) sensitivity to steroids and EDCs has long been considered to be restricted to vertebrates. In the present study, a computational simulation docking model was applied to qualitatively predict the binding behavior of two bivalve ERs to estradiol and compared the docking activity with zebra fish ERa. A novel reconstituted yeast system was constructed by using transcriptional activator GAL-4 consists of ER-expressing plasmid and ERE (estrogen responsive element)-containing plasmid. The assays showed that bivalve ER specifically activate transcription in response to tested steroids and EDCs, but the activation ability is weaker compared to zebra fish ERa. The results corroborate the presence of an active ER in bivalve molluscs and provide a promising tool for screening of marine environmental pollutants active in disturbing ERs of bivalves, as well as understanding the underlying mechanism across taxonomic groups and phyla.

Expression and functional analyses for estrogen receptor and estrogen related receptor of Yesso scallop, Patinopecten yessoensis

Estrogen receptors (ERs) were known as estrogen-activated transcription factors and function as major reproduction regulators in vertebrates. The presence of er genes had been reported in Molluscan cephalopods and gastropods. However, they were considered as constitutive activators with unknown biological functions since reporter assays for these ERs did not show a specific response to estrogens. In this study, we tried characterization of ER orthologues from the Yesso scallop, Patinopecten yessoensis, in which estrogens had been proven to be produced in the gonads and involved in the spermatogenesis and vitellogenesis. Identified ER and estrogen related receptor (ERR) of Yesso scallops, designated as py-ER and py-ERR, conserved specific domain structures for a nuclear receptor. Their DNA binding domains showed high similarities to those of vertebrate ER orthologues, while ligand binding domains had low similarities with them. Both the py-er and py-err expression levels decreased in the ovary at the mature stage while py-vitellogenin expression increased in the ovary by quantitative real-time RT-PCR. Also, the py-er and py-err showed higher expressions in the testis than ovary during the developing and mature period, suggesting both genes might function in the spermatogenesis and testis development. The py-ER showed binding affinities to vertebrate estradiol-17β (E₂). However, the intensity was weaker than the vertebrate ER, indicating scallops might exist endogenous estrogens with a different structure. On the other hand, the binding property of py-ERR to E₂ was not confirmed in this assay, speculating that py-ERR was a constitutive activator as other vertebrate ERRs. Further, the py-er was localized in the spermatogonia in the testis and in the auxiliary cells in the ovary by in situ hybridization, indicating its potential roles in promoting spermatogenesis and vitellogenesis. Taken together, the present study demonstrated that py-ER was an authentic E₂ receptor in the Yesso scallop and might have functions for the spermatogonia proliferation and vitellogenesis, while py-ERR was involved in the reproduction by undiscovered manners.

Sex and gametogenesis stage are strong drivers of gene expression in Mytilus edulis exposed to environmentally relevant plasticiser levels and pH 7.7

Plastic pollution and changes in oceanic pH are both pressing environmental issues. Little emphasis, however, has been placed on the influence of sex and gametogenesis stage when investigating the effects of such stressors. Here, we examined histology and molecular biomarkers of blue mussels Mytilus edulis exposed for 7 days to a pH 7.7 scenario (- 0.4 units) in combination with environmentally relevant concentrations (0, 0.5 and 50 µg/L) of the endocrine disrupting plasticiser di-2-ethylhexyl phthalate (DEHP). Through a factorial design, we investigated the gametogenesis cycle and sex-related expression of genes involved in pH homeostasis, stress response and oestrogen receptor-like pathways after the exposure to the two environmental stressors. As expected, we found sex-related differences in the proportion of developing, mature and spawning gonads in histological sections. Male gonads also showed higher levels of the acid-base regulator CA2, but females had a higher expression of stress response-related genes (i.e. sod, cat, hsp70). We found a significant effect of DEHP on stress response-related gene expression that was dependent on the gametogenesis stage, but there was only a trend towards downregulation of CA2 in response to pH 7.7. In addition, differences in gene expression between males and females were most pronounced in experimental conditions containing DEHP and/or acidified pH but never the control, indicating that it is important to consider sex and gametogenesis stage when studying the response of mussels to diverse stressors.

Estrogen pollution of the European aquatic environment: A critical review

Among the plethora of chemicals released into the environment, much attention is paid to endocrine disrupting compounds (EDCs). Natural estrogens, such as estrone (E1), 17β-estradiol (E2), estriol (E3) are excreted by humans as well as animals, and can enter the environment as a result of discharging domestic sewage and animal waste. These compounds can cause deleterious effects such as feminization, infertility and hermaphroditism in organisms that inhabit water bodies. This study provides an overview of the level of estrogen exposures in surface waters, groundwater and river sediments in European countries. The conducted review shows that estrogen concentrations were within the range of 0.1 ng L - 10 ng /L in the majority of the tested environmental samples. However, the authors of the study point out that there are still many unexplored areas and a limited amount of data that mainly concerns Eastern European countries. The study also analysed the factors that influence the increased emissions of estrogens to the environment, which may be helpful for identifying particularly polluted areas.

Gonadal Atresia, Estrogen-Responsive, and Apoptosis-Specific mRNA Expression in Marine Mussels from the East China Coast: A Preliminary Study

This preliminary survey analysed mussel atresia incidences, estrogen-responsive and apoptotic-specific molecular end points, and aqueous and gonadal levels of selected estrogens from the East China coast. Estrogen levels were low (e.g. < LOD-28.36 ng/L, < LOD-3.88 ng/g wet weight of tissue for BPA) relative to worldwide freshwater environments, but high oocyte follicle atresia incidences (up to 26.6%) occurred at selected sites. Expression of estrogen-responsive ER2 was significantly increased in males relative to females at sites with high atresia incidences in females. A second estrogen-responsive gene, V9, was significantly increased at two sites in April in females relative to males; the opposite was true for the remaining two sites. Apoptosis-specific genes (Bcl-2, fas) showed elevated expression in males relative to females at the site with the highest atresia incidence. These results provide coastal estrogen levels and the utility of several estrogen-specific molecular-level markers for marine mussels.

Behavioral, physiological and biochemical responses and differential gene expression in Mytilus galloprovincialis exposed to 17 alpha-ethinylestradiol and sodium lauryl sulfate

Mixture of contaminants often determine biological responses of marine species, making difficult the interpretation of toxicological data. The pharmaceutical 17 alpha-ethinylestradiol (EE2) and the surfactant Sodium Lauryl Sulfate (SLS) commonly co-occur in the marine environment. This study evaluated the effects of EE2 (125.0 ng/L) and SLS (4 mg/L), acting individually and combined, in the mussel Mytilus galloprovincialis. Contaminated mussels closed their valves for longer periods than control ones, especially in the presence of both contaminants, with longer closure periods immediately after spiking compared to values obtained one day after spiking. Nevertheless, males and females increased their metabolism when in the presence of both contaminants (males) and SLS (females), and independently on the treatment males and females were able to activate their antioxidant and biotransformation defences. Although enhancing defences mussels still presented cellular damage and loss of redox balance, especially noticed in the presence of EE2 for males and SLS for females. Histopathological damage was found at mussel's gills in single and mixture exposure, and qPCR analysis revealed a clear estrogen receptor expression with no additive effect due to combined stressors. The results obtained highlight the harmful capacity of both contaminants but further research on this matter is needed, namely considering different climate change scenarios.

How temperature rise will influence the toxic impacts of 17 α-ethinylestradiol in Mytilus galloprovincialis?

Pharmaceutical drugs are Contaminants of Emerging Concern (CECs) and are continuously discharged into the environment. As a result of human and veterinary use, these substances are reaching aquatic coastal systems, with limited information regarding the toxic effects of these compounds towards inhabiting organisms. Among CECs are pharmaceuticals like 17 α-ethinylestradiol (EE2), which is a synthetic hormone with high estrogenic potency. EE2 has been increasingly found in different aquatic systems but few studies addressed its potential toxicity to marine wildlife, in particular to bivalves. Therefore, the aim of the present study was to evaluate the influence of temperature (17 °C-control and 21 °C) on the potential effects of EE2 on the mussel Mytilus galloprovincialis. For this purpose, mussels were exposed to different concentrations of EE2 (5.0; 25.0; 125.0 and 625 ng/L), resembling low to highly polluted sites. Mussels exposed to each concentration were maintained under two temperatures, 17 and 21 °C, which represent actual and predicted warming conditions, respectively. After 28 days, oxidative stress status, metabolism related parameters, neurotoxicity and histopathological alterations were measured. The results obtained clearly showed an interactive effect of increased temperature and EE2, with limited antioxidant and biotransformation capacity when both stressors were acting together, leading to higher cellular damage. The combination of both stressors also enhanced mussels' metabolic capacity and neurotoxic effects. Nevertheless, loss of redox balance was confirmed by the strong decrease of the ratio between reduce glutathione (GSH) and oxidized glutathione (GSSG) in contaminated mussels, regardless the temperature. Histopathological indexes in contaminated mussels were significantly different from the control group, indicating impacts in gills and digestive glands of mussels due to EE2, with higher values observed at 21 °C. Overall, this study demonstrates that of EE2 represents a threat to mussels and predicted warming conditions will enhance the impacts, which in a near future might result in impairments at the population and community levels.

Consequences of combined exposure to thermal stress and the plasticiser DEHP in Mytilus spp. differ by sex

Little is known about the combined effect of environmental factors and contaminants on commercially important marine species, and whether this effect differs by sex. In this study, blue mussels were exposed for seven days to both single and combined stressors (i.e., +3 °C elevated temperature and two environmentally relevant concentrations of the plastic softener DEHP, 0.5 and 50 μg/l) in a factorial design. Males were observed to be more sensitive to high temperature, demonstrated by the significant increase in out-of-season spawning gonads and higher gene expression of the antioxidant catalase and the estrogen receptor genes. On the other hand, while the gametogenesis cycle in females was more resilient than in males, DEHP exposure altered the estrogen-related receptor gene expression. We show that the combined stressors DEHP and increased temperature, in environmentally relevant magnitudes, have different consequences in male and female mussels, with the potential to impact the timing and breeding season success in Mytilus spp.

Long-term exposure of marine mussels to paracetamol: is time a healer or a killer?

Pharmaceuticals pose a major threat to the marine environment, and several studies have recently described their negative effects on marine organisms. Pharmaceutical compounds are constantly being released into aquatic ecosystems, and chronic exposure, even at low concentrations, may have a major impact on marine organisms. The purpose of the present study is to evaluate the biological changes induced by one of the most widely used pharmaceuticals-paracetamol-in the blue mussel Mytilus edulis, after a long-term exposure at environmentally relevant concentrations. We present our data alongside and in comparison with results from a previous short-term exposure, to demonstrate the significance of exposure period on the effects of paracetamol in adult blue mussels. After 24 days of laboratory exposure, seven potential target genes were selected to examine toxicological effects in mussels' gonads and possible disruptive effects on reproductive processes. The results show the modulation of some important reproduction-related genes: estrogen receptor-2 (ER2), vitelline envelope zona pellucida domain-9 (V9), and vitellogenin (VTG). Variations in mRNA expression of four other genes involved in apoptosis (HSP70, CASP8, BCL2, and FAS) are also highlighted. Histopathological alterations caused by paracetamol, together with neutral red retention time response in mussels' hemocytes, are presented herein. Overall, this study highlights the exacerbated effects of low concentration of paracetamol after chronic exposure, similar to the damage induced by higher concentrations in a short exposure scenario, thus emphasizing the importance of length of exposure period when studying the effects of this substance. Additionally, this study also discusses the potential of paracetamol to inflict several major changes in the reproductive system of mussels and thus possibly affect the survival of populations.

Impact of Estrogens Present in Environment on Health and Welfare of Animals

Simple Summary

Estrogens are a group of steroid hormones that recently have gained even more attention in the eyes of scientists. There is an ongoing discussion in the scientific community about their relevance as environmental contaminants and the danger they pose to animal health and welfare. In available literature we can find many examples of their negative effects and mechanisms that are involved with such phenomena.

Abstract

Nowadays, there is a growing interest in environmental pollution; however, knowledge about this aspect is growing at an insufficient pace. There are many potential sources of environmental contamination, including sex hormones—especially estrogens. The analyzed literature shows that estrone (E1), estradiol (E2), estriol (E3), and synthetic ethinyloestradiol (EE2) are the most significant in terms of environmental impact. Potential sources of contamination are, among others, livestock farms, slaughterhouses, and large urban agglomerations. Estrogens occurring in the environment can negatively affect the organisms, such as animals, through phenomena such as feminization, dysregulation of natural processes related to reproduction, lowering the physiological condition of the organisms, disturbances in the regulation of both proapoptotic and anti-apoptotic processes, and even the occurrence of neoplastic processes thus drastically decreasing animal welfare. Unfortunately, the amount of research conducted on the negative consequences of their impact on animal organisms is many times smaller than that of humans, despite the great richness and diversity of the fauna. Therefore, there is a need for further research to help fill the gaps in our knowledge.

Vitellogenin gene expression in marine mussels exposed to ethinylestradiol: No induction at the transcriptional level

Vitellogenin (Vtg), a large multidomain protein precursor of egg-yolk proteins, is used as an endocrine disruption biomarker in fish, and in the last decades, its use has been extended to invertebrates like mollusks. However, it remains unclear whether invertebrate endocrine system produces Vtg in response to estrogens, like it occurs in oviparous vertebrates. In a previous study, no evidence of induction of Vtg expression at protein level was found in gonads of the marine mussel Mytilus galloprovincialis after exposure to the estrogenic chemical 17α-ethinylestradiol (EE2). In the present follow-up study, it was investigated whether there is any effect of EE2 on Vtg abundance at transcriptional level in M. galloprovincialis gonads. To this aim, RT-qPCR analysis targeting three different domains of Vtg transcript was performed on gonads of mussels that were exposed either 4 or 24 days to 100 ng/L EE2. In addition, several reference genes were analysed and a selection of these for potential use in further RT-qPCR analyses on mussel male and female gonads is provided. Results showed higher expression in females than in males for the three analysed Vtg domains, and no evidence of Vtg mRNA induction due to EE2 either in females or males. The present results, together with those obtained from previous analysis at protein level, support that Vtg is not an adequate biomarker for xenoestrogenicity in marine mussels. Additionally, nucleotide sequences of Vtg transcripts of three closely-related species from Mytilus edulis complex (M. galloprovincialis, M. edulis and M. trossulus) are provided and compared with Vtg sequences from other mollusk species to assess the level of conservation and evolutionary relationships among species.

Effects of a mixture of glyphosate, 17α-ethynylestradiol and amyl salicylate on cellular and biochemical parameters of the mussel Mytilus galloprovincialis

In this study the effects of a mixture of glyphosate (herbicide), 17a-ethinylestradiol (synthetic estrogen) and amyl salicylate (fragrance) to the mussel Mytilus galloprovincialis were evaluated. Mussels were exposed for 7 days to two realistic concentrations of the mixture (10 and 100 ng/L) and the effects on total haemocyte counts, haemocyte diameter and volume, haemocyte proliferation, haemolymph lactate dehydrogenase activity and haemocyte lysate lysozyme activity were measured. In addition, superoxide dismutase, catalase, acetylcholinesterase, glutathione-S-transferase and glutathione reductase activities were measured in gills and digestive gland. The survival-in-air test was also performed. Results demonstrated that the mixture affected both cellular and biochemical biomarkers, but not tolerance to aerial exposure of M. galloprovincialis. The negative effects recorded in this study suggested that more efforts should be done to assess the ecotoxicological risks posed by contaminant mixture to aquatic invertebrates.

Effects of Phenanthrene Stress on Gonads and Vitellogenin of Loach (Misgurnus anguillicaudatus)

Phenanthrene (PHE) as a tricyclic polycyclic aromatic hydrocarbon is one of the common pollutants in water and sediments, which can cause reproductive toxicity to aquatic organisms. In this study, enzyme-linked immunosorbent assay (ELISA) was used to detect the vitellogenin (VTG) of loach, and then to explore the estrogenic toxicity effect of PHE on loach. The results were as follows: (1) with the increase of PHE concentrations and the extension of exposure time, the gonadosomatic index (GSI) of males decreased significantly, while it increased in female loaches. In addition, males had more obvious changes than females and were more sensitive to PHE. (2) The increase of VTG contents in serum of males were stronger than that in females. Those results reveal that PHE has estrogenic effect, which can affect the generation of VTG, thus causing damage to the gonad development of loach.

Benzo[a]pyrene exposure disrupts steroidogenesis and impairs spermatogenesis in diverse reproductive stages of male scallop (Chlamys farreri)

Benzo[a]pyrene (BaP), a model compound of polycyclic aromatic hydrocarbon known to impair reproductive functions of vertebrates, while the data is scarce in marine invertebrates. To investigate the toxic effects of BaP on invertebrates reproduction, we exposed male scallop (Chlamys farreri) to BaP (0, 0.38 and 3.8 μg/L) throughout three stages of reproductive cycle (early gametogenesis stage, late gametogenesis stage and ripe stage). The results demonstrated that BaP decreased the gonadosomatic index and mature sperms counts in a dose-dependent manner. Significant changes in sex hormones contents and increased 17β-estradiol/testosterone ratio suggested that BaP produced the estrogenic endocrine effects in male scallops. In support of this view, we confirmed that BaP significantly altered transcripts of genes along the upstream PKA and PKC mediated signaling pathway like fshr, lhcgr, adcy, PKA, PKC, PLC and NR5A2. Subsequently, the expressions of genes encoding downstream steroidogenic enzymes (e.g., 3β-HSD, CYP17 and 17β-HSD) were impacted, which corresponded well with hormonal alterations. In addition, BaP suppressed transcriptions of spermatogenesis-related genes, including ccnd2, SCP3, NRF1 and AQP9. Due to different functional demands, these transcript profiles involved in spermatogenesis exhibited a stage-specific expression pattern. Furthermore, histopathological analysis determined that BaP significantly inhibited testicular development and maturation in male scallops. Overall, the present findings indicated that, playing as an estrogenic-like chemical, BaP could disrupt the steroidogenesis pathway, impair spermatogenesis and caused histological damages, thereby inducing reproductive toxicities with dose- and stage-specific effects in male scallops. And the adverse outcomes might threaten the stability of bivalve populations and destroy the function of marine ecosystems in the long term.

Glass reinforced plastic (GRP) a new emerging contaminant - First evidence of GRP impact on aquatic organisms

Plastics and synthetic materials are polluting the world's oceans. In this study we exposed juvenile mussels, Mytilus edulis, to glass reinforced plastic (GRP) dust, under laboratory conditions. The study ran for a period of 7 days, to test for the morphological and potential physiological impacts of GRP. Infrared spectroscopy has revealed that the GRP resin material is poly diallyl phthalate. In mussels, particulate glass and plastics were detected in the digestive tubules and gills, with a suite of inflammatory features observed in all examined organs. In parallel, we observed the effect of powdered GRP on swimming behaviour and survival of water fleas, Daphnia magna. Polymer particles and fibreglass adhered to the filament hairs on appendages, including the caudal spine, in exposed organisms. Most importantly, swimming impairment and sinking of the animals were recorded shortly after exposure. The potential implications for severe localized impact of GRP on aquatic environment are discussed.

A critical evaluation of some of the recent so-called 'evidence' for the involvement of vertebrate-type sex steroids in the reproduction of mollusks

Many studies on the control of reproduction in mollusks have focused on hormones (and proteins associated with the production and signaling of those hormones) which were originally discovered in humans, in the belief that if they are also present in mollusks, they must have the same role. However, although human sex steroids can be found in mollusks, they are so readily absorbed that their presence is not necessarily evidence of endogenous synthesis. A homolog of the vertebrate nuclear estrogen receptor has been found in mollusks, but it does not bind to estrogens or indeed to any steroid at all. Antibodies against human aromatase show positive immunostaining in mollusks, yet the aromatase gene has not been found in the genome of any invertebrates (let alone mollusks). This review will deal with these and other examples of contradictory evidence for a role of human hormones in invertebrate reproduction.

Effects of short-term exposure of paracetamol in the gonads of blue mussels Mytilus edulis

A growing body of literature suggests that pharmaceutical contamination poses an increasing risk to marine ecosystems. Paracetamol or acetaminophen is the most widely used medicine in the world and has recently been detected in seawater. Here, we present the results of 7 days' exposure of blue mussel adults to 40 ng/L, 250 ng/L and 100 μg/L of paracetamol. Histopathology shows that haemocytic infiltration is the most observed condition in the exposed mussels. The mRNA expression of VTG, V9, ER2, HSP70, CASP8, BCL2 and FAS in mussel gonads present different patterns of downregulation. VTG and CASP8 mRNA expression show downregulation in all exposed mussels, irrespective of sex. The V9, HSP70, BCL2 and FAS transcripts follow a concentration-dependent variation in gene expression and may therefore be considered good biomarker candidates. ER2 mRNA expression shows a downregulated trend, with a clearer dose-response relationship in males. In conclusion, this study suggests that paracetamol has the potential to alter the expression of several genes related to processes occurring in the reproductive system and may therefore impair reproduction in blue mussels.

Application of Biomarker Tools Using Bivalve Models Toward the Development of Adverse Outcome Pathways for Contaminants of Emerging Concern

As contaminant exposures in aquatic ecosystems continue to increase, the need for streamlining research efforts in environmental toxicology using predictive frameworks also grows. One such framework is the adverse outcome pathway (AOP). An AOP framework organizes and utilizes toxicological information to connect measurable molecular endpoints to an adverse outcome of regulatory relevance via a series of events at different levels of biological organization. Molecular endpoints or biomarkers are essential to develop AOPs and are valuable early warning signs of the toxicity of pollutants, including contaminants of emerging concern. Ecological risk-assessment approaches using tools such as biomarkers and AOPs benefit from identification of molecular targets conserved across species. Bivalve models are useful in such approaches and integral to our understanding of ecological and human health risks associated with contaminant exposures. We discuss the value of using biomarker approaches in bivalve models to meet the demands of twenty-first-century toxicology. Environ Toxicol Chem 2020;39:1472-1484. © 2020 SETAC.

Molecular and biochemical responses of vitellogenin in the mussel Mytilus galloprovincialis exposed to the glyphosate-based herbicide Roundup® Power 2.0

Glyphosate-based herbicides (GBHs) occur in aquatic ecosystems at concentrations of hundreds of micrograms per liter. As formulation adjuvants are suspected to be endocrine-disrupting chemicals, we assessed the effects of the recent GBH formulation Roundup® Power 2.0 on vitellogenin (VTG) in Mytilus galloprovincialis. Mussels were exposed for 7, 14, and 21 days to two concentrations of the commercial formulation, corresponding to 100 and 1000 μg/L of glyphosate. The expression of the vtg gene in gonads of females and males, as well as the levels of alkali labile phosphates (ALP) in gonads and non-gonadal tissues from the two sexes were measured. No significant alterations were observed in vtg expression values during the exposure. Conversely, a significant reduction in gonadal ALP levels was observed in females exposed for 21 days and in males exposed for 7 days. In addition, ALP levels increased significantly in gonads from males exposed for 21 days to the two concentrations of Roundup®. As for non-gonadal tissues, ALP levels did not change significantly in females, whereas ALP levels decreased significantly in non-gonadal tissues from males exposed for 21 days to the lowest concentration tested. An overall statistically significant difference in ALP levels was found between females and males. Although preliminary, our study suggests that GBH can affect reproduction-related parameters in mussels.

No evidence that vitellogenin protein expression is induced in marine mussels after exposure to an estrogenic chemical

A wide variety of endocrine disrupting chemicals reach the marine environment and can cause harmful effects in different marine organisms. Vitellogenin (Vtg), the egg-yolk precursor, is a commonly used endocrine disruption biomarker in fish and more recently in marine invertebrates under the assumption of high expected similarities in the endocrine system of vertebrates and invertebrates. However, this assumption has been recently questioned. The results from previous studies focused on bivalve molluscs showed that Vtg induction could be misleading because of the use of either non-robust or indirect techniques to measure Vtg. In this study, mussels (Mytilus galloprovincialis) were exposed to either 10 or 100 ng/L of the synthetic hormone 17α-ethinylestradiol (EE2) at different exposure times (4 and 24 days) and under different feeding regimes (representing different energy balances), and Vtg levels in both male and female mussel gonads were quantified by label free shotgun LC-MS/MS proteomic analysis. Vtg protein was not detected in male gonads. In female gonads, Vtg levels were not significantly affected by EE2 at any exposure time or EE2 concentration tested, whereas a significant correlation was found between the degree of maturation of the gonad and Vtg levels in females. Results obtained in the present study critically question the use of Vtg as a biomarker of endocrine disruption in marine mussels, and show that the degree of maturation of the gonad can be an important confounding factor in the attempts to evaluate estrogenic effects through Vtg measurement in mussel gonads.

Concentrations levels and effects of 17alpha-Ethinylestradiol in freshwater and marine waters and bivalves: A review

Pharmaceutical drugs are contaminants of emerging concern and are amongst the most frequent in the aquatic environment. Even though a vast literature indicate that pharmaceuticals exert negative impacts towards aquatic organisms, mainly in vertebrates, there is still limited information regarding the effects of these drugs in freshwater and marine bivalves. Marine bivalves have a high ecological and socio-economic value and are considered good bioindicator species in ecotoxicology and risk assessment programs. Furthermore, another lacking point on these studies is the absence of bioconcentration data, with no clear relationship between the concentration of drugs on tissue and the biological effects. 17alpha-ethinylestradiol (EE2) is a synthetic hormone with high estrogenic potency that was added to the Watch List adopted by the European Commission stating the priority substances to be monitored. Thus, this review summarizes the current knowledge on the concentration levels and effects of EE2 on freshwater and marine bivalves. The inclusion in the Watch List, the presence in freshwater and marine systems, and the impact exerted on aquatic biota, even at trace concentrations, justify the review devoted to this pharmaceutical drug. Globally the available studies found that EE2 induces individual and sub-individual (e.g. tissue, cellular, biochemical and molecular levels of biological organization) impacts in bivalves. Essentially, this estrogenic compound, even in trace concentrations, was found to have accumulated in wild and laboratory exposed bivalves. The most common effects reported were changes on the reproductive function and energy metabolism. The studies used in this review support keeping the EE2 on the Watch List and highlight the need to increase the number of monitorization studies since clear negative effects were exerted on bivalves by this drug.

Metabolomic Investigations of the Temporal Effects of Exposure to Pharmaceuticals and Personal Care Products and Their Mixture in the Eastern Oyster (Crassostrea virginica)

The eastern oyster (Crassostrea virginica) supports a large aquaculture industry and is a keystone species along the Atlantic seaboard. Native oysters are routinely exposed to a complex mixture of contaminants that increasingly includes pharmaceuticals and personal care products (PPCPs). Unfortunately, the biological effects of chemical mixtures on oysters are poorly understood. Untargeted gas chromatography-mass spectrometry metabolomics was utilized to quantify the response of oysters exposed to fluoxetine, N,N-diethyl-meta-toluamide, 17α-ethynylestradiol, diphenhydramine, and their mixture. Oysters were exposed to 1 µg/L of each chemical or mixture for 10 d, followed by an 8-d depuration period. Adductor muscle (n = 14/treatment) was sampled at days 0, 1, 5, 10, and 18. Trajectory analysis illustrated that metabolic effects and class separation of the treatments varied at each time point and that, overall, the oysters were only able to partially recover from these exposures post-depuration. Altered metabolites were associated with cellular energetics (i.e., Krebs cycle intermediates), as well as amino acid metabolism and fatty acids. Exposure to these PPCPs also affected metabolic pathways associated with anaerobic metabolism, osmotic stress, and oxidative stress, in addition to the physiological effects of each chemical's postulated mechanism of action. Following depuration, fewer metabolites were altered, but none of the treatments returned them to their initial control values, indicating that metabolic disruptions were long-lasting. Interestingly, the mixture did not directly cluster with individual treatments in the scores plot from partial least squares discriminant analysis, and many of its affected metabolic pathways were not well predicted from the individual treatments. The present study highlights the utility of untargeted metabolomics in developing exposure biomarkers for compounds with different modes of action in bivalves. Environ Toxicol Chem 2020;39:419-436. © 2019 SETAC.

Mytilidae as model organisms in the marine ecotoxicology of pharmaceuticals - A review

Growing production and consumption of pharmaceuticals is a global problem. Due to insufficient data on the concentration and distribution of pharmaceuticals in the marine environment, there are no appropriate legal regulations concerning their emission. In order to understand all aspects of the fate of pharmaceuticals in the marine environment and their effect on marine biota, it is necessary to find the most appropriate model organism for this purpose. This paper presents an overview of the ecotoxicological studies of pharmaceuticals, regarding the assessment of Mytilidae as suitable organisms for biomonitoring programs and toxicity tests. The use of mussels in the monitoring of pharmaceuticals allows the observation of changes in the concentration and distribution of these compounds. This in turn gives valuable information on the amount of pharmaceutical pollutants released into the environment in different areas. In this context, information necessary for the assessment of risks related to pharmaceuticals in the marine environment are provided based on what effective management procedures can be developed. However, the accumulation capacity of individual Mytilidae species, the bioavailability of pharmaceuticals and their biological effects should be further scrutinized.

Estrogenic compounds as exogenous modulators of physiological functions in molluscs: Signaling pathways and biological responses

Molluscs have been widely utilized to evaluate the effects of estrogenic compounds, one of the most widespread classes of Endocrine Disrupting Chemicals-EDCs. However, knowledge on steroid signaling and metabolism in molluscs has considerably increased in the last decade: from these studies, a considerable debate emerged on the role of 'natural' steroids in physiology, in particular in reproduction, of this invertebrate group. In this work, available information on the effects and mechanisms of action of estrogens in molluscs will be reviewed, with particular emphasis on bivalves that, widespread in aquatic ecosystems, are most likely affected by exposure to estrogenic EDCs. Recent advances in steroid uptake and metabolism, and estrogen receptors-ERs in molluscs, as well as in estrogen signaling in vertebrates, will be considered. The results so far obtained with 17β-estradiol and different estrogenic compounds in the model bivalve Mytilus spp., demonstrate specific effects on immune function, development and metabolism. Transcriptomic data reveal non genomic estrogen signaling pathways in mussel tissues that are supported by new observations at the cellular level. In vitro and in vivo data show, through independent lines of evidence, that estrogens act through non-genomic signaling pathways in bivalves. In this light, regardless of whether molluscs synthesize estrogens de novo or not, and despite their ERs are not directly activated by ligand binding, estrogens can interact with multiple signaling components, leading to modulation of different physiological functions. Increasing knowledge in endocrine physiology of molluscs will provide a framework for a better evaluation and interpretation of data on the impact of estrogenic EDCs in this invertebrate group.

Seasonal fluctuations of metal bioaccumulation and reproductive health of local oyster populations in a large contaminated estuary

Despite of much evidence of trace metal pollution in the Pearl River Estuary (PRE), the seasonal dynamics of metal bioavailability as well as the potential impacts of metal pollution on the local marine organisms in this estuary is poorly understood. In the present study, the accumulation of trace metals and reproductive states of three populations of oyster Crassostrea hongkongensis, a keystone bivalve species in the PRE, were for the first time investigated throughout a one-year field study. Significant temporal fluctuations of metal accumulation were observed in the somatic tissues of oysters, suggesting seasonal variations of metal bioavailability in the PRE. A major feature of the seasonal variations was the increased levels of metal bioaccumulation in the summer season for the contaminated sites nearby the major river inlets. High riverine inputs accompanied by relatively lower salinity in summer may greatly contribute to such variations. Furthermore, oyster populations from two contaminated sites had a poor reproductive condition in comparison with the reference oyster population, as reflected by a significant decrease of gonad-somatic index (GSI) and gonad cover area (GCA), as well as an obvious change of sex ratios. Gonadal metal accumulation of Cu, Zn, Ni, Co and Pb in the contaminated oysters was much higher than that in the relatively uncontaminated oysters. Especially, the concentrations of these metals in the gonad during the breeding season had significantly negative correlations with the gonad condition indexes (GSI and GCA). Our results suggested strong seasonal fluctuations of bioavailability of trace metals in this highly contaminated estuary as well as an adverse effect of metal pollution on the reproduction of local oyster populations.

The expression of estrogen receptors during the Mytilus galloprovincialis ovarian cycle

The aim of this paper is to assess, by real-time polymerase chain reaction and in situ hybridization, the expression of estrogen receptors ER1 and ER2 during the ovarian cycle of Mytilus galloprovincialis. By considering four phases of the reproductive cycle, that is stasis and previtellogenic stage (Stage 0), early vitellogenesis (Stage I), vitellogenesis (Stage II), full-grown oocyte (Stage III), our investigation demonstrates that the two receptors are differently expressed during the phases investigated of the ovarian cycle: ER1 reaches the highest level at Stage III, whereas ER2 reaches the highest level at Stage II, with ER2 always present at higher levels than ER1. The stage-dependent receptor expression was recorded within oocytes, follicle cells, and adipogranular cells. No ER1 and ER2 messenger RNAs (mRNAs) were found within vesicular cells. It is to be noted that the ER1 and ER2 expression within the growing oocytes, the follicular, and adipogranular cells overlaps with that of the mRNA for vitellogenin in the same cells, strongly suggesting that in Mytilus, as in vertebrates studied so far, the vitellogenin expression is under the control of estrogens.

Aromatisation of steroids in the bivalve Mytilus trossulus

In this study, we demonstrated the presence of the enzymatic complex able to perform aromatization (estrogen synthesis) in both, the microsomal and mitochondrial fractions of gills and gonads from Mytilus trossulus. Based on in vitro experiments, we highlighted the importance of temperature as the limiting factor of aromatisation efficiency (AE) in mussels. After testing range of temperatures (4–23 °C), the highest AE was found during incubation at 8 °C and pH 7.6 (41.66 pmol/h/mg protein in gills and 58.37 pmol/h/mg protein in gonads). The results were confirmed during field studies where the most efficient aromatisation occurred in bivalves collected in spring while the least effective in those collected in winter. During in vitro studies, AE turned out to be more intensive in female gonads than in male gonads. The process was also more intensive in mitochondrial fraction than in microsomal one (62.97 pmol/h/mg protein in male gills and 73.94 pmol/h/mg protein in female gonads). Enzymatic complex (aromatase-like enzyme) catalysing aromatisation in mussels was found to be insensitive to inhibitory effect of selective inhibitors of mammalian aromatase such as letrozole and anastrazole, suggesting its different structure from vertebrate aromatase. Further in vivo studies using ¹³C-labeled steroids at 8 °C temperature window confirmed that bivalves are able to uptake testosterone and androstenedione from the ambient environment and metabolise them to estrone and 17β-estradiol thus confirming endogenous estrogen’ synthesis.

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.

The concentration of dissolved organic matter impacts the metabolic response in Daphnia magna exposed to 17α-ethynylestradiol and perfluorooctane sulfonate

The pharmaceutical 17α-ethynylestradiol (EE2) and the industrial chemical perfluorooctane sulfonate (PFOS) are organic contaminants frequently detected in freshwater environments. It is hypothesized that hydrophobic organic contaminants can sorb to dissolved organic matter (DOM) and this may reduce the toxicity of these contaminants by reducing the contaminants' bioavailability. To investigate this hypothesis, ¹H nuclear magnetic resonance (NMR)-based metabolomics was used to determine how the metabolome of Daphnia magna changes when a range of DOM concentrations are added during EE2 and PFOS exposure experiments. D. magna were exposed for 48 h to sub-lethal concentrations of 1 mg/L EE2 or 30 mg/L PFOS in the presence of 0, 1, 2, 3 and 4 mg dissolved organic carbon (DOC)/L. EE2 exposure resulted in increased amino acids and decreased glucose in D. magna. All DOM concentrations were able to lessen these metabolite disturbances from EE2 exposure, likely due to reductions in the bioavailability of EE2 through interactions with DOM. Exposure to PFOS resulted in decreased amino acids, and the presence of 1 mg DOC/L did not alter this metabolic response. However, PFOS exposure with the higher DOM concentrations resulted in a different pattern of metabolite changes which may be due to combined impacts of PFOS and DOM on the metabolome or due to an increase in PFOS bioavailability and uptake in D. magna. These results suggest that the concentration of DOM influences the sensitive biochemical changes in organisms that occur during acute sub-lethal exposure to organic contaminants.

Freshwater snail Parafossarulus striatulus estrogen receptor: Characteristics and expression profiles under lab and field exposure

The modes of action by which putative endocrine disrupting chemicals (EDCs) elicit toxicity in mollusks remains unclear due to our limited understanding of the molluscan endocrine system. We identified and partially characterised the estrogen receptor (ER) of the mollusk Parafossarulus striatulus. The full-length cDNA of the ER of P. striatulus (psER) was isolated and found to have an ORF of 1386 bp which corresponded to 461 amino acids. Phylogenetic analysis revealed that psER is an orthologue of ER of other mollusks. Moreover, the DNA-binding domain, ligand-binding domain, P-box, D-box, and AF2 domain were also identified in psER. Exposure of females and males to 17β-estradiol (E2, 100 ng/L) for 24 h and 72 h did not alter psER transcription, but exposure to 17α-methyltestosterone (MT, 100 μg/L) for 72 h significantly decreased ER transcription in females only (p < 0.05). psER transcription was surveyed in males and females seeded in different regions in Taihu Lake, China. psER transcription were elevated among females and males maintained at site ML. This elevation was statistically significant (p < 0.05) among male snails as compared to snails held at the more pristine site of SZ. This was different to the results from lab, implying that some unknown chemicals or other environmental factors in field could affect psER transcription level in snails. Furthermore, females and males held at site ML also exhibited a significant elevation in vitellogenin transcription as compared to snails held at site SZ, suggesting that vitellogenin production may be directly regulated by psER or co-regulated with psER in this species.

Mating under the influence: male Siamese fighting fish prefer EE2-exposed females

Countless pharmaceuticals and endocrine disrupting chemicals (EDCs) exist on the market with more added each day. Many of these compounds are not removed during the wastewater treatment process and enter bodies of water in their active form. EDCs are known to have physiological and behavioral effects in exposed organisms. Exposure to the synthetic estrogen 17α-ethinylestradiol (EE2), a common EDC found in birth control pills, has been found to lead to population collapse after only a few generations in some fish species. Mechanisms identified as potential driving forces for collapse include feminization of males and altered fecundity in both sexes. However, an additional way in which EE2 could lead to population collapse is by altering courtship behavior, which could then change mating preferences and decrease mating opportunities. The current study had the following objectives: determine if exposing female Siamese fighting fish, Betta splendens, to EE2 changes mate choice in males; assess if the dose and duration of female exposure matters; and examine if exposing males to EE2 influences their mating preferences. Both unexposed and exposed males were presented with pairs of females that differed in EE2 dose and exposure duration. The results indicate that males were more responsive to EE2-exposed females than unexposed females, with males being most responsive to females exposed to the low versus high dose. Furthermore, exposed males responded less overall than unexposed males. If EE2 concentration increases in the environment, the likelihood of successful mating could decrease and, therefore, potentially lead to adverse population impacts.

Transcriptomic and Network Analyses Reveal Mechanistic-Based Biomarkers of Endocrine Disruption in the Marine Mussel, Mytilus edulis

Transcriptomics, high-throughput assays, and adverse outcome pathways (AOP) are promising approaches applied to toxicity monitoring in the 21st century, but development of these methods is challenging for nonmodel organisms and emerging contaminants. For example, Endocrine Disrupting Compounds (EDCs) may cause reproductive impairments and feminization of male bivalves; however, the mechanism linked to this adverse outcome is unknown. To develop mechanism-based biomarkers that may be linked through an AOP, we exposed Mytilus edulis to 17-alpha-ethinylestradiol (5 and 50 ng/L) and 4-nonylphenol (1 and 100 μg/L) for 32 and 39 days. When mussels were exposed to these EDCs, we found elevated female specific transcripts and significant female-skewed sex ratios using a RT-qPCR assay. We performed gene expression analysis on digestive gland tissue using an M. edulis microarray and through network and targeted analyses identified the nongenomic estrogen signaling pathway and steroidogenesis pathway as the likely mechanisms of action for a putative AOP. We also identified several homologues to genes within the vertebrate steroidogenesis pathway including the cholesterol side chain cleavage complex. From this AOP, we designed the Coastal Biosensor for Endocrine Disruption (C-BED) assay which was confirmed in the laboratory and tested in the field.

Bisphenol A (BPA) modulates the expression of endocrine and stress response genes in the freshwater snail Physa acuta

Bisphenol A (BPA), a known endocrine disrupting chemical (EDC) that can mimic the action of oestrogens by interacting with hormone receptors, is potentially able to influence reproductive functions in vertebrates and invertebrates. The freshwater pulmonate Physa acuta is a sensitive organism to xenobiotics appropriate for aquatic toxicity testing in environmental studies. This study was conducted to explore the effects of BPA on the Gastropoda endocrine system. The effects following a range of exposure times (5-96h) to BPA in P. acuta were evaluated at the molecular level by analysing changes in the transcriptional activity of the endocrine-related genes oestrogen receptor (ER), oestrogen-related receptor (ERR), and retinoid X receptor (RXR), as well as in genes involved in the stress response, such as hsp70 and hsp90. Real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis showed that BPA induced a significant increase in the mRNA levels of ER, ERR, and RXR, suggesting that these receptors could be involved in similar pathways or regulation events in the endocrine disruptor activity of this chemical at the molecular level in Gastropoda. Additionally, the hsp70 expression was upregulated after 5 and 72h of BPA exposures, but hsp90 was only upregulated after 5h of BPA exposure. Finally, we assessed the glutathione-S-transferase (GST) activity after BPA treatment and found that it was affected after 48h. In conclusion, these data provide, for the first time, evidences of molecular effects produced by BPA in the endocrine system of Gastropoda, supporting the potential of ER, ERR and RXR as biomarkers to analyse putative EDCs in ecotoxicological studies. Moreover, our results suggest that P. acuta is an appropriate sentinel organism to evaluate the effect of EDCs in the freshwater environment.

Contamination and risk implications of endocrine disrupting chemicals along the coastline of China: A systematic study using mussels and semipermeable membrane devices

A systematic study has been carried out to assess the contamination of endocrine disrupting chemicals (EDCs) in five highly urbanized coastal cities spanning from temperate to subtropical environments along the coastline of China. In each of these cities, species of native mussels (Mytilus galloprovincialis, M. coruscus or Perna viridis) were deployed alongside with semipermeable membrane devices (SPMDs) for one month at a reference site and a polluted site. The level of 4-nonylphenol (4-NP), bisphenol A (BPA), 17β-estradiol (E2) and 17α-ethynylestradiol (EE2) in SPMDs and transplanted mussels were determined and compared. The concentration of EDCs in mussels from polluted sites of Qingdao and Shenzhen ranged from 99.4±9.40 to 326.1±3.16ng/g dry wt. for 4-NP, Dalian and Shanghai from 170.3±4.00 to 437.2±36.8ng/g dry wt. for BPA, Dalian and Shenzhen from 82.9±3.03 to 315.6±6.50ng/g dry wt. for E2, and Shenzhen and Shanghai from 124.5±3.25 to 204.5±9.26ng/g dry wt. for EE2, respectively. These results demonstrate that concentrations of EDCs in mussels along the coastline of China are substantially higher than levels reported in mussels and seafood elsewhere. Despite high levels of EDCs and per capita seafood consumption in China, analysis indicated that 4-NP and BPA intake from mussels at polluted sites per se are still below the Tolerable Daily Intake (TDI). In contrast, the daily intake of E2 and EE2 (6.5 and 5.5μg/person/day, respectively) from mussel consumption exceeded the Acceptable Daily Intake (ADI) established by the WHO, USA and Australia by large margins, suggesting significant public health risks. A strong correlation was found between EDC concentrations in SPMDs and transplanted mussels, and the advantages of using mussels and SPMDs for monitoring EDCs in the aquatic environment are discussed.

Changes in steroid profiles of the blue mussel Mytilus trossulus as a function of season, stage of gametogenesis, sex, tissue and mussel bed depth

This paper describes changes in the content of free steroid hormones e.g. testosterone (T), estradiol-17β (E2), estrone (E1) and estriol (E3) of Mytilus trossulus from the southern Baltic Sea as a function of season, stage of gametogenesis, sex, tissue (gonadal and somatic) and depth. The highest levels of T, E2, E1 and E3 were found in mussels sampled in spring and summer while the lowest levels were found in winter. This pattern was stable and was seen in both sexes and tissues in mussels from both mussel beds. The spring and summer peaks in steroid levels (SL) coincided with advanced levels of gametogenesis (the highest gonadal index, GI) of our model species. But, the lowest GI (autumn) and the lowest steroids content (winter) did not overlap. Instead, water temperature increase was followed by increase of SL and vice versa. This suggests that steroids may not be actively involved in the early stages of gamete development and does not preclude them from potentially being involved as endogenous modulators in the final stages of reproduction (e.g. spawning). Hence, observed fluctuations in SL in our model species are unlikely to be caused by reproductive cycle but are rather of unknown nature, likely linked with environmental conditions. Sex-related differences in steroid content included estrogen domination in females and androgen domination in males. A trend towards higher level of steroids in gills than in gonads was found, supporting the hypothesis about an exogenous origin of steroids in bivalves. However, based on the present results, we cannot exclude the possibility that these steroids have both an endogenous and exogenous origin.

High estradiol exposure disrupts the reproductive cycle of the clam Ruditapes decussatus in a sex-specific way

Bivalve species may be susceptible to environmental estrogenic compounds including estradiol (E₂). However, they are able to biotransform the hormone quite readily and inactivate its estrogenic action. To study the long-term effects of elevated free E₂ tissue levels, we transiently exceeded the biotransformation capacity of the clam Ruditapes decussatus by exposing them with high E₂ concentrations (400 ng/L) and subsequently study the consequences on gametogenesis during the following reproductive cycle. Exposure to 400 ngE₂/L led to a significant increase in tissue free E₂ levels, which reached 10-50 ng E₂Eq/gww. No deleterious effect on gonado-somatic index (GSI), condition index (CI), or ability to respond to the stress on stress test could be detected after a month of exposure, suggesting the absence of negative effects on the clam's health. However, a marked increase in gametogenesis could be observed in both sexes during the exposure. Subsequent transplantation of the clams in the field allowed the normal development of the male clams and maturation of the gonads without any detrimental effect observed after 4 months. In contrast, in early July, all female clams formerly exposed to E₂ showed lower health status, and only ovaries with atretic oocytes while all control and indigenous females were normal and mature. These results show a sex-specific effect of high E₂ exposure and suggest either a direct or indirect role for E₂ in R. decussatus' reproduction.

Modeling the fate and transport of 17β-estradiol in the South River watershed in Virginia

Hormones excreted by livestock metabolisms often enter surface water through feces and urine and can potentially cause adverse impacts to aquatic biota. This study involved a modeling analysis of 17β-estradiol (E2), a prevalent estrogen, in the South River watershed located in Augusta County, Virginia from 2013 to 2015. Cattle manure, poultry litter, biosolids, septic systems, and wastewater treatment plants (WWTPs) were considered as sources of E2 in this study. The EPA's BASINS modeling framework was configured to track the fate and transport of E2. The first-order kinetics and the wash-off model were adopted to characterize the attenuation and the transport of E2. The modeling results indicated that the flow rate was a major input affecting the simulated E2 levels in the water. During storm events, E2 on the land surface was transported into the rivers by the surface runoff and the E2 released into streams was diluted by the high water flow. Variations of the simulated E2 concentrations in the South River depended on the relative magnitudes of the loads from point and nonpoint sources. Modeling results showed that E2 levels in the South River were below the lowest observable effect level (LOEL) for fish. However, the practices of storing manure before land application and fencing off rivers to keep cattle out of the water are encouraged to prevent the potential for high E2 levels in streams receiving feedlot runoff.

Contaminants of emerging concern in tributaries to the Laurentian Great Lakes: I. Patterns of occurrence

Human activities introduce a variety of chemicals to the Laurentian Great Lakes including pesticides, pharmaceuticals, flame retardants, plasticizers, and solvents (collectively referred to as contaminants of emerging concern or CECs) potentially threatening the vitality of these valuable ecosystems. We conducted a basin-wide study to identify the presence of CECs and other chemicals of interest in 12 U.S. tributaries to the Laurentian Great Lakes during 2013 and 2014. A total of 292 surface-water and 80 sediment samples were collected and analyzed for approximately 200 chemicals. A total of 32 and 28 chemicals were detected in at least 30% of water and sediment samples, respectively. Concentrations ranged from 0.0284 (indole) to 72.2 (cholesterol) μg/L in water and 1.75 (diphenhydramine) to 20,800 μg/kg (fluoranthene) in sediment. Cluster analyses revealed chemicals that frequently co-occurred such as pharmaceuticals and flame retardants at sites receiving similar inputs such as wastewater treatment plant effluent. Comparison of environmental concentrations to water and sediment-quality benchmarks revealed that polycyclic aromatic hydrocarbon concentrations often exceeded benchmarks in both water and sediment. Additionally, bis(2-ethylhexyl) phthalate and dichlorvos concentrations exceeded water-quality benchmarks in several rivers. Results from this study can be used to understand organism exposure, prioritize river basins for future management efforts, and guide detailed assessments of factors influencing transport and fate of CECs in the Great Lakes Basin.

An approach to the study of the immunity functions of bivalve haemocytes: Physiology and molecular aspects

The Mediterranean mussel Mytilus galloprovincialis is an ecologically and economically important species. It has been used in programs of monitoring of pollution, since it is sessile organism that is capable of accumulating pollutants in tissues through filter feeding. Due to an increase of pollutants in the environment, marine mussels present physiological alterations that compromise their innate immune system, which can latter lead to opportunistic diseases. The haemocytes are the cells in charge of the immune response in the Mediterranean mussel and in other mollusks. In this review, we summarize the physiological and genetic response capacity of these immune cells to the presence of xenobiotics, pathogens and the interplay. The identification of the basic mechanisms of immunity and their modulation in mussels can give important information for the possible utilization of this species as an invertebrate model for studies on innate immunity, future immunotoxicological studies, and predict changes in the community for the future.

Elevated gonadal atresia as biomarker of endocrine disruptors: Field and experimental studies using Mytilus trossulus (L.) and 17-alpha ethinylestradiol (EE2)

In the present work we compared the type and frequency of gonadal abnormalities among Mytilus trossulus populations from the Gulf of Gdańsk, Baltic Sea. Observed histopathologies were grouped as regressive changes (RC, gonadal atresia (GA) and regression (GR)), progressive changes (PC, gonadal tumors) and intersex. Sex-based and spatial differences in frequency of RC were found, with the highest frequency of RC and PC found in mussels from polluted station B followed by mussels from station A located near a purification plant outlet. Bivalves from the reference area had the lowest frequency of RC. In order to confirm biomarker applicability of RC, an exposure experiment with model xenoestrogen 17α-ethinylestradiol (EE2) was performed. The exposure of M. trossulus to 50 and 500ngdL^-1 of EE2 resulted in an increased frequency of gonadal regression and atresia, including melanized hemocytes infiltration in seminiferous tubules. We thus suggest that these changes can serve as biomarkers of endocrine disrupting compounds in biomonitoring studies.

Shotgun Proteomics Analysis Discards Alkali Labile Phosphate as a Reliable Method To Assess Vitellogenin Levels in Mytilus galloprovincialis

Vitellogenin, the egg yolk precursor, is a well-known biomarker of endocrine disruption in oviparous vertebrates. In invertebrates, such as bivalves, it has been used in the last 10 years for the same purpose, despite the limited knowledge of invertebrate endocrinology. In bivalves, vitellogenin levels are usually estimated using an indirect technique, alkali labile phosphate (ALP), that assumes that vitellogenin is the most abundant phosphorylated protein in the analyzed tissue. In this study, we applied shotgun proteomics for the identification and quantification of vitellogenin in marine mussel gonads and compared the results with those obtained with the ALP method. The proteomic analysis revealed that vitellogenin is only detected in female gonads with expression levels that are rather variable among female mussels at different stages of gonad development. ALP analysis, on the contrary, detected similar amounts of phosphorylated proteins regardless of sex or gonad development stage. These results show evidence that the ALP method is not providing reliable information about Vtg levels, at least in marine mussel gonads. ALP is not a good proxy to assess Vtg levels in marine mussels, and careful verification of the adequacy of the procedure should be done before ALP is further assumed as a proxy of Vtg in other bivalve mollusks.

The constitutively active estrogen receptor (ER) binds and activates the promoter of the vitellogenin (Vtg) gene in the Sydney rock oyster, Saccostrea glomerata

Vitellogenin (Vtg) is a well-established biomarker of estrogenic exposure in aquatic animals. In vertebrates, Vtg gene transcription is controlled by the estrogen receptors (ERs). Although an ER ortholog is present in molluscs, its role as a transcriptional regulator remains elusive. Here, we tested the hypothesis that in the Sydney rock oyster, Saccostrea glomerata, the ER ortholog activates Vtg gene transcription through specific interaction with its promoter. Luciferase reporter assays indicated that sgER activated both a minimal promoter containing the consensus estrogen-responsive elements (EREs) and the sgVtg promoter in an estrogen-independent manner. The sgVtg promoter-luciferase activation was significantly reduced when any of three putative ERE half sites (½EREs) in the promoter were mutated. Electrophoretic mobility shift assay (EMSA) confirmed that sgER binds specifically to a 68-bp promoter sequence where these ½EREs reside. Overall, the results suggest that sgER is a constitutively active transcription factor that binds and activates the sgVtg promoter.