The unpredictable effects of mixtures of androgenic and estrogenic chemicals on fish early life

An Overview of the Impact of Pharmaceuticals on Aquatic Microbial Communities

Pharmaceuticals are present as pollutants in several ecosystems worldwide. Despite the reduced concentrations at which they are detected, their negative impact on natural biota constitutes a global concern. The consequences of pharmaceuticals' presence in water sources and food have been evaluated with a higher detail for human health. However, although most of the pharmaceuticals detected in the environment had not been designed to act against microorganisms, it is of utmost importance to understand their impact on the environmental native microbiota. Microbial communities can suffer serious consequences from the presence of pharmaceuticals as pollutants in the environment, which may directly impact public health and ecosystem equilibrium. Among this class of pollutants, the ones that have been studied in more detail are antibiotics. This work aims to provide an overview of the impacts of different pharmaceuticals on environmental biofilms, more specifically in biofilms from aquatic ecosystems and engineered water systems. The alterations caused in the biofilm function and characteristics, as well as bacteria antimicrobial tolerance and consequently the associated risks for public health, are also reviewed. Despite the information already available on this topic, the need for additional data urges the assessment of emerging pollutants on microbial communities and the potential public health impacts.

Effects of tributyltin on gonad and brood pouch development of male pregnant lined seahorse (Hippocampus erectus) at environmentally relevant concentrations

The male pregnancy of seahorses is unique, but their reproductive response to environmental disturbances has not yet been clarified. Tributyltin (TBT) is known to have an endocrine disrupting effect on the reproductive system of coastal marine organisms. This study evaluated the potential effects of exposure to environmentally relevant concentrations of TBT on the development of gonads and brood pouch of the lined seahorse (Hippocampus erectus). Physiological, histological, and transcriptional analyses were conducted, and results showed that high levels of TBT bioaccumulation occurred in male and female seahorses. TBT led to ovarian follicular atresia and apoptosis with the elevation of androgen levels, accompanied by the induction of genes associated with lysosomes and autophagosomes. Comparative transcriptional analyses revealed the likely inhibition of spermatogenesis via the suppression of cyclic AMP and androgen synthesis. Notably, the transcriptional profiles showed that TBT potentially affects the immune system, angiogenesis, and embryo nourishment of the brood pouch, which indicates that it has negative effects on the male reproductive system of seahorses. In summary, this study reveals that environmental levels of TBT potentially affect the reproductive efficiency of seahorses, and may ultimately lead to a reduction in their populations in coastal environments.

When male seahorses take the female contraceptive pill

17α-ethinylestradiol (EE2), the female contraceptive pill, has been detected in mediterranean coasts where seahorse populations, Hippocampus guttulatus, live. Low environmental concentrations have the potential to disrupt growth but also endocrine metabolism, and this imbalance is all the more critical in early life stage. To investigate the impact of EE2 in reared seahorses, we exposed aged 2 months and sexually undifferentiated seahorses to an environmental concentration of 21 ng/L of EE2 for a period of 30 days. EE2 exposure led to a 19% reduction in weight, but also a mortality rate of 27%. This exposure predicted demasculinization of male individuals with a late onset of secondary sexual characteristics. EE2 exposure led to an increase of the free androgen index, but significant reductions of estradiol and testosterone in males were observed. This low estrogen concentration seemed to impact the positive feedback on luteinizing hormone (LH) with a decrease in LH production. Added to this, synthetic estrogen had a negative impact on the production and the release of follicle-stimulating hormone. Contrary to all expectations, females demonstrated a significant decrease in vitellogenin, following exposure to EE2 at 21 ng/L, while no changes were detected in males. This first study on the European long-snouted seahorses confirmed the deleterious impact of the female contraceptive pill with a real impact on growth, sexual differentiation, and maturation in young immature seahorses.

Linking chemical exposure to lipid homeostasis: A municipal waste water treatment plant influent is obesogenic for zebrafish larvae

Obesity, a risk factor for the development of type-2 diabetes, hypertension, cardiovascular disease, hepatic steatosis and some cancers, has been ranked in the top 10 health risk in the world by the World Health Organization. Despite the growing body of literature evidencing an association between the obesity epidemic and specific chemical exposure across a wide range of animal taxa, very few studies assessed the effects of chemical mixtures and environmental samples on lipid homeostasis. Additionally, the mode of action of several chemicals reported to alter lipid homeostasis is still poorly understood. Aiming to fill some of these gaps, we combined an in vivo assay with the model species zebrafish (Danio rerio) to screen lipid accumulation and evaluate expression changes of key genes involved in lipid homeostasis, alongside with an in vitro transactivation assay using human and zebrafish nuclear receptors, retinoid X receptor α and peroxisome proliferator-activated receptor γ. Zebrafish larvae were exposed from 4 th day post-fertilization until the end of the experiment (day 18), to six different treatments: experimental control, solvent control, tributyltin at 100 ng/L Sn and 200 ng/L Sn (positive control), and wastewater treatment plant influent at 1.25% and 2.5%. Exposure to tributyltin and to 2.5% influent led to a significant accumulation of lipids, with white adipose tissue deposits concentrating in the perivisceral area. The highest in vitro tested influent concentration (10%) was able to significantly transactivate the human heterodimer PPARγ/RXRα, thus suggesting the presence in the influent of HsPPARγ/RXRα agonists. Our results demonstrate, for the first time, the ability of complex environmental samples from a municipal waste water treatment plant influent to induce lipid accumulation in zebrafish larvae.

Populations Collapses in Marine Invertebrates Due to Endocrine Disruption: A Cause for Concern?

In the beginning of the twenty first century, the International Program on Chemical Safety published a document entitled Global Assessment of the State-Of-The-Science of Endocrine Disruptors. The work indicated only weak evidence of endocrine-related effects in human populations, and in wild animal populations. This document was revised in 2012 (State of the Science of Endocrine Disrupting Chemicals-2012) (1). The new document and the extensive scientific evidence it provided showed clearly that ED effects could be a risk to human and wildlife health. These works, however, were focused in human health and related animal models, mainly vertebrates and particularly mammals. It can be argued that invertebrates and many other taxa are important parts of all ecosystems, and, in many instances, have been shown to be also vulnerable to endocrine disruption. Thus, this work is aimed to show some observations on important marine invertebrate taxa, from an ecological point of view. The most important example of endocrine disruption in marine wild populations is the imposex response of marine gastropods, known for more than 40 years, and worldwide used to evaluate marine antifouling pollution. Among the mollusks, other important natural resources are bivalve species, used as human food sources and cephalopods, free-living, highly specialized mollusks, and also human food sources. Effects derived from endocrine disruptors in these species indicate that consumption could bring these compounds to human populations in an almost direct way, sometimes without any form of cooking or preparation. While discussing these questions, this work is also aimed to stimulate research on endocrine disruption among the invertebrate taxa that inhabited our oceans, and on which these effects are poorly known today.

A pilot study on polycystic ovarian syndrome caused by neonatal exposure to tributyltin and bisphenol A in rats

The development of polycystic ovary syndrome (PCOS) could be caused by exposure to environmental endocrine disrupting chemicals (EDCs). In the current study, two commonly found EDCs, bisphenol A (BPA) and tributyltin (TBT), were investigated for their effects on PCOS occurrence in neonatal female rats. TBT (10 and 100 ng kg^-1 d^-1), BPA (50 μg kg^-1 d^-1), and a mixture of the two (TBT 100 ng kg^-1 d^-1 with BPA 50 μg kg^-1 d^-1) were administered to female rats from postnatal day 1-16. TBT, BPA, and TBT + BPA treatment resulted in an irregular estrus cycle and disturbed ovarian development, with less corpora lutea and antral follicles, but more atretic follicles and cysts. In addition, serum testosterone and luteinizing hormone levels were significantly elevated, whereas a reduced level of serum sex hormone-binding globulin was observed after TBT100, BPA50, and TBT + BPA treatments. Moreover, gene expression analyses identified significant differential expression of the genes involved in a variety of biological pathways, such as lipid transport and steroidogenesis. Moreover, the expression level of proteins regulating lipid and androgen biosynthesis was elevated after the treatments. In conclusion, this study demonstrated that exposure to TBT, BPA, and a mixture of the two in newborn rats could contribute to a PCOS-like syndrome. The mechanism of PCOS pathogenesis caused by exposure to TBT and BPA is likely to be mediated by the lipid metabolism and steroidogenesis pathways. Our results provide novel insight into female reproduction affected by EDCs, which may be helpful for revealing the pathogenesis of PCOS.

New approaches to cope with possible harms of low-dose environmental chemicals

Low-dose environmental chemicals including endocrine-disrupting chemicals can disturb endocrine, nervous and immune systems. Traditional chemical-focused approaches, strict regulation and avoidance of exposure sources, can help protect humans from individual or several chemicals in the high-dose range, but their value in the low-dose range is questionable. First, exposure sources to problematic environmental chemicals are omnipresent, and many common pollutants present no safe level. In this situation, the value of any effort focusing on individual chemicals is very limited. Second, critical methodological issues, including the huge number of environmental chemicals, biological complexity of mixtures and non-linearity, make it difficult for risk assessment-based regulation to provide reliable permissible levels of individual chemicals. Third, the largest exposure source is already internal; human adipose tissue contains the most complex chemical mixtures. Thus, in the low-dose range, a paradigm shift is required from a chemical-focused to a human-focused approach for health protection. Two key questions are (1) how to control toxicokinetics of chemical mixtures to decrease their burden in critical organs and (2) how to mitigate early harmful effects of chemical mixtures at cellular levels. Many lifestyles can be evaluated for these purposes. Although both the chemical-focused and human-focused approaches are needed to protect humans, the human-focused holistic approach must be the primary measure in the low-dose range of environmental chemicals.

Expression of zona pellucida 3 gene is regulated by 17α-ethinylestradiol in adult topmouth culter Culter alburnus

Estrogen could lead to abnormal modulation or disruption of physical development, reproduction and sexual behavior in aquatic wildlife, especially in fish. Information on the toxicity of estrogens to native species in that can be used in site-specific risk assessments is scarce. In the present study, one zona pellucida 3 (ZP3) homologue termed CaZP3 was firstly identified from topmouth culter Culter alburnus, following its structural characteristics, tissue distribution and transcriptional modulation to 17α-ethinylestradiol (EE2) exposure were investigated. Meanwhile, vitellogenin (VTG) gene was employed to provide a comparison of the reactive ability to EE2 induction. The CaZP3 characterized with analogical functional domains such as ZP domain, SP, IHP, EHP, 12 cysteine residues, one N-linked glycosylation site and two conserved O-linked glycosylation sites and equal number of eight exons and seven introns with ZP3 counterparts of higher species. CaZP3 mRNA predominantly expressed in ovary, besides, highly expressed in female heart and male muscle and relatively high expressed in testis. CaZP3 has the lower reactive ability to EE2 induction in comparison with VTG, however, CaZP3 transcripts were significantly induced in gonads of both male and female culter by EE2 and could be used as an alternative biomarker to monitor EE2 activity. The present results supplement the database for toxicity of EE2, especially for fish species endemic to China and provide some useful information for the monitoring of EE2 activity in aquatic environment.

The effects of emerging environmental contaminants on Stenotrophomonas maltophilia isolated from drinking water in planktonic and sessile states

Concerns on the presence of emerging contaminants (ECs) in water sources have increased in recent years. The lack of efficient technologies to remove ECs from residual waters contributes for their appearance in drinking water distribution systems (DWDS). Therefore, sessile microorganisms on DWDS pipes are continuously exposed to trace concentrations of ECs. However, no data exists on the role of ECs on the resident microbiota. The present work aims to understand the effects of prolonged exposure of a bacterial strain of Stenotrophomonas maltophilia, isolated from a DWDS, in both planktonic and biofilm states, to trace concentrations of selected ECs (antipyrine-ANTP; diclofenac sodium salt-DCF; ibuprofen-IBP; galaxolide-GAL; tonalide-TON; carbamazepine-CBZ; clofibric acid-CA; tylosin-TY) on its tolerance to sodium hypochlorite (NaOCl) and resistance to antibiotics. Pre-established S. maltophilia biofilms were exposed to ECs for 26 d. Subsequently, the planktonic behaviour of the biofilm cells grown in the presence of ECS was characterized in terms of susceptibility to NaOCl and to selected antibiotics (levofloxacin and trimethoprim-sulfamethoxazole). Moreover, S.maltophilia was tested on its biofilm productivity in the presence of ECs (alone and mixed). These biofilms were challenged by NaOCl in order to assess the role of ECs on biofilm susceptibility. The results did not evidence remarkable effects of ECs on planktonic S. maltophilia susceptibility to NaOCl and antibiotics. However, S. maltophilia biofilm production and susceptibility to NaOCl was affected from ECs pre-exposure, particularly by the combination of different ECs (CA + CBZ, CA + IBP, CA + CBZ + IBP). S. maltophilia biofilms became more resistant to removal by NaOCl when developed in the presence of mixtures of CA + CBZ and CA + CBZ + IBP. Also, biofilm production was significantly affected. CA was present in all the combinations that altered biofilm behaviour. The overall results propose that exposure to ECs for 26 days had not a huge impact on S. maltophilia planktonic antimicrobial susceptibility. Nevertheless, the prolonged exposure to some ECs altered biofilm production and tolerance to NaOCl, with a potential practical outcome of hindering DWDS disinfection. The simultaneous presence of different ECs in the environment may amplify biofilm resilience.

Evidence of the Possible Harm of Endocrine-Disrupting Chemicals in Humans: Ongoing Debates and Key Issues

Evidence has emerged that endocrine-disrupting chemicals (EDCs) can produce adverse effects, even at low doses that are assumed safe. However, systemic reviews and meta-analyses focusing on human studies, especially of EDCs with short half-lives, have demonstrated inconsistent results. Epidemiological studies have insuperable methodological limitations, including the unpredictable net effects of mixtures, non-monotonic dose-response relationships, the non-existence of unexposed groups, and the low reliability of exposure assessment. Thus, despite increases in EDC-linked diseases, traditional epidemiological studies based on individual measurements of EDCs in bio-specimens may fail to provide consistent results. The exposome has been suggested as a promising approach to address the uncertainties surrounding human studies, but it is never free from these methodological issues. Although exposure to EDCs during critical developmental periods is a major concern, continuous exposure to EDCs during non-critical periods is also harmful. Indeed, the evolutionary aspects of epigenetic programming triggered by EDCs during development should be considered because it is a key mechanism for developmental plasticity. Presently, living without EDCs is impossible due to their omnipresence. Importantly, there are lifestyles which can increase the excretion of EDCs or mitigate their harmful effects through the activation of mitohormesis or xenohormesis. Effectiveness of lifestyle interventions should be evaluated as practical ways against EDCs in the real world.

DR, Lee DH. Persistent Organic Pollutants and Type 2 Diabetes: A Critical Review of Review Articles

Low dose persistent organic pollutants (POPs) have emerged as a new risk for type 2 diabetes (T2D). Despite substantial evidence from human and experimental studies, there are several critical issues which have not been properly addressed by POPs researchers. First, as POPs exist as mixtures, findings about POPs from human studies should be interpreted from the viewpoint of lipophilic chemical mixtures which include both measured and unmeasured POPs. Second, as POPs can directly reduce insulin secretion of beta cells, the role of POPs may be more prominent in the development of beta-cell dysfunction-dominant T2D rather than insulin resistance-dominant T2D. Third, there are multidimensional interrelationships between POPs and adipose tissue. Even though POPs are now considered as a new risk factor for T2D, independent of obesity, POPs and obesity are mechanistically linked to each other. POPs are involved in key mechanisms linking obesity and T2D, such as chronic inflammation of adipose tissue and lipotoxicity with ectopic fat accumulation. Also, POPs can explain puzzling human findings which suggest benefits of obesity because healthy adipose tissue can be protective by reducing the amount of POPs reaching other organs. Fourth, non-linear dose-response relationships between POPs and T2D are biologically possible. Although POPs are well-known endocrine disrupting chemicals (EDCs), mitochondrial dysfunction may be a more plausible mechanism due to unpredictability of EDC mixtures. As adipose tissue plays a role as an internal exposure source of POPs, how to manage POPs inside us may be essential to protect against harms of POPs.

Endocrine disruption in aquatic systems: up-scaling research to address ecological consequences

Endocrine‐disrupting chemicals (EDCs) can alter biological function in organisms at environmentally relevant concentrations and are a significant threat to aquatic biodiversity, but there is little understanding of exposure consequences for populations, communities and ecosystems. The pervasive nature of EDCs within aquatic environments and their multiple sub‐lethal effects make assessments of their impact especially important but also highly challenging. Herein, we review the data on EDC effects in aquatic systems focusing on studies assessing populations and ecosystems, and including how biotic and abiotic processes may affect, and be affected by, responses to EDCs. Recent research indicates a significant influence of behavioural responses (e.g. enhancing feeding rates), transgenerational effects and trophic cascades in the ecological consequences of EDC exposure. In addition, interactions between EDCs and other chemical, physical and biological factors generate uncertainty in our understanding of the ecological effects of EDCs within aquatic ecosystems. We illustrate how effect thresholds for EDCs generated from individual‐based experimental bioassays of the types commonly applied using chemical test guidelines [e.g. Organisation for Economic Co‐operation and Development (OECD)] may not necessarily reflect the hazards associated with endocrine disruption. We argue that improved risk assessment for EDCs in aquatic ecosystems urgently requires more ecologically oriented research as well as field‐based assessments at population‐, community‐ and food‐web levels.

Enhanced GSH synthesis by Bisphenol A exposure promoted DNA methylation process in the testes of adult rare minnow Gobiocypris rarus

DNA methylation is a commonly studied epigenetic modification. The mechanism of BPA on DNA methylation is poorly understood. The present study aims to explore whether GSH synthesis affects DNA methylation in the testes of adult male rare minnow Gobiocypris rarus in response to Bisphenol A (BPA). Male G. rarus was exposed to 1, 15 and 225μgL(-1) BPA for 7 days. The levels of global DNA methylation, hydrogen peroxide (H2O2) and glutathione (GSH) in the testes were analyzed. Meanwhile, the levels of enzymes involved in DNA methylation and de novo GSH synthesis, and the substrate contents for GSH production were measured. Furthermore, gene expression profiles of the corresponding genes of all studied enzymes were analyzed. Results indicated that BPA at 15 and 225μgL(-1) caused hypermethylation of global DNA in the testes. The 15μgL(-1) BPA resulted in significant decrease of ten-eleven translocation proteins (TETs) while 225μgL(-1) BPA caused significant increase of DNA methyltransferase proteins (DNMTs). Moreover, 225μgL(-1) BPA caused significant increase of H2O2 and GSH levels, and the de novo GSH synthesis was enhanced. These results indicated that the significant decrease of the level of TETs may be sufficient to cause the DNA hypermethylation by 15μgL(-1) BPA. However, the significantly increased of DNMTs contributed to the significant increase of DNA methylation levels by 225μgL(-1) BPA. Moreover, the elevated de novo GSH synthesis may promote the DNA methylation process.

Microarray analysis of di-n-butyl phthalate and 17α ethinyl-oestradiol responses in three-spined stickleback testes reveals novel candidate genes for endocrine disruption

Phthalate esters are plasticizers frequently found in wastewater effluents. Previous studies on phthalates have reported anti-androgenic activity in mammals, causing concerns of their potential effects on the reproduction of aquatic organisms. Another group of environmental endocrine disrupters, steroidal estrogens, are known to inhibit steroid biosynthesis in the gonads, but the effects related to spermatogenesis are not well understood in fish. In this study, three-spined sticklebacks were exposed to di-n-butyl phthalate (DBP) and 17α ethinyl-oestradiol (EE2) at nominal concentrations 35μg/L and 40ng/L, respectively, for four days. The aim of the study was to obtain insight into the acute transcriptional responses putatively associated with endocrine disruption. RNA samples from eight individual male fish per treatment (including controls) were used in microarray analysis, covering the expression of approximately 21,000 genes. In the EE2 treatment the results show transcriptional downregulation of genes associated with steroid biosynthesis pathway and up-regulation of genes involved in pathways related to epidermal growth factor signaling and xenobiotic metabolism. The transcriptional response to DBP was in general weaker than to EE2, but based on enrichment analysis, we suggest adverse effects on retinoid metabolism, creatine kinase activity and cell adhesion. Among the genes showing highest fold changes after DBP treatment compared to control was the teleost fish -specific cytochrome P450 17A2. Overall, this study promotes our understanding on molecular responses to anti-androgens and estrogens in fish testes.

The effects of model androgen 5α-dihydrotestosterone on mummichog (Fundulus heteroclitus) reproduction under different salinities

Endocrine disrupting substances (EDSs) have the potential to disturb sensitive hormone pathways, particularly those involved in development and reproduction. Both fresh and estuarine water bodies receive inputs of EDSs from a variety of sources, including sewage effluent, industrial effluent and agricultural runoff. Based on current literature, freshwater species appear to respond to lower levels of EDSs than estuarine or marine species. Therefore, effects elicited by EDSs in freshwater teleosts may not be an accurate representation of how EDSs affect teleosts in estuarine and marine environments. To address this potential difference, a short-term reproductive bioassay was conducted under conditions of low and high salinity using mummichog (Fundulus heteroclitus), a euryhaline species that is native to the east coast of North America. The goals of this study were to determine the response of mummichog when exposed to an androgenic EDS and whether salinity affected the response. A model androgen, 5α-dihydrotestosterone (DHT), was selected for this experiment. Impacts on reproduction were evaluated at multiple biological levels, including physiological (sex steroid levels), organismal (gonad size and gonad morphology), and functional (egg production) endpoints. Under conditions of high salinity, egg production was significantly reduced at all exposure concentrations. Under conditions of low salinity, there were no significant differences based on DHT treatment; however, egg production in all treatment groups including the control were significantly reduced relative to the high salinity control group. Other reproductive endpoints, such as sex steroid production, showed stronger correlation to fecundity in females than males. This study demonstrates that mummichog fecundity is sensitive to androgenic endocrine disruption while also underscoring the importance of how changes in salinity, an environmental variable, can impact reproduction.

Chronic effects of clofibric acid in zebrafish (Danio rerio): a multigenerational study

Clofibric acid (CA) is an active metabolite of the blood lipid lowering agent clofibrate, a pharmaceutical designed to work as agonist of peroxisome proliferator-activated receptor alpha (PPARa). It is the most commonly reported fibrate in aquatic environments with low degradation rate and potential environmental persistence. Previous fish exposures showed that CA may impact spermatogenesis, growth and the expression of fat binding protein genes. However, there are limited data on the effects of chronic multigenerational CA exposures. Here, we assessed chronic multigenerational effects of CA exposure using zebrafish (Danio rerio) as a teleost model. Zebrafish were exposed through the diet to CA (1 and 10mg/g) during their whole lifetime. Growth, reproduction-related parameters and embryonic development were assessed in the exposed fish (F1 generation) and their offspring (F2 generation), together with muscle triglyceride content and gonad histology. In order to study the potential underlying mechanisms, the transcription levels of genes coding for enzymes involved in lipid metabolism pathways were determined. The results show that chronic life-cycle exposure to CA induced a significant reduction in growth of F1 generation and lowered triglyceride muscle content (10mg/g group). Also, an impact in male gonad development was observed together with a decrease in the fecundity (10mg/g group) and higher frequency of embryo abnormalities in the offspring of fish exposed to the lowest CA dose. The profile of the target genes was sex- and tissue-dependent. In F1 an up-regulation of male hepatic pparaa, pparb and acox transcript levels was observed, suggesting an activation of the fatty acid metabolism (provided that transcript level change indicates also a protein level change). Interestingly, the F2 generation, raised with control diet, displayed a response pattern different from that observed in F1, showing an increase in weight in the descendants of CA exposed fish, in comparison with control animals, which points to a multigenerational effect.

Effects and bioaccumulation of 17β-estradiol and 17α-ethynylestradiol following long-term exposure in crucian carp

Bioaccumulation and effects of 17β-estradiol (E2) and 17α-ethynylestradiol (EE2) were assessed by crucian carp (Carassius auratus) following single and binary mixture exposures in flow-through exposure system for 16 months. In comparison with water control (DWC) and solvent control (SC), a significant reduction in body weight, body length and gonadosomatic index (GSI), and increase in hepatosomatic index (HSI) and plasma vitellogenin (VTG) levels were observed, in a time- and concentration-dependent manner. Bioconcentration factors (BCFs) of E2 and EE2 in fish muscle ranged from 3.2 to 40 and from 64 to 123, respectively. Crucian carp were found to be more sensitive to EE2 than E2. The bioaccumulation and toxicological effects in binary mixture exposed fish (mixture of E2 and EE2) were more significant than exposure of individual compound. Crucian carp is sensitive to E2 and EE2 in long-term laboratory exposure experiments and can be used as a potential model species for investigating the toxicity of hormones.

Effects of Tributyltin and Other Retinoid Receptor Agonists in Reproductive-Related Endpoints in the Zebrafish (Danio rerio)

Both field and experimental data examined the influence of exposure to environmental contaminant tributyltin (TBT) on marine organisms. Although most attention focused on the imposex phenomenon in gastropods, adverse effects were also observed in other taxonomic groups. It has been shown that imposex induction involves modulation of retinoid signaling in gastropods. Whether TBT influences similar pathways in fish is yet to be addressed. In this study, larvae of the model teleost Danio rerio were exposed to natural retinoids, all-trans-retinoic acid, 9-cis-retinoic acid, and all-trans-retinol, as well as to the RXR synthetic pan-agonist methoprene acid (MA) and to TBT. Larvae were exposed to TBT from 5 days post fertilization (dpf) to adulthood, and reproductive capacity was assessed and correlated with mode of action. TBT significantly decreased fecundity at environmentally relevant levels at 1 μg TBT Sn/g in diet. Interestingly, in contrast to previous reports, TBT altered zebrafish sex ratio toward females, whereas MA exposure biased sex toward males. Since fecundity was significantly altered in the TBT-exposed group with up to 62% decrease, the potentially affected pathways were investigated. Significant downregulation was observed in brain mRNA levels of aromatase b (CYP19a1b) in females and peroxisome proliferator activated receptor gamma (PPARg) in both males and females, suggesting an involvement of these pathways in reproductive impairment associated with TBT.

Reproductive health indicators of fishes from Pennsylvania watersheds: association with chemicals of emerging concern

Fishes were collected at 16 sites within the three major river drainages (Delaware, Susquehanna, and Ohio) of Pennsylvania. Three species were evaluated for biomarkers of estrogenic/antiandrogenic exposure, including plasma vitellogenin and testicular oocytes in male fishes. Smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, and redhorse sucker Moxostoma species were collected in the summer, a period of low flow and low reproductive activity. Smallmouth bass were the only species in which testicular oocytes were observed; however, measurable concentrations of plasma vitellogenin were found in male bass and white sucker. The percentage of male bass with testicular oocytes ranged from 10 to 100%, with the highest prevalence and severity in bass collected in the Susquehanna drainage. The percentage of males with plasma vitellogenin ranged from 0 to 100% in both bass and sucker. Biological findings were compared with chemical analyses of discrete water samples collected at the time of fish collections. Estrone concentrations correlated with testicular oocytes prevalence and severity and with the percentage of male bass with vitellogenin. No correlations were noted with the percentage of male sucker with vitellogenin and water chemical concentrations. The prevalence and severity of testicular oocytes in bass also correlated with the percent of agricultural land use in the watershed above a site. Two sites within the Susquehanna drainage and one in the Delaware were immediately downstream of wastewater treatment plants to compare results with upstream fish. The percentage of male bass with testicular oocytes was not consistently higher downstream; however, severity did tend to increase downstream.

Responsiveness of four gender-specific genes, figla, foxl2, scp3 and sox9a to 17α-ethinylestradiol in adult rare minnow Gobiocypris rarus

Proteins encoded by figla, foxl2, scp3 and sox9a play important roles in gonad differentiation and reproduction. In the present study, we aimed to determine the responsiveness of figla, foxl2, scp3 and sox9a to 17α-ethinylestradiol (EE2) in the gonads of adult Gobiocypris rarus. Full-length cDNAs of figla, scp3 and sox9a were cloned and characterized by RT-PCR and RACE methods. Expression patterns in adult tissues were investigated. Results indicated that figla was predominantly expressed in adult ovaries and scp3 was restrictively expressed in the male testes and sox9a was principally expressed in the brains of both genders and the testes of males. Gene expression profiles of figla, foxl2, scp3 and sox9a were analyzed in the gonads of adult G. rarus exposed to EE2 at 1, 5, 25, and 125ng/L for 3 and 6days. Three-day EE2 treatment at 1-125ng/L all caused a significant increase of figla transcript in testes and foxl2 transcript in ovaries. However, six-day EE2 exposure at 1-125ng/L repressed figla and scp3 transcript in testes and foxl2 transcript in ovaries. The present study indicates that the testicular transcripts of figla and scp3 in males and the ovarian foxl2 transcript in females have high responsiveness to EE2 and they can be used as sensitive molecular biomarkers for early warning to monitor the environmental estrogenic chemicals in fresh water environment. The present study also suggests that the effective EE2 dosage for feminization in male G. rarus might be at least 25ng/L.

Antagonistic effects of a mixture of low-dose nonylphenol and di-n-butyl phthalate (monobutyl phthalate) on the Sertoli cells and serum reproductive hormones in prepubertal male rats in vitro and in vivo

The estrogenic chemical nonylphenol (NP) and the antiandrogenic agent di-n-butyl phthalate (DBP) are regarded as widespread environmental endocrine disruptors (EDCs) which at high doses in some species of laboratory animals, such as mice and rats, have adverse effects on male reproduction and development. Given the ubiquitous coexistence of various classes of EDCs in the environment, their combined effects warrant clarification. In this study, we attempted to determine the mixture effects of NP and DBP on the testicular Sertoli cells and reproductive endocrine hormones in serum in male rats based on quantitative data analysis by a mathematical model. In the in vitro experiment, monobutyl phthalate (MBP), the active metabolite of DBP, was used instead of DBP. Sertoli cells were isolated from 9-day-old Sprague-Dawley rats followed by treatment with NP and MBP, singly or combined. Cell viability, apoptosis, necrosis, membrane integrity and inhibin-B concentration were tested. In the in vivo experiment, rats were gavaged on postnatal days 23-35 with a single or combined NP and DBP treatment. Serum reproductive hormone levels were recorded. Next, Bliss Independence model was employed to analyze the quantitative data obtained from the in vitro and in vivo investigation. Antagonism was identified as the mixture effects of NP and DBP (MBP). In this study, we demonstrate the potential of Bliss Independence model for the prediction of interactions between estrogenic and antiandrogenic agents.

Unexpected phenotypes of malformations induced in Xenopus tropicalis embryos by combined exposure to triphenyltin and 9-cis-retinoic acid

Xenopus tropicalis embryos were exposed for 48 hr to the mixtures of 5 μg Sn/L triphenyltin (TPT), which is a well-known endocrine disruptor, and 0.25-5 μg/L 9-cis retinoic acid (9c-RA), which is the natural ligand of retinoid X receptor. The phenotypes induced by combined exposure were more variable than those resulting from single exposure to either TPT or 9c-RA. The prominent phenotypes included underdeveloped head structures, abnormal eyes, narrow fins, enlarged proctodaeum, etc. Especially, combined exposure induced unexpected notochord malformations, which ranged from small swellings of the surface of the tails to the extension and extrusion of notochord out of the posterior tails. Compared with the 5 μg Sn/L TPT-treated group, the index of fin deficiency was not affected, and the index of axis deficiency was significantly increased with increasing RA concentrations in the mixtures. Our results suggest that combined exposure to TPT and 9c-RA induced not only more variable phenotypes of malformations than exposure to single compound but also some new and unexpected phenotypes.

Estrogenic chemical effects are independent from the degree of sex role reversal in pipefish

Endocrine disrupting chemicals (EDCs) have been reported to disturb several ecological relevant endpoints. Surprisingly, EDC-induced effects on fish sexual behaviour have been poorly studied despite the fact that even subtle alterations might contribute to a disruption of sexual interactions, thus negatively impacting reproduction. As the few assessments on sexual behaviour have been conducted in species with orthodox sex roles, it might be argued that sex-role reversed species might provide a potentially complementary system to further explore the effects of EDCs on reproduction. In the present study, two pipefish species with distinct degrees of sex-role reversal were selected to further elucidate the impact of chronic EE2 exposure on sexual behaviour and reproduction-related endpoints. The obtained results indicate that, independently of the degree of sex role reversal, courtship behaviour seems to resist oestrogenic chemical exposure. However, exposure to environmentally relevant EE2 levels did induce a complete absence of pregnancies at 18 ng/L. Even though pregnancies were observed at intermediate concentrations, the percentage of non-transferred or misplaced oocytes increased and a dose-dependent decrease of oocyte volume was observed. Imbalances in the oogenesis process, induction of vitellogenin in males and the absence of pregnancies highlight that environmental relevant concentrations of EE2 have the potential to negatively affect pipefish populations, most of them inhabiting coastal areas where oestrogenic contamination is more prevalent.

The effects of synthetic estrogen exposure on premating and postmating episodes of selection in sex-role-reversed Gulf pipefish

Environmental estrogens have been shown to affect populations of aquatic organisms in devastating ways, including feminization of males, alterations in mating behaviors, and disruption of sexual selection. Studies have shown 17α-ethinylestradiol (EE2) exposure to induce female-like secondary sexual traits in male Gulf pipefish, changing how females perceive affected males. We aimed to understand the effects of EE2 exposure on the sex-role-reversed mating system and the strength of selection in Gulf pipefish. We used artificial Gulf pipefish breeding aggregations and microsatellite-based parentage analysis to determine maternity. We then calculated the opportunity for selection and selection differentials on body size for both sexes during three consecutive episodes of selection. Exposure to EE2 did not affect the strength of selection, likely due to the unusual sex-role-reversed mating system found in this species. With respect to multiply mated females, EE2-exposed females produced more eggs with higher embryo survivorship than nonexposed females. Thus, short-term exposure to low concentrations (2.0 ng/L) of EE2 in Gulf pipefish enhanced female reproductive success. However, higher EE2 concentrations (5.0 ng/L) caused complete reproductive failure in Gulf pipefish males. These results call for more work on the long-term effects of EE2 exposure in Gulf pipefish in artificial and natural populations.

Expression of two zona pellucida genes is regulated by 17α-ethinylestradiol in adult rare minnow Gobiocypris rarus

Zona pellucida (ZP) proteins are glycoproteins synthesized in liver, ovary or in both tissues in fish. In the present study, we aimed to determine the responsiveness of ZP2 and ZP3 to 17α-ethinylestradiol (EE2) in adult rare minnow Gobiocypris rarus. The full length of ZP3 cDNA was firstly characterized and its tissue distribution revealed that ZP3 mRNA was predominantly expressed in ovary of G. rarus. The gene expression profiles of ZP2, ZP3 and vitellogenin (VTG) were analyzed in gonad and liver of adult G. rarus exposed to EE2 at 1, 5, 25, and 125 ng/L for 3 and 6 days. The results show that ZP2 is more sensitive than ZP3 in gonads of both genders, and VTG in liver is extremely sensitive to EE2 in male fish. However, at lower concentrations (1 and 5 ng/L), the ZP2 in testes shows higher responsiveness to EE2 compared with VTG in rare minnow. The 5' flanking regions of ZP2 and ZP3 were isolated and the comparison of transcription factors in the regions of ZP2 and ZP3 suggested that the disparity for the responsiveness of ZP2 and ZP3 to EE2 could partly be a result of differential cis-elements such as oocyte-specific protein (Osp1) binding sites or/and sex-determining region Y (SRY) binding site.

Chemical contaminants in water and sediment near fish nesting sites in the Potomac River basin: determining potential exposures to smallmouth bass (Micropterus dolomieu)

The Potomac River basin is an area where a high prevalence of abnormalities such as testicular oocytes (TO), skin lesions, and mortality has been observed in smallmouth bass (SMB, Micropterus dolomieu). Previous research documented a variety of chemicals in regional streams, implicating chemical exposure as one plausible explanation for these biological effects. Six stream sites in the Potomac basin (and one out-of-basin reference site) were sampled to provide an assessment of chemicals in these streams. Potential early life-stage exposure to chemicals detected was assessed by collecting samples in and around SMB nesting areas. Target chemicals included those known to be associated with important agricultural and municipal wastewater sources in the Potomac basin. The prevalence and severity of TO in SMB were also measured to determine potential relations between chemistry and biological effects. A total of 39 chemicals were detected at least once in the discrete-water samples, with atrazine, caffeine, deethylatrazine, simazine, and iso-chlorotetracycline being most frequently detected. Of the most frequently detected chemicals, only caffeine was detected in water from the reference site. No biogenic hormones/sterols were detected in the discrete-water samples. In contrast, 100 chemicals (including six biogenic hormones/sterols) were found in a least one passive-water sample, with 25 being detected at all such samples. In addition, 46 chemicals (including seven biogenic hormones/sterols) were found in the bed-sediment samples, with caffeine, cholesterol, indole, para-cresol, and sitosterol detected in all such samples. The number of herbicides detected in discrete-water samples per site had a significant positive relation to TO(rank) (a nonparametric indicator of TO), with significant positive relations between TO(rank) and atrazine concentrations in discrete-water samples and to total hormone/sterol concentration in bed-sediment samples. Such significant correlations do not necessarily imply causation, as these chemical compositions and concentrations likely do not adequately reflect total SMB exposure history, particularly during critical life stages.

Using physiology and behaviour to understand the responses of fish early life stages to toxicants

The use of early life stages of fishes (embryos and larvae) in toxicity testing has been in existence for a long time, generally utilizing endpoints such as morphological defects and mortality. Behavioural endpoints, however, may represent a more insightful evaluation of the ecological effects of toxicants. Indeed, recent years have seen a considerable increase in the use of behavioural measurements in early life stages reflecting a substantial rise in zebrafish Danio rerio early life-stage toxicity testing and the development of automated behavioural monitoring systems. Current behavioural endpoints identified for early life stages in response to toxicant exposure include spontaneous activity, predator avoidance, capture of live food, shoaling ability and interaction with other individuals. Less frequently used endpoints include measurement of anxiogenic behaviours and cognitive ability, both of which are suggested here as future indicators of toxicant disruption. For many simple behavioural endpoints, there is still a need to link behavioural effects with ecological relevance; currently, only a limited number of studies have addressed this issue. Understanding the physiological mechanisms that underlie toxicant effects on behaviour so early in life has received far less attention, perhaps because physiological measurements can be difficult to carry out on individuals of this size. The most commonly established physiological links with behavioural disruption in early life stages are similar to those seen in juveniles and adults including sensory deprivation (olfaction, lateral line and vision), altered neurogenesis and neurotransmitter concentrations. This review highlights the importance of understanding the integrated behavioural and physiological response of early life stages to toxicants and identifies knowledge gaps which present exciting areas for future research.

Sediment organic tin contamination promotes impoverishment of non-biting midge species communities in the Archipelago Sea, S-W Finland

Chironomid species are a vital component in many benthic and terrestrial food webs; they have an important role in the detritus cycle, and are an important source of food for many species. We studied how tributyltin (TBT) in brackish water sediments affect the composition of chironomid species communities. Emergence traps were used at selected sites on a TBT gradient in the Archipelago Sea, S-W Finland. Increased sediment TBT concentration was associated with significant chironomid species turnover, which in turn was related to decreased species diversity (number of species and genera). However, the overall number of individuals did not decrease markedly with increasing TBT contamination. This suggests that the ecological role of chironomids in the food web may be preserved even under severe impoverishment of the chironomid community due to organic tin contamination. The increased prevalence of more TBT tolerant species can potentially lead to a transport of organic tin compounds between aquatic and terrestrial food webs. Furthermore, the reduced diversity of an ecologically influential group might lower the resistance of the entire food web to other environmental hazards and perturbations.

Anticancer drugs in surface waters: what can we say about the occurrence and environmental significance of cytotoxic, cytostatic and endocrine therapy drugs?

This study considers the implications and research needs arising from anticancer (also referred to as antineoplastic) drugs being released into the aquatic environment, for the entire therapeutic classes used: cytotoxic, cytostatic and endocrine therapy drugs. A categorization approach, based on French consumption amounts, allowed to highlight parent molecules and several metabolites on which further occurrence and ecotoxicological studies should be conducted. Investigations of consumption trends at a national and a local scale show an increase in the use of anticancer drugs between 2004 and 2008, thus leading to increased levels released in the environment. It therefore appears necessary to continue surveying their presence in surface waters and in wastewater treatment plant (WWTP) effluents. Furthermore, due to the rise of anticancer home treatments, most of the prescribed molecules are now available in town pharmacies. Consequently, hospital effluents are no longer the main expected entry route of anticancer drugs into the aquatic environment. Concerning ecotoxicological risks, current knowledge remains insufficient to support a definitive conclusion. Risk posed by cytotoxic molecules is still not well documented and it is not possible to conclude on their long-term effects on non-target organisms. To date, ecotoxicological effects have been assessed using standardized or in vitro assays. Such tests however may not be suitable for anticancer drugs, and further work should focus on full-life cycle or even multigenerational tests. Environmental significance (i.e. occurrence and effects) of cytostatics (protein kinases inhibitors and monoclonal antibodies), if any, is not documented. Protein kinases inhibitors, in particular, deserve further investigation due to their universal mode of action. Finally, concerning endocrine therapy drugs, molecules such as antiestrogen Tamoxifen and its active metabolites, could be of concern. Overall, to accurately assess the ecotoxicological risk of anticancer drugs, we discuss the need to break away from tests on isolated molecules and to test effects of mixtures at the low ng.l(-1) range.

Rapid-behaviour responses as a reliable indicator of estrogenic chemical toxicity in zebrafish juveniles

Whereas biochemical and molecular parameters have been well recognised as important "signposts" of individual disturbance to endocrine disrupting chemical's (EDCs) exposure, behavioural endpoints are yet greatly overlooked as a routine tool in environmental risk assessment of EDCs. However, life histories are intimately associated with numerous inter- and intra-specific interactions, which invariably depend on the performance of effective behaviours. Within fish species, one of the most important factors influencing energy turnover earlier in the development is locomotor activity. This essential trait reflects the organism's ability to generate and coordinate the metabolic energy required for both reproductive and non-reproductive behaviours. Inappropriate movement responses due to toxic effects of contaminants may ultimately impact important ecological variables. Therefore, in the present study, the swimming bursts of zebrafish juveniles exposed for 40 d to the synthetic estrogen ethinylestradiol (EE(2)), tested at environmentally relevant concentrations (nominal concentrations of 0.5, 1 and 2 ng L(-1)), were investigated in order to address the potential of rapid-behaviour patterns as an effective response indicator of estrogenic endocrine disrupting chemical's exposure. This synthetic estrogen was selected due to its high prevalence in aquatic ecosystems, ability to mimic natural estrogens and proven record of causing negative effects in fish reproduction. The behavioural responses were compared with established endpoints used in the screening of EE(2) effects at adulthood. Results indicate that zebrafish juveniles' swimming activity was significantly decreased upon EE(2) exposure. Since reduced locomotion of zebrafish may impact foraging, predator avoidance, drift and transport, and even interfere with social and reproductive behaviours, a fitness decline of wild fish populations can ultimately be hypothesized. Furthermore, behavioural endpoints were found to display higher sensitivity to EE(2) than either vitellogenin gene induction or reproductive parameters determined at adulthood. Overall, the findings of this work not only demonstrate the power of high-throughput behavioural responses, able to act as sensitive early warning signals of EDC exposure, but also highlight the potential of behavioural endpoints in providing a more comprehensive and non-invasive measure of EDC's exposure.

Endocrine disrupting activities in sewage effluent and river water determined by chemical analysis and in vitro assay in the context of granular activated carbon upgrade

As part of endocrine disruption in catchments (EDCAT) programme, this work aims to assess the temporal and spatial variations of endocrine disrupting chemicals (EDCs) in River Ray, before and after the commissioning of a full-scale granular activated carbon (GAC) plant at a sewage treatment works (STW). Through spot and passive sampling from effluent and river sites, estrogenic and anti-androgenic activities were determined by chemical analysis and in vitro bio-assay. A correlation was found between chemical analyses of the most potent estrogens (estrone (E1), 17β-estradiol (E2), 17α-ethinylestradiol (EE2)) and yeast estrogen screen (YES) measurement, both showing clearly a reduction in estrogenic activity after the commissioning of the GAC plant at the STW. During the study period, the annual average concentrations of E1, E2 and EE2 had decreased from 3.5 ng L(-1), 3.1 ng L(-1) and 0.5 ng L(-1) to below their limit of detection (LOD), respectively, with a concentration reduction of at least 91%, 81% and 60%. Annual mean estrogenic activity measured by YES of spot samples varied from 1.9 ng L(-1) to 0.4 ng L(-1) E2 equivalent between 2006 and 2008 representing a 79% reduction. Similarly, anti-androgenic activity measured by yeast anti-androgen screen (anti-YAS) of spot samples was reduced from 148.8 to 22.4 μg flutamide L(-1), or by 85%. YES and anti-YAS values were related to each other, suggesting co-existence of both types of activities from chemical mixtures in environmental samples. The findings confirm the effectiveness of a full-scale GAC in removing both estrogenic and anti-androgenic activities from sewage effluent.

Drifting towards the surface: a shift in newborn pipefish's vertical distribution when exposed to the synthetic steroid ethinylestradiol

Endocrine disrupting chemical (EDC) effects during early life have the potential to modulate population structure, either directly through increased mortality or by causing inappropriate aggregation events, thus affecting the number of young that will reach adulthood. An alteration in the dispersal and recruitment patterns can also impair the connectivity among geographically distant populations. However, the detection of EDC-induced effects occurring after egg hatch, when newborns increase their chances of contacting with environmentally dispersed contaminants, is not a simple process as effects might be masked by the large natural mortality rates that usually occur during fish early life. Since there is a lack of information regarding the impact of EDCs on fish early life dispersal patterns, particularly on vertical migrations patterns, the effects of environmentally relevant concentrations of EE(2) on the vertical distribution of newborn fish was assessed through an ex situ exposure experiment. Syngnathus abaster newborns were exposed to EE(2) (nominal concentrations of 8, 12 and 36 ng L(-1)) and the dynamics of their vertical distribution was monitored for up to 40 d. No significant differences in overall mortality were observed between treatments or in the dynamics of the registered death curves. Nevertheless, an alteration in the distribution patterns was observed. The commonly benthic newborn tended to shift their vertical distribution towards the surface, in a dose-dependent manner. Curiously, a follow up of the exposed pipefish confirmed that EE(2) effects were also noticeable upon sexual maturity, namely by the alteration of several primary and secondary sexual characters. The observation that vertical distributional patterns, at least in pipefish, are clearly altered at environmentally relevant EE(2) concentrations indicates that EDC's impact in fish larvae behaviour should be considered when addressing the effects of contaminants, given the obvious implications on population connectivity, stability and persistence.