Parental effects of endocrine disrupting compounds in aquatic wildlife: Is there evidence of transgenerational inheritance?

Combined effects of binary mixtures of 17β-estradiol and testosterone in western mosquitofish (Gambusia affinis) after full life-cycle exposure

Estrogens and androgens are typical steroid hormones and often occur together in contaminated aquatic environments, but their mixed effects in aquatic organisms have been less well reported. In this study, the endocrine disrupting effects of binary mixtures of 17β-estradiol (E2) and testosterone (T) in western mosquitofish (Gambusia affinis) were assessed by analyzing the sex ratio, secondary sex characteristics, gonadal histology, and transcriptional expression of target genes related to the hypothalamic-pituitary-gonadal (HPG) axis in G. affinis (from embryos) continuously exposed to E2 (50 ng/L), T (T1: 50 ng/L; T2: 200 ng/L), and mixtures of both (E2 + T1: 50 + 50 ng/L; E2 + T2: 50 + 200 ng/L) for 119 d. The results showed that exposure to E2 + T1 and E2 + T2 reduced the length ratio of ray 4/6 ratio in male G. affinis, suggesting feminized phenomenon in male G. affinis. Furthermore, 16.7-38.5 % of female G. affinis showed masculinized anal fins and hemal spines when exposed to T alone and in combination with E2. Importantly, the transcriptional levels of certain target genes related to the HPG axis were significantly altered in G. affinis following exposure to E2 and T alone and in combinations. Moreover, exposure to E2 and T in combinations can lead to combined effects (such as synergistic and antagonistic effects) on the transcriptional levels of some genes. These results collectively suggest that exposure to environmentally relevant concentrations of E2 and T alone and in mixtures can impact the endocrine system of G. affinis, and may pose potential risks in aquatic systems.

Paternal exposures to endocrine-disrupting chemicals induce intergenerational epigenetic influences on offspring: A review

Endocrine-disrupting chemicals (EDCs) are ubiquitous in ecological environments and have become a great issue of public health concern since the 1990 s. There is a deep scientific understanding of the toxicity of EDCs. However, recent studies have found that the abnormal physiological functions of the parents caused by EDCs could be transmitted to their unexposed offspring, leading to intergenerational toxicity. We questioned whether sustained epigenetic changes occur through the male germline. In this review, we (1) systematically searched the available research on the intergenerational impacts of EDCs in aquatic and mammal organisms, including 42 articles, (2) summarized the intergenerational genetic effects, such as decreased offspring survival, abnormal reproductive dysfunction, metabolic disorders, and behavioral abnormalities, (3) summarized the mechanisms of intergenerational toxicity through paternal interactions, and (4) propose suggestions on future research directions to develop a deeper understanding of the ecological risk of EDCs.

Endocrine disruption in crustaceans: New findings and perspectives

A significant advance has been made, especially during the last two decades, in the knowledge of the effects on crustacean species of pollutants proven to be endocrine disruptors in vertebrates. Such effects have been also interpreted in the light of recent studies on crustacean endocrinology. Year after year, the increased number of reports refer to the effects of endocrine disruptors on several processes hormonally controlled. This review is aimed at summarizing and discussing the effects of several kinds of endocrine disruptors on the hormonal control of reproduction (including gonadal growth, sexual differentiation, and offspring development), molting, and intermediate metabolism of crustaceans. A final discussion about the state of the art, as well as the perspective of this toxicological research line is given.

Parental exposure to antidepressants has lasting effects on offspring? A case study with zebrafish

Fish have common neurotransmitter pathways with humans, exhibiting a significant degree of conservation and homology. Thus, exposure to fluoxetine makes fish potentially susceptible to biochemical and physiological changes, similarly to what is observed in humans. Over the years, several studies demonstrated the potential effects of fluoxetine on different fish species and at different levels of biological organization. However, the effects of parental exposure to unexposed offspring remain largely unknown. The consequences of 15-day parental exposure to relevant concentrations of fluoxetine (100 and 1000 ng/L) were assessed on offspring using zebrafish as a model organism. Parental exposure resulted in offspring early hatching, non-inflation of the swimming bladder, increased malformation frequency, decreased heart rate and blood flow, and reduced growth. Additionally, a significant behavioral impairment was also found (reduced startle response, basal locomotor activity, and altered non-associative learning during early stages and a negative geotaxis and scototaxis, reduced thigmotaxis, and anti-social behavior at later life stages). These behavior alterations are consistent with decreased anxiety, a significant increase in the expression of the monoaminergic genes slc6a4a (sert), slc6a3 (dat), slc18a2 (vmat2), mao, tph1a, and th2, and altered levels of monoaminergic neurotransmitters. Alterations in behavior, expression of monoaminergic genes, and neurotransmitter levels persisted until offspring adulthood. Given the high conservation of neuronal pathways between fish and humans, data show the possibility of potential transgenerational and multigenerational effects of pharmaceuticals' exposure. These results reinforce the need for transgenerational and multigenerational studies in fish, under realistic scenarios, to provide realistic insights into the impact of these pharmaceuticals.

Developmental cardiotoxicity of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in marine medaka (Oryzias melastigma)

The application of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as an antifouling biocide causes high toxicity to non-target marine organisms. To examine the developmental cardiotoxicity and mechanisms of DCOIT, we concurrently performed sub-chronic exposure and life-cycle exposure experiments using marine medaka embryos. After sub-chronic exposure to DCOIT at 1, 3, 10, and 33 μg/L, cardiac defects were caused by upregulation of cardiac gene transcriptions, decreasing heart size, and accelerating heartbeat. Hyperthyroidism in medaka larvae was identified as the cause of developmental cardiotoxicity of DCOIT sub-chronic exposure. In addition, parental life-cycle exposure to 1, 3, and 10 μg/L DCOIT led to transgenerational impairment of cardiogenesis in offspring medaka. A crossbreeding strategy discriminated a concentration-dependent mechanism of transgenerational cardiotoxicity. At 1 μg/L, the DCOIT-exposed female parent transferred a significantly higher amount of triiodothyronine (T3) hormone to offspring, corresponding to an accelerated heart rate. However, DCOIT at higher exposure concentrations modified the methylome imprinting in larval offspring, which was associated with cardiac dysfunction. Overall, the findings provide novel insights into the developmental cardiotoxicity of DCOIT. The high risks of DCOIT-even at environmentally realistic concentrations-raise concerns about its applicability as an antifoulant in a marine environment.

Embryonic exposure to environmentally relevant levels of tributyltin affects embryonic tributyltin bioaccumulation and the physiological responses of juveniles in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is a typical organic pollutant that persists in aquatic sediments due to its wide usage as an antifouling fungicide during the past few decades. Despite increased awareness of the serious negative consequences of TBT on aquatic species, studies on the effects of TBT exposure on cephalopod embryonic development and juvenile physiological performance are scarce. To investigate the lasting effects of TBT toxicity on Sepia pharaonis from embryo to hatchling, embryos (gastrula stage, 3-5 h post fertilization) were exposed to four levels of TBT until hatching: 0 (control), 30 (environmental level), 60, and 120 ng/L. Subsequently, juvenile growth performance endpoints and behavioral alterations were assessed over 15 days post-hatching. Egg hatchability was significantly reduced and embryonic development (i.e., premature hatching) was accelerated in response to 30 ng/L TBT exposure. Meanwhile, TBT-induced alterations in embryonic morphology primarily included yolk-sac lysis, embryonic malformations, and uneven pigment distributions. During the pre-middle stage of embryonic development, the eggshell serves as an effective barrier to safeguard the embryo from exposure to 30-60 ng/L TBT, according to patterns of TBT accumulation and distribution in the egg compartment. However, even environmental relevant levels of TBT (30 ng/L) exposure during embryonic development had a negative impact on juvenile behavior and growth, including slowing growth, shortening eating times, causing more irregular movements, and increasing inking times. These findings indicate that after TBT exposure, negative long-lasting effects on S. pharaonis development from embryo to hatchling persist, suggesting that long-lasting toxic effects endure from S. pharaonis embryos to hatchlings.

South American National Contributions to Knowledge of the Effects of Endocrine Disrupting Chemicals in Wild Animals: Current and Future Directions

Human pressure due to industrial and agricultural development has resulted in a biodiversity crisis. Environmental pollution is one of its drivers, including contamination of wildlife by chemicals emitted into the air, soil, and water. Chemicals released into the environment, even at low concentrations, may pose a negative effect on organisms. These chemicals might modify the synthesis, metabolism, and mode of action of hormones. This can lead to failures in reproduction, growth, and development of organisms potentially impacting their fitness. In this review, we focused on assessing the current knowledge on concentrations and possible effects of endocrine disruptor chemicals (metals, persistent organic pollutants, and others) in studies performed in South America, with findings at reproductive and thyroid levels. Our literature search revealed that most studies have focused on measuring the concentrations of compounds that act as endocrine disruptors in animals at the systemic level. However, few studies have evaluated the effects at a reproductive level, while information at thyroid disorders is scarce. Most studies have been conducted in fish by researchers from Brazil, Argentina, Chile, and Colombia. Comparison of results across studies is difficult due to the lack of standardization of units in the reported data. Future studies should prioritize research on emergent contaminants, evaluate effects on native species and the use of current available methods such as the OMICs. Additionally, there is a primary focus on organisms related to aquatic environments, and those inhabiting terrestrial environments are scarce or nonexistent. Finally, we highlight a lack of funding at a national level in the reviewed topic that may influence the observed low scientific productivity in several countries, which is often negatively associated with their percentage of protected areas.

Transgenerational effects of parental bisphenol S exposure on zebrafish (Danio rerio) reproduction

Bisphenol S (BPS) is extensively used for production of polycarbonates and other commodities, and is often detected in environment and biota. Parental BPS exposure has been reported to interfere with reproductive development of offspring, but limited information is available on its multigenerational reproductive toxicity. In our present study, zebrafish (Danio rerio) were exposed to BPS (1 and 100 μg/L) from 3 hpf to 120 dpf, and the effects on reproduction, sex steroid hormones, DNA methylation levels and gene transcription involved in steroidogenesis and DNA methylation were investigated in unexposed F1-2 offspring. The results showed that 100 μg/L BPS exposure increased DNA methylation in F1 testes, and 1 μg/L BPS led to DNA methylation in F2 ovaries. The increased DNA methylation levels led to decreased expression of steroidogenic enzymes, including cyp11a, cyp17 and 3βhsd, which might be a main reason for the elevated plasma 17β-estradiol and decreased testosterone levels. In addition, sex ratio indicated a female dominance trend, and reproductive capacity of male fish was severely impaired. Overall, these findings suggest that parental BPS exposure impairs reproductive development of unexposed offspring via DNA methylation and BPS-induced epigenetic modification inheritance has a long-term effect on the fitness and sustainability of fish populations.

Epigenetic mechanisms of DNA methylation in the transgenerational effect of ethylhexyl salicylate on zebrafish

In this study, a 120-day whole-life cycle exposure and oviposition experiment on zebrafish with maternal and paternal mixed mating strategy was conducted to investigate the epigenetic mechanism of DNA methylation in ethylhexyl salicylate (EHS, 1, 10, 100 μg/L)-induced transgenerational effects. Results showed that EHS could induce the decrease of DNA methyltransferase 1 (DNMT1) activity and average global DNA methylation level in maternal parents and the increase of the above indexes in paternal parents, while the change of glycine N-methyltransferase activity was opposite to DNMT1. The average global DNA methylation levels were significantly increased in the offsprings of both parents exposed and father-only exposed to EHS, suggesting that EHS-induced epigenetic modifications may be stable and heritable. Hierarchical clustering analysis of promoter at different methylation sites showed that the DNA methylation pattern of offsprings were similar to that of the paternal parents, meaning that the offsprings may have inherited paternal DNA methylation pattern with eya2, pcdh2g5 and pcdh2g1 as key genes and lead to high locomotor activity in offsprings. KEGG pathway analysis showed that parental exposure to EHS may interfere with the central nervous system, insulin function system, melanogenesis system and the normal development of somatic axis of offsprings.

Epigenetic biomarkers as tools for chemical hazard assessment: Gene expression profiling using the model Danio rerio

Recent reports raise the concern that exposure to several environmental chemicals may induce persistent changes that go beyond the exposed organisms, being transferred to subsequent generations even in the absence of the original chemical insult. These changes in subsequent non-exposed generations have been related to epigenetic changes. Although highly relevant for hazard and risk assessment, biomarkers of epigenetic modifications that can be associated with adversity, are still not integrated into hazard assessment frameworks. Here, in order to validate new biomarkers of epigenetic modifications in a popular animal model, zebrafish embryos were exposed to different concentrations of Bisphenol A (0.01, 0.1, 1 and 10 mg/L) and Valproic Acid (0.8, 4, 20 and 100 mg/L), two chemicals reported to alter the modulation of the epigenome. Morphological abnormalities and epigenetic changes were assessed at 80 hours-post fertilization, including DNA global methylation and gene expression of both DNA and histone epigenetic modifications. Gene expression changes were detected at concentrations below those inducing morphological abnormalities. These results further support the importance of combining epigenetic biomarkers with apical endpoints to improve guidelines for chemical testing and hazard assessment, and favour the integration of new biomarkers of epigenetic modifications into the standardized OECD test guideline 236 with zebrafish embryos.

Zebrafish as the toxicant screening model: Transgenic and omics approaches

The production of large amounts of synthetic industrial and biomedical compounds, together with environmental pollutants, poses a risk to our ecosystem and induces negative effects on the health of wildlife and human beings. With the emergence of the global problem of chemical contamination, the adverse biological effects of these chemicals are gaining attention among the scientific communities, industry, governments, and the public. Among these chemicals, endocrine disrupting chemicals (EDCs) are regarded as one of the major global issues that potentially affecting our health. There is an urgent need of understanding the potential hazards of such chemicals. Zebrafish have been widely used in the aquatic toxicology. In this review, we first discuss the strategy of transgenic lines that used in the toxicological studies, followed by summarizing the current omics approaches (transcriptomics, proteomics, metabolomics, and epigenomics) on toxicities of EDCs in this model. We will also discuss the possible transgenerational effects in zebrafish and future prospective of the integrated omics approaches with customized transgenic organism. To conclude, we summarize the current findings in the field, and provide our opinions on future environmental toxicity research in the zebrafish model.

Developmental assays using invasive cane toads, Rhinella marina, reveal safety concerns of a common formulation of the rice herbicide, butachlor

Identifying the adverse impacts of pesticide exposure is essential to guide regulations that are protective of wildlife and human health. Within rice ecosystems, amphibians are valuable indicators because pesticide applications coincide with sensitive reproductive and developmental life stages. We conducted two experiments using wild cane toads (Rhinella marina) to test 1) whether environmentally relevant exposure to a commercial formulation of butachlor, an acetanilide herbicide used extensively in rice, affects amphibian development and 2) whether cane toad tadpoles are capable of acclimatizing to sub-lethal exposure. First, we exposed wild cane toads to 0.002, 0.02, or 0.2 mg/L of butachlor (Machete EC), during distinct development stages (as eggs and hatchlings, as tadpoles, or continuously) for 12 days. Next, we exposed a subset of animals from the first experiment to a second, lethal concentration and examined survivorship. We found that cane toads exposed to butachlor developed slower and weighed less than controls, and that development of the thyroid gland was affected: exposed individuals had smaller thyroid glands and thyrocyte cells, and more individual follicles. Analyses of the transcriptome revealed that butachlor exposure resulted in downregulation of transcripts related to metabolic processes, anatomic structure development, immune system function, and response to stress. Last, we observed evidence of acclimatization, where animals exposed to butachlor early in life performed better than naïve animals during a second exposure. Our findings indicate that the commercial formulation of butachlor, Machete EC, causes thyroid endocrine disruption in vertebrates, and suggest that exposure in lowland irrigated rice fields presents a concern for wildlife and human health. Furthermore, we establish that developmental assays with cane toads can be used to screen for adverse effects of pesticides in rice fields.

Parental exposure to polystyrene microplastics at environmentally relevant concentrations has negligible transgenerational effects on zebrafish (Danio rerio)

Waterborne exposure to highly persistent microplastic pollutants is a major concern for aquatic species worldwide. There are still gaps in knowledge on microplastics' potential transgenerational effects on offspring generation. Using zebrafish, this study investigated the survival and early development of offspring through a 21-day continuous parental treatment with polystyrene microplastics. The results showed that continuous waterborne exposure to high concentrations (>100 μg/L) of polystyrene microplastics (1 μm) for 21 days resulted in notable microplastic accumulation in adult fish intestines. Exposure at microplastic concentrations greater than 100 μg/L also induced significant changes in steroidogenic mRNA expression in zebrafish gonads. However, no significant changes in the cumulative number of eggs spawned and fertilization rate were observed at any parental exposure concentrations when compared to the control. Early development of derived offspring, in terms of hatching rate, body length, malformation rate and mortality rate, did not significantly differ from that of the control. This study showed that transgenerational effects of parental exposure to polystyrene microplastics in zebrafish might be negligible or recoverable. This study provided new results and insights on the transgenerational effects of microplastics on a freshwater fish species and can help to understand impacts of microplastics on freshwater ecosystems.

Parental exposure to the synthetic estrogen 17α-ethinylestradiol (EE2) affects offspring development in the Sydney rock oyster, Saccostrea glomerata

Very little is currently known regarding the effects of estrogenic endocrine disrupting chemicals on embryonic and larval development in molluscs, nor the potential effects of parental (F₀) exposure on resultant F₁ offspring. In this study, we assessed the embryotoxic impacts of exposure to environmentally relevant concentrations of the synthetic estrogen, 17α-ethinylestradiol (EE2), to male and female parents (50 ng/L) and their offspring (5 and 50 ng/L) in the native Australian Sydney rock oyster, Saccostrea glomerata. There were no detectable effects of parental exposure on fertilisation success, proportions of early larval (F₁) morphs and unfertilised eggs. Offspring impacts were evidenced in terms of developmental delays, with decreased percentages of D-veligers retained by 45 μm mesh, along with a reduction of swimming capabilities of larvae at 2 days post-fertilisation (dpf) when both parents had been exposed to 50 ng/L EE2. Although no significant parental effects were found on the survival of F₁ larvae at 9 dpf, retardation of shell growth was observed on F₁ larvae in treatments where both parents had been exposed to 50 ng/L EE2. Subsequent larval exposure from 2 to 9 dpf caused declines in survival and reduction of shell length in F₁ larvae at both 5 and 50 ng/L EE2 across all parental exposure treatments. Collectively, parental EE2 imparts effects on offspring in terms of retardation of larval development, and subsequent offspring exposure to EE2 further exacerbates impacts to development. Future research should aim to understand the potential mechanisms of EE2 induced toxicity and its transmission resulting in altered phenotypes of the F₁ generation.

Invertebrates facing environmental contamination by endocrine disruptors: Novel evidences and recent insights

The crisis of biodiversity we currently experience raises the question of the impact of anthropogenic chemicals on wild life health. Endocrine disruptors are notably incriminated because of their possible effects on development and reproduction, including at very low doses. As commonly recorded in the field, the burden they impose on wild species also concerns invertebrates, with possible specificities linked with the specific physiology of these animals. A better understanding of chemically-mediated endocrine disruption in these species has clearly gained from knowledge accumulated on vertebrate models. But the molecular pathways specific to invertebrates also need to be reckoned, which implies dedicated research efforts to decipher their basic functioning in order to be able to assess its possible disruption. The recent rising of omics technologies opens the way to an intensification of these efforts on both aspects, even in species almost uninvestigated so far.

Paternal Exposure to Carbamazepine Impacts Zebrafish Offspring Reproduction Over Multiple Generations

Chronic low-concentration chemical exposures may have both direct health outcomes on adults and indirect effects on their offspring. Using zebrafish, we examined the impacts of chronic, low-concentration carbamazepine (CBZ) exposure on a suite of male reproductive endpoints in the parents and four generations of offspring reared in clean water. CBZ is one of the most frequently detected pharmaceutical residues in water, is a histone deacetylase inhibitor in mammals, and is reported to lower androgens in mammals and fish. Exposure of adult zebrafish to 10 μg/L CBZ for 6 weeks decreased reproductive output, courtship and aggressive behaviors, 11-ketotestosterone (11KT), and sperm morphology but did not impact milt volume or sperm swimming speed. Pairwise breeding generated lineages of offspring with both parents exposed and two lineages where only one parent was exposed; the control lineage had unexposed parents. Reproductive output and male reproductive indices were assessed in F₁-F₄ offspring to determine whether parental CBZ exposure had transgenerational impacts. The offspring of CBZ-exposed males had lower 11KT, reproductive output, altered courtship, aggression, and sperm morphology compared to the lineage from unexposed parents. Our results indicate that parental carbamazepine exposure history impacts the unexposed progeny up to the F₄ generations and that paternal, but not maternal, exposure is most important for the reproductive health of male offspring.

Parental Exposure to Perfluorobutanesulfonate Impairs Offspring Development through Inheritance of Paternal Methylome

Perfluorobutanesulfonate (PFBS), an environmental pollutant of emerging concern, significantly impairs offspring development and overall health after parental exposure. However, the true inducer of offspring developmental defects among the complexity of parental influences remains unknown. In the present study, marine medaka (Oryzias melastigma) were exposed to environmentally realistic concentrations of PFBS (0, 1, 3, and 10 μg/L) for an entire life cycle. By mixing and mating control and exposed medaka (male or female), a crossbreeding strategy was employed to produce offspring eggs from various crossbreeds, with the aim of differentiating the maternal and paternal influences. Measurements of swimming performance in larval offspring showed that larvae of exposed male parents swam hyperactively in comparison to the control larvae. Contrasting trends in PFBS transfer and maternal factor transfer (e.g., proteins and lipids) to that of swimming behavior eliminated these two factors as major inducers of offspring developmental impairment. Inheritance of the exposed paternal methylome marks in offspring may be partially responsible for abnormal swimming behavior, although different toxic mechanisms may be involved depending on the exposure concentration. Overall, these findings suggest that inheritance of epigenetic modifications implicates a long-lasting threat of PFBS to the fitness and sustainability of fish populations.

Perfluorobutanesulfonate Exposure Skews Sex Ratio in Fish and Transgenerationally Impairs Reproduction

Perfluorobutanesulfonate (PFBS) is increasingly polluting aquatic environments due to worldwide manufacturing and application. However, toxicological knowledge regarding PFBS exposure remains scarce. Here, we showed that PFBS life-cycle exposure at environmentally realistic concentrations (0, 1.0, 2.9, and 9.5 μg/L) skewed the sex ratio in fish toward male dominance, while reproductive functions of female fish were greatly impaired, as characterized by extremely small ovaries, blocked oocyte development, and decreased egg production. Endocrine disruption through the hypothalamus-pituitary-gonad axis was induced by PFBS exposure, showing antiestrogenic activity in females but estrogenic activity in males. PFBS was found to gradually accumulate in F0 adults during continuous exposure but can be rapidly eliminated when depurated in clean water. Parental exposure also transferred PFBS pollutant to F1 offspring eggs. Although no trace of PFBS was detected in F1 adults and F2 eggs, adverse effects from parental exposure persisted in F1 and F2 offspring. These transgenerational effects implicate PFBS as an ongoing threat to the fitness and sustainability of fish populations. The dramatic impairment of fish reproduction highlights the urgency of re-evaluations of the ecological and evolutionary consequences of PFBS exposure.

Parental gemfibrozil exposure impacts zebrafish F1 offspring, but not subsequent generations

Gemfibrozil (GEM) is a fibrate lipid regulator and one of the most commonly occurring fresh water pharmaceuticals. The negative effects of fibrates including GEM on fish reproduction have been frequently reported including effects of F₀ GEM exposure on reproduction of the unexposed F₁ offspring. We predicted that chronic, direct exposure of zebrafish with low concentrations of GEM would adversely affect parental male reproduction and unexposed offspring for multiple generations. Adult zebrafish were exposed to 10 μg/L GEM for 6 weeks and a range of reproductive indices were analyzed. The F₁-F₄ offspring were reared in clean water from 3 distinct lineages where only a single or both parents were exposed and compared to a control lineage where parents were unexposed. Reproductive indices were examined in unexposed F₁-F₄ offspring to test the hypothesis of multi- or trans- generational impacts. Exposure to GEM caused a decline in breeding success and mean embryo production in F₀ parents and a reduction in whole body 11-ketotestosterone (11-KT), altered male courtship, aggression and sperm morphology. Our results indicate that paternal exposure alone is sufficient to result in reproductive effects in unexposed male offspring but that effects are mostly limited to F₁. We suggest that GEM may act as a reproductive endocrine disruptor in fish and that chronic exposure reduced male reproductive fitness but not over multiple generations.

Parental exposure to 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) induced transgenerational thyroid hormone disruption in zebrafish

Although 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), an alternative to perfluorooctanesulfonate (PFOS), has been regularly detected in different environmental matrices, information regarding its toxicity remains limited. To explore the transgenerational thyroid-disrupting capacity of F-53B, adult zebrafish (F0) were exposed to different concentrations of F-53B (0, 5, 50, or 500μg/L) for 180d, with their offspring (F1 and F2) subsequently reared in uncontaminated water. Thyroid disturbances were then examined in the three (F0, F1, and F2) generations. For F0 adult fish, thyroxine (T4) increased in both sexes after exposure to 50μg/LF-53B, whereas 3,5,3'-triiodothyronine (T3) decreased in all groups, except for 50μg/LF-53B-treated males. For F1 embryos, parental exposure resulted in F-53B transfer as well as an increase in T4 content. At 5days post-fertilization, the significant increase in T4 and decrease in T3 were accompanied by a decrease in body length, increase in mortality, and increase in uninflated posterior swim bladder occurrence in F1 larvae. Although thyroid hormone levels were not changed significantly in F1 adult fish or F2 offspring compared with the control, the transcription levels of several genes along the hypothalamus-pituitary-thyroid axis were significantly modified. Our study demonstrated that F-53B possesses transgenerational thyroid-disrupting capability in zebrafish, indicating it might not be a safer alternative to PFOS.

Timing of maternal exposure to toxic cyanobacteria and offspring fitness in Daphnia magna: Implications for the evolution of anticipatory maternal effects

Organisms that regularly encounter stressful environments are expected to use cues to develop an appropriate phenotype. Water fleas (Daphnia spp.) are exposed to toxic cyanobacteria during seasonal algal blooms, which reduce growth and reproductive investment. Because generation time is typically shorter than the exposure to cyanobacteria, maternal effects provide information about the local conditions subsequent generations will experience. Here, we evaluate if maternal effects in response to microcystin, a toxin produced by cyanobacteria, represent an inheritance system evolved to transmit information in Daphnia magna. We exposed mothers as juveniles and/or as adults, and tested the offspring's fitness in toxic and non-toxic environments. Maternal exposure until reproduction reduced offspring fitness, both in the presence and in the absence of toxic cyanobacteria. However, this effect was accompanied by a small positive fitness effect, relative to offspring from unexposed mothers, in the presence of toxic cyanobacteria. This effect was mainly elicited in response to maternal exposure to toxic cyanobacteria early in life and less so during reproduction. None of these effects were explained by changes in egg size. A meta-analysis using our and others' experiments suggests that the adaptive value of maternal effects to cyanobacteria exposure is weak at best. We suggest that the beneficial maternal effect in our study is an example of phenotypic accommodation spanning generations, rather than a mechanism evolved to transmit information about cyanobacteria presence between generations.

Multigenerational Disruption of the Thyroid Endocrine System in Marine Medaka after a Life-Cycle Exposure to Perfluorobutanesulfonate

Accumulation of perfluorobutanesulfonate (PFBS) is frequently detected in biota, raising concerns about its ecological safety. However, hazardous effects of PFBS remain largely unexplored, especially for endocrine disrupting potency. In the present study, the multigenerational endocrine disrupting potential of PFBS was investigated by exposing F0 marine medaka eggs to PFBS at different concentrations (0, 1.0, 2.9, and 9.5 μg/L) until sexual maturity. The F1 and F2 generations were reared without continued exposure. Thyroidal disturbances were examined in all three generations. PFBS exposure decreased the levels of 3,5,3'-triiodothyronine (T3) in F0 female blood; however, it increased T3 or thyroxine (T4) levels in F0 brains, in which hyperthyroidism suppressed the local transcription of 5'-deiodinase 2 ( Dio2). Obviously decreased T3 was transferred to F1 eggs, although the parental influences were reversed in F1 larvae. Delayed hatching was coupled with elevated T3 levels in F1 larvae. F1 adults showed comparable symptoms of thyroidal disruption with F0 adults. A slight recovery was noted in the F2 generation, although F2 larvae still exhibited thyroid disruption and synthesized excessive T4. Our results suggested that the offspring suffered more severe dysfunction of the thyroidal axis albeit without direct exposure. This study provided the first molecular insight about PFBS toxicology on the thyroid, beneficial to both human and environmental risk assessment.

Transgenerational impairments of reproduction and development of the marine invertebrate Crepidula onyx resulted from long-term dietary exposure of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47)

Polybrominated diphenyl ethers have become ubiquitous in the environment and elevated concentrations have often been found in marine organisms. Using the gastropod Crepidula onyx as a study model, this multigenerational study sets out to test the hypotheses that 1) parental dietary exposure to environmentally realistic levels of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) would lead to transgenerational impairments on fitness traits of marine invertebrates, and 2) the organisms might develop adaptation/acclimation after exposure for one or more generations. F₀ generation of C. onyx was fed with the dinoflagellate Isochrysis galbana encapsulated with two concentrations of BDE-47 (1.78 and 16.0 ng million cells^-1, respectively), and half of the F₁ offspring from the higher concentration treatment was returned to control condition (transgenerational group), while the other half received BDE-47 treatment continuously (continuous treatment group). Bioaccumulation and maternal transfer of BDE-47 were evident in all life stages of the F₀ generation and in F₁ eggs, respectively. Exposure to BDE-47 reduced fecundity, delayed sexual maturity, and impeded embryonic development in F₀ to F₂. In particular, developmental toxicity of F₂ embryos was apparent in the transgenerational group, but not in the continuous treatment group, even when BDE-47 was not detected in the F₂ embryos nor in their mothers and they have never been exposed to the chemical. This study also suggested that the offspring might have developed adaptation/acclimation to the exposure of BDE-47 within two generations of exposure, and that the physiological alterations associated with acclimation/adaptation might have hindered the normal larval development under a stress free condition. These findings highlighted the need for long-term multigenerational studies in the ecological risk assessment of chemicals alike.

Parental exposure to bisphenol A and its analogs influences zebrafish offspring immunity

Transgenerational effects of environmental pollutants on humans and animals are complex. Thus, we used zebrafish to evaluate the effects of parental whole-life cycle exposure to bisphenol A and its analogs (bisphenol S and F) on offspring innate immunity. At adulthood, offspring were examined with/without continued chemicals treatment until 72h post-fertilization (hpf). To measure offspring immune function, larvae at 72 hpf were expose for 24h with/without the viral mimic polyinosinic-cytidylic acid (Poly I:C) or the bacterial mimic Pam3Cys-Ser-Lys4 (PAM3CSK4). Data show modified immunity in offspring. Specifically, lysozyme activity was significantly induced in F1 larvae and respiratory burst response and oxidative defense genes were inhibited. Genes of the innate immune system including Toll-like receptors and their downstream molecules and inflammatory cytokines were significantly down-regulated, whereas matrix metalloproteinases were up-regulated in larvae. In addition, recombination-activating genes in the immature adaptive immune system were significantly reduced. Thus, immune defense is diminished by exposing parental generations of zebrafish to environmentally relevant concentration of bisphenols and this suggests that fish chronically exposed to bisphenols in the wild may be vulnerable to pathogens.

Concentration and timing of application reveal strong fungistatic effect of tebuconazole in a Daphnia-microparasitic yeast model

Given the importance of pollutant effects on host-parasite relationships and disease spread, the main goal of this study was to assess the influence of different exposure scenarios for the fungicide tebuconazole (concentration×timing of application) on a Daphnia-microparasitic yeast experimental system. Previous results had demonstrated that tebuconazole is able to suppress Metschnikowia bicuspidata infection at ecologically-relevant concentrations; here, we aimed to obtain an understanding of the mechanism underlying the anti-parasitic (fungicidal or fungistatic) action of tebuconazole. We exposed the Daphnia-yeast system to four nominal tebuconazole concentrations at four timings of application (according to the predicted stage of parasite development), replicated on two Daphnia genotypes, in a fully crossed experiment. An "all-or-nothing" effect was observed, with tebuconazole completely suppressing infection from 13.5μgl^-1 upwards, independent of the timing of tebuconazole application. A follow-up experiment confirmed that the suppression of infection occurred within a narrow range of tebuconazole concentrations (3.65-13.5μgl^-1), although a later application of the fungicide had to be compensated for by a slight increase in concentration to elicit the same anti-parasitic effect. The mechanism behind this anti-parasitic effect seems to be the inhibition of M. bicuspidata sporulation, since tebuconazole was effective in preventing ascospore production even when applied at a later time. However, this fungicide also seemed to affect the vegetative growth of the yeast, as demonstrated by the enhanced negative effect of the parasite (increasing mortality in one of the host genotypes) at a later time of application of tebuconazole, when no signs of infection were observed. Fungicide contamination can thus affect the severity and spread of disease in natural populations, as well as the inherent co-evolutionary dynamics in host-parasite systems.

Reproductive Impacts of Endocrine-Disrupting Chemicals on Wildlife Species: Implications for Conservation of Endangered Species

Wildlife have proven valuable to our understanding of the potential effects of endocrine-disrupting chemicals (EDCs) on human health by contributing considerably to our understanding of the mechanisms and consequences of EDC exposure. But the threats EDCs present to populations of wildlife species themselves are significant, particularly for endangered species whose existence is vulnerable to any reproductive perturbation. However, few studies address the threats EDCs pose to endangered species owing to challenges associated with their study. Here, we highlight those barriers and review the available literature concerning EDC effects on endangered species. Drawing from other investigations into nonthreatened wildlife species, we highlight opportunities for new approaches to advance our understanding and potentially mitigate the effects of EDCs on endangered species to enhance their fertility.

Tools to minimize interlaboratory variability in vitellogenin gene expression monitoring programs

The egg yolk precursor protein vitellogenin is widely used as a biomarker of estrogen exposure in male fish. However, standardized methodology is lacking and little is known regarding the reproducibility of results among laboratories using different equipment, reagents, protocols, and data analysis programs. To address this data gap we tested the reproducibility across laboratories to evaluate vitellogenin gene (vtg) expression and assessed the value of using a freely available software data analysis program. Samples collected from studies of male fathead minnows (Pimephales promelas) exposed to 17α-ethinylestradiol (EE2) and minnows exposed to processed wastewater effluent were evaluated for vtg expression in 4 laboratories. Our results indicate reasonable consistency among laboratories if the free software for expression analysis LinRegPCR is used, with 3 of 4 laboratories detecting vtg in fish exposed to 5 ng/L EE2 (n = 5). All 4 laboratories detected significantly increased vtg levels in 15 male fish exposed to wastewater effluent compared with 15 male fish held in a control stream. Finally, we were able to determine that the source of high interlaboratory variability from complementary deoxyribonucleic acid (cDNA) to quantitative polymerase chain reaction (qPCR) analyses was the expression analysis software unique to each real-time qPCR machine. We successfully eliminated the interlaboratory variability by reanalyzing raw fluorescence data with independent freeware, which yielded cycle thresholds and polymerase chain reaction (PCR) efficiencies that calculated results independently of proprietary software. Our results suggest that laboratories engaged in monitoring programs should validate their PCR protocols and analyze their gene expression data following the guidelines established in the present study for all gene expression biomarkers. Environ Toxicol Chem 2017;36:3102-3107. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Parental diuron-exposure alters offspring transcriptome and fitness in Pacific oyster Crassostrea gigas

One of the primary challenges in ecotoxicology is to contribute to the assessment of the ecological status of ecosystems. In this study, we used Pacific oyster Crassostrea gigas to explore the effects of a parental exposure to diuron, a herbicide frequently detected in marine coastal environments. The present toxicogenomic study provides evidence that exposure of oyster genitors to diuron during gametogenesis results in changes in offspring, namely, transcriptomic profile alterations, increased global DNA methylation levels and reduced growth and survival within the first year of life. Importantly, we highlighted the limitations to identify particular genes or gene expression signatures that could serve as biomarkers for parental herbicide-exposure and further for multigenerational and transgenerational effects of specific chemical stressors. By analyzing samples from two independent experiments, we demonstrated that, due to complex confounding effects with both tested solvent vehicles, diuron non-specifically affected the offspring transcriptome. These original results question the potential development of predictive genomic tools for detecting specific indirect impacts of contaminants in environmental risk assessments. However, our results indicate that chronic environmental exposure to diuron over several generations may have significant long term impacts on oyster populations with adverse health outcomes.

Generational comparisons (F1 versus F3) of vinclozolin induced epigenetic transgenerational inheritance of sperm differential DNA methylation regions (epimutations) using MeDIP-Seq

Environmentally induced epigenetic transgenerational inheritance of disease and phenotypic variation has been shown to involve DNA methylation alterations in the germline (e.g. sperm). These differential DNA methylation regions (DMRs) are termed epimutations and in part transmit the transgenerational phenotypes. The agricultural fungicide vinclozolin exposure of a gestating female rat has previously been shown to promote transgenerational disease and epimutations in F3 generation (great-grand-offspring) animals. The current study was designed to investigate the actions of direct fetal exposure on the F1 generation rat sperm DMRs compared to the F3 transgenerational sperm DMRs. A protocol involving methylated DNA immunoprecipitation (MeDIP) followed by next-generation sequencing (Seq) was used in the current study. Bioinformatics analysis of the MeDIP-Seq data was developed and several different variations in the bioinformatic analysis were evaluated. Observations indicate needs to be considered. Interestingly, the F1 generation DMRs were found to be fewer in number and for the most part distinct from the F3 generation epimutations. Observations suggest the direct exposure induced F1 generation sperm DMRs appear to promote in subsequent generations alterations in the germ cell developmental programming that leads to the distinct epimutations in the F3 generation. This may help explain the differences in disease and phenotypes between the direct exposure F1 generation and transgenerational F3 generation. Observations demonstrate a distinction between the direct exposure versus transgenerational epigenetic programming induced by environmental exposures and provide insights into the molecular mechanisms involved in the epigenetic transgenerational inheritance phenomenon.

Uncertainties in biological responses that influence hazard and risk approaches to the regulation of endocrine active substances

Endocrine-disrupting substances (EDS) may have certain biological effects including delayed effects, multigenerational effects, and may display nonmonotonic dose-response (NMDR) relationships that require careful consideration when determining environmental hazards. Endocrine disrupting substances can have specific and profound effects when exposure occurs during sensitive windows of the life cycle (development, reproduction). This creates the potential for delayed effects that manifest when exposure has ceased, possibly in a different life stage. This potential underscores the need for testing in appropriate (sensitive) life stages and full life cycle designs. Such tests are available in the Organisation for Economic Co-operation and Development (OECD) tool box and should be used to derive endpoints that can be considered protective of all life stages. Similarly, the potential for effects to be manifest in subsequent generations (multigenerational effects) has also been raised as a potential issue in the derivation of appropriate endpoints for EDS. However, multigenerational studies showing increasing sensitivity of successive generations are uncommon. Indeed this is reflected in the design of new higher tier tests to assess endocrine active substances (EAS) that move to extended one-generation designs and away from multi-generational studies. The occurrence of NMDRs is also considered a limiting factor for reliable risk assessment of EDS. Evidence to date indicates NMDRs are more prevalent in in vitro and mechanistic data, not often translating to adverse apical endpoints that would be used in risk assessment. A series of steps to evaluate NMDRs in the context of endocrine hazard and risk assessment procedures is presented. If careful consideration of delayed, multigenerational effects and NMDRs is made, it is feasible to assess environmental endocrine hazards and derive robust apical endpoints for risk assessment procedures ensuring a high level of environmental protection. Integr Environ Assess Manag 2017;13:293-301. © 2016 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Impact of micropollutants on the life-history traits of the mosquito Aedes aegypti: On the relevance of transgenerational studies

Hazard assessment of chemical contaminants often relies on short term or partial life-cycle ecotoxicological tests, while the impact of low dose throughout the entire life cycle of species across multiple generations has been neglected. This study aimed at identifying the individual and population-level consequences of chronic water contamination by environmental concentrations of three organic micropollutants, ibuprofen, bisphenol A and benzo[a]pyrene, on Aedes aegypti mosquito populations in experimental conditions. Life-history assays spanning the full life-cycle of exposed individuals and their progeny associated with population dynamics modelling evidenced life-history traits alterations in unexposed progenies of individuals chronically exposed to 1 μg/L ibuprofen or 0.6 μg/L benzo[a]pyrene. The progeny of individuals exposed to ibuprofen showed an accelerated development while the progeny of individuals exposed to benzo[a]pyrene showed a developmental acceleration associated with an increase in mortality rate during development. These life-history changes due to pollutants exposure resulted in relatively shallow increase of Ae. aegypti asymptotic population growth rate. Multigenerational exposure for six generations revealed an evolution of population response to ibuprofen and benzo[a]pyrene across generations, leading to a loss of previously identified transgenerational effects and to the emergence of a tolerance to the bioinsecticide Bacillus turingiensis israelensis (Bti). This study shed light on the short and long term impact of environmentally relevant doses of ibuprofen and benzo[a]pyrene on Ae. aegypti life-history traits and insecticide tolerance, raising unprecedented perspectives about the influence of surface water pollution on vector-control strategies. Overall, our approach highlights the importance of considering the entire life cycle of organisms, and the necessity to assess the transgenerational effects of pollutants in ecotoxicological studies for ecological risk assessment. Finally, this multi-generational study gives new insight about the influence of surface water pollution on microevolutionary processes.

Developmental toxicity of the common UV filter, benophenone-2, in zebrafish embryos

Benozophenone (BP) type UV filters are extensively used in the personal care products to provide protection against the harmful effects of UV radiation. BPs are one of the primary components in the UV filter family, in which benophenone-2 (BP2) is widely used as a UV filter reagent in the sunscreen. Humans used these personal care products directly on skin and the chemicals will be washed away to the water system. BP2 has been identified as one of the endocrine disruptor chemicals, which can inference the synthesis, metabolism, and action of endogenous hormones. Environmentally, it has been found to contaminate water worldwide. In this study, we aimed to unfold the possible developmental toxicology of this chemical. Zebrafish are used as the screening model to perform in situ hybridization staining to investigate the effects of BP2 on segmentation, brain regionalization, and facial formation at four developmental stages (10-12 somite, prim-5, 2 and 5 days post-fertilization). Results showed 40 μM (9.85 mg L^-1) or above BP2 exposure in zebrafish embryos for 5 days resulted in lipid accumulation in the yolk sac and facial malformation via affecting the lipid processing and the expression of cranial neural crest cells respectively. To conclude, the study alarmed its potential developmental toxicities at high dosage exposure.

Delayed impacts of developmental exposure to 17-α-ethinylestradiol in the self-fertilizing fish Kryptolebias marmoratus

17-α-ethinylestradiol (EE2) is one of the most potent endocrine disrupting compounds found in the aquatic environments, and is known to strongly alter fish reproduction and fitness. While the effects of direct exposure to EE2 are well studied in adults, there is an increasing need to assess the impacts of exposure during early life stages. Sensitivity to pollutants during this critical window can potentially affect the phenotype later in life or in subsequent generations. This study investigated phenotypic outcome of early-life exposure to 17-α-ethinylestradiol during development and in adults of the mangrove rivulus, Kryptolebias marmoratus. Being one of the only two known self-fertilizing hermaphroditic vertebrates, this fish makes it possible to work with genetically identical individuals. Therefore, using rivulus makes it possible to examine, explicitly, the phenotypic effects of environmental variance while eliminating the effects of genetic variance. Genetically identical rivulus were exposed for the first 28days post hatching (dph) to 0, 4 or 120ng/L of EE2, and then were reared in uncontaminated water until 168dph. Growth, egg laying and steroid hormone levels (estradiol, cortisol, 11-ketotestosterone, testosterone) were measured throughout development. Exposed fish showed a reduction in standard length directly after exposure (28dph), which was more pronounced in the 120ng/L group. This was followed by compensatory growth when reared in clean water: all fish recovered a similar size as controls by 91dph. There was no difference in the age at maturity and the proportions of mature, non-mature and male individuals at 168dph. At 4ng/L, fish layed significantly fewer eggs than controls, while, surprisingly, reproduction was not affected at 120ng/L. Despite a decrease in fecundity at 4ng/L, there were no changes in hormones levels at the lower concentration. In addition, there were no significant differences among treatments immediately after exposure. However, 120ng/L exposed fish exhibited significantly higher levels of testosterone at 91 and 168dph and 11-ketotestosterone at 168dph, up to 140days after exposure. These results indicate that early-life exposure to EE2 had both immediate and delayed impacts on the adult's phenotype. While fish growth was impaired during exposure, compensatory growth, reduced fecundity and modification of the endocrine status were observed after exposure ceased.

Estimating the effects of 17α-ethinylestradiol on stochastic population growth rate of fathead minnows: a population synthesis of empirically derived vital rates

Urban freshwater streams in arid climates are wastewater effluent dominated ecosystems particularly impacted by bioactive chemicals including steroid estrogens that disrupt vertebrate reproduction. However, more understanding of the population and ecological consequences of exposure to wastewater effluent is needed. We used empirically derived vital rate estimates from a mesocosm study to develop a stochastic stage-structured population model and evaluated the effect of 17α-ethinylestradiol (EE2), the estrogen in human contraceptive pills, on fathead minnow Pimephales promelas stochastic population growth rate. Tested EE2 concentrations ranged from 3.2 to 10.9 ng L(-1) and produced stochastic population growth rates (λ S ) below 1 at the lowest concentration, indicating potential for population decline. Declines in λ S compared to controls were evident in treatments that were lethal to adult males despite statistically insignificant effects on egg production and juvenile recruitment. In fact, results indicated that λ S was most sensitive to the survival of juveniles and female egg production. More broadly, our results document that population model results may differ even when empirically derived estimates of vital rates are similar among experimental treatments, and demonstrate how population models integrate and project the effects of stressors throughout the life cycle. Thus, stochastic population models can more effectively evaluate the ecological consequences of experimentally derived vital rates.