Intersex manifestation in the rainbow darter (Etheostoma caeruleum): Are adult male fish susceptible to developing and recovering from intersex after exposure to endocrine active compounds?

For over a decade, intersex has been observed in rainbow darter (RD) (Etheostoma caeruleum) populations living downstream wastewater treatment plants (WWTPs) in the Grand River, Ontario, Canada. To further our understanding of intersex development in adult male fish, the current study addressed three objectives: i) can intersex be induced in adult male fish, ii) is there a specific window of exposure when adult male fish are more susceptible to developing intersex, and iii) can pre-exposed adult male fish recover from intersex? To assess intersex induction in adult male fish, wild male RD were exposed in the laboratory for 22 weeks (during periods of spawning, gonadal regression, and gonadal recrudescence) to environmentally relevant concentrations of 17α-ethinylestradiol (EE2) including nominal 0, 1, and 10 ng/L. Intersex rates and severity at 10 ng/L EE2 were similar to those observed historically in adult male populations living downstream WWTPs in the Grand River and confirmed previous predictions that 1-10 ng/L EE2 would cause these adverse effects. To assess a window of sensitivity in developing intersex, male RD were exposed to nominal 0, 1 or 10 ng/L EE2 for 4 weeks during three different periods of gonadal development, including (i) spawning, (ii) early recrudescence and (iii) late recrudescence. These short-term exposures revealed that intersex incidence and severity were greater when RD were exposed while gonads were fully developed (during spawning) compared to periods of recrudescence. To assess if RD recover from intersex, wild fish were collected downstream WWTPs in the Grand River and assessed for intersex both before and after a 22-week recovery period in clean water that included gonadal regression and recrudescence. Results showed that fish did not recover from intersex, with intersex rates and severity similar to those both before and after the transition to clean water. This study further advances our knowledge on intersex manifestation in adult male fish including their sensitivity to endocrine active compounds during different periods of their annual reproductive cycle and their limited ability to recover from intersex after onset of the condition.

Modeling the exposure of wild fish to endocrine active chemicals: Potential linkages of total estrogenicity to field-observed intersex

Decades of studies on endocrine disruption have suggested the need to manage the release of key estrogens from municipal wastewater treatment plants (WWTP). However, the proposed thresholds are below the detection limits of most routine chemical analysis, thereby restricting the ability of watershed managers to assess the environmental exposure appropriately. In this study, we demonstrated the utility of a mechanistic model to address the data gaps on estrogen exposure. Concentrations of the prominent estrogenic contaminants in wastewaters (estrone, estradiol, and ethinylestradiol) were simulated in the Grand River in southern Ontario (Canada) for nine years, including a period when major WWTP upgrades occurred. The predicted concentrations expressed as total estrogenicity (E2 equivalent concentrations) were contrasted to a key estrogenic response (i.e., intersex) in rainbow darter (Etheostoma caeruleum), a wild sentinel fish species. A predicted total estrogenicity in the river of ≥10 ng/L E2 equivalents was associated with high intersex incidence and severity, whereas concentrations <0.1 ng/L E2 equivalents were associated with minimal intersex expression. Exposure to a predicted river concentration of 0.4 ng/L E2 equivalents, the environmental quality standard (EQS) proposed by the European Union for estradiol, was associated with 34% (95% CI:30-38) intersex incidence and a very low severity score of 0.6 (95% CI:0.5-0.7). This exposure is not predicted to cause adverse effects in rainbow darter. The analyses completed in this study were only based on the predicted presence of three major estrogens (E1, E2, EE2), so caution must be exercised when interpreting the results. Nevertheless, this study illustrates the use of models for exposure assessment, especially when measured data are not available.

Returning to normal? Assessing transcriptome recovery over time in male rainbow darter (Etheostoma caeruleum) liver in response to wastewater-treatment plant upgrades

The present study measured hepatic transcriptome responses in male rainbow darter (Etheostoma caeruleum) exposed to 2 municipal wastewater-treatment plants (MWWTPs; Kitchener and Waterloo) over 4 fall seasons (2011-2014) in the Grand River (Ontario, Canada). The overall goal was to determine if upgrades at the Kitchener MWWTP (in 2012) resulted in transcriptome responses indicative of improved effluent quality. The number of differentially expressed probes in fish downstream of the Kitchener outfall (904-1223) remained comparable to that downstream of Waterloo (767-3867). Noteworthy was that year and the interaction of year and site explained variability in more than twice the number of transcripts than site alone, suggesting that year and the interaction of year and site had a greater effect on the transcriptome than site alone. Gene set enrichment analysis revealed a gradual reduction in the number of gene ontologies over time at exposure sites, which corresponded with lower contaminant load. Subnetwork enrichment analysis revealed that there were noticeable shifts in the cell pathways differently expressed in the liver preupgrade and postupgrade. The dominant pathways altered preupgrade were related to genetic modifications and cell division, whereas postupgrade they were associated with the immune system, reproduction, and biochemical responses. Molecular pathways were dynamic over time, and following the upgrades, there was little evidence that gene expression profiles in fish collected from high-impact sites postupgrade were more similar to those in fish collected from reference site. Environ Toxicol Chem 2017;36:2108-2122. © 2017 SETAC.

Severe intersex is predictive of poor fertilization success in populations of rainbow darter (Etheostoma caeruleum)

Municipal wastewater effluent (MWWE) contains emerging contaminants such as pharmaceuticals and personal care products (PPCPs) that have estrogenic properties. PPCPs are thought to be responsible for feminization of male fish in heavily urbanized areas around the globe. While many observations of feminized male fish have been made, the impact of feminization on reproductive success is not well understood. To address this lack of knowledge of the impacts of feminization, we examined the reproductive fitness of rainbow darter (Etheostoma caeruleum), a fish that is also known to have been feminized in some reaches of the Grand River, Kitchener-Waterloo, Ontario, Canada. In order to assess their reproductive health, somatic indices, gonadal steroid production, fecundity, and histological severity of intersex were measured in male rainbow darter collected through an urban gradient. Reproductive fitness was assessed by stripping milt and eggs from wild spawning fish, fertilizing eggs manually, and rearing embryos to hatch. The fertilization success and survival of embryos to hatch were compared among sites. In this study, it was found that rainbow darter collected at sites near a large municipal wastewater treatment plant (MWWTP) had decreased gonad size, increased severity of intersex, and decreased androgen production relative to other sites. Fish collected near the largest MWWTP also had lower fertilization success and survival to hatch. In contrast, fish collected near a second MWWTP farther upstream had comparable fertilization success, but lower survival to hatch relative to the upstream rural reference site. Intersex severity was negatively correlated with fertilization success, but not survival to hatch, suggesting that intersex is a good indicator of a population's fertilization success. Further investigation is required in order to determine if feminization will impact the sustainability of wild populations of fish.

Part A

Municipal wastewater effluents (MWWEs) contain anthropogenic substances that can exhibit endocrine-disrupting activity. These complex mixtures have been observed to exert adverse effects on fish. Rainbow darter (Etheostoma caeruleum, RBD) is a small benthic fish that is widespread throughout the Grand River, Ontario, Canada, and has been previously shown to be adversely affected by MWWE exposure in this watershed. The objectives of this study were to quantify biological responses in this sentinel species and intersex severity in male fish, in relation to the area of urbanization. It focused on RBD populations adjacent to wastewater outfalls in the Grand River watershed. In May 2011, nine sites across the urban gradient were selected to evaluate the impact of MWWEs. Endpoints for energy storage (i.e. condition factor, k; liversomatic index, LSI) as well as reproductive endpoints (i.e. gonadosomatic index, GSI; gonad development, hormone production), and intersex were assessed in the fish. Rainbow darter showed a high incidence of intersex downstream of the wastewater outfalls, especially below the largest treatment plant outfall at Kitchener (∼85%). We applied an intersex index (score from 0 to 7) that considers the number of eggs within the testis and the stage of maturation of the egg. RBD exposed downstream of the largest wastewater outfall at Kitchener had a score of 3.81±0.37 compared to upstream to the urban areas where there were no intersex males found other than a single individual with a score 1 (average intersex score of site 0.06±0.06). In addition, several fish associated with the Kitchener outfall had macroscopic vitellogenic eggs in the testes (intersex scores 5 and 6). The sub-population of fish located at the wastewater outfall also showed a tendency towards skewed sex ratios (greater proportion of females to male fish) compared to the population at the reference sites. Male fish inhabiting the urbanized area of the Grand River also showed reduced levels of testosterone (T) and 11-ketotestosterone (11KT). Intersex males had the lower levels of 11KT relative to the upstream reference fish but could not be distinguished from normal males collected at the exposed sites. Despite the high levels of intersex at these sites, no relationships were evident among intersex severity and other measured endpoints such as GSI, LSI or in vitro steroid production. The effects observed appear to be associated with urbanization and exposure to treated MWWEs in the watershed. Although intersex incidence and severity was a very good indicator of wastewater exposure, intersex could not be directly linked to other effects in this wild population. The effects of MWWEs on transcriptional changes in adult RBD exposed to the effluents are reported in the corresponding report (Part B).

Molecular signatures in rainbow darter (Etheostoma caeruleum) inhabiting an urbanized river reach receiving wastewater effluents

Rainbow darter (Etheostoma caeruleum) is a small benthic fish species found in North America that are abundant and distributed throughout the Grand River watershed, ON, Canada. Rainbow darter exhibit intersex in males at sites adjacent to municipal wastewater effluents (MWWE). In October 2010, female and male rainbow darter were collected at 3 sites (1 upstream reference and 2 downstream exposed sites) in the Grand River near the cities of Kitchener and Waterloo. The primary objectives of this research were (1) to characterize the responses of whole organism endpoints (i.e. condition factor (K), liversomatic (LSI) and gonadosomatic index (GSI), histopathology) to MWWEs and (2) to identify transcripts showing altered steady state abundance with exposure to MWWE in fish inhabiting municipal wastewater effluent-exposed areas. Genes measured in this study included vitellogenin, Sry-box containing protein 9 (sox9), forkhead box L2 (foxl2), doublesex and mab-3 related transcription factor 1 (dmrt1), cytochrome P450, family 11, subfamily A, polypeptide 1 (cyp11a) as well as estrogen (esr1, esrb) and androgen (ar) receptors. There were no changes in condition factor; however, there was a significant increase in LSI and a decrease in GSI in fish inhabiting downstream environments when compared with fish collected from the reference site. Males had a high incidence (∼ 70%) of intersex in downstream sites; characterized by the presence of oocytes within the testis. In the gonad, there were sex specific differences for genes related to sexual differentiation; dmrt1 was only expressed in males whereas foxl2 and sox9 were highly expressed in females compared to males. Expression levels of ar and esr1 were higher in females than males. Conversely, esrb was not differentially expressed between sexes or among sites. There were no differences detected for the genes investigated within sex among sites. This study is the first to report on gene expression changes in the rainbow darter, with emphasis on the differences in transcript abundance between sexes and how these changes relate to exposures to MWWEs. Molecular approaches are being investigated for their potential application to field ecotoxicology, and molecular bioassays for relevant, sentinel species in environmental monitoring programs are required to better understand the impact of anthropogenic impacts on species at risk in river systems.