Behavioral responses of adult male and female fathead minnows to a model estrogenic effluent and its effects on exposure regime and reproductive success

Independent and synergistic effects of microplastics and endocrine-disrupting chemicals on the reproductive social behavior of fathead minnows (Pimephales promelas)

Microplastics (MPs) have become an environmental concern in recent years, with most research focused on the physiological effects of exposure. Comparatively little consideration has been given to the potential behavioral impacts of exposure, which may also have fitness consequences for individuals. Moreover, MPs can serve as vectors for endocrine-disrupting chemicals and other locally co-occurring contaminants known to impair behavioral responses. This project aimed to determine whether MPs alone or in association with a common environmental EDC (17-alpha ethinyl estradiol; EE2) alter reproductive behavior and decision-making in fish. Male and female fathead minnows (Pimephales promelas) were exposed to MPs associated with either a low (10 ng/L; MPEE2 10) or high (50 ng/L, MPEE2 50) concentration of EE2, or MPs without EE2 (MPvirgin) for 30 days via a dietary feeding protocol. Behavioral trials were conducted on Day 31 to determine the effects of exposure on male-female social interactions. The expression of male sexually selected traits, including courtship, was unaffected by exposure. However, non-exposed females in all treatment groups trended toward discrimination against exposed males, which reached statistical significance for the MPEE2 50 group. Female fish exposed to MPs, alone or in association with EE2, were equally likely to approach and associate with non-exposed and exposed males. The results from this study suggest that MPs may alter social behavior in fishes and that the behavioral impacts of exposure may be more strongly pronounced in females than males. Such individual-level changes in fitness have the potential to impact population size, with downstream effects on the broader aquatic community.

Impact of Long-Term Exposure to 17α-Ethinylestradiol in the Live-Bearing Fish Heterandria formosa

17α-ethinylestradiol (EE2) is a potent synthetic estrogen that is routinely detected in aquatic ecosystems and exhibits estrogenic activity. Acute and chronic toxicity have been described for oviparous and ovoviviparous fish species; however, no information is available on the impacts of EE2 on viviparous, matrotrophic fish despite their ecological importance. The present study investigated the consequences of long-term EE2 exposure in the least killifish (Heterandria formosa). Effects on growth, time-to-sexual maturity, fecundity, and offspring survival were examined in an 8-month, life-cycle experiment. Starting as 0-6-day-old fish, least killifish were continuously exposed to EE2 at nominal concentrations of 0, 5, or 25 ng/L (measured concentrations averaged 0, 4.3, and 21.5 ng/L respectively). In the F0 generation, EE2-exposure did not affect survival but resulted in increased time-to-sexual maturity and a sex-dependent effect on size; female standard length was reduced while male standard length was increased. This caused the ordinarily larger females and smaller males to become more similar in size. Condition factor was reduced for both sexes. Fecundity was reduced by 50% and 75% at 5 and 25 ng/L EE2-exposure respectively. Continued EE2-exposure in the F1 generation resulted in significantly reduced survival. These results suggest that despite their matrotrophic development, these fish experience delayed development and reduced reproductive success from EE2-exposure and that effects appear to intensify in the second generation.

Temporal evaluation of estrogenic endocrine disruption markers in smallmouth bass (Micropterus dolomieu) reveals seasonal variability in intersex

A reconnaissance project completed in 2009 identified intersex and elevated plasma vitellogenin in male smallmouth bass inhabiting the Missisquoi River, VT. In an attempt to identify the presence and seasonality of putative endocrine disrupting chemicals or other factors associated with these observations, a comprehensive reevaluation was conducted between September 2012 and June 2014. Here, we collected smallmouth bass from three physically partitioned reaches along the river to measure biomarkers of estrogenic endocrine disruption in smallmouth bass. In addition, polar organic chemical integrative samples (POCIS) were deployed to identify specific chemicals associated with biological observations. We did not observe biological differences across reaches indicating the absence of clear point source contributions to the observation of intersex. Interestingly, intersex prevalence and severity decreased in a stepwise manner over the timespan of the project. Intersex decreased from 92.8% to 28.1%. The only significant predictor of intersex prevalence was year of capture, based on logistic regression analysis. The mixed model of fish length and year-of-capture best predicted intersex severity. Intersex severity was also significantly different across late summer and early spring collections indicating seasonal changes in this metric. Plasma vitellogenin and liver vitellogenin Aa transcript abundance in males did not indicate exposure to estrogenic endocrine disrupting chemicals at any of the four sample collections. Analysis of chemicals captured by the POCIS as well as results of screening discrete water samples or POCIS extracts did not indicate the contribution of appreciable estrogenic chemicals. It is possible that unreported changes in land-use activity have ameliorated the problem, and our observations indicate recovery. Regardless, this work clearly emphasizes that single, snap shot sampling for intersex may not yield representative data given that the manifestation of this condition within a population can change dramatically over time.

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.

Biological response of high-back crucian carp (Carassius auratus) during different life stages to wastewater treatment plant effluent

This study presents the adverse effects of endocrine disrupting chemicals (EDCs) in effluent of wastewater treatment plants (WwTPs) on fish health. A study of chronic exposure to WwTPs effluent for 10 months was undertaken in high-back crucian carp (Carassius auratus) during different life stages, covering early-life-stage (ELS), prespawning period, and postspawning period. Condition factor (CF), gonadosomatic index (GSI), hepatosomatic index (HSI), and plasma vitellogenin (VTG) levels were employed as indicators to assess biological effects of effluent on this gynogenesis species. Meanwhile, some high-back crucian carp were caged in Demonstration Base of Biological Purification for Filter-feeding Fish (hereinafter, Demonstration Base), as WwTPs effluent exposure controls. In the meantime, a depuration study was carried out to determine whether or not the estrogenic effects caused by effluent exposure could be reduced after moving fish into EDCs-free water. CF, HSI, GSI, and plasma Vtg levels of high-back crucian carp caged in Demonstration Base were generally in accordance with seasonal change. Effluent exposure inhibited gonadal growth, reducing GSI in ELS while increasing it around spawning, sharpened liver burdens, increasing HSI, and induced abnormal Vtg expression in juvenile high-back crucian carp, augmenting Vtg concentrations in plasma. Around spawning period, Vtg in high-back crucian carp were mainly induced by endogenous estrogens, and EDCs in effluent had less influence on them. Staying in EDCs-free water for 30 days made high-back crucian carp recover from effects of previous effluent exposure, relieving inhibition of gonadal development and hypertrophy of liver as well as reducing Vtg induced by EDCs in effluent. The results revealed that high-back crucian carp in ELS are more sensitive to WwTPs effluent exposure. Additionally, the depuration study showed a clearance of the estrogenic effects caused by effluent.

Impact of organic carbon on the biodegradation of estrone in mixed culture systems

The effects of organic carbon concentrations and loading on the degradation of estrone (E1) were examined under various conditions in batch reactors and membrane-coupled bioreactors (MBRs). Experiments examined effects on individual microorganisms (substrate competition and growth) and on the whole community (selection). Substrate competition with organic carbon (competitive inhibition and catabolic repression) was not a factor in E1 degradation (P = 0.19 and 0.29 for two different analyses). Conversely, addition of organic carbon increased E1 degradation rates, attributable to biomass growth in feast-famine reactors over a five-day period (P = 0.016). Subsequently, however, community dynamics controlled E1 degradation rates, with other organisms outcompeting E1 degraders. More moderate but sustained increases in E1 degradation rates were observed under starvation conditions. Low influent organic carbon strength was detrimental to E1 degradation in MBRs, where organic carbon concentration and loading were decoupled (P = 0.018). These results point to the importance of multiple substrate utilizers in E1 degradation. They also suggest that while initial growth of biomass depends on the presence of sufficient organic carbon, further enrichment under starvation conditions may improve E1 degradation capability via the growth and/or stimulation of multiple substrate utilizers rather than heterotrophs characterized by an r-strategist growth regime.

Impairments in aromatase expression, reproductive behavior, and sperm quality of male fish exposed to 17β-estradiol

Growing evidence shows that environmental estrogen can reach levels that are high enough to exert adverse reproductive effects on wild fish populations. The authors report different parameters of male reproductive behavior, brain, and gonadal aromatase expression, as well as sperm quality in an internally fertilizing fish species (Jenynsia multidentata, Jenyns) exposed to environmentally relevant concentrations of 17β-estradiol (E(2) ). Adult males were exposed to 0, 50, 100, and 250 ng/L E(2) over 28 d. The authors' findings demonstrate that E(2) exposure resulted in a very clear increase in brain aromatase transcript abundance at all assayed concentrations compared with control; however, no effects on gonadal aromatase expression were observed. Behavioral measures revealed increased sexual activity at 50 ng/L but not 100 or 250 ng/L E(2) . In contrast to the molecular and behavioral responses, the condition factor, gonadosomatic index, and sperm quality were unaltered by E(2) exposure. The results from the present work suggest that E(2) affects some aspects of the reproductive biology of J. multidentata. These modifications in the reproductive biology caused by exposure to E(2) could potentially lead to long-term effects at population levels that may not always be immediately evident. To the best of the authors' knowledge, this is the first report on the combined effect of E(2) on aromatase expression, sexual behavior, and sperm parameters in fish.