Long-Term Exposure to Environmental Concentrations of the Pharmaceutical Ethynylestradiol Causes Reproductive Failure in Fish

Abstract

Heightened concern over endocrine-disrupting chemicals is driven by the hypothesis that they could reduce reproductive success and affect wildlife populations, but there is little evidence for this expectation. The pharmaceutical ethynylestradiol (EE2) is a potent endocrine modulator and is present in the aquatic environment at biologically active concentrations. To investigate impacts on reproductive success and mechanisms of disruption, we exposed breeding populations (n = 12) of zebrafish (Danio rerio) over multiple generations to environmentally relevant concentrations of EE2. Life-long exposure to 5 ng/L EE2 in the F1 generation caused a 56% reduction in fecundity and complete population failure with no fertilization. Conversely, the same level of exposure for up to 40 days in mature adults in the parental F0 generation had no impact on reproductive success. Infertility in the F1 generation after life-long exposure to 5 ng/L EE2 was due to disturbed sexual differentiation, with males having no functional testes and either undifferentiated or inter-sex gonads. These F1 males also showed a reduced vitellogenic response when compared with F0 males, indicating an acclimation to EE2 exposure. Depuration studies found only a partial recovery in reproductive capacity after 5 months. Significantly, even though the F1 males lacked functional testes, they showed male-pattern reproductive behavior, inducing the spawning act and competing with healthy males to disrupt fertilization. Endocrine disruption is therefore likely to affect breeding dynamics and reproductive success in group-spawning fish. Our findings raise major concerns about the population-level impacts for wildlife of long-term exposure to low concentrations of estrogenic endocrine disruptors.

Multi-endpoint toxicities on Chinese rare minnow (Gobiocypris rarus) fed with different diets

“…However, significant induction of Vtg was only found in the males fed with pellet food for the adult fish of generation F0 in the present study. The observation was similar with the result reported by Nash et al (2004). It may be an acclimation to the long-term exposure.…”

“…Reproductive performance has been considered to be a key parameter affecting the stabilization of fish populations. In recent years, many studies have found that the reproductive success of fish has been impaired after exposed to different pollutants (Mills et al, 2003;Nash et al, 2004). Länge et al (2001) demonstrated that there was a general trend toward a decrease in spawning in fathead minnow after EE 2 long-term exposure at 0.2 and 1 ng L −1 .…”

Ecotoxicological aspects related to the presence of pharmaceuticals in the aquatic environment

“…Concentrations above 1 ng L −1 of EE2 also induced higher vitellogenin plasma lev-els in both males and females [149,150]. Nash et al [151] registered similar findings for zebrafish males by simply performing the assay with 0.5 ng L −1 of EE2. Life-long exposure of zebrafish to 5 ng L −1 of EE2 has led to reproductive failure due to the absence of sec-ondary male sex characteristics and normal testes [151].…”

Chronic exposure to environmental levels of tribromophenol impairs zebrafish reproduction

“…This is the first report to describe that the sex ratio in zebrafish is male biased in response to TBP exposure, and this observation suggests that long-term exposure to TBP affects sex differentiation and sex determination in zebrafish. Indeed, teleost populations exposed to estrogenic compounds showed skewing of the sex ratio in favor of females (Metcalfe et al, 2001;Lange et al, 2001;Nash et al, 2004;Zhong et al, 2005;Zha et al, 2008). The changes in sex ratios to femalebiased types are known to be caused by the transformation of the testis to ovaries under the direct influence of environmental estrogen during early gonadal development (Lange et al, 2001;Nash et al, 2004).…”

“…Indeed, teleost populations exposed to estrogenic compounds showed skewing of the sex ratio in favor of females (Metcalfe et al, 2001;Lange et al, 2001;Nash et al, 2004;Zhong et al, 2005;Zha et al, 2008). The changes in sex ratios to femalebiased types are known to be caused by the transformation of the testis to ovaries under the direct influence of environmental estrogen during early gonadal development (Lange et al, 2001;Nash et al, 2004). Therefore, the balance between estrogens and androgens is crucial for sex differentiation in fish; the inhibition of aromatase suppresses estrogen formation, thereby disturbing the normal sex ratio and resulting in a male-dominant population.…”