Low environmental levels of fluoxetine induce spawning and changes in endogenous estradiol levels in the zebra mussel Dreissena polymorpha

The pharmaceutical fluoxetine, a selective serotonin reuptake inhibitor (SSRI), is often detected in municipal wastewater treatment plant effluents and surface waters within the ng/l range. There is, however, insufficient research evaluating potential hazards of fluoxetine in aquatic organisms at environmentally relevant concentrations. Taking into account that several SSRIs (fluoxetine, fluvoxamine) act as spawning inducers in bivalves, this study aimed at investigating the effects of fluoxetine exposure in the zebra mussel (Dreissena polymorpha) by assessing its potential to induce spawning at environmentally relevant concentrations (20 and 200 ng/l), as well as alterations of endogenous levels of testosterone and estradiol. Histological analyses of female and male gonads showed a concentration dependent decrease of oocyte and spermatozoan density, with a reduction in the number of oocytes per follicle of 40–70%, and spermatozoan density of 21–25%, relative to controls, following exposure to 20 and 200 ng/l of fluoxetine for 6 days, respectively. There was also a significant increase (1.5-fold) in the endogenous level of esterified estradiol in organisms exposed to 200 ng/l fluoxetine. Overall, the study shows that exposure to low levels of fluoxetine may effectively induce gamete liberation in the zebra mussel as well as alter endogenous levels of estradiol, and evidences the need of further investigating the potential of fluoxetine to alter the endocrine system of molluscs at environmentally relevant concentrations.

► We studied effects of low fluoxetine levels on zebra mussel gonads and steroid levels.
► Fluoxetine decreases the number of gametes in female and male mussels.
► Fluoxetine increases the levels of esterified estradiol.
► Results indicate that fluoxetine at low levels induced spawning and steroid levels in mussels.