Exposure to SSRI-type antidepressants increases righting time in the marine snail Ilyanassa obsoleta.

Exposure to human antidepressants has been shown to disrupt locomotion and other foot-mediated mechanisms in aquatic snails. We tested the effect of three selective serotonin reuptake inhibitor (SSRI)- and one selective serotonin-norepinephrine reuptake inhibitor (SNRI)-type antidepressants on the righting response in the marine snail, Ilyanassa obsoleta. All four antidepressants (fluoxetine, sertraline, paroxetine, venlafaxine) significantly increased righting time compared with controls with an exposure time as short as 1 h. Dose responses were nonmonotonic with effects seen mainly at the lowest exposure concentrations and shortest duration. The lowest concentration to show an effect was 3.45 μg/L fluoxetine with a 2-h exposure period and is about 3.71 times higher than environmental concentrations. Our results highlight rapid disruption of another foot-mediated behavior in aquatic snails by SSRI-type antidepressants. We discuss these and other reported nonmonotonic dose responses caused by antidepressants in terms of the various possible physiological mechanisms of action in nontarget aquatic species.