Effects of antidepressant drug pollution on molluscs

Abstract

There are growing concerns molluscs may be more vulnerable to the effects of antidepressant drug pollution than any other animal phylum as a multitude of key physiological processes are regulated by monoamines, the target of antidepressants, in molluscs. However, target-mediated effects of different classes of antidepressants at environmental levels in molluscs remain to be understood as currently existing studies have largely focused on effects of concentrations that are not environmentally relevant. Moreover, the effects of antidepressants on overarching physiological processes such as feeding and reproductive behaviours (shell mounting and intromission) have not been reported in any molluscan species in addition to the absence of report on the effects of two major classes of antidepressant drugs on fecundity in molluscs. Furthermore, according to the read-across hypothesis, pharmacological responses (target-mediated effects) of a pharmaceutical would occur in an organism in which the drug targets are conserved if the plasma concentrations of the pharmaceutical approaches its human therapeutic plasma concentration. Despite this, hemolymph levels of antidepressants have not also been reported in any molluscan species. To address this critical knowledge gap, a systematic review of the literature was conducted; and the effects and hemolymph levels of environmentally relevant concentrations of widely prescribed antidepressant drugs (3 classes) including amitriptyline (10, 100, 500 and 1000 ng/L), fluoxetine (10, 100 and 500 ng/L) and venlafaxine (0.5, 1, 2, 4 and 55 μg/L) in the freshwater mollusc, Biomphalaria glabrata, were investigated over a period of 28 days. The endpoints included feeding, reproduction (fecundity), growth, substrate attachment, spatial distribution, shell mounting and intromission. Feeding and reproduction were disrupted at particularly low hemolymph levels of antidepressants (with venlafaxine being the least potent), while the systematic review reveals that immunosuppression is a major target-mediated effect of antidepressants in molluscs. The study provides novel critical data relevant to regulatory decision-making and future research direction.