pH-dependent toxicity of serotonin selective reuptake inhibitors in taxonomically diverse freshwater invertebrate species

Abstract

Serotonin selective reuptake inhibitors (SSRIs) are pollutants that influence behaviour, physiology and survival of freshwater animals. Factors influencing the sensitivity of freshwater invertebrates to these drugs must be understood in order to predict their effects on freshwater ecosystems. The toxicities of fluoxetine (Prozac), paroxetine (Paxil) and citalopram (Celexa), were tested in larval Aedes aegypti (Insecta, Diptera), Cypridopsis vidua (Crustacea, Ostracoda) and Hydra vulgaris (Cnidaria, Hydrozoa) across a broad range of ambient pH values. H. vulgaris were most sensitive, with minimal survival in the presence of drugs (1×10–5 molL–1) in all but acidic media, whereas A. aegypti larvae were least sensitive. In all species tested the drugs were toxic in neutral and alkaline media but showed minimal or no toxicity in acidic media, whereas citalopram and fluoxetine enhanced survival of C. vidua in pH 4 media. Increased toxicity in alkaline media supports the hypothesis that the ionisation states of the drugs influences their toxicity by effects on membrane permeability, whereas enhanced survival of C. vidua in acidic media in the presence of SSRIs suggests that serotonergic pathways may be involved in regulation of acid–base balance in this species.