Polluting antidepressants are more potent in high-pH systems

Posted on December 13, 2016

The increased use of antidepressants in society means that the pollution of freshwater systems by SSRIs (serotonin selective reuptake inhibitors) is becoming more prevalent. SSRIs persist in the environment, bioaccumulate in animals, influence a wide range of physiological and behavioural processes and are toxic at high concentrations. Although it’s been established that SSRI toxicity is affected by environmental pH, little is known about the relative sensitivity of different animal groups. In laboratory experiments, researchers compared the responses of an insect species (the mosquito Aedes aegypti), a seed shrimp (Cypridopsis vidua) and a cnidarian (Hydra vulgaris) to water at different levels of pH between 3 and 12 over a three-day period. The animals were then exposed either to different drug treatments (by adding citalopram, paroxetine or fluoxetine to the water), or to control treatments, in which no drugs were added. Then they were monitored for another three days at 25oC. Although the test species varied in their responses to the drugs, in all three cases survival was significantly affected by the interaction between drug application and pH, and for almost all drug-species combinations, the survival rates of control animals were significantly higher than those of treatment animals. Toxicity increased with pH, survival being low or zero under neutral and alkaline conditions. Hydra vulgaris was the most sensitive species, probably because it lacks an external skeleton and relies on direct diffusion of gases between its cells and the surrounding water. It seems that SSRIs, at concentrations similar to those recorded in the environment, can eliminate sensitive freshwater species under alkaline conditions.

Reference: Sundaram, R. et al. 2015. pH-dependent toxicity of serotonin selective
reuptake inhibitors in taxonomically diverse
freshwater invertebrate species. Marine and Freshwater Research 66, 518–525. http://www.publish.csiro.au/mf/pdf/MF14015