Abstract
Four drugs, erythromycin, fluoxetine, naproxen and gemfibrozil, belonging to different therapeutic classes, were chosen to examine their toxicity to selected plankton organisms from different trophic levels: algae (Chlorella vulgaris and Ankestrodesmus falcatus), protozoa (Paramecium caudatum), rotifera (Brachionus calyciflorus) and cladocera (Daphnia longispina). LC50 values for three of the drugs were between 12 and 82 mg l(-1), with algae and protozoans being most sensitive. Fluoxetine showed LC50 values between 40 and 830 mu g l(-1), algae again being most sensitive. The lower test concentrations of fluoxetine enhanced the growth rates of both B. calyciflorus and D. longispina. Even at low test concentrations, erythromycin decreased the growth rates of all the tested organisms. Paramecium caudatum was the species most sensitive to naproxen exposure. After 24 h, gemfibrozil had the least effect on all tested organisms. All the surviving tested organisms underwent oxidative stress to different degrees as a result of drug exposure. The activity of the antioxidant enzymes superoxide dismutase and catalase was reduced, and lipid peroxidation levels were elevated in all tested species after exposure, compared to their levels in the control group. Although the test concentrations were above those commonly found in the environment, the occurrence of sublethal effects at all test concentrations suggests that the potential risk for non- target organisms warrants further investigation.