Four drugs belonging to different therapeutic classes were chosen to examine their toxicity on some plankton organisms of different trophic levels. They include algae (Chlorella vulgaris and Ankestrodesmus falcatus), protozoa (Paramecium caudatum), rotifers (Brachionus calyciflorus) and cladocerans (Daphnia longispina). The tested drugs are erythromycin (antibiotic), fluoxetine (antidepressant), naproxen (a nonsteroidal anti-inflammatory) and gemfibrozil (lipid regulator). Algae were found to be more sensitive than other tested species to all tested drugs. The antibiotic erythromycin seriously affected the tested organisms even at low concentrations causing remarkable drop in their growth rates compared to the Control of each species. The acute exposure to fluoxetine during the present experiment exerted dramatic effect on both tested algae, with average LC50 values of 36 and 40 µg l-1for A. falcatus and C. vulgaris, respectively. On the contrary, fluoxetine enhanced the growth rates for both B. calyciflorus and D. longispina at low concentrations. P. caudatum was the most sensitive species to naproxen exposure, recording the lowest average LC50 value of 36 mg l-1 among the tested species after 24 h. Gemfibrozil had the least effect on the tested aquatic organisms with average LC50 values ranging between a minimum value of 56 mg l-1recorded for A. falcatus and 78 mg l-1 for B. calyciflorus. All the tested organisms suffered from oxidative stress in different degrees as a result of drug exposure. Our results showed reduction in the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) activities and elevation in lipid peroxidation (TBARS) levels in all tested species after exposure when compared with their activities in the control group. The results presented in this study suggest that the drugs investigated have toxic effects on the aquatic organisms tested. We concluded that there is a potential risk for non-target organisms associated with low levels of pharmaceuticals in surface waters. Chronic responses of non-target biota are not fully expected. Therefore, safe ways of discarding drug residues should be developed in order to protect the aquatic fauna.
Key words: Catalase, lipid peroxidation, algae, zooplankton, pharmaceuticals.
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