Background, aims and scope: In view of the limited amount of information on the potential hazard of the ever increasing amounts of drugs in surface waters to aquatic biota, a study was undertaken to determine the effect levels of 28 selected pharmaceuticals to the crustacean test species Thamnocephalus platyurus. The drugs belong to 5 different groups: non steroidal anti-inflammatory agents, biocides, cardiovascular compounds, nervous system drugs and pu rine alkaloids
Methods: Toxicity tests were carried out with the 1h Rapidtoxkit and the 24h Thamnotoxkit microbiotests in order to make a comparison of sublethal effects (visible as stress through absence of feeding) measured after a very short time of exposure (1h) and lethal effects after prolonged exposure (24h). Dilution series starting at 200 mg l(-1) were prepared and applied, and median effects levels were calculated and transformed into Toxic Units (TU) for easy data comparison.
Results and discussion: The toxic effects found have been ranked into 4 arbitrary toxicity classes: not toxic (TU<0.2), low toxicity (0.2<TU<1.0), toxic (1.0<TU<10) and very toxic (TU>10). The toxicity levels noted ranged from virtually no effects for a few of the pharmaceuticals, at the highest concentration tested out, to LC50's below 1 mg l(-1) (>100 TU) for 3 nervous system drugs (Amitryptiline, Thioridazine and Chlorpromazine). According to the toxicity classification, 17 of the 28 compounds (i.e. 67%), belong to the same class for the lethal and the sublethal tests. More pronounced differences in effect levels between the two assays were observed mainly for the pharmaceuticals which were either not toxic or only slightly toxic at the 200 mg l(-1) level. For 90% of the toxic drugs the ratio between the toxicity values for both tests is below 5.
Conclusion: An overall correlation coefficient of 0.96 was found between the 2 microbiotests, confirming the good predictive potential of the 1h stress-based Rapidtoxkit in revealing important biological effects (mortality) after more prolonged exposure of the crustacean test species to chemical compounds.
Recommendation and outlook: The present study clearly shows that new microbiotests such as the 1h Rapidtoxkit and the 24h Thamnotoxkit are attractive tools for rapid cost-effective screening of 'new' pollutants such as drugs which may threaten the biological communities of the aquatic environment.