Comparative investigation on the effect of a herbicide on aquatic organisms in single species tests and aquatic microcosms

In the present investigation the effect of the herbicide isoproturon on freshwater and sediment organisms was comparatively investigated in single species tests and a microcosm study. In single species tests the photosynthesis inhibitor isoproturon affected the growth rate of algae. For Chlamydomonas rheinhardi the EC50; i.e. the concentration, where the growth rate is inhibited to 50 per cent, was observed at 40 mu g/l. The growth rate of the ciliate Tetrahymena pyriformis was slightly inhibited at 700 mu g/l, whereas other heterotrophic organisms (Daphnia magna and the nematode Caenorhabditis elegans) were not affected by isoproturon up to concentrations of 1000 mu g/l. In the microcosm study application of isoproturon to the microcosms up to a concentration of 90 mu g/l neither affected the abundance nor the community composition of the phytoplankton, the zooplankton and the sediment dwelling nematodes. However, there was a distinct effect on anaerobic microbial degradation activity in the sediment.