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Mesocosm experiments in the approval procedure for pesticides 1 ObjectiveWhen evaluating the effects of pesticides on the aquatic environment, system level analyses (mesocosm experiments) are undertaken when lower tier tests (1) indicate a risk for effects in the emvironment, (2) to increase the confidence in the risk assessment, (3) to elucidate effects on organism interactions and (4) to quantify indirect effects of pesticides. When used for risk evaluation, the most important limitations of mesocosm experiments are the lack of a standardised design and ambiguous interpretation of results. The primary objective of mesocosm investigations is to demonstrate whether a given pesticide is toxic or not under near-natural conditions. Based on a critical analysis of already published results of mesocosm experiments, the objective of the present project is to elaborate guidance for evaluating mesocosms in connection with the approval procedure. |