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Mesocosm experiments in the approval procedure for pesticides ForewordExisting knowledge indicates that agriculture can contribute to deterioration of water quality through the release of pesticides into surface water either directly by wind drift or indirectly through runoff. To evaluate the potential hazard of various pesticides to aquatic life several approaches are available to managers and regulatory authorities. For "problematic" pesticides extended risk evaluations often are based on tests carried out under near-natural conditions in mesocosms. However, the most important limitations of mesocosm experiments are the lack of a standardised design and ambiguous interpretation of results. This report is intended to provide guidance to managers how to interpret results from mesocosm studies and in specific to identify "good" experiments encompassing sensitive organismic groups, presence of sediment and macrophytes etc. The guidance was developed from a critical analysis of already published results of mesocosm experiments. In addition to analysis of sensitivities of different taxonomic groups and comparison of effects in mesocosms to extrapolated hazard concentrations the influences of mesocosm size, location (latitude) and season were quantified. The main results are summarised in chapter 8 and the appendices provide detailed information on the mesocosm experiments included in the analysis.
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