Biological impacts of pesticides in freshwater courses

Abstract

The current knowledge about the biological impacts of pesticides in water courses is at first linked to assessment tools. They include single species bioassays, which provide most of the ecotoxicological data used in products registration, and more complex approaches, like micro or mesocosms and field studies. Among other uses, single species data are used in many industrialised countries for media quality criteria development. Then, simple comparisons of monitoring results with these criteria will allow to draw a first quality diagnosis, which is in fact similar to a rough risk estimate for the receiving ecosystem. More quantitative assessments are also possible at various geographic scales, by comparing bioassays results and monitored concentrations respective distributions. In this context, effect assessments solely relying on single species bioassays raise many methodological issues, including the relevance of exposure conditions in bioassays, as compared to those in rivers. Furthermore, pesticides are assessed separately, while the current situation in water courses involves mixtures, not only pesticides. Moreover, available effect assessment methods (i.e. bioassays and other tools) do not allow to describe several types of sublethal effects, which are potentially dangerous for ecosystem reliability. It is thus rather difficult to draw an exhaustive picture of biological impacts of pesticides in water courses. Methodological improvements are desirable in various domains, including exposure conditions (scenarios), toxicity mechanisms (also at low concentrations levels) and interactions between chemicals.