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(366) Predicting risks of toxicants in freshwater ecosystems: Linking laboratory and mesocosm observations to protection targets. Brock, Theo 1, Heimbach, Fred2, Van den Brink, Paul1, 1 2 ABSTRACT- The current approach for cost-effective risk assessment of contaminants in freshwater ecosystems faces two important questions, viz.: 1) To what extent is it possible to extrapolate results of standardised and additional laboratory single species toxicity tests to the field? 2) When setting environmental quality standards on basis of these tests, should these standards be similar for freshwater ecosystems that differ in structure, functioning and functionality? This paper addresses these questions by presenting results of single-species and mesocosm experiments performed with herbicides that differ in toxic mode of action and persistence in the aquatic environment. The herbicides evaluated include photosynthesis-inhibitors (e.g. linuron, metamitron) and the auxin-simulator 2,4-D. In addition, concepts are discussed that may be used to evaluate the acceptability of potential toxic effects in different types of ecosystem. These concepts include the stress prevention principle, the carrying capacity principle and the functional redundancy principle. The significance of laboratory single species tests in predicting direct toxic effects depends on factors like toxic mode of action and exposure regime of the chemical, and on laboratory test species selected and number of toxicity data available. In addition, to predict indirect effects and recovery also requires information on life-histories, ecophysiology and ecological role (functional groups) of affected populations. Furthermore, in order to link laboratory and mesocosm observations and/or model predictions to protection targets, we need clear reference and target images of the different types of freshwater ecosystem potentially at risk. Key words: single species tests, mesocosms, water quality standards, protection targets |
