Aquatic ecotoxicology: On the problems of extrapolation from laboratory experiments with individuals and populations to community effects in the field

Abstract 1. 1. Ecotoxicology is defined as the study of the effect of toxicants on structure and function of ecosystems. 2. 2. Properties of individuals and populations in laboratory experiments differ from those in the field with respect to distribution in space and time as well as to genetic structure. 3. 3. Studies of community response can only be extrapolated to other systems if they include the analysis of the causal chain. 4. 4. Causal explanations require a system analysis at different trophic levels as well as a modelling of the system and an analysis of sensitivity. 5. 5. A research project is presented which covers most of the suggested problems.