Ecological risk assessment: risk for what? How do we decide?

Ecological risk assessment is defined both in theory and in practice. To do it properly, we need to know what targets we are protecting, but these targets are not always obvious and clearly defined. The pragmatic approach, used most generally in the context of environmental protection legislation, is the risk quotient method. Two other approaches involving more transparency and ecological relevance are critically assessed. One is based on species sensitivity distributions; the other is based on generalized population dynamics. Challenges for the future are considered.