In the light of climate change it is of importance to evaluate how temperature increase will influence the effects of chemicals. In this project first the chronic effects of PFOS will be assessed on aquatic invertebrates. After that the effect of temperature on this toxicity will be assessed by performing toxicity tests at different temperatures. When these experiments have been performed successfully, a mesocosm experiment will be performed to assess the effect of temperature and PFOS, as well as their interaction on aquatic ecosystems.