1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland, ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zurich, Switzerland, and National Research Centre for Environmental Toxicology (EnTox), University of Queensland, 39 Kessels Rd, Brisbane, Qld 4108, Australia