1. Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80177, 3508 TD Utrecht, The Netherlands, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, P.O. Box 611, 8600 Dübendorf, Switzerland, ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, CHN G50.3, Universitätstrasse 16, 8092 Zürich, Switzerland, and The University of Queensland, National Research Centre for Environmental Toxicology (Entox), 39 Kessels Road, Coopers Plain QLD 4108, Australia