1. Swiss Federal Institute of Aquatic Science and Technology, Eawag, Ueberlandstrasse 133, P.O. Box 611, CH-8600 Duebendorf, Switzerland, Department of Biochemistry and Pharmacy, Åbo Akademi University, BioCity, Tykistökatu 6A, 20520 Turku, Finland, Division of Environmental and Applied Biology, College of Life Sciences, University of Dundee, Dundee DD1 4HN, Scotland, U.K., and Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland