1. School of Chemical and Biological Engineering, College of Engineering, Seoul National University, San 56-1, Sillim-dong, Gwanak-gu, Seoul 151-742, Korea, Swiss Federal Institute for Aquatic Science and Technology, EAWAG, 8600 Dübendorf, Switzerland, Chemical Analysis Department, DVGW-Water Technology Center (TZW), Karlsruher Str. 84, 76139 Karlsruhe, Germany, and Institute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland