1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland
2. Department of Civil, Environmental and Geomatic Engineering, ETH Zürich, Stefano-Franscini-Platz 5, 8093 Zürich, Switzerland
3. School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.