1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, 8600 Dübendorf, Switzerland, Center for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science, 334 Nguyen Trai, Hanoi, Vietnam, and Institute for Mineralogy and Geochemistry, University of Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany