1. Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Sciences, ETH Zurich, CHN, CH-8092 Zurich, Switzerland, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Ueberlandstrasse 133, CH-8600 Dübendorf, Switzerland, and Department of Civil Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh