1. Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Sciences, ETH Zurich, CHN F23.2, CH-8092 Zurich, Switzerland, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland, Department of Civil Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh, and Department of Civil Engineering, Dhaka University of Engineering and Technology, Dhaka 1700, Bangladesh