1. Laboratory of Organic Geochemistry (LOG), Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan, Water Quality Team, Water Environment Research Group, Public Works Research Institute, 1-6 minamihara, Tsukuba, Ibaraki 305-8516, Japan, and Department of Urban Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan