1. Department of Environmental Medicine, Institute of Community Medicine, and Master's Program in Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan, Analytical Instruments Division, JEOL Ltd., 3-1-1 Musashino, Akishima, Tokyo 196, Japan, and First Department of Internal Medicine, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kyoto 602, Japan