1. Institute of Environmental and Occupational Toxicology, Casella Postale 108, 6780 Airolo, Switzerland, Walther-Straub-Institut fuer Pharmakologie und Toxikologie, Ludwig-Maximilians-Universitaet Muenchen, 80336 Muenchen, Germany, Department of Environmental and Occupational Medicine, The Medical School, University of Newcastle upon Tyne, Newcastle Upon Tyne, United Kingdom, and Chinese Academy of Preventive Medicine, Nan Wei Road 29, Beijing 100050, People's Republic of China