1. Institute for Tumor Biology-Cancer Research, University of Vienna, Borschkegasse 8a, A-1090 Vienna, Austria, Institut for Medical Microbiology and Hygiene, Faculty of Clinical Medicine, Mannheim, University Heidelberg, P.O. Box 100023, D-68167 Mannheim, Germany, U.S. Environmental Protection Agency, Genetic Toxicology Division, Research Triangle Park, North Carolina 27711, and Department of Environmental Hygiene, Tongij Medical University Wuhan, Wuhan, People's Republic of China