1. Department of Occupational and Environmental Health Sciences, School of Public Health, Peking University, Beijing, P. R. China;
2. Department of Environmental Health Sciences, Jonathan and Karin Fielding School of Public Health, University of California Los Angeles, Los Angeles, CA, USA;
3. Jinan Center for Disease Control and Prevention, Jinan, Shandong, P. R. China;
4. Beijing Municipal Institute of Labor Protection, Beijing, P. R. China;
5. Shandong Center for Disease Control and Prevention, Jinan, Shandong, P.R. China;
6. Zibo Prevention and Treatment Hospital for Occupation Diseases, Zibo, Shandong, P.R. China