1. Key Laboratory; National Institute for Occupational Health and Poison Control, Chinese Center for Disease Control and Prevention; Beijing 100050 China
2. Occupational and Environmental Epidemiology Branch; National Cancer Institute; Rockville Maryland
3. Department of Toxicology School of Public Health; Hebei Medical University; Shijiazhuang China
4. Jiao Zuo Center for Disease Control and Prevention; Jiaozuo China
5. Division of Environmental Epidemiology; Institute for Risk Assessment Sciences, Utrecht University; Utrecht the Netherlands
6. Henan Provincial Institute for Occupational Health; Zhengzhou China