1. Department of Occupational Health and Environmental Health, School of Public Health, Guangxi Medical University, Nanning, P.R. China
2. Department of Social Medicine, School of Public Health, Guangxi Medical University, Nanning, P.R. China
3. Department of Toxicology, School of Public Health, Guangxi Medical University, Nanning, P.R. China
4. Department of Epidemiology and Biostatistics, School of Public Health, Guangxi Medical University, Nanning, P.R. China