1. College of Environment and Resource, Research Center of Environment and Health, Shanxi University, Taiyuan, Shanxi 030006, P. R. China
2. Department of Environmental Health, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi 030001, P. R. China
3. Key Laboratory of Coal Environmental Pathogenicity and Prevention (Shanxi Medical University), Ministry of Education, Taiyuan, Shanxi 030001, P. R. China