1. School of Public Health, Xi’an Jiaotong University Health Science Center, Key Laboratory of Trace Elements and Endemic Diseases, National Health and Family Planning Commission, Xi’an, Shaanxi, 710061, P. R. China
2. Department of Occupational and Environmental Health, School of Public Health, Xi’an Jiaotong University Health Science Center, Xi’an, Shaanxi, 710061, P. R. China
3. Clinical Research Center for Endemic Disease of Shaanxi Province, The Second Affiliated Hospital of Xi’an Jiaotong University, No. 157 Xi Wu Road, Xi’an, Shaanxi Province, 710004, People's Republic of China
4. School of Nursing, Health Science Center, Xi’an Jiaotong University, Xi’an, 710061, China