1. Institute of Environmental Protection, Guangdong Power Grid, Guangzhou, Guangdong 510080, P.R. China
2. Department of Obstetrics, The Sixth Affiliated Hospital of Sun Yat‑sen University, Guangzhou, Guangdong 510655, P.R. China
3. Department of Radiation Medicine, Guangdong Provincial Key Laboratory of Tropical Disease Research, School of Public Health, Southern Medical University, Guangzhou, Guangdong 510515, P.R. China