1. College of Environmental Science and Engineering, Hunan University, Changsha 410082, P. R. China
2. Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, P. R. China
3. School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, P. R. China
4. Department of Pharmacy, National University of Singapore, S9, 4 Science Drive 2, Singapore 117544, Singapore