Acknowledgments
The authors would appreciate the financial support to this study provided by MOST Project of China (no.2008BAC32B06) and NSFC of China (nos. 21076188,20836008, 20976158, 20990221, and 21076189), and the Key Innovation Team for Science and Technology of Zhejiang Province of China (2009R50047). They are sincerely grateful to Professor Jiang Guibin and Zhang Qinghua in Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing for providing us with sample pretreatment and analytical method.