1. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, P. O. Box 2871, Beijing 100085, China, Department of Chemistry and Biochemistry, MSN 3E2, George Mason University, 4400 University Drive, Fairfax, Virginia 22030-4444, and Department of Plant and Soil Science, University of Massachusetts, Stockbridge Hall, 80 Campus Center Way, Amherst, Massachusetts 01003-9246