National Natural Science Foundation of China [21007014, 21107024]; Start Foundation of Hunan Agricultural University [10YJ01]; National Science and Technology Major Projects [2009ZX07212-001-05]; National Environmental Protection Public Welfare Program [201009047]; Key Laboratory of Production Environment; Agro-product Safety of Ministry of Agriculture, Tianjin Key Laboratory of Agro-environment and Food Safety [2010-KJ-KF-03]; Scientific Research Fund of Hunan Provincial Education Department [11C0650]