Residue detection and degradation of thiamethoxam in paddy soil and rice

Thiamethoxam is commonly used to control rice planthoppers, leafhoppers and other pests. In order to study its residue dynamic, a method for the analysis of thiamethoxam residues in paddy soil and rice was established by high performance liquid chromatography(HPLC), and the method was used to detect the thiamethoxam in paddy soil and rice in Kaiyang, Huangping and Tongzi(Guizhou province). Results showed that within the range of 0.05~10.00 mg/L, it had good linear relationship between the peak area and mass concentration of thiamethoxam, and the linear correlation coefficient for thiamethoxam was 0.9994. The detection limit of thiamethoxam was 1.0 ×10-10g, and the lowest concentration detected was 0.004 mg/kg in paddy soil, 0.001 mg/kg in rice straw, 0.003 mg/kg in brown rice, and 0.003 mg/kg in chaff. On addition level of 0.1 ~1.0 mg/kg range, the recovery of thiamethoxam for paddy soil and rice was 90.97% ~100.32% and 88.96% ~100.32% respectively, and relative standard deviation(RSD) was 1.77% ~2.93% and 0.57% ~3.05% respectively. The degradation research of thiamethoxam in paddy soil and rice suggested that their degradation curves accorded with the first-order kinetics equation. Thiamethoxam degraded fast in rice plant, and the half-life of thiamethoxam in rice plant was 1.73 ~2.14 d. Thiamethoxam degraded more slow in paddy soil than in rice plant. Their half-life of thiamethoxam in paddy soil was 2.79~ 3.03 d. It was indicated that the thiamethoxam degraded easily in paddy soil and rice.