Analysis on Residues and Dissipation Dynamics of Thiamethoxam in Wheat and Soil under Field Conditions

To assess the safety of thiamethoxam in wheat and soil,and provide an important scientific basis for the rational use of the pesticides in the wheat,the issipation dynamics and residues of thiamethoxam in wheat grains,wheat plant and soil was investigated under field conditions.The thiamethoxam was determined by HPLC-UVD,and risk assessment was conducted by dietary intake of thiamethoxam residue in Wheat.The results showed,fortified recoveries of thiamethoxam in wheat grains,wheat plant and soil at 0.01~1.0mg·kg-1 were 79.62%~94.70%,with the relative standard deviation of 0.91%~6.56%,the limit of detection of the analytical method was 5.0×10-8g at a signal-to-noise ratio of 3,and the limit of quantification were 0.01mg·kg-1 in wheat grains,wheat plant and soil.The residue analysis method was sensitive and simple,and could met the demands of pesticide residue analysis.Residue analysis and dissipation of thiamethoxam investigated in the field trials in Henan,Heilongjiang and Jiangsu Province in the years of 2011and 2012indicated that,thehalf-lives of thiamethoxam in wheat plant and soil was 0.85~2.24dand 2.77~4.79d,respectively;The final residues of thiamethoxam in wheat grains were all≤0.038mg·kg-1in different dosage level,pre-harvest interval and application frequency.The estimated daily intake of thiamethoxam for general population was 0.25mg,accounting for about 15.04% of the acceptable daily intake(ADI),spraying thiamethoxam using this method should not produce an unacceptable risk to the health of general population.This work would be helpful in establishing the maximum residue limit(MRL)for thiamethoxam in wheat in China,and provide guidance to the proper and safe use of this pesticide in agriculture.