Studyonresiduebehaviorofcypermethrininchrysanthemumandlettuces

In order to determine the residue behavior of cypermethrin in chrysanthemum and lettuces, supervised residue field trial was conducted in Shanxi, Shandong, Tianjin, Anhui, Yunnan and Henan in 2016. Final residue tests in the six regions and pesticide dissipation dynamics test at one place for both vegetables were carried out. According to the current national standard method for the determination of pyrethroid pesticide residues in vegetables, the samples were tested and the effectiveness of the method was evaluated. According to the results of supervised residue trials, the dissipation equations of cypermethrin in chrysanthemum and lettuces fit the first-order kinetics equation with half-lives of 3.2 d and 1.8 d, respectively. The median values of cypermethrin residue in chrysanthemum lettuces were 1.64, 1.19 and 0.89 mg/kg, and the median values of cypermethrin residue in lettuces were 0.84, 0.50 and 0.28 mg/kg, respectively. By comparing the average temperature at different test points during the experiment period, it is discovered that the temperature has a significant effect on cypermethrin residues in chrysanthemum and lettuces. Given the slow decomposition of cypermethrin in chrysanthemum and lettuces, the residue risk increased significantly at lower temperature. It is recommended that the harvest interval should be appropriately extended when it comes to cold weather, and the effect of meteorological conditions on the results of supervised residue trial should be taken into account.