Effects of Altitude on Residues and Degradation Dynamics of Imidacloprid and Acetamiprid in Four Leaf Vegetables

To explore the effects of altitude on residues and degradation dynamics of imidacloprid and acetamiprid in four leaf vegetables, digestion and residue test of imidacloprid and acetamiprid in four leaf vegetables were studied at Lhasa, Xizang and Pengzhou, Sichuan. A UPLC-MS/MS method was established to determining the residual quantity of imidacloprid and acetamiprid in Chinese cabbage, bok choy, lettuce and celery. The results showed that the calibration curves had good linears in the concentrations range of 0.005 to 0.5 mg/L. When the four leaf vegetables were spiked with imidacloprid and acetamiprid at the levels of 0.01, 0.10 and 0.50 mg/kg, the average recoveries were 81.22%~116.95%, the relative standard deviations (RSD) were 1.2%~7.1%, the limits of detection (LOD, S/N≥3) were 0.11~1.21 µg/kg while the limits of quantitation (LOQ, S/N≥10) were 0.38~0.69 µg/kg. The results of field experiments showed that the degradation dynamics of imidacloprid and acetamiprid in four leaf vegetables were followed with the first-order kinetic equation. The final residue test results showed that the residue values of two insecticides were consistent with the maximum residue limit value stipulated in the national standard of food safety from 7 days to harvest. The half-lives of two pesticides in four leaf vegetables at Lhasa were shorter than that at Pengzhou. However, there was no significant difference in the half-lives of two pesticides in four leaf vegetables at different areas, the half-life of imidacloprid and acetamiprid in Lhasa and Pengzhou were all lettuce, bok choy, Chinese cabbage and celery from short to long. The vegetable varieties and growing environment in different areas would be closely related to the residues and degradation dynamics of imidacloprid and acetamiprid.