Dissipation and residues distribution of imidacloprid, difenoconazole and chlorothalonil in cabbage

The dissipation dynamics and residue distribution of imidacloprid, difenoconazole and chlorothalonil in cabbage grown in open field were investigated. The field experiments were carried out and liquid chromatography-mass spectrometry and gas chromatograph were used to determine the pesticide residues of cabbage samples at different time intervals after pesticide application. The results showed that the dissipation dynamics of three pesticides were accorded with the first-order kinetics model, and the half-lives were 1.35, 2.28 and 2.47 days, respectively. The dissipation rate of imidacloprid was the fastest, followed by difenoconazole and chlorothalonil. The residues of imidacloprid and chlorothalonil were lower than the maximum residue limits (MRLs) in cabbages on 7 days and 14 days after application, however, the residue of difenoconazole was slightly higher than the MRL on 14 days after application. The residues of three pesticides in different parts of cabbage showed significant differences (P<0.05). The pesticide residues in cabbage inner bulb were not detected or very low in cabbage inner bulbar leaves. The initial residue in cabbage outer bulbar leaves was low either, and it was reduced below MRL from 1 to 5 d. However, the pesticide residues in cabbage outer leaves were significantly higher than those in other parts. It can be concluded that removing the outer leaves of cabbage could reduce the pesticide residues and improve the safety and quality of cabbage effectively.