Dissipation of 8 pesticides on bok choy (Brassicachinensis) with once and multiple times application under field condition.

For better understanding the impact of multiple applications on the possible residue risk of pesticides on vegetables, a field trial was performed to evaluate eight pesticides (Phoxim, dichlorvos, cyhalothrin, β-cypermethrin, deltamethrin, fenvalerate, dimethoate and chlorothalonil) on bok choy. The dissipation of the selected pesticides was monitored after once application (OA) or multiple applications (MA). The suitability of multiple applications strategy of the selected pesticides for pest management on bok choy was also evaluated. The deposition ratio for all the pesticides ranged from 0.77‰ to 9.7‰. Dissipation of all the pesticides followed a typical first-order pattern. The estimated degradation half-lives of all the pesticides ranged from 0.6 to 11.95 days and from 0.68 to 11.87 days for OA and MA, respectively. However, the practical concentrations of all the pesticides measured at 2 h after the last application raged from 1.43 to 14.61 mg·kg and from 2.34 to 21.29 mg·kg for OA and MA, respectively. It is acceptable for the recommend doses for phoxim, dichlorvos, cyhalothrin, and β-cypermethrinon on bok choy for OA or MA in the present study. For the sake of food safety and sustainable use of pesticides, however, special attention needs to be paid to the MA of deltamethrin and fenvalerate. The MA of dimethoate and chlorothalonil on bok choy was not recommended.