Abstract
This study was designed to understand the dissipation of fipronil, cypermethrin, and tebuconazole in green onions and mustard greens grown in Central Vietnam. A field trial on ca. 400 m2 was implemented for two months with three different cropping regimes (natural plot-fully exposed to natural conditions; bed plot-fenced in by plastic sheets with an open roof; and protected plot-fully covered by plastic sheets) for each vegetable. A first-order kinetic model was successfully employed to interpret the dissipation data of each studied pesticide. A comparing the dissipation rate constants obtained under the same crop and growing regime between chemicals suggested that, among the chemicals examined, fipronil dissipated most readily. The pesticides were also proven to be more persistent in crops grown in protected plots than those grown in natural plots. The half-lives for fipronil, cypermethrin, and tebuconazole fluctuated, occurring at 0.4-2.2 days, 2.0-6.0 days, and 0.9-3.3 days, respectively.