Diazinon residues and degradation kinetics for grapes under field conditions

The dissipation of diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) in grapes was investigated to determine its pre-harvest interval (PHI). Diazinon was applied to grapes at the recommended dosage (0.9 g a.i. L(-1)) and twice the recommended dosage (1.8 g a.i. L(-1)) three times, at the fruit formation stage, the sour stage, and the ripening stage, in a field trial with three replications. Samples were taken at 0, 1, 2, 4, 7, 11, 15, 20, 26 and 32 days after spraying. The residue was extracted using a water/methanol/acetonitrile (1:1:1, v/v/v) solvent and solid phase extraction was employed for cleanup. Quantitative analysis was performed using a gas chromatograph equipped with a nitrogen-phosphorus detector. The dissipation trend for the recommended dosage and twice the recommend dosage followed the simple first-order kinetic model (SFOK) (DT(50) = 3.29 days, DT(90) = 11 days, PHI = 13.5 days) and first-order double-exponential decay (FODED) model (DT(50) = 1.08 days, DT(90) = 5.82 days, PHI = 15.29 days), respectively. The average initial deposit of diazinon at the recommended dosage was 9.04 mg kg(-1)and for twice the recommended dosage was 27.38 mg kg(-1)and it dissipated rapidly within days of spraying.