Dissipation Characteristics of Insecticide Phenthoate in Minor Crop Millet during Cultivation

Abstract

Phenthoate is a widely used organothiophosphate insecticide during cultivation of various crops such as red pepper, green onion, cucumber, and tomato. This study investigated the dissipation characteristics of phenthoate in grain and straw of minor crop millet after spraying phenthoate 47.5% emulsifiable concentrate (EC) formulation. For field trial, the pesticide was treated on 4 plots (Plot1

40/30 days, Plot 2

30/21 days, Plot 3

21/14 days and Plot 4

14/7 days before harvest) by three replicates. The residue of the pesticide was analyzed by LC-MS/MS and method limit of quantitation (MLOQ) were 0.01 mg/kg. The linearity (r2) of calibration curve was ≥ 0.999 at the calibration range of 0.005-0.5 grade g/mL. After harvest, maximum phenthoate residues in plot 1 were 0.02 mg/kg in both of grain and straw. In plot 2 the residues were 0.15 mg/kg (grain) and 0.04 mg/kg (straw), while the residue in plot 3 were 0.61 and 0.18 mg/kg in grain and straw, respectively. In plot 4, 0.72 mg/kg (grain) and 0.38 mg/kg (straw) of residue were observed. These results will be used for establishing pre-harvest interval (PHI) of phenthoate during cultivation of millet. The dissipation pattern and half-life of phenthoate in soil was also evaluated in laboratory condition. Ten grams of soils which were fortified with phenthoate standard solution at the concentration of 0.75 mg/kg were incubated at 25℃ in the dark condition. The soil samples were collected at 0 hr, 2 hr, 6 hr, 12 hr, 24 hr (1 days), 48 hr (2 days), 72 hr (3 days), 120 hr (5 days), 168 hr (7 days), 336 hr (14 days), and 672 hr (28 days) after treatment. The residue of the pesticide was analyzed by GC-µECD (Agilent-7890). The MLOQ was 0.005 mg/kg. The linearity (r2) of calibration curve was ≥ 0.999 at the calibration range of 0.005-0.5 µg/mL. The phenthoate was dissipated rapidly in soil with the dissipation curve of y=556.09e-0.009x (r2=0.9796) while the 77.0 hours (3.2 days) of 1º-half-life was determined.