Abstract
The current study aimed to examine dissipation dynamics of cypermethrin, emamectin benzoate, and indoxacarb insecticides in different parts of amaranth (Amaranthus tricolor L) and mustard greens (Brassica juncea) and determine their half-lives for a safe harvest. Two experiments, one in the open-field and one in a net-house were set up to grow the two crops; the three insecticides were applied 20 days after transplanting. Different crop parts (leaves, stem, and root) were collected after 2 hours, 2, 4, 6, 8, and 10 days after the insecticide application for measurements of their residue using GC-MS/MS (cypermethrin and indoxacarb) and LC-MS/MS (emamectin benzoate). Results showed that dissipation dynamics of the pesticides fitted well to the pseudo-first-order kinetics model with three parameters. The pesticide’s half-lives were significantly dependent on the crop types and crop parts. The half-lives of cypermethrin varied from 3.0 – 5.3 days; the half-lives of emamectin benzoate were from 0.37 – 0.64 days, and those of indoxacarb were from 12.5 – 13.5 hours. The highest half-lives were in the stem part. The open-field conditions resulted in shorter half-lives than the net-house condition. Based on the Codex Maximum Residue Limit, harvesting the leaves of amaranth and mustard greens in the open-field condition should not be carried out until after 7.7 and 7.1 days respectively from the last application of cypermethrin and after 1.4 and 1.3 days of emamectin benzoate. In the net-house condition, the harvest of the leaves of amaranth and mustard greens could be implemented after 9.4 and 7.8 days for cypermethrin and after 1.8 and 1.4 days for emamectin benzoate, respectively. Meanwhile, it could be safe to harvest the leaf part of the two tested crops after 12 hours from the last application of indoxacarb.
