Abstract:
An analytical investigation was carried out to study the dissipation rate of two commonly used
pesticides, Thiamethoxam (neonicotinoid insecticide) and propamocarb hydrochloride (carbamate
fungicide) applied to four vegetable crops: cucumber, zucchini, lettuce and pepper, after open-
field application. Samples were harvested according to a scheduled plan followed by QuEChERS
extraction, then thiamethoxam residues were analyzed using a GC-ECD method, while
propamocarb HCl residues were analyzed using an HPLC-UV method. Validation parameters
were attained for both methods and the kinetic profile was studied which fitted the first –order
kinetics where k, t ½ and t90 were calculated. The proper pre-harvest interval (PHI) was studied
for each crop to ensure that the residues levels declined to reach below the maximum residue limit (MRL) where the crop is suitable for edible use. These values were found to be different from
labelled values which proves that the PHIs are greatly affected by changing weather conditions.
