Dissipation of neonicotinoid insecticides imidacloprid, indoxacarb and thiamethoxam on pomegranate (Punica granatum L.)

摘要

Neonicotinoid insecticides such as imidacloprid, indoxacarb and thiamethoxam are widely used for control of a large number of insect pests of pomegranate crop. Their residue levels were evaluated on pomegranate fruits over 2 years during the same cropping season. The QuEChERS analytical method in conjunction with LC-MS/MS was validated to analyse the insecticides on pomegranate fruits with peel (whole fruit), without peel (aril) and in the field soil. The method performance was satisfactory with the limit of quantification (LOQ) of 0.005 mg/kg which was below the maximum residue limits (MRLs) in pomegranate for the 3 compounds. A first order reaction kinetics was observed for the three insecticides with the half-life of degradation of 8-11.1 days for imidacloprid; 7.4-8.4 days for indoxacarb and 9.8-14.2 days for thiamethoxam. Though the insecticides are systemic in nature, the residues in the edible pomegranate aril were always LOQ. The maximum residue levels of imidacloprid on pomegranate was less than its MRL of 1 mg/kg, so the pre-harvest interval (PHI) required was 1 day only. For indoxacarb, 31-42 days PHI was needed for the residues to reduce to its MRL of 0.02 mg/kg. The PHI of thiamethoxam was 46-77 days, the time required for its residues to reduce to its MRL of 0.01 mg/kg. Higher rainfall possibly facilitated faster dissipation of imidacloprid residues from pomegranate whereas indoxacarb and thiamethoxam remained unaffected. The results of the study can be utilized to incorporate these three chemicals in the plant protection program of pomegranate and fixation of MRL in India.