Dissipation kinetics, decontamination and dietary risk assessment of imidacloprid residue in bitter gourd and soil

Imidacloprid is a broad-spectrum neonicotinoid class insecticide with systemic action, widely used on vegetables in India for the management of sucking insect pests. The overall pesticide usage profile in gourds growing districts of Tamil Nadu showed that imidacloprid as the most commonly used insecticide. The present study aimed to develop and validate an analytical approach for detecting imidacloprid and 6-chloronicotinic acid residues in bitter gourd fruit, juice and soil using LC-EI-MS (liquid chromatography coupled with electron ionization mass spectrometry) was undertaken. The persistence pattern, effect of household processing and risk assessment of imidacloprid on bitter gourd was studied by conducting field trials at single and double doses of 20 and 40 g a.i ha-1. Calibration curves showed a good linear relationship (r2>0.99) with the concentrations (0.0025–0.5 µg mL-1) of imidacloprid and 6-chloronicotinic acid. The limit of detection and quantification of the method were 0.008 and 0.025 mg kg-1, respectively. Accuracy of imidacloprid and 6-chloronicotinic acid residue recovery was in the range of 88–101 per cent with RSD of less than six per cent in all the matrices of bitter gourd. Initial deposits of imidacloprid at 20 and 40 g a.i ha-1 were 0.68 and 1.25 mg kg-1 and the residues persisted up to 10 and 15 days with their respective half-lives of 2.51 and 3.13 days. Simple decontamination techniques showed 33 to 80 per cent reduction of residues in samples collected up to 10 days after treatment. The estimated RQ was less than one indicating the level of risk to the consumer is negligible.