Metabolism and persistence of imidacloprid in different types of soils under laboratory conditions

To study the metabolism and persistence of imidacloprid, samples of sandy loam, loamy sand and clay loam soils were collected from different geographical locations of Punjab. The soil samples were autoclaved at 120°C at 15 psi for 15 min before initiating the experiment, and then each soil type was fortified at three levels of imidacloprid i.e. 100, 200 and 400 mg kg⁻¹ in three replications and kept at 25 ± 2°C under laboratory conditions. The residues of imidacloprid and its metabolites were quantified by high-performance liquid chromatography. The limit of quantification (LOQ) of imidacloprid and its metabolites was worked out to be 0.01 mg kg⁻¹. Total residues of imidacloprid 7 days after treatment at 100 mg kg⁻¹ were found to be 69.74, 72.66 and 77.20 mg kg⁻¹ in sandy loam, loamy sand and clay loam soil, respectively, whereas residues from 200 mg kg⁻¹ were 144.32, 146.56 and 150.25 mg kg⁻¹ and from 400 mg kg⁻¹ application, residues were 308.23, 312.54 and 327.95 mg kg⁻¹ corresponding to three soils under study. Imidacloprid residues degraded to chloronicotinic acid, imidacloprid-nitroguanidine, nitrosimine, olefin and 5-hydroxy imidacloprid in all the three types of soils. Imidacloprid urea metabolite was not found in any of the soil. The persistence of imidacloprid was found to be more in clay loam soil as compared to loamy sand and sandy loam soils. Dissipation of imidacloprid residues in soils was not found to follow the first-order kinetics. The half-life (T _1/2) value of total imidacloprid was observed to be highest (43 days) in clay loam soil, followed by loamy sand (38 days) and sandy loam (32 days).