SORPTION-DESORPTION OF IMIDACLOPRID AND ITS METABOLITES IN SOILS

Sorption-desorption of imidacloprid o-3-pyridinyl)methyl]-N-nitro-2-im idazolidinimine] and metabolites 1-[(6-chloro-3-pyridinyl)methyl]-2-im idazolidinone (imidacloprid-urea), -pyridinyl)methyl]-4,5-dihydro-1H-i midazol-2-amine (imidacloprid-guanidine), and [(6-chloro-3-pyridinyl)m ethyl]-1H-imidazol-2-amine (imidacloprid-guanidine-olefin) in three so ils was determined using the batch equilibration technique with initia l concentrations for the four chemicals ranging from 0.05 to 1.5 mu g mL(-1), which corresponds to a field application rate of 0.2-1.0 kg ha (-1) Calculated slopes of the Freundlich sorption isotherms were signi ficantly less than 1. The order of sorption (K-f) was imidacloprid-gua nidine > imidacloprid-guanidine-olefin > imidacloprid > imidacloprid-u rea in the three soils. Average Kf-oc values were 203, 412, 2740, and 3200 for imidacloprid-urea, imidacloprid, imidacloprid-guanidine-olefi n, and imidacloprid-guanidine, respectively. Desorption was hysteretic for all chemicals in all soils. Greatest hysteresis was observed with imidacloprid-guanidine and imidacloprid-guanidine-olefin. Sorption-de sorption of imidacloprid determined at half the solubility (250 mu g m L(-1)) (K-oc = 77) greatly overpredicts potential leaching compared to K-oc determined at field application rates (Kf-oc = 411).