Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/1997
Publication Date: N/A
Interpretive Summary: Imidacloprid is a new systemic insecticide of the chemical group of the nitroguanidines. Very little information is published concerning the fate of imidacloprid in soil. Sorption-desorption processes are important in determining the fate and distribution of agrochemicals in the soil/water environment, since they determine the amount of pesticide that can reach the target organism and the amounts that can be volatilized, degraded and leached. However, there is no information available on changes in sorption- desorption of imidacloprid as it ages in the field. The objective of the present paper was to characterize the sorption-desorption of imidacloprid as a function of residence time in soil. Sorption of imidacloprid is affected by soil properties, increasing with soil organic carbon content. Sorption also increased by a factor of 3 during the incubation period. At normal field application rates, it appears the leaching potential of imidacloprid in soil is minimal and the longer it is in the field the leaching potential further decreases. These results help us to understand the factors that minimize potential leaching of pesticides to ground water. The results will also improve use of pesticide leaching models that are used to reduce pesticide use and risk in agricultural production systems.
Technical Abstract: Changes in sorption of the insecticide imidacloprid (1-[(6-chloro-3- pyridinyl)-methyl]-N-nitro-2-imidazolidinimine) during aging in three soils have been determined. Soil moisture was adjusted to -33 KPa and **14C- and analytical-grade imidacloprid was added to the soil at a rate of 1 mg kg** -1. Imidacloprid spiked soils were incubated at 25 degrees C for 16 weeks. Replicate soil samples were periodically extracted successively with 0.01 N CaCl2, acetonitrile, and 1 N HCl. Sorption, as indicated by Kd values, was higher in the soil with the highest OC content and increased during the incubation period by a factor of 3. This increase is correlated to the decrease in the imidacloprid extractable with CaCl2 (soluble phase) and the increase in the amount of imidacloprid extractable with acetonitrile and HCl (sorbed phase) with incubation time. These factors should be taken into oaccount when extrapolating sorption data to mathematical models of pesticide leaching.