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United States Department of Agriculture

Agricultural Research Service

Title: Changes in Bioavailability of Imidacloprid and Two Metabolites in Soil with Incubation Time

item Koskinen, William

Submitted to: International Symposium on Environmental Aspects of Pesticide Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 1999
Publication Date: N/A

Technical Abstract: Changes in bioavailability of the insecticide imidacloprid and two metabolites, imidacloprid-urea and imidacloprid-guanidine, with aging in different soils have been determined. Soil moisture was adjusted to -33 KPa and 14C- and analytical-grade imidacloprid or metabolite were added to the soil at a rate of 1.0 mg/kg. Spiked soils were incubated at 25C for 16 wks (imidacloprid) or 8 wks (metabolites). Replicate soil samples were periodically extracted successively with 0.01 N CaCl2, acetonitrile, and 1 N HCl. The bioavailability of all three chemicals in all soils decreased with aging, as indicated by decreases in the amounts of imidacloprid and metabolites extractable with CaCl2 (bioavailable chemical) and increases in the amounts extractable with acetonitrile and HCl (bound chemical) with incubation time. Calculated sorption coefficients (solvent extractable/CaCl2 extractable) increased by factors of 1.5 to 3.3. It is not known whether the decrease in bioavailability (or increase in sorption was the result of imidacloprid and metabolite diffusion to less accessible or stronger binding sites with time, a rate of degradation in solution and on labile sites that was faster than the rate of desorption from more strongly sorbing sites, or a combination of the two processes. These results are, however, further evidence that changes in bioavailability during pesticide aging should be taken into account during characterization of the biodegradation process for mathematical models of pesticide fate and behavior in soils.

Last Modified: 4/22/2015
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