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United States Department of Agriculture

Agricultural Research Service

Research Project: WATER QUALITY IMPROVEMENT FROM MANAGEMENT PRACTICES IN AGRICULTURAL WATERSHEDS Title: Degradation and Sorption of Imidacloprid in Dissimilar Surface and Subsurface Soils

Authors
item Anhalt, Jennifer - IA STATE UNIVERSITY
item Moorman, Thomas
item Koskinen, William

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 10, 2007
Publication Date: March 1, 2008
Citation: Anhalt, J.C., Moorman, T.B., Koskinen, W.C. 2008. Degradation and Sorption of Imidacloprid in Dissimilar Surface and Subsurface Soils. Journal of Environmental Science and Health. 43(3):207-213.

Interpretive Summary: Degradation and sorption/desorption are important processes affecting the leaching of pesticides through soil. Once pesticides move past the surface soil layers, subsurface soil physical, chemical, and biological properties significantly affect pesticide fate and the potential for groundwater contamination. This research characterized the degradation and sorption of imidacloprid in Drummer (silty clay loam) and Exeter (sandy loam) surface soils and their corresponding subsurface soils. Imidacloprid is an insecticide with wide use in a variety of crops using sequential extraction methods over 400 days. Imidacloprid degraded more quickly in the Exter soil than the Drummer soil and more quickly in surface soils than subsurface soils. Water extractable imidacloprid was present even after 400 days suggesting that imidacloprid was bioavailable to degrading soil microorganisms and sorption/desorption was not the limiting factor for biodegradation. Qualitative differences in the microbial communities appear to limit the degradation of imidacloprid in the subsurface soils. The research shows that imidacloprid that is transported from surface soils to subsurface soils will degrade very slowly and have increasing potential to move into groundwater. This information will be useful to industry scientists and regualtory agencies.

Technical Abstract: Degradation and sorption/desorption are important processes affecting the leaching of pesticides through soil. Once pesticides move past the surface soil layers, subsurface soil physical, chemical, and biological properties significantly affect pesticide fate and the potential for groundwater contamination. This research characterized the degradation and sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine) in Drummer (silty clay loam) and Exeter (sandy loam) surface soils and their corresponding subsurface soils using sequential extraction methods over 400 days. By the end of the incubation, approximately 55% of imidacloprid applied at a rate of 1.0 mg kg-1 dissipated in the Exeter SL surface and subsurface soils, compared to 40% of applied imidacloprid within 300 days in Drummer surface and subsurface soils. At the 0.1 mg kg-1 application rate, dissipation was slower for all four soils. Water-extractable imidacloprid in Exeter surface soil decreased from 98% of applied at Day 1 to >70% of the imidacloprid remaining after 400 d, as compared to 55% in the Drummer surface soil at Day 1 and 12% at Day 400. These data suggest that imidacloprid was bioavailable to degrading soil microorganisms and sorption/desorption was not the limiting factor for biodegradation. In subsurface soils > 40% of 14C-benzoic acid was mineralized over 21 days, demonstrating an active microbial community. In contrast, cumulative 14CO2 was less than 1.5% of applied 14C-imidacloprid in all soils over 400 d. Qualitative differences in the microbial communities appear to limit the degradation of imidacloprid in the subsurface soils.

Last Modified: 9/23/2014
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