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United States Department of Agriculture

Agricultural Research Service

Research Project: PROTECTING SURFACE AND GROUND WATERS IN EMERGING FARMING SYSTEMS OF THE NORTH CENTRAL UNITED STATES Title: Characterization of ‘Aged’ Metolachlor Sorption in Soil Using an Accelerated Solvent Extraction (ASE) Technique

Authors
item Cabrera, Alegria -
item Koskinen, William
item Papiernik, Sharon

Submitted to: SETAC Conference
Publication Type: Abstract Only
Publication Acceptance Date: May 23, 2010
Publication Date: May 23, 2010
Citation: Cabrera, A., Koskinen, W.C., Papiernik, S.K. 2010. Characterization of ‘Aged’ Metolachlor Sorption in Soil Using an Accelerated Solvent Extraction (ASE) Technique [abstract]. SETAC Conference. No. MO 118.

Technical Abstract: Sorption interactions of pesticides with soil determine pesticide availability for transport and degradation in soil. Thus, knowing and understanding pesticide sorption, particularly in aged soils, is important in determining pesticide fate in soils. Sorption of pesticides is traditionally characterized by determination of sorption coefficients (Kd) using the batch slurry direct method. However, there are many criticisms of this technique: a small amount of soil is equilibrated with a large volume of pesticide solution, a ratio which is not representative typical field soil moisture levels; experimental conditions such as temperature, type of shaking, and centrifugation speed are not completely standardized; and it does not characterize sorption of aged pesticide residues. The objective of this work was to use a sequential solvent extraction method with an accelerated solvent extraction (ASE) system to determine the sorption Kd values of the herbicide metolachlor in freshly treated and aged soils. Soils differing properties were obtained from a hillside, which had eroded and rehabilitated landforms in which topsoil was moved from the lower slope to the upper slope. Soils treated with metolachlor at a rate of 5 ug g-1 were incubated for varying times at constant temperature (25ºC). At time zero, and selected times, samples were removed and sequentially extracted using the ASE, first with 0.01M CaCl2, and then with acetonitrile-water (90:10, v:v). Sorption coefficients (Kd) were calculated as the ratio of organic solvent extractable to aqueous solvent extractable metolachlor. Dissipation half-lives of metolachlor were calculated from the total extractable amounts with time. Sequential extraction by ASE is an easy method to characterize sorption of aged residues in soils.

Last Modified: 10/22/2014
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