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United States Department of Agriculture

Agricultural Research Service

Title: Sorption of Aged Dicamba Residues in Soil

Authors
item Menasseri, S - ENSAR, RENNES, FRANCE
item Koskinen, William
item Yen, P - UNIV. OF MINNESOTA

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 2003
Publication Date: November 3, 2003
Citation: Menasseri, S., Koskinen, W.C., Yen, P.Y. 2004. Sorption of aged dicamba residues in soil. Pest Management Science. 60:297-304.

Interpretive Summary: The capacity of soil to retain or sorb herbicides from aqueous solutions is a key parameter controlling the extent to which pesticides leach through soil into ground water or run off into surface water. Herbicides that are more readily available for movement are those that are less tightly bound to soil, and the strength of pesticide binding depends on the types of bonds between the organic molecule and the surface. While sorption is affected by the physical and chemical properties of the pesticide and soil, it also appears that sorption can be affected by the residence time in the soil. The objectives of this research were to determine the effect of aging on sorption of dicamba, a potentially mobile herbicide, to soil. We found that dicamba was weakly sorbed to soil, but in contrast to other classes of pesticides, sorption did not significantly increase with aging, at least not until < 15% of the applied dicamba remained. In contrast to dicamba, sorption of its main degradate, 3,6-DSCA is strongly sorbed to soil and sorption increased with aging. While it appears that sorption can be well characterized for weakly sorbed pesticides using the batch equilibration method with freshly treated soils, it may not be adequate for more strongly sorbed pesticides and their degradates. By understanding the complex interactions of the sorption-desorption and degradation processes, particularly for aged herbicide residues, and those chemicals that are not appreciably sorbed to soils, such as found in this research, scientists will be able to improve models describing pesticide availability for transport and biodegradation in soil.

Technical Abstract: The effect of aging on dicamba (3,6-dichloro-2-methoxybenzoic acid) and a major metabolite, 3,6-dichlorosalicylic acid (3,6-DCSA) on sorption was determined in an unamended and a carbon-amended sandy loam soil. During the incubation, sequential solvent extraction with 0.01 N CaCl2 and aqueous acetonitrile/HCl was used to detemine the solution and sorbed concentrations of dicamba and 3,6-DSCA and sorption coefficients were calculated. Dicamba was weakly sorbed to soil (Kd < 0.7). In contrast to other classes of pesticides, sorption of dicamba did not significantly increase with aging, at least not until < 15% of the applied dicamba remained. In contrast to dicamba, sorption of its main degradate, 3,6-DSCA is strongly sorbed to soil (Kd > 8) and Kd increased with aging. While it appears that sorption can be well characterized for weakly sorbed pesticides using the batch equilibration method with freshly treated soils, it may not be adequate for more strongly sorbed pesticides and their degradates.

Last Modified: 10/1/2014
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