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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: Sorption of the herbicide aminocyclopyrachlor by cation modified clay minerals

Authors
item Cabrera, A -
item Trigo, C -
item Cox, L -
item Celis, R -
item Hermosin, M -
item Cornejo, J -
item Koskinen, William

Submitted to: European Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2012
Publication Date: July 10, 2012
Citation: Cabrera, A., Trigo, C., Cox, L., Celis, R., Hermosin, M.C., Cornejo, J., Koskinen, W.C. 2012. Sorption of the herbicide aminocyclopyrachlor by cation modified clay minerals. European Journal of Soil Science. Available at: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2389.2012.01466.x/abstract. DOI: 10.1111/j.1365-2389.2012.01466.x.

Interpretive Summary: Weak acid herbicides are generally weakly retained by most soil and sediment components and are subject to potential offsite transport. One strategy to minimize the risk of offsite transport associated with weakly sorbed, highly mobile pesticides is the application of these chemicals with a sorbent, such as mineral clays exchanged with inorganic and organic cations. The aim of this work was to determine the ability of unmodified and modified clays to sorb aminocyclopyrachlor, a newly registered weak acid herbicide for the control of broadleaf weeds, grasses, vines and woody species in non-crops, turf, sod farms, and residential areas. Two montmorillonites (Ca-Arizona montorillonite (SAz-1) and Na-Wyoming montmorillonite (SWy-2) were used as unmodified clays and were also modified with an inorganic cation (Fe3+ ), soil clay constituents (ferrihydrite (Fe), humic acid), and organic cations (hexadecyltrimethylammonium (HDTMA), hexadimethrine, spermine). Higher sorption of aminocyclopyrachlor was observed in the sorbent-solution systems with lower pH values, presumably due to protonation of the herbicide anion at low pH and subsequent sorption of molecular species and cationic species. FeSWy-2 was found to be the best sorbent for aminocyclopyrachlor (86% of applied). The best organoclay (SA-HDTMA) sorbed 53% of the applied herbicide. Soil clay constituents did not sorb aminocyclopyrachlor. Modification of mineral clays with inorganic and organic cations, and their use as herbicide sorbents can be an efficient strategy to reduce the risk of offsite transport associated with anionic and highly mobile herbicides, such as aminocyclopirachlor.

Technical Abstract: Aminocyclopyrachlor is a newly registered herbicide for the control of broadleaf weeds, grasses, vines and woody species in non-crops, turf, sod farms, and residential areas. At typical soil pH levels, aminocyclopyrachlor is in the anionic form. Anionic pesticides are generally weakly retained by most soil and sediment components and are subject to potential offsite transport. One strategy to minimize the risk of offsite transport associated with weakly sorbed, highly mobile pesticides is the application of these chemicals supported with a sorbent, such as mineral clays exchanged with inorganic and organic cations. The aim of this work was to determine the ability of unmodified and modified clays to sorb aminocyclopyrachlor. Two montmorillonites (Ca-Arizona montorillonite (SAz-1) and Na-Wyoming montmorillonite (SWy-2) were used as unmodified clays and were also modified with an inorganic cation (Fe3+ ), soil clay constituents (ferrihydrite, humic acid), and organic cations (hexadecyltrimethylammonium (HDTMA), hexadimethrine, spermine). Higher sorption of aminocyclopyrachlor was observed in the sorbent-solution systems with lower pH values, presumably due to protonation of the herbicide anion at low pH and subsequent sorption of molecular species and cationic species. FeSWy-2 (system pH = 4.6) was found to be the best sorbent for aminocyclopyrachlor (86% of applied). The best organoclay (SA-HDTMA) (system pH = 6.1) sorbed 53% of the applied herbicide. Soil clay constituents (system pH > 6.7) did not sorb aminocyclopyrachlor. Modification of mineral clays with inorganic and organic cations, and their use as herbicide sorbents can be an efficient strategy to reduce the risk of offsite transport associated with anionic and highly mobile herbicides, such as aminocyclopirachlor.

Last Modified: 11/26/2014
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