Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2003
Publication Date: 6/15/2003
Citation: Carrizosa, M.J., Hermosin, M.C., Koskinen, W.C., Cornejo, J. 2003. Organosmectites to reduce leaching losses of acidic herbicides. Soil Science Society of America Journal. 67:511-517. Interpretive Summary: The sorptive capacity of clays for organic compounds, such as pesticides, can be enhanced by chemical modification, whereby the native inorganic exchangeable cations are replaced with organic cations via ion exchange reactions. Organoclays (OCls) have been shown to be good sorbents for removing polar pesticides from water. Recent studies further suggest the use of OCls to protect soil and water from acidic herbicides as well as potential carriers in slow-release formulations for polar and hydrophobic pesticides. Acidic herbicides such as bentazone and dicamba have been used as models of very mobile and leachable herbicides. The aim of this work was to assess the potential use of organoclays as matrices for controlled release formulations of bentazone and dicamba to reduce herbicide concentrations in soil solution and leaching through soil columns. Results show that OCls have potential to be carriers in slow release formulations of acidic herbicides, such as bentazone and dicamba, in order to decrease their concentration in surface water and in soil leachates. Our results suggest that OCls with low and intermediate sorption capacity decrease herbicide leaching while retaining their efficacy. These herbicide-OCl formulations may be effective in reducing herbicide losses associated to leaching and hence the risk of acidic herbicides to reach and contaminate water, while maintaining the efficiency for weed control. Scientists now have the results necessary to design research to test these OCls in the field.
Technical Abstract: The modification of smectitic clays with organic cations via cation exchange reactions produces sorbents with an increased sorption capacity for organic compounds such acidic pesticides. These organoclays (OCls) could be used as carriers in controlled release formulations of pesticides to decrease their contamination potential. Various OCls and two acidic herbicides (bentazone and dicamba) were selected and herbicide-OCl complexes were prepared by either sorbing the herbicides on the OCl from solution or by dry mixing of both components. Those preparations were assayed as controlled release formulations under static (water solution) and dynamic (soil column leaching) conditions. Herbicide release in closed (static) systems was fast and reached a maximum concentration after 10-20 h. The total herbicide released ranged from 20 to 100 % of the active ingredient initially incorporated in the complex depending on the sorption capacity of the OCl for the herbicide and the strength of herbicide-OCl interaction (aging time). Total leaching losses in soil columns were reduced from 94 % for free technical bentazone to 55-90% for bentazone-OCl complexes, and from 100% for technical dicamba to 50-100% for dicamba-OCls complexes. Maximum concentrations in the leaching profiles of the herbicide-OCl complexes were much smaller than for the technical compounds. Bioassays of dicamba-OCl complexes as preemergence herbicide showed the same efficiency as the technical compound. These results suggest organoclays as possible carriers in controlled release formulations for very mobile and persistent acidic herbicides, thereby decreasing their potential for surface and ground water contamination.