Clay-herbicide complexes to retard picloram leaching in soil

An approach for minimizing the risk of ground water contamination for highly mobile pesticides is to enhance the soil sorption process through the application of the pesticide together with a sorbent which limits the amount of pesticide immediately available for undesirable leaching losses. In this work, a number of clays exchanged with different inorganic and organic cations were assayed as sorbents of the acidic herbicide picloram (4-amino-3,5,6-trichloropyridine-2-carboxylic acid) and the ability of three selected clays to retard the release of picloram into water and to reduce picloram leaching through a soil column was investigated. For the selected clays, Fe3+-saturated Wyoming montmorillonite (Fe-SW), octadecylammonium-treated Arizona montmorillonite (ODA-SA(1)) and hexadecyltrimethylammonium-saturated Arizona montomorillonite (HDTMA-SA(2)), two types of clay picloram complexes ( a physical mixture, PM, and a strongly-sorbed complex, SC) were prepared. All clay picloram complexes yielded slow release of the herbicide and retarded its vertical movement through soil columns compared to the free technical compound, showing that clay pesticide complexes prepared from selectively-modified clays may be useful in reducing rapid leaching of highly mobile pesticides such as picloram.