Submitted to: Clays and Clay Minerals
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/16/2004
Publication Date: 6/15/2004
Citation: Carrizosa, M.J., Rice, P.J., Koskinen, W.C., Carrizosa, I., Hermosin, M.C. 2004. Sorption of isoxaflutole and DKN on organoclays. Clays and Clay Minerals. 52:341-349. Interpretive Summary: Herbicides that are highly soluble in water, minimally sorbed by soil particles, and not readily degradable can move rapidly with water and hence, have a high potential to be found in surface and ground waters. Many more newly developed herbicides, such as isoxaflutole, and herbicide breakdown products have these characteristics, and thus if accidentally reach high concentrations in soil as in an accidental spill, they have to be immobilized as soon as possible to avoid further potential water contamination. The potential off-site movement of these agrochemicals can be decreased by creation of sorptive or immobilising zones in the soils by incorporating an appropriate adsorbent in the affected area. Synthetic organic clays (OCls), obtained by exchange of the original inorganic exchangeable cation on the natural clayby large alkylammonium ones, showed an increased adsorption capacity for organic pollutants, such as polar pesticides in water. The objectives of this work were to assess the adsorption-desorption capacity of different OCls for the herbicide isoxaaflutole and its main breakdown product, a diketonitrile, and their ability to immobilize them in soil. We found that some organoclays rapidly decomposed isoxaflutole to its diketonitrile breakdown product, which in turn was bound to the clays. While the results appear promising, additional research is still needed to determine if these types of organoclays would be good sorbents for remediation of contaminated soil and water. These results will aid scientists in their development of inexpensive and efficient organoclays to be used to decontaminate spill sites.
Technical Abstract: Isoxaflutole is a new corn preemergence herbicide, which rapidly converts to its active diketonitrile degradate, DKN. Sorptive behavior of isoxaflutole and DKN on natural clays, Arizona and Wyoming montmorillonites and hectorite, and their organoderivatives (octadecylammonium- and hexadecyltrimethylammonium-exchanged clays), has been investigated. Isoxaflutole degradation was measured over time in an herbicide solution with or without clay. A qualitative kinetic evaluation was performed to characterize the sorption of isoxaflutole during the degradation process to DKN. After 48 h, 82 % of the isoxaflutole remained in the clay-free solution, 65-82% in solution with natural clays, and only 2% in solution with organoclays. Hydrolysis in presence of organoclays occurred so rapidly that sorption could not be characterized. DKN sorption-desorption isotherms were fitted to the Freundlich equation. No measurable sorption was observed for the natural clays. DKN sorption was greater on paraffin-like organoclays (prepared from high-charge Arizona montmorillonite), than on bilayered or monolayered organoclays (prepared from medium and low charge clays, Wyonimg montmorillonite and hectorite). The nature and amount of organic cation in the interlayer also influenced DKN sorption on the different organoclays. Desorption isotherms revealed irreversibility of the sorption-desorption process.