Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2004
Publication Date: 11/3/2004
Citation: Carrizosa, M.J., Koskinen, W.C., Hermosin, M.C. 2004. Interactions of acidic herbicides bentazon and dicamba with organoclays. Soil Science Society of America Journal. 68:1863-1866. 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 widely-used acidic herbicides, such as bentazon and dicamba, 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 clay by large alkylammonium ones, showed an increased adsorption capacity for organic pollutants, such as polar pesticides in water. The objective of this work was to determine the sorption mechanism of the herbicides bentazon and dicamba on different OCls. We were able to determine the mechanism of their binding to soil and the reason why they do not release from the clay particle. These results will aid scientists in their development of inexpensive and efficient organoclays to be used to decontaminate spill sites.
Technical Abstract: We determined the sorption mechanism of the acidic herbicides bentazon and dicamba on two organoclays (OCls), octadecylammonium and hexadecyltrimethylammonium-exchanged montmorillonite, as part of a study to determine their potential use as sorbent materials for ionizable organic pollutants. To determine the mechanisms involved in the sorption process, herbicide-OCl complexes were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). In general, the d001 values of the two OCl samples expanded after herbicide saturation, indicating interlayer sorption of the herbicide. Also, FT-IR spectroscopic studies suggested weak hydrophobic interactions between these herbicides and the interlayer organic phase of the OCls. However, hydrogen bonding between these herbicides and the monosubstituted amino group in octadecylammonium-exchanged OCls reinforced the strength of the hydrophobic interactions resulting in irreversibility of the sorption process. These results suggest that OCls can be used to remove this type of pollutants from water or soils.