Interactions of acidic herbicides bentazon and dicamba with organoclays

We determined the sorption mechanism of the acidic herbicides bentazon [3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and dicamba (3,6-dichloro-2-methoxybenzoic acid) on two organoclays, octadecylammonium (ODA)- and hexadecyltrimethylammonium (HDTMA)-exchanged Arizona montmorillonite (SAz-1), as part of a study to determine their potential use assorbent materials for ionizable organic pollutants. To determine the mechanisms involved in the sorption process, herbicide-organoclay complexes were characterized by x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In general, the d001 values of SAz-HDTMA and SAz-ODA organoclays expanded after herbicide saturation, indicating interlayer sorption of the herbicide. Also, FTIR spectroscopic studies suggested weak Hydrophobic interactions between these herbicides and the interlayer organic phase of the organoclays. However, H bonding between these herbicides and the monosubstituted amino group in SAz-ODA reinforced the strength of the hydrophobic interactions resulting in nonreadily reversible sorption on that organoclay. These results suggest that organoclays can be used to remove this type of pollutants from water or soils.

This work has been partially financed by Spanish CICYT through Project AMB 96-0445-CO2-01 by the Predoctoral Fellowship of PFPI of the Spanish MEC. This research was done by M.J. Carrizosa in the USDA-ARS Laboratory at the Department of Soil Water and Climate, University of Minnesota, and at IRNAS-CSIC laboratory.

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