Adsorption and Photo-reactivity of Bensulfuron-Methyl On Homoionic Clays

The adsorption and photolysis of the herbicide bensulfuron-methyl [2-(4, 6dimethoxypyrimidin-2-carbamoylsulfamoyl)-o-toluic acid methyl ester] on homoionic Na+ -, Ca2+ - and Fe3+ montmorillonite and kaolinite clays were studied. The Freundlich adsorption coefficient, Kf, measured from isotherms on clays followed the order Na+ < Ca2+ < Fe3+. Montmorillonite showed a greater adsorptive capacity than kaolinite. Analysis of Fourier transform infrared spectra of bensulfuron-methyl adsorbed on clay suggested probable bonding interactions between bensulfuron-methyl and homoionic clays. The photolysis rate of herbicide adsorbed on homoionic clay surfaces was quite slow to its free state and decreased in the order Na+ > Ca2+ > Fe3+, indicatingthat adsorption may have prevented photolysis.