Degradation of bensulfuron-methyl on various minerals and humic acids

The chemical degradation of bensulfuron-methyl on various dry minerals (kaolinite, silica gel, alumina, H+ bentonite, montmorillonite K 10) and on solid humic acid was investigated at 30 degrees C. Kaolinite presented a very low activity in comparison with the systematically higher degradation rates obtained using other selected minerals. An acceptable correlation with pseudo-first-order kinetics was frequently observed, allowing degradation rate constants to be established. The influence of the herbicide deposition technique used, sample stirring and moisture content were studied. Most of the solids selected, which have an acidic surface, induced only the breakdown of the herbicide molecule's benzyl-sulfonylurea bridge. In contrast, the basic surface of alumina preferentially induced saponification of the carbomethoxy substituent fixed to the aromatic ring. The degradation compounds obtained generally remained stable, with the exception of phenylsulfonamide, which cyclized rapidly on alumina. The suggested degradation path is similar to that previously proposed for chemical hydrolysis.