Degradation of bensulfuron‐methyl on various minerals and humic acids

Abstract

Summary The chemical degradation of bensulfuron‐methyl on various dry minerals (kaolinite, silica gel, alumina, H + bentonite, montmorillonite KIO) and on solid humic acid was investigated at 30°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 alumkia preferentially induced sapontfication of the carbonie‐thoxy subsiituent fixed to the aromatic ring. The degradation compounds obtained generally remained stable, with the exception of phcnyl‐sulfonamide, which cyclized rapidly on alumina. The suggested degradalion path is similar to that previously proposed for chemical hydrolysis.