Polymerization of the Herbicide Bentazon and Its Metabolite with Humic Monomers by Oxidoreductive Catalysts

Abstract

and Backgrounds The formation of covalent bonds between pesticides and their metabolites, which structurally resemble phenolic and aniline compounds and soil organic matters, is mediated by biotic or abiotic catalysts andresults in stabilization against bioavailability. The herbicide bentazon in the soil environment has shown that it can be degraded by hydroxylation at the 6 or 8 positions on the phenyl ring and its metabolites can be incorporated into soil organic matters. To elucidate the binding mechanism of the bentazon and its metabolite 8-hydroxybentazon to humic substances, bentazon and 8-hydroxybentazon were incubated with catechol in the presence of laccase an oxidoreductive catalyst. A product with a molecular weight of 348 identified as a dimer was composed of one catechol and one bentazon molecule. A second reaction product with a molecular weight of 586 appeared to be a trimer, consisting of one catechol molecule and two bentazon molecules. Data of 1 H-NMR and 1 3 C-NMR spectroscopy indicate that the herbicide bentazon can be incorporated into soil organic matter by nucleophilic addition to quinone-like substrate during humification process. In case of the 8-hydroxybentazon, the three intermediates were confirmed in polymerization reaction mixture of 8-hydroxybentazon by HPLC and LC-MS.