Microbial Metabolism and Further Fate of Bentazon in Soil

The transformation of the herbicide bentazon in soil was investigated with radiolabeled bentazon and its derivatives 8-hydroxybentazon, 8-methoxybentazon, and N-methylbentazon. Mineralization of bentazon was a microbial activity which required the presence of oxygen and was impeded by additional carbon substrates such as powdered alfalfa (Medicago sativa) residues. The formation of bound residues of bentazon in humic substance depended on microbial activity, too, and was stimulated by the presence of oxygen; however, there was also a significant immobilization of bentazon in the absence of oxygen. A culture of the fungus Phanerochaete chrysosporium converted 8-hydroxybentazon to a dimeric derivative. The same dimer was formed by the action of laccase. This dimer and the monomeric 8-OH-bentazon acted as key metabolites in the formation of bound residues from bentazon. The further mineralization of bound bentazon residues was a slow process, with 9.3% mineralization within 141 d.