Microbial Metabolism and Further Fate of Bentazon in Soil

Abstract

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.