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-methoxybenta zon, and N-methylbentazon. Mineralization of bentazon was a microbial activ ity which required the presence of oxygen and was impeded by additional car bon substrates such as powdered alfalfa (Medicago sativa) residues. The for mation of bound residues of bentazon in humic substance depended on microbi al activity, too, and was stimulated by the presence of oxygen; however, th ere was also a significant immobilization of bentazon in the absence of oxy gen. A culture of the fungus Phanerochaete chrysosporium converted 8-hydrox ybentazon 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 metabol ites in the formation of bound residues from bentazon. The further minerali zation of bound bentazon residues was a slow process, with 9.3% mineralizat ion within 141 d.