| Abstract
| - This study was performed to determine which oxidoreductive catalysts were most efficient in catalyzingthe binding of 8-hydroxybentazon to soil humic substances. 8-Hydroxybentazon was completelytransformed by an oxidoreductive enzyme, laccase of Myceliophthora thermophila, at pH 3.0−7.0within 30 min. When abiotic catalysts, manganese(IV), iron(III), and aluminum oxides were used inthe same pH range, 8-hydroxybentazon was completely transformed only by manganese(IV) oxide(δ-MnO2), but a relatively small amount of 8-hydroxybentazon was transformed by iron(III) oxide andaluminum oxide. The adsorption of 8-hydroxybentazon in the soil showed an H-type and coincidedwell with the Langmuir isotherm. To better understand the factors involved in the rapid and strongbinding of 8-hydroxybentazon with soil humic substances, 8-hydroxybentazon transformation byoxidoreductive catalysts was studied in various soil conditions: air-dried, preincubated, sterilized,and iron(III) oxide and manganese(IV) oxide free. 8-Hydroxybentazon was completely transformedwithin 24 h in the decreasing order of preincubated, air-dried, and sterilized soils. However, littletransformation was observed in the iron(III) oxide and manganese(IV) oxide free soils. These resultssuggest that the major catalyst responsible for the rapid and strong binding of 8-hydroxybentazon tosoil humic substances is a metal oxide, manganese(IV) oxide, not a soil oxidoreductive enzyme. Keywords: Bentazon; hydroxybentazon; oxidoreductive catalyst; laccase; metal oxide; oxidativecoupling
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