Sorption of Bentazon and Degradation Products in Two Mississippi Soils

Abstract

Bentazon degradation in soil typically proceeds with development of bound residue. Low sorption of bentazon suggests that this residue consists of degradation products; however, there is little data on the sorption behavior of these products. This study was undertaken to determine the sorption of bentazon and the degradation products 2-amino-N-isopropyl benzamide, 2-aminobenzoic acid, andN-methyl bentazon in Dundee silt loam and Sharkey clay, two common agricultural soils of the Mississippi Delta. Greater sorption of bentazon and degradation products in the Sharkey soil was related to finer texture and higher organic C content. Isotherms were nonlinear, with sorption increasing in the order bentazon ≪ 2-amino-N-isopropyl benzamide <N-methyl bentazon. In general, methanol extraction indicated reversible sorption of these compounds. Therefore, it is unlikely that sorption of either 2-amino-N-isopropyl benzamide orN-methyl bentazon contributes to bound residue. In contrast, essentially all of the14C sorbed from radiolabeled 2-aminobenzoic acid solution remained bound after methanol extraction. However, due to degradation of 2-aminobenzoic acid, it was not possible to conclude the extent to which this compound contributed to bound14C. Sorption of14C from 2-aminobenzoic acid exceeded that ofN-methyl bentazon, and at low initial concentrations (≤ 20 μM) was nearly 1000-fold greater than bentazon sorption.