Behavior of the Chiral Herbicide Imazamox in Soils: pH-Dependent, Enantioselective Degradation, Formation and Degradation of Several Chiral Metabolites

Many pesticides show a pronounced bi-phasic degradation in soil, typically with a faster initial phase, followed by a slower decline. For chiral compounds, a bi-phasic decline of the total concentration may result from enantioselective degradation. In this study with the chiral herbicide imazamox, bi-phasic degradation was observed in most of the eighteen soils investigated. In neutral soils, degradation was, in fact, enantioselective with faster degradation of (+)-imazamox. In slightly acidic soils, differences between enantiomers were not pronounced, and in strongly acidic soils, degradation was again enantioselective, but with reversed preference. Additional experiments with pure enantiomers indicated no interconversion. Enantioselective degradation thus contributed to the bi-phasic decline of the total concentration in certain soils. However, this was not the only factor since degradation of the individual enantiomers was bi-phasic in itself. In addition to the observed correlation between enantiosele...