Behavior of the enantiomers of the herbicide imazaquin in agricultural soils under different application regimes

Abstract

Sorption, persistence, and leaching of the enantiomers of the herbicide imazaquin, S-imazaquin and R-imazaquin, in two soils under different application regimes were studied. Imazaquin dissipation was evaluated after a single application of the racemic herbicide and the pure enantiomers, and after a repeated application of the racemic herbicide. The effects of adding two olive-mill wastes (ALP and ALPc), biochar (BC), and organoclay (SA-HDTMA) on sorption, dissipation, and leaching of imazaquin enantiomers applied as racemic herbicide to the soils was also evaluated. For all treatments, sorption, dissipation, and leaching of imazaquin in the soils were either non-enantioselective or scarcely enantioselective. No interconversion of R-imazaquin to S-imazaquin or vice-versa was observed in the experiments with the pure isomers. Addition of ALP, ALPc, or BC did not enhance the negligible sorption of imazaquin enantiomers by the soils, but accelerated their dissipation. Addition of SA-HDTMA increased sorption of both enantiomers and delayed their dissipation and leaching. The results illustrate how agricultural practices can impact the behavior of imazaquin enantiomers in soils and support the suitability of replacing currently used racemic formulations of imazaquin with formulations based on the single biologically-active (R) enantiomer to reduce the environmental impact of this chiral pesticide.