Extractable and nonextractable (bound) residues of acifluorfen in an organic soil

Acifluorfen (AC), 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid, was applied to an organic soil at 220 mg kg(-1) in a laboratory incubation study. A conventional extraction method with solvents and supercritical fluid extraction (SFE) were used to evaluate extractable and nonextractable (bound) residues of AC and its metabolites in the soil. Over an incubation period of 7 months, the soil contained 22% AC of the initially applied herbicide and the residues were almost completely extracted with aqueous methanol. Only 0.8% AC was found in the bound form. Seventy-five percent AC applied was degraded to aminoacifluorfen (AAC) (due to reduction of nitro group to amino group) of which 60% was extracted by aqueous methanol, and 15% was in the bound form, mainly associated with the humin fraction of the soil organic matter. No further transformation of AAC to other metabolites was observed.