Acifluorfen Sorption and Sorption Kinetics in Soil

Factors which influence kinetics of sorption for acifluorfen, a postemergence herbicide, in soil were evaluated. Twelve soils of varying characteristics were used in this study. Sorption kinetics experiments with 5.86 μM 14C-labeled (19.6 Bq mL-1) acifluorfen were conducted for equilibration times up to 96 h. Sorption was rapid for all soils, and most soils reached a pseudo-equilibrium after 24−48 h of equilibration. Apparent sorption increased at later times, possibly reflecting sorption of acifluorfen or metabolites, since acifluorfen is subject to biotransformation. Further investigation comparing sorption at 4 and 25 °C indicated that microbial metabolism was occurring for some soils at equilibration times longer than 24−48 h. Aminoacifluorfen was observed in methanol extracts of soils equilibrated 96 h. Soils were equilibrated for 24 h with 14C-labeled acifluorfen (2.6−65.8 μM, 19.5 Bq mL-1) to obtain sorption isotherms. Capacity for acifluorfen sorption in these soils generally increased with increasing soil organic carbon content, cation exchange capacity, and soil acidity. Keywords: Herbicide; acifluorfen; diphenyl ether; sorption; organic carbon; tillage