ACIFLUORFEN SORPTION AND SORPTION KINETICS IN SOIL

Factors which influence kinetics of sorption for acifluorfen, a postem ergence herbicide, in soil were evaluated. Twelve soils of varying cha racteristics were used in this study. Sorption kinetics experiments wi th 5.86 mu M C-14-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 equilibra tion. Apparent sorption increased at later times, possibly reflecting sorption of acifluorfen or metabolites, since acifluorfen is subject t o biotransformation. Further investigation comparing sorption at 4 and 25 degrees C indicated that microbial metabolism was occurring for so me soils at equilibration times longer than 24-48 h. Aminoacifluorfen was observed in methanol extracts of soils equilibrated 96 h. Soils we re equilibrated for 24 h with C-14-labeled acifluorfen (2.6-65.8 mu M, 19.5 Bq mL(-1)) to obtain sorption isotherms. Capacity for acifluorfe n sorption in these soils generally increased with increasing soil org anic carbon content, cation exchange capacity, and soil acidity.