EFFECT OF METAL-BINDING ABILITY ON THE ADSORPTION OF ACIFLUORFEN ON SOIL

The adsorption of acifluorfen, the sodium salt of 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid, on six soils of various physical and chemical properties as well as its dependence on the exchangeable cation (Ca2+ and Na+) and on soil pH was studied. Adsorption isotherms conformed to the Freundlich equation. Soil saturation by Na+ ions produced a strong decrease in acifluorfen adsorption, whereas the opposite finding was observed for Ca-saturated soils. Adsorption was found to, be correlated with cation-exchange capacity (CEC) much better than with other soil properties and decreased with increasing pH. At comparable pH, variations of k(f) values after Ca saturation of soils indicated that complex formation reactions, leading to precipitation of insoluble complexes, contribute to simulate high adsorption.