The sorption of nonionic pesticides onto clays and the influence of natural organic carbon

The sorption and desorption of alachlor, metolachlor and linuron onto kaolinite and Namontmorillonite and the influence of natural organic matter sorbed to these clays was examined. The intensity of adsorption was a function of the herbicide and clay. Sorption isotherms conformed to the Freundlich equation with Kf(ads) values ranging from l.63 x 10−3 for metolachlor to 2.84 x 10−2 for linuron onto Na-montmorillonite. The n values ranged from 0.78 for linuron to 1.92 for metolachlor. The three herbicides adsorbed to kaolinite to a much lesser extent. When Na-montmorillonite was coated with organic matter, alachlor sorption decreased proportionally to the foc sorbed to the clay. However, for metolachlor and linuron, sorption effects were more sensitive to the type of organic coating. Desorption isotherms deviated from sorption isotherms and both Kf and n varied.