Submitted to: 226th American Chemical Society National Meeting
Publication Type: Proceedings
Publication Acceptance Date: 9/11/2003
Publication Date: 9/11/2003
Citation: HUI, L., TEPPEN, B., JOHNSTON, C., LAIRD, D.A., BOYD, S. MANIPULATION OF PESTICIDE SORPTION ON SMECTITE CLAY VIA CATION EXCHANGE. 226TH AMERICAN CHEMICAL SOCIETY NATIONAL MEETING. 2003. V. 43(2). P. 1212-1215.
Technical Abstract: Retention of nonpolar organic compounds by soils from aqueous solutions is strongly correlated with soil organic matter content, however, many important categories of pesticides and organic contaminants have polar moieties and recent research has shown that these compounds are strongly adsorbed by soil clays. Pesticide adsorption by soil clays is often dramatically influenced by the exchangeable cations present. Among the common exchangeable cations in soils (Ca, Mg, K, and Na), K-saturated minerals frequently demonstrate the strongest sorption of pesticides. We hypothesize that the magnitude of pesticide sorption is proportional to the fraction of clay interlayers occupied by K ions. To test this hypothesis, we measured sorption isotherms of three pesticides with different polarity (dichlobenil, monuron, and biphenyl) on a smectite (SWy-2) containing various populations of K and Ca ions on the exchange sites and used x-ray diffraction to evaluate the extent of demixing in the distribution of the interlayer K and Ca ions. In general, sorption of dichlobenil increased with the K/Ca ratio above a threshold K/Ca ratio of 0.01 M/0.08 M. Similar sorption enhancement was observed for monuron but to a much lesser extent. Nonpolar biphenyl displays the same sorption capacities on Ca- and K-SWy-2. The study suggests that the magnitude of pesticide sorption on clay minerals can be manipulated by controlling the exchangeable cation population on the mineral surfaces.