INTERACTIONS OF METHOMYL WITH MONTMORILLONITES

The adsorption of the insecticide methomyl (S-methyl N-(methylcarbamoy loxy)thioacetimidate) by smectites with different layer charge (SWy an d SAz montmorillonites and SH-Ca hectorite) has been determined. Adsor ption has been expressed as the adsorbent/adsorbate distribution coeff icient Kd. which increased when the layer charge of the smectite decre ased. The Kd values for homoionic SWy montmorillonite samples increase d when the ionic potential of the interlayer cation decreased, except for SWy-Fe3+. Infrared (IR) spectra and X-ray diffraction (XRD) analys is of the SWy-K+ and SWy-Na+ montmorillonites treated with methomyl su ggest that pesticide molecules interact through polar bonds with the i nterlamellar cation. In the case of SWy-Fe3+, kinetic studies high per formance liquid chromatography (HPLC), IR and XRD data indicated that adsorption and degradation both account for the high Kd value obtained .