Adsorption of chloroacetanilide herbicides on homoionic montmorillonite was studied by coupling batch equilibration and FT-IR analysis. Adsorption decreased in the order metolachlor>acetochlor> alachlor>propachlor on Ca2+-or Mg2+-saturated clays and in the order metolachlor>alachlor> acetachlor>propachlor on Al3+-or Fe3+-saturated clays. FT-IR spectra showed that the carbonyl group of the herbicide molecule was involved in bonding. For the same herbicide, adsorption of alachlor, acetachlor, and metolachlor on clay followed the order Ca2+ Mg2+<Al3+e Fe3+, which coincided with the increasing acidity of homoionic clays. Adsorption of propachlor, however, showed an opposite dependence, suggesting a different governing interaction. In clay and humic acid mixtures, herbicide adsorption was less than that expected from independent additive adsorption by the individual constituents, and the deviation was dependent on the clay-to-humic acid ratio, with the greatest deviation consistently occurring at a 60:40 clay-to-humic acid ratio.

Degradation of aqueous 250mg/L 4-chlorophenol (4-CP) by high-

Adsorption of the chloroacetanilide herbicides acetochlor, alachlor, metolachlor, and propachlor was determined on soils and soil components, and their structural differences were used to explain their sorptivity orders. On all soils and soil humic acids, adsorption decreased in the order: metolachlor >acetochlor>propachlor>alachlor. On Ca2+-saturated montmorillonite, the order changed to metolachlor >acetochlor>alachlor>propachlor. FT-IR differential spectra of herbicide-clay or herbicide-humic acid-clay showed possible formation of hydrogen bonds and charge-transfer bonds between herbicides and adsorbents. The different substitutions and their spatial arrangement in the herbicide molecule were found to affect the relative sorptivity of these herbicides by influencing the reactivity of functional groups participating in these bond interactions. It was further suggested that structural characteristics of pesticides from the same class could be used to improve prediction of pesticide adsorption on soil.

Sorption and catalytic hydrolysis of the herbicide diethatyl-ethyl [N-chloroacetyl-N-(2,6-diethylphenyl) glycine ethyl ester] on homoionic Na+-, K+-, Ca2+-, and Mg2+-montmorillonite clays were studied in aqueous media. The Freundlich sorption coefficient, Kf, measured from isotherms on clay followed the order of Na+≈K+>Mg2+≈Ca2+. Analysis of FT-IR spectra of diethatyl-ethyl sorbed on clay suggests probable bonding at the carboxyl and amide carbonyl groups of the herbicide. The rate of herbicide hydrolysis in homoionic clay suspensions followed the same order as that for sorption, indicating that sorption may have preceded and thus caused hydrolysis. Preliminary product identification showed that hydrolysis occurred via nucleophilic substitution at the carboxyl carbon, causing cleavage of the ester bond and formation of diethatyl and its dechlorinated derivative, and at the amide carbon, yielding an ethyl ester derivative and its acid. These pathways also suggest that hydrolysis of diethatyl-ethyl was catalyzed by sorption on the clay surface.