Structural influences in relative sorptivity of chloroacetanilide herbicides on soil

Adsorption of the chloroacetanilide herbicides acetochlor, alachlor, metola chlor, and propachlor was determined on soils and soil components, and thei r structural differences were used to explain their sorptivity orders. On a ll soils and soil humic acids, adsorption decreased in the order: metolachl or > 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 her bicides and adsorbents. The different substitutions and their spatial arran gement in the herbicide molecule were found to affect the relative sorptivi ty of these herbicides by influencing the reactivity of functional groups p articipating in these bond interactions. It was further suggested that stru ctural characteristics of pesticides from the same class could be used to i mprove prediction of pesticide adsorption on soil.