Adsorption of chloroacetanilide herbicides on soil (I). Structural
influence of chloroacetanilide herbicide for their adsorption on soils and its
components
Affiliations: Institute of Environmental Science, Zhejiang
University at Yuquan Campus, Hangzhou 310027, China; E-mail:
wpliu@mail.hz.zj.cn
Note: [] Corresponding author
Abstract: Adsorption of chloroacetanilide herbicide acetochlor,alachlor,
metolachlor and propachlor on soils and soil components was determined, and the
structural differences of these herbicides were used to explain the order of
sorptivity. Adsorption isotherms for all herbicide-soil combinations conformed
to the Freundlich equation, and K_f increased with increasing soil organic
carbon content. K_d on soil humic acid was greater than that on clay, but
association of humic acid with clay reduced the overall adsorption. On all
soils and soil humic acids, herbicide adsorption decreased in the order:
metolachlor > acetochlor > propachlor > alachlor. On
Ca^2^+-montmorrilonite, the order changed to metolachlor > acetochlor >
alachlor > propachlor. FT-IR spectra of herbicide-clay or herbicide-humic
acid-clay mixtures showed that H-bonding and charge transfer were the primary
interaction pathways between these compounds and the surface of clay or humic
acids. The different moieties attached to 2-chloro-acetanilide and their unique
arrangement may have influenced the binding mechanisms and thus the sorptivity
of these herbicides. This study indicates that the structural difference of
pesticides in the same classes may be used as a molecular probe to obtain a
better understanding of sorption mechanisms of pesticides on soil.