Sorption Properties Of Chloroacetanilide Herbicidesand Correspongding Ethanesulfonicacid Intermediates On Three Typicalsoilminerals

Nowdays, the environmental studies of pesticides are largely focused onthe parent compounds, less involved in their degradation products. However,degradation products are detected from environment frequently, and some ofthese products were much more toxic than their parent compounds.Chloroacetanilide herbicides are the mainstay of modern preemergenceherbicides, which were released into air, water and soil through various waysduring applications. Part of the herbicides transfered to more persistentproducts like ethane sulfonic acids （ESA）. In this work, we investigated theadsorption properties of chloroacetanilide herbicides and their ESAdegradates on montmorillonit, kaolinite, and aluminum oxide.Firstly, adsorption rate increased rapidly from a very small value; as timepassed, adsorption rate increased slowly and became steady after a certaintime, equilibrium time was200min. The Equilibrium adsorption rate ofalachlor was higher than that of acetochlor, and alachlor ESA adsorption rateshowed the same trend comparing with acetochlor ESA. To compare ESAwith its parent compound, the adsorption rate declined.The adsorption process could be well described by thepseudo-second-order kinetics model. The value of kinetic constants K₂wasaluminum oxide> kaolinite> montmorillonit, acetochlor> alachlor, acetochlor ESA> alachlor ESA. Time for equilibrium adsorption shortened asK₂grew. The results showed that the Freundlich isotherm was moreapplicable for the adsorption system. The value of Freundlich constants Kfwas Montmorillonite> kaolin≥alumina, alachlor> acetochlor> alachlorESA> acetochlor ESA. Freundlich exponent n was less than1that indicatedthat the three adsorbents have higher attraction at low concentration ofherbicides and their ESAs.These results indicated that pH plays the same role on adsorption of boththe herbicides and ESAs. Adsorption rates increased as pH decreased.However, the influence of ionic strength on the adsorption is totally different.The adsorption of the parent compounds on mineral surface is inverselyproportional to ionic strength. But for ESAs, the ionic strength can enhancetheir adsorption in a certain range, with an optimal value. The effect of humicacid on the adsorption is not apparent, needed further research. Metal ionsweakened the adsorption of alachlor and its ESAon the mineral surface.The BET surface areas of the adsorbents followed the ordersmontmorillonit （325.11m₂/g）>> kaolinite （25.22m₂/g）> aluminum oxide（17.29m₂/g）. At the same condition, adsorption rate of alachlor, acetochlorand two ESAs on mineral surface followed the orders of montmorillonit>>kaolinite and aluminum oxide, and the adsorption rate on kaolinite is slightlylarger than that on aluminum oxide.This study revealed that adsorption efficiency, influencing factors, and the adsorption mechanism of chloroacetanilide herbicides and their ESAs onmontmorillonit, kaolinite and aluminum oxide. This study made sense forreach the migration, conversion of herbicides and its degradation product,revealed part of their environmental behavior, and strengthened theunderstanding of the environmental pollution.