Photodegradation Of Atrazine In The Presence Of Indole-3-acetic Acid And Natural Montmorillonite Clay Minerals

Atrazine(2-chloro-4-ethylamino-6-isopropylamino-s-triazine)is a widely used agricultural herbicide throughout the world.Because of its widespread usage,relatively high water solubility and recalcitrant behavior,it is still frequently detected in surface and ground water,even though it has been phased out of use for many years in Europe.Moreover,because of the carcinogenic and endocrine-disrupting property of atrazine,its environmental behavior has caused much attention in order to fully understand its impact on the health of ecosystems.In this study,a new natural degradation pathway of atrazine was proposed.Our results show that atrazine could be photo-oxidized in the presence of indole-3-acetic acid and natural montmorillonite clay under environmentally relevant conditions.The reaction was initiated by the production of hydrated electrons generated from the photoionization of indole-3-acetic acid,and then hydrated electrons were transformed into hydroxyl radicals via reaction with protons and dissolved oxygen.Our results clearly indicate that the presence of montmorillonite greatly enhances the yield of hydrated electrons and promotes further degradation of atrazine by hydroxyl radical.The degradation process is strongly affected by solution pH,the type of exchangeable cation present in clay interlayer and the hydration status of montmorillonite.The lower pH favors this reaction and K+-montmorillonite promotes the degradation of atrazine more significaltly than Ca2+-montmorillonite.The swelling status of montmorillonite also makes a difference,in which case montmorillonite with less interlayer water layers shows a superiority.In this surface reaction,montmorillonite clay mineral not only increases the yield and prolongs the lifetime of hydrated electrons by stabilizing radical cations through electrostatic attraction with the negative charges embedded in the interlayer,but also provides a confined space where the probability of contact between atrazine and active radicals is markedly increased.Since both indole-3-acetic acid and montmorillonite clay are widely distributed in the environment,the proposed reaction would be important for the degradation of organic contaminants,especially for persistent compounds in natural circumstances.