Study On The Mechanism Of Generation And Photodegradation Of Chlorinated Products Of Estrogens

Estrogens,as a kind of common endocrine disrupting chemicals（EDCs）,exist widely in natural waters and have been demonstrated to exhibit enormous threat on animal and human,as well as ecosystem.Municipal sewage treatment plants effluents are the main source of estrogen pollutants in the receiving waters.During the chlorine disinfection process of effluents,a series of chlorination by-products of estrogens will be formed,which may show higher estrogen receptor binding activity than the parent compounds.In recent years,these chlorination by-products of estrogens have been frequently detected in natural water.Nevertheless,to date,few studies have reported their fate in aquatic environment.In previous studies,an interesting phenomenon wasfound that UV absorption redshift,along with absorbance increase,occurs after chlorination of estrogens,leading to overlap with the spectrum of terrestrial sunlight.Thus,the direct photodegradation of chlorination by-products of estrogens will become an important migration and transformation pathway.It is urgent to study the fate of chlorination by-products of estrogens under sunlight.Four common estrogens,including estrone（E1）,17β-estradiol（E2）,ethinyloestradiol（EE2）and estriol（E3）,were selected as the research object in this study.By the reaction between estrogen and sodium hypochlorite,the effect of p H,initial substrate concentration,and sodium hypochlorite dose on the chlorination of estrogens was investigated.The chlorination by-products of 17β-estradiol were identified and the chlorination pathway was proposed.The two main by-products from chlorination of 17β-estradiol was separated via preparative liquid chromatography.The direct photodegradation of these two chlorination by-products under simulated sunlight was further investigated,including the effect of initial substrate concentration and p H on the direct photodegradation and the photodegradation mechanism of chlorination by-products.The estrogenic activity changes of chlorination by-products after photolysis were also determined.The reaction between estrogen and sodium hypochlorite indicated that:1)the reaction between estrogen and sodium hypochlorite followed pseudo-first-order kinetic model;2)the reaction rate of chlorination of estrogens decreased with the increase of initial substrate concentration and increased with the increase of sodium hypochlorite dose;3)increasing p H can promote the chlorination reaction of estrogens in the range of p H6.0-9.0;4)the reaction level of chlorination of estrogens decreased with the increase of molecular weight in the order of EE2<E3<E2<E1;5)according to the chlorination kinetic model of estrogens,the reaction rate constant of neutral estrogens（Estrogen）with HCl O was calculated to be 7.51×10⁴M^-1s^-1,and the reaction rate constant of deprotonated estrogens（Estrogen^-）with Cl O^-was 1.34×10⁹M^-1s^-1;6)high resolutionliquid chromatography-mass spectrometry（HR-LC-MS）showed that the main chlorination by-products of 17β-estradiol were 2,4-dichloro-17β-estradiol（2,4-di Cl E2）and2-chloro-17β-estradiol（2-Cl E2）.The direct photodegradation of chlorination by-products of 17β-estradiol indicated that:1)during the chlorination of 17β-estradiol,the UV absorption redshift,along with the increase of absorbance,occurred,leading to overlap with the spectrum of terrestrial sunlight;2)the degradation of 2-Cl E2 and 2,4-di Cl E2 was negligible in dark,while a rapid direct photodegradation was observed under simulated sunlight,which followed pseudo-first-order kinetic;3)the direct photodegradation rate of 2-Cl E2 and 2,4-di Cl E2decreased with the increase of substrate concentration and increased with the p H;4)a series of quenching experiments suggested that the direct photodegradation of 2-Cl E2 and2,4-di Cl E2 under simulated sunlight was mainly attributed to their excited triplet states andsingletstate oxygen（¹O₂）,and hydroxyl radical（^·OH）exhibited negligible influence on the direct photodegradation;5)the estrogenic activities of 2-Cl E2 and 2,4-di Cl E2 were negligible after photolysis.