Photodegradation Behaviors And Mechanism Of 17?-estradiol In Water Environment

17P-estradiol(E2)is a typical endocrine disrupting compound will pose a potential risk to aquatic life and human health.In recent years,the frequently detected E2 exposure in aquatic environment has caused worldwide concerns.However,the photodegradation mechanism of E2 under sun light,the mechanism of the coexistence of substrate on E2 photodegradation and the contribution of different reactive oxygen species(ROS)to E2 photodegradation are not clear and need further systematical research.In this study,the photodegradation behaviors of E2 in ultrapure water and under different water matrix such as HCO3-,NO3-,NO2-and humic acid(HA)were investigated under simulated irradiation using a 300 W xenon lamp.Four classified HA fractions(FA,FB,FC,FD)with different molecular weights were obtained by ultrafiltration before Fourier transform infrared spectroscopy and UV-Vis absorption spectroscopy characterization,and their effects on the degradation of E2 were investigated.Finally,the photodegradation products of E2 were analyzed by LC-MS/MS and the photodegradation pathway of E2 was deduced.The results showed that E2 photodegradation in all cases followed pseudo-first-order kinetics.In ultrapure water solution,the photodegradation rate constant and half-life of E2 were 0.1304 h'1 and 5.32 h respectively,and the contributions of direct photolysis,hydroxyl radials(·OH)and singlet oxygen free radicals(102)for E2 removal were 72%,21.2%and 6.8%,respectively.Different concentrations of HCO3-,NO3-,NO2-and HA exhibited obviously different effects on the photodegradation behavior of E2.In the presence of HCO3-(0.16?2.46 mmol/L),the removal rate of E2 decreased from 0.1236 h-1 to 0.1144 h-1 with the HCO3-concentration increasing,and quenching experiments verified that the contribution of OH was reduced gradually from 21.2%to 10.9%.In contrast,in the presence of NO3-(0?1.29 mmol/L),NO2-(0?1.29 mmol/L)and HA(0-12 mg/L),the removal rate of E2 increased significantly with the concentration increasing,and quenching experiments verified that the contribution of OH was enhanced to 24.8%,29.1%and 62.4%,respectively.The results also demonstrated that HA had a catalytic effect on E2 photodegradation kinetics.The photodegradation kinetics of E2 increased rapidly with increasing initial concentration of HA from 0 mg/L to 12 mg/L.However,when HA concentration rose to 24 mg/L,the promotion of E2 photodegradation would be weakened due to the scavenging of ROS.The electron paramagnetic resonance(EPR)analysis directly proved that hydroxyl radicals(·OH)was produced in the process of E2 photodegradation with HA,resulting in an enhanced photodegradation rate of E2.The low removal rate of TOC in the process of E2 photodegradation indicated that E2 has not been completely mineralization during photodegradation.HA classification results showed that the removal rate of E2 increased significantly with the HA's fractions molecular weight decreasing.LC-MS/MS analysis results indicated that E2 had four isomeric photodegradation products whose molecular formula is C18H21O3.