Study On Photodegradation And Biodegradation Mechanism Of Typical Bromophenol By Compound Specific Isotope Analysis

Since the 21st century,with the wide use of electronic products,Brominated flame retardants have been detected frequently,and their environmental and human health hazards have aroused widespread concern.Bromophenols（BPS）are important brominated flame retardants.And toxicological studies have shown that bromophenol may interfere with animal and human endocrine system,cause liver toxicity and a series of adverse effects.Therefore,in this thesie,bromophenols（2-bromophenol,3-bromophenol,4-bromophenol,2,3-dibromophenol,2,4-dibromophenol,2,5-dibromophenol,2,6-diphenylbromophenol,3,4-dibromophenol,3,5-dibromophenol,2,3,4-tribromophenol,2,3,6-tribromophenol,2,4,5-tribromophenol,3,4,5-tribromophenol,2,4,6-tribromophenol,2,3,4,6-tetrabromophenol,2,3,4,5-tetrabromophenol,2,3,4,6-tetrabromophenol,Pentabromophenol）was selected as the research object,and the photodegradation mechanism and biodegradation mechanism of bromophenol under simulated light were systematically studied by means of high performance liquid chromatography,ion chromatography,total organic carbon analyzer and gas chromatography/combustion/isotope rafto mass spectrometer（GC/C/IRMS）.he intermediate products of bromophenol photolysis and the changes of carbon isotope in the process of bromophenols photolysis were focused.This thesis focuses on the following aspects:Firstly,photodegradation is one of the most important degradation methods of organic pollutants in the environment.In this work,the photodegradation of bromophenol under simulated sunlight was studied to find out the mechanism of the migration and transformation of bromophenol.Firstly,the degradation rate of bromophenol increased first and then decreased under 100 W simulated fluorescent lamp,which may be due to the rapid increase of intermediate products of bromophenol degradation competing for photons with bromophenol.Secondly,the change rate of Br⁺concentration gradually slows down with the increase of time.On the one hand,it may be due to the rapid accumulation of intermediate products of bromophenol degradation,on the other hand,it may be due to the formation of Br-,bro-,and Br O3^-.Within 30 min,the degradation rate and debromination rate of bromophenol were above 60%except for 3-Bromophenol.Total organic carbon（TOC）is the content of organic carbon in the whole solution,so it is slightly mineralized in the degradation period of bromophenol,and then almost not mineralized,which may be due to the formation of intermediate products with light resistance.At the same time,the photodegradation products of bromophenol were identified by GC/MS,and the possible degradation pathway was put forward,and the degradation mechanism of monobromophenol was mainly explained.Resorcinol and catechol are the main photodegradation products of 3-Bromophenol and 2-bromophenol respectively,which may be related to the position of bromine atom on the aromatic ring.The bromine transfer of 2-bromophenol to 4-bromophenol may be due to the weak intramolecular hydrogen bond and the easy dissociation of bromine atoms.3-Bromophenol reacts through ionic mechanism,including heterocleavage of C-Br bond.4-bromophenol is photodegradated by free radical pathway,accompanied by homolysis of C-Br bond.It was found that in addition to the widely known hydroxyl substitution and debromination,2,6-dibromophenol-1,4-diol and 2,4,6-tribromophenol were detected in all dibromophenols except 3,5-dibromophenol,which may be due to the reaction of dibromophenol with Br-,Br O^-,and Br O3 to form tribromophenol,which was further degraded.Then,the mechanism of bromophenol photodegradation was further studied by using stable isotope analysis（CSIA）,and the changes of carbon isotopes in the process of bromophenol photodegradation were determined by GC/C/IRMS.The akiec values of 4-bromophenol,2,5-dibromophenol,2,6-bromophenol and 3,5-dibromophenol ranged from1.0076 to 1.0176,and positive carbon isotope effects were observed.The result may be caused by the fracture of C-X bond.But in addition,the akiec of other bromophenols are less than 1.We speculate that the isotopic effect may be the superposition of mass dependent kinetic isotopic effect and mass independent magnetic isotopic effect.Finally,the biodegradation of bromophenol by microorganisms was explored,and the change of biodegradation rate and carbon isotope effect were studied.It was found that the degradation rate of bromophenol was very slow in four days,and then rapidly,and the degradation rate of dibromophenol was higher than that of monobromophenol.In the process of microbial degradation of bromophenol,the start and end of the process are differentΔδ¹³C is less than the allowable error of the instrument±0.5‰.Therefore,the carbon isotope fractionation of bromophenol was not occurred or obvious during the degradation of EM.