Study On Carbon And Bromine Isotopic Effects Of Typical PBDEs Congeners

Poly Brominated Diphenyl Ethers(PBDEs)are a kind of important additive brominated flame retardants,which are widely used in the textile and circuit board etc.Because of lacking chemical bond bondage,they are easily releasing from the matrix and getting into the environment,causing widespread pollution in spheres.Some PBDEs conergers have been listed in persistent organic pollutants.Conventional method of concentration often can not provide enough information on the source and degradation of PBDEs.Compound specific stable isotope analysis(CSIA)and analyze stable isotopic composition of specific element(such as carbon,bromine)in PBDEs,which can overcome the shortcoming of traditional quantitative method effectively and trace source and pollution process of PBDEs.Compound specific bromine isotope analysis developed very late.The traditional analysis method(offline-IRMS)is high accuracy,but the application is limited by tedious pre-treatment processes,requirement of large sample size and problems of separation and concentration.Recently new method for bromine isotope analysis online by coupled gas chromatography and multiple-collector inductively coupled plasma mass spectrometry(GC-MC-ICPMS)is not good enough for PBDEs analysis because of large molecular weight and low vapour pressure of PBDEs.Furthermore,sophisticated instrument of GC-MC-ICPMS makes it difficult to achieve in ordinary laboratories.Limited by bromine isotope analysis method,there is no two-dimensional isotopes(carbon and bromine)data of PBDEs from different sources reported currently,and the two-dimensional isotopic effect of PBDEs during degradation process has not been studied.Base on National Natural Science Foundation of China and earlier research on inorganic bromine isotope,typical PBDE congeners 2,2',4,4'-tetrabromodiphenyl ether(BDE-47)decabromo-diphenyl ether(BDE-209)are chosen to estabilish bromine stable isotopic analysis method online and explore carbon and bromine isotopic fractionation during BDE-47 degradation.In addition,two-dimensional isotopic characteristics of BDE-209 and BDE-47 reagents are analyzed,which provide foundation for the indication of coumpound spedific carbon and bromine isotopes analysis to trace source,migration and transformation processes of PBDEs.The research has an important theoretical and practical significance for comprehensively understanding behavior of PBDEs,preventing pollution of PBDEs in the environment effectively.The conclusions are as follows:1.Analysis methods of content,carbon and bromine isotopes for BDE-47 in water.(1)BDE-47 content measurement based on ultrasound assisted liquid liquid extraction-gas chromatography microelectronics capture detector(ULL-GC-mECD)method.BDE-47 is extracted from water samples by ultrasound assisted liquid liquid extraction method and then analyzed by GC-mECD.Under condition of repeated three times,10 min for each time and the volume ratio of 1:1 between extracting solvent and water sample,stable extraction efficiency up to 80% can be obtained during extraction of BDE-47 from water sample by ultrasound-assisted liquid-liquid extraction method,which is satisfied test requirement.Relative standard deviation of 2.11% is obtained after determining BDE-47 standard solution three times by GC-mECD.(2)Carbon isotopic analysis for BDE-47 in water by head space solid phase microextraction-gas chromatography-combustion oven-isotope ratio mass spectrometer(HS-SPME-GC-C-IRMS)method.HS-SPME is chosen to accumulate BDE-47 in water sample for carbon isotope determination,which simplifies extraction process.Considering the safety,stability of extraction and running time of isotope ratio mass spectrometer,the heating temperature of 140 oC and extraction time of 60 min are chosen for extracting BDE-47 from water sample by HS-SPME,and pH of water sample has no significant influence on extraction efficiency.Reproducibility of the method is 0.15 ‰(n = 7),which is better than internationally recognized error(± 0.5 ‰).Meanwhile,the data is in good agreement with that determined by EA-IRMS method,indicating that dissolution and HS-SPME process has no influence on carbon isotope compositon,and HS-SPME is suitable for carbon isotopic analysis of BDE-47 in water.(3)Bromine isotope determination by gas chromatography quadrupole mass spectrometry(GC-qMS)method for BDE-47 in water sample.BDE-47 in water is extracted into n-hexane and introduced into GC-qMS system.Molecular ions 12C121H616O79Br4+(m/z=482)and 12C121H616O79Br381Br+(m/z=484),fragment ions 12C121H616O79Br2+(m/z=324)and 12C121H616O79Br81Br+(m/z=326)are choosen to calculate bromine isotopic composition of BDE-47 by mathematical formula.When dwell time is 50 ms and injected amount of BDE-47 is between 2.5 and 5ng,the bromine isotopic composition calculated by multiple ions method is stable with the standard deviation of ± 1.76‰ ~ ± 2.40‰.GC-qMS method is easy to operate and does not require a tedious preprocessing(separation,concentration and conversion processes of offline method)and sophisticated instrumentation(such as GC-MC-ICPMS),and only requires small sample size,which has reduced the difficulty of bromine isotopic analysis and has an great advantage in analysis trace organic pollutants such as PBDEs in the environment.2.Study on kinetics and factors of degradation BDE-47 by Fenton system.(1)Influence of reaction condition on BDE-47 degradation by Fenton system.At different initial pH,H2O2 and FeSO4 concentrations,degradation of BDE-47 by Fenton system are fitting very well by the pseudo-second reaction kinetic model.Considering pseudo-second reaction rate constant,equilibrium degradation rate and economy,when the concentration of BDE-47 is C(BDE-47)=1.029×10-6 mol/L,pH=2.97,C(H2O2)=3.918×10-2 mol/L and C(FeSO4)= 3.918×10-3mol/L are the best reaction condition.When the dosage of H2O2 is decided,multiple-adding is more conducive to degradate BDE-47 than adding once.(2)Effect of inorganic anions on BDE-47 degradation by Fenton system.By capturing hydroxyl radicals or changing efficient Fe form in the system,Cl?,Br?and SO42?inhibite degradation reaction of BDE-47 by Fenton system.And this inhibition effect enhances with elevated anion concentrations.The suppression is Cl-> SO42-> Brunder same condition.(3)Effect of heavy metals on BDE-47 degradation by Fenton system.Heavy metal ions Cu2+ and Cr(VI)can catalyze H2O2 to intiate Fenton-like reaction to degradate BDE-47 and the efficiency increases with the metal ion concentration.Degradation rate of BDE-47 is Cu2+/H2O2 >> Cr(VI)/H2O2 under same condition.3.Carbon and bromine isotopic compositions of PBDE congeners reagents.(1)Carbon and bromine isotopic compositions of BDE-47 and BDE-209 from different suppliers and the reasons for the varied compositons.BDE-47 and BDE-209 from different suppliers exibit unique carbon and bromine isotopic compositions.d13C of these congeners vary from-25.57‰ and-28.44‰,and d81Br vary from-0.34‰ to +0.50‰.Both the degree of bromination and substitution of bromine atoms affect the carbon and bromine isotopic composition of PBDEs.The carbon isotopic composition of PBDEs is close to the carbon isotopic composition of petroleum etc.,indicating that the carbon in PBDEs is mainly derived from natural hydrocarbon.And bromine is mainly from seawater and brine enriched in bromine.Because of natural variation,these materials have different carbon and bromine isotopic compositions.In addition,the production processes(selected pathway,degree of reaction and reaction temperature,etc.)would result in isotopic fractionation related to the kinetic isotope effect(heavy isotope reacts slower than light isotope).(2)Indication of carbon and bromine isotopic compositions to the source identification of PBDEs.PBDEs from different sources exhibit unique carbon and bromine isotopic compositions due to differences in precursors and experienced processes,which suggests that carbon and bromine isotopic composition can be used to identify the source of PBDEs.It is also worth noting that the uncertainty of this method does exist,the difference of isotopic composition among PBDEs from different sources may not be significant(less than the analytical accuracy).In addition,isotopic fractionation during degradation processes should be considered when source identification is applied by isotopic compositions.Therefore,the source identification of PBDEs by isotopic composition characteristics should be used carefully,combining environmental behavior of PBDEs and isotopic compositions at the same time would get good results.4.Isotope effects for BDE-47 during different degradation processes.In order to investigate the carbon and bromine isotopic effects of BDE-47 during degradation processes,BDE-47 is oxidized by Fenton reagent,and the biomimetic degradation by vitamin B12 and TiCl3 is also studied for comparasion.Affected by isotope dilution effect and secondary isotope effect,carbon and bromine isotopic compositions did not change with reaction in both Fenton and Vitamin B12 system,which suggests that carbon and bromine isotopic compositions can not used to indicate degradation of BDE-47.However,the conserved behaviors of carbon and bromine isotopes make it more reliable to use them to identify pollution source of BDE-47 in field applications.Further research is needed on isotopes effect during natural attenuation process to verify the effectiveness of source identification by isotopic compositions.The innovations of this research are:(1)A simple and convenient method based on GC-qMS for stable bromine isotope analysis online is established.(2)The two-dimensional isotopic compositions(carbon and bromide)of typical PBDEs congeners are analyzed for the first time,which lay the foundation for the construction of two-dimensional isotope information base for PBDEs.(3)This study reveals the carbon and bromine isotopic effects of BDE-47 during Fenton oxidation and bio-simulated reduction,which provide a theoretical basis for indication of carbon and bromine isotopic technology in PBDEs migration and transformation.