Dynamics And Stable Carbon Isotopic Fractionation Of Hexabromocyclododecanes In FeS-Water System

Hexabromocyclododecanes(HBCDs) are one of the bromine alicyclic hydrocarbons. As an additive flame retardant, they are widely used throughout the world and thus it becomes ubiquitous contaminants in the environment and humans. Now, it has been an increasing concern of researchers on their degradation pathway in environmental media, including physical degradation, chemical degradation and biological and non-biological degradation. At present, there are many research conducted on the degradation pathways of HBCDs(light degradation, thermal degradation, biological transformation, etc.). However, there is lack of research about the abiotic degradation and transformation process of HBCDs under anaerobic environment.Ferrous sulfide(FeS) is one of the most abundant natural pyrites; they are widely distributed in natural water bodies, sediments, lakes, and groundwater environment. Compared with other reducing substances, FeS has two active reducing ingredients as ferrous ions and divalent sulfur ions. Therefore, the reducing power of FeS to some of organic pollutants would become stronger when it occured on the interface of water and sediment. In the present study, the author takes HBCDs as the research object to study their abiotic transformation dynamics characteristics in FeS-water system in the laboratory and the characteristics of stable carbon isotope fractionation in the transformation process. The purpose of this study is enhancing the understanding of HBCDs environmental behavior through laboratory research, and exploring the possibility to applying the compound-specific isotope analysis(CSIA) in research of environmental behavior of organic pollutants.In the first part of this thesis, a method was established by applying high performance liquid chromatography(HPLC) to separate the three major HBCD diastereoisomers(α-, β-, and γ-HBCD) and measure the stable carbon isotope ratio of HBCDs by GC-IRMS. Finally, an EA-IRMS analysis was used to verify the accuracy of this method. The result shows that the method established in this study was with good precision, accuracy and repeatability, and there is no carbon isotope fractionation in the process of determination by this method.In the second part of this thesis, the dynamics characteristic of HBCDs in anaerobic FeS-water system was studied. The results show that the degradation of HBCDs was very effective in FeS-water system. However, the degradation trend of α-HBCD、β-HBCD and γ-HBCD is not consistent in FeS-water system. The inconsistent of degradation of HBCD diastereoisomers was thought to be caused by the different degradation rate between diastereoisomers or the transformation of HBCD diastereoisomers in FeS-water system.In the third part of this thesis, the isotopic composition of HBCDs was analyzed in FeS-water system. Results show that there are an obviously isotope fractionation for α-HBCD、β-HBCD and γ-HBCD, during the degradation process in FeS-water system. The accumulation degree of δ13C values are 1.76 ‰、0.54 ‰、0.67 ‰ for β-HBCD, α-HBCD and γ-HBCD respectively. The fitting result by Rayleigh Fractionation model shows that β-HBCD and γ-HBCD follow the Rayleigh behavior well. In combination with the degradation kinetics data and isotopic fractionation, it can be proved in some degree that the transformation of HBCD diastereoisomers has happened in FeS-water system.The results of this thesis have an important supporting for insight into HBCDs environmental behavior in natural environment. The isotopic fractionation effect of HBCDs in abiotic transformation process indicating that compound-specific isotope analysis has a great application prospect in natural environment degradation behavior of organic pollutants.