Photochemical Formation Of Hydroxylated Polybrominated Diphenyl Ethers From2,2’,4,4’-Tetrabromodiphenyl Ether In Aquatic Environment

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs), as the hydroxylated derivatives of polybrominated diphenyl ethers (PBDEs), are a group of emerging organic pollutants. It is worth noting that OH-PBDEs are not originally manmade chemicals, therefore the origin of OH-PBDEs has attracted great attention. Recently the results of OH-PBDEs concentration in atmospheric precipitation and chemical calcultion suggested that OH-PBDEs could likely be formed in through the reaction of PBDEs with atmospheric hydroxyl radical (·OH). In aquatic environment, photolysis is one of the most important transformation pathways for organic compounds, and·OH generated by various photoactive compounds could impact the phototransformation pathway of the organic pollutants. Therefore, the photo formation of OH-PBDEs from PBDEs could be a possible process.In this dissertation,2,2’,4,4’-tetrabromodiphenyl ether (BDE-47) was selected as model compound, and its photoformation pathway and mechanism to OH-PBDEs in aqueous solution, and effects of some important aquatic environmental factors on this process are fully investigated. The following works have been done:(1) The pentafluorobenzoyl chloride (PFBC1) derivatization method coupled with gas chromatography-electron capture detector (GC-ECD) was established to analyze the hydroxylated polybrominated diphenyl ethers (OH-PBDEs) in water. The conditions for the PFBC1derivatization of OH-PBDEs at trace level in water samples were optimized. The optimal conditions were obtained as follow:the derivatization buffer solvent of mixed acetonitrile/methanol/water/pyridine solution150μL, extraction solvent (isooctane, after the derivatization was realized)1mL and derivatization time10min. The method detection limits for these OH-PBDEs (4-OH-BDE-42,4’-OH-BDE-49,6-OH-BDE-47,2’-OH-BDE-68, and6’-OH-BDE-99) were ranged from0.37-2.80pg/L under the optimal conditions. The relative standard deviations were less than10%. The results for the detection of OH-PBDEs in water samples showed that this method had satisfactory recoveries for the OH-PBDEs derivatives, indicating that this method was suitable for determination of trace OH-PBDEs in water.(2) The effects of environmental factors on the phototransformation of BDE-47in the natural seawater have been investigated. The phototransformation rate of BDE-47in the natural seawater was significantly higher that in Milli-Q water under irraditation. Then ferric ion (Fe(Ⅲ)) has been found to promote the phototransformation of BDE-47, and this process is further enhanced with the added Cl-. The results of electron spin resonance (ESR) showed that the added Cl-could enhanced the generation of·OH by the cycle of Fe(Ⅱ)/Fe(Ⅲ), leading to improved photo transformation of BDE-47in Fe(Ⅲ) solution with Cl-.In Fe(Ⅲ) and Cl-solution, the reaction of Cl-with Fe(Ⅲ) species under irradiation, yielding·OH and chloride radicals. With these radicals, the photodebromination and photochlorination were the major phototransformation pathways of BDE-47in Fe(Ⅲ) and Cl-solution.(3) The photochemical formation of OH-PBDEs from BDE-47was investigated in Fe(Ⅲ) solution. In this process, the ortho-substituted OH-PBDEs,6-OH-BDE-47and2’-OH-BDE-68, were determined as the hydroxylated derivatives during the phototransformation of BDE-47in Fe(Ⅲ) solution at pH5.6(±0.1) under irradiation. The liquid chromatography-triple quadrupole mass spectrometer (LC-MS/MS) and ESR results indicated that the formation of OH-PBDEs likely resulted from the the additive reaction of aryl radical and·OH. When these two radicals coexist in solution, the ortho-substituted OH-PBDEs are the dominant hydroxylated products. The Oxygen-18radionuclide tracer experiment suggested that the·OH was produced from water and oxygen dissolved in water.(4) The effects of Fe(Ⅲ) and fulvic acid (FA) on the photochemical formation of6-OH-BDE-47and2’-OH-BDE-68were investigated under irradiation. In Fe(Ⅲ) solution, the concentrations of OH-PBDEs increased with the increasing Fe(Ⅲ) concentrations ([Fe(Ⅲ)]) from2μM to5μM, while it was decreased when [Fe(Ⅲ)] arrived at10μM. With increasing pH, the concentration of OH-PBDEs decreased. FA had been found to promote the OH-PBDEs formation, when [FA] changed from0.2to1mg/L, while it was suppressed with increasing [FA] up to10mg/L. The results of ESR indicated that·OH generated by Fe(Ⅲ) or FA was a main factor affecting the formation of OH-PBDEs. The phototransformation of BDE-47in the natural fresh water resulted in OH-PBDEs forming, and the increasing initial concentration of BDE-47geratly promoted the photochemical formation of OH-PBDEs.All above experiments in this dissertation showed that the aquatic environmental factors could affect the phototransformation rate and pathway of PBDEs. Moreover, the toxicity effect and ecological risk of PBDEs photoproducts, such as lower brominated PBDEs, OH-PBDEs and chlorinated PBDEs, are likely to be higher than those of the parent compounds. These findings are helpful for gaining a better understanding of the photochemical behaviour of PBDEs and the source of OH-PBDEs in natural environment.