| The hydroxylated polyhalogenated diphenyl ethers(OH-PCDEs and OH-PBDEs) and halogenated dibenzo-p-dioxins/dibenzofurans(PBDD/Fs) have been frequently found in various environment mediums. They are recognized as emerging organic pollutants of high toxicity and persistence. Generally, the origin of OH-PCDEs and OH-PBDEs has been attributed to biological metabolism of polychloronated diphenyl ethers(PCDEs) and polybrominated diphenyl ethers(PBDEs). The focus on current research is source of dioxins. Numerous studies have shown that dioxins can be converted by photochemical reaction or burning process in environment. However, the reasons for high concentration dioxins in the soil and the uneven distribution of all kinds of homologue have no clear explanation. Therefore, we explored the formation process and mechanism of OH-PCDEs, OH-PBDEs, PCDD/Fs, and PBDD/Fs via α-FeOOH or natural manages oxides sand-catalyzed oxidation of phenols(such as CPs and BPs). The main research results include:(1) We characterized the commercial, laboratory synthetic goethite and natural manages oxide by the scanning electron microscope(SEM), X-ray diffraction(XRD) and the specific surface area measurement. Results showed that syn-FeOOH and α-FeOOH has different crystal morphology. In addition, SEM images exhibit a different external characteristics compared including α-FeOOH, syn-FeOOH and MnOx. The surface areas of α-FeOOH, syn-FeOOH and MnOx were determined, respectively.(2) We demonstrated the formation of 2,8-DCDD from the oxidation of TCS by α-FeOOH,syn-FeOOH and MnOx. Experiments at room temperature and under dry conditions showed that Fe and Mn oxides readily catalyzed the conversion of TCS to 2,8-DCDD and other products. However, the presence of water in the samples significantly inhibited the formation of 2,8-DCDD. Besides 2,8-DCDD, 2,4-dichlorphenol(2,4-DCP), 4-chlorobenzene-1,2-diol, 2-chloro-5-(2,4-dichlorophenoxy)benzene-1,4-diol, and 2-chloro-5-(2,4-dichlorophenoxy)-1,4-benzouinone were identified in the reactions. The possible pathways for the formation of reaction products were proposed. This study suggests that Fe and Mn oxides-mediated transformation of TCS under dry conditions might be another potential pathway for the formation of 2,8-DCDD in the natural environment.(3) We focuses on the formation of PCDD/Fs from simple chlorophenol(e.g., 2,4,6-TCP or 2,4-DCP). Results showed that TCP could be transformed to 1,3,6,8-TCDD and 1,3,7,9-TCDD by α-FeOOH and MnOx. Similarly, DCP could be transformed to 1,3,8-TCDD and 1,3,7,9-TCDF by α-FeOOH and MnOx.We also report the formation of the direct precursors 2?-OH-PeCDE and 4?-OH-PeCDE of the most toxic PCDD/Fs congener, 1,3,6,8-TCDD, 1,3,7,9-TCDD from the reaction of 2,4,6-TCP with α-FeOOH and MnOx sand in the room temperature. In addition, 1,3,8-TCDD, 2,4,6,8-TCDF and several OH-PCDEs were also detected from the reaction of 2,4-DCP withα-FeOOH and MnOx at the same condition. We propose plausible reaction pathways. This study provides the direct evidence for formation of TCDD and TCDF supporting the plausibility of its in situ formation in soils.(4) We explored the origin of hydroxylated polybrominated diphenyl ethers(OH-PBDEs) and brominated dibenzo-p-dioxins, dibenzofurans(PBDD/Fs) in soil from the α-FeOOH-catalyzed oxidation of simple bromophenols(2,4-DBP and 2,4,6-TBP). Experiments at room temperature showed that α-FeOOH readily catalyzed the conversion of 2,4-DBP and 2,4,6-TBP to OH-PBDEs PBDD/Fs in dry condition. 2,4,6-TBP were transformed and part of them can be converted to 2′-OH-BDE-121 and 4′-OH-BDE-121, which subsequently undergo further conversion to 1,3,6,8-TBDD and 1,3,7,9-TBDD by α-FeOOH through smiles rearrangement. Similarly, 2,4-DBP were oxidized and partly transformed to 2′-OH-BDE-68 and 2,2’-OH-BB-80, which may subsequently undergo further conversion to 1,3,8-TBDD and 2,4,6,8-TBDF by α-FeOOH. The probable mechanism of transformation of bromophenols byα-FeOOH was derived by the tentative reaction products and knowledge of previous studies, this mechanism provides new insight into the soil production of OH-PBDEs and PBDD/Fs by α-FeOOH.(5)Herein we report the synthesis, purification and identification of several typical hydroxylated polybrominated diphenyl ethers(OH-PBDEs) and polybrominated diphenyls(OH-PBBs) based on the basic organic reactions of coupling, oxidation and bromination. The crude products were purified using a C18 column on a semi-preparative high-performance liquid chromatography. The purified products were further identified with gas chromatography-mass spectrometer and 1H-nuclear magnetic resonance. Results showed that the products obtained in this study were the target compounds with a purity > 99%.In addition, We demonstrated the oxidation of 2’-OH-BDE-68 å'Œ 2,2’-di OH-BB-80 by α-Fe OOH and Mn Ox. Results also showed that 2’-OH-BDE-68 å'Œ 2,2’-di OH-BB-80 were transformed to 1,3,8-TBDD and 2,4,6,8-TBDF by α-Fe OOH and Mn Ox. Besides, 2,4-DBP, 2,4-dibromobenzene-1,2-diol, and 2’,5 ’-OH-BDE-25 were identified in the reactions. The possible pathways for the formation of reaction products were proposed. This study suggests that Fe and Mn oxides-mediated transformation of 2’-OH-BDE-68 and 2,2’-di OH-BB-80 under dry condition. |
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