【作者】 陈蕾；

【导师】 陈英旭； 沈超峰；

【作者基本信息】 浙江大学 ， 环境污染修复， 2012， 博士

【摘要】 多氯联苯具有高毒性、环境持久性与长距离迁移特性,能在生物体内富集并通过食物链得到放大,对生态环境安全与人体健康存在极大的威胁,已被列为《斯德哥尔摩公约》首批控制的持久性有机污染物(persistent organic pollutants, POPs)之一。在自然环境中多氯联苯能一定程度地进行光降解与微生物降解,然而环境因子如普遍存在的作为疏水性有机污染物承载介质的天然有机质对多氯联苯的自然消减影响及影响机制却尚未明晰。由于电子电器废弃物的拆解是导致我国多氯联苯区域性污染的主要原因,本论文首先以台州电子电器废弃物拆解点为例,通过毒理诊断与化学诊断相结合的方法对该地区南官河表层沉积物进行了污染风险评价,通过源解析与相关性分析筛选风险的关键因子；然后结合实验室模拟与野外调查,考察了水-沉积物体系中多氯联苯的自然消减现象及有机质、光照等环境因子的影响；之后通过模拟光照条件添加天然有机质及特异性分子探针研究天然有机质重要的光化学过程对多氯联苯的耦合降解机制；通过从沉积物中富集得到腐殖质还原菌加入到多氯联苯的厌氧反应体系中,结合微生物的分子生物学方法,研究了天然有机质参与的醌呼吸过程对多氯联苯的祸合降解机制；同时探索了电化学-质谱技术及量子化学计算方法在此类研究中的应用,并结合传统的气相-色谱技术探讨了体系中多氯联苯的转化路径。主要的研究结果如下：1)粗放型的电子电器废弃物的拆解是导致研究河段表层沉积物受严重污染的主要原因,且多氯联苯沉积物生态风险产生的关键因子之一。实验室模拟消减研究发现水-沉积物体系中多氯联苯商业混合物Aroclor1254存在明显的消减现象,90天后沉积物中总多氯联苯的降解率达到了14.8～28.8%,同时高含量的有机质与光照均有利于多氯联苯的消减。野外调查发现前后五年沉积物中多氯联苯的浓度显著降低,其中总多氯联苯的降解率达40.3-70.0%,且与沉积物的有机质含量存在显著相关。2)天然有机质在模拟太阳光照下对多氯联苯2,4’,5-三氯联苯(PCB-31)和2,2’,4,4’,5,5’-六氯联苯(PCB-153)的光降解产生显著的促进作用,其中在5mg/L的腐殖酸(HA)溶液中PCB-31和PCB-153的准一级光解速率常数分别达到了0.0933h-1和0.0413h-1。天然有机质中芳香结构的含量对多氯联苯的敏化光解作用存在较大的影响,因而不同来源的天然有机质对多氯联苯敏化光解的作用存在显著的差异。结合气相色谱-质谱方法、电化学-质谱技术及量子化学计算,得出多氯联苯分子结构中对位为优先发生化学反应的位点,光解产物主要为羟基化多氯联苯及氯代苯甲酸,中间产物双羟基多氯联苯易与天然有机质的亲核结构形成结合残留态产物。采用电子自旋共振技术及分子探针的方法鉴定出了敏化光解过程中存在的活性氧物种,其中羟基自由基(·OH)和天然有机质内部疏水微区中的单线态氧(1O2)起着主要的作用。利用分子探针捕获与模型拟合方法,估算出了·OH和HA内部疏水微区’O2的稳态浓度分别约为1.75×10-17mol/L和5.79×10-10mol/L。3)从高有机质含量的沉积物中富集培养得到的腐殖质还原菌在厌氧条件下能使PCB-153脱氯转化,其中在添加1mmol/L的蒽醌-2,6-双磺酸钠(AQDS)和200mg/L的HA体系中,15天后PCB-153的去除率分别达到了43.5%和56.2%。采用气相色谱-质谱方法鉴定出降解产物为对位脱氯产物2,2’,4,5,5’-五氯多氯联苯(PCB-101)和2,2’,5,5’-四氯多氯联苯(PCB-52);电化学-质谱的结果表明PCB-153的化学还原产物为PCB-101；根据量子化学空间位阻效应理论,亦可推断对位为优先脱氯位点。在机理研究中发现,PCB-153的降解很大程度地依赖醌呼吸过程,无菌的还原态AQDS对PCB-153亦存在一定的化学降解作用,结合关键微生物的分子生物学研究结果,可以推断醌呼吸过程对多氯联苯的耦合降解过程中同时存在共代谢脱氯及电子穿梭的机制,其中共代谢脱氯为主要的方式。本研究从天然有机质的光化学与醌呼吸过程的角度,探讨了天然有机质介导的多氯联苯环境转化与降解机制,研究结果对揭示自然环境中多氯联苯的消减机制具有重要的意义,同时也为发展新的多氯联苯污染修复技术提供一定的理论依据。更多还原

【Abstract】 Polychlorinated biphenyls (PCBs), one of the persistent organic pollutants, show high toxicity and high environment persistence and can transport at long distances. The contamination of PCBs has caused high risk to the ecological safety and human health. Though PCBs can be reduced by photo-degradation and biodegradation in the nature, the impact of natural organic matter (NOM) which is universal in the environment is still unclear.The primitive recycling of electronic waste (e-waste) is the main cause for the regional contamination of PCBs in China. In this study, one e-waste recycling site in Taizhou was taken as an example. Bioassay and chemical analysis were performed to determine the contamination levels and ecological risk of the surface sediments from Nanguan River. Source analysis and correlation analysis were carried out afterwards to find the key factor for the risk. Natural attenuation of PCBs in water-sediment was studied by lab simulation as well as field investigation. Coupled degradation mechanism by the photochemical process of NOM was studied by adding NOM and specific molecule probes under simulated sunlight. Humic respiration bacteria were enriched from the sediment and added into the reaction solutions of PCBs. Coupled degradation mechanism by the quinone respiration process of NOM was discussed according to the degradation results and the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) results. In the same time, the application of electrochemistry MS (EC-MS) and quantum chemistry calculation were explored and transformation pathways of PCBs in the natural attenuation processes were accordingly proposed. The main results of this research are as follows:1) The disassembly process of electronic waste was the main cause for the contamination in the surface sediment and polychlorinated biphenyls (PCBs) were mainly responsible for the ecological risk of the sediments. Attenuation of the commercial PCB mixture Aroclor1254was observed in the lab study. The total PCBs turned out to be degraded after90days in water-sediment systems with the loss of14.8～28.8%. Besides, high content of organic matter and solar irradiation accelerated the degradation of PCBs. Significant attenuation of PCBs was also observed in the real environment according to the field investigation. Degradation percentages of the total PCBs were in range of40.3～70.0%, with a significant correlation with the organic matter contents in the sediments.2) Addition of NOM accelerated the photo-degradation of2,4’,5-trichlorobiphenyl (PCB-31) and2,2’,4,4’,5,5’-hexachlorobiphenyl (PCB-153) significantly, with a pseudo-first-order rate constant of0.0933h-1and0.0413h-1respectively in presence of5mg/L humic acid (HA). The content of aromatic moieties could make a difference on the degradation of PCBs. The photo-degradation products of PCBs were hydroxylated PCBs and polychlorinated benzoic acid identified by GC-MS. The results from electrochemistry MS (EC-MS) study showed the binding of di hydroxy-PCBs with NOM. According to the quantum chemistry calculation the para-Cl was supposed to be more reactive. Reactive oxygen species (ROS) involved in the photo-sensitized degradation of PCBs were determined by ESR and molecule probe methods, among which·OH and intra-1O2were mostly important. By using molecule probes and modeling the steady-state concentrations of·OH and intra-1O2were calculated, approximately1.75×1O-17mol/L and5.79×10-10mol/L respectively.3) The humic respiration bacteria enriched from the sediment showed acceleration to the anaerobic degradation of PCB-153. The loss percentages of PCB-153after15days reached43.5%and56.2%in1mmol/L of antraquinona2,6-disulfonato (AQDS), and200mg/L HA solutions respectively. The degradation products were identified to be2,2’,4,5,5’-Pentachlorobiphenyl (PCB-101) and2,2’,5,5’-Tetrachlorobiphenyl (PCB-52), the para-dechlorination products. PCB-101was suggested to be the main chemical reduction product of PCB-153according to the result of EC-MS. The para position was also the preferential reaction position from the viewpoint of stereo-hindrance effect. The degradation of PCB-153mostly depended on the quinone respiration. According to the fact that PCB-153could be reduced by AH2QDS chemically and the results from PCR-DGGE study for microorganisms, it is suggested that co-metabolism dechlorination was the major mechanism for the degradation of PCB-153by humic respiration bacteria as well as the electron shuttling mechanism. In general, the role of natural organic matter (NOM) in the attenuation of PCBs in water-sediment systems was studied from the aspects of its photochemical process and quinone respiration in this research. The results will help us to understand the natural attenuation mechanisms better and also provide a new way for the remediation of PCB contamination.更多还原