【作者】 单慧媚；

【导师】 马腾；

【作者基本信息】 中国地质大学 ， 地下水科学与工程， 2014， 博士

【摘要】 多溴联苯醚(Poly Brominated Diphenyl Ethers, PBDEs),作为一种新兴的全球性持久性有机污染物(Emerging POPs),已经在全球范围内的大气、水体、沉积物、生物以及人体中被广泛检出。PBDEs对人体的神经、内分泌、甲状腺、肝脏、肾脏等存在着潜在威胁,同时还可能存在胚胎致畸的作用。当前,有关PBDEs环境问题的研究已成为国际学术界的热点。水环境是PBDEs全球循环的重要组成部分,PBDEs通过地表径流、大气干湿沉降或其他方式等进入到水环境,又在特定条件下重新释放进入土壤和大气或被生物利用并通过食物链逐级累积,再次参与到全球循环中。PBDEs进入水环境的一个重要途径即污水排放或灌溉,因为污水处理厂的水处理过程并不能显著降解或去除PBDEs.大量调查结果显示,污水排放及灌溉己成为水环境中PBDEs污染的不可忽略的面状污染源。尽管PBDEs具有疏水性,土壤、沉积物对其有较强的固着能力,但大量野外调查显示地表水体已广泛受到PBDEs污染,最新的研究证明PBDEs已进入地下水。值得注意的是,地下水中的PBDEs极有可能通过饮用或植物生长等在人体或农作物中累积,对人体及地下水环境存在潜在污染风险。然而,人们关于PBDEs对地下水的污染及其在包气带中行为机理的认识非常有限,并不清楚这种新兴的疏水性有机卤化物如何“穿透”包气带进入地下水,并且在这相对黑暗的环境中发生了怎样的迁移及转化。本论文针对PBDEs全球循环研究的空缺区—地下水领域,被忽略的面状污染源—污水灌溉等问题,以山西省太原市小店污灌区作为研究区,开展与地下水中PBDEs污染及其行为特征相关的研究,提出"PBDEs在地下水中如何分布”、“疏水性的PBDEs如何穿透包气带进入地下水”"PBDEs在土壤一地下水系统中发生了怎样的行为过程”等关键问题。针对以上问题,本研究：(1)采集污水、污泥、土壤和地下水等样品进行PBDEs测试分析,查明典型污灌区内PBDEs污染现状,识别PBDEs在环境中的主要存在单体和污染源；(2)针对研究区内主要PBDEs污染物,开展其在土壤、石英砂、胶体等的静态吸附实验,查明PBDEs在饱和多孔介质中的吸附特征；(3)以石英砂为吸附质,重点开展HA有机质胶体影响下,主要PBDEs污染物在饱和多孔介质中的吸附和迁移实验,构建胶体作用下PBDEs在饱和多孔介质中迁移过程的数值模型。此外,为了避免常规PBDEs测试方法在研究PBDEs迁移机理中的不足,研发荧光光谱法在线测试PBDEs含量并将其应用于该实验研究。(4)构建典型胡敏酸(HA)胶体与PBDEs分子相互作用的三维模型,从分子尺度上识别胶体对PBDEs地球化学行为的影响。研究发现：(1)太原市小店污灌区土壤中PBDEs污染物的种类随环境改变而变化,2011年研究区内土壤中主要PBDEs污染物为：BDE47, BDE100, BDE154和BDE153,而2012年土壤中主要PBDEs污染物为：BDE71, BDE85, BDE99和BDE154。污水和浅层地下水中主要PBDEs污染物为：BDE47和BDE28,其主要赋存于<2μm的胶体及颗粒物上。污水灌溉是土壤和地下水中PBDEs的主要污染源,降雨或灌溉条件下农用地膜中释放的PBDEs是其潜在污染源。(2)水体中主要污染物—BDE28和BDE47在土壤和石英砂上的吸附主要是受化学作用控制,该吸附过程可以分为三个阶段：极快吸附,0.5-1h内含量下降至初始浓度的(35%-40%),为表面扩散过程；快速吸附,1-10h间含量下降至初始浓度的25%,此时PBDEs取代表面水分子而吸附在内/外表面：慢吸附,10-24h间,PBDEs进入颗粒内部微孔,含量下降至初始浓度的24%。(3)土壤中有机质含量显著高于石英砂,导致BDE28和BDE47在土壤上的吸附量高于在石英砂上的吸附量。其中,BDE28溶液(4-30μg/L)在土壤和石英砂上的Kd值分别为773-1456L/kg和456-1103L/kg,有机质均一化后获得其土壤和石英砂上的有机碳吸附系数(Log Koc)均在4.59-5.87之间。BDE47溶液(1-15μg/L)在土壤和石英砂上的Kd值分别为901-1547L/kg和482-850L/kg, Log K。。分别在4.5-5.3和4.8-5.4范围之间。(4)随着HA有机质胶体含量的增加,BDE47在石英砂上的平衡吸附量减少。线性吸附模型计算显示HA浓度分别为0、0.1和1mg/L条件下,BDE47在石英砂上的平均Kd值依次为：853.3L/kg (616.33-972.63L/kg)、12.63L/kg (8.99-14.76L/kg)和2.47L/kg (2.12-3.48L/kg)。表明HA与石英砂存在对BDE47的竞争吸附,且HA含量越高,对石英砂吸附BDE47过程的阻碍越强。(5)与传统的GCMS法相比,研发的荧光光谱法操作简便,测试快捷,可以很好的应用于HA对PBDEs吸附和迁移的影响机理研究。在此基础上,建立HA胶体影响下PBDEs在饱和砂柱中迁移的数值模型,可以很好的与实验数据拟合。实验与模拟结果发现：HA浓度分别为0,0.1和1mg/L时,BDE47穿透过程分别经过8×104PV,(7-8)×102PV和120PV,这进一步证明HA胶体显著促进了BDE47在饱和砂柱中的迁移。(6) PBDEs与HA分子相互作用主要通过氢键或羟基发生。作用后,二者的分子构型都发生了改变。该变化导致PBDEs的栅格表面积、体积和极性均增强,疏水性显著降低,从而增强了其在水环境中的迁移性。最后,在以上研究结果的基础上,构建HA胶体作用下,污灌区土壤—地下水系统中PBDEs的迁移模型,对PBDEs的形态转化过程进行分析认为：水溶态PBDEs与HA胶体作用后转化成胶体态PBDEs,以及土壤及沉积物上吸附态PBDEs在降雨及灌溉作用下部分转化成胶体态PBDEs,是PBDEs穿透包气带进入地下水的关键途径。本文的创新点为：(1)提出“胶体颗粒是PBDEs进入地下水的关键途径”的假设,通过开展污灌区土壤—地下水系统中胶体对PBDEs的协同迁移行为研究,从分子尺度上揭示出HA胶体对PBDEs在土壤—地下水系统中迁移过程的影响机理,科学回答了“持久性的疏水有机物PBDEs如何污染地下水”这一问题：(2)首次建立水体中PBDEs的荧光光谱分析法,并将其很好的应用于HA胶体作用下PBDEs迁移机理研究,为水环境中PBDEs污染物的在线快速监测提供了新的手段。更多还原

【Abstract】 Poly Brominated Diphenyl Ethers (PBDEs) were widely detected in the air, water, sediment, animal and human body in the environment has been recognized to be a kind of global Emerging Persistent Organic Pollutants (POPs). PBDEs may affect human nerve, endocrine, thyroid, liver and kidney; they may also lead to embryonic malformation. At present, studies of environmental problems of PBDEs have become hot spots of international academia.Water environment is an important part of PBDEs global cycle. PBDEs can go into water environment through surface runoff, atmospheric dry and wet deposition, or other paths. They can also be released back into the soil and atmospheric, or be used by organisms and accumulated as food chain under certain conditions, which make them into the global cycle again. One important source of PBDEs into water environment is wastewater discharge or irrigation, because it was found that water treatment processes in the Sewage treatment plant cannot significantly degrade or eliminate PBDEs. Investigation results showed that wastewater discharge or irrigation has become a significant pollution source of PBDEs into water environment.Although PBDEs are hydrophobic and can be strongly adsorbed on soil and sediment, they have been detected in groundwater. It was worth noting that PBDEs in groundwater may accumulate in human body or crops by drinking water or plant growth, these will be a potential risk for human health and water environment. However, our knowledge of PBDEs pollution in groundwater and their behavior mechanism in the unsaturated zone is limited. It is still unknown that how these hydrophobic POPs breakthrough unsaturated zone and into groundwater system, and what has happened during their migration and transformation in this dark environment.This study focused on this global Emerging POPs-PBDEs and the vacant area of their global circulation-groundwater environment. The typical sewage irrigation area of Xiaodian Irrigation Area in Taiyuan city was selected as the study area to study PBDEs behavior in groundwater environment. We are aimed to figure out three problems, that is,"How does PBDEs distribute in groundwater","How does hydrophobic PBDEs go through unsaturated zone and into groundwater environment", and "What has happened for PBDEs in soil-groundwater system". For the above questions, in this study:(1) Wastewater, soil, sludge and groundwater samples were collected for PBDEs measurement to analyze the distribution characteristics of PBDEs in the Irrigation Area and identify their major species and pollution sources.(2) Soil, sand and colloid were used as adsorbent to study the adsorption characteristics of major PBDEs on them.(3) Column experiments were carried out to test the effect of HA colloid on the adsorption and migration of PBDEs in saturated porous media. The numberical models of PBDEs migration in saturated porous media were built to fit experiment data. In addition, a new method of fluorescence spectra for aqueous PBDEs analysis was developed and used in this experiment.(4) Interaction of HA colloid and PBDEs were modeled to identify the effect of colloid on PBDEs geochemical behavior on the molecular scale.It was found that:(1) The major species of PBDEs were variable as the environment change, the major species of PBDEs in soil samples in2011were BDE47, BDE100, BDE154and BDE153, while that of PBDEs in soil samples in2012were BDE71, BDE85, BDE95and BDE154. The major species of PBDEs in wastewater and shallow groundwater samples were BDE47and BDE28, and they mainly distributed in the colloid or particles with the size of<2μm in water samples. Wastewater irrigation was the main pollution source for PBDEs in this area, meanwhile, widespread use of agricultural film could be a potential source of PBDEs in soil and groundwater.(2) Adsorption of BDE28and BDE47on soil and sand was mainly controlled by chemical action, their adsorption processes were divided into three stages:(i) highly quick absorption, their contents decreased to be35%-40%of original concentration in0.5-1h, which is controlled by surface diffusion process;(ii) quick adsorption, their contents decreased to be25%of original concentration in1-10h, which means that PBDEs take place of water molecular and are adsorbed on the inside/outside of surfaces; and (iii) slow adsorption, their contents decreased to be about24%of original concentration in10-24h, PBDEs have go to the inside of particle.(3) Under the influence of organic matter content, adsorptive capacity of both BDE28and BDE47on soil was higher than that on quartz sand. In the equilibrium concentrations of4-30μg/L, the Kd of BDE28on soil and sand were773-1456L/kg and456-1103L/kg, respectively. Their Log Koc was in the ranges of4.59-5.87. In the equilibrium concentrations of1-15μg/L, the Kd of BDE47on soil and sand were901-1547L/kg and482-850L/kg, respectively. Their Log Koc was in the ranges of4.5-5.3and4.8-5.4, respectively.(4) After added HA, equilibrium adsorption of BDE47on quartz sand decreased obviously. The Kd value of BDE47on sand with0,0.1and1mg/L HA in solutions were calculated by linear adsorption model to be853.3L/kg (616.33-972.63L/kg),12.63L/kg (8.99-14.76L/kg) and2.47L/kg (2.12-3.48L/kg), respectively. These indicated that there is competitive adsorption of BDE47on HA colloid and sand. The higher of HA content in the liquid phase, the inhibition of hydrophobic BDE47adsorption on solid was stronger. (5) Compared with conventional GC-based analytical methods, the fluorescence spectroscopy method is more efficient for PBDEs migration study, because it only uses a small amount of samples (4ml), avoids lengthy complicated concentration and extraction steps, and has a low detection limit of a few ng/L. Based on this method, models of PBDEs transport in saturated sand column under the effect of HA colloid were conducted to fit the experimental data well. When HA concentrations were0,0.1and1mg/L, the breakthrough time of BDE47into column were8×10,(7-8)×102and120pore volumes, respectively. These further confirmed that HA colloid significantly promoted BDE47migration.(6) HA interacted with PBDEs mainly by hydrogen bonding or hydroxyl. After interaction with HA, the surface area, volume and polarity of PBDEs increased while their hydrophobicity decreased, which increased PBDEs migration in water environment.Finally, based on the reported study, field investigation and laboratory experiments, migration model of PBDEs in soil and groundwater system in irrigation area was constructed. Speciation change analysis result showed that the key processes of PBDEs go through unsaturated zone and into groundwater were (i) aqueous PBDEs reacted with HA colloid to form colloidal PBDEs, and (ii) adsorbed PBDEs on soil and sediment transferred to colloidal PBDEs under the effect of rainfall and irrigation.The innovations of this paper are:(1) We first proposed that "Colloid may be the key path of PBDEs into groundwater". The effect of colloid on PBDEs transportation between soil and groundwater was studied to explain that how PBDEs go through soil and into groundwater and3D structures of PBDEs and HA were modeled to further explain the geochemical behavior of PBDEs in the system of soil and groundwater.(2) A new method was developed for rapid and direct measurement of aqueous PBDEs using fluorescence spectroscopy, which can be well applied on migration mechanism study of PBDEs under the effect of HA colloid, and will supply a new tool for PBDEs in situ measurement in water environment.更多还原