【作者】 吴济舟；

【导师】 孙红文；

【作者基本信息】 南开大学 ， 环境科学， 2012， 博士

【摘要】 天然溶解性有机质（dissolved organic matter，DOM）存在于所有的水环境中，它通常定义为可以通过0.45μm孔径滤膜的、大小和结构不同的、有机分子的连续统一体，其分子量在几百到几万道尔顿之间变化，这使得DOM具有异质性。DOM含有酚基、羟基、羧基、羰基和硫醇基等多种官能团，是水环境中重要的配位体和吸附载体，对重金属元素和疏水性有机污染物（hydrophobic organic contaminants，HOCs）在水环境中的迁移，归宿和生物有效性具有重要影响。多环芳烃（polycyclic aromatic hydrocarbons，PAHs）是国际上广泛关注的持久性有机污染物（persistent organic pollutants，POPs），其经大气沉降、地表累积、雨水冲刷等过程，可迁移至湖泊、海洋，对各种水生生物造成影响。PAHs在水环境中的迁移转化行为以及对水生生物的影响与DOM等因素有关，其机理十分复杂。因此，本论文以河口沉积物提取的DOMbulk为对象，分别按照分子量和极性分组，研究了不同组分的DOM对芘的结合系数、生物有效性及吸附/解吸行为等的影响。本文取得了以下有价值的研究成果：（1）利用水提法从沉积物中提取出DOMbulk，按照分子量（molecularweight，MW）大小将其分为<1000D（aDOM<1000）、1000-14000D（aDOM1000-14000）和>14000Da（DOM>14000）三组分，按照极性特性将其分为疏水性酸性有机质（hydrophobic acid，HOA）、疏水性碱性有机质（hydrophobic base，HOB）、疏水性中性有机质（hydrophobic neutral，HON）、亲水性酸性有机质（hydrophilicacid，HIA）、亲水性碱性有机质（hydrophilic base，HIB）和亲水性中性有机质（hydrophilic neutral，HIN）六组分。各组分的光学性质、元素比、官能团含量之间存在着良好的相关性。（2）阳离子可显著影响芘与DOM的结合。利用荧光猝灭法测定芘与DOM的结合系数，KDOM，其随离子强度的变化趋势呈现出“四阶段变化模式”：先减少，后增加，最后趋于平衡。表明离子强度对芘与DOM结合作用的影响机制非常复杂，本文分别对盐析效应及DOM构象的变化进行了深入的讨论。不同种类阳离子对KDOM值造成不同程度的影响，与电荷密度具有密切关系。电荷密度越大，KDOM达到最小值时所需浓度（cmin）越小，而KDOM从最小值到稳定值的变化斜率（KDOM-I）越大。由于DOM本身大多具有负电荷的官能团，所以阴离子对KDOM值的影响不显著。（3）大分子量DOM（DOM14000）比小分子量DOM（DOM<1000和DOM1000-14000）的结合能力要强，这是因为前者具有更小的极性，更大的芳香性，更强的作用力。DOM不同分子量组分结合芘的KDOM值在阳离子作用下的变化趋势也符合“四阶段模型”。此外pH增加导致KDOM发生先增加后减少的变化。KDOM随水化学条件变化而变化的现象可以通过DOM构象的变化来阐述原因。聚合态DOM减少了吸附位点，但当聚合体变大形成疏水性结构又可以增加对芘的结合，而聚合体进一步增大一些内部位点不易到达，结合能力便稳定在一定水平上。（4）对于DOM不同极性组分的研究表明，DOM结合芘的能力与其自身大分子构象上的芳香结构密切相关。KDOM与ε280正相关，但是C/H比并不能充当芳香度的指示剂。而KDOM与(N+O)/C比负相关，这说明极性也会对其产生影响。疏水性（hydrophobic，HO）组分结合芘的能力强于亲水性（hydrophilic，HI）组分，其中以HON的能力最强。HO组分的Stern-Volmer plots线性更强。HON与芘结合，除了疏水性作用力之外，还存在电子-供体-受体（electron-donor-acceptor，EDA）作用力。DOM的构象也会影响其对PAHs的结合能力。如果减少DOM表面的极性组分，HOCs可以更容易进入DOM的疏水性内核，从而增加DOM对HOCs的结合量。（5）本研究使用了一种新型的基于半透膜被动采样技术SPMD的微萃取方法（semi-permeable membrane based micro-extraction，SPM-ME）。DOM减少了SPM-ME对芘的富集，分子量越大，减少量越大；液相扩散层及鱼体自身的活动影响下，DOM增加锦鲤对芘的富集，其中增加了芘在鱼鳃和内脏上的富集，而减少了芘在肌肉上的富集。分子量越大，变化值越大。DOM结合态的芘部分部鱼体利用，但富集量主要还是主自由态芘的浓度决定。DOM只是影响了锦鲤对芘的富集速率，并不会影响其BCF值。SPM-ME对芘的富集量远小于传统半透膜被动采样技术（semi-permeable membrane device，SMPD），减少了与锦鲤富集量的差异，能更好地模拟锦鲤对芘的富集。锦鲤体内芘的释放速度较快，在24h内释放绝大部分，其释放行为可以用双区一级动力学描述。DOM能加快芘的释放。（6）芘在DOM上的结合-解离是完全可逆的过程。加入DOM抑制了泥炭对芘的吸附，促进了芘的解吸，但DOM不同分子量组分产生的抑制和促进效应不一样，DOM不同分子量组分之间所产生的抑制和促进效应存在着显著差异。DOM对芘的抑制和促进效应随着其分子量的增加而增强。加入DOM促进了高岭土对芘的吸附，亦促进了芘的解吸，但DOM不同分子量组分产生的促进效应不一样，DOM不同分子量组分之间所产生的促进效应存在着显著差异。DOM对芘的促进效应随着其分子量的增加而增强。这些抑制或促进效应是多种因素共同作用的结果，如芳香度，极性，分子结构等。更多还原

【Abstract】 Dissolved organic matter (DOM) is widely present in the aquatic environment,which is often defined operationally as a continuum of organic molecules ofdifferent sizes and structures that passes through a filter of0.45μm pore size, withthe molecular weight from several hundred to several ten thousand Da, which resultsin its heterogeneous nature. It contains carboxyl, phenol, ethanol, hydroxyl, carbonyl,amine and thiol functional groups and has been shown to be one of the key factorsaffecting the fate, transport, bioavailability, and chemical and biological reactivity ofHOCs as the result of combining with them.Polycyclic aromatic hadrocarbons (PAHs), the representative persistent organicpollutants (POPs), have drawn the world-wide concern. A proportion of PAHs endup in lakes or oceans, bind to DOM, and exert hazardous effects on aquaticorganism via atmospheric sedimentation, accumulation on land surface, and rainwashing. The transport and transformation behaviours of PAHs and its influence onthe aquatic organism are affected by DOM, which mechanism is quite complicated.In this study, DOM fractions with different molecular weight and polarity wereselected to study the binding coefficient with pyrene and its influence on thebioavailability and sorption/desorption behaviours.The main conclusions drawn in this dissertation are as following:(1)The DOMbulkwas extracted by water from the sediment of the BeitangEstuary，Tianjin，China. Then it was separated into three different molecular weight(MW) fractions by dialysis technique,<1000Da (DOM<1000),1000-14000Da(DOM1000-14000) and>14000Da (DOM>14000). Additionally, six hydrophobic andhydrophilic fractions, i.e. hydrophobic acid (HOA), hydrophobic base (HOB),hydrophobic neutral (HON), hydrophilic acid (HIA), hydrophilic base (HIB),hydrophilic neutral (HIN), were isolated using resins. All the fractions have good relationships with its optical properties, elemental ratio and the content of functionalgroups.(2) KDOMvalues of pyrene were measured using fluorescence quenchingmethod, and possible binding mechanisms were discussed. Different cationic ionshad varied impacts on KDOMof pyrene, which has relation with the charge-density.With increasing concentration of cationic ions, KDOMof pyrene showed a complexpattern of increasing initially, then decreasing, and finally stabilizing at a plateau,which followed four-stage variation model．It is showed that the ion strength has ancomplex effect on the pyrene binding to DOM, which is explained by the salt-outeffect and DOM conformation. The tested anionic ions did not show significantinfluence since the DOM itself are negatively charged.(3) DOM fraction with larger MW (14000Da) showed a greater bindingcapacity (KDOM=2.02×105) as compared to those of smaller MW, with KDOMbeing1.16×105for the fraction with MW of100014000Da,1.13×105for the fractionwith MW of1000Da. Positive correlation was acquired between KDOMand ε280and negative for KDOMand (O+C)/N, indicating the positive effect of DOMaromacity and negative effect of DOM polarity. Infrared spectroscopy revealedstronger interaction between pyrene and DOM fraction with larger MW. KDOMvaried in a complex pattern with increasing pH and cation concentration, and thiscould be ascribed to the change in DOM conformation. Aggregation leads to areduction in binding sites. however when aggregate acts as an hydrophobic moiety,its binding capacity increases; further increase in aggregation makes interior sitesless accessed and binding capacity does not increase further. The changing of KDOMof different DOM MW fractions is of similar pattern, but with different rates.(4) The KDOMof pyrene binding to the six DOM fractions with various polaritywere determined by fluorescence quenching. The KDOMvalues binding to thehydrophobic fractions were larger than those to the hydrophilic fractions, with thelargest value for HON. Besides hydrophobic interaction, there is π-π electron donoracceptor interactions. A significant correlation of KDOMwith ε280was observed,while atomic ratio of C/H was found to be a poor indicator for aromaticity. Otherstructural properties, such as polarity influenced the DOM-fraction ability to bind pyrene. If the hydrophobic domains were less covered by the surface polarcomponents, the PAHs may have accessed to more alkyl and aromatic domains inthe DOM-fractions, resulting in a high sorption capacity.(5) The effect of different MW DOM on the bioaccumulation of pyrene inBrocarded Carp and semi-permeable membrane (SPM) was studied. DOM reducedthe accumulation of pyrene in SPM and the muscles of fish and enhanced those inthe gills and guts of fish, and as a whole enhanced pyrene accumulation in fish.DOM with larger MW exhibited stronger influence. Additionally, the bound pyreneby DOM was partly available for accumulation by fish but the free dissolved form isthe primarily source. The accumulation of pyrene in SPM-ME (Semipermeablemembrane-microextraction) accumulation of pyrene compared with the traditionalSPM and it can be preferably applied to simulate the fish accumulation of freeHOCs in aqueous environment. The release rate of pyrene in fish is very fast, andmost of the accumulated pyrene was released in24h. DOM can make the stepquicker.(6) DOM significantly reduce the sorption capacity of peat for pyrene andaccelerated desorption of pyrene from peat. However, the sorption and desorption ofpyrene on kaolinte was accelerated by DOM. The larger MW DOM, the strongereffect, which is affected by many factors, such as aromaticity, polarity, molecularconformation.更多还原