Collaborative Research: The Direct and Indirect Photolytic Fate of Persistent Organic Pollutants in Arctic Surface Waters

摘要：持久性有机污染物(POPs)能够通过远距离过程(即全球蒸馏)输送到北极，并通过海冰和径流从局部污染地区输送到北极。人们对这些持久性污染物对北极生态系统的影响知之甚少，但有证据表明，某些污染物会发生生物积累，特别是可能对营养水平最高的生物和土著人民构成威胁。溶解有机物(DOM)普遍存在于北极所有表层水域，并可能对持久性有机污染物的命运起到重要作用。DOM能够起到“准吸着剂”的作用，从而改变水柱中持久性有机污染物的形态。DOM也具有高度的光反应性，能够形成化学瞬变，将持久性有机污染物转化为其他物质。考虑到北极夏季发生的高度光子通量，光解过程可能对北极表层水域的POP命运起到重要作用。这项研究正在探索在北极淡水(图利克湖)和海洋遗址(易货岛)的地表水中存在DOM的情况下，控制持久性有机污染物命运的过程。具体目标包括：1.确定和量化两个地点地表水中持久性有机污染物的污染水平；2.收集、分离和阐明这两个地点的持久性有机污染物的结构和光解特性；3.在实验室和图利克湖实地使用太阳模拟器测量持久性有机污染物发生直接和间接光解的程度；4.确定和量化由DOM的光解形成的暂态物种的类型和数量；和5.研究持久性有机污染物及其子产物直接和间接光解的反应动力学和机理。该项目是俄亥俄州立大学/BPRC(CHIN)和科罗拉多大学/INSTAAR(McKnight)的研究人员合作开展的。之所以选择七氯、六氯苯、顺氯丹、林丹和两种多氯联苯同系物进行研究，是因为它们代表了在北极表面水域、动物和土著居民中常见的污染物，而且它们具有广泛的物理化学和光化学性质。将使用最先进的分离和定量光敏剂的方法。这些装置包括切向流超滤装置和反相柱，用于浓缩这两个地点的DOM。目前处于环境现实水平的DOM分离物将在实验室和室外光解实验中使用，以确定这些光敏剂在转化POPs方面的效果。人们将密切关注这些反应，以量化母体化合物及其光衍生物的变化。该项目的其他方面将尝试使用“探测器”来“捕捉”光瞬变，以努力阐明重要的光解途径。拟议中的项目将为未来研究控制北极POP命运的过程提供基础。最后，积累的信息将有助于那些负责管理这些生态系统的各方。

Abstract:Persistent organic pollutants (POPs) are capable of being transported to the Arctic by long-range processes (i.e., global distillation), and from locally contaminated areas by sea ice and runoff. The effect of these persistent pollutants on arctic ecosystems is poorly understood, but evidence shows that bioaccumulation occurs for some contaminants, and in particular may pose a threat to organisms at the highest trophic levels and indigenous people. Dissolved organic matter (DOM) is ubiquitous to all surface waters in the Arctic, and may play an important role in the fate of POPs. DOM is capable of acting as a "quasi-sorbent" thereby altering the speciation of POPs in the water column. DOM is also highly photoreactive and is able of forming chemical transients that can transform POPs to other substances. Given the high degree of photon flux that occurs during the boreal summer, photolytic processes may play an important role in POP fate in arctic surface waters. This research is exploring processes that control the fate of POPs in the presence of DOM from surface waters at a freshwater (Toolik Lake) and a marine site (Barter Island) in the Arctic. Specific objectives include:1. identify and quantify the level of POP contamination in the surface waters at the two sites;2. collect, isolate, and elucidate the structural and photolytic properties of DOM at these two sites;3. measure the degree to which direct and indirect photolysis occurs for POPs using solar simulators in the lab and at the Toolik Lake field site;4. identify and quantify the types and amounts of transient species formed by the photolysis of DOM; and5. study the reaction kinetics and mechanisms for the direct and indirect photolysis of POPs and their daughter products.The project is a collaborative effort between investigators at Ohio State University/BPRC (Chin) and the University of Colorado/INSTAAR (McKnight). Heptachlor, hexachlorobenzene, cis-chlordane, lindane, and two PCB congeners have been selected for study because they represent contaminants commonly detected in arctic surface waters, fauna, and the aboriginal people, and because they possess a wide range of physicochemical and photochemical properties. State-of-the-art methods for isolating and quantifying photosensitizers will be used. These include tangential-flow ultrafiltration unit and reverse-phase columns for concentrating DOM from the two sites. DOM isolates present at environmentally realistic levels will be used in both lab and outdoor photolysis experiments to determine the efficacy of these photosensitizers at transforming POPs. The reactions will be followed closely to quantify changes in both the parent compound and their photoderivatives. Other aspects of the project will attempt to "trap" phototransients using "probes" in an effort to elucidate important photolytic pathways. The proposed project will provide the basis for future research into the processes that control POP fate in the Arctic. Finally, information accrued will aid those parties responsible for the stewardship of these ecosystems.