Elucidating a novel photodegradation pathway: impact of halides on the photodestruction of organic contaminants in estuarine and marine systems

PI: William mitch提案编号：cbet -1066526机构：耶鲁大学标题：阐明一种新的光降解途径：卤化物对河口和海洋系统中有机污染物光破坏的影响河口长期以来一直被认为是关键的生态系统，为许多海洋生物提供营养丰富的托儿所。然而，随着沿海地区人口的激增，人们越来越关注来自点源、非点源、甚至水产养殖或石油泄漏直接负荷的有机污染物对河口生物的负面影响。虽然光解降解是污染物命运的重要控制因素之一，但对于河口和海洋系统的决定性特征——盐对污染物光解的影响，还没有系统的评价。在最近发表的一篇文章中，PI证明海水中卤化物的浓度使溶解有机物（DOM）发色团的光漂白能力提高了40%。控制离子强度的实验表明，这种效应是特定于卤化物的，并且与选择性靶向富电子发色团的氧化剂的形成一致；这类氧化剂包括单线态氧或活性卤素（RHS，如Br?），它们是由激发态三重态发色团直接氧化卤化物形成的。PI提供的初步数据表明，卤化物还显著增强了四环素的直接光降解和17<e:1> -雌二醇的间接光降解。此外，他还利用探针证明了卤化物增加了激发态三重态发色团的稳态浓度，这是形成单线态氧和卤素自由基的关键中间体。最后，他提出的结果表明，单线态氧和卤素自由基的促进可能在有机污染物的光降解中起重要作用，并且在卤素自由基的情况下，可能会使污染物卤化。拟议的研究将采用两种方法系统地评估卤化物对直接和间接光解有机污染物光降解的影响。在实际层面上，第一种方法将通过卤化物浓度梯度量化污染物的直接和间接光降解率，以表明卤化物对河口污染物光命运的重要性。将在有和没有离子强度控制的情况下进行实验，以区分盐的影响是普遍的离子强度效应还是特定于卤化物。在基本层面上，第二种方法将探索潜在的机制。他们将使用探针来量化有机污染物（在直接光解的情况下）或DOM发色团（在间接光解的情况下）的稳态浓度和光激发三重态的形成和清除速率。这些实验将与使用额外的探针相结合，以量化由光激发三重态有机中间体形成的选择性氧化剂单线态氧的稳态浓度和形成和清除速率。虽然还没有开发出类似的探针来测量RHS，但我们将使用RHS清除剂来表明这些物种是否在河口的有机污染物光降解中发挥重要作用。作为RHS作用的另一个指示，我们将评估有机污染物是否发生卤化。尽管对污染物光解的研究已有多年，但对卤化物在促进污染物光解中的作用还没有系统的研究。一般来说，卤化物被认为是改变离子强度，而不是参与特定的光化学反应。因此，适用于淡水系统的反应途径已应用于咸水。对特定卤化物辅助光解途径的系统表征将改变我们对盐在水光化学中的作用的理解，并使我们能够更准确地预测河口和海洋系统中有机污染物负荷增加的命运。特定卤化物辅助光解途径的表征将与理解海洋DOM的转换非常相关，DOM是全球碳循环的重要组成部分。此外，定义有机卤素形成的非生物途径将是重要的，因为海洋系统中卤化有机物的起源是海洋学中的一个重要问题。除了为研究生和本科生提供研究机会外，一名高中科学教师将协助暑期研究，着眼于将实验纳入接下来一年的课程。在老师的帮助下，代表性不足的高中学生将被确定为在接下来的两个夏天协助研究。

PI: William MitchProposal Number: CBET-1066526Institution: Yale UniversityTitle: Elucidating a novel photodegradation pathway: impact of halides on the photodestruction of organic contaminants in estuarine and marine systemsEstuaries have long been considered critical ecosystems, serving as nutrient-rich nurseries for a host of marine life. However, as populations surge in coastal areas, there are increasing concerns regarding the negative impacts on estuarine organisms of organic contaminants from point sources, nonpoint sources, and even direct loadings from aquaculture or oil spills. Although photolytic degradation is among the more important controls on contaminant fate, there has been no systematic evaluation of the effect of salt, the defining characteristic of estuarine and marine systems, on contaminant photolysis. In a recent publication, the PI demonstrated that seawater concentrations of halides enhanced the photobleaching of dissolved organic matter (DOM) chromophores by 40%. Experiments controlling for ionic strength demonstrated that the effect was specific to halides, and consistent with the formation of oxidants that selectively target electron-rich chromophores; such oxidants include singlet oxygen or reactive halogen species (RHS; e.g., Br?) formed by the direct oxidation of halides by excited state triplet chromophores. The PI presents preliminary data indicating that halides also significantly enhance the direct photodegradation of tetracycline and the indirect photodegradation of 17â-estradiol. Additionally, he employed probes to demonstrate that halides increase the steady-state concentration of excited state triplet chromophores, critical intermediates in the formation of singlet oxygen and halogen radicals. Lastly, he presents results indicating that promotion of singlet oxygen and halogen radicals may play important roles in organic contaminant photodegradation, and in the case of halogen radicals, may halogenate contaminants.The proposed research would employ two approaches to systematically evaluate the impact of halides on the photodegradation of organic contaminants subject to both direct and indirect photolysis. On a practical level, the first approach would quantify the direct and indirect photodegradation rates of contaminants across halide concentration gradients to indicate the importance of halides for the photo-fate of contaminants in estuaries. Experiments would be conducted with and without ionic strength control to distinguish whether the influence of salts is a generalized ionic strength effect or specific to halides. On a fundamental level, the second approach would explore the underlying mechanisms. They will employ a probe to quantify the steady-state concentrations and rates of formation and scavenging of photo-excited triplet states of the organic contaminant (in the case of direct photolysis) or DOM chromophores (in the case of indirect photolysis). These experiments will be coupled with use of an additional probe to quantify the steady-state concentrations and rates of formation and scavenging of the selective oxidant, singlet oxygen, formed from the photo-excited triplet state organic intermediates. Although similar probes have not been developed to measure RHS, we will employ a RHS scavenger to indicate whether these species play an important role in organic contaminant photodegradation in estuaries. As an additional indication of a role for RHS, we will evaluate whether halogenation of organic contaminants occurs. Despite years of research on contaminant photolysis, there has been no systematic investigation of a role for halides in promoting contaminant photolysis. Generally, halides are considered to modify ionic strength, not to participate in specific photochemical reactions. Accordingly, reaction pathways applicable to freshwater systems have been applied to saline waters. The systematic characterization of specific halide-assisted photolysis pathways would transform our understanding of the role of salts in aqueous photochemistry, and enable more accurate predictions of the fate of the increasing loadings of organic contaminants expected in estuaries and marine systems.The characterization of specific halide-assisted photolysis pathways would be very relevant to understanding the turnover of marine DOM, an important component of the global carbon cycle. Moreover, the definition of an abiotic pathway to organohalogen formation would be important as the origin of halogenated organics in marine systems is a significant issue in oceanography. In addition to the research opportunities afforded to graduate and undergraduate students, a high school science teacher will assist in summer research, with an eye to incorporating experiments into the curriculum over the following year. With the help of the teacher, underrepresented high school students will be identified to assist in the research over the following two summers.