Delineating Nitroxyl Formation Pathways from Chloramines and Free Chlorine and Cascades of Reactive Nitrogen Species to N-Nitrosamines and N-Nitramines

消毒是水处理中用于保护公众免受水传播疾病的关键单元操作。在美国，大约一半的饮用水是用氯胺消毒的。氯胺在水消毒中的使用提供了几个优点。由于它们比氯反应性更低且更稳定，氯胺通过与溶解有机物（DOM）反应形成消毒副产物的倾向要小得多。此外，氯胺提供更持久的消毒和更好的保护，防止微生物再生和污染，因为处理过的水通过分配管网输送。然而，最近的研究将饮用水中致癌化合物N-亚硝基二甲胺（NDMA）的存在与水消毒中使用的氯胺系统中形成的活性氮物质（RNS）联系起来。本研究的目的是探讨在氯胺水消毒系统中RNS在NDMA形成中的作用。 该项目的成功完成将通过开发新的知识和见解来控制和减轻氯胺水消毒系统中NDMA的形成，从而造福社会。通过对学生的教育和培训，包括对一名博士生和一名本科生的指导，将为社会带来进一步的好处。长期以来，人们一直认为在水消毒中使用的氯胺系统中会形成活性氮物质（RNS）。然而，这些RNS的识别和划定其在形成有毒消毒副产物（DBPs），如N-亚硝基二甲胺（NDMA）的作用仍然难以捉摸。因此，有一个关键的需要，以确定从氯胺和游离氯形成的RNS，并描绘随后的RNS级联启动NDMA在饮用水中的形成。该项目的目标是解决这些知识差距。为了实现这一目标，PI建议检验假设，即硝酰基是理解NDMA形成的“缺失环节”，NDMA形成通过（1）二氯胺水解和（2）一氯胺或次氯酸与羟胺的反应。该项目将整合批量动力学实验和建模，以（1）评估过氧亚硝酸盐作为母体亚硝化剂的形成和作用，（2）描述氯胺和游离氯的硝酰基形成途径，以及（3）确定在水消毒过程中使用的典型氯胺化条件下通过硝酰基途径形成的N-亚硝胺（例如NDMA）和N-亚硝胺的比例。动力学实验将测量和量化相关活性物质的浓度，包括反应物（游离氯、氯胺物质、前体和溶解氧）、RNS中间体、稳定产物（一氧化二氮、氮气、亚硝酸盐和硝酸盐）以及N-亚硝胺和N-亚硝胺。因此，该项目的成功完成有可能通过开发新的基础知识产生变革性影响，这些知识可以控制和缓解氯胺水消毒系统中有毒DBP（如NDMA）的形成。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Disinfection is a critical unit operation used in water treatment to protect the public from waterborne diseases. Chloroamines are utilized to disinfect about one-half of the drinking water produced in the United States. The use of chloramines in water disinfection provides several advantages. Because they are less reactive and more stable than chlorine, chloroamines have much less tendency to form disinfection by-products by reacting with dissolved organic matter (DOM). In addition, chloramines provide longer-lasting disinfection and better protection against microorganism regrowth and contamination as treated water is delivered through the distribution pipe networks. However, recent research has linked the presence of the cancer-causing compound N-nitrosodimethylamine (NDMA)in drinking water to reactive nitrogen species (RNS) that are formed in chloramine systems used in water disinfection. The goal of this research is to investigate the role of RNS in the formation of NDMA in chloroamine water disinfection systems. The successful completion of this project will benefit society through the development of new knowledge and insight to control and mitigate the formation of NDMA in chloramine water disinfection systems. Further benefits to society will be achieved through student education and training including the mentoring of a doctoral student and an undergraduate student.Reactive nitrogen species (RNS) have long been postulated to form in chloramine systems used in water disinfection. However, the identification of these RNS and delineation of their roles in the formation of toxic disinfection by-products (DBPs) such as N-nitrosodimethylamine (NDMA) has remained elusive. Thus, there is a critical need to identify RNS formed from chloramines and free chlorine and delineate the subsequent RNS cascades that initiate NDMA formation in drinking water. The goal of this project is to address these knowledge gaps. To achieve this goal, the PI propose to test the hypothesis that that nitroxyl is the “missing link” in understanding NDMA formation via (1) dichloramine hydrolysis and (2) the reactions of monochloramine or hypochlorous acid with hydroxylamine. The project will integrate batch kinetic experiments and modeling to (1) evaluate the formation and role of peroxynitrite as a parent nitrosating agent, (2) delineate nitroxyl formation pathways from chloramines and free chlorine, and (3) determine the proportion of N-nitrosamines (e.g. NDMA) and N-nitramines formed through the nitroxyl pathway under typical chloramination conditions used during water disinfection. The kinetic experiments will measure and quantify the concentrations of the relevant reactive species including reactants (free chlorine, chloramine species, precursors, and dissolved oxygen), RNS intermediates, stable products (nitrous oxide, nitrogen gas, nitrite, and nitrate), and N-nitrosamines and N-nitramines. Thus, the successful completion of this project has the potential for transformative impact through the development of new fundamental knowledge that could enable the control and mitigation of the formation of toxic DBPs such as NDMA in chloramine water disinfection systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.