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Maintaining the quality of raw waters and wastewaters and providing access to safe drinking water are some of the major environmental issues. While chemical disinfection through chlorination, chloramination, and ozonation are widely used methods for pathogen elimination, these approaches can give rise to potentially toxic disinfection by-products (DBPs) through reactions of the disinfectant with organic material and aquatic micropollutants. Unfortunately, the pathways leading to DBPs are poorly understood and it is currently impossible to assess the DBP formation kinetics and potential in raw waters and wastewaters by characterizing organic precursors and inorganic solutes. Moreover, even though a large number of chlorinated and N-containing DBPs including trihalomethanes, haloacetic acids, N-nitrosamines is known, only a minor share can be attributed to identifiable precursors. Novel approaches are therefore required to elucidate the reaction kinetics and pathways of disinfectants with natural organic matter and organic micropollutant leading to toxic DBPs and to develop methods that allow for predicting DBP formation potentials. One innovative approach, which we intend to pursue with the proposed project, is to obtain a reaction-related characterization of the functional groups responsible for DBPs from the use of isotope effects (i) as probes for reactive precursor moieties and (ii) as means to elucidate the mechanisms of DBP formation. Over the last years, we have been able to show how C, H, and N-kinetic isotope effects pertinent to chemical reactions can be applied to elucidate transformation mechanisms of organic micropollutants via identification of the chemical bonds and functional groups involved therein. In the proposed study, we build on this knowledge and aim at using compound-specific isotope analysis to infer isotope effects and reaction mechanisms leading to the highly carcinogenic N-nitrosodimethylamine (NDMA) from natural and anthropogenic precursor materials. We will develop model systems for drinking water and wastewater disinfection/oxidation with ozone, chlorine, and chloramine, in which we can study a combination of C, H, N, and O isotope fractionation of NDMA, selected precursor materials, as well as other water constituents and reaction intermediates. Our approach is based on the investigation of three proposed pathways of NDMA formation via (a) a hypohalous acid induced ozonation of sulfamides, (b) nitrosation, and (c) dimethylhydrazine-mediated process. These pathways are very likely to produce NDMA in reactions giving rise to distinctly different isotope effects. Isotope fractionation trends in NDMA will be used to identify the pathways and precursors responsible for NDMA during disinfection/oxidation of micropollutant-containing raw waters and wastewater effluents. Scientific evidence obtained in this project will contribute to an improved assessment of the NDMA formation potential in waters from various sources and will aid in developing improved control strategies.
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