Proposing strategies to avoid the formation of N-nitrosodimethylamine (NDMA) during water treatment with chlor(am)ine or ozone, requires a detailed understanding of the mechanisms leading to NDMA and the identification of precursor materials. While numerous natural and man-made precursors have been identified (including natural organic matter and micropollutants), to date the reaction mechanisms of NDMA formation are still unclear, thus making NDMA mitigation challenging. We explored the use of compound-specific isotope analysis (CSIA) to identify reactive NDMA precursors in raw waters and to delineate different formation pathways based on the evolution of the isotopic composition of NDMA at natural isotope abundance. We developed procedures for C-, H-, and N-isotope ratio measurements of N-nitrosamines by gas chromatography coupled to isotope ratio mass spectrometry (GC/IRMS) and applied them to analyze NDMA formation in laboratory experiments. Chloramination of the pharmaceutical ranitidine and a hypothesized reaction intermediate, 5-(dimethylaminomethyl)furfuryl alcohol (DFUR), were studied as model systems, in which high yields of NDMA were observed (>70%). During NDMA formation from both precursors, the 15N/14N composition of NDMA changed substantially and led to a continuous enrichment of 15N in NDMA. The 13C/12C and 2H/1H ratios of NDMA, in contrast, remained unchanged but differed significantly from the C-isotope ratios of the reactants. Such observations suggest (1) that a C-N bond cleavage occurs in the rate-limiting reaction step of NDMA formation and (2) that DFUR is indeed a reactive intermediate arising from ranitidine. Together with the absence of C- and H-isotope fractionation in NDMA, our results imply that the N,N-dimethylamine functional group is transferred from ranitidine to NDMA. Site-specific natural abundance isotope ratio measurements by 2H-NMR further confirm this mechanistic interpretation. Our approach is a first step towards using the evolution of NDMA isotope ratios as proxies for its formation pathways during waste and drinking water disinfection.

Tracking <i>N</i>-nitrosodimethylamine formation during water disinfection processes by multi-element isotope fractionation analysis

248th National Meeting (2014)

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Tracking N-nitrosodimethylamine formation during water disinfection processes by multi-element isotope fractionation analysis