Mechanistic studies of N-nitrosodimethylamine (NDMA) in model drinking waters

N-nitrosodimethylamine (NDMA) has been recently observed in treated drinking water and wastewater. This is a concern because NDMA is classified as probable human carcinogen. Several recent studies suggest that its formation is somehow related to treatment and disinfection practices involving chlorination or chloramination in particular. Considering reaction kinetics, it did not seem likely that the formation of NDMA in drinking water could be accounted for the well-known nitrosation reaction mechanism involving a reaction between nitrite and common organic nitrogen precursors, such as dimethylamine (DMA).; This dissertation presents an investigation of several reaction mechanisms and pathways that were hypothesized as being potentially responsible for the elevated NDMA concentrations in some drinking waters. The work included studies of NDMA formation as a consequence of water chlorination and chloramination, as well as an evaluation of NDMA formation from some novel organic nitrogen precursors.; Particularly, this work brought into the light two new pathways, which may contribute significantly to NDMA formation in chlorinated and chloraminated water: (1) a haloamine-UDMH (1,1-dimethylhydrazine) pathway, and (2) an HOCl-enhanced nitrosation pathway. In the haloamine-UDMH pathway, the reaction of monochloramine or monobromamine with a precursor amine leads to NDMA formation via an UDMH intermediate. In this pathway, ammonia is the source of the nitroso group in NDMA. The formation of NDMA was enhanced by the interaction of HOCl with nitrite. In the proposed mechanism, the oxidation of nitrite by HOCl results in the formation of an effective nitrosating agent. Also, in this work, the catalytic role of bromide in both pathways via its oxidation by HOCl or monochloramine was elucidated. Lastly, studies show that some precursors containing the thiocarbonyl group are generally more nitrosatable than DMA and hence their presence in water or wastewater may have potential importance in NDMA formation.; Reaction pathways proposed can account for both fast NDMA formation and comparatively slow formation. The fast processes may be more important in the water treatment plant, while the slow, more important in the distribution system.