N-nitrosamine formation during chlorination/chloramination of bromide-containing water

This study investigated the impact of bromide on the formation of N-nitrosamines during chlorination and chloramination, and tried to identify the reactive intermediates responsible for variations in the yield of N-nitrosamines. As an intermediate of the reaction between bromide and HOCl, bromine chloride (BrCl) may improve the yield of N-nitrosodimethylamine (NDMA) formation. But increasing the amount of bromide added would result in BrCl being converted into HOBr, which is a weaker oxidant than HOCl. This would result in less nitrite being formed, leading to a decreased yield of NDMA via the nitrosation pathway. When NH₄⁺, was present with the bromide during chlorination, both the rate of formation and yield of N-nitrosamines were improved markedly by highly reactive bromamines. Interestingly, bromide had an inhibitory effect on NDMA formation during the chloramination process when tertiary alkylamines, such as 3-(Dimethylaminomethyl) indole (DMAI) and trimethylamine (TMA), were used as precursors. This phenomenon provides indirect evidence for the hypothesis that the pathway of NDMA formation using tertiary amines with DMA groups is different from that of NDMA formation using secondary alkylamines.