Validation of the promotion mechanism between bromide and UDMH to form NDMA during ozonation
Unsymmetrical dimethylhydrazine (UDMH) is found to generate substantial carcinogenic nitroso-dimethylamine (NDMA) during ozonation , moreover, its formation is promoted by ubiquitous bromide ions (Br − ) in water matrixes, but the mechanism is still unclear. In this study, effects of Br − on NDMA formation during ozonation of UDMH were studied, meanwhile, its promotion pathways were also determined. The results demonstrated that Br − promoted NDMA formation from UDMH during ozonation, the formation rate constant with Br − is over 7 times of that without Br − . NDMA amount raised from 142.5 to 327.5 μg/L when Br − dosages increased from 0 to 100 μM. No matter with or without Br − , the augment of O 3 dosages facilitated NDMA formation; the maximum value was achieved at pH 8. NDMA decreased dramatically from 173.8 to 123.5 μg/L with HCO 3 − raising from 0 to 160 μM, while increasing remarkably to 222.5 μg/L with SO 4 2− dosing. In addition, NOM inhibited NDMA formation from UDMH during ozonation. The mass spectrum of LC-MS/MS verified that the generation of Br-UDMH was main cause for promoting NDMA formation. Moreover, hypobromous acid (HBrO) was confirmed to be responsible for Br-UDMH formation. In addition, the position that oxidants and Br − attacked was demonstrated based on Gaussian calculation. The results of this study could provide theoretical basis for the application of ozonation in bromine-containing water matrixes.
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