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 pg/L when Br dosages increased from 0 to 100 mu M. 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 mu g/L with HCO3- raising from 0 to 160 mu M, while increasing remarkably to 222.5 mu g/L with SO42- 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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study found that bromide ions (Br-) promoted the formation of carcinogenic nitroso-dimethylamine (NDMA) during ozonation of unsymmetrical dimethylhydrazine (UDMH). The formation rate constant of NDMA with Br was over 7 times higher than without Br. Additionally, increasing bromide and ozone dosages facilitated NDMA formation, while different effects were observed with the addition of bicarbonate (HCO3-) and sulfate (SO42-).