New perspective of Br−'s role on NDMA formation from daminozide (DMNZD) during ozonation
N-nitrosodimethylamine (NDMA) has recently been discovered to generate from daminozide (DMNZD) during ozonation . Moreover, its formation is affected by the presence of bromine ion (Br − ) in water, but the mechanism is still unclear. In this study, the effect of Br − on NDMA formation from DMNZD during ozonation at various oxidation conditions (ozone dosages, pH) and distinct water parameters was studied. In addition, the transformation pathways with/without Br − were determined. The results demonstrated that low levels of Br − promoted NDMA formation from DMNZD during ozonation. When Br − dosages increased from 0 to 1 μM, the concentration of NDMA augmented from 138 to 195.5 μg/L. However, when Br − concentration raised to 100 μM, NDMA amounts dropped to 80 μg/L. Increasing pH can raise the ratio of deprotonated DMNZD no matter with or without Br − , and promote its reaction with O 3 molecular to achieve the maximum NDMA formation at pH = 7. The amounts of NDMA decreased dramatically (from 155 to 74 μg/L) when HCO 3 – dosages increased from 0 to 160 μM with 0.1 μM Br − , however, its concentration increased remarkably (from 155 to 225 μg/L) with increasing SO 4 2− (from 0 to 20 μM). Low levels of HA (0.1–0.2 mg/L) boosted NDMA formation while relatively abundant of HA (≥0.4 mg/L) suppressed its formation. In addition, the presence of NOM inhibited NDMA formation from DMNZD during ozonation no matter Br − existed or not. Based on the results of LC/MS/MS, GC/MS and IC-MS, the transformation pathways of DMNZD with/without Br − during ozonation were proposed. This study provided new insights into the role of Br − on NDMA formation from typical amine compounds during ozonation.
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