NDMA formation during ozonation of DMAPA: Influencing factors, mechanisms, and new pathway exploration

Aliphatic amines, common constituents that contribute to dissolved organic nitrogen (DON), can quickly react with ozone due to the lone electron pair on the nitrogen atom and this may produce carcinogen N-Nitrosodimethylamine (NDMA). 3-(Dimethylamino)-1-propylamine (DMAPA) was chosen as a representative to elucidate the NDMA formation characteristics, kinetic rates, reaction pathways, and influencing factors during ozonation in this study. The results demonstrated that NDMA generated directly from DMAPA during ozonation. Moreover, the NDMA yields increased with ozone dosages. The NDMA molar yield increased and then decreased when the pH raised from 5 to 9, achieving the maximum value at pH 8. Hydroxyl radical (∙OH) played a promotional role in NDMA formation, and its scavenger dramatically cut down its yields. Low levels of Br^- facilitated NDMA formation, while the value significantly reduced when Br^- was up to 1 mM. The NDMA amount was slightly raised by NO₂^-, but it was inhibited by NH₄⁺ and NO₃^-. Moreover, it was also depressed by co-existing components in actual lake water. Based on the result of the Gaussian calculation, the LC-MS/MS and GC-MS analysis, four possible transformation pathways were proposed. The radical recombination was verified to be the primary pathway for ozone promoting NDMA formation from DMAPA.