NDMA formation from 4,4′-hexamethylenebis (HDMS) during ozonation: influencing factors and mechanisms

• Published in: Environmental science and pollution research international 2019-01, Vol.26 (2), p.1584-1594
• Main Authors: Shen, Linlu, Liao, Xiaobin, Qi, Huan, Zhao, Lei, Li, Fei, Yuan, Baoling
• Format: Article
• Language: English
• Subjects: Alcohols; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Bicarbonates; Butanol; Dimethylhydrazines; Disinfection; Disinfection & disinfectants; Drinking water; Earth and Environmental Science; Ecotoxicology; Effluents; Environment; Environmental Chemistry; Environmental Health; Environmental science; Experiments; Humic acids; Hydroxyl radicals; Intermediates; N-Nitrosodimethylamine; Organic matter; Oxidation; Ozonation; Ozone; pH effects; Research Article; Roles; Scavenging; Sulfates; Surface water; Waste Water Technology; Water Management; Water Pollution Control; Yellowing
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-018-3684-5

N-nitrosodimethylamine (NDMA), a toxic disinfection byproduct commonly associated with chloramination, has recently been found to form from an anti-yellowing agent (4,4′-hexamethylenebis (1,1-dimethylsemicarbazide) (HDMS)) during ozonation but the mechanisms are unclear. In this paper, the potential roles of molecular ozone (O 3 ) and hydroxyl radical (∙OH) on NDMA formation from HDMS were investigated under various oxidation conditions (ozone dosages, pH) and different components in water (bromide ion (Br − ), bicarbonate ion (HCO 3 − ), sulfate ion (SO 4 2− ), and humic acid (HA), as well as natural organic matter (NOM) from a lake). Moreover, HDMS transformation pathways by ozonation were determined. The results indicated that the formation of NDMA was enhanced through the combined effect of O 3 and ∙OH compared to that by O 3 alone (addition of tert-butyl alcohol (tBA) as ∙OH scavenger). ∙OH itself cannot generate NDMA directly; however, it can transform HDMS to intermediates with higher NDMA yield than parent compound. The NDMA generation was affected (small dosages promoted but high dosages inhibited) by HA or Br − no matter with or without tBA. The presence of SO 4 2− and HCO 3 − ions lowered NDMA formation through ∙OH scavenging effect. Increasing pH not only increased degradation rate constant by enhancing ∙OH generation but also affected HDMS dissociation ratio, reaching the maximum NDMA formation at pH 7–8. Natural constituents in selected water matrix inhibited NDMA formation. Impacts of these influencing factors on NDMA formation by only O 3 however were significantly less pronounced over that by the joint roles of O 3 and ∙OH. Based on the result of Q-TOF, LC/MS/MS, and GC/MS, the possible transformation pathways of HDMS by ozonation were proposed. The NDMA enhancement mechanism by the combined effect of O 3 and ∙OH can be attributed to greater amounts of intermediates with higher NDMA yield (such as unsymmetrical dimethylhydrazine (UDMH)) produced. These findings provide new understanding of NDMA formation upon ozonation of typical amine-based compounds.