Formation of N-nitrosodimethylamine from dimethylamine compounds during UV disinfection in the presence of nitrite

Abstract

UV-based treatment technologies have been widely applied in wastewater treatment plants due to its high efficiency in deactivating pathogens and degrading organic contaminants. However, this study demonstrates that N-nitrosodimethylamine (NDMA), a probable human carcinogen, can be generated during UV treatment of dimethylamine (DMA) pollutants of concern, for example isoproturon (IPU), in the presence of nitrite (NO2–). Quenching tests have identified that in addition to direct photolysis, hydroxyl radicals (HO•) and nitrogen oxide radicals (NO• and NO2•) generated from NO2– photolysis play a crucial role in the reaction. They can react with IPU, leading to hydroxylated and nitrated products. More importantly, NO2• couples with a NO• or another NO2• to form N2O3 and N2O4, respectively. As nitrosating agents, N2O3 and N2O4 directly attack the released DMA during IPU degradation, yielding NDMA. At IPU initial concentration of 50 μM, the highest concentration of NDMA was 5.62 μg/L in 2.5 h by UV/NO2–, corresponding to the molar yield of 0.22%. This study further reveals that other dimethylamine compounds, such as diuron, imipramine, and tetracyclines, can also serve as NDMA precursors during UV disinfection with NO2– present. Given that many environmental contaminants contain DMA moieties and NO2– is ubiquitously present in wastewaters, formation of NDMA during UV disinfection is probably a common but overlooked problem, which deserves emerging concern.