Aqueous N-nitrosamines: Precursors, occurrence, oxidation processes, and role of inorganic ions

N-Nitrosamines, well-known human carcinogens, are widely considered to be formed through the disinfection of waters containing compounds with amine moieties. The formation mechanisms of nitrosamines during the disinfection of drinking water and wastewater have been previously reviewed in the literature. However, no study to date has reviewed the effects of inorganic ions on nitrosamines formation during disinfection. Inorganic ions are ubiquitous in the environment and are present at significant concentrations in water and wastewater. Their presence influences aqueous nitrosamines formation, depending on the type, concentration, and environmental conditions. In this review, we have critically reviewed nitrosamines' precursors and occurrence, disinfection processes associated with nitrosamines' formation/destruction, and the impact of inorganic ions on the formation or removal of nitrosamines during disinfection of water and wastewater. The disinfectants reviewed in the study were chlorine, chloramine, chlorine dioxide, ozone, and radicals generated through advanced oxidation processes (AOPs). N-Nitrosodimethylamine formation pathways, in the presence and absence of inorganic ions, were also reviewed to summarize our current understanding. Although chloramination has been associated with the formation of nitrosamines, many ozonation studies have also shown significant levels of nitrosamines formation. Pre-oxidation and AOPs have been reported as the most promising mitigation strategies for controlling nitrosamines formation, requiring prolonged exposure of precursors for effective mineralization.