Emerging higher-carbon nitrogenous disinfection byproducts: A brief review of structures, occurrence, and research needs

Disinfection/oxidation byproducts (DBPs) are formed during water treatment. Nitrogenous DBPs (N-DBPs) are generally more toxic than the DBPs without nitrogen. Recently, DBPs of more than two carbons (“higher-carbon DBPs”) have been reported, but the status of higher-carbon N-DBP research has not been reviewed. This review assembled 355 individual compounds/structures of emerging higher-carbon N-DBPs and summarized the occurrence, precursors, and oxidation treatment for the 12 major classes (196 compounds/structures), including halogenated aromatic/cyclic compounds (nitrophenols, anilines, benzoquinone imines, pyridines, pyrroles, imidazoles, indoles, and nucleobases), as well as aliphatic/aromatic/cyclic compounds featuring nitrile, amide, and imide functional groups. Almost half of the major higher-carbon N-DBPs were confirmed by standards, but mass spectrometry-based identification is also common. Chlorination was the most studied disinfection method for higher-carbon N-DBPs, followed by chloramination and pre-ozonation, while chlorine dioxide and UV were not commonly considered. The levels of higher-carbon N-DBPs in real water samples ranged from <0.1 to ∼100 ng/L based on the limited studies, but their global occurrence remains unknown. Preliminary toxicity assessment showed that higher-carbon N-DBPs were more toxic than their non-nitrogenous analogues and the regulated DBPs. Potential synergy between the research of DBPs and contaminants of emerging concern (CECs) was discussed, as CECs can serve as a significant but previously overlooked source of precursors for both higher-carbon N-DBPs and the high-priority small-molecule DBPs. Strengthening the synergy between the research on DBPs and advanced oxidation processes (AOPs), especially regarding nitrogen-incorporation during AOP, will contribute to our understanding on the formation of higher-carbon N-DBPs.