Revisiting the chloramination of phenolic compounds: Formation of novel high-molecular-weight nitrogenous disinfection byproducts.

Disinfection is critical for ensuring water safety; however, the potential risks posed by disinfection byproducts (DBPs) have raised public concern. Previous studies have largely focused on low-molecular-weight DBPs with one or two carbon atoms, leaving the formation of high-molecular-weight DBPs (HMW DBPs, with more than two carbon atoms) less understood. This study explores the formation of HMW DBPs during the chloramination of phenolic compounds using a novel approach that combines high-resolution mass spectrometry with density functional theory (DFT) calculations. For the first time, we identified nearly 100 previously unreported HMW nitrogenous DBPs (N-DBPs), with nearly half of those being halogenated N-DBPs. These N-DBPs were tentatively identified as heterocyclic (e.g., pyrrole and pyridine analogs) and coupling heterocyclic N-DBPs. Through detailed structure analysis and DFT calculations, the key formation steps of heterocyclic N-DBPs (monochloramine-mediated ring-opening reactions of halobenzoquinones) and new bonding mechanisms (C-N, C-O, and C-C bonding) of the coupling heterocyclic N-DBPs were elucidated. The selective formation of these novel N-DBPs was significantly influenced by factors such as contact time, monochloramine dosage, pH, and bromide concentration. Our findings emphasize the occurrence of diverse HMW heterocyclic N-DBPs, which are likely toxicologically significant, underscoring the need for further research to evaluate and mitigate their potential health risks in water disinfection.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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