Identification of N-nitrosamines and nitrogenous heterocyclic byproducts during chloramination of aromatic secondary amine precursors

With diminishing pristine water, wastewater-affected waters that contain complex anthropogenic compounds are becoming important sources of drinking water, and the compounds will inevitably react with disinfectants to form disinfection byproducts (DBPs). Secondary amines such as diphenylamine (DPA) analogues are considered as potential precursors of N-nitrosamines. In this study, an in-situ 14N/15N-labeling and screening workflow was used to systematically investigate the formation of nitrogenous DBPs (N-DBPs) and putative reaction pathways. Twenty-four N-DBPs were generated and identified from chloramination of DPA through two main pathways, in which chloramines reacted with the amino and phenyl functional groups to form N-nitrosodiphenylamine and monochlorinated 5,10-dihydro-phenazine (Cl-DiH-Phe), respectively. Cl-DiH-Phe could further produce phenazine and the coupling products with another DPA molecule. Selective N-DBP formation was pH and dose-dependent, and the same reactions were observed for additional two aromatic DPA analogues. Effects of alkyl substituent on the formation pathways were investigated by using a series of dialkyl and N-alkyl aromatic analogues. Only the amino pathway to form nitrosamines was noticed for dialkyl amines, nevertheless, both the two main reactions occurred for the N-alkyl aromatic amines. These findings suggested reaction with chloramines through a phenyl pathway was likely to be crucial for novel nitrogenous heterocyclic byproducts.