N-nitrosamine disinfection byproducts (DBPs) are a health concern because they are probable human carcinogens. Complex organic nitrogenous compounds, nitrosamine precursors, are largely unidentified in source water. Using stable isotopic labeling enhanced nontargeted analysis, we identified a natural product N-heterocyclic amine 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCCA) in source water. Interestingly, we discovered that chloramination of water containing MTCCA could produce four nitrosamines: methylethylnitrosamine, N-nitrosopyrrolidine, N-nitrosoanatabine and N-nitrosoanabasine. Computational modeling and experimental results helped explain potential pathways of nitrosamines generated from chloramination of MTCCA. Further investigations confirmed widespread occurrence of MTCCA in source water and wastewater. Its concentration ranged from high in upstream creeks (23.2 to 332.2 ng L-1) to lower in the river (5.7-37.6 ng L-1) during the 2020 spring runoffs, indicating that sources of MTCCA came from creeks around farms. Analysis of wastewater before and after ultraviolet, as well as microfiltration with subsequent ozonation treatments showed increased MTCCA after treatments, demonstrating a difficulty to degrade and remove MTCCA in water. This study discovered extensive presence of MTCCA in source water and wastewater, suggesting natural N-heterocyclic compounds may serve as a new source of nitrosamine precursors.

Nontargeted identification of a N-heterocyclic compound in source water and wastewater as a precursor of multiple nitrosamines

ACS Fall 2021

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