Identification of N-Nitrosodimethylamine precursors to improve their control
N-nitrosodimethylamine (NDMA) is a probable human carcinogen and drinking water disinfection by-product. NDMA forms as the product of reactions between chloramines and precursor compounds in water. This dissertation aims to provide insight into the removal of NDMA precursors, their nature, and a method to aid in their identification. Watershed-derived precursors accounted for more of and greater variability to NDMA formation upon chloramination than polymer-derived precursors in environmental samples. Coagulation polymers are quaternary amines, which have low NDMA yield but high use rates. Watershed-derived precursors were removed up to 90% by sorption to activated carbon, but activated carbon exhibited much less (<10%) sorption of polymer-derived precursors. Combined with literature NDMA molar yields of model anthropogenic compounds, where anthropogenic chemicals in some cases have NDMA yields >90% and biological compounds always have yields <2%, trace, organic, amine containing, anthropogenic chemicals were implicated as the most likely source of NDMA precursors in the watershed. Although activated carbon removes these precursors well, identification of individual compounds may result in more cost effective mitigation strategies. Therefore, I developed a method to isolate NDMA precursors from other organic matter into methanol to facilitate their identification. Optimization of the method resulted in a median recovery of NDMA precursors of 82% from 10 surface waters and one wastewater. The method produces 1,000X concentrated NDMA precursors and, in collaboration with the University of Colorado Center for Environmental Mass Spectrometry, time of flight mass spectrometry (TOF-MS) was performed on multiple treated wastewater and raw drinking water isolates. During TOF-MS, tertiary amines can cleave to form a neutral loss and an R group ion that is dependent on the original structure and I wrote a software program to “trawl” exported TOF-MS spectra for the diagnostic neutral loss resulting from fragmentation of tertiary amines. Methadone was identified as one new NDMA precursor that occurs at concentrations that form physiologically relevant levels of NDMA in surface water and wastewater. The approach used here to identify NDMA precursors is adaptable to other unknown disinfection by-product precursors given that a functional group is known that can 1)control sorption and 2)produce a predictable diagnostic fragment.