Water Resources Research Act Program

Details for Project ID 2019AR007B

Nitroxyl – The missing link in NDMA formation in chloramine systems

Institute: Arkansas
Year Established: 2019 Start Date: 2019-05-31 End Date: 2020-05-30
Total Federal Funds: $10,000 Total Non-Federal Funds: $22,789

Principal Investigators: Julian Fairey

Abstract: The goal of this project is to investigate the role of nitroxyl and peroxynitrite, both chloramine decay intermediates, in the formation of N-nitrosodimethylamine (NDMA) in chloraminated drinking water systems. NDMA is a concern because of its potential carcinogenicity and occurrence at toxicologically-relevant levels in chloraminated drinking water. However, the widely-accepted NDMA formation pathway does not adequately explain the formation of NDMA under realistic chloramination conditions. Specifically, NDMA formation at pH 9 – a typical operating pH for chloramine utilities – is underpredicted by one order of magnitude or more using numerical models that rely on the widely accepted NDMA formation pathway. Elucidating the NDMA formation pathway is needed to devise strategies to control NDMA formation in chloramine systems. Based on preliminary data, we hypothesize that there is an additional NDMA formation pathway that involves nitroxyl (HNO), an intermediate from the decomposition of chloramine species. HNO can be generated abiotically from monochloramine breakdown through dichloramine or biotically through monochloramine reactions with hydroxylamine, NH2OH, an intermediate released by nitrifying bacteria during ammonia oxidation. Under aerobic conditions, HNO reacts with dissolved oxygen to form peroxynitrite, ONOO-, which can directly react with the organic precursors of disinfection byproducts to form NDMA. Preliminary data presented in this proposal shows that the addition of a peroxynitrite scavenger (uric acid) or a nitroxyl scavenger (glutathione) results in lower NDMA yields by 60% and 55%, respectively. Importantly, these scavenger additions do not impact chloramine species concentrations, which implicates peroxynitrite and nitroxyl in the NDMA formation pathway. The proposed study will focus on generating kinetic data of reactive nitrogen species such as nitrous oxide (N2O), nitrite, and nitrate and dissolved oxygen during the formation of NDMA in chloraminated waters. Further, a mechanistic kinetic model will be validated to support the newly discovered NDMA formation pathway. The results of this study will provide additional insight into the NDMA formation in drinking water systems which then could be used to develop control strategies to limits its formation in chloraminated distribution systems.