title: Formation of N-Nitrosodimethylamine during Chloramination of Secondary and Tertiary Amines: Role of Molecular Oxygen and Radical Intermediates.
abstract: N-Nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct from water chloramination. Despite the identification of numerous NDMA precursors, essential parts of the reaction mechanism such as the incorporation of molecular O2are poorly understood. In laboratory model systems for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the stoichiometries of monochloramine (NH2Cl) and aqueous O2consumption, derived18O-kinetic isotope effects (18O-KIE) for the reactions of aqueous O2, and studied the impact of radical scavengers on NDMA formation. Although the molar NDMA yields from five N,N-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O2per N,N-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small18O-KIEs between 1.0026 ± 0.0003 and 1.0092 ± 0.0009 found for all precursors as well as completely inhibited NDMA formation in the presence of radical scavengers (ABTS and trolox) imply that O2reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH2Cl and N-peroxyl radicals from the reaction of aminyl radicals with aqueous O2are part of the NDMA formation mechanism.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf, Switzerland.|School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Federale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Spahr
authors.affiliation: Center for Applied Geoscience, University of Tübingen , D-72074 Tübingen, Germany.
authors.forename: Olaf A
authors.identifier: 0000-0003-3509-4118
authors.initials: OA
authors.lastname: Cirpka
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf, Switzerland.|School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Federale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich , CH-8092 Zürich, Switzerland.
authors.forename: Urs
authors.initials: U
authors.lastname: von Gunten
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich , CH-8092 Zürich, Switzerland.
authors.forename: Thomas B
authors.identifier: 0000-0003-1906-367X
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D000588:Amines; D002273:Carcinogens; D004128:Dimethylnitrosamine; D004203:Disinfection; D010100:Oxygen; D018508:Water Purification
chemical_list: D000588:Amines; D002273:Carcinogens; D004128:Dimethylnitrosamine; D010100:Oxygen