title: Unveiling formation mechanism of carcinogenic N-nitrosodimethylamine in ozonation of dimethylamine: a density functional theoretical investigation.
abstract: Recent studies found that ozonation of organic pollutants with dimethylamino groups produces N-nitrosodimethylamine (NDMA) that is highly carcinogenic to humans. However, the formation mechanism of NDMA remains inexplicit, and previously proposed mechanisms are inconsistent with experimental observations. In this study, the formation mechanism of NDMA in ozonation was explored by density functional theory (DFT) calculations, with dimethylamine (DMA) as a model compound. By calculating Gibbs energies and energy barriers, formation of NDMA in ozonation of DMA was observed to proceed through a hydroxylamine mechanism. The calculation results show that hydroxylamine is generated through DMA reacting with hydroxyl radicals (HO•) formed from hydrolysis of ozone. DMA reacting with hydroxylamine can produce unsymmetrical dimethylhydrazine (UDMH), a well-known NDMA precursor. Transformation of UDMH to NDMA is mainly induced by ozone or HO• rather than dissolved oxygen proposed previously. The reaction of DMA and hydroxylamine is pH dependent, with energy barriers increasing from neutral pH to the second pKa of hydroxylamine and then decreasing. This is in accordance with the experimentally observed pH dependence of NDMA yield in ozonation, indicating that the hydroxylamine mechanism is responsible for the NDMA formation in ozonation.
authors: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, POPs Research Center, Tsinghua University, Beijing 100084, China; Veolia Environment Joint Research Center for Advanced Technology, Tsinghua University, Beijing 100084, China.
authors: Siyu
authors: S
authors: Zhang
authors: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, POPs Research Center, Tsinghua University, Beijing 100084, China; Veolia Environment Joint Research Center for Advanced Technology, Tsinghua University, Beijing 100084, China. Electronic address: yg-den@mail.tsinghua.edu.cn.
authors: Gang
authors: G
authors: Yu
authors: Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
authors: Jingwen
authors: J
authors: Chen
authors: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, POPs Research Center, Tsinghua University, Beijing 100084, China; Veolia Environment Joint Research Center for Advanced Technology, Tsinghua University, Beijing 100084, China.
authors: Bin
authors: B
authors: Wang
authors: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, POPs Research Center, Tsinghua University, Beijing 100084, China; Veolia Environment Joint Research Center for Advanced Technology, Tsinghua University, Beijing 100084, China.
authors: Jun
authors: J
authors: Huang
authors: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, POPs Research Center, Tsinghua University, Beijing 100084, China; Veolia Environment Joint Research Center for Advanced Technology, Tsinghua University, Beijing 100084, China.
authors: Shubo
authors: S
authors: Deng
mesh_terms: D002273:Carcinogens / Q000737:chemistry*; D004123:Dimethylamines / Q000737:chemistry*; D004128:Dimethylnitrosamine / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D019811:Hydroxylamine / Q000737:chemistry; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*
chemical_list: D002273:Carcinogens; D004123:Dimethylamines; D004785:Environmental Pollutants; D019811:Hydroxylamine; D010126:Ozone; C034516:dimethylamine; D004128:Dimethylnitrosamine
keywords: Density functional theory; Dimethylamine; Hydroxylamine; N-nitrosodimethylamine; Ozonation