Mechanistic Insight into the Degradation of Nitrosamines via Aqueous-Phase UV Photolysis or a UV-Based Advanced Oxidation Process: Quantum Mechanical Calculations

Abstract

Nitrosamines are a group of carcinogenic chemicals that are present in aquatic environments that result from byproducts of industrial processes and disinfection products. As indirect and direct potable reuse increase, the presence of trace nitrosamines presents challenges to water infrastructures that incorporate effluent from wastewater treatment. Ultraviolet (UV) photolysis or UV-based advanced oxidation processes that produce highly reactive hydroxyl radicals are promising technologies to remove nitrosamines from water. However, complex reaction mechanisms involving radicals limit our understandings of the elementary reaction pathways embedded in the overall reactions identified experimentally. In this study, we perform quantum mechanical calculations to identify the hydroxyl radical-induced initial elementary reactions with N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine, and N-nitrosomethylbutylamine. We also investigate the UV-induced NDMA degradation mechanisms. Our calculations reveal that the alkyl side chains of nitrosamine affect the reaction mechanism of hydroxyl radicals with each nitrosamine investigated in this study. Nitrosamines with one- or two-carbon alkyl chains caused the delocalization of the electron density, leading to slower subsequent degradation. Additionally, three major initial elementary reactions and the subsequent radical-involved reaction pathways are identified in the UV-induced NDMA degradation process. This study provides mechanistic insight into the elementary reaction pathways, and a future study will combine these results with the kinetic information to predict the time-dependent concentration profiles of nitrosamines and their transformation products.

N-Nitrosodimethylamine (NDMA) Degradation by the Ultraviolet/Peroxodisulfate Process

“…It is noteworthy that as the quasi-steady state concentration of the chlorine radical is 6–7 magnitudes lower than that of the dichloride radical anion (Figure S10) and that of the carbonate radical (Figure S11), it is unlikely that the chlorine radical contributes significantly to NDMA degradation. In fact, we can estimate that the activation energy for all elementary reactions of the chlorine radical and NDMA (addition to the N atoms, hydrogen abstraction from the methyl groups) is higher than that of their equivalent elementary reactions with the hydroxyl radicals. , Consequently, the aggregate bimolecular reaction rate constant of the chlorine radical with NDMA must be lower than that of its equivalent reaction with the hydroxyl radical (Table , reaction 10).…”

“…In fact, we can estimate that the activation energy for all elementary reactions of the chlorine radical and NDMA (addition to the N atoms, hydrogen abstraction from the methyl groups) is higher than that of their equivalent elementary reactions with the hydroxyl radicals. 41,42 Consequently, the aggregate bimolecular reaction rate constant of the chlorine radical with NDMA must be lower than that of its equivalent reaction with the hydroxyl radical (Table 1, reaction 10).…”

Investigation on the compositions of unsymmetrical dimethylhydrazine treatment with different oxidants using solid-phase micro-extraction-gas chromatography–mass spectrometer

“…Previous studies have shown that NDMA destruction by Fenton's reagent is most efficient at low pH. Minakata [34] et al proposed that NDMA has three potential initial degradation mechanisms: (i) H atom abstraction from a C−H bond of the methyl group, (ii) HO· addition to amine nitrogen, and (iii) HO· addition to nitrosyl nitrogen. …”

Stability Indicating Method for a Thiazolylhydrazone Derivative with Antifungal Activity and Experimental/Theoretical Elucidation of Its Degradation Products

“…QMC approach may support experimental data by calculating the reaction energy using statistical thermodynamics. 13 Hence, the aims of this study were to develop and validate a stability-indicating method by high-performance liquid chromatography with diode-array detection (HPLC-DAD) and to evaluate the stability of RN104 in a forced degradation study under different conditions (acidic, alkaline and neutral hydrolysis, oxidation, photolysis and thermolysis). In addition, we proposed the chemical structures of the DP formed in the forced degradation studies.…”