Assessment of N-Oxide Formation during Wastewater Ozonation

Abstract

Worldwide, ozonation of secondary wastewater effluents is increasingly considered in order to decrease the load of organic contaminants before environmental discharge. However, despite the constantly growing knowledge of ozonation over the past few years, the characterization of transformation products (TPs) is still a major concern, particularly because such TPs might remain biologically active. It has been shown for selected tertiary amine pharmaceuticals that they react with ozone and form the corresponding N-oxides. This study therefore applies liquid chromatography-high resolution mass spectrometry (LC-HRMS) to assess the overall N-oxide formation during the pilot-scale ozonation of a secondary wastewater effluent from a major city in Germany. Sample analysis by LC-HRMS revealed the occurrence of 1,229 compounds, among which 853 were precursors attenuated by ozone and 165 were TPs. Further examination of precursors and TPs using Kendrick mass and Kendrick mass defect analysis revealed 34 pairs of precursors and products corresponding to a mono-oxygenation. Among these, 27 pairs (16% of all TPs) were consistent with N-oxides since the TP had a higher retention time than the precursor, a characteristic of these compounds. Using high resolution tandem mass spectrometry, 10 of these N-oxides could be identified and were shown to be stable during a subsequent filtration step.

Nontarget Screening with High Resolution Mass Spectrometry in the Environment: Ready to Go?

“…Experiment-driven Frequency, signal intensity of masses 14,33 Persistence 34 , elimination/formation 29 over process Component with characteristic isotope pattern (C, Cl, Br, N, O, S) 13,19,35 Reaction-based search of transformation products to link masses before and after treatment 30 Part of homologue series (mass difference, Kendrick mass defect) 13,36,37 Biological 28 , electrochemical 38 , oxidative 32 transformation product formation Suspect screening (looking for "known" or predicted chemicals without standard) 39,40 Reaction with isotopically-labelled reagents 31 Specific functional groups (MS/MS, derivatisation, neutral loss) 41,42 Effect-directed selection of masses in toxic fractions 43,44 Temporal or spatial profile over several samples 24,33 A second limitation is accounting for potential toxicity during prioritization. Approaches such as Effect-Directed Analysis use biological effect tests to prioritize chromatographic fractions with unknown components associated with specific toxic effects for identification.…”

In Vitro Metabolism of Donepezil in Liver Microsomes Using Non-Targeted Metabolomics

“…Characteristic fragment ions of donepezil N -oxide at m/z 91.1, 151.1, 243.1, and 288.2 were also reported in previous studies [ 35 , 37 ]. Metabolite M4 had a longer retention time compared with that of the parent drug, which is characteristic of N -oxide metabolite reported for several drugs [ 7 , 39 ].…”

Benefits of ozonation before activated carbon adsorption for the removal of organic micropollutants from wastewater effluents

“…In addition, the use of activated carbon should allow the adsorption of ozonation byproducts formed during ozonation (e.g. hydroxylated products or N-oxides) (Merel et al, 2017). Additional studies should be conducted (e.g.…”