BOOK OF ABSTRACTS 113 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL53 Heterocyclic Organic Chloramines as Chlorinating Agents toward Phenolic Moieties in DOM: Implications for Disinfection Byproduct Formation Sungeun Lim1 1 Eawag, Uchem, Ueberlandstrasse 133 8600 Duebendorf Switzerland, sungeun.lim@eawag. ch Chlorine is a widely used disinfectant in water treatment. While it effectively safeguards water quality against pathogens, it can also lead to the formation of harmful disinfection byproducts (DBPs) through reactions with dissolved organic matter (DOM). Climate change (e.g., rising temperature and algal blooms) and anthropogenic impacts (e.g., agricultural and urban runoffs) are increasing the levels of organic nitrogen in water bodies. Consequently, understanding the role of organic nitrogen in DOM on DBP formation during chlorination becomes increasingly important. Organic chloramines, common initial products formed from reactions between chlorine and organic nitrogen moieties, may contribute to DBP formation by subsequently chlorinating activated aromatic compounds (e.g., phenolic structures prevalent in DOM). Previous studies have investigated the reaction kinetics of organic chloramines with phenol, but primarily for those derived from aliphatic amines and amides. Nitrogen-containing heterocycles, despite their widespread occurrence in biomolecules and anthropogenic compounds, remain largely unexplored. Furthermore, conventional kinetic methods face challenges due to the inherent instability of organic chloramines, which readily revert to their parent compounds. This reversibility complicates kinetic measurements, particularly when chlorine quenchers are used, as these promote back-reaction. In this study, I investigated the reaction of heterocyclic organic chloramines with phenolic structures using uridine as a model compound. I determined the second-order rate constant (k) for the reaction of N-chlorouridine with phenol and identified reaction products, using an online reaction monitoring setup combining a programmable liquid handling module with high-resolution mass spectrometry (HRMS). This approach enables kinetic measurements without the need for chemical standards and avoids the use of chlorine quenchers. The apparent k of N-chlorouridine with phenol at pH 7 was determined to be 2.9 × 102 M-1s-1, which is 5-6 orders of magnitude higher than reported values for organic chloramines derived from aliphatic amines and amides (typical range 10-4 – 10-3 M-1s-1 [1,2]). Notably, this reactivity is even higher
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