IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 56 Analysis and Characterization Tuesday, 25 August 2026 / Hall B+C monochloramine. Formation of DBPs causing oxidative stess still occured after coagulation treatment when dosing monochloramine, however not in samples after chlorination indicating selective removal of precursors that can form oxidative stress-inducing DBPs with hypochlorite during the coagulation treatment. Genotoxicity could be detected in all samples subjected to normal dose hypochlorite at WTP C, from raw water to drinking water, while none could be detected for the high dose or during chloramination. An explaination to the pronounced higher toxicity using normal dose chlorine could be that a high chlorine residual drives the formation of DBPs towards Cl-containing compounds while a relatively higher proportion of the, generally considered, more toxic bromine or iodine-containing DBPs can be formed using the lower hypochlorite dose [4]. This may be further accentuated due to selective removal of dissolved organic carbon (DOC) over Br and I during treatment leading to higher Br/DOC and I/DOC rations as the raw water is gradually treated into drinking water. The amount and composition of DBP precursors (NOM) and formed DBPs were analyzed with bulk parameters such as DOC, UV absorbance and concentrations of THMs and HAAs and on a molecular level using ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). This will give further insights on which DBPs that are causing oxidative stress and genotoxicity and which DOM components that should be targeted during treatment to aviod the formation of toxic DBPs. References 1. Lavonen et al, ES&T 47 (2013) 5. 2. Directive (EU) 2020/2184 of the European Parliament and of the Council of 16 December 2020 on the quality of water intended for human consumption. 3. Richardsson & Plewa, J. Environ. Chem. Eng. 8 (2020) 4. 4. Andersson et al, Environ. Sci: Wat. Res. Technol. 6 (2020) 779.
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