BOOK OF ABSTRACTS 55 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Tuesday, 25 August 2026 / Hall B+C Analysis and Characterization SL21 Toxic Effects from Emerging Disinfection By-Products Elin Lavonen1, Sofija Djukanovic1 1 Aalto University, Dept. of Built Environment, Water and Wastewater Engineering, FI-00076 Aalto, Finland Natural organic matter (NOM) act as precursors for halogenated disinfection by-products (DBPs) during drinking water chlorination and chloramination. Due to the complexity of NOM, hundreds of different organic DBPs may be formed [1] but regulation only includes two groups – trihalomethanes (THMs) and haloacetic acids (HAAs) [2]. Lately, it has been shown that regulated DBPs are not the ones that drive the toxicity of DBP mixtures, nor can they be used as surrogates for the more toxic ones [3]. Therefore, studies focusing on toxic effects from the whole complex mixtures of DBPs are needed. To protect human health, it is important to identify the most problematic DBPs, and the NOM components that act as precursors to optimize removal prior to disinfection. In this study, samples were taken from three Finnish drinking water treatment plants (WTP A, B and C) prior to their full scale chloramination and subjected to laboratory scale chlorination and chloramination using two doses; normal dose, representing what is currently applied at the studied treatment plants (0.2 mg Cl2/mg dissolved organic carbon (DOC)), and high dose (twice the normal dose, 0.4 mg Cl2/mg DOC). Samples were also taken after full-scale chloramination prior to the distribution to study potential differences between lab scale and full scale disinfection practices. At WTP C, samples were collected also from raw water and after various treatment steps (coagulation + sand filtration, ozonation, GAC filtration + UV disinfection) to investigate changes in DBP precursors through selective removal of NOM during treatment and effects on the DBP formation. In vitro effect-based methods was used to measure two DBP-induced toxic effects; oxidative stress (Nrf2 activity) and genotoxicity (micronucleus assay). No toxic effects were detected in samples prior to lab och full scale disinfection and therefore all measured toxicity after disinfection could be attributed to the formation of DBPs. During full and lab scale chloramination of drinking water there was no formation of DBPs causing oxidative stress or genotoxicity showing good agreement between the lab experiment and full scale practices. At WTPs A and B, oxidative stress was induced both after normal and high dose chlorination of drinking water while no genotoxicity was detected. No toxicity was induced from chloramination. At WTP C, chlorination and chloramination of raw water caused genotoxicity for both doses and oxidative stress in all except normal dose
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