BOOK OF ABSTRACTS 107 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL50 UV/chlorine for Pesticides Degradation: Which NOM Fractions Affected Treatment Efficiency of Emerging Contaminants? Alex Yuichiro Murata1,2,*, Hiroshi Sakai2, Jean-Philippe Croué1 1 Université de Poitiers, UMR 7285 CNRS, Institut de Chimie des Milieux et Matériaux, 7 rue Marcel Doré – TSA 41105, 86073 Poitiers Cedex 9, France 2 Tokyo Metropolitan University, Department of Civil and Environmental Engineering, 1-1 Minami-osawa, Hachioji-city, 1920397 Tokyo, Japan * yuichiro.murata@univ-poitiers.fr Advanced oxidation processes (AOPs) are promising methods to decompose refractory micropollutants. [1] Among variety types of AOPs, ultraviolet-based activation of aqueous free chlorine (UV/chlorine) demonstrated capability in degradation efficiency of various micropollutants. [2,3] Meanwhile, practical application of UV/chlorine is still limited, and one of the major obstacles is inhibition of treatment efficiency in environmental water due to inherent water matrix. This study profiled compositions of natural organic matter (NOM) using LC-ESI-Orbitrap-MS to reveal organic features interrupting reactions between UV/chlorine and selected micropollutants. Target micropollutants included three organophosphate insecticides acephate, methamidophos, and dimethoate. Because of aiming at investigating effects by different sources and fractions, NOM was extracted from raw and treated Seine River and Colorado River waters by XAD resins fractionation protocol [4]. One milli-molar phosphate buffer (pH 7.0) containing five micro-molar target compounds (mixed solution) and one mg C L−1 NOM isolate were irradiated under low-pressure mercury UV light (254 nm, 0.148 µE s−1) in the presence of 50 μM chlorine. Dark chlorination without UV irradiation was also performed. Concentrations of the parent compounds were quantified using LC-ESI(+)-Orbitrap-MS (Q Exactive, Thermo Scientific). Non-target analysis for NOM alteration was performed on samples prepared by solid phase extraction using Bond Elut PPL cartridge (Agilent Technologies). MS spectra for screening process were obtained using LC-ESI(+/−)-Orbitrap-MS and analysed by Compound Discoverer (CD 3.4). Degradation efficiency of the target insecticides was inhibited in the presence of NOM, compared to samples without NOM. NOM characters had stronger impacts on UV/chlorine reactions than dark chlorination. NOM with larger half-width of fluorescence emission spectra at 254 nm excitation wavelength tended to inhibit degradation of the pesticides, suggesting that fluorophore by UV light in NOM influenced the
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