IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 102 NOM and Aquatic Systems Thursday, 27 August 2026 / Hall C redox cycle, thereby promoting •OH generation. However, the experiments revealed the opposite: MnO2 addition at 10 mg Mn²⁺/L equivalents suppressed •OH production, attributable to the well-known catalytic decomposition of H2O2 by MnO2. This finding indicates that Mn speciation and concentration critically govern whether Mn enhances or inhibits •OH production. To date, experimental conditions that sustain the complete three-component cycle have not yet been achieved. Ongoing work is focused on identifying the concentration ranges and redox gradients under which the full three-component cycle becomes operative, as predicted by the thermodynamic framework. In parallel, a deployable •OH trapping sampler for use at the lake floor of Lake Biwa has been developed. The device exploits the surface of PET (polyethylene terephthalate) plate material: alkaline hydrolysis (1 N NaOH, 333 K, 24 h) exposes terephthalic acid moieties on the surface, which trap ambient •OH as hydroxyterephthalic acid. After field deployment, a second hydrolysis step recovers the trapped product, which is then concentrated by solid-phase extraction on a C18 cartridge and quantified by fluorescence-detection HPLC. Optimization using a Fe(NO3)3/ H2O2 model solution confirmed that the 24 h alkaline treatment maximizes trapping capacity. Recovery of hydroxyterephthalic acid (0.5 μmol/L) by SPE was 21.4% with a relative standard deviation of 5.3%, demonstrating acceptable reproducibility; however, the absolute signal-to-noise ratio under simulated environmental •OH concentrations remains insufficient for reliable field quantification. Modifications to the SPE protocol and pre-concentration strategy are currently underway to improve detection sensitivity, with the goal of achieving the first direct in situ measurement of •OH in the BTL of Lake Biwa.
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