Decoding periodate-driven phototransformation of dissolved organic matter in sunlit waters: Multidimensional property...

Residual periodate (PI) from advanced oxidation processes poses emerging threats to aquatic carbon cycling, yet its role in reprogramming the phototransformation of dissolved organic matter (DOM) remains poorly understood. Here, we reveal the multidimensional effects of PI residues (20.0-300.0 μM) on DOM under solar irradiation by real-time photophysical, electrochemical, and photochemical tracking; molecular reactomics via FT-ICR MS with paired mass distance networks; and interpretable machine learning. PI residues induced aromatic structure fragmentation, reductions in apparent molecular weight, and increases in redox capacity by 1.4-3.6 times. The solar/PI system enhanced photochemical reactivity, elevating the quantum yields of ³DOM* (humic acid (HA): 0.50→0.75; Suwannee River HA (SRHA): 0.78→1.44) and ^•OH (HA: 1.85→2.38; SRHA: 1.82→3.19) via quinone-mediated pathways. Propertied correlations varied depending on the DOM source. Molecular reactomics revealed PI-driven CN bond cleavage (18.18 % increase in N-group removal) and the polymerisation of small molecules (e.g., tannins accumulated by 8.5 %) in contrast to natural photoageing. SHAP analysis using XGBoost further highlighted the significance of nitrogen and bidirectional control of the O/C ratio. These findings redefine DOM transformation mechanisms in carbon-nitrogen cycling towards N-centred under anthropogenic oxidant stress, accelerating dissolved organic nitrogen production, and increasing the risk of nitrogenous disinfection by-products.