Molecular-level mapping of high-valent metal-governed reaction patterns of micropollutants and dissolved organic matter

High-valent metal-based oxidation systems have been receiving extensive attention for their high reactivity and selectivity toward recalcitrant organic contaminants. However, the molecular insights into the elimination of organic micropollutants (especially their highly concerned transformation products (TPs)) and dissolved organic matter (DOM) by these oxidation systems remain unclear. This study evaluated the degradation of nine TPs of different precursors (sulfonamides, carbamazepine, and atrazine) under ferrate(VI)/sulfite (Fe(VI)/S(IV)), permanganate(VII)/sulfite (Mn(VII)/S(IV)), cobalt(II)/peroxymonosulfate (Co(II)/PMS), and copper(II)/peroxymonosulfate (Cu(II)/PMS)-based oxidation together with the elucidation of the molecular-level alterations of DOM. Findings revealed both Mn(VII)/S(IV) and Co(II)/PMS achieved superior TP removal (up to 99 % in 20 min) under optimized conditions. Analyzing oxidized products (OPs) indicated their distinct transformation pathways, with multiple OPs exhibiting enhanced persistence, mobility, or chronic toxicity. Fourier-transform ion cyclotron resonance mass spectrometry analysis suggested the compositional restructuration in DOM molecules. Successive transformation of DOM, including oxygen addition, decarboxylation, and selective attack of nitrogen/sulfur-containing moieties, occurred to yield oxygen-enriched, low-molecular-weight fractions. Machine learning and SHAP analysis identified molecular weight as the most dominant predictor of DOM reactivity toward oxidation. These findings enhance the understanding of the availability of TP abatement by high-valent metal-mediated oxidation systems and provide further insights into the DOM transformation during oxidative water treatment.