Electron-Driven Processes for Sustained Dark Hydroxyl Radical Generation under Redox Fluctuations in Mangrove Soils

• • Solid-phase components contributed 94.5%–97.6% of total electron donating capacity (EDC) in mangrove soil suspensions, underscoring the dominance of particulate organic matter and mineral-bound Fe(II) in sustaining electron supply for dark ·OH generation. • • Reactive Fe(II) species dominated EDC during initial redox cycles, but reduced organic matter progressively took over, indicating a shift in electron donor pools over time that is critical for predicting long-term ·OH production. • • Humic acids with quinone moieties acted as reversible electron shuttles, enabling sustained redox activity across multiple cycles, a mechanism that can be harnessed for remediation of redox-fluctuating contaminated sites. • • Geothermobacter and Desulfobulbus were identified as key iron-reducing bacteria, suggesting that microbial-driven Fe(III) reduction is essential for regenerating Fe(II) and maintaining ·OH generation, with implications for biogeochemical modeling.