Dependence of Biotic and Abiotic H₂O₂ and •OH Production on the Redox Conditions and Compositions of Sediment during Oxygenation

Reactive oxygen species (ROS) production in O₂-perturbed subsurface environments has been increasingly documented in recent years. However, the constraining conditions under which abiotic and/or biotic mechanisms predominate for ROS production remain ambiguous. Here, we demonstrate that the ROS production mechanism, biotic and abiotic, is determined by sediment redox properties and sediment compositions. Upon the oxygenation of 10 field sediments, the cumulative H₂O₂ concentrations reached up to 554 μmol/kg within 2 h. The autoclaving sterilization experiments showed that H₂O₂ could be produced by both biotic and abiotic processes depending on the redox conditions. However, only the abiotic process could produce significant levels of •OH, and the production yield was closely related to the sediment components, particularly sediment Fe­(II) and organic matter. Fe­(II) bound with organic matter led to high yields of H₂O₂ and •OH production. Sediment oxygenation contributed to the appearance of H₂O₂ in groundwater, with the abiotic mechanism producing higher instantaneous H₂O₂ concentrations than the biotic mechanism. These findings reveal that the redox conditions, compositions, and texture of sediments collectively control abiotic and biotic mechanisms for ROS production, which assists the identification of ROS production hotspots and the understanding of ROS distribution and utilization in the subsurface.