Distribution Hotspots, Formation Mechanisms, and Ecological Effects of Reactive Oxygen Species in Soil and Sediment: A Critical Review

Reactive oxygen species (ROS), including superoxide radical (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen (1O2), are commonly present in soil and sediment, playing a crucial role in the nutrient biogeochemical cycle, pollutant transformation, and microbial ecology. Previous reviews mainly emphasized ROS toxicity and Fenton chemistry-related reactions, neglecting a comprehensive understanding of ROS distribution and hotspots, formation mechanisms, and ecological effects. Here, the most advanced in situ and ex situ detection methods of ROS in soil and sediment are first summarized to address these gaps. ROS hotspots are identified as active microinterfaces and oxic-anoxic fluctuation zones by graphing the distribution of ROS in soil and sediment. Second, ROS formation processes and mechanisms are outlined, which involve natural organic matter (NOM) and biochar (acting as electron shuttle, geobattery, geoconductor, and photosensitizer), transition metals (mainly via Fenton and Fenton-like reactions), and microbes (producing extracellular ROS and mediating NOM decomposition or metal oxides reduction). Further, as for the ecological effects of ROS, they impact the microbial community, nutrient cycle, and the transformation of organic pollutants and multivalence heavy metals. Finally, we call for more future research that focuses on developing rapid and in situ ROS detection techniques, elucidating the interactive ROS formation mechanisms by trace environmental components, analyzing ecological consequences in ROS hotspots, and practically applying ROS in soil and sediment. A comprehensive understanding of the ROS formation process in soil and sediment is crucial for the study of soil carbon sequestration and natural remediation processes in the context of global green and low-carbon development.