Microbial antimonate reduction in contaminated sediments driven by photoreactive DOM Under hydrochemical fluctuations

Mining-impacted river systems often accumulate elevated antimony (Sb) levels; however, the environmental controls on anaerobic microbial Sb(V) reduction remain poorly understood. This study shows that dissolved organic matter (DOM) in sediment can influence Sb(V) redox processes through its photochemical reactivity rather than solely serving as a heterotrophic carbon source. Microcosm experiments combined with field observations were used to assess whether photoreactive DOM facilitates microbial Sb(V) reduction in anoxic sediments. Substantial Sb(V) reduction (up to 42%) occurred only when light, DOM, and active microorganisms were co-present. Photostimulation selectively enriched taxa such as Bradyrhizobium, Cupriavidus, Microbacterium and Skermanella, suggesting their critical role in Sb(V) reduction via utilizing photoreactive DOM-derived photoelectrons. Across three Sb-contaminated river systems, variations in DOM photochemical composition were observed. Model analysis further suggested that DOM photochemical characteristics, rather than Sb concentrations alone, shaped microbial community assembly under environmental fluctuations. These findings expand the understanding of microbial Sb(V) reduction by highlighting the photochemical role of DOM in anoxic sediments.