“…High-arsenic (As) groundwater (As > 10 μg/L, WHO guideline) is placing millions of people across the world under the risk of severe health problems, including skin, lung, bladder, liver, and kidney cancers. , Interactions between indigenous aquifer microbial communities and associated hydro-geochemical processes are key to understanding As behavior in natural groundwater systems . The microbially mediated reductive dissolution of As-bearing Fe(III) oxides (the dominant As sink in aquifer sediments) is the most commonly accepted mechanism of groundwater As enrichment. ,− Multiple electron donors can support the microbial reduction of Fe(III) oxides, including organic matter, elemental sulfur (S 0 ), , ammonium, and methane, which have all been reported in high-As aquifers. ,− Given the coexistence of these potential electron donors for microbial Fe(III) oxide reduction in natural groundwater systems, groundwater As enrichment is tightly interconnected with the biogeochemical transformations of C, N, S, and Fe. ,, …”