Enhanced As(III) adsorption-oxidation via synergistic interactions between bacteria and goethite

The adsorption and oxidation of arsenite [As(III)] by soil components are critical processes that influence its toxicity and mobility. However, the specific mechanisms driving the synergistic interactions among bacteria, soil minerals, and humic acid (HA) in these processes remain insufficiently understood. This study investigated the effects of goethite and HA association on As(III) adsorption-oxidation by the As(III)-oxidizing bacterium SY8 using batch incubation experiments and spectroscopic analyses. The results indicated that goethite inhibited the growth of SY8, but its binary and ternary composites with HA and SY8 substantially enhanced the adsorption and oxidation of As(III) compared to SY8 alone. This enhancement could be attributed to the generation of hydroxyl radicals (·OH) through Fenton-like reactions that contribute to the enhanced oxidation of As(III). The Fenton-like reactions involved interactions between H₂O₂ and goethite, as well as the activation of molecular O₂ by structural Fe(II). Furthermore, the proportion of As(V) associated with the solids was lower than that in the solution, suggesting that As(III) oxidation by SY8 was potentially inhibited by As(III) adsorption on goethite. Additionally, HA did not affect SY8 growth or its As(III) oxidation capability, but slightly enhanced As adsorption on the composites. These findings reveal a complex interplay among microbial, mineral, and organic matter interactions. Understanding these interactions is essential for elucidating soil As biogeochemical processes and developing effective remediation strategies for As-contaminated environments.