Anaerobic oxidation of antimony under ambient conditions: Complex roles of pH value, soil adsorption and microbial community

Abstract

The oxidation of Sb(III) to Sb(V) reduces the toxicity of Sb, and nitrate acts as an electron acceptor coupled with Sb(III) oxidation under anaerobic conditions. However, the behavior of antimony anaerobic oxidation under ambient conditions has not been well elucidated. This work investigated the anaerobic oxidation of Sb(III) in soil and soilless microcosms, and the soil adsorption, microbial adsorption and intracellular accumulation of Sb(III) and Sb(V) at different pH values were tracked. In soil microcosms, up to 96.5 % Sb(III) and 19.4 % Sb(V) were adsorbed by soil, and acidic conditions facilitated Sb(V) adsorption. In soilless microcosms, microbial effects on Sb were also pH-dependent. More Sb(III) was adsorbed to the cell surface than Sb(V) under alkaline conditions, and the intracellular accumulation of Sb(III) and Sb(V) achieved a maximum under neutral conditions. The presence of soil significantly changed the composition of the microbial community, enriching anaerobic Sb-oxidizing taxa, including Bacillus and Ensifer, and potentially enhancing overall microbial metabolic activities. These results suggested that the Sb anaerobic oxidation under ambient conditions was a complex process involving many abiotic and biotic factors. Soil adsorption was the main factor that resulted in notable interference when capturing the weak nitrate-dependent Sb oxidation. In this study, the effects of soil pH and microbial influences on Sb presence patterns and potential transport behaviours were investigated to provide important insights into the remediation of Sb-contaminated soils, particularly in anaerobic environments.