Antimony speciation and its environmental impact: A comparative analysis across contaminated sites.

Characterizing the solid-phase speciation of antimony (Sb) at contaminated sites is essential for assessing its mobility, bioavailability, and environmental risk. However, comparative field studies across contrasting contamination sources and environments remain limited. To address this gap, we investigated the mineralogy and speciation of Sb-bearing phases in soil and rock samples collected from three distinct sites: an Sb mine, a shooting range, and an Sb refinery, and evaluated their relationships with local biogeochemical parameters. X-ray spectroscopic analyses showed that Sb(V) dominated across all sites, while Sb speciation varied markedly. Tripuhyite (an Sb(V)-ferric mineral) and/or roméite (a Ca-dominant pyrochlore-group Sb(V) oxide) were present at the mine and refinery as oxidation products of Sb(III) phases. In contrast, shooting range soils contained surface-associated Sb(V) immobilized by iron (Fe) phases. Microbial community analysis showed negligible abundance of Sb(III)-oxidizing bacteria and minimal Sb influence on community composition, likely reflecting low Sb bioavailability. Instead, microbial communities consisted of taxa exhibiting metabolic diversity and adaptation to the contaminated environments. Overall, long-term Sb speciation across the three sites is controlled by site-specific contamination sources and abiotic processes, particularly oxidation and stabilization mediated by Fe phases, rather than direct microbial involvement. These findings highlight the importance of comparative field studies for advancing our understanding of Sb behavior in contaminated environments.