Application of Antimony Stable Isotopes in Revealing the Source and Vertical Migration of Sb in Soil

Antimony (Sb) is a widespread contaminant that poses potential carcinogenic risks worldwide. Many countries are grappling with significant historical Sb-containing waste, leading to soil contamination, which is of international concern. The lack of clarity on Sb sources and migration mechanisms in soil limits the effective prevention and control of soil pollution. This study utilized Sb stable isotope techniques to analyze soil profiles from two pollution scenarios, with the aims of quantifying Sb sources, understanding migration processes, and elucidating isotopic fractionation mechanisms in soil. The results reveal that surface soil Sb originates primarily from atmospheric dry deposition (31.7–56.3%), wet deposition (19.6–32.7%), and rock weathering (<21.0%). In subsurface soils, Sb mainly comes from solutions resulting from desorption in upper soil layers, with adsorption by iron minerals, manganese (hydr-)oxides, and organic matter impeding its downward movement. Deeper soil layers contain Sb derived from parent rock weathering, with migration impacted by secondary mineral adsorption. Groundwater aids in Sb migration and influences isotopic fractionation during water–soil exchange. This research introduces a novel framework for quantitatively tracking Sb pollution and enhances the scientific understanding of the geochemical behavior of Sb in soil.