Mineral and pedogenic controls on metal(loid) retention in contaminated agricultural topsoils

Arsenic concentrations reached up to 2000 mg/kg, while soils impacted by historical mining were enriched in Sb (≤ 540 mg/kg), Cu (≤ 1600 mg/kg), Pb (≤ 4460 mg/kg), and Zn (≤ 3630 mg/kg). These contaminants accumulated in the <10 μm fraction, posing increased health risk from wind transport and inhalation. Iron (oxyhydr)oxides in soil aggregates were dominant hosts of As, Cu, Pb, and Zn, with minor contribution from Mn (oxyhydr)oxides. In contrast, Sb was primarily associated with clay-rich aggregates, indicating stronger affinity for clays. Among discrete minerals, arsenates and (hydroxy)sulfates were the most common metal(loid)-bearing minerals. Ammonium sulfate extractions revealed a moderate potential mobility of As, Sb, Cu, and Zn (0.6–1.0%), while Pb was much less extractable (<0.05%). The patterns of potential mobility followed soil pH, increasing for As, Sb, and Cu at higher pH and for Zn and Pb at lower pH, reflecting their distinct adsorption behavior in soils. Our results highlight the key role of mineralogical associations in controlling the potential mobility of metal(loid)s in contaminated agricultural soils, with Sb showing notably different behavior from As.