Chemical extractability of As and Pb from soils across long-term abandoned metallic mine sites in Korea and their phytoavailability assessed by Brassica juncea

The chemical extractability of As and Pb (by 5 mM CaCl₂, 0.1 M HCl, 0.05 M NH₄ (H₂PO₄), and aqua regia) from soils and their phytoavailability (by Brassica juncea) were assessed using 16 soil samples collected as a function of distance from mine pits across three long-term abandoned metallic mine sites. The total concentrations of As and Pb (17–41,000 and 27–10,047 mg kg⁻¹, respectively) decreased with increasing separation distance from the mine pits along a declining slope. However, the percentage of chemically leachable As and Pb mass (e.g., by 5 mM CaCl₂, 0.1 M HCl, or 0.05 M NH₄(H₂PO₄)) relative to total mass (e.g., by aqua regia) tended to increase exponentially with distance, indicating more chemically labile fractions present in less contaminated downgradient soils. Among soil components, extractable As concentrations were best described by coupling DCB-Al with other Al and Fe oxides. For Pb concentration, pH coupled to DCB-Al or Ox-Al provided a good predictive relationship. The inhibitory growth and uptake by plants were best correlated with the extractable concentrations by 5 mM CaCl₂ and 0.1 M HCl. In conclusion, the chemical extractability and phytoavailability of As and Pb are highly influenced by the relative labile fraction in abandoned mine soils, and its distribution in soils is essentially correlated with sampling distance from mine pits.