Transference of potentially toxic elements from soils to plants in a derelict Pb–Zn mining area (San Quintín mine, South-Central Spain)

Abstract

Abandoned mining areas represent critical environmental pollution hotspots due to the persistence of waste materials enriched in potentially toxic elements (PTEs). This study evaluates the transfer of PTEs from contaminated soils to six plant species in the vicinity of the San Quintín Pb–Zn mine (Ciudad Real, Spain), a site impacted by over a century of mining activity. Methods The studied species include the tree Quercus ilex, the shrubs Retama sphaerocarpa and Scrophularia canina, and the annual herbaceous species Spergularia rubra, Rumex bucephalophorus, and Hirschfeldia incana. Soil and plant tissue samples were analysed using X-ray fluorescence and atomic absorption spectrometry to determine concentrations of Zn, Pb, Hg, Cu, and other PTEs. Results Results revealed a high heterogeneity in the bioaccumulation of elements such as Zn, Pb, Hg, and Cu among the studied species, with Spergularia rubra and Rumex bucephalophorus emerging as effective bioindicators of soil contamination. The presence of acid mine drainage (AMD) significantly reduced soil pH (average ≈ 5.7), enhancing PTE solubility (e.g., Zn2+ release) and facilitating their uptake by plants (Bravo et al., 2017). Specific correlations between soil and plant concentrations were identified, and atmospheric uptake was found to significantly influence Hg accumulation in plant tissues. Conclusions This study revealed high PTE contamination and spatial heterogeneity in the San Quintín mining area, with concentration ranges (mg kg−1) of 13–806 for Sb, 70–57,270 for Pb, 68–48,460 for Zn, 18–1680 for Cu, and 3–1920 for Hg, as the most significant elements. Species such as Spergularia rubra and Rumex bucephalophorus exhibited strong metal accumulation, with average concentrations (mg kg−1) of 1460 and 552 for Pb, 1232 and 927 for Zn, 36 and 22 for Cu, and 28 and 9 for Hg, respectively, and the average Pb BAC for S. rubra of 0.15, significantly higher than that of other species. These results indicate the potential of these two species for bioindication and phytoremediation. Furthermore, Hg accumulation in S. rubra follows a logarithmic trend (R2 = 0.98), confirming that atmospheric uptake by leaves supposes an important contribution to bioaccumulation of the element in plants. These results indicate the potential of both species for bioindication and phytoremediation. Mercury uptake was influenced not only by the edaphic compartment but also by atmospheric deposition and plant foliar traits. Overall, these findings provide a better understanding of PTE dynamics within the soil–plant system and support phytoremediation strategies in degraded mining environments.