Ecological Risk Assessment of Innovative Soil Substitute Cover in Post-Mining Land Reclamation: A Case Study of the Janina Mine Spoil Heap

Artificial soils derived from coal combustion by-products and industrial waste have been successfully used for mine spoil reclamation; however, their ecological risk and toxic element migration in the soil–plant system have not been assessed. The objective of this study was to evaluate the ecological risks in soil substitute covers after five years of their exposition, using the ecological risk factor (ERi), potential ecological risk index (PERI) and geoaccumulation index. The modified BCR-sequential extraction method was applied to determine the chemical partitioning of the most toxic heavy metals (Cd, Cr, Cu, Ni, Pb, Zn). Additionally, the bioconcentration and translocation factors were used to assess the uptake of toxic elements by Phragmites australis. Findings from PERI indicate a moderate risk (239 and 258), mainly associated with moderate and considerable ERi for Cd and Hg, respectively. The other toxic metals are associated with a low risk (ERi < 40). Sequential extraction results showed the lowest concentrations of heavy metals in F1 fraction (0–30%) and increased in subsequent fractions: F2 (1–43%), F3 (10–62%) and F4 (10–89%). The calculated BCF values were below 1, indicating that the concentration of toxic metals in plants was lower than that in the soil substitute. The only exception was observed for Mn and Sn (BCF > 1). The results suggest that the tested soil substitutes are suitable for the reclamation of post-mining areas and may support sustainable biomass production. However, due to industrial atmospheric deposition and ecological risk associated with selected trace elements, continued monitoring of toxic metals is recommended.