Evaluation of mobility, fractionation, and potential environmental risk of trace metals present in soils from Struibult gold mine dumps

This study reports the fractionation of trace metals such as As, Bi, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Se, Tl and Zn in soils collected from Struibult gold mine dump, Gauteng, South Africa using a modified three-step BCR sequential extraction procedure. The extractable fractions such as exchangeable, easily reducible and oxidizable fractions were used assessed to the mobility and potential bioavailability of each investigated metal. Fractionation results revealed that As (55.4–80.6%), Bi (16.8–42.2%), Cr (83.3–94.8%), Cu (0–51.5%), Mo (0–80.4%), Ni (13.2–100%), Pb (55.6–79.6%), Sb (61.9–93.3%), Se (47.3–77.9%), Tl (58.8–100%) and Zn (8.7–100%) predominant metals in the residual fraction (F4) of soil samples. Individual contamination factors (ICF), geo-accumulation index (I_geo), contamination factor (CF), risk assessment code (RAC) and enrichment factor (EF) were used for assessment of the environmental impacts of trace metals in soil samples. The RAC and ICF values showed that Co, Ni and Zn have high environmental risk. The bioaccumulation of trace metals in the plants (Chrysopogon zizanioides) growing at the foot of the mine dump was assessed. Chrysopogon zizanioides was found to accumulate most of the studied metals that were available for uptake, with bioaccumulation factor (BAF>1). These results suggested that this plant species is a good accumulator for toxic metals in mining areas.