Effects of wood bark and fertilizer amendment on trace element mobility in mine soils, Broken Hill, Australia: implications for mined land reclamation

Soil amendments can immobilize metals in soils, reducing the risks of metal exposure and associated impacts to flora, fauna and human health. In this study, soil amendments were compared, based on "closed system" water extracts, for reducing metal mobility in metal-contaminated soil from the Broken Hill mining center, Australia. Phosphatefertilizer (bovine bone meal, superphosphate, triple superphosphate, potassium orthophosphate) and pine bark (Pinus radiata) were applied to two soils (BH1, BH2) contaminated with mining waste. Both soils had near neutral to alkaline pH values, were sulfide- or sulfate-rich, and contained metal and metalloid at concentrations that pose high environmental risks (e.g., Pb = 1.25 wt% and 0.55 wt%, Zn = 0.71 wt% and 0.47 wt% for BH1 and BH2, respectively). The addition of fertilizers and/or pine bark to both soil types increased water extractable metals and metalloids concentrations (As, Cd, Cu, Fe, Mn, Pb, Sb, Zn) compared with nonamended soils. One or more of the elements As, Cd, Cu, Mn, Pb, and Zn increased significantly in extracts of a range of different soil+pine bark and soil+fertilizer+piner+pine bark tests in response to increased pine bark doses. By contrast, Fe and Sb concentrations in extracts did not change significantly with pine bark addition. Solution pH was decreased by phosphate fertilizers (except for bovine bone meal) and pine bark, and pine bark enhanced dissolved organic carbon. At least in the short-term, the application of phosphate fertilizers and pine bark proved to be an ineffective method for controlling metal and metalloid mobility in soils that contain admixtures of polymetallic, polymineralic mine wastes.