Heavy metals in mine-tailing soil mixtures cultivated with Ricinus communis L.

Ricinus communis L. was found to vegetate mine tailings with high concentrations of Al (4,456 mg kg^-1), As (3,473 mg kg^-1), Cd (120 mg kg^-1), Cr (14 mg kg^-1), Cu (1,147 mg kg^-1), and Pb (910 mg kg^-1). We investigated how this plant responded to increased heavy metal concentrations by mixing mine tailing at 0%, 50%, 70%, and 100% with soil at 100%, 50%, 30%, and 0%, while metal concentrations in the rhizosphere, roots, and aboveground parts of R. communis were monitored. Ricinus communis shoots were 19% smaller and roots 8% in soil mixed with an equal amount of mine tailings compared to plants cultivated in soil and 33% and 54%, respectively, when cultivated in mine tailings. The ratio of As, Cd, Cu, and Pb in the aboveground plant parts to the concentration in soil remained <0.12, while that of the roots <0.25. The As concentration was 35% lower in the bulk soil than in the rhizosphere. We found that R. communis growth was inhibited strongly when cultivated in mine tailings, but less so when mixed with soil, and metals did not accumulate in the roots and aboveground plant parts. These characteristics make R. communis ideal to vegetate metal-contaminated soil, thereby reducing the environmental hazards of mine tailings.