A multi-element study was performed for metal-tolerant plants and the associated soils collected from four mineralized areas in Botswana using ICP-AES and ICP-MS. The elements were determined in the roots, stems and leaves of the three metallophytes, Blepharis aspera, Blepharis diversispina and Helichrysum candolleanum, previously known to accumulate Cu and Ni. The limits of detection (LOD) obtained for ICP-AES were in the ppm range while those for ICP-MS were down to sub-ppb level, allowing determination of elements in a wide concentration range.
Of the 62 elements studied, the following were found in higher concentrations than normal for plants: Al, Co, Cr, Cu, Fe and Ni in B. aspera; Al, Fe and Ti in B. diversispina; and Al, Ba, Cd, Cr, Cu, Fe, Ti and V in H. candolleanum. The rare earth elements (REEs) were also found in concentrations above normal for all plants: about one order of magnitude higher for the light REEs and two to three orders of magnitude for the heavy REEs. When the total contents of metals present in higher than normal amounts in the leaves were calculated, the concentrations were c. 0.3% for B. aspera, 0.1–0.2% for B. diversispina and 0.4–1% for H. candolleanum. When the macronutrient metals (Ca, Mg, Mn, K, Na, Si and Zn) were included, the leaf total metal burden was in the range 6–9% for B. diversispina and c. 3% for both H. candolleanum and B. aspera which grew side by side. The three plants showed different metal distribution patterns and levels. The elements that were found in the plants in amounts higher than normal also had elevated concentrations in the host soil.