Heavy metal accumulation of aquatic grasses from mine tailing's wastewater drainage spillway of BCL Cu-Ni mine in Selebi Phikwe, Botswana

Mining activities introduce countless contaminants into the environment, including toxic levels of heavy metals that accumulate in soil and water, requiring environmental management to prevent detrimental effects. One strategy is to use plants because of their natural ability to adsorb and accumulate different contaminants in their tissues. To develop a rhizofiltration technique for mine wastewater in Botswana, there is a need to identify suitable aquatic plant species which can remove heavy metals from acid mine drainage and associated sediments. Plant species growing in the vicinity of acid mine drainage at the BCL mine were sampled and analyzed for heavy metal concentration in the various plant tissues.

The plants analyzed were: Cyperus papyrus; Phragmites australis; Schoenoplectus tabernaemontani; and Baumea rubiginosa. These plants all accumulated above-average concentrations of Co, Cr, Cu, Ni, and Zn in their tissues, especially Cr, Cu, and Ni. C. papyrus accumulates more Cr (up to 6080.86 mg kg⁻¹in shoots and 5047.15 mg kg⁻¹ in roots), Cu (up to 2166.43 mg kg⁻¹ in roots and 1231.12 mg kg⁻¹ in shoots), and Ni (up to 949.97 mg kg⁻¹ in roots and 1163.42 mg kg⁻¹ in shoots). P. australis accumulates more Cu in roots (up to 7416.87 mg kg⁻¹) than in shoots (221.71 mg kg⁻¹). S. tabernaemontani accumulates more Ni than Cu and Cr which it mostly retains in the roots (1015.88 mg kg⁻¹). B. rubiginosa accumulates more Cu than Ni with a concentration up to 927.36 mg kg⁻¹ in shoots and 401.70 mg kg⁻¹ in roots (BAF 35.53; TF 0.90). Among these plants' species, C. papyrus had the ability for multi-metal accumulation, retaining Cr, Cu, and Ni.