A Comparative Study on Metal Accumulation in E. indica,C. citratus and V. zizanioides Grown on Copper Mine Waste

The concentrations of different forms of heavy metals (Cu, Ni and Mn) were determined in a mine dump material rich in chalcopyrite and compared with those of the natural vegetation colonizing in the dump. Dump materials are slightly acidic in nature, having low organic carbon and cation exchange capacity. Copper was the most abundant heavy metal, in both total (acid extractable) and bioavailable forms, and the relative abundance of metals was Cu>Ni>Mn. The Cu concentration in the CaCl $_2$ extracts varied between 0.2 and 0.5 mgkg $^{-1}$ and concentrations of average Ni and Mn were below detection limit. The heavy metal contents in the spontaneously occurring vegetation in the dump ranged between 5.4 and 217 mg Cu kg $^{-1}$ , 10 and 81 mg Ni kg $^{-1}$ , 8.5 and 264 mg Mn kg $^{-1}$ when considering all the plant samples analysed. Naturally, colonized grass Elusine indica was found to accumulate highest concentrations of Cu, Ni and Mn followed by planted grass species Cymbpopogon citratus and Vetiveria zizanioides. However, V. zizanioides was found to uptake more Mn than C. citratus. The native plant species may contribute to decrease the heavy metal contents in the dump materials.