Uptake of heavy metals by Typha capensis from wetland sites polluted by effluent from mineral processing plants: implications of metal-metal interactions.

The aim of the present work was to demonstrate the existence of metal-metal interactions in plants and their implications for the absorption of toxic elements like Cr. Typha capensis, a good accumulator of heavy metals, was chosen for the study. Levels of Fe, Cr, Ni, Cd, Pb, Cu and Zn were determined in the soil and roots, rhizomes, stems and leaves of T. capensis from three Sites A, B and C polluted by effluent from a chrome ore processing plant, a gold ore processing plant, and a nickel ore processing plant, respectively. The levels of Cr were extremely high at Site A at 5415 and 786-16,047 μg g-1 dry weight in the soil and the plant, respectively, while the levels of Ni were high at Site C at 176 and 24-891 μg g-1 in the soil and the plant, respectively. The levels of Fe were high at all three sites at 2502-7500 and 906-13,833 μg g-1 in the soil and plant, respectively. For the rest of the metals, levels were modest at 8.5-148 and 2-264 μg g-1 in the soil and plant, respectively. Pearson's correlation analysis confirmed mutual synergistic metal-metal interactions in the uptake of Zn, Cu, Co, Ni, Fe, and Cr, which are attributed to the similarity in the radii and coordination geometry of the cations of these elements. The implications of such metal-metal interactions (or effects of one metal on the behaviour of another) on the uptake of Cr, a toxic element, and possible Cr detoxification mechanism within the plant, are discussed.