Cadmium (Cd) and Zinc (Zn) tolerance and phytoextraction efficiency of arum (Colocasia esculenta L.) were investigated in hydroponics. Plants were grown for 60 d in nutrient solution after addition of Cd and Zn at the levels of 0, 15, 30 and 60 mol L 1 and 0, 100, 500 and 1,000 mol L 1 , respectively. Growth of arum was unaffected by low levels of metal concentration (15 mol L 1 Cd and 100 mol L 1 Zn) whereas it decreased gradually with the increase of metal concentration in solution.

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... ion of metals in parts of arum increased significantly (P 0.05) with the levels of metals in growth media. In arum shoots, Cd and Zn concentrations were 713 and 10,120 mg kg 1 respectively, at their low levels in solution. These concentrations (15 mol L 1 Cd and 100 mol L 1 Zn) did not cause any growth retardation indicating that arum is a metal hyperaccumulator. Transfer factor (TF) greater than one confirmed the hyperaccumulating behavior of arum for Cd and Zn in solution. Cadmium and Zn uptake in arum shoots without growth retardation and TF of these metals in arum indicates that this plant is a suitable candidate for the phytoremediation of water contaminated with Cd and Zn.