Bio-remediation by natural zeolite on plants cultivated in a heavy metal-contaminated medium

Natural zeolitic tuff from the deposit of Nizny Hrabovec (Slovakia) is capable to protect plants against toxic effects of heavy metals. This protective effect was manifested by hydroponical growth of maize in Knop's nutrition medium contaminated by copper, mercury or cadmium chlorides. The use of 6.7 g zeolitic tuff per L of Knop's nutrition medium polluted with 30 mu mol of Cu, Cd or Hg resulted in almost 100% restoration of plant growth, as far as the plant size and dry matter (DM) are concerned. It was found that the heavy metals are absorbed and disposed mainly by maize roots. However, a considerable amount of cadmium has been distributed into the plant's shoots and leaves (140 mg Cd per kg DM of each). This feature of the maize could be utilized for phytoremediation of Cd-contaminated soils after the verification of this effect at long-term experiments.