Extraction of Heavy Metals from Contaminated Soil by Two Amaranthus spp.

Two medicinal species of amaranth, Amaranthus viridis L. and A. caudatus L. were evaluated for their ability to uptake heavy metals from a contaminated soil. Twenty healthy plants of each species were transplanted to plastic pots containing the soil contaminated with elevated concentrations of Cd, Cr, Cu, Ni, Pb, and Zn. The plants were harvested after 45 days. Below- and above-ground tissues (roots and shoots) were analyzed separately to determine metals concentrations. Compared with the control group, the effects of S,S-ethylenediaminedisuccinic acid (S,S-EDDS) on the uptake of Cd, Cr, Cu, Ni, Pb, and Zn by two medicinal plants were also investigated. The initial contaminant concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in soil were 2.34, 30.53, 16.14, 20.99, 35.77, and 102.31mg/kg, respectively. The results of metal accumulation with EDDS application showed that EDDS was more efficient at solubilizing Cu and Zn than the control group. Translocation of metals from roots to shoots was most pronounced for Cu and Zn. The only metal that did not result in a transfer factor (TF) 0.3 for at least one of the two test species was Pb. The enrichment factor (E) was also low for Pb. The lower TF and E for Pb illustrated the tendency of that metal to remain bound to soil particles and not transfer into plant tissues. These data suggest that these two medicinal species of Amaranthus could be hyperaccumulators of several of these metals, and were particularly effective in accumulating Zn and Cu. Pb and Cd, while accumulated in measurable amounts, did not decrease significantly in the soil, suggesting these species may not be the best choice for plants to be used when bioremediating Pb- or Cd-contaminated areas.