Phytoextraction of lead, nickel and cadmium by biomass plants

Phytoextraction of heavy metals with no food cultivations, such as biomass and energy crops, is considered a cost effective strategy for soil remediation. Sorghum and giant reed tolerance to high amounts of Pb, Ni and Cd and their ability to accumulate the metals were evaluated in semi-natural conditions. Among the many metals which are of global concern with regard to soil pollution, lead, nickel and cadmium have been chosen for this study because of their different pattern of solubility in soils and translocation to the above-ground parts. Specific aims of this work were to observe the concentration of metals in plant tissues during the life cycle and to determine the amount of metals removed by the crops. In addition, bioavailability and translocation within the plants of Pb, Ni and Cd were quantified by the phytoextraction coefficients. Sorghum bicolor and Arundo donax were grown in a sandy-loam soil at two levels of contamination, L1 (500, 50, 50 μg g-1) and L2 (1000, 100, 100 μg g-1) of Pb, Ni and Cd, respectively, and one control. Pots were placed in a natural environment so water supply was both by natural precipitation and by using a sprinkler irrigation system. Nitrogen fertilization was provided at the beginning of stem elongation for both crops. Sampling of sorghum started 30 days after sowing (April 2007) and was repeated at the end of stem elongation and at the emission of inflorescence. Giant reed was harvested in fall, leaving roots in the pots for a 2nd-year experiment. At each sampling time different plant organs, i.e., roots, stems, leaves and seeds, when available, were separated, oven dried, weighted, milled and analysed for total metals concentration. Compared with the controls, the impact of heavy metals on stems height and diameter and the number of nodes, recorded every 15 days during the growing period, was negligible in both crops. Results on heavy metals accumulation in plant tissues are promising for the cultivation of these biomass crops for phytoremediation purposes.