Potential of Sorghum bicolor and Arundo donax for lead, nickel and cadmium phytoextraction

Phytoextraction of heavy metals with non-food cultivations, such as biomass and energy crops, is considered a cost effective strategy for soil remediation. 1- and 2-year pot experiments were respectively carried out with sorghum (Sorghum bicolor L.) and giant reed (Arundo donax L.) in order to assess plant accumulation and removal of Pb, Ni and Cd. 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. The plants were grown in a sandy-loam soil at two concentration levels, L1 (555, 156 and 50 mg kg-1) and L2 (984, 197 and 99 mg kg-1) of Pb, Ni and Cd, respectively. Pots were placed in semi-natural conditions so water supply was both by natural precipitation and by using a sprinkler irrigation system. Nitrogen fertilization was provided at tillering for both crops. Sampling of sorghum was performed at five leaf and boot stages. Giant reed was harvested in fall, leaving roots in the pots for the 2nd-year growing season. At each sampling time different plant organs, i.e., leaves, stems, roots, and rhizome, when available, were separated, oven dried, weighted, milled and analysed for metals concentration. Changes in soil bioavailable and pseudo-total contents of Pb, Ni and Cd due to plant growth and uptake were determined by DTPA and aqua regia extraction procedures. The phytoextraction potential of sorghum and giant reed was evaluated by the offtake of metals of the harvestable parts, the bioaccumulation factor (shoot/soil concentration ratio) and the translocation factor (shoot/root concentration ratio)