Potential use of Sorghum bicolor and Carthamus tinctorius in phytoremediation of nickel, lead and zinc

Metals are very common contaminants in the soil. High-yielding biomass crops offer good potential for the phytoremediation of soils contaminated with heavy metals. Biomass fuel crops grown on contaminated land have several advantages as site remediation combined with bioenergy production. In this context, two energy crops, Sorghum bicolor and Carthamus tinctorius, were grown hydroponically to assess their potential use in phytoremediation of nickel (Ni), lead (Pb) and zinc (Zn) and biomass production. The experiment was carried out in a growth chamber using half-strength Hoagland's solution spiked separately with five concentrations for Ni, Pb and Zn (between 5 and 100 mg L-1). Shoot and root biomass were determined and analyzed for their metals contents. Results showed that the tested plants were able to uptake Ni, Pb and Zn. Furthermore, roots accumulated more metals than shoots. Ni seems to be more toxic than Zn and Pb. In fact, both species were unable to grow at Ni concentration above 10 mg L-1. Metal toxicity ranked as follows: Ni > Zn > Pb. High toxicity symptoms and biomass reduction were observed at concentrations of Pb and Zn above 25 mg L-1 for both species. S. bicolor was more efficient than C. tinctorius in metal uptake due to the high biomass production and the relatively high shoot concentration of metal. S. bicolor could be successfully used in phytoremediation applications in marginal soils with moderately heavy metal contamination. However, results obtained through the hydroponic experiment need to be confirmed by field experiments.