Phytoextraction of heavy metal from tailing waste using Napier grass

• Napier can grow under mild toxic stress and take up contaminants during growth.
• Fibrous roots absorb and transport both nutrients and contaminants.
• Contaminants are transported from roots to shoots and stored in all plant.
• Stem stores most of contaminants and fibrous roots with the highest metal contents.

Hybrid giant Napier (HGN) grass was used to examine its phytoextraction potential for removing heavy metal(oid)s from contaminated tailings. Following a two-year cultivation of HGN, the amount of heavy metal(oid)s Zn, Mn, Cu, Pb, Cd, Cr and As removed ranged from 12% to 26% in the tailings and 16% to 74% in the control soil. The root distribution profile and chemical analysis of the plant in the growth media suggest that heavy metal was phytoextracted by fibrous roots, then transported from roots to shoots and stored to all parts of the plant including fibrous roots, tap roots, stem and leaves. Most of the heavy metal was stored in the plant's stem due to its high biomass, although the highest concentration of the metal occurred in the fibrous roots. The plants grown in the contaminated tailings were generally stunted compared to those in the control soil, due to heavy metal phytotoxicity. Less biomass was produced in the HGN planted in the contaminated tailings, which was less than 1/2 amount of biomass yielded in the control soil. The biomass has the potential to be used in energy production. The phytoextraction of heavy metal by the HGN in this study was attributed to the well-developed root systems in the plant which is capable of phytoaccumulating nutrients and heavy metals. Results suggest that HGN has good phytoextraction potential in removing heavy metal(oid)s from contaminated tailing wastes and producing biomass.