Soil lead (Pb) contamination is a recognized environmental and global health problem. Phytoextraction of Pb using switchgrass (Panicum virgatum L.), a second-generation biofuel crop, is typically enhanced by soil chelation. The effectiveness of four different chelating agents, phytic acid (inositol hexaphosphate), citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediaminetetraacetic acid) was examined in pot culture. Plants treated with EDTA (1 mM) showed significantly higher shoot Pb concentrations compared to control plants and plants treated with other chelates. Lead-solubility following phytoextraction was examined by soil washing using 0.01 and 0.05 M acetic acid as an extractant solution revealed no significant differences in Pb concentrations in soil among different chelate treatments and control. Furthermore, the effects of different concentrations (1, 2, 5 and 10 mM) of NTA on Pb phytoextraction of switchgrass were examined. Plants receiving 5 mM and 10 mM NTA had significantly higher foliage concentrations of Pb compared to plants treated with lower levels (1 and 2 mM) of NTA. Moreover, the effect of NTA application alone was significantly improved by a combined application of Triton X-100, an alkyl polyglucoside (APG); the Pb concentration in the foliage of switchgrass was more than doubled when treated with NTA combined with APG. The use of NTA combined with APG has great potential in improving phytoextraction efficiencies of switchgrass on Pb-contaminated soils.

The accumulation of Pb deposits in soil is a growing global concern. Soil remediation options include phytoextraction that involves the use of plants and associated soil microorganism. Switchgrass (Panicum virgatum L.), a second-generation bioenergy crop was used in this study due to its ability to produce high biomass and grow in metal polluted soils. Plants were grown in Pb-contaminated soil (5,802.5 mg kg−1) in an environmentally controlled greenhouse. Plants were treated with exogenous application of the plant growth regulator (PGR) benzylaminopurine (BAP) or complete foliar nutrient solution (Triple-12®) twice a week until harvested. Plants also received the soil fungicide propiconazole (Infuse™) that was followed by the soil chelate nitrilotriacetic acid (NTA). Two concentrations of NTA were compared (5 mM and 10 mM) and combined application of NTA (10 mM) + APG (alkyl polyglucoside). Soil fungicide (propiconazole) was used to arrest arbuscular mycorrhizal fungi (AMF) activities in the roots of switchgrass in order to enhance Pb-phytoextraction. Lead (Pb) was measured in dry plant materials using an ICP-OES. Phytoextraction by switchgrass was significantly improved by dual soil applications of 10 mM NTA, APG and foliar applications of BAP which resulted in the greatestaverage Pb concentration of 5,942 mg kg−1. The average dry mass of plants and the average value for total phytoextracted Pb (mg) per pot were significantly greatestfor plants treated with 10 mM NTA, APG and BAP. Also, plants treated with NTA and BAP showed average bioconcentration factor of 1.02. The results suggested that chemically enhanced phytoextraction significantly improved biomass production of switchgrass and at the same time increased phytoextracted Pb which is important for phytoremediation and bioenergy industry.