Phytoremediation and its effect on the mobility of metals in soil: a fractionation study

Studies were conducted to investigate the effect of phytoremediation on the immobilization of Cu, Pb, Mn and Zn in soils at different stages of plant growth. Two multi-metal soil concentrations were examined in pot experiments by growing five different plant species: Lolium perenne L. (perennial rye grass), Festuca rubra L. (creeping red fescue), Helianthus annuus L. (sunflower), Poa pratensis L. (Kentucky bluegrass) and Brassica napus L. (rape) for this study. Selective sequential extraction techniques differentiated the mobile and immobile metal fractions in the soil. Soil-metal conversions due to plant growth appear to follow the order: organic Cu to oxide Cu; oxide Pb to organic Pb; oxide Mn to exchangeable Mn; and exchangeable Zn to oxide Zn. As the growth of plants proceeded from 90 to 120 days after sowing, the relatively immobile fractions such as the oxide and organic fractions dominated in the soils growing Festuca, Lolium and Poa. The oxide fraction increased in soils growing Festuca, the organic fraction in soils growing Lolium and Poa, and the exchangeable fraction in soils growing Helianthus and Brassica. Based on the partitioning of metals in various soil fractions, Lolium, Poa and Festuca are identified as being suitable for the phytostabilization of metals (Cu, Pb, Mn and Zn) in moderately contaminated acid soil.