Metal removal from contaminated soil by hyper-accumulating plants : effects of repeated croppings
Phytoremediation, i.e., the use of plants to clean up contaminated soil, may serve as a feasible alternative if a high-biomass crop can be found that accumulates metals to a high.degree. Two plant species, corn (Zea mays) and Indian mustard (Brassica juncea), were grown in soil from a Superfund site contaminated with Pb and Cd (PbTota, = 65,200 mg/kg and CdTotI = 52 mglkg) over two croppings. Soil treatments consisted of composted sewage sludge (CSS), ethylenediaminetetraacetic acid (EDTA), and sodium citrate at two concentrations. In most cases, the EDTA and citrate treatments were superior in terms of extracting soil Pb into root tissue, and translocation of Pb into aboveground biomass. The CSS treatment typically resulted in the lowest Pb removal efficiencies. The high pH (7.4) and high exchange capacity of the CSS may have immobilized soil Pb. Soil Cd was generally more mobile than soil Pb. The EDTA2 treatment was most effective in removing soil Pb into roots, and translocation to shoots. Lead remaining in the soil after two croppings was mainly associated with the carbonate, organic, and residual fractions, which represent the less bioavailable form of this metal.