Uptake of lead and zinc by wild plants growing on contaminated soils

In studies performed in the Aznalcóllar area (Southern Spain), several plant species have been identified as not only being able to grow on these polluted soils, but also to accumulate high amounts of the pollutants in their shoots. A pot experiment was conducted to investigate the phytoextraction efficiency of 11 plant species to extract and accumulate Pb and Zn gradually added to soil, and, therefore, to establish the suitability of these species for remediation of Pb and Zn polluted soils. The experiment was performed with the plants at a concentration of Pb of 500 mg Pb kg−1, and a concentration of Zn of 130 mg Zn kg−1, for 6 weeks of exposure. The mean shoot biomass production was not significantly different from the control for Pb and Zn treatments. It was found that the highest mean concentrations of Pb and Zn were accumulated in shoots of Amaranthus blitoides, Cynodon dactylon, Cichorium intybus and Sylibum marianum. For C. intybus, Pb concentrations in shoots were >1000 mg kg−1, indicating hyperaccumulation for this element. The traslocation of Pb from roots to shoots was minimum in Chenopodium album, indicating significant metal inmobilisation by the roots, and, therefore, this species could be useful in phytostabilization of soils. When the biomass values were taken into account, C. dactylon, Hirsfeldia incana, Malva nicaeensis and Silybum marianum were more effective in removing Pb and/or Zn from the contaminated soil.