Phytoextraction, one type of phytoremediation processes, has been widely used in the removal of heavy metals from polluted soil. This paper reviewed literature on metal uptake by plants and characterized the metal uptake by types of metals (Zn, Cu, Pb, Cd, and As), plant species, initial metal concentrations in soil and the distribution of metals in different parts of plants. The potential of metal accumulation and transport by plants was closely related to plants species, types of metals, and initial metal concentrations in soil. The plants belonging to Brassicaceae, Solanaceae, Poaceae, and Convolvulaceae families have shown the high potential capacity of Cd accumulation. The Gentianaceae, Euphorbiaceae, and Polygonaceae families have exhibited relatively high Pb uptake potential while the Pteridaceae and Cyperaceae families have shown relatively high Zn uptake potential. The Pteridaceae family could uptake a remarkably high amount of As compared with other plant families. The potential metal accumulation per plant biomass has increased with increasing initial metal concentration in soil up to a certain level and then decreased for Cd and Zn. For As, only Pteris vittata had a linear relationship between initial concentration in soil and potential of metal uptake. However, a meaningful relationship for Pb was not found in this study. Generally, the plants having high metal uptake potential for Cd or Pb mainly accumulated the metal in their roots. However, the Euphorbiaceae family has accumulated more than 80% of Pb in shoot. Zn has evenly accumulated in roots and stems except for the plants belonging to the Polygonaceae and Rosaceae families which accumulated Zn in their leaves. The Pteridaceae family has accumulated a higher amount of As in leaves than roots. The types of metals, plant species, and initial metal concentration in soil influence the metal uptake by plants. It is important to select site-specific plant species for effective removal of metals in soil. Therefore, this study may provide useful and beneficial information on metal accumulation by plants for the in situ phytoremediation.

Keywords: Heavy metals;Phytoremediation;Accumulator;Plant species;