http://lamar.colostate.edu/~samcox/Phytoremediation.html
Phytoremediation
Plants can extract Cd from the soil and transport it via the xylem into shoots and leaves where it can accumulate (Blaylock, et al. 1997) . It has been shown that pollutants can be removed from a contaminated site by harvesting the plant biomass containing the pollutant. This is referred to as phytoextraction (Chaney, 1983). Sometimes, plants will simply stabilize the contaminant in the soil through various mechanisms (phytostabilization), and this is also sometimes desirable (Kabata-Pendius and Pendius, 1992). Other aspects of phytoremediation focus on the ability of plants to directly or indirectly degrade pollutants (phytodegradation, phytostimulation, phytovolatilization) but since metals cannot be degraded the way organic molecules can, only phytoextraction and phytostabilization are applicable to Cd remediation.
Advantages of Phtyoremediation
Phytoremediation has received considerable attention because it offers a cheaper, easier and environmentally sound pollution-remediation option. Seeding a field of plants and harvesting them to extract the pollutant is much cheaper than removing huge amounts of contaminated soil. In some cases, the extracted biomass can be incinerated and the metals recovered and sold for profit (Salt, et al. 1998). In cases where it is not economically feasible to recycle the metals, it is still cheaper to dispose of a small amount of contaminated plant mass in a hazardous waste landfill rather than acres of topsoil. Phytroremediation is non-invasive and does not require heavy machinery to excavate soil. For this reason it is aesthetically more pleasing. Most importantly, it is a real solution to cleaning up a substrate. Excavating and transferring contaminated soil or water to a hazardous waste storage facility is simply moving the problem without cleaning anything, whereas phytoredmediation is real remediation of the substrate.
Limitations of Phytoremediation
Phytoremediation does have its limitations. It is a slower process than traditional means. Plants remove or degrade only small amounts of contaminants each growing season, so it can take several decades to adequately clean up a site. Additionally, there are limits to plant growth such as temperature, soil type and water availability that may make a site unsuitable for phytoremediation. Lastly, only lightly contaminated soils can be phytoremediated because most plants will not grow on heavily-contaminated sites.