Phytoextraction (or phytoaccumulation) uses plants to remove contaminants from soils, sediments or water into harvestable plant biomass. Phytoextraction is growing rapidly in popularity world-wide. Generally this process has been more effective for extracting heavy metals than organics. It is clean, efficient, inexpensive and less environmentally desruptive than processes that require excavation of soil. At the time of disposal contaminants are typically concentrated in a much smaller volume of plant matter than an inital contaminated soil or sediment.
After the plant absorbs contaminants through the root system it will either store them in the root biomass or transport them up into the stems and leaves. A living plant may continue to absorb contaminants until it is harvested. After harvest a lower level of the contaminant will remain in the soil, so the growth/harvest cycle must be repeated through several crops to achieve a significant cleanup. After the process, the soil usually is fertile and can support other vegetation.
There are two versions of phytoextraction:
* natural hyper-accumulation, where plants naturally take up the contaminants in soil unassisted, and
* induced or assisted hyper-accumulation, in which a conditioning fluid containing a chelator or another agent is added to soil to increase metal solubility or mobilization so that the plants can absorb them much easily.
Examples of Phytoextraction from Soils:
* Lead, using Indian Mustard, Ragweed or Hemp Dogbane.
* Arsenic, using the Sunflower (Helianthus annuus), or the bracken fern, a hyperaccumulator. Bracken can store arsenic in its leaves, as much as 200 times that present in the soil.
* Cadmium and zinc, using alpine pennycress (Brassicaceae), a hyperaccumulator of these metals at levels that would be toxic to many plants.
* Uranium, using Sunflowers, as used after the Chernobyl accident.
Cite: Wikipedia
source : hydroponicarticle
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