Phytoremediation
[1] It is defined as "the use of green plants and the associated microorganisms, along with proper soil amendments and agronomic techniques to either contain, remove or render toxic environmental contaminants harmless".
Although attractive for its cost, phytoremediation has not been demonstrated to redress any significant environmental challenge to the extent that contaminated space has been reclaimed.
This technology has been increasingly investigated and employed at sites with soils contaminated heavy metals like with cadmium, lead, aluminum, arsenic and antimony.
[citation needed] Contaminants such as metals, pesticides, solvents, explosives,[8] and crude oil and its derivatives, have been mitigated in phytoremediation projects worldwide.
The roots take up substances from the soil or water and concentrate them above ground in the plant biomass[10] Organisms that can uptake high amounts of contaminants are called hyperaccumulators.
[13] Phytoextraction can also be performed by plants (e.g. Populus and Salix) that take up lower levels of pollutants, but due to their high growth rate and biomass production, may remove a considerable amount of contaminants from the soil.
After harvest, a lower level of the contaminant will remain in the soil, so the growth/harvest cycle must usually be repeated through several crops to achieve a significant cleanup.
Induced or assisted phytoextraction is a process where 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 more easily.
[citation needed] Unlike phytoextraction, phytostabilization focuses mainly on sequestering pollutants in soil near the roots but not in plant tissues.
The plants can also excrete a substance that produces a chemical reaction, converting the heavy metal pollutant into a less toxic form.
[28][29] Vidal et al. 2000 find the root mats of meadow grasses are effective at demobilising radiosource materials especially with certain combinations of other agricultural practices.
[citation needed] Phase I and II reactions serve to increase the polarity and reduce the toxicity of the compounds, although many exceptions to the rule are seen.
[citation needed] In the final stage of phytotransformation (Phase III metabolism), a sequestration of the xenobiotic occurs within the plant.
[30] Plants release carbohydrates and acids that stimulate microorganism activity which results in the biodegradation of the organic contaminants.
[9] Poplar trees are one of the most successful plants for removing VOCs through this process due to its high transpiration rate.
[15] Rhizofiltration is a process that filters water through a mass of roots to remove toxic substances or excess nutrients.
Genes for phytoremediation may originate from a micro-organism or may be transferred from one plant to another variety better adapted to the environmental conditions at the cleanup site.
[42] This capacity for accumulation is due to hypertolerance, or phytotolerance: the result of adaptative evolution from the plants to hostile environments through many generations.
[48] To ease field implementation of phytoscreening, standard methods have been developed to extract a section of the tree trunk for later laboratory analysis, often by using an increment borer.
