In many respects, phytostabilisation has close similarities with both phytoextraction and rhizofiltration in that it too makes use of the uptake and accumulation by, adsorption onto, or precipitation around, the roots of plants. On first inspection, the difference between these approaches is difficult to see, since in effect, phy-tostabilisation does employ both extractive and filtrative techniques. However, what distinguishes this particular phytoremediation strategy is that, unlike the preceding regimes, harvesting the grown plants is not a feature of the process. In this sense, it does not remove the pollutants, but immobilises them, delib-erately concentrating and containing them within a living system, where they subsequently remain. The idea behind this is to accumulate soil or groundwater contaminants, locking them up within the plant biomass or within the rhizosphere, thus reducing their bio-availability and preventing their migration off site. Metals do not ultimately degrade, so it can be argued that holding them in place in this way is the best practicable environmental option for sites where the contamina-tion is low, or for large areas of pollution, for which large-scale remediation by other means would simply not be possible.
A second benefit of this method is that on sites where elevated concentrations of metals in the soil inhibits natural plant growth, the use of species which have a high tolerance to the contaminants present enables a cover of vegetation to be re-established. This can be of particular importance for exposed sites, min-imising the effects of wind erosion, wash off or soil leaching, which otherwise can significantly hasten the spread of pollutants around and beyond the affected land itself.
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