Phytostabilisation

The phytostabilisation is the recourse to vascular plants to reduce the mobility and diffusion of the pollutants contained in a ground in the environment: that it is in the form of Poussière S, of ions or particles washed by water, or transported by fauna (Bioturbation), these three means of transports of pollutants being generally the first causes of recontamination of the environment on and around the polluted sites. The phytostabilisation thus does not treat truly the Pollution; it is only fixed.

The “vegetable carpet”, as well as the Rosée which it maintains - under certain conditions - contribute to effectively locally fixing many pollutants.
Le fabrics racinaire limit the effect of the erosion wind and hydrous, as well as the horizontal and vertical circulation of certain toxic ions.

This technique is locally used for - temporarily - protecting from the grounds polluted by Métaux and Métalloïde S, Pesticide S, Solvant S, Explosif S, Pétrole gross and its derivatives, Radionucléide S or other contaminants.

Factors of effectiveness

the pollutants should not migrate easily in the grounds (it is the case of the Plomb in the grounds basic or rich in complexes argilohumic for example);
the pollutants should not be acessibles at the organizations Herbivore S, or with the pollinating insects via the Pollen for example, which implies:

- the choice of suitable plants which do not bioaccumulent not the pollutants in question,

- a management of the site aiming at eliminating from other likely plants of bioaccumuler the poisons which one seeks to stabilize.

a certain threshold of toxicity should not be exceeded for the plant: A ground too polluted keep silent the plants which push there or strongly inhibits their growth, obérant any phytostabilisation.
a hydraulic control , or phytohydroregulation usefully optimizes the stabilizing effect of the vegetable layer (généralemnet a herbaceous layer, sometimes accompanied by plantations of trees, spaced so that the light allows the growth of the vegetable carpet on the ground).
Via them evapotranspiration, certain plants can absorb the water of the Lithosphère without absorbing enough contaminants to die about it (and - in some cases - apparently without suffering from it). By slackening this water in the atmosphere, they contribute to maintain (by clear nights and without wind) the phenomenon of Rosée which fixes dust and of many pollutants, but also to limit the descent of the poisons of the ground towards the tablecloth by maintaining an increase deeper water by Capillarité. This " pumping hydraulique" (literal translation of English) is started when the roots reach subterranean water and take broad volumes of water there, by controlling some the hydraulic gradient and the side migrations of contaminants within the aquifer, but in moderate or circumpolar zone, this “biological pumping” will have a very seasonal effect. And in tropical zone, this type of protection is attenuated by the rains of monsoons and their floods.
the geological configuration plays a big role: if an argillaceous or permeable layer is subjacent, the use of plants with strong evapotranspiration will effectively reduce the side movement (horizontal) of the pollutants.
the acid grounds facilitating the circulation of the poisons, one uses sometimes basic Amendement S. Some organic compounds or mineral, natural or artificial can also fix chemically certain pollutants in the ground by limiting their dispersion in water surface or underground like their biodisponibility. Certain chelating which would effectively fix (with Ligants) of heavy metals or radionuclides can however also fix useful or vital ions for the plant, and cause phenomena of deficiency or of died of the plant.

Effect rhizospheric

The Rhizosphère (volume of ground subjected to the influence of the racinaire activity) varies according to the plants, the ground and the content of pollutants which generally differs according to the site and the depth on the same site. The rhizosphère has a protective effect on the ground, but it is also the habitat of many micro-organisms, and invertebrates such as the worms of ground or other invertebrates which can contaminate themselves in the ground and export (Bioturbation) the poisons that they accumulated in the trophic Réseau. This risk is to be examined on a case-by-case basis, according to the site and the pollutants considered. It can be limited by limiting the attractivity of the site for the predatory ones of these species.

Contribution to decontamination

The phytostabilisation does not treat pollution. It only aims at reducing, at least temporarily, the mobility of the contaminants.

The phytostabilisation can to some extent passively contribute to decontamination in the case of polluting Biodégradable S or “dégradables” in time. But one speaks about Phytoremédiation if it is the plant itself which contributes to degrade the pollutant to metabolize it or to store it (the Phytoextraction then allowing the export and the treatment of the plants which have bioaccumulé the Toxique.

Conclusion

Except in the case of polluting quickly dégradables, a ground phytostabilized is not to in no case a ground cleansed .
Néanmoins, after a provisional stage of stabilization, other plants can possibly also - in certain conditions - contribute to depollution, by techniques of Phytoremédiation.
Sur small surfaces, installation of a plastic cover, a sealing (standard Géomembrane) or the treatment ex-situ of the ground, or its setting in controlled discharge can be more effective and useful. On vast surfaces, or where financial means misses, the phytostabilisation , then the Phytoremédiation are often less expensive than the traditional processes of depollution.
Cette solution is not appropriate on the too polluted ground, too arid to let live the plants, and it is less effective in the zones subjected to strong rains and Inondation S.

Sources and References

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