THESE NATURAL AND SUSTAINABLE TECHNIQUES ARE SOME OF THE MOST PROMISING FOR THE REHABILITATION OF THE SOILS. HOWEVER, ITS DEVELOPMENT IS LIMITED BY THE LACK OF VALORIZATION OF ITS HARVEST.
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PLANT HOLDS IT IN PLACE.
The plant holds the contaminant in place so that it does not move off site. This occurs because vegetation is physically covering the contamination and the plant may also release phytochemicals into soil that bind contaminants and make them less bioavailable. In addition, phytoaccumulation refers to the collection of airborne polluants onto leaf surfaces, physically filtering contaminants out of the air and holding them in place.
PLANT AND MICROBES IN THE SOIL DESTROY IT.
This mechanism is the process in which a contaminant is taken up by the plant or microbes and broken down into smaller parts. In most cases the smaller parts, called metabolites, are non-toxic.
The plant often uses the byproduct metabolites in its growth process, so little contamination remains. The degradation occurs during photosynthesis or by internal enzymes and/or microorganisms living within the plant.
PLANT USES IT IN GROWTH, INCORPORATES IT INTO BIOMASS.
For plants to grow, they need nutrients as building blocks for photosynthesis and biomass creation. Phytometabolism is the process in which the nutrients needed by plants (inorganic elements such as N, P, K) are processed and turned into plant parts. In addition, once organic contaminants have been broken down by a plant (phytodegradation), the metabolites tat are left over from the process are often phytometabolized and incorporated into the plant's biomass.
PLANT EXTRACTS IT, AND FOR INORGANICS IT IS STORED AND MUST BE HARVESTED FOR REMOVAL.
Phytoextraction is the ability of the plant to take up a pollutant from soils and water and move it into plant parts.
When phytoexctraction is coupled with phytodegradation for organics, the contaminant essentially disappears from site.
However, since inorganics are elements on the periodic table, they cannot be degraded and broken down into smaller parts. Instead, the plant stores away the exctracted inorganic pollutant in the shoots and leaves. For the pollutant to be removed from the site, the plant must be harvested before the leaves drop or the plant dies back. The harvested plant material can be burned, followed by disposal in valuable metals (called phytomining).
PLANT RELEASES IT AS GAS.
Contaminants can exist in several forms, for example as a solid, liquid and a gas. In this mechanism, the plant takes up the pollutant in either form and transpires it to the atmosphere as a gas, thus removing it from the site. The gas is usually released slowly enough that the surrounding air quality is not significantly impacted. The net benefit of removing the contaminant from the ground is typically better than any effect of releasing the pollutant into the atmosphere. In some cases, a breakdown product derived from the previous mechanisms of rhizodegradation or phytodegradation may be volatilized.