آليات الفيتومديشن

Phytomediation Mechanisms

• Researchers have identified seven mechanisms by which plants can affect contaminant levels in soil, sediments, and water.
• Each mechanism is explained in detail.

Phytoextraction/Phytoaccumulation

• Phytoextraction is the ability of plants to remove metals and other compounds from the subsurface and transfer them to leaves or other plant tissues.
• This method uses non-food plants.
• Phytoaccumulation also involves absorbing metals with the roots and transporting them to above-ground plant parts.
• Some plants have genetic and physiological potential for high metal accumulation, translocation, and tolerance.
• This is important for phytoextraction technology.
• Discoveries in wild plants with high metal accumulation capacity demonstrate their potential to remove heavy metals (HMs) from soils.
• Phytoextraction is the process of using plants to remove contaminants from the environment and concentrate them in above-ground plant tissues.
• "Metal hyperaccumulators" can accumulate toxic metals 10-500 times higher than cultivated crops.
• This process exists in two forms: natural and continuous.

Phytostabilization

• Phytostabilization removes soil metals via root absorption, adsorption, or precipitation within the root zone.
• This process renders contaminated metals around the roots insoluble and immobilized.
• The process might involve sorption, precipitation, complexation, or metal valence reduction.
• It is highly effective for rapid immobilization required for groundwater and surface water preservation.
• The goal of phytostabilization isn't to remove pollutants entirely, but to stabilize them and prevent groundwater or air contamination.
• Plants used in phytostabilization are poor translocators of metals from roots to shoots, minimizing exposure to toxic elements (ex. grasses).
• This technique is crucial for preserving groundwater and surface water and immobilizing contaminants within the soil.

Phytodegradation/Phytotransformation

• Phytodegradation, often called phytotransformation, involves breaking down absorbed contaminants into simpler or less-toxic molecules within plant vascular systems.
• Plants produce enzymes (e.g., dehalogenases, oxygenases, reductases) for this process only after the contaminants are taken up by the plant.
• Phytodegradation is effective for certain organic contaminants (e.g., chlorinated solvents, herbicides).
• Plants typically transform organic compounds and then conjugate or bind the products to cell walls or store them in vacuoles.
• Catabolic microorganisms transform organic compounds into carbon dioxide and water during metabolism.

Phytovolatilization/Biovolatilization

• Phytovolatilization involves the accumulation of toxic compounds from the soil, transformation into volatile forms, and release into the atmosphere by transpiration.
• This process may occur with soil, sediment, and water contaminants like volatile organic compounds, or inorganic chemicals with volatile forms (selenium, mercury, and arsenic).
• The contaminants move from the roots to the leaves and then volatilize into the atmosphere at relatively low concentrations.
• Diffusion of contaminants can occur through the stem or other parts of the plant and then reach the leaves.
• This technique removes contaminants from soil and groundwater but does not eliminate them from the environment.
• It is successfully used for remediating soils contaminated with arsenic, mercury, and selenium.
• This technique can be limited by potential migration to other areas post-removal.

Rhizofiltration

• Rhizofiltration is a phytoremediation technique using terrestrial or aquatic plants to soak up, concentrate, and precipitate metals from contaminated sources through their root systems.
• This process is effective in cleaning up contaminated water (damp soil, groundwater) of toxic metals derived from aquatic environments.
• Highly effective because certain plants can absorb large amounts of metals from soil and accumulated water.
• An effective process needs extensive root systems, root biomass, and plant tolerance to higher amounts of toxic metals.
• Rhizofiltration involves removing contaminants through the harvesting process, concentrating them in the root system.
• The technique is commonly used in groundwater, surface water, or wastewater.

Rhizodegradation

• Rhizodegradation, also known as phytostimulation, is the breakdown of soil contaminants by microbial activity in the rhizosphere (root zone).
• This process may involve microbial activity in the rhizosphere to decompose contaminants, including organic compounds (fuels, solvents).
• Rhizodegradation is supported by exudates containing organic compounds that create beneficial conditions for microbial growth.
• Microorganisms are prevalent in the rhizosphere due to exudates from plants, like sugars, amino acids, enzymes, and other components.
• Roots provide a surface area for microbes to expand and a pathway for oxygen transport.
• Rhizodegradation is primarily effective in contaminated soil.

Phytorestoration

• Phytorestoration is a complete remediation (bringing contaminated soil to a non-contaminated standard) of metal-contaminated soil.
• This process typically uses native plants in particular areas to restore the land to its natural state.
• It aims to clean the soil to meet legal levels of compliance and allow soil usage again; however, fully restoring the environmentally contaminated land is considerably complex.

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