Green technology-An approach towards a toxic free environment
Introduction to phytoremediation:
Phytoremediation is used to improve the functionality of soil and to recover contaminated soil using plants and microbes associated with it. The term is amalgam of Greek word phyto meaning plant and a Latin word remedium meaning restoring balance. It is also termed as botanical bioremediation or green remediation. S.D Cunningham and R.R.Brooks in the beginning of 1990s have found the method to treat contaminated soils using plants as the potential use of plants to metabolize toxic organic products in soils appears promising. Various natural processes and anthropogenic meaning industrial activities have lead to rapid increase in accumulation of heavy metals in the soil. So heavy metals being non biodegradable persist in the environment and have the potential to enter the food chain through crop plants, and eventually end up getting accumulated in the human body through biomagnifications. Owing to their toxic nature, heavy metal contamination has posed a serious threat to the human health and the ecosystem. Therefore, remediation of land contamination is of paramount importance. Phytoremediation can be a successful mitigation measure to revegetate heavy metal polluted soil in a cost effective way as it is eco friendly.
Requirement for phytoremediation:
It has three effective requirements which are as follows: Firstly make an assessment to the site correctly there after selecting plant species and then implementing a suitable plant or crop management regime. To enhance plant growth and contaminant uptake some soil amendments may be added. It is proposed as a cost effective plant based approach for environmental remediation which takes the advantage of the plant ability to concentrate elements and compounds from environment and to detoxify various compounds. The ability of plants called hyperaccumulators to bioaccumulate chemicals results in concentrating effect with different remediation effect. Organic pollutants can be easily degraded and are generally major target for phytoremediation as toxic heavy metals cannot be degraded.
It is a technology that is applicable to a broad range of contamination which include metal and radionuclide, organic compounds such as chlorinated solvents, polycyclic aromatic hydrocarbons, pesticides , explosives and surfactants etc.
What are the forms of phytoremediations:
The phytoremediation comes in several forms or techniques which are:
Phytoextraction: Is removal of metals or organics from soil by accumulating them in biomass form in plants.
Phytodegradation or Phytotransformation: Where plant are used to uptake, store and degrade organic pollutants. Rhizofiltration will remove pollutants from aqueous sources by plant roots.
Phytostabilization: It will reduce the bioavailability of pollutants either by binding or immobilizing them to soil matrix.
Phytovolatilization: Makes use of plants to take pollutants from the growth matrix to transform them and release it into the atmosphere.
Phytodesalination: Removes the excess salts from saline soils by halophytes.
Out of which the environmental and commercial interest now focuses on phytoextraction and phytodegradation which uses selected plant species grown on contaminated soils that have accumulated in their tissues. These can be harvested to remove the plants along with the pollutants that have accumulated in their tissues and based on the type of contamination; the plants can either be disposed of or used in alternative processes like burning for energy production. In essence, phytoextraction removes pollutants from contaminated soils, concentrates them in biomass and further concentrates the pollutants by combustion.
Why plants are referred to phytoremediator?
Plants are used as phytoremediator where it uptake the contaminant from soil particles or soil liquid into their roots and bind to the contaminant present into their root tissues physically or chemically and transport the contaminant from roots into growing shoots and prevent or inhibit the contaminant from leaching out of the soil and then accumulate, degrade or volatilize the contaminants and plant can be easily harvested as it can grow quickly in different environmental conditions.
Advantages and Limitations of phytoremediation:
Also phytoremediation provides several striking advantages when compared with conventional methods of soil remediation. It is carbon dioxide neutral technology if the harvested biomass is burned with no additional carbon dioxide being released in the atmosphere beyond what was originally assimilated by plants during the growth. Phytoremediation is also cost effective as the marginal cost only applies for harvesting and field management, such as weed control. Also it is a potentially profitable technology as the resulting biomass can be used for heat and energy production in specialized facilities and after applications the land is left for cultivation. It has certain limitation as phytoremediation is limited to the surface area and to depth occupied by the roots. It requires long term commitment due to slow growth and low biomass. It is also not possible to completely prevent the leaching of contaminants into the ground water with plant based systems of remediation. The general condition of the soil and the toxicity present in the contaminated land represents the survival of the plants. Bio- accumulation of contaminants, especially metals, into the plants which then pass into to the food chain from primary level consumers upwards and/ or requires the safe disposal of the affected plant material.
Results and discussion:
So as plants can take up heavy metals by their roots or via stems or leaves and get accumulate in their organs. Based on the plant species, chemical and bioavailability , redox , pH , cation exchange capacity , dissolved oxygen , temperature and secretion of the roots the accumulation and distribution of the heavy metals in the plant takes place. To treat the decontamination of heavy metals in polluted water, plants are employed and have demonstrated high performances in treating mineral tailing water and industrial effluents.
Phytoremediation, which makes use of vegetation to remove, detoxify or stabilize persistent pollutants, is a green and environmentally-friendly tool for cleaning polluted soil and water. The advantage of high biomass productive and easy disposal makes plants most useful to remediate heavy metals on site. So based on knowledge of heavy metal accumlation in plants it is possible to select those species of crops and pasturage herbs , which accumulate fewer heavy metals for food cultivation and fodder for animals; and to select those hyperaccumulation species for extracting heavy metals from soil and water.
Dept. of Biochemistry and Biotechnology
St. Xavier’s College, Ahmedabad
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Berti, W. R., and Cunningham, S. D. (2000). “Phytostabilization of metals,” in Phytoremediation of Toxic Metals: Using Plants to Clean-up the Environment, eds I. Raskin and B. D. Ensley (New York, NY: John Wiley & Sons, Inc.), 71–88.
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