Green Clean Technology: A novel tool for remediation of hazardous toxicants
Authors: Vipin Kumar Gupta and Preeti Gupta
This article summarizes the use of various live green plants present in our diverse ecosystem to destroy or reduce amount of toxicants in environment. The plants have natural, inherent capability to attenuate or reduce the toxicity, volume, mass, concentration of contaminants in nature without human intervention. Green clean or phyto- technology is an approach of decontaminating soil, water and waste. It encompasses a group of methods that use plants for remediating environmental contaminants. It is a better procedure than conventional methods of remediation e.g. incineration, chemical decomposition etc., as basically, it is “phyto” mediated decomposition of many toxicants like pesticides, explosives, heavy metal and oil etc. It is a superior technique over using chemicals, as plants are easy to grow and handle and it is solely a green eco-friendly technology of remediation. The inherent biological, chemical or physical activities and processes are the basic mechanism that results to phyto-technology. It involves growing of green flora in a toxic and contaminated matrix, for a defined period of time for removal or containment or degradation of the xenobiotic compounds. The plants can be subsequently harvested, processed and disposed.
How plants use the toxicants:
Root system of the plant is the principle component in which mechanisms for removal of contaminant and toxicants are found. It offers an enormous surface area to soak, accumulates the water and nutrients along with other non-essential toxicants. Root of plants also releases some compounds in the root zone that influence the action of microflora and fauna, distribution of soil particles around the root and further affects availability of the contaminants. The exudates of root changed the soil quality, chemical composition and microbial activity around it and increase or decrease the availability of the contaminants or toxicants.
Different categories of green clean technology:
These are divided into various categories depending on the processes, type of contaminant etc., first is Phyto-transformation; uptake, store and break down of the toxicants, Phyto-extraction; absorb, translocate and store toxic contaminants in its body parts i.e. phyto-accumulation, Phyto-stabilization; reducing the movement or transfer, so reduces their bioavailability, Phyto-volatilization; uptake, transform and release the toxicant into the air, possibly after degradation, Rhizofiltration; uptake, store contaminants from an aqueous growth matrix and Phyto-stimulation; enhancement of microbial activity in nearby area and break down of pollutant through symbiotic or other associations.
Remediation of hazardous toxicants with green plants:
Phyto-transformation, phyto-volatilization and phyto-stimulation techniques are used to treat hydrocarbon or organic contaminants. Phyto-transformation process break down trichloroethylene (TCE), pesticides, herbicides, solvents, industrial chemicals and war material wastes etc. into simpler molecules, which further utilized for plant tissues growth. Plant enzymes play a major role in degradation processes. Certain plants, such as cannas, render this detoxification by utilizing their metabolic processes (Kvesitadze et al., 2006). The term "Green Liver" is used to describe phyto-transformation (Sanderman, 1994) and it is also called as phyto-degradation approach of green clean technology. Phyto-volatilization process uptake, transform and release the toxicant into the air, as such or after modification. The compound trichloroethylene (TCE) and some other contaminants have been shown to transpire by poplar trees. In phyto-stimulation technique, some substances are released by the plant roots like sugars, acids, and alcohols, enhance the activity of soil microflora which biodegrade the hazardous substance into harm less compound. Aquatic plants hornwort stimulates the microbial degradation of atrazine (Rupassara et al., 2002). This process is also called as rhizo-degradation or plant aided biodegradation.
Phyto-accumulation, phyto-stabilization and rhizo-filtration approaches are used mostly to clean heavy metal contaminants than for organics. Phyto-accumulation or phyto-extraction technique treats cadmium, copper and zinc compounds using willow plant (Greger and Landberg, 1999), and lead by growing Indian mustard, poplar and hemp plants. The plant uptake metals from soil through its roots into body parts. After particular grown period, they are harvested and either incinerated or composted to recycle heavy metals, this process also called as phyto-mining. Rhizo-filtration is similar to phyto- accumulation, but the plants are used to treat contaminated water rather than soil matrix. In Chernobyl disaster, Use of sunflowers was seen to clean ponds water from Caesium- 137 and strontium- 90 (Adler, 1996). In phyto-stabilization, some plant species reduces the mobility of the contaminant and limits leaching to the groundwater or air and consequently decrease entry of it into the food chain.
Biological hydraulic control is another way, often used to slow the movement of contaminated groundwater. Trees like poplar pumps the water upward through its roots to keep it from moving, and out through of the plant decreases the movement of soluble contaminants downwards, deeper into the site toward clean areas, and into the groundwater (Evans and Furlong, 2010).
This is very effective, low cost, solar energy driven, eco-friendly approach. This technology offers the possibility to destroy hazardous toxic contaminants or render harmless using natural biological, chemical and physical processes. Green plants will acts as an excellent bioremediation tool. It is not only effective for the degradation of pollutants but it can also be used to clean unwanted substances from air, soil, water and raw materials from waste. Further the natural cleaning capacity of green plants can be increased by using breeding and genetic engineering tool.
Adler, T. (1996). "Botanical cleanup crews: using plants to tackle polluted water and soil" . Science News.
Evans, Gareth M.; Furlong, Judith C. (2010). Phyto-technology and Photosynthesis . John Wiley & Sons, Ltd. pp. 145.
Greger, M. & Landberg, T. (1999), "Using of Willow in Phyto-extraction", International Journal of Phytoremediation, 1 (2): 115–123.
Kvesitadze, G. et al. (2006), Biochemical Mechanisms of Detoxification in Higher Plants, Berlin, Heidelberg: Springer, ISBN 978-3-540-28996-8
Rupassara, S. I.; Larson, R. A.; Sims, G. K. & Marley, K. A. (2002), "Degradation of Atrazine by Hornwort in Aquatic Systems", Bioremediation Journal, 6 (3): 217–224.
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USEPA (2012), a citizen’s guide to phytoremediation, EPA 542-F-12-016.
About Author / Additional Info:
I am posted as Assistant Professor in the discipline Veterinary Public Health & Epidemiology
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