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Phytoremediation: A Technology to Clean Environments

BY: Dr. Darshan Dharajiya | Category: Environmental-Biotechnology | Submitted: 2017-02-17 08:58:57
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Article Summary: "Now a day, spreading of contaminants into the natural environments is becoming a threat to humankind as well as other life forms. Phytoremediation, as a technique of bioremediation, is the implication of plants to remove contaminants from the polluted sites. The use of genetic engineering in might enhances the efficiency of the .."


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Phytoremediation: A Technology to Clean Environments
Author: Darshan Dharajiya

Pollution: It is the introduction of contaminants into the natural environment that cause adverse change, in the form of killing of life, toxicity of the environment, damage to ecosystems and aesthetics of our surrounding.

Types of Pollution: Air Pollution, Water Pollution, Noise Pollution, Littering (spilling of oils in oceans), Soil contamination, Radioactive contamination and Thermal pollution.

Bioremediation:
It is a treatment that uses naturally occurring organisms to break down hazardous substances into less toxic or non-toxic substances.

Strategies of Bioremediation: Biostimulation, Bioleaching, Phytoremediation, Bioreactor, Biocomposting, Bioaugmentation and Bioventing.

Phytoremediation:

Phytoremediation is the use of green plants in the removal of environmental pollutants from soil, water or air, which is recognized as a cost effective, sustainable, and environmentally friendly approach that has many advantages during the large-scale cleanup of contaminated sites. In a simple sense, it can be regarded as a solar driven pump for the extraction of heavy metals from the environment and degradation of organic pollutants. Due in large part to its aesthetic appeal, this technology has gained increasing attention over the past 10 years. Heavy metal pollutants, because of their non destroy ability and non biodegradability; continue to be a global concern. Heavy metal ions are highly carcinogenic, teratogenic and mutagenic even at trace concentration. Almost all heavy metals are toxic at a higher concentration and a few are severe poisonous for all forms of life, including microorganisms, higher plants, animals and man. Of greater concern is the exposure of these heavy metals for a longer duration of life resulting in carcinogenic effects. The volume of toxic waste produced as a result, is generally a fraction of that of many current, more invasive remediation technologies, and the associated costs are much less.

According to the nature of the contaminant to be dealt with phytoremediation includes different strategies as given below (Gill, 2014).

  1. Phytostablisation: The use of plants to reduce the mobility and bioavailability of pollutants in the environment, thus preventing their migration to groundwater or their entry into the food chain.
  2. Phytoextraction: The use of pollutant-accumulating plants to remove pollutants like metal organics from soil by concentrating them in harvestable plant parts.
  3. Rizofiltration: The use of plant roots to ab/adsorb pollutants, mainly metals, but also organic pollutants, from water and aqueous waste streams.
  4. Phytotransformation: The degradation of complex organic to simple molecules or the incorporation of these molecules into plants tissues.
  5. Phytodegradation: The enzymatic breakdown of organic pollutants such as trichloroethylene (TCE) and herbicides, both internally and externally and through secreted plant enzymes.
  6. Rizodegradation/Phytostimulation: The breakdown of contaminants in the rhizosphere (soil surrounding the roots of plants) through microbial activity that is enhanced by the presence of plant roots and is a much slower process than phytodegradation.
  7. Phytovolatilisation: The use of plants to volatilize pollutants or metabolites.
Properties of a good Phytoremediator:

  • Able to compete with other species
  • Large, deep root system
  • High biomass production and fast growth
  • Good accumulator/degrader of pollutant
  • Economic value
  • High tolerance to the pollutants
Remediation of different pollutants:

  1. Inorganics
  • Metals (e.g. Pb, Cd, Zn, Cr, Hg, Ni, Cu)
  • Metalloids (e.g. Se, As, Sb)
  • Nutrients (e.g. K, P, N, S)
  • Radionuclides (e.g. Cs, U, Sr)
  1. Organics
  • Polychlorinated biphenyls (PCBs)
  • Polynuclear Aromatic Hydrocarbons (PAHs)
  • Chlorinated solvent (e.g. TCE, PCE)
  • Explosives (e.g. TNT, DNT, RDX)
  • Pesticides (e.g. atrazine, bentazone)
  • Chlorinated and nitro-aromatic compounds
  • Petroleum hydrocarbons (e.g. BTEX)
Use of genetic engineering to enhance phytoremediation potential:

One promising approach for manipulation of plants character is through recombinant DNA technology. It has vastly proven its potential in phytoremediation process and many modifications are already made to change the property of plants. Recombinant DNA technologies combine the potentially more powerful ability to more selectively and proactively choose the traits to be introduced into the plant cell, via the introduction of DNA encoding enzymes or other proteins from other living organisms, or even completely synthetic genes designed to encode enhanced enzymes.

Different genes from different sources need to be transferred into plants to increase phytoremediation efficiency. These genes include, genes for biodegradative enzymes, genes for enhanced biomass production of plant, genes for metal transport protein, genes to enhance metal chelators and transporters, genes for metal sequestering protein, genes to increase root depth, genes to change oxidation status of metals, and genes to increase growth rate. Increased invasiveness and decreased genetic variability of native plants due to interbreeding are wo major concerns over field release of such. The knowledge of detoxification mechanisms used by plants to tackle with pollutants is a major procedural constriction for focused engineering approach. Such enzymological knowledge for xenobiotics provides informed decisions on which genes to engineer.

Advantages of phytoremediation:

  • Amendable to a variety of organic and inorganic compounds
  • Lower cost
  • Easy implementation, maintenance and monitoring
  • Recovery and re-use of valuable metals (by “phyto-mining”)
  • Least harmful method
  • Preserves the environment in a more natural state
  • Better public acceptance
  • Mineralization of the contaminant can occur with the help of rhizodegradation
Limitations of phytoremediation:

  • Limited to the surface area and depth occupied by the roots
  • Long-term process
  • It is not possible to completely prevent the leaching of contaminants into the groundwater
  • The survival of the plants is affected by the toxicity of the contaminated land
Effect of condition of the soil on plant growth

References

Bhuiyan, M.S.U., Min, S.R., Jeong, W.J., Sultana, S., Choi, K.S., Song, W.Y., Lee, Y., Lim, Y.P., and Liu, J.R. (2011). Overexpression of a yeast cadmium factor 1 (YCF1) enhances heavy metal tolerance and accumulation in Brassica juncea. Plant Cell, Tissue and Organ Culture, 105(1): 85-91.

Fu, X.Y., Zhao, W., Xiong, A.S., Tian, Y.S., Zhu, B., Peng, R.H., and Yao, Q.H. (2013). Phytoremediation of triphenylmethane dyes by overexpressing a Citrobacter sp. triphenylmethane reductase in transgenic Arabidopsis. Applied Microbiology and Biotechnology, 97(4): 1799-1806.

Gill, M. (2014). Phytoremediation: green technology to clean the environment. International Journal, 2(8): 879-886.

He, J., Li, H., Ma, C., Zhang, Y., Polle, A., Rennenberg, H., Cheng, X., and Luo, Z. B. (2015). Overexpression of bacterial γ‐glutamylcysteine synthetase mediates changes in cadmium influx, allocation and detoxification in poplar. New Phytologist, 205(1): 240-254.

Rylott, E.L., Budarina, M.V., Barker, A., Lorenz, A., Strand, S.E., and Bruce, N.C. (2011). Engineering plants for the phytoremediation of RDX in the presence of the co‐contaminating explosive TNT. New Phytologist, 192(2): 405-413.

Sone, Y., Nakamura, R., Pan-Hou, H., Sato, M.H., Itoh, T., and Kiyono, M. (2013). Increase methylmercury accumulation in Arabidopsis thaliana expressing bacterial broad-spectrum mercury transporter MerE. AMB Express, 3(1): 1


About Author / Additional Info:
I am currently working as a Senior Research Fellow at S.D. Agricultural University. I have done Ph.D. in Plant Molecular Biology & Biotechnology and M.Sc. in Biotechnology. I have also worked with S.D.Agricultural University as a Visiting Lecturer for 4 years.

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