Contact: to feature here

Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Phytoremediation Applying Biotechnological Methods
The technique of utilization of biological agents for degradation of pollutants is known as bioremediation. Phytoremediation is a branch of bioremediation wherein plants are employed for the purpose of removal of pollutants from a specific area.

Plants aid in phytoremediation by absorption, assimilation of compounds, vaporization of pollutants, metabolic digestion, or by microbial degradation by plant associated microbes. The plants which can accumulate and degrade the contaminants are known as ‘hyperaccumulaters’ which play a major role in phytoremediation.

Different modes of Phytoremediation
Depending on the technique applied phytoremediation can be subdivided into many kinds:

(i) Phytoextraction: it refers to a process in which plants breakdown contaminants and adsorbs the same into its tissues. After adsorption, plants can be removed from site and disposed or incinerated. Different plant types have different ability of phytoextraction and the plants with most effectiveness are chosen usually. This process is mostly used for treatment of metal pollutants in soil.

(ii) Rhizofiltrtion: in this process the pollutants gets adsorbed and deposited, not on the shoot tissues but in this case, in the root or rather in the rhizosphere of plants. This technique is specifically employed for waste removal from contaminated water sources.

(iii) Phytostabilisation: this concept involves immobilization of the pollutants following absorption and adsorption of it by plant roots and finally precipitation of the pollutant in the root so that it does not migrate from soil into air or other sources.

(iv) Phytotransformation: it deals with transformation or degradation of pollutants as a result of various metabolic processes by plants. Thus it is also known as phytodegradation.

(v) Phytovolatilization : the contaminants are absorbed by plants, undergo many changes and finally gets volatized from leaf surface during transpiration process of plants.

(vi) Phytostimulation: the microbial population near the root system of plants gets induced by the presence of rhizosphere which initiates them to break down the pollutants. This process is also known as rhizosphere degradation.

Role of biotechnology in phytoremediation:
Off late, biotechnology has been found to increase its wide spectrum of applications into phytoremediation as well. Plants adopted for phytoremediation are usually found to exhibit the specific property due to the presence the special genes coding for it. These plants are usually seen in area where metal ores exist. The genes responsible for this resistance by such plants are isolated and expressed in wide variety of transgenic plants so that they can be made resistant as well. This increases the number of plant species that can be used for such purpose. It is also possible with the help of biotechnology to increase the gene expression for maximum resistance.

Certain plants are seen to show increased resistance under the presence of certain microbes. Biotechnology makes it possible to isolate such microbes and enrich the soil so as to enhance the phytoremediation by respective plants.

Examples of application of biotechnological aspects in phytoremediation

Selenium: The micronutrient selenium is known to induce toxicity in the soil where the concentration of the same is found to be high. It is found that methylation of amino acids at specific site can result in volatilization of selenium compound. Thus a transgenic plant is constructed which has the ability to volatize the same by following the guidelines of genetic engineering and utilizing the information obtained by studying hyperaccumulators of selenium.

Mercury: Mercury can be degraded by certain bacterium due to the presence of merA and merB genes. Thus integration of these genes into certain plant genomes has seen effective mercury degradation by such transgenic plants. The genes are targeted to be expressed in chloroplasts so that after degradation into relatively less toxic form, it is volatized. Thus transgenic tobacco produced by this phenomenon was shown to exhibit mercuric resistance.

Arsenic: Certain bacterial genes present in E. coli, such as ArsC is responsible for reduction of arsenic and formation of a complex in the presence of glutathione(GSH). An increased amount of GSH can be produced by expression of glutamyl cysteine synthetase enzyme. These genes are isolated and transferred to form a transgenic plant which can effectively absorb arsenic and accumulate the same in its vacuoles resulting in phytoremediation.

Thus it can be concluded that biotechnological tools can be utilized to improvise many existing phytoremediation systems yielding more effective and faster results.
Like Post Reply
Advantages of phytoremediation over other remediation methods

Phytoremediation is process of removing toxins, heavy metals, organic pollutants and other waste using specifically selected or genetically engineered plants. Soil microorganisms (living in rhizosphere) are contributing to the phytoremediation process.

Plants absorb different chemicals from the ground and transform them into valuable nutrients (used for their own growth) or less harmful substances that could evaporate through their leaves. Trace elements are essential for the plant grown. They are found in the soil as well as heavy metals. Due to high similarity between essential and toxic (metal) elements, plant will absorb them all. Heavy metals will be bioaccumulated in plants tissue. Some plants contain 1000 times more heavy metals than surrounding soil. Best results in soil remediation will be achieved in the 3-6 feet wide area around the root. Besides being active in absorbing and transforming pollutants from the ground, plants can accelerate bioremediation by increasing the number and activity of the soil microorganisms. Constant exchange of nutrients and oxygen between the root and soil result in increased activity of microorganisms that are responsible for faster degradation of the soil contaminants. Carbohydrates, amino acids and mucigel (gelatinous substance that facilitate root penetration through the ground during the growth) are the most important nutrients for the microbial growth. On the other hand, after organic pollutants are degraded by soil microorganism, plant will have enough nutrients (C, N, P, K and S) for its own growth.

Phytoremediation in real life examples:

A mustard green (Brassica juncea) is used to decrease the amount of lead in the children’s park in Boston. Plants were removed and safely disposed after they absorbed 45% of the lead from the ground. Pumpkin vine (Cucurbita pepo maxima) is used for cleaning the old Magic Marker factory in New Jersey. After Chernobyl nuclear catastrophe, sunflowers (Helianthus annuus) were used to absorb radioactive waste.

Large plant species are used when big amount of water (and associated contaminants) need to be absorbed from the ground. Single willow tree (Salix alba) can transpire 5,000 gallons of water in a summer day. One hectare of saltwater cordgrass (Spartina alterniflora) will evapo-transpirate (sum of evaporation and transpiration) 21,000 gallons of water per day. All heavy metals and various pollutants will be absorbed with the water and metabolized (or accumulated) in the plant.

Halophytes are interesting group of plants that could be used in phytoremediation as well. These plants could tolerate high level of the salt in the ground. In 2 years long project of phytoremediation of the gas and oil contaminated soil in Oklahoma, they managed to reduce the level of salt for 65%. After excess salt was removed, ground was colonized by the plants that lived there before “ecological disaster”.

List of pollutants that could be easily removed from the ground using phytoremediation: petroleum hydrocarbons, polycyclic aromatic hydrocarbons, chlorinated pesticides, polychlorinated biphenyls, trichloroethylene, explosives (TNT, DNT), organophosphate insecticides (diazanon and parathion), surfactants (detergents)…

List of plants used in phytoremediation:

Alfalfa is living in symbiosis with hydrocarbon-degrading bacteria. Arabidopsis can transform Hg into a gaseous state thanks to inserted bacterial gene. Bamboo family can accumulate silica in its stalk and N in its leaves. Bladder campion can accumulate Zn and Cu. Brassica juncea can accumulate Se, S, Pb, Cr, Cd, Ni, Zn, and Cu. Buxaceae and Euphorbiaceae can accumulate Ni. Compositae family is living in symbiosis with Arthrobacter bacteria and accumulates Cs and Sr. Ordinary tomato and alpine pennycress can accumulate Pb, Zn and Cd. Poplar is used for the absorption of the atrazine (pesticide).

Phytoremediation is cost effective because planting doesn't require specific equipment or technology (same methods are used in agriculture). This type of remediation is less expensive than conventionally used chemical, physical or thermal methods. It’s also less expensive than bioremediation. Removal of the pollutants from the top 15 centimeters of the contaminated soil using plants will cost between 2,500 to 15,000 dollars per hectare, compared to 7,500 to 20,000 dollars when microorganisms are used. Other advantage of phytoremediation over conventional methods is that it’s happening in situ. Contaminants are simply immobilized and transformed or stored within the plant after extraction. Conventional methods are more complicated since extracted contaminated material needs to be stored and transported to the landfill where it will be incinerated. Also, conventional methods are less eco-friendly.
Like Post Reply

Users browsing this thread:
1 Guest(s)

Phytoremediation Applying Biotechnological Methods00