Phytoremediation, Defination, Types, Examples, Advantages

Phytoremediation harnesses the natural power of specific plants to absorb, degrade, or contain contaminants like heavy metals (arsenic, lead), pesticides, and industrial solvents. Wondering how this green technology works? The core process involves planting hyperaccumulator species (e.g., Indian Mustard for lead/cadmium, Sunflowers for radionuclides, Water Hyacinth for organic pollutants) whose roots extract or break down toxins from the environment. Key types of phytoremediation include Phytoextraction (uptake into harvestable biomass), Phytostabilization (immobilizing contaminants), Phytodegradation (plant enzymes break down organics), and Rhizofiltration (root filtration of polluted water).

In recent years, phytoremediation, which utilizes the ability of plants to absorb water and nutrients, has been attracting attention as a low-cost, low-environmental-impact environmental remediation technology. To date, plants that excel at environmental remediation, such as heavy metal hyperaccumulators, have been discovered to improve heavy metal contamination in soil and water environments, and their application to environmental remediation technology is being researched. Recently, it is expected that these plants will not only remove pollution, but also contribute to the production of useful plants, the conservation of biodiversity, and the mitigation of global warming.

Phytoremediation Definition 

• Phytoremediation technology is an environmental pollution control technology that uses plants and their coexisting microbial systems to remove pollutants from the environment.

• The process in which plants are used to remove or decompose pollutants such as heavy metals, organic matter, etc from the contaminated land or groundwater.

• Phytoremediation is the use of green plants to transfer, contain or transform pollutants to make them harmless from the environment. 

What is Phytoremediation?

• Phytoremediation is a compound word of the Greek word “phyto” meaning “plant” and the Latin word “remediation” meaning “repair or treatment”.
• Phytoremediation is a process in which plants are used to remove heavy metals polluting the environment.
• Phytoextraction, Rhizofiltration Bio-accumulation phytostabilization is collectively known as phytoremediation.
• It is a technology that uses microorganisms living in plants and the rhizosphere (roots and the soil around them) to absorb, accumulate, stabilize, and decompose pollutants in soil and water, and has six main remediation mechanisms.
• Phytoremediation is a very unique pollution control technology as compared with physical, chemical, and microbial treatment technologies.
• Phytoremediation is a cheap and efficient method to remove Pollutants/Contaminants from land, air, and water.
• This technology is an environmentally friendly technology that helps remove, fix, and prevent the diffusion of pollutants in the environment using only sunlight and carbon dioxide, which are necessary for plant growth, and contributes to improving the surrounding environment.
• It is particularly suitable for purifying low-concentration, wide-area soil and water pollution, and has the advantage of being applicable to a wide range of substances, including inorganic pollutants, organic pollutants, and radioactive pollutants.
• However, this technology has the disadvantages of low treatment efficiency and long period of time required for remediation, and it is necessary to comprehensively evaluate the state of contamination before applying the technology.
• Contaminants such as heavy metals, organic matter, radioactive elements, pesticides, explosives, and crude oil can remove by phytoremediation.
• Many plants are used in phytoremediation such as mustard plants, sunflower alpine pennycress, Spinach, hemp, and pigweed to remove contaminants. 
• The US state of New Jersey has successfully used phytoremediation to restore lead-contaminated land due to the manufacture of batteries.
• Plant examples in phytoremediation: Plants used in phytoremediation screen used already in studies for carrying out for the carrying out the removal of contaminants from the environment are alfalfa, ryegrass, alpine bluegrass, maize, mustard, duckweed, arrowroot, Sudan grass, Bermuda grass, and yellow or white water lilies.

Research in Phytoremediation 

• Biotechnology Researchers are trying to develop new plant varieties that can accumulate heavy metals in large quantities for phytoremediation.
• The research work on phytoremediation is mainly carried out by the following two strategies. 
• The first is to enhance the ability of plants to accumulate heavy metals by expressing a large number of single genes that already exist in the body and are related to the accumulation of heavy metals. 
• Another method is to transfer a complete set of foreign enzymes involved in the metabolism, absorption, and accumulation of heavy metals into plants using gene transfer. 
• There have been many examples of the successful production of heavy metal-resistant plants using gene transfer technology. 
• For example, researchers in Israel added a gene with transporter function to tobacco, so that tobacco can grow in an environment containing high concentrations of nickel. 
• In addition, researchers in Spain have found that the transgenic plants in Arabidopsis can be induced by cadmium, and then affect the gene of glutathione (glutathione) concentration in the plant accumulated in the leaves.

Principle of Phytoremediation 

The principle is divided into three parts, pollutants extraction, fixation, and degradation.

• Absorption/Extraction is to absorb heavy metals from the soil, water, or the environment and store them in hyperaccumulator plants to reduce environmental pollution.
• Fixation/Immobilization is the immobilization of heavy metals by plant roots or symbiotic microorganisms to prevent their transfer.
• Degradation is naturally the reduction of heavy metals to harmless zero-valent states through the metabolism of plants themselves and the decomposition and reduction of symbiotic microorganisms.

Types of Phytoremediation

There are different types of phytoremediation techniques: Rhizofiltration, Phytoextraction, Phytotransformation, Phyto-stimulation, and Phytostabilization.

Quick Reference: Phytoremediation Types

1) Rhizofiltration 

• Rhizofiltration is a type of phytoremediation
• Rhizofiltration processes use hydroponics to remove water contaminants.
• It is a water remediation technique that involves the uptake of contaminants by plant roots. 
• It is mainly used for the disposal of contaminated surface water, wastewater water sewage containing low amounts of heavy metals or radionuclides. 
• It involves the adsorption and precipitation of the metal pollutants onto the roots or absorption by the roots, therefore plants with large root systems are preferred.
• Plants Such as tobacco, Indian mustard, hyacinth, duckweed, Spinach, sunflower are used in hemofiltration.
• Heavy metals such as Copper, lead, arsenic, cadmium, uranium, cobalt can be efficiently removed through the hemofiltration technique.
• Example: Hydroponically-grown sunflowers are used to remove cobalt, lead, copper, zinc uranium, strontium, cesium, etc.

2) Phytoextraction

• Phytoextraction is a subtype of phytoremediation.
• Phytoextraction is a process in which plants remove contaminants, elements, or compounds from water, soil.
• Phytoextraction is most usually used for the extraction of heavy metals which has high density. 
• For the process of phytoextraction, plant with good tolerance to high concentrations of heavy metals, high growth rate, and hyperaccumulators plants are used.
• The heavy metal absorbed are stored in the aerial portions of the plants (Stems & Leaves).  
• Hyperaccumulator plants are capable of absorbing a larger amount of metal in comparison to other plants.
• After the accumulation of heavy metals, they are harvested or disposed of by incineration or be composted to recycle metals. 
• Although plants that were incinerated will be disposed of in a hazardous waste landfill.
• Brake fern (Pteris vittata) hyper accumulates arsenic in its shoots more than 200 times higher than those found in the soil. Other target metals include Nickel, lead, cadmium,  zinc, chromium, radionuclides, etc.

3) Phytotransformation /Phytodegradation 

• Phytotransformation is the breakdown of organic contaminants with the help of plants.
• Phytotransformation is also known as phytodegradation.
• It applies to both soil and water, involving the degradation of contaminants through plant metabolism.
• In Phytotransformation organic contaminants are degraded or transformed into simpler compounds that are integrated with plant tissue.
• In phytotransformation plant species such as Mustard, parrot feather, Sunflower, Eurasian watermilfoil, hydrilla, and waterweed are used.
• Even there are some fungal strains, such as white rot that are capable of xenobiotic biodegradation. 
• The best example of a species that can convert toxins found in soil is Periwinkle (Catharanthus).
• Example: Some enzymes break down explosives, chlorinated solvents, or herbicides.

4) Phytostimulation

• This process occurs within the rhizosphere, which is the layer of soil that surrounds the roots.
• Phytostimulation effective process of degrading pollutants such as petroleum hydrocarbons, PCBs, and PAHs.
• This technique is also used for both soil and water, which involves the stimulation of microbial biodegradation through the activities of plants in the root zone, and 

5) Phytovolatilization

• It is another subtype of phytoremediation.
• In this process, plants extract contaminants from the soil and modify or release these contaminants into the atmosphere via evapotranspiration from foliage.
• Examples: Targets of this technology include PCBs (polychlorinated biphenyls), TCEs (trichloroethylenes), PAHs (polyaromatic hydrocarbons), pesticide residues, and various explosives. Poplar trees have been shown to volatilize 90% of the TCE taken up.

6) Phytostabilization

• Phytostabilization involves the establishment of a plant cover on the surface of contaminated sites.
• The purpose of phytostabilization is the reduction of contaminants from the atmosphere.
• For example, if a wasteland or Barren land is contaminated or polluted, there we can plant different types of plants that will absorb heavy metals, contaminants, and pollutants from the soil.
• Phytostabilization can be enhanced by using soil amendments that are effective in the immobilization of metals and radially suited to the monitored natural remediation contaminated site.
• For phytoremediation soil characteristics such as pH, redox potential, presence of contaminants, plant growth, microbial population, nutrients are necessary.
• Volatilization of contaminated into the atmosphere via plants may be an important process in the phytostabilization of soil where a high concentration of organic contaminants is present.

Advantages of Phytoremediation

• Phytoremediation technology has been accepted by people as an emerging and efficient phytoremediation approach and is gradually becoming commercialized
• The main advantages of phytoremediation are it has low cost, no damage to soil and air, and no secondary pollution.
• It has simple equipment and sustainable high output.
• It is most suitable for treating soil polluted by shooting range in a small area, separating heavy metals from the soil, sediment, and waste residue, cleaning soil, and restoring normal soil function. 
• The pollutants are completely degraded, and the organic pollutants can be degraded into completely harmless inorganic substances.
• By understanding the survival strategies of plants in the environment of heavy metals, it is helpful for human beings to use biotechnology to create plants that can absorb a large number of heavy metals. 
• It increases soil health, yield, and plant phytochemicals and reduces soil erosion.
• It maintains soil fertility and preserves the topsoil.

Disadvantages of Phytoremediation

• Limited surface area and depth due to the roots.
• The period required for phytoremediation is relatively long, generally more than 3 years.
• These methods are a long-term commitment and usually take many years to clean up the site.
• This method is slower than the conventional methods.
• This method does not completely remove the contaminants from the environment and there are chances that some of the contaminants down up to the groundwater.
•  If the contaminants are toxic in nature they may affect the survival of the plants these may affect the health of the soil and does that process may harm the plants is also associated with that method.
• Plants that accumulate toxic contaminants into the tissues, this contaminants can enter the food chain, and does it can affect the living organisms.
• Besides that, there is also a requirement of safe disposal of such plant materials that are containing toxic contaminants that can affect the health of the soil as well as of the plants