A process of extracting and eliminating elemental contaminants from the environment or reducing their bioavailability in soil is called phytoremediation. Even at low concentrations, ionic compounds can be taken up by plants through their roots from the soil. The rhizosphere ecosystem, which is formed when plants extend their root systems into the soil matrix, accumulates heavy metals and modifies their bioavailability in order to repair damaged soil and maintain soil fertility.
Concept of Phytoremediation
• When soil, air, or water are contaminated with harmful contaminants, phytoremediation procedures are utilized to clear them up.
• "The use of green plants and associated microbes, as well as appropriate soil amendments and agronomic techniques, to either contain, remove, or render harmful environmental toxins harmless," is how it is defined.
• Numerous plants have proven their capacity to hyper accumulate poisons at toxic waste sites, including mustard, alpine pennycress, hemp, and pigweed.
• The recovery of abandoned metal mine workings, the mitigation of ongoing coal mine emissions, and the reduction of contaminants in soils, water, and the air have all been accomplished through the use of phytoremediation.
• Around the world, phytoremediation activities have lowered the levels of metals, pesticides, solvents, explosives, crude oil, and its derivatives.
Types of Phytoremediation
Plant Removal and Plant Accumulation
• The process through which plants store contaminants in their roots, branches, or leaves above ground is known as phytoextraction or phytoaccumulation.
• The roots concentrate nutrients in the biomass of the plant above ground after absorbing them from the soil or water.
• Approximately twenty years ago, phytoextraction began to quickly gain acceptance worldwide. Phytoextraction is a typical method used to remove heavy metals and other inorganic materials.
• At the time of disposal, contaminants are frequently concentrated in a much smaller amount of plant matter than they were in the original contaminated soil or silt.
• In order to achieve a meaningful cleanup, the growth/harvest cycle must typically be repeated over a number of crops because a lower level of contaminant stays in the soil after harvest. Following the operation, the soil is remedied.
Plant deterioration and transformation
• The process of converting organic contaminants from soil, sediments, or water into a more stable, risk-free, and immobile state is known as phytotransformation, sometimes known as phytodegradation.
• The organic molecules are broken down by the enzymes secreted by the plant roots, which are then ingested by the plant and eliminated through transpiration.
• The best organic contaminants for this technique are herbicides, trichloroethylene, and methyl tert-butyl ether.
• Phytotransformation is the term describing the chemical alteration of ambient substances as a direct result of plant metabolism, and it frequently leads to their inactivation, degradation (phytodegradation), or immobilization (phytostabilization).
• The metabolism of some plants, including Cannas, renders organic toxins, like pesticides, explosives, solvents, industrial chemicals, and other xenobiotic substances, non-toxic.
• In other instances, microorganisms that live close to plant roots may metabolize these substances in soil or water.
• Plants can control the mobility and migration of contaminated soil through a process known as phytostabilization.
• Leachable substances create an unstable mass of plant from which poisons cannot re-enter the environment by becoming adsorbent and bonding with the structure of the plant.
• The plant immobilizes pollutants by bonding them to soil particles, which reduces their availability for plant or human uptake.
• Contrary to phytoextraction, phytostabilization focuses on securing pollutants in the soil close to the roots rather than in plant tissues.
• Exposure lowers as pollutant bioavailability goes down.
• A substance that triggers a chemical process and allows the heavy metal pollution to change into a less dangerous form can likewise be excreted by plants.
• Stabilisation lowers the bioavailability of the contaminant while also reducing erosion, runoff, and leaching.
• An illustration of phytostabilization in action is the employment of a vegetative cover to stabilise and contain mining tailings.
Phytostimulation and Rhizodegradation
• Pollutants are broken down via rhizosphere activity, also referred to as phytostimulation or rhizodegradation.
• This action is brought about by the presence of proteins and enzymes produced by plants or soil organisms like bacteria, yeast, and fungi.
• These microorganisms may transform harmful pollutants like fuels and solvents into benign and unharmful byproducts.
• Natural carbon-containing substances that are released by plants, such as sugar, alcohols, and acids, give microorganisms more food and stimulate their activity.
• Better plant-microbe interactions in transgenic plants may increase production.
• It would be easier for the plant to exude the natural compounds that fuel microbial activity.
• Rhizofiltration is a process that filters water via a dense network of roots to remove dangerous pollutants and extra nutrients.
• The roots can take up the pollutants or transfer them to them.
• By planting directly in the contaminated region or by removing the contaminated water and sending it to these plants off-site, this technique is widely employed to clean up contaminated groundwater.
• In either case, plants are often grown under controlled conditions in a greenhouse.
• In wetlands and estuaries, pollution is reduced with this method.
• A type of bioremediation called mycoremediation uses fungi to clean up a location.
• It has been demonstrated that using fungi may efficiently and sustainably remove a variety of toxins from contaminated environments or wastewater.
• These contaminants include heavy metals, organic pollutants, textile dyes, chemicals and effluent from leather tanning, petroleum fuels, polycyclic aromatic hydrocarbons, pharmaceuticals and personal care items, pesticides, and herbicides in ecosystems on land, in freshwater, and in the ocean.
• Enzymes and edible or therapeutic mushrooms are examples of remediation byproducts that can be important resources in and of themselves and increase the profitability of cleanup.
• In extremely cold or radioactive environments, when traditional cleanup processes are either too expensive or impossible to use due to the harsh conditions, some fungi can assist with the biodegradation of contaminants.
• Similar techniques include mycofiltration, which uses fungus mycelium to filter hazardous waste and pathogens from water in soil.
• Fungal mycelium is said to use techniques like biosorption, bioaccumulation, and biodegradation to remove contaminants and xenobiotic.
• It has been discovered that a number of fungus species have exceptional capacity to absorb and eliminate metals and other pollutants from waste and/or runoff water.
• In addition to having a high biosorption capacity for metals like Cu, Zn, Fe, and Mn, fungi also have the power to transform drug resistance and degrade insecticides, whether they are living or in the form of dried biomass.
• Environmentally Friendly Alternative: This method can reduce the amount of pollutants that is exposed to the environment and ecosystem.
• Application and Ease of Disposal: This technique can be used on a sizable field and is simple to discard.
• Avoids Erosion And Spreading: By stabilizing heavy metals and lowering the likelihood of pollutants spreading, it avoids erosion and metal leaching.
• Enhance Soil Fertility: By releasing different organic materials into the soil, it can also enhance soil fertility.
• Phytoremediation does not remove dangerous heavy metals from the environment; rather, it relocates them.
• Limited Application: Phytoremediation can only take place at the surface area and depth occupied by the roots.
• Slow Growth And Limited Biomass: A long-term commitment is needed due to the slow growth and limited biomass.
• Cannot Completely Avoid Pollutants: Using plant-based remediation strategies, contaminant leaching into groundwater cannot be completely avoided.
• Impact on Plant Survival: Both the overall soil quality and the toxicity of polluted land have an effect on plant survival.
• Metal Bonding to Organic Material: When a plant takes up a heavy metal, the metal may link to the organic material in the soil, rendering removal by the plant impossible.
• Applications of phytoremediation in Soil and Water: Stable polluted soil or aquatic habitats are common applications for phytoremediation.
• Restoring abandoned metal mine workings and locations where polychlorinated biphenyls were dumped during production, as well as mitigating active coal mine discharges to lessen the impact of toxins in soils, water, or the air, are just a few examples.
• Pesticides, Crude Oil and Derivatives: Phytoremediation procedures have been used in countries all over the world to remove metals, pesticides, solvents, explosives, and crude oil and its derivatives.
• Toxic Waste Sites: Many plants have proven their capacity to hyperaccumulate poisons at toxic waste sites, including mustard, alpine pennycress, hemp, and pigweed.
In the phytoremediation process, heavy metal detoxification is an essential phase. Thus, plants use either tolerance or avoidance as a form of protection against the toxicity of heavy metals. These two techniques are used by plants to maintain heavy metal levels in their cells below the toxicity threshold levels. It serves as the first line of defense at the extracellular level through a number of mechanisms, including root adsorption, metal ion precipitation, and metal exclusion.