Phytoremediation of inorganic pollutants: An eco-friendly approach, its types and mechanisms

Abstract

Heavy metals are inevitable in every ecosystem. Some of them are essential, few are contaminants after permissible limits, but some are toxic to microbe, plant and human. These heavy metals also deteriorate soil fertility and its health by affecting their physical, chemical, and biological properties.  Out of numerous heavy metals, arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), and lead (Pb) can cause toxic effects on human health when inhaled, ingested, or taken up by them. Many remediation technologies are employed to avoid heavy metal toxicity. Among those, phytoremediation is the most economical and eco-friendly approach. It includes different techniques i.e., phytoextraction, phytofiltration, phytostabilization, phytovolatilization and phytodegradation/rhizodegradation. For use as phytoremediants, it is required that plants should have the specific properties to accumulate, degrade or stabilize contaminants in its tissues i.e., plants should have tolerance against heavy metals which are accumulated in their tissues, should have fast-growing behavior, widespread branches and extensive root system, easily harvestable and non-consumable by humans and animals, ability to grow on nutrient-deficient soils. But phytoremediation technique is limited by some factors like it takes more time than chemical remediation and it requires labor and high capital investment initially. But it has the advantage of being a reliable, eco-friendly, and durable technique. This review explains the different phytoremediation approaches and mechanisms that are used by the plants to develop resistance against heavy metal toxicity. This review also elaborates the different phytoremediation approaches while explaining the basic differences among them.