Phytoremediation

Phytoremediation Heavy metals, one of the contaminant groups considered to be most noxious, enter the environmental segments through natural as well as anthropogenic activities and are then primarily accumulated in soils and water bodies. Soils act as a sink, where the metals are sequestered in different fractions, and some of these sequester fractions become stable and difficult to remove from the soil. However, some fractions are present in labile form and can be removed using different categories of plants. Toxic metals and metalloid arsenic have adverse effects on plants, animals, and humans.

It is essential to remediate the soils and water bodies for safe use to mitigate contamination effects. Different physical and chemical methods can remediate soils. Removal of contaminated soils through excavation is needed in extreme cases. Washing, leaching, and flushing with chemical agents can be effective, and mixing unpolluted soils with the surface soils can solve the problem. Some other chemical techniques are also applied in some cases. The use of plants for the removal of contaminants, however, is a widely used technique known as phytoremediation.

Plants are recognized to decrease their environmental impact by absorbing, moving, or accumulating certain poisonous metals and chemicals through the roots. Plant remediation methods help to preserve natural environmental situations. Processes involved in phytoremediation processes can be briefly classified as follows: Phytoextraction (with nutrients plants can extract toxic metals also and accumulate in different parts of it which depends on the mobility of the metals inside the plants), rhizofiltration (adsorbing or depositing metals in the roots or absorbing metals to purify contaminated surface water or wastewater; Phytostabilization (fixation of soil or sediment by root absorption, adsorption of roots or moisture in the rhizome), Phytodegradation (enzymatic degradation or removal of organic pollutants by internal or secreted plant enzymes), Rhizodegradation (destruction of organic contaminants by microorganisms), Phytovotalization (absorption of some pollutants (e.g. Hg or Se) by plants into the atmosphere by evaporation in their unique form or after metabolic transformation) and hydraulic control (absorption of high amount of water to preclude the dispersal of tainted wastewater into unpolluted nearby regions. The following table shows the mechanisms and importance of phytotechnology for the removal of pollutants by different plants. The above-ground portion of plants is involved in Phytovolatilization, Phytoevaporation, and Phytoextraction, whereas the below-ground parts are engaged in Phytostabilization, Rhizofiltration, Rhizodegradation, and Phytosalination.

Despite some limitations, phytoremediation techniques are used worldwide to remove pollutants from contaminated soil and water. Several studies and laboratories are involved in surpassing their limits. [Sirajul Hoque and Mumtahina Riza]