• Phytofiltration

• Phytovolatilization

• Phytodegradation

Phytoextraction

It is also called phytoabsorption or phtyoaccumulation and phytosequestration. The process which

involves the elimination of toxic contaminants such as heavy metals and metalloids from water

and soil by using the roots of plants is known as phytoextraction (Ghosh and Singh 2005). These

pollutants can be moved and collected in shoots (Muthusaravanan et al. 2018).

The process in which

contaminants can be gathered in shoots is a very important procedure as if the material is gathered

in roots, then harvesting of biomass of roots is not possible (Halim et al. 2003, McIntyre 2003).

If phytoextraction is done continuously then a very large number of pollutants can be collected in

plants (Sarwar et al. 2017).

The following steps are involved in the phytoextraction process:

• The first step involves the mobilization of contaminants in the rhizosphere.

• The roots can absorb toxic contaminants like heavy metals and metalloids (Memon and Schröder

2009).

• The pollutants are translocated toward the airy parts.

• The contaminants are separated from the tissues of plants (Ali et al. 2013).

For the phytoextractions, the hyperaccumulator plants are used that must have the following

properties: the growth rate of plants should be a high, large biomass (Khalid et al. 2017), tolerance

to a wide variety of contaminants, the branched root system, adjustment to native environmental

situation, immunity against pest and pathogen, high crop production and a higher ability to

accumulate pollutants (Mahar et al. 2016, Sarwar et al. 2017).

The efficacy of the phytoextraction process depends upon the following three facts viz. the

climatic condition (Bhargava et al. 2012), weather and the growth rate of plant roots.

This process can be improved by using various agents such as nitrilotriacetic acid, amino

polycarboxylic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid and citric acid. This

process is used for the elimination of contaminants from the contaminated areas.

There are also many disadvantages to this process. As it requires specific conditions that are

necessary for the plant’s tolerance to contaminants and their growth. It also requires a longer time

to completely remediate the areas.

Phytostabilization

It is also called phytoimmobilization. The process in which plants can be used to reduce the

bioavailability or mobility of contaminants either by ceasing the leaching to the underground water

table (Sarwar et al. 2017) or its entrance into the food chain through a process such as the production

of compounds that are not soluble in the roots zone or adsorption by the roots of plants (Khan et al.

2019). The properties of this process are:

• The reduction of contaminants in the polluted region by assimilation and adsorption on the

roots and precipitation by roots.

• The deployment of the plant’s roots to avoid pollutants movements by water, wind, draining

and soil dispersal (USEPA 1999).

The goal of this process is the stabilization of contaminants rather than their elimination. It

decreases their risk to humans and nature (Bolan et al. 201

1). Phytostabilization not only reduces the

concentration of contaminants, but also lessens the contaminant of the surrounding region (Khalid

et al. 2017).

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Bioremediation for Sustainable Environmental Cleanup