Bioremediation of Heavy Metals from Aquatic Environments 233

Phytostabilization has various advantages over other techniques of phytoremediation (Jadia

and Fulekar 2009). It can be an effective technology when immobilization is required to protect

the surface and groundwater (Gomes et al.

2016). It can be used for the bioremediation of various

metals such as chromium and lead that are stabilized in the soil region (Mahar et al. 2016). It also

decreases the interaction of pollutants with biota.

Phytofiltration

Rhizofilteration is another name for phytofiltration that requires two processes such as adsorption

and precipitation of contaminant into the roots zone. Some plants contain various ‘phytochelatins’

which enhance the “binding capacity” of contaminants like metal ions.

The plants which are suitable for phytofiltration should have some properties such as:

• Their roots should grow rapidly with the ability to eliminate pollutants (Dhanam 2017).

• ‘Terrestrial plants’ are used for this process because they have a fibrous root system. This

root system helps them to remove pollutants from the rhizospheric zone and the earth’s water

(Ali et al. 2013, Khan et al. 2019).

Phytovolatilization

The process by which plants can be used to absorb pollutants, and then convert them into compounds

that are volatile is called phytovolatilization. These compounds are released into the air in a changed

form or the same due to various forces such as transpiration and metabolism (Kumar et al. 2017).

The process in which evaporation of ‘water vapors’ occurs from the leaf through the stomata into

the air is called transpiration. Plants which have long root systems often have the capacity to absorb

and transform pollutants through the formation of various enzymes (Muthusaravanan et al. 2018).

In the process of phytovolatilization, contaminants are taken up from the water or soil. These

pollutants are then changed into vapors that are less toxic (Khalid et al. 2017). The pollutants are

released into the atmosphere or air through the transpiration process. This method can be used

for contaminants that are organic and heavy metals such as mercury and arsenic as these exist in

gaseous form. There are very few plants that convert metals into volatile forms. Therefore, plants

that are genetically modified can be used in the phytovolatilization process (Khalid et al. 2017).

There are some limitations of this process, as the phytovolatilization process does not remove

all contaminants from the environment because the pollutants are changed from one part of their

physical environment to the other (Ali et al. 2013).

Phytodegradation

The process in which nutrients and pollutants are captured from the soil, water and sediments and

chemical modification of pollutants takes place by the plant’s metabolism is called phytodegradation

(Gomes et al. 2016). It causes pollutant

degradation and inactivation in the roots or shoots of plants

(Bulak et al. 2014). It is also known as phytotransformation.

The plants can destroy the pollutants

into less toxic compounds. Plants’ metabolic processes or enzymes can be used in this process

(Muthusaravanan et al. 2018).

13.4 Conclusion

Bioremediation is an effective and environment-friendly technique to biologically degrade various

pollutants. In the bioremediation process, many microorganisms play a major role such as bacteria,

fungi, algae and other plants. Furthermore, fungus microorganisms can effectively degrade many

toxic environmental pollutants. Phytoremediation represents an emerging technology through which

plants can be used to remove pollution from the soil, water and other environments. Bioremediation

requires less effort, is less labor intensive, cheap, eco-friendly, sustainable and relatively easy to

implement. Various bioremediation methods are used to convert toxic heavy metals into non-toxic

or environmentally friendly products. Biosorption, bioaccumulation, bioleaching, biotransformation