biodegradation (breakdown of complex organic pollutants into simple and smaller
unit molecules), and mineralization (complete biodegradation of organic matter into
inorganic constituents such as CO 2 or H 2 O) (Saxena and Bharagava 2017; Saxena
and Bharagava 2015; Pilon-Smits 2005).
On the basis of application potential, bioremediation can be applied as ex situ and
in situ. In situ bioremediation technologies involve treatment of pollutants at the site
of pollution, do not require any excavation means, do not pose any disturbance to
soil environment, and require continuous oxygen supply for proper aeration to
support the microbial growth for degradation of contaminants (Vidali 2001). In
situ bioremediation technologies are cost-effective as these uses microbes for pollutant removal from contaminated matrix and for the degradation and detoxification
of polyaromatic hydrocarbons, azo dyes, chlorinated solvents, and heavy metals
(Kumar et al. 2011; Folch et al. 2013; Kim et al. 2014; Frascari et al. 2015; Roy et al.
2015). In situ bioremediation technologies are biosparging, bioventing, and
phytoremediation.
Ex situ bioremediation technologies involve the treatment of pollutants at any place
other than the site of pollution and require excavation of contaminated soil or pumping
of groundwater to enhance the microbial degradation process. These remediation
approaches are costly, and their applicability depends on the pollutants type, pollution
strength and depth, and geographic conditions of contaminated sites (Philp and Atlas
2005). These approaches are classified into two methods: solid phase system (including land treatment and soil piles) and slurry phase systems (including solid liquid
suspensions in bioreactors) (Kumar et al. 2013).
3.2 Phytoremediation
Phytoremediation is an eco-friendly phytotechnology that involves the use of plants/
trees for the treatment and restoration of contaminated sites/wastewaters/groundwater (Saxena et al. 2019; Chandra et al. 2015). By using green plants, the pollutants
such as metals, pesticides, herbicides, explosives, oil, solvents, and their derivatives
can be removed and cleaned up from polluted and contaminated soil, streams, and
groundwater (Meagher 2000; Pilon-Smits 2005). Phytoremediation technologies
may be inexpensive and harmless process than traditional ones and offer easy
plant control and re-use of valuable metals. Exudates released by roots in the
rhizosphere of plants also support the growth of soil beneficial microbes that
participate in the degradation and detoxification of pollutants (rhizoremediation),
and chelating agents help to convert non-available elements into bioavailable forms
for plant uptake for growth (Suresh and Ravishankar 2004; Abhilash et al. 2009).
The genetically engineered plants have been developed through transgenic engineering to degrade and detoxify the organic and inorganic pollutants (Zhu et al.
1999; Abhilash et al. 2009). The increased accumulation of pollutants (in case of
heavy metals) facilitates their removal from contaminated matrix and, thus, prevents
their migration to other environments where these can create pollution and health
1 Genetically Modified Organisms (GMOs) and Their Potential in. . .
5
unit molecules), and mineralization (complete biodegradation of organic matter into
inorganic constituents such as CO 2 or H 2 O) (Saxena and Bharagava 2017; Saxena
and Bharagava 2015; Pilon-Smits 2005).
On the basis of application potential, bioremediation can be applied as ex situ and
in situ. In situ bioremediation technologies involve treatment of pollutants at the site
of pollution, do not require any excavation means, do not pose any disturbance to
soil environment, and require continuous oxygen supply for proper aeration to
support the microbial growth for degradation of contaminants (Vidali 2001). In
situ bioremediation technologies are cost-effective as these uses microbes for pollutant removal from contaminated matrix and for the degradation and detoxification
of polyaromatic hydrocarbons, azo dyes, chlorinated solvents, and heavy metals
(Kumar et al. 2011; Folch et al. 2013; Kim et al. 2014; Frascari et al. 2015; Roy et al.
2015). In situ bioremediation technologies are biosparging, bioventing, and
phytoremediation.
Ex situ bioremediation technologies involve the treatment of pollutants at any place
other than the site of pollution and require excavation of contaminated soil or pumping
of groundwater to enhance the microbial degradation process. These remediation
approaches are costly, and their applicability depends on the pollutants type, pollution
strength and depth, and geographic conditions of contaminated sites (Philp and Atlas
2005). These approaches are classified into two methods: solid phase system (including land treatment and soil piles) and slurry phase systems (including solid liquid
suspensions in bioreactors) (Kumar et al. 2013).
3.2 Phytoremediation
Phytoremediation is an eco-friendly phytotechnology that involves the use of plants/
trees for the treatment and restoration of contaminated sites/wastewaters/groundwater (Saxena et al. 2019; Chandra et al. 2015). By using green plants, the pollutants
such as metals, pesticides, herbicides, explosives, oil, solvents, and their derivatives
can be removed and cleaned up from polluted and contaminated soil, streams, and
groundwater (Meagher 2000; Pilon-Smits 2005). Phytoremediation technologies
may be inexpensive and harmless process than traditional ones and offer easy
plant control and re-use of valuable metals. Exudates released by roots in the
rhizosphere of plants also support the growth of soil beneficial microbes that
participate in the degradation and detoxification of pollutants (rhizoremediation),
and chelating agents help to convert non-available elements into bioavailable forms
for plant uptake for growth (Suresh and Ravishankar 2004; Abhilash et al. 2009).
The genetically engineered plants have been developed through transgenic engineering to degrade and detoxify the organic and inorganic pollutants (Zhu et al.
1999; Abhilash et al. 2009). The increased accumulation of pollutants (in case of
heavy metals) facilitates their removal from contaminated matrix and, thus, prevents
their migration to other environments where these can create pollution and health
1 Genetically Modified Organisms (GMOs) and Their Potential in. . .
5