erosion, and reducing pollutant solubility or bioavailability to the food chain
(Radziemska et al. 2007). Solubility of metals in soil is decreased by the addition
of soil amendments (organic matter, phosphates, alkalizing agents, and biosolids).
Plant roots accumulate the contaminants and reduce the mobility of contaminants.
Phytoextraction Phytoextraction is the extraction of dangerous elements or compounds from soil or water with the help of plants. Hyperaccumulators of plants are
used for phytoextraction method that absorbed extremely large amounts of heavy
metals (Garbisu and Alkorta 2001). Absorption of heavy metal is completed by
following five steps:
1. The metal must dissolve in some chemical (rhizospheric chemical).
2. The heavy metal is absorbed by plant root.
3. The plant must chelate the metal to protect itself and increase the mobility of the
metal (this can also happen before the metal is absorbed).
4. Chelated metal is stored at safe place.
5. Finally, the plant recovers the damages caused during transportation and storage
(Suman et al. 2018). Systems that transport and store heavy metals are the most
critical systems in a hyperaccumulator. Sometimes, heavy metals are stored in
leaves by hyperaccumulators.
Stored heavy metals were digested by the phytoremedation process like
phytotransformation (Chaudhry et al. 1998; Broyer et al. 1972; Malone et al.
1974). In this method, plants also decrease toxicity and sequester the xenobiotics.
The trinitrotoluene phytotransformation method has been widely studied, and a
transformation pathway has been projected (Subramanian et al. 2006). Other bioremediation techniques are phytovolatilization (Lewis et al. 1966; Terry et al. 1992;
Banuelos et al. 1993a, b; Wilber 1980; Suszcynsky and Shann 1995; Brooks 1998b),
phytodegradation or rhizoremediation (Hoagland et al. 1994; Jacobsen 1997;
Zablotowicz et al. 1994), and bioaugmentation (Fig. 6.6; Table 6.5).
6.8 Factors Responsible for Remediation
1. Type of soil: Uptake and tolerance of heavy metal depend on physiochemical
properties of soil and soil microbes.
2. Gene expression: In legume plants, appearance of phytochelatin synthase gene
(PCS1) also increased the heavy metal accumulation (Zhang et al. 2010a, b; Xu
et al. 2014).
3. pH: The active uptake of cations via plasma lemma of roots includes H
+ excretion
while anion uptake involves OH
À or HCO
3À excretion (Bolan et al. 1991). In
symbiotic association with rhizobia, plants accumulate most of their N through
N 2 fixation method. In this process, legume plants consume more cations than
anions and discharge more H
+ ions from roots to soil and create acidic environment for the rhizosphere and bulk soil (Zhao et al. 2009). HM mobility and
6 VAM: An Alternate Strategy for Bioremediation of Polluted Environment
169
(Radziemska et al. 2007). Solubility of metals in soil is decreased by the addition
of soil amendments (organic matter, phosphates, alkalizing agents, and biosolids).
Plant roots accumulate the contaminants and reduce the mobility of contaminants.
Phytoextraction Phytoextraction is the extraction of dangerous elements or compounds from soil or water with the help of plants. Hyperaccumulators of plants are
used for phytoextraction method that absorbed extremely large amounts of heavy
metals (Garbisu and Alkorta 2001). Absorption of heavy metal is completed by
following five steps:
1. The metal must dissolve in some chemical (rhizospheric chemical).
2. The heavy metal is absorbed by plant root.
3. The plant must chelate the metal to protect itself and increase the mobility of the
metal (this can also happen before the metal is absorbed).
4. Chelated metal is stored at safe place.
5. Finally, the plant recovers the damages caused during transportation and storage
(Suman et al. 2018). Systems that transport and store heavy metals are the most
critical systems in a hyperaccumulator. Sometimes, heavy metals are stored in
leaves by hyperaccumulators.
Stored heavy metals were digested by the phytoremedation process like
phytotransformation (Chaudhry et al. 1998; Broyer et al. 1972; Malone et al.
1974). In this method, plants also decrease toxicity and sequester the xenobiotics.
The trinitrotoluene phytotransformation method has been widely studied, and a
transformation pathway has been projected (Subramanian et al. 2006). Other bioremediation techniques are phytovolatilization (Lewis et al. 1966; Terry et al. 1992;
Banuelos et al. 1993a, b; Wilber 1980; Suszcynsky and Shann 1995; Brooks 1998b),
phytodegradation or rhizoremediation (Hoagland et al. 1994; Jacobsen 1997;
Zablotowicz et al. 1994), and bioaugmentation (Fig. 6.6; Table 6.5).
6.8 Factors Responsible for Remediation
1. Type of soil: Uptake and tolerance of heavy metal depend on physiochemical
properties of soil and soil microbes.
2. Gene expression: In legume plants, appearance of phytochelatin synthase gene
(PCS1) also increased the heavy metal accumulation (Zhang et al. 2010a, b; Xu
et al. 2014).
3. pH: The active uptake of cations via plasma lemma of roots includes H
+ excretion
while anion uptake involves OH
À or HCO
3À excretion (Bolan et al. 1991). In
symbiotic association with rhizobia, plants accumulate most of their N through
N 2 fixation method. In this process, legume plants consume more cations than
anions and discharge more H
+ ions from roots to soil and create acidic environment for the rhizosphere and bulk soil (Zhao et al. 2009). HM mobility and
6 VAM: An Alternate Strategy for Bioremediation of Polluted Environment
169