cesium from the surface-contaminated ponds [30]. The terrestrial plants, like Brassica juncea (L.) Czern. and Helianthus annuus L., and various grasses grown on
surface water, effectively remove toxic metals such as Cu
2+ , Cd
2+ , Cr
6+ , Ni
2+ , Pb
2+ ,
and Zn
2+ through their roots from water [62].
1.5.4 Phytostabilization
The technique in this remediation aims to reduce the amount of pollutants especially
metals, percolating through the soil matrix [63] to reduce the bioavailability.
Phytostabilization is the use of certain plant species for immobilizing contaminants
in the soil and groundwater by means of adsorption and accumulation onto the roots,
or to precipitate within the plant root zone. This mechanism prevents the mobility of
the contaminant to the ground and lowers the bioavailability of metal into the food
chain. To restore the vegetation at contaminated sites, metal-tolerant plant species is
to be employed [28]. Thus, it reduces the contaminant exposure, without being
destructive to the structure and biological activity of soils. In addition, the generation
of by-products is minimized [64]. The association of the plant and the microbes
helps in the immobilization mechanisms or in inactive form. Figure 4 presents
phytostabilization process.
The mechanisms for metal immobilization in plants are the following:
1. The entry of the metal through permeable barrier is prevented/concentration
gradient of metal outside the cell.
2. The adhesion to the extracellular polymers.
3. The transformation where the metal can be chemically modified to less simple
active form. The interaction of heavy metals with amine and amide functional
group, sulfonate, hydroxyl, carboxyl, and sulfhydryl group leads to the immobilization and the prevention for the entry to the root system.
Metals bind to the extracellular polymers which consist of polysaccharide and
proteins [33]. Dense root system stabilizes the soil and soil erosion can be prevented.
It is effectual when there is a need of preserving the groundwater and surface water,
and the disposal of biomass can be prevented. Plants may be identified or can be
engineered. The secreted compounds by the plants could have the ability of
immobilizing contaminants by redox processes or by precipitating the insoluble
compounds in the rhizosphere, e.g., Pb is precipitated as phosphate, and Cd forms
complexes with sulfide in the roots and the rhizosphere of Agrostis capillaris and
Silene vulgaris, respectively [65]. However, the major drawback of this technique is
the contaminant remains in soil and therefore requires regular monitoring [66]. The
cleanup site must be properly controlled and monitored to achieve such cause [67].
1.5.5 Phytovolatilization
In phytovolatilization [68], the pollutants are taken by the plants from the growth
matrix, transformed, and released into the atmosphere. The contaminant is
54
S. Sophia and V. Shetty Kodialbail
surface water, effectively remove toxic metals such as Cu
2+ , Cd
2+ , Cr
6+ , Ni
2+ , Pb
2+ ,
and Zn
2+ through their roots from water [62].
1.5.4 Phytostabilization
The technique in this remediation aims to reduce the amount of pollutants especially
metals, percolating through the soil matrix [63] to reduce the bioavailability.
Phytostabilization is the use of certain plant species for immobilizing contaminants
in the soil and groundwater by means of adsorption and accumulation onto the roots,
or to precipitate within the plant root zone. This mechanism prevents the mobility of
the contaminant to the ground and lowers the bioavailability of metal into the food
chain. To restore the vegetation at contaminated sites, metal-tolerant plant species is
to be employed [28]. Thus, it reduces the contaminant exposure, without being
destructive to the structure and biological activity of soils. In addition, the generation
of by-products is minimized [64]. The association of the plant and the microbes
helps in the immobilization mechanisms or in inactive form. Figure 4 presents
phytostabilization process.
The mechanisms for metal immobilization in plants are the following:
1. The entry of the metal through permeable barrier is prevented/concentration
gradient of metal outside the cell.
2. The adhesion to the extracellular polymers.
3. The transformation where the metal can be chemically modified to less simple
active form. The interaction of heavy metals with amine and amide functional
group, sulfonate, hydroxyl, carboxyl, and sulfhydryl group leads to the immobilization and the prevention for the entry to the root system.
Metals bind to the extracellular polymers which consist of polysaccharide and
proteins [33]. Dense root system stabilizes the soil and soil erosion can be prevented.
It is effectual when there is a need of preserving the groundwater and surface water,
and the disposal of biomass can be prevented. Plants may be identified or can be
engineered. The secreted compounds by the plants could have the ability of
immobilizing contaminants by redox processes or by precipitating the insoluble
compounds in the rhizosphere, e.g., Pb is precipitated as phosphate, and Cd forms
complexes with sulfide in the roots and the rhizosphere of Agrostis capillaris and
Silene vulgaris, respectively [65]. However, the major drawback of this technique is
the contaminant remains in soil and therefore requires regular monitoring [66]. The
cleanup site must be properly controlled and monitored to achieve such cause [67].
1.5.5 Phytovolatilization
In phytovolatilization [68], the pollutants are taken by the plants from the growth
matrix, transformed, and released into the atmosphere. The contaminant is
54
S. Sophia and V. Shetty Kodialbail