In the present chapter, an attempt has been made to review the recent advances on
phytoremediation potential of heavy metal-contaminated soils with the help of plant
growth-promoting rhizobacteria, earthworms, fungi, etc.
14.2 Toxicity of Heavy Metals and Other Xenobiotics
on Plants
Heavy metals released from industrial effluents and the excessive use of pesticides in
agricultural fields are reducing crop production by polluting environment and
degrading the food quality (Shahzad et al. 2018). These heavy metals are taken up
from the soil through the roots of plants and are translocated to other parts of plants
or are accumulated in the roots of plants. The increase in the level of heavy metals in
plant’s rhizosphere has caused various negative effects on physiological and biochemical processes of plants (Shahzad et al. 2016). Heavy metal toxicity induces
formation of free radicals which leads to generation of various reactive species and
causes oxidative, nitrosative stress in plants (Dubey et al. 2018). Heavy metal stress
disturbed the structure as well as permeability of the organelles and membranes;
decreased photosynthetic rate, transpiration rate, and nutrient imbalance; etc. (Green
et al. 2003). Increased amount of these pollutants in soil render the soil unfit for
vegetation and hamper the biodiversity (Setia et al. 2008). Different heavy metals,
pesticides, and the toxicity caused in plants due to these pollutants are given in
Table 14.1.
14.3 Phytoremediation
Phytoremediation is an emerging, green, and eco-friendly technology for removing
contaminants from the soils with the help of plants (Yang et al. 2019). Plants have
the potential to cope up with various contaminants present in soil by changing soil
properties, fertility, and efficacy. Phytoremediation approach includes
phytoextraction, phytovolatilization, phytodegradation, phytotransformation,
rhizodegradation, and phytostabilization (Fig. 14.1) (Marques et al. 2009; Bhargava
et al. 2012).
Baker (1981) in his study categorized the plants into three main categories—
excluders, accumulators, and indicators. Excluders play a role in the stabilization of
soil by preventing soil erosion, reducing uptake of heavy metals to critical level
(Lasat 2002). Accumulators have the potential to bioaccumulate the contaminants,
whereas indicators show the level of contamination (McGrath et al. 2002).
Hyperaccumulators are considered as subclass of accumulators which have very
high potential to accumulate the contaminants in their aboveground tissues without
14 PGPR and Earthworm-Assisted Phytoremediation of Heavy Metals
229
phytoremediation potential of heavy metal-contaminated soils with the help of plant
growth-promoting rhizobacteria, earthworms, fungi, etc.
14.2 Toxicity of Heavy Metals and Other Xenobiotics
on Plants
Heavy metals released from industrial effluents and the excessive use of pesticides in
agricultural fields are reducing crop production by polluting environment and
degrading the food quality (Shahzad et al. 2018). These heavy metals are taken up
from the soil through the roots of plants and are translocated to other parts of plants
or are accumulated in the roots of plants. The increase in the level of heavy metals in
plant’s rhizosphere has caused various negative effects on physiological and biochemical processes of plants (Shahzad et al. 2016). Heavy metal toxicity induces
formation of free radicals which leads to generation of various reactive species and
causes oxidative, nitrosative stress in plants (Dubey et al. 2018). Heavy metal stress
disturbed the structure as well as permeability of the organelles and membranes;
decreased photosynthetic rate, transpiration rate, and nutrient imbalance; etc. (Green
et al. 2003). Increased amount of these pollutants in soil render the soil unfit for
vegetation and hamper the biodiversity (Setia et al. 2008). Different heavy metals,
pesticides, and the toxicity caused in plants due to these pollutants are given in
Table 14.1.
14.3 Phytoremediation
Phytoremediation is an emerging, green, and eco-friendly technology for removing
contaminants from the soils with the help of plants (Yang et al. 2019). Plants have
the potential to cope up with various contaminants present in soil by changing soil
properties, fertility, and efficacy. Phytoremediation approach includes
phytoextraction, phytovolatilization, phytodegradation, phytotransformation,
rhizodegradation, and phytostabilization (Fig. 14.1) (Marques et al. 2009; Bhargava
et al. 2012).
Baker (1981) in his study categorized the plants into three main categories—
excluders, accumulators, and indicators. Excluders play a role in the stabilization of
soil by preventing soil erosion, reducing uptake of heavy metals to critical level
(Lasat 2002). Accumulators have the potential to bioaccumulate the contaminants,
whereas indicators show the level of contamination (McGrath et al. 2002).
Hyperaccumulators are considered as subclass of accumulators which have very
high potential to accumulate the contaminants in their aboveground tissues without
14 PGPR and Earthworm-Assisted Phytoremediation of Heavy Metals
229