the immense salt concentration in wastewater (Paliwal et al. 1998; Fendri et al.
2013). A study performed by Gupta et al. (2011) in Burdwan, West Bengal,
amended mixture of industrial wastewater from Tamla drain water. This mixture
integrated with wastewater of steel plants, thermal power plants, alloy steel plants,
and also untreated sewage; it is applied to irrigation of mustard (Brassica nigra),
radish (Raphanus sativus), and Colocasia (Colocasia esculenta). As per experiment
plants respond negatively with wastewater. Amino acid content lowers in the shoot
and root of Colocasia, Brassica, and the root of Raphanus. Studies have shown that
stress induces the decline in insoluble protein and total chlorophyll contents in plants
(Hsu and Kao 2003; Rong Guo et al. 2007). The results show a slight increase in
phenol content in all three plants. An increase in phenol concentration was observed
in either stress condition or a favorable environment (Dučić et al. 2008). The other
biochemical parameter, i.e., ascorbic acid, is found to increase marginally in all
wastewater-irrigated plants than control. Ascorbic acid as an antioxidant plays an
important role in the protection against physiological stress (Guo et al. 2005).
Reactive oxygen species (ROS) are produced in plants in response to the damaging
effects of environmental stresses, and plants have evolved a variety of antioxidant
defense mechanisms in response to stress (Chow et al. 2017, 2018). An experiment
was performed at Morocco in a 3 m  2 m plot amended with 10 L crude olive mill
wastewater/m
2 for maize production. The result concluded that the release of
phenolic compound and secretion of total peroxidase activity in plants deliver an
evidence of their protective role against the physiological stress-induced treatment of
olive mill wastewater (Belaqziz et al. 2016). Thus, heavy metal accumulation shows
an increase in ascorbic acid content. The effect of toxicants varies from species to
species depending upon several factors (Singh et al. 2010) (Fig. 8.1).
8.5 Use of Agricultural Residues to Reduce Metal
Contamination
With the above discussion, it is now clear that the major challenge in using
wastewater for irrigating the agricultural fields is heavy metal contamination. Particularly, contamination of heavy metals of soil and plant system is one of the major
environmental concerns in the world due to its impact on human health
(Nkwunonwo et al. 2020). In order to reduce this problem, various remediation
options are in practice like pneumatic fracturing, vitrification, chemical reduction/
oxidation, and electrokinetics, but they are not found to be very cost-effective and
thus not environmentally sustainable techniques. Over to these techniques, there are
other cost-effective and less disturbing techniques, which can be easily applied in
metal-contaminated system to reduce heavy metal availability. For reducing the
availability, many amendments have been used such as addition of lime (Rinklebe
et al. 2015), phosphate (Shaheen et al. 2017), and organic and inorganic fertilizers.
These amendments lead to the changes in physicochemical properties of the soil
186
Monika et al.
2013). A study performed by Gupta et al. (2011) in Burdwan, West Bengal,
amended mixture of industrial wastewater from Tamla drain water. This mixture
integrated with wastewater of steel plants, thermal power plants, alloy steel plants,
and also untreated sewage; it is applied to irrigation of mustard (Brassica nigra),
radish (Raphanus sativus), and Colocasia (Colocasia esculenta). As per experiment
plants respond negatively with wastewater. Amino acid content lowers in the shoot
and root of Colocasia, Brassica, and the root of Raphanus. Studies have shown that
stress induces the decline in insoluble protein and total chlorophyll contents in plants
(Hsu and Kao 2003; Rong Guo et al. 2007). The results show a slight increase in
phenol content in all three plants. An increase in phenol concentration was observed
in either stress condition or a favorable environment (Dučić et al. 2008). The other
biochemical parameter, i.e., ascorbic acid, is found to increase marginally in all
wastewater-irrigated plants than control. Ascorbic acid as an antioxidant plays an
important role in the protection against physiological stress (Guo et al. 2005).
Reactive oxygen species (ROS) are produced in plants in response to the damaging
effects of environmental stresses, and plants have evolved a variety of antioxidant
defense mechanisms in response to stress (Chow et al. 2017, 2018). An experiment
was performed at Morocco in a 3 m  2 m plot amended with 10 L crude olive mill
wastewater/m
2 for maize production. The result concluded that the release of
phenolic compound and secretion of total peroxidase activity in plants deliver an
evidence of their protective role against the physiological stress-induced treatment of
olive mill wastewater (Belaqziz et al. 2016). Thus, heavy metal accumulation shows
an increase in ascorbic acid content. The effect of toxicants varies from species to
species depending upon several factors (Singh et al. 2010) (Fig. 8.1).
8.5 Use of Agricultural Residues to Reduce Metal
Contamination
With the above discussion, it is now clear that the major challenge in using
wastewater for irrigating the agricultural fields is heavy metal contamination. Particularly, contamination of heavy metals of soil and plant system is one of the major
environmental concerns in the world due to its impact on human health
(Nkwunonwo et al. 2020). In order to reduce this problem, various remediation
options are in practice like pneumatic fracturing, vitrification, chemical reduction/
oxidation, and electrokinetics, but they are not found to be very cost-effective and
thus not environmentally sustainable techniques. Over to these techniques, there are
other cost-effective and less disturbing techniques, which can be easily applied in
metal-contaminated system to reduce heavy metal availability. For reducing the
availability, many amendments have been used such as addition of lime (Rinklebe
et al. 2015), phosphate (Shaheen et al. 2017), and organic and inorganic fertilizers.
These amendments lead to the changes in physicochemical properties of the soil
186
Monika et al.