Lead Induced Toxicity, Detoxification and Bioremediation 193

within cytoplasm before it enters vacuoles and chloroplast, thereby minimizing the toxic effects of

Pb on the plant cell (Pourrut et al. 2013).

11.3.3 Activation of Antioxidative Defense System (ADS)

Harmful effects of Pb-induced ROS generation and oxidative stress are reciprocated by ADS

activation, which involves both enzymatic and non-enzymatic antioxidants. The activities of

several enzymes, i.e., superoxide dismutase (SOD), guaicol peroxidase (POD), catalase (CAT),

Glutathione Reductase (GR), Glutathione-S-Transferase (GST), glutathione peroxidase (GPOX),

polyphenol peroxidase (PPO), etc., is found to be upregulated in many plant species such as wheat,

rice, sunflower, mung bean, black grams and maize (Kandziora-Ciupa et al. 2013). Levels of

non-enzymatic antioxidants, including glutathione, tocopherols and ascorbic acid, have also been

reported to get enhanced significantly as their functional groups help in the sequestration of Pb by

forming stable metal-chelating complexes.

These detoxification mechanisms help in the survival of plants in Pb stressed habitats. However,

it is the need of the hour to cease human activities which introduce Pb into the environment as under

adverse conditions, even these processes may fail and hence lead to plant death.

11.4 Lead Bioremediation

Extensive reports indicate that continuous industrial, mining, urban development and overpopulation

are releasing toxic metal lead (Pb) persistently in soil flora beyond the permissible threshold value.

Being a non-biodegradable and biologically non-functional element, Pb is accountable for its toxicity

in rhizospheric flora, environment and all-living entities, resulting in consequential health issues

to human beings. Therefore, there is an urgent need to explore efficient and ecological friendly

sustainable techniques to minimize heavy metal contaminants like Pb, which are released in soil,

water, etc. The conventional physico-chemical methods such as landfill, soil incineration, chemical

precipitation, electrokinetic system, ion exchange, ultrafiltration, adsorption, etc., are effective,

but these approaches are very expensive and also generate secondary waste, that are the major

constraints for soil fertility, loss of biota and rhizospheric microbial flora (Akmal and Jianming,

2009, Li et al. 2014, Akhtar et al. 2017).

Hence, advancements in bioengineering are allowing more competitive approaches to grow

efficient, cost-effective, environment-friendly and sustainable methods for the remediation/

detoxification of non-biodegradable toxic Pb metal contaminants from the environment into

non-hazardous forms (Su 2014, Kushwaha et al. 2018). The latest researches are signifying a

sustainable bioremediation strategy for remediation of lead contaminated soil repositories either

via phytoremediation methods (using plants) or microbial remediation (via microbes) (Wuana and

Okieimen 2011, Kushwaha et al. 2018).

Bioremediation is a process where highly toxic, harmful pollutants such as Pb are transformed/

degraded to a non-reactive oxidative state or reduced to minerals via in- and ex-situ practices

(Kumar et al. 2021). Plants via the process of phytoremediation, recently played a promising role to

extract, immobilize, stabilize and transform the toxic ionization state of lead (Pb) from contaminated

sites through different processes viz. phytoextraction, phytostabilization, accumulation of toxic

compounds and rhizofiltration (Chibuike and Obiora 2014, Rigoletto et al. 2020) (Figure 11.3).

Currently, phytoremediation techniques have emerged as techniques of great interest due to their

cost-effectiveness, efficiency and environmental sustainability (Prakash et al. 2013).

Similarly, microbial communities also engage in different defensive strategies to combat fatal

toxicity by influencing the activity of Pb through siderophore, ion chelator production, biosorption,

extracellular sequestration, efflux, compartmentalization, etc. Thus, microbes and plants are

promising resolutions for sustainable development by restoring the contaminated sites of soil, water

and the environment. Next divergent bioremediation strategies by using microbes, plants, and algae

for the detoxification, stabilization and removal of lead from contaminated areas are described.