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Bioremediation for Sustainable Environmental Cleanup

9.6.2 Cadmium

In their analysis of 465 studies on the level of heavy metal contamination in Chinese agricultural

soils (Zhang et al. 2015); the findings revealed that heavy metals polluted around 10.18% of arable

soil, with cadmium (Cd²⁺) having the highest contamination rate at 7.75%. Through the food chain

and the soil-crop system, Cd²⁺ causes a health risk to humans (Nogawa and Kido 1996). According to

research, Cd²⁺ causes lesions on bone, renal problems and pulmonary inadequacy in people (Sharma

1995, Chakravarty et al. 2010). As a result, steps should be taken to reduce or neutralize its negative

effects in Cd-contaminated soil. To treat heavy metal-affected soils, microbial bioremediation is a

promising approach. Based on its 16s rRNA sequence and metabolic profile, a study was undertaken

in Wuhan, China (Xu et al. 2019). In which Raoultella sp. strain X13 was discovered to be a Cd­

resistant bacterium that was isolated from a heavy metal-affected soil environment in southern

China, demonstrated Cd²⁺ biosorption and bioaccumulation abilities and depicted tolerance of up

to 8 mM Cd in LB medium. As a result, strain X13 has been proven to be used as a possible Cd²⁺

immobilizing substance in contaminated soil since it promotes plant development as well as Cd²⁺

fixation. In the case of Cd²⁺ pollution, many studies have shown that metal-resilient PGP microbes

may promote plant development, improve heavy metal stability and raise plant resistance to heavy

metals (Das et al. 2014).

9.6.3 Mercury

Mercury pollution has become a global problem, more precisely in the soil environment. It is a big

problem in mercury mining locations, artisanal gold smelting areas and chlorine industrial plants,

among other places, resulting in a lot of contamination of mercury (Driscoll et al. 2013).

The mercury mining regions of Wuchuan and Wanshan in China (Qiu et al. 2006, Li et al. 2008),

Almadén, a mercury mining zone in the Amazon, are located in the heart of the region, these regions

are mercury-prone areas (Higueras et al. 2006). In Dehua, Fujian Province, China, small-scale and

artisanal gold mining activities occur, and an abandoned gold mining and smelting area (United

Nations Environment Programme 2013) are all examples of mercury-polluted locations that cause

serious ecological and environmental risks. Remediating mercury-polluted sites is an imminent

but pressing task. In an investigation carried out in Beijing, China (Xun et al. 2017), Cyrtomium

macrophyllum was naturally growing in the soil mercury region. Cyrtomium macrophyllum

demonstrated remarkable mercury accumulation and translocation capabilities (Xun et al. 2017).

9.7 Future and Prospects

Rapidly increasing industrialization and rampant development have their share of negative impacts,

such as contamination of soil and damage to soil health. The potential threat to living organisms

due to the heavy metals contamination in soil and water cannot be overlooked. Many techniques

or methods have served to reduce the risk, including many biological methods. The bioremediation

method can be used ideally for the reduction of toxicity aroused by metal contaminants in soil. It

is a safe and accommodating technique based on microbes present in soil essentially and does not

cause harmful hazards in the habitat and organisms surviving in that region (Tarekegn et al. 2020).

However, there are some limitations in the bioremediation methods, all microorganisms are not

capable of removing toxic substances and this process hinders the effects of the microbes’ activity

(Dixit et al. 2015). Heavy metals are deleterious to living beings as it is followed by accumulation in

tissues of the body that persist in the organs like kidneys, liver and bones for a longer time (Kapahi

and Sachdeva 2019).

Conventional techniques for treatment have many limitations and would be replaced by low

cost, efficient and eco-friendly methods like nature base solutions. To overcome the shortcomings,

the need of the hour is to utilize advanced techniques like bioremediation that either chemically

converts these compounds into less harmful products or degrades them together. Bioremediation