Bhatia, Mayuri and Khan, Mohammed Latif and Qureshi, Asif
(2022)
Microbial remediation of mercury-contaminated soils.
In:
Microbes and Microbial Biotechnology for Green Remediation.
Elsevier, pp. 633-649.
ISBN 978-032390452-0, 978-032390453-7
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Abstract
Microbial remediation is considered to be a green technology for in situ and ex situ remediation of contaminated environment. It helps in restoring the soil quality to its indigenous state. Increasing mercury emissions from various anthropogenic sources pose a serious health hazard and make mercury toxicity a global concern. Mercury is present in elemental, organic, and inorganic forms in the environment and has different routes to enter the human body. Mercury uptake through inhalation, dermal contact, and ingestion cause adverse health impacts such as neurotoxicity, respiratory failure, kidney and cardiovascular system damage. Mobility and transformation into various chemical forms cause mercury to transfer reversibly between soil, air, and water. In the terrestrial environment, inorganic mercury may be converted to the highly toxic organic mercury, which accumulates in the food chain. High amounts of mercury in soil can thus lead to future mobilization and contamination of aquatic environments, causing bioaccumulation and future human exposure. Additionally, contaminated soil can act as a source of mercury to the atmosphere, the emitted mercury being added to the global mercury pool and polluting downstream environments. Hence, it is desirable to treat (release from soil and capture within a controlled collection unit) soil contaminated with mercury. Treatment of mercury-contaminated soil can be performed by thermal decomposition, immobilization on bioadsorbents, containment using wetlands, phytoremediation, and microbial demethylation of organic mercury to inorganic mercury and subsequent reduction to elemental mercury which should be subsequently captured. Indigenous bacterial and fungal species have been used for microbial remediation of mercury-contaminated soils. Mercury-resistant fungal strains transport, absorb, and accumulate soil-mercury in the cells restricting mercury flow in the environment. Bacterial strains have the mer operon that reduces inorganic mercury to elemental mercury. Different classes of mer genes and gene products are involved in mercury tolerance and reduction. In some instances, plant growth-promoting bacteria present in the soil also assist in remediation indirectly by improving mercury mobility and bioavailability in soil leading to enhanced mercury uptake by plants; however, this should be performed ex situ to avoid uncontrolled losses. Microbial remediation, in general, is considered eco-friendly. This chapter reviews the current literature on applications of microbial remediation in treatment of mercury-contaminated soil, its limitations, and its potential for scale-up as a green technology. © 2022 Elsevier Inc. All rights reserved.
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