Abstract
Arsenic (As) pollution in drinking water and soils poses a threat to over 100 million people worldwide, making it one of the largest environmental catastrophes particularly in Bangladesh and West Bengal- where more than one-third of the population are at risk. Microbial As metabolism and mobilization in aqua system is relatively a recent issue.The presence of the arsenic oxidation, reduction, and extrusion genes (aioA, arrA, arsB, and acr3) are explored within microorganisms retrieved from As-contaminated environments. However, the nature of microbiome involved within a certain As transformation environment is still an area of research, specifically how microbial redox transformations occur, that can be exploited to mitigate the longstanding problem. The present chapter overviews the mechanism of As pollution in various environment, microbial diversity in such environment, correlation of their activities to the biogeochemistry of As and finally application of microbes as a bioremediation tool for As detoxification and bioremediation.
TopArsenic exists in the environment mainly in four oxidation states, As(-3) (arsine), As(0) (native or elemental arsenic), As(+3) (arsenite) and As(+5) (arsenate). The first two forms are relatively rare, whereas arsenite and arsenate are the two main forms occurring in aquatic environments (Lièvremont, Bertin, & Lett, 2009). Both biological and chemical parameters especially the redox potential (Eh) and the pH are important for the stability, speciation and distribution of arsenite [As(III)] and arsenate [As(V)] in the environment. As(V) is predicted to be thermodynamically stable form at Eh values > ca. -100 mV at pH 8.0, and > 300 mV at pH 4.0. Below those redox potentials, As(III) is the thermodynamically stable oxidation state, present either as H3AsO30 species, as As-S complexes (e.g. H2As3S6-) or as As(III) solid phases such as As2S3(Inskeep, McDermott, & Fendorf, 2002) (Figure 1). Due to various pKa values of arsenate (H3AsO4) (pKa1 = 2.19, pKa2 = 6.94 and pKa3 = 11.5), the H2AsO-4 form predominates in oxidizing environment with pH between 2.5 and ca. 7.0, whereas the HAsO42- is the predominant form of As(V) between pH 7.0 and 11.0. For arsenite, the lowest pKa value is equal to 9.22. So, H3AsO30 is the predominant form of As(III) in slightly reductive environments with a pH level below 9.2 (Figure 1)
Key Terms in this Chapter
Toxicology: Toxicology studies the harmful effects of chemical, biological and physical agents in biological systems that establish the extent of damage in living organisms.
Microbial Detoxification: Microbial detoxification is the neutralization of the toxic substances by using various novel enzymes.
Metalloid: A metalloid is a chemical element AU382: The URL http://en.wikipedia.org/wiki/Chemical_element has been redirected to https://en.wikipedia.org/wiki/Chemical_element. Please verify the URL. with properties in between, or that are a mixture of, those of metals AU383: The URL http://en.wikipedia.org/wiki/Metal has been redirected to https://en.wikipedia.org/wiki/Metal. Please verify the URL. and nonmetals AU384: The URL http://en.wikipedia.org/wiki/Nonmetal has been redirected to https://en.wikipedia.org/wiki/Nonmetal. Please verify the URL. .
Bacterial Community: The composition and interaction of bacterial populations and the abundance of its members.
Bioremediation: Bioremediation is a waste management system that involves the use of organisms to remove or neutralize pollutants from a contaminated site.
Environmental Pollution: Environmental pollution is the introduction of contaminants AU381: The URL http://en.wikipedia.org/wiki/Contaminant has been redirected to https://en.wikipedia.org/wiki/Contaminant. Please verify the URL. into the natural environment that causes adverse change.
Arsenic Metabolism: Arsenic metabolism is the set of life AU378: The URL http://en.wikipedia.org/wiki/Life has been redirected to https://en.wikipedia.org/wiki/Life. Please verify the URL. -sustaining chemical transformations AU379: The URL http://en.wikipedia.org/wiki/Chemical_reactions has been redirected to https://en.wikipedia.org/wiki/Chemical_reactions. Please verify the URL. of As within the cells of living organisms AU380: The URL http://en.wikipedia.org/wiki/Organisms has been redirected to https://en.wikipedia.org/wiki/Organisms. Please verify the URL. .