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"Arsenic Biodegradation."
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Arsenic contamination in the environment : the issues and solutions
This book provides an overview to researchers, graduate, and undergraduate students, as well as academicians who are interested in arsenic. It covers human health risks and established cases of human ailments and sheds light on prospective control measures, both biological and physico-chemical. Arsenic (As) is a widely distributed element in the environment having no known useful physiological function in plants or animals. Historically, this metalloid has been known to be used widely as a poison. Effects of arsenic have come to light in the past few decades due to its increasing contamination in several parts of world, with the worst situation being in Bangladesh and West Bengal, India. The worrying issue is the ingestion of arsenic through water and food and associated health risks due to its carcinogenic and neurotoxic nature. The impact of the problem is widespread, and it has led to extensive research on finding both the causes and solutions. These attempts have allowed us to understand the various probable causes of arsenic contamination in the environment, and at the same time, have provided a number of possible solutions. It is reported that more than 200 mineral species contain As. Generally, As binds with iron and sulfur to form arsenopyrite. According to one estimate from the World Health Organization (WHO), contextual levels of As in soil ranges from 1 to 40 mg kg-1. Arsenic toxicity is related to its oxidation state which is present in the medium. As is a protoplastic toxin, due to its consequence on sulphydryl group it interferes in cell enzymes, cell respiration and in mitosis. Exposure of As may occur to humans via several industries, such as refining or smelting of metal ores, microelectronics, wood preservation, battery manufacturing, and also to those who work in power plants that burn arsenic-rich coal.
Book
Efficient removal of arsenic (V) and methyl orange from aqueous solution using hollow magnetic chitosan composite microspheres: Low arsenic concentration, high adsorption capacity, and minimal adsorbent requirement
In this study, hollow Fe3O4-SiO2-chitosan adsorbent with an optimal chitosan concentration of 2% (w/v) was synthesized to enhance arsenic (V) adsorption performance from low-concentration aqueous solutions. The hollowing process was used to enhance the surface area of the adsorbent and compensate for the surface area reduction of Fe3O4 nanoparticles induced by SiO2 and chitosan coating layers. Furthermore, the adsorption properties of organic pollutants were evaluated using methyl orange as the adsorbate. The microspheres underwent systematic characterization, and their arsenic (V) and methyl orange adsorption capacities were evaluated under various influencing factors. The results indicated improved surface area (202.174 m2/g) compared to non-hollow magnetic adsorbents (110 m2/g) reported in previous studies. Complete arsenic (V) removal (100%) was achieved within 60 minutes at a concentration of 0.2 mg/L, using an adsorbent dose of 0.012 g at pH 5. The optimal adsorbent doses for methyl orange (0.1 g/L) and arsenic (V) (0.5 g/L) were notably lower than those reported in previous studies. The electrostatic attraction was likely the dominant mechanism for arsenic (V) adsorption, whereas methyl orange adsorption may involve n-π interactions, hydrogen bonding, and electrostatic forces. The adsorption process followed the pseudo-second-order kinetics model and the Langmuir isotherm, with maximum adsorption capacities of 175.086 mg/g for arsenic (V) at pH 5 and 2399.910 mg/g for methyl orange at pH 3. The adsorbent showed significant potential for removing arsenic (V) and methyl orange, particularly from acidic wastewater. Moreover, the adsorbent maintained significant portion of its initial adsorption capacity for As(V) and methyl orange even in the presence of competing anions such as phosphate, sulfate, chloride, and nitrate. After four adsorption-desorption cycles, it retained over 90% of its adsorption capacity, demonstrating excellent selectivity, stability, and strong potential for the effective removal of both As(V) and methyl orange from aqueous solutions.
Journal Article
Isothermal and Kinetics Modeling Approach for the Bioremediation of Potentially Toxic Trace Metal Ions Using a Novel Biosorbent Acalypha wilkesiana (Copperleaf) Leaves
The presence of trace metals in wastewater brings serious environmental pollution that threatens human health as well as the ecosystem throughout the world due to their non-biodegradability nature. The present study focuses on the bioremediation of toxic trace metals, namely arsenic (As), cadmium (Cd), and chromium (Cr), using
Acalypha wilkesiana
leaf raw biomass. The optimization of various process variables was done to determine the removal percentage of trace metal using
Acalypha wilkesiana
leaf raw biomass, and the optimum conditions were an adsorbent dose of 0.5 g, contact time 10 h, 8 h, and 10 h, process temperature 30 °C, initial concentration of trace metal as 30 µg/L, 30 mg//L, and 40 mg/L, and pH of 7.5, 7 and 7.5 for As
5+
, and Cd
2+
and Cr
6+
, respectively.
Acalypha wilkesiana
leaf raw biomass is characterized using a scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier transformation infrared spectroscopy (FTIR), zeta potential before and after adsorption of the trace metal ions. The study was well fitted for the equilibrium data for Langmuir isotherm for As
5+
, Cd
2+
, and Cr
6+
, Freundlich for As
5+
, Dubinin-Radushkevinch (D-R) for Cr
6+
, and Temkin for As
5+
and Cr
6+
. The adsorption of all three trace metals was confirmed by the kinetics and thermodynamic studies to be following pseudo-second-order kinetics with endothermic as well as spontaneous processes, respectively. Thus, the present study indicates
Acalypha wilkesiana
leaf raw biomass as an effective and efficient novel biosorbent to remediate different trace metals from aqueous systems with its possible application in existing and novel methods for wastewater management.
Journal Article
Synthetic bacteria designed using ars operons: a promising solution for arsenic biosensing and bioremediation
The global concern over arsenic contamination in water due to its natural occurrence and human activities has led to the development of innovative solutions for its detection and remediation. Microbial metabolism and mobilization play crucial roles in the global cycle of arsenic. Many microbial arsenic-resistance systems, especially the
ars
operons, prevalent in bacterial plasmids and genomes, play vital roles in arsenic resistance and are utilized as templates for designing synthetic bacteria. This review novelty focuses on the use of these tailored bacteria, engineered with
ars
operons, for arsenic biosensing and bioremediation. We discuss the advantages and disadvantages of using synthetic bacteria in arsenic pollution treatment. We highlight the importance of genetic circuit design, reporter development, and chassis cell optimization to improve biosensors’ performance. Bacterial arsenic resistances involving several processes, such as uptake, transformation, and methylation, engineered in customized bacteria have been summarized for arsenic bioaccumulation, detoxification, and biosorption. In this review, we present recent insights on the use of synthetic bacteria designed with
ars
operons for developing tailored bacteria for controlling arsenic pollution, offering a promising avenue for future research and application in environmental protection.
Graphical abstract
Journal Article
Bacterial Arsenic Metabolism and Its Role in Arsenic Bioremediation
Arsenic contaminations, often adversely influencing the living organisms, including plants, animals, and the microbial communities, are of grave apprehension. Many physical, chemical, and biological techniques are now being explored to minimize the adverse affects of arsenic toxicity. Bioremediation of arsenic species using arsenic loving bacteria has drawn much attention. Arsenate and arsenite are mostly uptaken by bacteria through aquaglycoporins and phosphate transporters. After entering arsenic inside bacterial cell arsenic get metabolized (e.g., reduction, oxidation, methylation, etc.) into different forms. Arsenite is sequentially methylated into monomethyl arsenic acid (MMA) and dimethyl arsenic acid (DMA), followed by a transformation of less toxic, volatile trimethyl arsenic acid (TMA). Passive remediation techniques, including adsorption, biomineralization, bioaccumulation, bioleaching, and so on are exploited by bacteria. Rhizospheric bacterial association with some specific plants enhances phytoextraction process. Arsenic-resistant rhizospheric bacteria have immense role in enhancement of crop plant growth and development, but their applications are not well studied till date. Emerging techniques like phytosuction separation (PS-S) have a promising future, but still light to be focused on these techniques. Plant-associated bioremediation processes like phytoextraction and phytosuction separation (PS-S) techniques might be modified by treating with potent bacteria for furtherance.
Journal Article
Evaluation of arsenic-Tolerant plant growth-promoting rhizobacteria from Manipur for mitigating arsenic translocation and enhancing growth in rice (Oryza sativa)
Arsenic (As) contamination in paddy fields poses a serious risk to food safety by promoting arsenic accumulation in rice. This study evaluates the bioremediation potential of two arsenic-tolerant plant growth-promoting rhizobacteria (PGPR)—
Bacillus paramycoides
TNCB-27 and
Pseudomonas shirazica
TNB-16—isolated from agricultural soils in Thoubal, Manipur, India. Greenhouse experiments were conducted to assess their effects on arsenic uptake, translocation, and rice plant growth under arsenite [As(III)]- and arsenate [As(V)]- spiked conditions. Inoculated plants showed significantly reduced arsenic levels in shoots, likely due to enhanced root sequestration and microbial transformation of arsenic, as indicated by lower translocation factors. Morphological alterations in bacterial cells post-arsenic exposure were observed via scanning and transmission electron microscopy (SEM, TEM). Fourier transform infrared spectroscopy (FTIR) revealed changes in bacterial functional groups and exopolysaccharides, suggesting their role in arsenic binding. This is the first report on PGPR from Manipur demonstrating both arsenic remediation and plant growth-promoting abilities, offering a sustainable microbial approach to reduce arsenic bioavailability and accumulation in rice agroecosystems.
Journal Article
Adverse effect of heavy metals (As, Pb, Hg, and Cr) on health and their bioremediation strategies: a review
Currently, heavy metal pollution becomes a severe problem whole over the world, and these toxic metals enter into the environment either by natural phenomena or due to extensive industrialization. The discharged effluents containing toxic heavy metals mixed with soil/water and change their natural composition. These heavy metals have adverse effects on living beings and cause damage to the vital body organs of animals as well as humans. The heavy metal pollution also inhibits the biodegradation of the chlorinated organic compounds (another type of environmental pollution) by interacting with metabolizing enzymes and inhibits their functioning. Earlier studies described that heavy metals cannot be fully removed from the environment, but they can be effectively neutralized or transformed into less toxic form so that their harmful effect on the environment can be reduced. The distinctive enzymatic apparatus within microbial system plays a major role in the transformation of heavy metals in the environment. A considerable advancement has been made during recent years to transform the heavy metals by utilizing the bioremediation potential of genetically engineered (GE) microorganisms. These transgenics are very much efficient in heavy metal transformations and still, we have to discover more to additionally utilize their full biotransformation potential. In the present review article, the detailed description of the adverse effects of four heavy metals (arsenic, lead, mercury, and chromium) and their adverse effect on our environment and human beings is discussed. Furthermore, the use of microorganisms/GE organisms for the bioremediation of heavy metals from the environment is also discussed along with their detailed bioremediation mechanism
Journal Article
Speciation of Arsenic in Medium Containing Bacterial Strains of Lysinibacillus boronitolerans and Bacillus cereus: Mechanism of Arsenic Removal
Environmental issues have become increasingly critical and frequent in recent decades due to excessive population growth and intensified industrial and mining activities. Among the most concerning contaminants is arsenic (As), a toxic element associated with severe environmental and human health risks. This study aimed to investigate the bioremediation potential of the bacterial strains Lysinibacillus boronitolerans and Bacillus cereus, elucidating the mechanisms involved in arsenic transformation and removal under controlled conditions. The strains were cultivated in liquid medium containing known concentrations of As(III) and As(V), and the chemical forms of arsenic were analyzed using High-Performance Liquid Chromatography coupled with Inductively Coupled Plasma Mass Spectrometry (LC-ICP-MS). The production of exopolysaccharides (EPSs) and arsenite oxidase activity were also evaluated. Morphological and elemental analyses were performed using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). The bacterial strains exhibited significant 69.38–85.72% reductions in arsenic concentration and approximately 14–15% volatilization rates. No EPS production or arsenite oxidase activity was detected, suggesting alternative detoxification pathways. SEM-EDS analyses revealed intracellular accumulation of arsenic, while LC-ICP-MS speciation confirmed interconversion between As(III) and As(V), indicating the action of methylation-dependent detoxification and membrane transport mechanisms. The findings demonstrate that L. boronitolerans and B. cereus possess efficient arsenic resistance and transformation mechanisms, even without conventional enzymatic pathways. These strains show strong potential for use in sustainable bioremediation of arsenic-contaminated environments, particularly in regions affected by mining activities.
Journal Article
Genetic basis and importance of metal resistant genes in bacteria for bioremediation of contaminated environments with toxic metal pollutants
Metal pollution is one of the most persistent and complex environmental issues, causing threat to the ecosystem and human health. On exposure to several toxic metals such as arsenic, cadmium, chromium, copper, lead, and mercury, several bacteria has evolved with many metal-resistant genes as a means of their adaptation. These genes can be further exploited for bioremediation of the metal-contaminated environments. Many operon-clustered metal-resistant genes such as cadB, chrA, copAB, pbrA, merA, and NiCoT have been reported in bacterial systems for cadmium, chromium, copper, lead, mercury, and nickel resistance and detoxification, respectively. The field of environmental bioremediation has been ameliorated by exploiting diverse bacterial detoxification genes. Genetic engineering integrated with bioremediation assists in manipulation of bacterial genome which can enhance toxic metal detoxification that is not usually performed by normal bacteria. These techniques include genetic engineering with single genes or operons, pathway construction, and alternations of the sequences of existing genes. However, numerous facets of bacterial novel metal-resistant genes are yet to be explored for application in microbial bioremediation practices. This review describes the role of bacteria and their adaptive mechanisms for toxic metal detoxification and restoration of contaminated sites.
Journal Article
Arsenic-induced enhancement of diazotrophic recruitment and nitrogen fixation in Pteris vittata rhizosphere
Heavy metal contamination poses an escalating global challenge to soil ecosystems, with hyperaccumulators playing a crucial role in environmental remediation and resource recovery. The enrichment of diazotrophs and resulting nitrogen accumulation promoted hyperaccumulator growth and facilitated phytoremediation. Nonetheless, the regulatory mechanism of hyperaccumulator biological nitrogen fixation has remained elusive. Here, we report the mechanism by which arsenic regulates biological nitrogen fixation in the arsenic-hyperaccumulator
Pteris vittata
. Field investigations and greenhouse experiments, based on multi-omics approaches, reveal that elevated arsenic stress induces an enrichment of key diazotrophs, enhances plant nitrogen acquisition, and thus improves plant growth. Metabolomic analysis and microfluidic experiments further demonstrate that the upregulation of specific root metabolites plays a crucial role in recruiting key diazotrophic bacteria. These findings highlight the pivotal role of nitrogen-acquisition mechanisms in the arsenic hyperaccumulation of
Pteris vittata
, and provide valuable insights into the plant stress resistance.
Elevated arsenic is found to enhance plant nitrogen acquisition and plant growth of the arsenic hyperaccumulator
Pteris vittate
. Multi-omics analysis reveals the interaction between root metabolites and key diazotrophs underlying this effect.
Journal Article