Arsenic: An Overview of Applications, Health, and Environmental Concerns and Removal Processes
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Abstract:
Arsenic is a toxic element and has been responsible for many accidental, occupational, deliberate, and therapeutic poisonings since its discovery in 1250. It occurs in natural waters as the arsenite (As3+) and arsenate (As5+) ions. The solubility of arsenite and arsenate compounds is relatively high so that these ions are readily transported through aqueous routes into the environment. Arsenic can be transferred from soils to crops and accumulates in various food crops and aquatic plants. The fascinating chemistry and toxicity potential make arsenic and its compounds of particular scientific interest and environmental concern. The conventional removal of heavy metals from wastewater, natural waters, and drinking water has only limited effects on arsenic removal. In this review, the main engineering and medical applications, salient health and environmental concerns, novel research on treatment for arsenic poisoning, and removal technologies for arsenic and their derivatives are discussed and enumerated with a view to pursue valuable applied research in order to protect the environment from arsenic toxicity.Keywords:
Arsenic toxicity
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Abstract An Anabaena oscillaroides‐bacteria assemblage, isolated from the arsenic‐rich Waikato River, was able to take up and reduce arsenate to arsenite. The assemblage growing in continuous culture with cyanophyte and bacterial densities of 4 × 105 and 6 × 105 cells ml ‐1 respectively, could reduce arsenate to arsenite at a rate of 12 ng As 106 cells‐1 d‐1. The assemblage bacteria were separated from the A. oscillaroides filaments and found to be capable of arsenate reduction to arsenite. These results provide a possible explanation for previously unexplained changes in arsenic speciation in the Waikato River, from the thermodynamically favoured arsenate to arsenite. Keywords: arsenicarsenatearsenite Anabaena oscillaroides bacteriabiogeochemistryWaikato River Notes Present address: Biotechnology Department, Massey University, Private Bag, Palmerston North, New Zealand
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The presence of arsenic (As) in soil and groundwater has become a serious environmental issue of various regions of India. A haloalkaliphilic Exiguobacterium sp. (As-9) was isolated via enrichment culture technique from an arsenic-rich soil of the Rajnandgaon district in the state of Chhattisgarh, India, and characterized as a novel arsenic removing bacteria. The isolate proved to be capable of growing over a broad range of arsenic concentration and was resistant to relatively high levels of arsenate (700 mM) and arsenite (180 mM). It displayed great potential in removing about 99% arsenic under aerobic conditions from the aqueous environment in ten days at 37°C at 100 rpm. Electron microscopy revealed a fourfold increase in the cell size due to intracellular accumulation of arsenic. Selective enzyme assays confirmed that the two intracellular enzymes, namely arsenate reductase and arsenite oxidase played a significant role in arsenate reduction and arsenite oxidation, respectively, thereby contributing to the effective removal of arsenic. These results provide evidence for the occurrence of two distinct mechanisms involved in arsenic resistance; one via arsenate reduction and the other via arsenite oxidation. Moreover, the study reports for the first time the role of arsenic transforming bacteria from this region which could resist and transform exceptionally high concentrations of arsenic oxyanions. Such metabolically active bacterial strain may find application in the treatment of arsenic contaminated soil and aquifers in the near future.
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