Physical and chemical properties of arsenic pdf
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- Arsenic, Physical and Chemical Properties
- Arsenic Metal
- Physical, Chemical, and Biological Methods for the Removal of Arsenic Compounds
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Lim, M. Shukor, H. Arsenic is a toxic metalloid which is widely distributed in nature. It is normally present as arsenate under oxic conditions while arsenite is predominant under reducing condition. The major discharges of arsenic in the environment are mainly due to natural sources such as aquifers and anthropogenic sources. It is known that arsenite salts are more toxic than arsenate as it binds with vicinal thiols in pyruvate dehydrogenase while arsenate inhibits the oxidative phosphorylation process.
The common mechanisms for arsenic detoxification are uptaken by phosphate transporters, aquaglyceroporins, and active extrusion system and reduced by arsenate reductases via dissimilatory reduction mechanism.
Some species of autotrophic and heterotrophic microorganisms use arsenic oxyanions for their regeneration of energy. Certain species of microorganisms are able to use arsenate as their nutrient in respiratory process.
Detoxification operons are a common form of arsenic resistance in microorganisms. Hence, the use of bioremediation could be an effective and economic way to reduce this pollutant from the environment. The intrusion of orogenesis and granitic magma have resulted in the formation of arsenopyrite [ 1 ].
Arsenic was first discovered by Albertus Magnus in the year [ 3 ]. Under natural condition, arsenic normally cycled at the earth surface where the breakdown of rocks has converted arsenic sulfides into arsenic trioxide [ 2 , 4 ].
Furthermore, arsenic is known to have multiple oxidation states where they are present in either organic or inorganic compounds in an aquatic environment [ 5 , 6 ]. Both Zobrist et al. It is known that ferric iron phase plays an important role for the sorption of dissolved arsenate in oxic groundwater [ 8 ].
Meanwhile, the reduction of arsenate into arsenite in the transition from aerobic to anoxic pore waters is often mediated by microbial activity, which includes detoxification and metabolic mechanisms [ 8 ].
In another study, Saalfield and Bostick [ 9 ] proposed that the presence of calcium and bicarbonate from the byproducts of biological processes in the aquifers will enhance the release of arsenic and the correlations between calcium and bicarbonate with arsenic were then observed. Of the two oxidation states, arsenate is the main species associated with soil arsenic contaminations, and it is often written as which is very similar to phosphate [ 11 , 12 ].
Arsenate could act as a potential oxidative phosphorylation inhibitor. This is a cause for concern since oxidation phosphorylation is the main key reaction of energy metabolism in humans and metazoans [ 4 ]. Arsenite has been reported as the most toxic and soluble form of arsenic when compared to arsenate, and it can bind with reactive sulfur atoms present in many enzymes, including enzymes which are involved in respiration [ 4 , 13 ]. Furthermore, it is known that soluble inorganic arsenic is often more toxic than the organic form [ 2 ].
Unlike arsenate and arsenite, arsine is often available as highly toxic gases such as CH 3 3 and H 3 As and often present at low concentration in the environment [ 4 ]. Meanwhile, the average concentration of arsenic in fresh water is around 0. However, the thermal activity in some places has caused high level of arsenic in waters with the concentration of arsenic in geothermal water in Japan ranging from 1.
On the other hand, the concentration of arsenic in plants is solely depending on the amount of arsenic that the plant is being exposed to where the concentration of arsenic could range from less than 0. Unlike plant, the concentration of arsenic in marine organisms and mammals has a wide range of variations ranging from 0.
Presence of humic acid in the shallow subsurface could affect the mobility of arsenic since humic acid could interact with aqueous arsenic for the formation of stable colloidal complexes that might play a prominent role in the enhancement of arsenic mobility. Furthermore, the combination of humic acid together with ferric hydroxide surface will lead to the formation of stable complexes that would compete with arsenic for its adsorption sites [ 32 ]. The first usage of arsenic in medicine could be dated around years ago where it was mainly consumed for the improvement of breathing problems as well as to give freshness, beauty, and plumpness figures in women [ 2 ].
Arsenic in the form of arsenical salvarsan arsenic containing drug was the initial antimicrobial agent used in the treatment of infectious diseases such as syphilis and sleeping sickness in [ 3 ]. This drug was specifically developed by Sahachiro Hata under the guidance of Paul Ehrlich in where they named the drug as arsphenamine no.
Meanwhile, arsenic in the form of arsenic trioxide As 2 O 3 is one of the most common forms of arsenic, which is often used in manufacturing and agriculture industry and for medical purposes such as in the treatment of acute promyelocytic leukemia [ 34 ]. Arsenic trioxide is also proven to be useful in criminal homicides due to its characteristic, which is tasteless, colorless, highly toxic, and soluble in water [ 2 , 4 ].
Arsenic was also used as cotton desiccants and wood preservatives in United States [ 2 ]. The usage of arsenic as the cotton desiccant was introduced around year and was widely used due to its effectiveness and affordable price [ 36 ]. Besides that, arsenic was also being used in ceramic and glass industry, pharmaceutical industry, and food additives as well as pigments in paint [ 13 , 34 ].
Meanwhile, arsenic in the form of 4-aminoben-zenearsenic acid p-arsenilic acid, p-ASA has been used as animals food additive for feeding of boiler chickens [ 37 ].
It has been noticed that the extensive usage of arsenic in the industrial and agrochemical applications is of few causes of groundwater and sediment arsenic contamination in the environment [ 6 , 38 ] in which effects are much smaller compared to the natural causes [ 39 ]. The presence of arsenic in soil and water has become an increasing problem in many countries around the world, including Bangladesh, India, Chile, and Taiwan [ 2 , 40 , 41 ], and natural geological source is one of the main causes of contamination [ 34 ].
Consumption of drinking water that has been contaminated by hazardous level of arsenic will lead to a wide range of diseases such as arsenic dermatosis, lung cancer, liver cancer, uterus cancer, skin cancer and occurrence of skin, and bladder and hepatocellular carcinoma that will result in slow and painful death [ 1 , 2 , 41 — 43 ].
In Southwestern Taiwan, the human consumption of artesian well waters which contains high concentration of arsenic has also led to Blackfoot disease, which is an endemic peripheral vascular disease in that area [ 40 ]. In China, up to the year , 19 provinces had been found to have As concentration in drinking water exceeding the standard level 0. Deltaic plain contaminated groundwater of Ganges-Meghna-Brahmaputra rivers in Bangladesh and West Bengal had resulted in an alarming environmental problem as this water is often consumed by people who live in that area [ 6 , 45 ].
The presence of aqueous arsenic is mainly due to rock weathering as well as sediment deposition and downstream transport of rich mineral arsenic that was originally present in Himalayas [ 4 ]. Massive constructions of wells which are meant to supply an improved quality of water with waterborne pathogens free to the people living in this area had created another problem as the ground water in that area was arsenic contaminated [ 4 ].
In Nepal, arsenic As contamination was a major issue in water supply drinking systems especially in high density population such as Terai districts. The local inhabitants still use hand tube and dug wells with hand held pumps that are bored at shallow to medium depth for their daily water requirements [ 46 ].
Recent status from over , samples tested has shown that 7. The symptoms of acute arsenic poisoning are vomiting, abdominal pain, diarrhea, and cramping, which will then cause renal failure, haematological abnormalities such as leukemia and anemia, pulmonary oedema, and respiratory failure, and it could further lead to shock, coma, and death [ 1 , 2 , 34 ].
In another study, Lai et al. Arsenic contamination from industrial sources has also led to skin manifestation of chronic arsenic poisoning, which affected On the other hand, arsenic poisoning caused by ingestion of food especially seafood product and beverages contaminated by arsenic has been reported in Japan, England, Germany, and China [ 2 ]. In Campinas, Brazil, samples of seafood used for sashimi making from Japanese restaurants have been evaluated for the presence of As [ 49 ]. It was concluded that the octopus was the sashimi which most contributed to arsenic.
In other case, the arsenic concentration in rice was found to be high in Bangladesh [ 50 ]. Phosphate fertilization is suggested to lower the arsenate uptake in plants because both compounds enter the rice via the same transporter. Presence of over 1. Significant correlation was also observed with levels in human urine, toenail, and hair samples [ 31 ].
Arsenic uptake is adventitious because arsenate and arsenite are chemically similar to the required nutrients [ 53 ]. At neutral pH, the trivalent forms of these metalloids are structurally similar to glycerol, and hence they can enter cells through aquaporins [ 54 ].
Technologies for removing arsenic from the environment should meet several basic technical criteria that include robustness, no other side effect on the environment, and the ability to sustain water supply systems for long terms and meet the quality requirement of physical chemical, and microbiological approaches [ 1 ].
Currently, there are many methods for removing arsenic from the soil contaminated with arsenic, which could be divided into three categories, including physical, chemical, and biological approaches [ 14 ]. In the physical approaches, the concentration of arsenic in soil could be reduced by mixture of both contaminated and uncontaminated soils together that will lead to an acceptable level of arsenic dilution [ 14 ]. Soil washing is another method which is grouped under physical approaches whereby arsenic contaminated soil will be washed with different concentration of chemicals such as sulfuric acid, nitric acid, phosphoric acid, and hydrogen bromide [ 14 ].
The choice of chemicals used for extractant and high cost have often restricted the usage of soil washing into a smaller-scale operations as it is the disadvantages of using soil washing method [ 14 ]. Meanwhile, cement can immobilise soluble arsenites and has been successfully used to stabilise As-rich sludges which may be suitable for treating sludges generated from precipitative removal units [ 15 ].
In this process, brine resulting from the regeneration of activated alumina filters is likely to accelerate cement hydration. Furthermore, additives surfactants, cosolvents, etc. It often gives moderate efficiencies by using only one product surfactant, cosolvent, and cyclodextrin. On the other hand, the use of more complex methods with polymer injection leads to higher efficiencies [ 16 ].
The current available chemical remediation approaches mainly involving methods such as adsorption by using specific media, immobilization, modified coagulation along with filtration, precipitations, immobilizations, and complexation reactions [ 1 , 14 ]. The formation of stable phases, for example, insoluble FeAsO 4 and hydrous species of this compound such as scorodite, FeAsO 4 2H 2 O , is beneficial for the stabilization procedure [ 17 ].
Furthermore, the use of selective stabilizing amendments is a challenging task as the majority of polluted sites are contaminated with multiple metal loid s. It is reported that chemical remediation gained popularity because of its high success rate, but it could be expensive when someone would like to remediate a large area [ 14 ].
In contrast, biological remediation or bioremediation of soils contaminated with either inorganic or organic arsenic present in pesticides and hydrocarbons have been widely accepted in some places [ 14 ]. Even though bioremediation suffers several limitations, these approaches have been gaining interest for the remediation of metal loid contaminated soils due to their cost effectiveness [ 14 ]. Basically, bioremediation technology could be divided into subcategories: intrinsic bioremediation and engineered bioremediation [ 14 ].
Intrinsic bioremediation is generally referred to as the degradation of arsenic by naturally occurring microorganisms without intervention by human, and this method is more suitable for remediation of soil with a low level of contaminants [ 14 ]. Engineered bioremediation often relies on intervention of human for optimizing the environment conditions to promote the proliferation and activity of microorganisms that lived in that area.
As a result, the usage of engineered bioremediation method is more favorable in the highly contaminated area [ 14 ]. Mechanism for arsenic detoxification can be divided into four which known as uptake of As V in the form of arsenate by phosphate transporters, uptake of As III in the form of arsenite by aquaglyceroporins, reduction of As V to As III by arsenate reductases, and extrusion or sequestration of As III [ 57 ].
AQPs have been shown to facilitate diffusion of arsenic [ 53 , 54 ]. The microbial oxidation of As in Altiplano basins rivers in northern Chile was demonstrated by Leiva et al. In situ oxidation experiments demonstrated that the As oxidation required a biological activity, and microbiological molecular analysis had confirmed the presence of As III -oxidizing groups aro A-like genes in the system.
In addition, the pH measurements and solid phase analysis strongly suggest that As removal mechanism must involve adsorption or coprecipitation with Fe-oxyhydroxides. Taken together, these results indicated that the microorganism-mediated As oxidation contributed to the attenuation of As concentrations and the stabilization of As in the solid phase, therefore controlling the amount of As transported downstream [ 20 ].
Since most of the cases of arsenic poisoning are due to the consumption of water contaminated by arsenic, the process of cleaning up or reducing arsenic concentration in water becomes very important. Methods used in reducing arsenic levels in water are primarily divided into i physiochemical methods, which include filtration or coagulation sedimentation, osmosis or electrodialysis, adsorptions, and chemical precipitations and ii biological methods such as phytoremediation by using aquatic plants or microbial detoxification of arsenic [ 14 ].
Generally, two approaches are mainly employed in the phytoremediation method. The second approach uses aquatic rooted plants i.
Yang et al. Two important processes in the removal of arsenic from water by microorganisms are biosorption and biomethylation [ 14 ]. It is reported that biomethylation by As III S -adenosylmethionine methyltransferase is the reliable biological process for removing arsenic from aquatic media [ 14 ]. Recently, the arsenite As III S -adenosylmethionine methyltransferase ArsM gene has been inserted into the chromosome of Pseudomonas putida KT for potential bioremediation of environmental arsenic [ 59 ].
The first structure of As III S -adenosylmethionine methyltransferase by X-ray crystallography was described by [ 60 ]. In this enzyme, there are three conserved cysteine residues at positions 72, , and in the CmArsM orthologue from the thermophilic eukaryotic alga Cyanidioschyzon sp.
Arsenic, Physical and Chemical Properties
Arsenic appears in three allotropic forms: yellow, black and grey; the stable form is a silver-gray, brittle crystalline solid. It tarnishes rapidly in air, and at high temperatures burns forming a white cloud of arsenic trioxide. Arsenic is a member of group Va of the periodic table , which combines readily with many elements. The metallic form is brittle, tharnishes and when heated it rapidly oxidizes to arsenic trioxide, which has a garlic odor. The non metallic form is less reactive but will dissolve when heated with strong oxidizing acids and alkalis.
NCBI Bookshelf. Arsenic, Metals, Fibres and Dusts. Since that time, new data have become available, these have been incorported in the Monograph , and taken into consideration in the present evaluation. Information on the physical and chemical properties of arsenic and arsenic compounds can be found in Table 1. The list is not exhaustive, nor does it comprise necessarily the most commercially important arsenic-containing substances; rather, it indicates the range of arsenic compounds available.
Metrics details. Field-based research on naturally occurring arsenic contamination of surface waters and groundwaters and the mechanisms of contamination are reviewed. The distribution of arsenic is strongly related to areas of active plate tectonics, magmatism and associated hydrothermal activity, and high rates of erosion. The promotion of the reduction and oxidation of arsenic source minerals by in situ microbial activity is an important secondary mechanism that often determines arsenic levels in groundwater. Anthropogenic activities, such as geothermal and mining operations, as well as excess pumping of shallow groundwaters, disperse arsenic in the environment, thereby expanding areas of arsenic contamination. Human beings are facing a crisis of an increasing demand for freshwater in the face of decreasing freshwater resources.
Information on the physical and chemical properties of arsenic and arsenic at tcl-toulon.org and.
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Arsenic occurs in many minerals, usually in combination with sulfur and metals , but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes , but only the gray form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead for example, in car batteries and ammunition. Arsenic is a common n-type dopant in semiconductor electronic devices.
Physical, Chemical, and Biological Methods for the Removal of Arsenic Compounds
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Arsenic As , a chemical element in the nitrogen group Group 15 [Va] of the periodic table , existing in both gray and yellow crystalline forms. Arsenic was known in the form of certain of its compounds long before it was clearly recognized as a chemical element. In the 4th century bce Aristotle wrote of a substance called sandarache, now believed to have been the mineral realgar , a sulfide of arsenic.