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It occurs in trace quantities in all rock, soil, water and air. Arsenic can exist in four valency states: Under reducing conditions, arsenite As III is the dominant form; arsenate As V is generally the stable form in oxygenated environments.

Elemental arsenic is not soluble in water. Arsenic salts exhibit a wide range of solubilities depending on pH and the ionic environment.

There is a variety of instrumental techniques for the determination of arsenic. Some of these e. ICP-MS can serve as element-specific detectors when coupled to chromatographic separation techniques e. These so-called "hyphenated" methods are used for determining individual arsenic species.

Additional sensitivity for a limited range of arsenic compounds can often be achieved by the use of hydride generation techniques.

martin millward technical editing services

It has been estimated that about one-third of the atmospheric flux of arsenic is of natural origin. Volcanic action is the most important natural source of arsenic, followed by low-temperature volatilization.

Inorganic arsenic of geological origin is found in groundwater used as drinking-water in several parts of the world, for example Bangladesh.

Organic arsenic compounds such as arsenobetaine, arsenocholine, tetramethylarsonium salts, arsenosugars and arsenic-containing lipids are mainly found in marine organisms although some of these compounds have also been found in terrestrial species.

Elemental arsenic is produced by reduction of arsenic trioxide As2O3 with charcoal. As2O3 is produced as a by-product of metal smelting operations. Mining, smelting of non-ferrous metals and burning of fossil fuels are the major industrial processes that contribute to anthropogenic arsenic contamination of air, water and soil.

Historically, use of arsenic-containing pesticides has left large tracts of agricultural land contaminated. The use of arsenic in the preservation of timber has also led to contamination of the environment.

Natural low-temperature biomethylation and reduction to arsines also releases arsenic into the atmosphere. Arsenic is released into the atmosphere primarily as As2O3 and exists mainly adsorbed on particulate matter.

These particles are dispersed by the wind and are returned to the earth by wet or dry deposition.

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Arsines released from microbial sources in soils or sediments undergo oxidation in the air, reconverting the arsenic to non-volatile forms, which settle back to the ground. Dissolved forms of arsenic in the water column include arsenate, arsenite, methylarsonic acid MMA and dimethylarsinic acid DMA.

In well-oxygenated water and sediments, nearly all arsenic is present in the thermodynamically more stable pentavalent state arsenate.

Some arsenite and arsenate species can interchange oxidation state depending on redox potential EhpH and biological processes. Some arsenic species have an affinity for clay mineral surfaces and organic matter and this can affect their environmental behaviour.

There is potential for arsenic release when there is fluctuation in Eh, pH, soluble arsenic concentration and sediment organic content. Weathered rock and soil may be transported by wind or water erosion. Many arsenic compounds tend to adsorb to soils, and leaching usually results in transportation over only short distances in soil.Star Trek () cast and crew credits, including actors, actresses, directors, writers and more.

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1. SUMMARY Properties and analytical procedures. Arsenic is a metalloid widely distributed in the earth’s crust and present at an average concentration of 2 mg/kg.

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