Introduction

• ground water,
• mineral ore, and
• geothermal processes.

Natural and Industrial Sources

Arsenic is released into the air by volcanoes, through weathering of arsenic-containing minerals and ores, and by commercial or industrial processes.

Arsenic occurs naturally in the earth’s crust, and much of its dispersion in the environment stems from mining and commercial uses. In industry, arsenic is a byproduct of the smelting process (separation of metal from rock) for many metal ores such as

• cobalt,
• gold,
• lead,
• nickel, and
• zinc.

Arsenic Products

There has been no domestic production of arsenic since 1985. In 2003, the world’s largest producer of arsenic compounds was China, followed by Chile and Peru. In 2003, the United States was the world’s largest consumer of arsenic [ATSDR 2007].

In the past, the United States primarily used arsenic in insecticides such as ant killers and animal dips (the concentrated liquid forms of these are most toxic to humans). However, regulatory restrictions for arsenic, especially for home products, have reduced its use and should also reduce the exposure risk to it [NAS 1977].

Other sources include

• algaecides,
• desiccants used in mechanical cotton harvesting,
• glass manufacturing,
• herbicides (such as weed killers for telephone and railroad posts and Agent Blue, which was used by U.S. troops in Vietnam), and
• nonferrous alloys [Garcia-Vargas and Cebrian 1996].

Arsenic trioxide may be found in pesticides and defoliants and as a contaminant of moonshine whiskey [Murunga and Zawada 2007].

Presently, arsenic is widely used in the electronics industry in the form of gallium arsenide and arsine gas as components in semiconductor devices.

Production of wood preservatives, primarily copper chromated arsenate (CCA), accounted for more than 90% of domestic consumption of arsenic trioxide in 2003. Wood treated with CCA is known as “pressure treated wood”. In response to consumer concerns, U.S. manufacturers of arsenical wood preservative began a voluntary transition from CCA to other wood preservatives for certain residential wood products. In 2002, the U.S. Environmental Protection Agency (EPA) reached an agreement with the manufacturers of wood preservative products containing CCA to cancel the registration of CCA for use in virtually all residential applications. As of December 31, 2003, it is illegal to treat dimensional lumber used in residential applications with CCA. However, wood treated prior to this date can still be used, and CCA-treated wood products continue to be used in industrial applications [ATSDR 2007]. There are sealants that can be used to reduce the leaching of arsenic from CCA-treated wood for up to twelve months of natural weathering [EPA 2007].

Many outdoor wood structures such as playgrounds and decks have been treated with copper chromated arsenate wood preservative. The photo at the left below shows one such playground. The preservative often gives wood a greenish color, as seen in the photo at the right below.

Arsenic in Drugs

• Arsenic is currently used for induction and consolidation chemotherapy for acute promyelocytic leukemia and other cancers [Miller et al. 2002; Hu et al. 2005].
• Arsenic may be found in some traditional remedies from a number of Asian countries [Garvey et al. 2001; Chan 1994]. Arsenic may also be found in some naturopathic or homeopathic remedies [Kerr and Saryan 1986].
• “Fowlers solution,” which is 1% arsenic trioxide, was used historically to treat skin conditions such as psoriasis and eczema. It was also used to treat leukemia and stomatitis. When skin cancer resulted from the use of Fowler’s solution, there was a marked decrease in medicinal use of arsenic [Rossman 2007].
• Arsphenamin (Salvarsan) was the first effective cure for syphilis until replaced by antibiotics after World War II [Rossman 2007].

Industrial Production of Arsenic

Component Uses of Arsenicals

Discontinued arsenic-containing pesticides may still be found in some U.S. farms and homes [ATSDR 2007].

Gallium arsenide is used in integral components of

• discrete microwave devices,
• lasers,
• light-emitting diodes,
• photoelectric chemical cells, and
• semiconductor devices.

Arsine gas, the most toxic arsenical (acute exposures), is used commercially in the microelectronics industry, and it is encountered accidentally in metallurgical and mining processes.

Arsine gas is used in the production of semiconductors, although substitutes of lower toxicity such as tributylarsine have also been used.

Arsine forms when acid or other reducing substances are added to arsenic-containing compounds, such as metals in which arsenic is a low level contaminant [ATSDR 2007].

Arsine gas produces a clinical syndrome very different from other arsenic compounds.

Use of Arsenicals in Chemical Warfare

• Chlorovinyl dichloroarsine (also known as lewisite) was developed as a chemical warfare vesicant in the 1920s. It was declared obsolete in the 1950s in the United States and stockpiles were neutralized and disposed of. Unexploded ordnance containing Lewisite can still be found at U.S. former munition ranges [EPA 2008]. Lewisite is a compound from the chemical family of arsines that has different health effects than arsenic compounds. For example, it causes severe skin burns on contact at very low concentrations.

Other Industrial Processes

Other industrial processes that use arsenic include

• coal-fired power plants,
• hardening metal alloys, and
• purifying industrial gases (removal of sulfur).

Food

Arsenic may be found in foods.

• Seafood (especially bivalves [clams, oysters, scallops, mussels], crustaceans [crabs, lobsters], and certain cold water and bottom feeding finfish, and seaweed/kelp.
• The organic forms of arsenic found in seafood (mainly arsenobetaine and arsenocholine, also referred to as “fish arsenic”) are generally considered to be nontoxic, and are excreted in urine within 48 hours of ingestion [ATSDR 2007].
• However, inorganic forms of arsenic have been found in some types of seaweed. Recent literature suggests hijiki seaweed has very high levels of inorganic arsenic (MMA) [Rose et al. 2007].

(for larger view, click on image)

While found in lower amounts in many foods and particularly seafoods, higher concentrations of dietary organic arsenic may be found in bivalve mollusks (clams, oysters, mussels) and crustaceans (crabs and lobsters). The organic forms of arsenic found in seafood (mainly arsenobetaine and arsenocholine, also referred to as "fish arsenic") are generally considered to be nontoxic, and are excreted in urine within 48 hours of ingestion [ATSDR 2007].

Progress Check