Arsenic

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Arsenic (As) is a naturally occurring element that has been used in a variety of applications—in pesticides, as wood preservatives, and as a treatment for syphilis. Throughout history, arsenic was the most often used poison. Some historians believe that Nero used arsenic to poison Claudius in 54 C . E . Arsenic has also been the poison of choice in murder mysteries due to its easy availability in rat poison and insecticides.

In its elemental form, arsenic is a steel gray metal-like material. Combined with carbon and hydrogen, it forms organic arsenic compounds. When combined with oxygen, chloride, and sulfur, it forms inorganic arsenic compounds. Organic arsenic is generally less toxic than inorganic arsenic. Chromated copper arsenate (CCA), a pesticidal compound, has been widely used as a wood preservative. In February 2002 industry announced a voluntary decision to remove arsenic-treated lumber products (play structures, picnic tables, deck wood, etc.) from the market. By January 2004 the Environmental Protection Agency (EPA) will no longer allow CCA products for residential use. Although the EPA has not concluded that arsenic-treated wood poses an "unreasonable risk" to the public, arsenic is a known human carcinogen and any decrease in exposure from any source is desirable. Over 100,000 tons of arsenic are produced worldwide, most of which is a by-product of the smelting of metals such as copper and lead.

Arsenic occurs naturally in soils, rocks, water, and air. The burning of high-arsenic coal, the use of arsenical pesticides, and metals manufacturing has redistributed arsenic throughout the environment. Human exposure to arsenic occurs through ingestion of water and food contaminated with arsenic or the inhalation of contaminated air. The greatest human exposure to arsenic is through consumption of contaminated seafood. However, the arsenic in seafood is organic arsenic, which is low in toxicity. Ingestion of inorganic arsenic in drinking water represents the greatest health hazard.

Ingestion of large amounts of inorganic arsenic is extremely toxic and can be fatal. Although environmental levels of arsenic are much lower, exposure to arsenic in drinking water has been associated with increased risks of cancer of the bladder, kidney, skin, and lung. Noncarcinogenic effects include lesions of the skin; blackfoot disease, a peripheral vascular disorder; cardiovascular and neurological diseases; and possible adverse effects on the reproductive system. Recent research has shown arsenic to be an endocrine disruptor, blocking a steroid that regulates a number of biological processes.

Arsenic contamination of drinking water supplies is a worldwide problem. Areas where drinking water is of specific concern include Bangladesh, India, Hungary, Chile, China, Argentina, Taiwan, Ghana, Mexico, the Philippines, New Zealand, and the United States (primarily the western states). The World Health Organization (WHO) has established a guideline of 10 micrograms (μg) of arsenic per liter, or ten parts per billion (ppb), in drinking water. In February 2002 the EPA announced the new arsenic drinking water standard of ten ppb. By 2006 community drinking water systems across the United States must be in compliance. There are several methods to removing arsenic from drinking water, including:

• Coprecipitation, where iron binds with arsenic and the particles settle out or are removed.
• Adsorption, where arsenic adheres to aluminum or iron and can be removed.
• Membrane filtration, where arsenic is filtered out of the water.
• Ion exchange, where a chemical process exchanges chloride for arsenic.

The estimated cost for compliance of the new arsenic drinking water standard in the United States is approximately $177 million per year. The average cost per household is dependent upon the size of the community water system—the smaller the system, the higher the cost.

Arsenic has also been identified in hazardous waste sites within the United States. Scientists at the University of Florida's Institute of Food and Agriculture Sciences have identified the brake fern, Pteris vittata, which absorbs arsenic from the soil. The potential use of this fern to clean up arsenic from such sites is called phytoremediation, where plants and trees are used to extract contaminates from the soil. Many arsenic compounds dissolve in water, and thus, the cleanup of these waste sites would protect the underlying aquifers.

SEE ALSO B IOREMEDIATION ; E NDOCRINE D ISRUPTION ; H EALTH, H UMAN ; R ISK ; S MELTING ; W ATER T REATMENT .

Bibliography

Chappell, W.R.; Abernathy, C.O.; and Calderon, R.L., eds. (1999). Arsenic Exposure and Health Effects. New York: Elsevier, 1999.

Internet Resources

Agency for Toxic Substances and Disease Registry. "Public Health Statement for Arsenic." Available from www.atsdr.cdc.gov .

World Health Organization. "Arsenic in Drinking Water." Fact Sheet No. 210. Available from www.who.org .

Betsy T. Kagey