Arsenic (Encyclopedia of Environmental Issues, Revised Edition)
Arsenic is naturally brittle and relatively soluble in water. It is found activated in the environment owing to a combination of natural processes (weathering, biological activity, and volcanic eruptions) and human activities. In some cases arsenic is naturally present in aquifers. It is also associated with geothermal waters, and its presence has been reported in several areas with hot springs. Human beings have played a significant role in increasing the rate of natural mobilization of arsenic through activities such as mining, combustion of fossil fuels, and the use of arsenic in pesticides, herbicides, crop desiccants, and food additives. Industrial effluents add to the environmental availability of arsenic. Even though human use of arsenic has been significantly reduced since the mid-twentieth century, the impacts of arsenic on the environment are likely to continue for some time.
Arsenic is found in various forms and is a major constituent of more than two hundred different minerals. Some of the elements with which arsenic often forms compounds are oxygen, chlorine, tungsten, tin, molybdenum, cadmium, sulphur, lead, silver, iron, and even gold. Arsenic is widely found in ores such as arsenopyrite.
Contamination of drinking water is one of the most significant ways in which arsenic threatens human health. Commonly four types of arsenic compounds exist in water: arsenite and arsenate, which are inorganic arsenic compounds, and...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Henke, Kevin R. Arsenic: Environmental Chemistry, Health Threats, and Waste Treatment. Hoboken, N.J.: John Wiley & Sons, 2009.
Hill, Marquita K. “Drinking-Water Pollution.” In Understanding Environmental Pollution. 3d ed. New York: Cambridge University Press, 2010.
Miller, G. Tyler, Jr., and Scott Spoolman. “Water Pollution.” In Living in the Environment: Principles, Connections, and Solutions. 16th ed. Belmont, Calif.: Brooks/Cole, 2009.
Ravenscroft, Peter, Hugh Brammer, and Keith Richards. Arsenic Pollution: A Global Synthesis. Malden, Mass.: Blackwell, 2009.
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Arsenic (Forensic Science)
Life- or health-threatening exposure to the toxic chemical arsenic can result from industrial contact, from deliberate poisoning, or from naturally contaminated food or drinking water. Arsenic poisoning may be acute or chronic, depending on whether a large dose is ingested at one time or smaller doses are taken over a lengthy period.
Acute arsenic poisoning is often associated with attempted murder of the victim. Ingestion of as little as two-tenths of a gram of arsenic trioxide (the arsenic compound most commonly used by poisoners, found in insecticides and weed killers) is followed by intense pain in the stomach and esophagus, followed by vomiting and diarrhea. Chronic poisoning by low levels of arsenic such as may be found in contaminated drinking water produces thickening of the skin (hyperkeratosis) of the hands and feet as well as white lines on the fingernails. Cancer of the bladder or other organs can result with long exposure. Neurological effects are also observed, including weakness in the hands and feet (peripheral neuropathy). These symptoms are not always recognized as arsenic-related unless suitable forensic tests are done.
Arsenic binds to proteins and exerts its toxic effects on the body by interfering with vital enzymes. The presence of arsenic in blood or urine can be confirmed through atomic absorption spectrophotometry, a method developed in the second half of the twentieth century. Previously, the primary method...
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Arsenic Exposure (Forensic Science)
In the past, the dangers of arsenic were often treated casually, with the result that many people experienced unnecessary, sometimes dangerous, levels of exposure to the chemical. The use of arsenates as pesticides, now minimal in the United States, once was widespread. Fruit, vegetable, and tobacco crops were often sprayed with such pesticides, and high levels of arsenic were left in the soil and on the crops themselves. When humans suffered ill health as a result, forensic scientists needed to find the source of the trouble. In France, arsenate pesticide residues on grapes found their way into wine that poisoned hundreds of French sailors in 1932. Plants grown on contaminated soil can pick up enough arsenic content to be toxic for human or animal consumption, and residues on tobacco are eventually inhaled by smokers.
Chromated copper arsenate is still used as a wood preservative, but many products that formerly contained arsenic no longer do so. Arsenical pigments were long used in wallpaper and in paint, and this led to many poisonings. Research over many years revealed that wallpaper with pigments such as Paris green or Scheele’s green (both arsenicals) could generate arsenic-containing vapors (known as Gosio gas, for Italian physician Bartolomeo Gosio, who published his research on the topic in 1893) if moisture and certain microorganisms were present. This type of vapor, which caused some mysterious deaths in the...
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Murder by Arsenic (Forensic Science)
Foul play may be suspected in the death of an otherwise healthy person who develops the symptoms of arsenic poisoning. When such a person dies, forensic testing done postmortem can substantiate toxic levels of arsenic in the liver and other organs, in the stomach contents, and in the blood. If high levels are found, investigators must try to find the source of the poison and its mode of delivery. Accidental or environmental sources must be considered; for example, the victim may have used medicines containing arsenic or taken herbal supplements with arsenic content. If malicious intent is suspected, the dietary habits of the victim may suggest how the poison could have been administered. Any remnants of food or drink known to be ingested by the victim should be tested for arsenic, and those who have had access to the victim or the victim’s food should be investigated to see if they have obtained poison or are currently in possession of some.
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Further Reading (Forensic Science)
Emsley, John. The Elements of Murder: A History of Poison. New York: Oxford University Press, 2005. Discusses the use of arsenic and other poisons in murder. Describes a number of cases in detail, many of which involve one spouse poisoning the other.
Gerber, Samuel M., and Richard Saferstein, eds. More Chemistry and Crime: From Marsh Arsenic Test to DNA Profile. Washington, D.C.: American Chemical Society, 1997. Collection of chapters covers the history of forensic science as well as developments in the field through the 1990’s. Includes chapters that focus on forensic toxicology, on the search for arsenic, and on the depiction of forensic science in detective fiction.
Jones, David. “The Singular Case of Napoleon’s Wallpaper.” New Scientist, October 14, 1982, 101-104. Discusses the case of Napoleon I, who, in exile on the island of Saint Helena, stayed in a house where the wallpaper contained toxic levels of arsenic. Modern scientists have found elevated arsenic levels in samples of Napoleon’s hair, which could have been caused by the wallpaper through Gosio gas.
Meharg, Andrew A. Venomous Earth: How Arsenic Caused the World’s Worst Mass Poisoning. New York: Macmillan, 2005. Focuses on the health consequences of the arsenic contamination of drinking water (from minerals near the water table) in Bangladesh. Also notes other areas of the world where the problem...
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Where Found (Encyclopedia of Global Resources)
Elemental arsenic is occasionally found in minerals, but more frequently it is combined chemically with sulfur, either alone or with metals such as copper, nickel, cobalt, or iron. China is the world’s largest producer of elemental arsenic. Because of the health risks of arsenic, there has been no U.S. production of arsenic trioxide or arsenic metal since 1985.
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Primary Uses (Encyclopedia of Global Resources)
Wood preservatives, herbicides, and insecticides are major uses of arsenic chemicals. Arsenic is used to harden lead alloys for battery plates, solder, and lead shot, while arsenides of gallium and indium have uses in lasers, light-emitting diodes, and transistors. In the United States, approximately 4 percent of arsenic (measured in metric tons of arsenic content) goes to agricultural chemicals, 3 percent to glass products, 3 percent to nonferrous alloys and electronics, and 90 percent to pressure-treated wood. The electronics industry uses a very pure form of arsenic in gallium-arsenide semiconductors for solar cells, space research, and telecommunications.
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Technical Definition (Encyclopedia of Global Resources)
Arsenic (abbreviated As), atomic number 33, belongs to Group V of the periodic table of the elements and is classified as a metalloid, rather than a metal or nonmetal. There is only one naturally occurring isotope, with an atomic weight of 74.93. Elemental arsenic exhibits gray, yellow, and black forms with densities of 5.73, 1.97, and 4.73 grams per cubic centimeter. The common gray form sublimes when heated to 613° Celsius and melts under a pressure of 28 atmospheres (2.8 million pascals) at 817° Celsius.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Arsenic is widely distributed and is found in soils and seawater in trace amounts: 1 to 40 parts per million in soil, and 2 to 5 parts per billion in seawater. It averages about 1.8 parts per million by weight. The most abundant arsenic mineral is arsenical pyrite (also called arsenopyrite or mispickel), a sulfide of iron and arsenic. Other significant ores are arsenolite (arsenious oxide), orpiment (As2S3), and realgar (As4S4). Seawater averages 0.5 to 2 parts per billion of arsenate, but lakes and streams often have higher concentrations; these vary from one body of water to another. Lake Michigan, for example, has levels of 0.5 to 2.4 parts per billion. Fish and shellfish have arsenic levels about one thousand times greater than seawater and much higher than federal drinking water standards (0.05 part per million). Arsenobetaine, with a formula of (+)(CH3)3As-CH2-CO2(-), is common in fish, and many other methylated compounds are found in marine organisms.
Arsenic toxicity is highly dependent on the state of chemical combination of the element. Elemental arsenic is less toxic than combined forms; the most dangerous forms are arsine, arsenites, and arsenious oxide. Ingestion of as little as 0.1 gram of arsenious oxide has caused death. Methylated compounds such as arsenobetaine are much less toxic.
Arsenic intoxication symptoms include skin rashes, anemia, gastrointestinal distress, internal...
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History (Encyclopedia of Global Resources)
Arsenic was known in early times in India, Persia, and Mesopotamia, and it is mentioned in the writings of Aristotle, Hippocrates, and Pliny the Elder. These ancient writings are often vague and do not allow the modern reader to decide exactly whether elemental arsenic or some compound such as an oxide or sulfide is described. European alchemists such as Albertus Magnus (thirteenth century) and Johannes Schröder (seventeenth century) published procedures for preparing arsenic from orpiment (As2S3) or arsenious oxide (As2O3), but priority in discovery is considered uncertain.
The toxic characteristics of arsenious oxide were noticed long ago, and the substance became notorious in various homicidal poisoning cases. The Roman emperor Nero, for example, poisoned his own brother. Accidental arsenic poisoning is exemplified by the events reported in 1973 in Pelham, Minnesota, where a well had been drilled on land that had received heavy dosages of arsenic insecticides.
In spite of the danger, pigments containing arsenic were still used in cakes and candy in the nineteenth century, and arsenic-containing medicines of dubious value were used in the early twentieth century. Arsenicals are still occasionally used to treat stubborn parasitic diseases (trypanosomiasis, amoebiasis).
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Obtaining Arsenic (Encyclopedia of Global Resources)
There are more than two hundred recognized arsenic-containing minerals. Arsenic is leached into water by weathering of rocks and is distributed by volcanic action. In the soil, microorganisms can metabolize arsenate or arsenite, producing a variety of organic methylated compounds that find their way into water and into the bodies of all sorts of marine creatures. An estimated 40,000 metric tons of arsenic are added to the world’s oceans annually by weathering of rocks, as compared with world industrial production of 55,000 to 70,000 metric tons per year.
Human activity accounts for significant releases of arsenic into the air, water, and soil. Smelters emit arsenic oxide dust, and herbicides and insecticides remain in the soil. One of the large smelters in the United States (no longer operating) emitted 181 metric tons of arsenious oxide per year into the area surrounding Tacoma, Washington.
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Uses of Arsenic (Encyclopedia of Global Resources)
Production of arsenic has ceased in the United States, and uses are subject to increasingly severe regulation. Nevertheless, the United States still imports about several thousand metric tons per year, mainly for wood preservation and pesticide uses.
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Further Reading (Encyclopedia of Global Resources)
Adriano, Domy C. “Arsenic.” In Trace Elements in Terrestrial Environments: Biogeochemistry, Bioavailability, and Risks of Metals. 2d ed. New York: Springer, 2001.
Fowler, Bruce A., ed. Biological and Environmental Effects of Arsenic. New York: Elsevier, 1983.
Greenwood, N. N., and A. Earnshaw. “Arsenic, Antimony, and Bismuth.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Henderson, William. “The Group 15 (Pnictogen) Elements: Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth.” In Main Group Chemistry. Cambridge, England: Royal Society of Chemistry, 2000.
Massey, A. G. “Group 15: The Pnictides—Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
Naidu, Ravi, et al., eds. Managing Arsenic in the Environment: From Soil to Human Health. Enfield, N.H.: Science Publishers, 2006.
Ng, J., ed. Arsenic and Arsenic Compounds. 2d ed. Geneva, Switzerland: World Health Organization, 2001.
Nriagu, Jerome O., ed. Arsenic in the Environment. 2 vols. New York: Wiley, 1994.
Ravenscroft, Peter, Hugh Brammer, and Keith Richards. Arsenic Pollution: A Global Synthesis. Malden, Mass.: Wiley-Blackwell, 2009.
Thayer, John S. Environmental Chemistry of the Heavy Elements: Hydrido and Organo Compounds....
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Arsenic (Chemical Elements)
Arsenic compounds have been known since at least the days of Ancient Greece and Rome (thousands of years ago). They were used by physicians and poisoners. The compound most often used for both purposes was arsenic sulfide (As23).
Arsenic was first recognized as an element by alchemists. Alchemy was a kind of pre-science that existed from about 500 B.C. to about the end of the 16th century. People who studied alchemylchemistsanted to find a way of changing lead, iron, and other metals into gold. They were also looking for a way to have eternal life. Alchemy contained too much magic and mysticism to be a real science, but alchemists developed a number of techniques and produced many new materials that were later found to be useful in modern chemistry.
A small amount of arsenic is used in alloys. An alloy is made by melting and then mixing two or...
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Arsenic (Encyclopedia of Public Health)
Arsenic (As) is a silver-gray metal that gained much of its notoriety because of its historical use as a human poison (approximately 70 to 180 milligrams of arsenic is fatal to an adult). Arsenic is present in the earth's crust at an average concentration of 2 to 5 mg/kg, with low levels commonly found in the air, water, and soil. In the eighteenth and nineteenth centuries, arsenic was used as a preservative in animal hides, and as an ingredient in pigments, dyes, glass, pharmaceuticals, and pesticides.
In the first half of the twentieth century, arsenic was used in pharmaceuticals intended to treat syphilis (e.g., arsphenamine), skin diseases (e.g., Fowler's solution, a 1% potassium arsenate solution), and parasites (e.g., Pearson's Arsenical Solution). Arsenic is still used as an ingredient in pesticides, wood preservatives, copper and lead alloys, glass, semiconductor devices, and veterinary medicines.
Although arsenic is found in nature in its elemental form (arsenic metal), it occurs most commonly in inorganic or organic compounds. Common inorganic arsenic compounds are trivalent arsenic (e.g., arsenite, H3AsO3) and pentavalent arsenic (e.g., arsenate, H2AsO4, HAsO42). Common organic arsenic compounds are monomethyl arsonic acid (MMA), dimethyl arsinic acid (DMA, also known as cacodylic acid), and roxarsone.
Adverse health effects are dependent on the chemical form and physical state of the specific arsenic compound. In general, organic arsenic is less acutely toxic than inorganic arsenic. The health effects of arsenic are widely variable, and are primarily due to differences in the oxidation state of the two predominant forms: trivalent arsenite and pentavalent arsenate. Several organic arsenicals that accumulate in fish and shellfish are essentially nontoxic. Human exposure to arsenic compounds occurs primarily in occupational settings and by the ingestion of contaminated drinking water and seafood. Arsenic toxicity due to natural contamination of drinking water has been recently noted as a significant public health problem in Bangladesh. Predominant adverse health effects associated with acute arsenic exposure include fever, melanosis, hepatomegaly, cardiac arrhythmia, peripheral neuropathy, nephrotoxicity, diarrhea and vomiting, and, at sufficiently high doses (70 to 180 milligrams for an adult), death. Chronic exposure to arsenic may lead to neurotoxicity (evidenced by sensory changes, paresthesia, and muscle weakness), cancer (basal cell and squamous cell carcinoma of the skin, lung cancer, or bladder cancer), cardiovascular effects (including "blackfoot disease," so called because the soles of the feet and toes turn black with gangrene), skin disorders such as hyperpigmentation, and birth defects.
Arsine gas is a potent hemolytic agent. The International Agency for Cancer Research (IARC) and the U.S. Environmental Protection Agency (EPA) classify arsenic as a carcinogen based upon epidemiological evidence demonstrating a causal association between arsenic exposure and specific cancers, such as skin cancer and lung cancer. Arsenic can accumulate in hair and nails, and measurement of arsenic levels in these tissues may be a useful indicator of past exposures, while measurement of urine is considered a good indicator of current arsenic exposure. Arsenic is primarily excreted from the body in urine (30 to 85% of absorbed arsenic is excreted via urine). Scientists have puzzled for decades over arsenic's mechanism of carcinogenicity due to the discordance between the results of human and animal bioassays. Animals appear to be substantially less susceptible to arsenic-induced toxicity than humans. Investigations in animals have suggested that inorganic arsenic can be an essential trace element in some animals. In contrast, arsenic has not been determined to be an essential trace element in humans.
MARGARET H. WHITAKER
BRUCE A. FOWLER
(SEE ALSO: Carcinogen; Heavy Metals)
International Agency for Research on Cancer (IARC) (1980). Some Metals and Metallic Compounds. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 23. Lyon, France: IARC.
National Research Council (1999). Arsenic in Drinking Water. Washington, DC: National Academy Press.
U.S. Environmental Protection Agency (2000). Arsenic Record. Integrated Risk Information Service (IRIS). Available at http://www.epa.gov/iris.