Cadmium

Cadmium

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melting point: 320.9°C
boiling point: 767°C
density: 8.642 g/cm³
most common ions: Cd²⁺

Cadmium is a silver-white, malleable metal that exists as crystals having the hexagonal close-packed arrangement, and is usually found combined with other elements in mineral compounds (e.g., cadmium oxide, cadmium chloride, cadmium sulfate, and cadmium sulfide). Cadmium dust can ignite spontaneously in air and is both flammable and explosive when exposed to heat, flame, or oxidizing agents. Toxic fumes are emitted when cadmium metal is heated to high temperatures. Cadmium lacks a definite taste or odor. It was discovered as an impurity in zinc carbonate by Friedrich Strohmeyer in Germany in 1817. Most cadmium is obtained as a byproduct of the chemical treatment of copper, lead, and zinc ores, although it is a naturally occurring element in Earth's crust.

Industrial uses of cadmium include electroplating and the manufacture of batteries, metal coatings, and alloys . Cadmium is also used as a pigment in paints and plastics. Some fertilizers also contain cadmium.

Food and cigarette smoke are the most likely sources of cadmium exposure for the general population. The total daily intake of cadmium from food, water, and air for an adult living in North America or Europe is estimated to be between 10 and 40 micrograms (3.53 × 10⁻⁷ and 1.41 × 10⁻⁶ ounces). The U.S. Environmental Protection Agency has established oral reference doses for cadmium: 0.0005 mg/kg/day (from water) and 0.001mg/kg/day (from food). The reference dose is the level that may be consumed over a lifetime with minimal risk of adverse effects. Occupational exposure may occur in individuals who work with cadmium or in industries that produce cadmium. About 15 percent of inhaled cadmium is absorbed by the body, whereas 5 to 8 percent is absorbed from the gastrointestinal tract following cadmium ingestion. Cadmium is transported in the blood by hemoglobin, as well as by albumin and other large molecular weight proteins. The half-life for cadmium in the body is about thirty days, with most of the excess cadmium accumulating in the liver and kidneys. Cadmium is excreted primarily in the urine.

Acute toxicity may result from the ingestion of cadmium. Symptoms that follow cadmium ingestion may include abdominal pain, nausea, and vomiting; symptoms that follow inhalation include acute respiratory irritation and/or inflammation. Epidemiologic studies in humans have found associations between cadmium exposure and lung cancer, and between cadmium exposure and prostate cancer. Other evidence of the carcinogenic potential of cadmium has been found in the results of animal studies.

see also Toxicity.

Ronald Brecher

Bibliography

Agency for Toxic Substances and Disease Registry (ATSDR) (1999). Toxicological Profiles. Boca Raton, FL: CRC Press.

Klaassen, C. D., ed. (1996). Casarett and Doull's Toxicology: The Basic Science of Poisons, 5th edition. New York: McGraw-Hill.

Lide, D. R., ed. (2001). CRC Handbook of Chemistry and Physics, 82nd edition. Boca Raton, FL: CRC Press.

Lewis, R. J., ed. (1992). Sax's Dangerous Properties of Industrial Materials, 8th edition. New York: Van Nostrand Reinhold York.

Internet Resources

Integrated Risk Information System (IRIS), U.S. Environmental Protection Agency (USEPA). Available from <http://www.epa.gov/iris/>.

Toxicology Data Network, National Library of Medicine. Hazardous Substances Data Bank (HSDB). Available from <http://toxnet.nlm.nih.gov>.

Web Elements—The Periodic Table on the WWW:Professional Edition. Cadmium. Available from<http://www.webelements.com>.