Dioxin (Encyclopedia of Environmental Issues, Revised Edition)
Approximately seventy-five different types of dioxins exist, but the term “dioxin” is commonly used to refer to a variety known as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a highly toxic chemical that has caused great concern among environmentalists. Dioxin can be destroyed by exposure to direct sunlight in the presence of hydrogen, but the chemical can remain under the surface of the ground for ten years or longer.
One of the earliest documented cases of dioxin exposure occurred in West Germany in 1957, when thirty-one workers at a chemical plant developed chloracne, a skin disease that is one of the characteristic effects of exposure. In 1977 investigators in the Netherlands discovered dioxin in fly ash from a municipal incinerator. By 1980 scientists had determined that dioxin is produced when practically any organic substance is burned.
At first it was thought that chloracne was the only effect of exposure to dioxin. As time went on, however, experiments with animals revealed that dioxin is highly toxic. Researchers found that guinea pigs could be killed by as little as 1 microgram of dioxin per kilogram of body weight, but hamsters could take a dose of 5,000 micrograms per kilogram. Further experimentation showed that the organs within different animals were also affected differently by the chemical. Such differences among animal species and organs had never been found with any previously tested substance, and they...
(The entire section is 834 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Friis, Robert H. “Pesticides and Other Organic Chemicals.” In Essentials of Environmental Health. Sudbury, Mass.: Jones and Bartlett, 2007.
Schecter, Arnold, and Thomas Gasiewicz, eds. Dioxins and Health. 2d ed. New York: Taylor & Francis, 2002.
Young, Alvin Lee. The History, Use, Disposition, and Environmental Fate of Agent Orange. New York: Springer, 2009.
(The entire section is 50 words.)
Dioxin (Encyclopedia of Science)
The term dioxin refers to a large group of organic compounds that are structurally related to benzene (a colorless, flammable, and toxic [poisonous] liquid hydrocarbon, meaning it contains both carbon and hydrogen atoms) and may contain one or more chlorine atoms in their structures. Those compounds that do contain chlorine are known as chlorinated dioxins and are of the greatest environmental interest today.
Production and use
Dioxins have no particular uses. They are not manufactured intentionally but are often formed as by-products of other chemical procedures. Two such processes involve the manufacture of 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) and hexachlorophene. 2,4,5-T was once a popular herbicide (weed-killing agent), while hexachlorophene was an antibacterial agent used in soaps and other cleaning products. The use of both compounds has now been banned in the United States.
Dioxins are also formed as by-products of other industrial operations, such as the incineration of municipal wastes and the bleaching of wood pulp.
All 75 chlorinated dioxins known to science are believed to be toxic to some organisms at one level or another. The most toxic of these compounds is believed to be TCDD, or 2,3,7,8-tetrachlorodibenzo-p-dioxin. The differences in toxicities of the...
(The entire section is 821 words.)