dioxin

Any of a family of over 200 organic chemicals, all of which are heterocyclic hydrocarbons (see cyclic compounds). The term is commonly applied, however, to only one member of the family, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), a highly toxic chemical that occurs, for example, as an impurity in the defoliant Agent Orange, used in the Vietnam War, and sometimes in the weedkiller 2,4,5-T. It has been associated with chloracne (a disfiguring skin complaint), birth defects, miscarriages, and cancer.

Disasters involving accidental release of large amounts of dioxin into the environment have occurred at Seveso, Italy, and Times Beach, Missouri, USA. Small amounts of dioxins are released by the burning of a wide range of chlorinated materials (treated wood, exhaust fumes from fuels treated with chlorinated additives, and plastics) and as a side effect of some techniques of paper-making. Dioxin may also be produced as a by-product in the manufacture of the bactericide hexachlorophene.

The possibility of food becoming contaminated by dioxins in the environment led the European Union (EU) to decrease significantly the allowed levels of dioxin emissions from incinerators.