dioxin

noun

1. (countable)The unsaturated six-membered heterocycle having four carbon atoms, two oxygen atoms, and two double bonds (molecular formula C₄H₄O₂); 1,2-dioxin and 1,4-dioxin.

   “Dioxin is a specific organic unsaturated non-antiaromatic six-membered ring compound with a chemical formula of C4H4O2. However, the term dioxin is used generically by most authorities to include chlorinated dioxins with furans and many derivative compounds as a complex of at least 75 ubiquitous and environmentally persistent organochlorine compounds, of variable toxicity.”

2. (countable)The parent compound dibenzo-1,4-dioxin or dibenzo-p-dioxin (molecular formula C₁₂H₈O₂), in which two benzene rings are connected through two oxygen atoms; dibenzodioxin, oxanthrene.

   “Dioxins are not a single chemical. They are a family of chemicals that contain two benzene rings connected by a pair of oxygen molecules. When chlorine atoms are connected to the benzene rings, we have a chlorinated dioxin. The particular chlorinated dioxin of greatest interest and concern is 2,3,7,8-tetrachlorodibenzo-p-dioxin (generally abbreviated TCDD).”

3. (countable)Any of a broad range of toxic or carcinogenic halogenated polycyclic compounds that occur as byproducts of herbicides.

   “The detection of dioxin (specifically, the 2,3,7,8-tetrachlorodibenzo-pdioxin TCDD) in 2,4,5-T raised the question whether dioxin might be present in other herbicides.”

   “Poisonous residues carelessly treated today can produce calamities miles away and decades later. One example is dioxin, a waste left behind in factories after the production of hexachlorophene, a potent antiseptic. Dioxins are lethal, capable of killing people in concentrations as diluted as one part in a million. Oils containing discarded dioxins have been sprayed on horse farms in Missouri to control dust. Horses subsequently died.”

   “Dioxins are polychlorinated isomers that form as by-products either during combustion of waste products or afterward in the incinerator stack. They include dibenzo-dioxins (PCDD), dibenzofurans (PCDF), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). 2,3,7,8-TCDD is one of the extremely carcinogenic groups of dioxin compounds. A risk of exposure to humans occurs once dioxin compounds are released from the stack of the incinerator and are transported by the wind elsewhere.”

   “EPA [the Environmental Protection Agency] characterizes 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as a Human Carcinogen based on weight of evidence and characterizes other dioxins, furans, and PCBs [polychlorinated biphenyls] as Likely Human Carcinogens. The toxicity of all of the dioxin, furan, and PCB congeners considered in this analysis is based on the toxicity of the most highly characterized congener, 2,3,7,8-TCDD [...].”

4. (broadly, specifically, uncountable)Any of a broad range of toxic or carcinogenic halogenated polycyclic compounds that occur as byproducts of herbicides.

   “The 2,4,5-T used by Courtney and co-workers [...] was contaminated with approximately 30 ppm of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin). [...] The present work describes the results of our teratogenic studies on hamsters with samples of 2,4,5-T containing varying amounts of dioxin and with samples of 2,4-D from different manufacturers.”

   “When manufacture of 2,4,5-T is controlled carefully, dioxin contamination is less than 1 ppm. Dioxin was identified in 1962 as the culprit of damage and death in 1957 of uncounted numbers of chicks. Dioxin produces neurological disturbances and is teratogenic.”

   “Dioxin—2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)—is not manufactured commercially but is present as an impurity in 2,4,5-trichlorophenol (TCP). Minute traces may be present in the herbicide 2,4,5-T and in the antibacterial agent hexachlorophene, which are produced from trichlorophenol.”

   “Dioxin or TCDD is a chemical contaminant that occurs as chlorine byproduct of the paper bleaching manufacturing process. Although it is useless on its own, dioxin is a common environmental contaminant. Dioxin was also released as a contaminant of the pesticide Agent Orange, which was used as a defoliant by U.S. forces in Vietnam. The highest concentrations of dioxin result from the incineration of medical waste.”