Dioxin

One of a number of poisonous petroleum-derived chemicals which are produced when herbicides (substances used for killing plants) are made or when plastics are burned. Dioxins are chemically dibenzo-p-dioxins. One of the best known is TCDD (2, 3, 7, 8-TCDD). Dioxins cause skin disease (chloracne). In animal tests, dioxins are teratogens (agents that cause birth defects and miscarriages), mutagens (agents that cause mutations) and carcinogens (agents that cause cancer). In 2001 the US government added the TCDD to the list of substances that are known carcinogens based on "sufficient evidence of carcinogenicity from studies in humans." The National Institutes of Health (NIH) concluded that: "It is now clear that there is a causal relationship between exposure to TCDD and human cancer." A factory explosion in northern Italy in 1976 polluted the town of Seveso with dioxin. Some defoliants such as Agent Orange, which was used in the Vietnam war, contain dioxin.

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1. A ring consisting of two oxygen atoms, four CH groups, and two double bonds; the positions of the oxygen atoms are specified by prefixes, as in 1,4-d.. 2. Abbreviation for dibenzo[b,e][1,4]d. which may be visualized as an anhydride of two molecules of 1,2-benzenediol (pyrocatechol), thus forming two oxygen bridges between two benzene moieties, or as a 1,4-d. with a benzene ring fused to catch each of the two CH=CH groups. 3. A contaminant in the herbicide, 2,4,5-T; it is potentially toxic, teratogenic, and carcinogenic.

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di·ox·in (')dī-'äk-sən n any of several persistent toxic heterocyclic hydrocarbons that occur esp. as by-products of various industrial processes (as pesticide manufacture and paper milling) and waste incineration esp TCDD see AGENT ORANGE

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di·ox·in (di-okґsin) any of the heterocyclic hydrocarbons present as a trace contaminant in herbicides, especially the chlorinated dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin; many are teratogenic and carcinogenic.