Dioxin bactericide

Dioxins are a family of heterocyclic hydrocarbons, mostly poisonous chemical by-products of the manufacture of certain herbicides and bactericides. The most toxic are polychlorinated dibenzo-p-dioxins (CDDs) and dibenzo-furans (CDFs, also called dioxins) [514,515]. Amongst the most dangerous are the isomers of the 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzo-furan (TCDF). The former occurs in small amounts in some herbicides and defoliants, including the so-called Agent Orange (a highly toxic herbicide sprayed as a defoliant in chemical warfare) [466]. 

Substances often called dioxins have been present as contaminants in many pesticide formulations and in some bactericidal products. Dioxins are found in smoke from refuse incinerators and in effluents from the wood pulp industry, which uses chlorine as a bleaching agent. The magnesium industry used a production method that caused the formation of many "dioxins" (strictly speaking, dibenzofurans). Car exhaust fumes and cigarette smoke also have a low concentration. But dioxins may also be formed from more natural processes such as forest fires and cremations. Forest fires are suspected of producing 59 kg of dioxin per year in Canada alone. Humans have thus been exposed to dioxins long before the modern age. 

Few chemicals have acquired as much notoriety as 2,3,7,8-tetrachlorooxanthrene, or -di-benzo[ft,e][l,4]dioxin. The compound, commonly referred to as TCDD, or simply but misleading as dioxin, is formed as a by-product in the commercial preparation of 2,4,5-trichlorophenol, an intermediate in the manufacture of the bactericide hexachlorophene and the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). The commercial production of 2,4,5-trichlorophenol, during which TCDD is generated, involves the reaction of 1,2,4,5-tetrachlorobenzene with base TCDD is formed if the product reacts further. 

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