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Polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of polyhalogenated organic compounds that are significant environmental pollutants. They are commonly but inaccurately referred to as dioxins for simplicity, because every PCDD molecule contains a dibenzo-1,4-dioxin skeletal structure, with 1,4-dioxin as the central ring. Members of the PCDD family bioaccumulate in humans and wildlife because of their lipophilic properties, and may cause developmental disturbances and cancer. Dioxins occur as by-products in the manufacture of some organochlorides, in the incineration of chlorine-containing substances such as polyvinyl chloride (PVC), in the chlorine bleaching of paper, and from natural sources such as volcanoes and forest fires. There have been many incidents of dioxin pollution resulting from industrial emissions and accidents; the earliest such incidents were in the mid 19th century during the Industrial Revolution. The word "dioxins" may also refer to other similarly acting chlorinated compounds (see Dioxins and dioxin-like compounds). ==Chemical structure of dibenzo-1,4-dioxins== The structure of dibenzo-1,4-dioxin consists of two benzene rings joined by two oxygen bridges. This makes the compound an aromatic diether. The name dioxin formally refers to the central dioxygenated ring, which is stabilized by the two flanking benzene rings. In PCDDs, chlorine atoms are attached to this structure at any of 8 different places on the molecule, at positions 1–4 and 6–9. There are 75 different PCDD congeners (that is, related dioxin compounds).〔(Nomenclature and physico-chemical properties of PCDDs and PCDFs. In: Dioxins in the Environment: What are the health risks? INSERM Collective Expert Evaluation Reports (2000) ). Ncbi.nlm.nih.gov (2011-03-18). Retrieved on 2011-06-09.〕 The toxicity of PCDDs depends on the number and positions of the chlorine atoms. Congeners that have chlorine in the 2, 3, 7, and 8 positions have been found to be significantly toxic. In fact, 7 congeners have chlorine atoms in the relevant positions which were considered toxic by the World Health Organization toxic equivalent (WHO-TEQ) scheme. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polychlorinated dibenzodioxins」の詳細全文を読む スポンサード リンク
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