Dibenzo-p-Dioxins: 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

Chlorinated dibenzo-para-dioxins or dibenzo-p-dioxins (CDDs) are a class of compounds with 75 possible congeners. When the CDDs contain more than one chlorine they are termed polychlorinated dibenzo-p-dioxins (PCDDs). Most of the information is for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), the most toxic congener. The bulk of the material in this chapter relates to this compound. The toxic PCDD congeners are substituted with chlorines in the 2,3,7, and 8 positions. The least toxic congeners are the monochlorinated PCDDs and octachlorodibenzo-p-dioxin [CAS RN 3268-87-9], the fully chlorinated PCDD. PCDDs often are accompanied by the dibenzofuran analogs, the polychlorinated dibenzofurans (PCDFs), and the diphenyl ether analogs, the polychlorinated diphenyl ethers (PCDPEs). The cumulative toxicity of the toxic congeners of polychlorinated biphenyls (PCBs), PCDDs, PCDFs, and PCDPEs in a sample is expressed through the 2,3,7,8-TCDD toxicity equivalent (TEQ) and toxicity equivalency factor (TEF) concepts because real-life exposures are to mixtures of PCDDs, PCDFs, PCDEs, and PCBs rather than to 2,3,7,8-TCDD alone. Keywords: 2,3,7,8-Tetrachlorodibenzo-p-dioxin; accidents; Agent Orange; body burden; Cachexia; chloracne; chlorinated dibenzo-p-dioxins; dioxin; endocrine effects; IARC carcinogenic evaluation; tissues; US/foreign standards