ABSTRACT
The chlorinated dibenzo-p-dioxins and dibenzofurans are produced as byproducts during the formation of many other chemicals, including 2,4,5-T, hexachlorophene, pentachlorophenol and other chlorinated phenols, and polychlorinated biphenyls (360). Chlorinated dioxins have been found in the fly ash and flue gases from municipal generators in Switzerland, presumably due to pyrolysis of chlorophenol salts, and the formation of chlorinated furans has been tied to the pyrolysis of polychlorinated biphenyls and polychlorinated diphenyl ethers. These compounds are used as heat exchange fluids and as hydraulic liquids. From 3 to 25% of the polychlorinated biphenyls burned may be converted to chlorinated dibenzofurans (360). There is no known technical use for the chlorinated dibenzo-pdioxins, of which 75 congeners can exist, and the chlorinated dibenzofurans, of which there are 135 theoretical congeners (360). The positional isomers of the dioxins vary greatly in their acute toxicity and biological activity, and the most potent isomer, 2, 3, 7. 8-tetrachlorodibenzo-p-dioxin (TCDD), is considered the most potent lowmolecular-weight toxin known (mean lethal dose in guinea pigs 0.6 μg/kg body weight) (387).
