Destruction of polychlorodibenzo-p-dioxins

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Abstract
The release of 2,4,5-T containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at Seveso [Italy] highlighted the need for an efficient control procedure for the highly toxic dioxin. The concomitant formation of the dioxin and trichlorophenol during hydrolysis of sym-tetrachlorobenzene led to demands for restrictions on the use of 2,4,5-T and related herbicides. An environmental hazard was also presented by pentachlorophenol which include the more highly chlorinated dioxins, in particular octachlorodibenzo-p-dioxin (OCDD). The use of pholychlorophenol formulations was banned in Sweden on the grounds that heat-stable chlorodioxins were formed during incineration. This also pointed to the need for degradation by chemical means. Dehalogenation of polychlorodibenzodioxins (PCDD) was accomplished by photolysis in laboratory conditions but material adsorbed on soil was little affected. Cleavage of ether linkages with the formation of halophenols may be achieved by treatment with strong acids or quaternary ammonium salts. The dibenzodioxin nucleus was resistant to chemical attack and in the absence of a suitable control procedure the use of 2,4,5-T was restricted by the USA Environmental Protection Agency. Oxidative degradation of TCDD and related compounds by ruthenium tetroxide is reported.