Destruction of polychlorodibenzo-p-dioxins

Abstract

The release of 2,4,5-trichlorophenol (2,4,5-T) containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at Sèveso¹ highlighted the need for an efficient control procedure for the highly toxic² dioxin. The concomitant formation of the dioxin and the trichlorophenol during hydrolysis of sym-tetra-chlorobenzene has lead to demands for restrictions on the use of 2,4,5-T and related herbicides³. An environmental hazard is also presented by pentachlorophenol⁴ which includes the more highly chlorinated dioxins, in particular octachlorodibenzo-p-dioxin (OCDD). The use of pholychlorophenol formulations has been banned in Sweden on the grounds⁵ that heat-stable chlorodioxins are formed during incineration; this also points to the need for degradation by chemical means. Dehalogenation of polychlorodibenzodioxins (PCDD) can be accomplished by photolysis in laboratory conditions⁶, but material adsorbed on soil is little affected⁷. Cleavage of the ether linkages with the formation of halophenols may be achieved by treatment with strong acids or quaternary ammonium salts⁸. The dibenzodioxin nucleus, is however, rather resistant to chemical attack⁹ and in the absence of a suitable control procedure the use of 2,4,5-T has been restricted in the US by the Environmental Protection Agency^10,11. I now report the oxidative degradation of TCDD and related compounds by ruthenium tetroxide.