Environmental generation and degradation of dibenzodioxins and dibenzofurans.

Chlorinated dibenzo-p-dioxins and dibenzofurans have been known to chemists for many years. 2,8-Dichlorodibenzo-p-dioxin was first reported in 1941 (1); the 2,3,7,8tetrachloro(TCDD) and octachloro(OCDD) analogs followed in 1957 (2). Extensive research by Gilman (3) and by Pohland and Yang (4) provided data on many others. Likewise, simple chlorinated dibenzofurans have been reported since the early 1930's (5), while experience with the more highly chlorinated ones is comparatively recent (6, 7). Although the unusual toxicity of certain of these compounds was recognized at an early date through occupational illness and toxic effects on domestic animals (8), major concern arose only when the toxic and teratogenic properties of TCDD became apparent in widely-distributed pesticides such as 2,4,5-T (9, 10). Subsequent analysis (7, 11, 12) showed that a variety of chlorinated dibenzo-p-dioxins and dibenzofurans can occur as impurities from the manufacture of many industrial and agricultural chemicals based on chlorophenols and certain chlorinated aromatic hydrocarbons. To cite but a single example, production statistics (13) suggest that at least 50 million pounds of 2,4,5-trichlorophenol and its derivatives are manufactured in the United States each year,