Concern about delayed toxic effects which may follow exposure to 2,3,7,8tetrachlorodibenzo-p-dioxin (TCDD) is widespread, since diverse groups have been exposed to this potent chemical toxin. TCDD is formed during the synthesis of the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) from trichlorophenol (TCP) and is also generated when TCP is synthesized from tetrachlorobenzene. Workers have potential to be exposed to TCDD during these manufacturing processes, as well as in 2,4,5-T application [I, 21. Soldiers and civilians in Vietnam during the 1960's had potential exposure, since TCDD-contaminated 2,4,5-T was a principal ingredient of the defoliant Agent Orange. Residents of communities have been exposed following industrial accidents-as in Seveso, Italy in 1976; through contact with soil-as in Times Beach, Missouri, where TCDD-contaminated waste oil was used for dust control; and from exposure to the TCDD-contaminated combustion products of electrical transformer fires.
Acute toxicologic testing led to the discovery that TCDD was lethal to some species in doses of less than one microgram/kilogram of body weight. That finding earned TCDD the sobriquet of "most toxic man-made chemical. " Additional manifestations of acute animal toxicity include profound wasting, thymic atrophy, bone marrow suppression, hepatotoxicity, and microsomal enzyme induction [3-61. In addition, TCDD has been found to be teratogenic and fetotoxic in pregnant female mice [7-91. Finally, TCDD has been demonstrated to be carcinogenic in rats and mice [ 10,111. Preliminary data collected by the National Institute for Occupational Safety and Health (NIOSH) suggest a possible association between occupational exposure to TCDD and an increased number of deaths from soft-tissue sarcoma [12]. Further investigation will be required, however, to confirm that association.
Work by American, British, German, and Czechoslovakian physicians suggests that there is a range of toxic effects associated with TCDD exposure in man, especially in heavily exposed workers. Chloracne, an atypically persistent form of Division of Surveillance, Hazard Evaluations and Field Studies (DSHEFS), National Institute for Occupational Safety and Health (NIOSH),