Carcinogenesis bioassay of chlorinated dibenzodioxins and related chemicals.

Chlorinated dibenzo-p-dioxins have been identified as trace contaminants of herbicides and pesticides. They may be formed as byproducts in the manufacture of chlorinated phenols and, for this reason, were implicated in outbreaks of chick edema disease (1). Fat trimmings obtained from animal hides preserved with dioxin-containing chlorophenol products and subsequently used in chicken feed contained the chick edema factor. Chloracne had been earlier observed in workers who had handled technical quality 2,4,5-trichlorophenol (2). Occasionally the condition was complicated by liver involvement and psychopathological changes. Pure 2,4,5-trichlorophenol had no effect when tested in an animal bioassay system. Tetrachlorodibenzodioxin (TCDD), which was isolated from the technical mixture, produced an effect at a concentration of 0.005%7, however (13). In addition, TDCC is the contaminant of the herbicide 2,4,5-T that produced teratogenic effects in rats (4). Subsequent work with pure TCDI) has indeed shown teratogenic and embryotoxic effects in rats and mice (5-7). The fact that the chlorinated dioxins are highly toxic, teratogenic, and acnegenic does not of necessity indicate they are carcinogens