The repeated dose toxicity of a zinc oxide/hexachloroethane smoke.

Mice, rats and guinea pigs were exposed to the smoke produced by ignition of a zinc oxide/hexachloroethane pyrotechnic composition, 1 h/day, 5 days/week, at three different dose levels, together with controls. The animals received 100 exposures except for the high dose guinea pigs, which underwent 15 exposures, because of high death rate during the first few days of exposure. The test material had very little effect on weight gain, but there was a high rate of early deaths in the top dose of mice. A variety of incidental findings was seen in both decedents and survivors, but organ specific toxicity was, with one exception, confined to the respiratory tract. The most important of these findings was a statistically significant increase in the frequency of alveologenic carcinoma in the high dose group mice (p less than 0.01) and a statistically significant trend in the prevalence of the same tumour over all dose groups and the controls. A variety of inflammatory changes was seen in the lungs of all species and some appeared to be treatment-related. Fatty change in the mouse liver was more common in the middle and high dose groups than the controls. The aetiology of the tumour incidence is discussed and it is pointed out that hexachloroethane and zinc, as well as carbon tetrachloride, which may be present in the smoke, may be animal carcinogens in appropriate circumstances. Carbon tetrachloride is a known human carcinogen.