Carcinogenicity of dichloroacetylene: an inhalation study.

Dichloroacetylene (DCA) is a by-product of the synthesis of certain chlorinated, aliphatic hydrocarbons (e.g., vinylidene chloride). In a long-term carcinogenicity inhalation study, groups of 30 male and 30 female rats and mice were exposed to DCA vapour under the following conditions: mice, group I: 9 p.p.m. 6 h/day, 1 day/week for 12 months; group II: 2 p.p.m. 6 h/day, 1 day/week for 18 months; group III: 2 p.p.m. 6 h/day, 2 days/week for 18 months; rats: 14 p.p.m. 6 h/day, 2 days/week for 18 months; controls: under identical conditions except for addition of DCA to breathing air. The most important result is a striking increase in the formation of kidney cystadenomas of the proximal tubuli in all DCA exposed animals. The median latency time of this tumor varied widely in both mice and rats. Renal cystic adenocarcinomas were found in statistically significant numbers in male mice. In addition to kidney tumors, the development of cystadenomas of the Harderian gland in mice and of liver cholangiomas in rats were highly significant findings. DCA failed to induce liver tumors in mice. Our results confirm that DCA possesses a high carcinogenic potential, pronounced organotropic properties and distinct species differences referring to the number and nature of the induced tumors. The risk associated with handling chlorinated aliphatic hydrocarbons is essentially increased by the decomposition product DCA.