C.I. vat yellow 4, a commercial formulation containing dibenzo(b,def)chrysene-7,14-dione, is used by the armed services as a smokescreen and as a signaling agent. Smoke dyes were effectively used to mask the movement of troops in World War II and in Korea, where in some instances men were exposed to chemical smokescreens for several months.
A bioassay of C.I. vat yellow 4 for possible carcinogenicity was conducted by administering the test chemical in feed to Fischer 344 rats and B6C3F1 mice.
Groups of 50 rats of each sex and 50 mice of each sex were administered C.I. vat yellow 4 in the diet at one of two doses, either 3,500 or 7,000 ppm for the rats, either 25,000 or 50,000 ppm for male mice, and either 12,500 or 25,000 ppm for the female mice. The rats were administered the test chemical for 104 weeks; the mice, for 106 weeks. Matched controls consisted of 20 untreated rats and 20 untreated mice of each sex. All surviving animals were killed at the end of the period of administration of the test chemical.
Mean body weights of the dosed rats were lower than those of corresponding controls throughout the bioassay, but the differences in weights were slight for the males. Mean body weights of the dosed mice were not affected by the test chemical. Survival of the rats and mice were not affected adversely by the chemical, and sufficient numbers of dosedand control rats and mice of each sex were at risk for the development of late-appearing tumors.
In the male and female rats and the female mice, no tumors occurred at incidences that were significantly higher in dosed groups than in control groups.
In the male mice, lymphomas occurred at incidences that were dose related (P=0.002) and, in a direct comparison, the incidence of the tumor in the high-dose group was significantly higher (P=0.019) than that in the control group (controls 3/20, or 15%; low-dose 7/47, or 15%; high-dose 22/50, or 44%). The incidence of lymphomas and leukemias in historical-control male B6C3F1 mice, at this laboratory was 38/323 (12%).
It is concluded that under the conditions of this bioassay, the formulated product containing C.I. vat yellow 4 was not carcinogenic for male or female Fischer 344 rats or for female B6C3F1 mice, but was carcinogenic for male B6C3F1 mice, causing an increased incidence of lymphomas.