Trichlorofluoromethane, a widely used halocarbon aerosol propellant and refrigerant, was selected for bioassay by the National Cancer Institute because of widespread exposure to this compound resulting from the indiscriminate use of aerosol sprays, and the well-documented hepatocarcinogenicity of the structurally analogous compound, carbon tetrachloride.
The bioassay of technical-grade trichlorofluoromethane for possible carcinogenicity was conducted using Osborne-Mendel rats and B6C3F1 mice. Trichlorofluoromethane in corn oil was administered by gavage, at either of two dosages, to groups of 50 male and 50 female animals of each species, 5 days per week, over a period of 78 weeks. The time-weighted average high and low dosages of trichlorofluoromethane in the chronic bioassay were, respectively, 977 and 488 mg/kg/day for male rats, 1,077 and 538 mg/kg/day for female rats, and 3,925 and 1,962 mg/kg/day for mice of both sexes. After a 78-week dosing period, rats were observed for an additional period of up to 33 weeks and mice were observed for an additional period of up to 13 weeks.
For each species, 20 animals of each sex were placed on test as vehicle controls. These animals were gavaged with corn oil at the same time that dosed animals were gavaged with trichlorofluoromethane. Twenty animals of each sex were placed on test as untreated controls for each species. These animals were not gavaged.
A high rate of early deaths occurred among male and female rats in this bioassay. An insufficient number of rats of either sex survived long enough to be at risk from late-developing tumors. Survival of mice was adequate for meaningful statistical analysis of late-developing tumors.
Results of a time-adjusted statistical analysis of tumor incidence in rats indicated no significant positive associations between administration of trichlorofluoromethane and tumor incidence.
No groups of male or female mice dosed with trichlorofluoromethane had significantly increased tumor incidences relative to their respective control groups.
The results of the bioassay of trichlorofluoromethane in Osborne-Mendel rats for possible carcinogenicity are not conclusive because inadequate numbers of rats survived sufficiently long enough to be at risk from late-developing tumors. Under the conditions of this bioassay, trichlorofluoromethane was not carcinogenic to male or female B6C3F1 mice.
|Male Rats:||Inadequate Study|
|Female Rats:||Inadequate Study|