Abstract for TR-272

Toxicology and Carcinogenesis Studies of Propylene in F344/N Rats and B6C3F1 Mice (Inhalation Studies)

CASRN: 115-07-1
Chemical Formula: C3H6
Molecular Weight: 42.08
Synonyms/Common Names: Propene; methylethylene; methylethene
Report Date: November 1985

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Propylene is used as a starting material in the production of polypropylene plastics and various other chemicals, including acrylonitrile, isopropyl alcohol, propylene oxide, butyraldehyde, cumene, dodecane, nonene, and allyl chloride. The major derivatives are polypropylene (25%), acrylonitrile (15%), isopropyl alcohol (10%), and propylene oxide (10%). It is also a valuable feed-stock chemical for the production of gasoline. Other miscellaneous applications include use as a starting material for polymerization reactions to form vinyl chloride copolymers and low-molecular-weight homopolymers that are used as additives in lubricating oils and in the manufacture of hydroquinone. The chemical is also used as an aerosol propellant or component. The major end uses of propylene are in the production of fabricated plastics (50%) and fibers (15%).

Toxicology and carcinogenesis studies of propylene (greater than 99% pure) were conducted by exposing groups of 50 F344/N rats and 49 or 50 B6C3F1 mice of each sex to propylene in air by inhalation at concentrations of 5,000 or 10,000 ppm, 6 hours per day, 5 days per week, for 103 weeks. Other groups of 50 rats and 50 mice of each sex in chambers received air only on the same schedule and served as chamber controls. The highest concentration of propylene that was considered safe for these studies was 10,000 ppm because of the risk of explosion that can occur at higher concentrations.

The survival of exposed and control rats and mice was comparable. Throughout most of the studies, mean body weights of exposed male and female rats were slightly lower (0%-5%) than those of the controls, but the decrements were not concentration related. After week 59 of the study, mean body weights of 10,000-ppm male mice were usually slightly lower (5%) than those of the controls, whereas those in other exposed groups of male and female mice were generally comparable with those of the controls. No compound-related adverse clinical signs were observed in either species.

An increased incidence of squamous metaplasia of the nasal cavity was observed in female rats exposed at the 5,000-ppm and 10,000-ppm concentrations (control, 0/49; low, 15/50; high, 6/50) and in male rats exposed at 5,000 ppm (2/50; 19/50; 7/50). Epithelial hyperplasia of the nasal cavity was increased in female rats exposed at the 10,000-ppm concentration (0/49; 4/50; 9/50); the incidences in male rats were 2/50, 2/50, and 5/50. Inflammation of the nasal cavity, characterized by an influx of lymphocytes, macrophages, and granulocytes into the submucosa and by granulocytes into the lumen, occurred at increased incidences in low concentration and high concentration male rats and in high concentration female rats. Chronic focal inflammation of the kidneys occurred at an increased incidence in low concentration and high concentration mice of each sex.

Hemangiosarcomas were found in one low dose male mouse (liver), two high dose male mice (spleen), and three high dose female mice (subcutis, spleen, and uterus). Hemangiomas were found in one low dose and in one high dose female mouse (liver). Vascular tumors were not found in control mice of either sex. The low incidences of vascular tumors and their occurrence in a variety of organs suggest that they are not related to administration of propylene.

The occurrence of uterine endometrial stromal polyps in female mice showed a positive trend (P<0.05; 0/47; 0/47; 3/48); the incidence in the 10,000-ppm group was not significantly greater than that in the concurrent control group, but the incidence was higher than the mean historical control rate (22/2,411, 0.9%) and was within the range (0%-6%) observed in studies throughout the Carcinogenesis Program. The occurrence of endometrial stromal polyps in three high concentration female mice was not considered to be clearly related to exposure to propylene.

The incidence of male mice with alveolar/bronchiolar adenomas or carcinomas (combined) occurred with a negative trend (P<0.05; 16/50; 4/49; 7/50), and the reduced incidences in both exposed groups were less (P<0.05) than that in the control group. The control incidence of these tumors in an inhalation study conducted concurrently at the same laboratory was similar (15/50), suggesting a possible exposure-related decrease. The biologic significance of this decrease in male mice is difficult to assess; the incidences seen in these control and exposed animals are within the range of incidences (2%-34%; mean, 16.7%) observed in control male mice in other studies throughout the Carcinogenesis Program.

An audit of the experimental data was conducted for these carcinogenesis studies on propylene. No data discrepancies were found that influenced the final interpretations.

Under the conditions of these studies, there was no evidence of carcinogenicity in male and female F344/N rats or in male and female B6C3F1 mice exposed to propylene by inhalation at concentrations of 5,000 or 10,000 ppm for 103 weeks. In the nasal cavity, propylene induced squamous metaplasia of the respiratory epithelium in male and female rats and epithelial hyperplasia in female rats.