Abstract for TR-288

Toxicology and Carcinogenesis Studies of 1,3-Butadienein B6C3F1 Mice (Inhalation Studies)

CASRN: 106-99-0
Chemical Formula: C4H6
Molecular Weight: 54.09
Synonyms/Common Names: butadiene; biethylene; bivinyl; divinyl; erythrene; vinylethylene; pyrrolylene
Report Date: August 1984

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1,3-Butadiene is used as an intermediate in the production of elastomers, polymers, and other chemicals. Of the 1,3-butadiene used in 1978, 44% was used to manufacture styrene-butadiene rubber (a substitute for natural rubber, produced by copolymerization of 1,3-butadiene with styrene), and 19% was used to produce polybutane elastomer (a substance that increases resistance of tire products to wear, heat degradation, and blowouts). Chloroprene monomer, derived from 1,3-butadiene, is used exclusively to manufacture neoprene elastomers for non-tire and latex applications. Commercial nitrile rubber, used largely in rubber hoses, seals, and gaskets for automobiles, is a copolymer of 1,3-butadiene and acrylonitrile. Acrylonitrile- butadiene- styrene resins, usually containing 20%-30% 1,3-butadiene by weight, are used to make parts for automobiles and appliances. Other polymer uses include specialty polybutadiene polymers, thermoplastic elastomers, nitrile barrier resins, and K resins®. 1,3-Butadiene is used as an intermediate in the production of a variety of industrial chemicals, including two fungicides, captan and captofol. It is approved by the U.S. Food and Drug Administration for use in the production of adhesives used in articles for packaging, transporting, or holding food; in components of paper and paperboard that are in contact with dry food; and as a modifier in the production of semigrid and rigid vinyl chloride plastic food-contact articles. No information was located on the levels of monomer or on its elution rate from any of the commercially available polymers. It is not known if unreacted 1,3-butadiene migrated from packaging materials.

Male and female B6C3F1 mice were exposed to air containing 1,3-butadiene (greater than 99% pure) at concentrations of 0-8,000 ppm in 15-day and 14-week inhalation studies. In the 15-day studies, survival was unaffected by dose, and no pathologic effects were observed; slight decreases in mean body weight occurred at the high concentrations. In the 14-week studies, mean body weight gain decreased with dose, and survival in the 5,000-ppm and 8,000-ppm groups of males was markedly reduced; no other compound-related effects were reported.

Inhalation carcinogenesis studies of 1,3-butadiene were conducted by exposing groups of 50 male and female B6C3F1 mice 6 hours per day for 5 days per week to air containing the test chemical at concentrations of 0 (chamber controls), 625, or 1,250 ppm. These studies were planned for 103-week exposures but were terminated at week 60 for male mice and week 61 for female mice because of the rapidly declining survival, primarily due to neoplasia. Body weights were not affected by 1,3-butadiene.

Significantly increased incidences of neoplasms at multiple sites were observed in mice exposed to 1,3-butadiene. Hemangiosarcomas of the heart occurred at increased incidences in exposed males and females (male: control, 0/50; low dose, 16/49; high dose, 7/49; female: 0/50; 11/48; 18/49). Hemangiosarcomas were also observed in the peritoneal cavity (one high dose male), subcutaneous tissue (two low dose females), and liver (one high dose female).

Malignant lymphomas, diagnosed as early as week 20, were observed at increased incidences in exposed male and female mice (male: 0/50; 23/50; 29/50; female: 1/50; 10/49; 10/49).

Alveolar/bronchiolar adenomas and alveolar/bronchiolar (both separately and combined) occurred at increased incidences in exposed male and female mice (combined incidences -- male: 2/50; 14/49; 15/49; female: 3/49; 12/48; 23/49).

Epithelial hyperplasia of the forestomach occurred at increased incidences in dosed mice (male: 0/49; 5/40; 7/44; female: 0/49; 5/42; 9/49). Papillomas of the forestomach occurred in low dose male and in low dose and high dose female mice (male: 0/49; 5/40; 0/44; female: 0/49; 4/42; 10/49). Squamous cell carcinomas of the forestomach were observed in dosed mice (male: 0/49, 2/40, 1/44; female: 0/49, 1/42, 1/49).

Acinar cell carcinomas of the mammary gland were observed at an increased incidence in high dose female mice (0/50; 2/49; 6/49); adenosquamous carcinomas were found in four low dose females. The incidences of granulosa cell tumors of the ovary were increased in dosed females (0/49; 6/45; 12/48). A granulosa cell carcinoma was observed in another high dose female. Gliomas were observed in two 68- to 69-week-old low dose and one high dose male mice; brain tumors are uncommon even in 2-year old mice.

Liver necrosis occurred at increased incidences in dosed male and low dose female mice (male; 1/50, 8/49, 8/49; female: 6/50, 15/47, 6/49). Hepatocellular adenomas or carcinomas (combined) were observed at an increased incidence in high dose female mice (0/50, 2/47 5/49).

No neoplastic lesions of the nasal cavity were observed at any dose level. The following nonneoplastic lesions of the nasal cavity occurred in mice exposed at 1,250 ppm: chronic inflammation (male, 35/50; female, 2/49); fibrosis (male, 33/50; female, 2/49); cartilaginous metaplasia (male, 16/50; female, 1/49); osseous metaplasia (male, 11/50; female, 2/49); and atrophy of the sensory epithelium (male, 32/50). No nonneoplastic lesions of the nasal cavity were found in the controls. The incidence of testicular atrophy (0/50, 19/49, 11/48) or ovarian atrophy (2/49, 40/45, 40/48) was increased in exposed male or female mice.

An audit of the experimental data from these studies on 1,3-butadiene was conducted by the National Toxicology Program. No data discrepancies were found that influenced the final interpretation of these experiments.

Under the conditions of these studies, there was clear evidence of carcinogenicity for 1,3-butadiene in male and female B6C3F1 mice, as shown by increased incidences and early induction of hemangiosarcomas of the heart, malignant lymphomas, alveolar/bronchiolar adenomas and carcinomas, and papillomas of the stomach in males and females; and of acinar cell carcinomas of the mammary gland, granulosa cell tumors of the ovary, and hepatocellular adenomas and adenomas or carcinomas (combined) in females. 1,3-Butadiene was associated with nonneoplastic lesions in the respiratory epithelium, liver necrosis, and testicular or ovarian atrophy.

Note: See subsequent 1,3-Butadiene study, TR-434, reported May 1993.