Acrylonitrile is used in the production of acrylic and modacrylic fibers, elastomers, acrylonitrile-butadiene-styrene and styrene-acrylonitrile resins, nitrile rubbers, gas barrier resins, and chemical intermediates such as adiponitrile and acrylamide. Acrylonitrile was nominated for study by the National Institute of Environmental Health Sciences because of its potential for human exposure, its classification as a probable human carcinogen, evidence of its carcinogenicity in rats, and the lack of carcinogenicity studies in a second animal species. Male and female B6C3F1 mice received acrylonitrile (greater than 99% pure) in deionized water by gavage for 14 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, L5178Y mouse lymphoma cells, cultured Chinese hamster ovary cells, Drosophila melanogaster, and mouse peripheral blood erythrocytes.
Fourteen-week study
Groups of 10 male and 10 female mice were administered 0, 5, 10, 20, 40, or 60 mg acrylonitrile/kg body weight in deionized water by gavage, 5 days per week, for 14 weeks. All male and nine female mice in the 60 mg/kg groups and eight male and three female mice in the 40 mg/kg groups died on the first day of the study. The mean body weight gain of 20 mg/kg males was less than that of the vehicle control group. Clinical findings included lethargy and abnormal breathing in the 40 mg/kg groups. Leukocyte and lymphocyte counts were decreased in 20 mg/kg males and 40 mg/kg females, and a minimal hemolytic anemia was observed in 40 mg/kg females. Heart weights of 20 mg/kg males were significantly greater than those of the vehicle controls, and left cauda epididymis weights of 10 and 20 mg/kg males were significantly increased. The incidences of chronic active inflammation and hyperplasia in the forestomach of 40 mg/kg females were significantly increased.Two-year study
Groups of 50 male and 50 female mice were administered acrylonitrile in deionized water by gavage at doses of 0, 2.5, 10, or 20 mg/kg, 5 days per week, for 104 to 105 weeks. Urine from five male and five female mice from each group was collected at 2 weeks and at 3, 12, and 18 months and analyzed for thiocyanate and N-acetyl-S-(2-cyanoethyl)-L-cysteine concentrations as markers of exposure to acrylonitrile.
Survival, body weights, and urinary metabolite analyses
Survival of 20 mg/kg mice was significantly less than that of the vehicle control groups. Mean body weights of 20 mg/kg males and females were generally less than those of the vehicle controls throughout most of the study. Dose-related increases in urinary thiocyanate and N-acetyl-S-(2-cyanoethyl)-L-cysteine concentrations occurred in all dosed groups at 2 weeks and at 3, 12, and 18 months.
Pathology findings
The incidences of squamous cell papilloma, squamous cell carcinoma, and squamous cell papilloma or carcinoma (combined) of the forestomach occurred with positive trends in males and females, and were present in 50% or greater of mice administered 10 or 20 mg/kg. The incidences of mild focal or multifocal epithelial hyperplasia (combined) of the forestomach in 20 mg/kg males and females and of mild diffuse or focal hyper-keratosis (combined) in 20 mg/kg males were increased. The incidences of harderian gland adenoma and adenoma or carcinoma (combined) were significantly increased in all dosed groups of males and in 10 and 20 mg/kg females, and the incidence of harderian gland hyperplasia was significantly increased in 10 mg/kg males.
The incidence of benign or malignant granulosa cell tumor (combined) in the ovary of 10 mg/kg females was greater than that in the vehicle controls. The incidences of atrophy and cyst in the ovary of 10 and 20 mg/kg females were significantly increased. The incidence of alveolar/bronchiolar adenoma or carcinoma (combined) in 10 mg/kg females was significantly increased.
Genetic toxicology
Acrylonitrile was mutagenic in S. typhimurium strains TA100 and TA1535 in the presence of S9 liver enzymes; it was not mutagenic without S9 activation in these two strains. No mutagenic activity was observed in strain TA97 or TA98 with or without S9. Acrylonitrile was mutagenic in mouse lymphoma L5178Y cells in the absence of S9; it was not tested with S9. In cultured Chinese hamster ovary cells, acrylonitrile induced sister chromatid exchanges with and without S9; chromosomal aberrations were significantly increased in the presence of S9 only. Tests for induction of sex-linked recessive lethal mutations in germ cells of male D. melanogaster were negative when acrylonitrile was administered in feed or by injection. A test for induction of reciprocal translocations in male D. melanogaster was negative. In contrast to the induction of chromosomal damage by acrylonitrile in mammalian cells in vitro, no increase in the frequency of micronucleated normochromatic erythrocytes was observed in peripheral blood samples from male or female mice administered acrylonitrile by gavage for 14 weeks. In summary, acrylonitrile induced genetic damage in vitro in bacterial and mammalian cells, but in vivo test results in D. melanogaster and in mice were negative.Conclusions
Under the conditions of this 2-year gavage study, there was clear evidence of carcinogenic activity of acrylonitrile in male and female B6C3F1 mice based on increased incidences of forestomach and harderian gland neoplasms. Neoplasms of the ovary and lung in female mice may have been related to administration of acrylonitrile.
Nonneoplastic lesions of the forestomach and harderian gland in males and of the forestomach and ovary in females were associated with administration of acrylonitrile by gavage for 2 years.