National Toxicology Program

National Toxicology Program
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Abstract for TR-375 - Vinyl Toluene (Mixed Isomers) (65% meta-isomer and 32-35% para-isomer) (CASRN 25013-15-4)

ABSTRACT

Toxicology and Carcinogenesis Studies of Vinyl Toluene (Mixed Isomers) (65%-71% meta-isomer and 32-35% para-isomer) (CAS No. 25013-15-4) in F344/N Rats and B6C3F1 Mice (Inhalation Studies)

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Chemical Formula: C9H10

Vinyl Toluene is used as a monomer in the plastics and surface-coating industries. Toxicology and carcinogenesis studies were conducted by exposing groups of F344/N rats and B6C3F1 mice of each sex to vinyl toluene (mixed isomers: 65%-71% meta and 32%-35% para) by inhalation 6 hours per day, 5 days per week, for 15 days, 13 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, mouse L5178Y cells, and Chinese hamster ovary (CHO) cells.

Fifteen-Day Studies:

Rats were exposed to 0, 200, 400, 800, or 1,300 ppm vinyl toluene, and mice were exposed to 0, 10, 25, 50, 100, or 200 ppm. All rats lived to the end of the studies. The mean body weights at necropsy of rats exposed to 400-1,300 ppm were 13%-19% lower than that of controls for males and 9%-13% lower for females. Most male rats exposed to 1,300 ppm had centrilobular necrosis and focal inflammatory cell infiltration of the liver, whereas minimal centrilobular vacuolization of the liver was seen in all female rats exposed to 1,300 ppm. Dysplasia of the bronchial epithelial lining, chronic bronchitis, and lymphoid hyperplasia of the lung were observed in all rats exposed to 1,300 ppm.

Three of five male mice exposed to 200 ppm vinyl toluene died before the end of the studies. Four of five male mice exposed to 200 ppm had moderate-to-severe hepatocellular necrosis; all female mice exposed to 200 ppm had hyperplasia of the epithelium of the intrapulmonary bronchi and centrilobular necrosis, vacuolization, and inflammatory cell infiltrates in the liver.

Thirteen-Week Studies:

Rats were exposed to 0, 25, 60, 160, 400, or 1,000 ppm vinyl toluene. All rats lived to the end of the studies. The final mean body weights of rats exposed to 400-1,000 ppm were 8%-19% lower than that of controls for males and 6%-12% lower for females. Relative liver weights for rats at 1,000 ppm were significantly greater than those for controls. The severity of nephropathy was increased in male rats exposed to 160, 400, or 1,000 ppm. Compound-related lesions were not observed in female rats.

Mice were exposed to 0, 10, 25, 60, or 160 ppm vinyl toluene. The final mean body weights of mice exposed to 25-160 ppm were 12%-20% lower than that of controls for males and 13%-16% lower for females. Inflammation of the lung was observed in 5/10 male and 3/9 female mice exposed to 160 ppm. Metaplasia of the nasal turbinates was seen in all exposed groups.

Based on these results, 2-year studies were conducted by exposing groups of 49 or 50 rats of each sex to 0, 100, or 300 ppm vinyl toluene by inhalation, 6 hours per day, 5 days per week for 103 weeks. Groups of 50 mice of each sex were exposed to 0, 10, or 25 ppm on the same schedule.

Body Weights and Survival in the Two-Year Studies:

Mean body weights of male rats exposed to 300 ppm vinyl toluene and those of female rats exposed to 100 and 300 ppm were generally 4%-11% lower than those of controls. No significant differences in survival were seen between any groups of rats of either sex (male: control, 19/49; low dose, 17/50; high dose, 19/50; female: 31/50; 28/50; 26/50). Mean body weights of mice exposed to 25 ppm were 10%-23% lower than those of controls after week 8, whereas mice exposed to 10 ppm showed a weight decrement that was generally less than 10%. The survival of male mice exposed to 25 ppm was significantly greater than that of controls. No other significant differences in survival were seen between any groups of mice of either sex (male: 33/50; 30/50; 41/50; female: 36/50; 37/50; 34/50).

Nonneoplastic and Neoplastic Effects in the Two-Year Studies:

Degenerative and nonneoplastic proliferative lesions of the nasal mucosa were observed at increased incidences in exposed rats. These lesions included diffuse hyperplasia (goblet cell) of the respiratory epithelium with intraepithelial mucous cysts and focal erosion of the olfactory epithelium with cystic dilation (cysts) of the Bowman's glands. Focal respiratory epithelial metaplasia of the olfactory epithelium was seen in some exposed males, and cells with homogeneous eosinophilic cytoplasm in the olfactory epithelium occurred at increased incidences in exposed female rats. Neoplasms of the nasal mucosa were not seen in male or female rats.

There were no chemically related increases in neoplasm incidence in exposed male or female rats.

Degenerative and inflammatory lesions of the nasal mucosa were observed at increased incidences in exposed mice. These lesions included focal chronic active inflammation and diffuse hyperplasia of the respiratory epithelium. Chronic active inflammation of the bronchioles occurred in many exposed mice but not in controls. Neoplasms of the nasal passage were not observed in mice.

There were no chemically related increases in neoplasm incidence in exposed male or female mice. Exposure-related decreased incidences included alveolar/bronchiolar neoplasms (control, 12/50; 10 ppm, 5/49; 25 ppm, 2/49) and malignant lymphomas (7/50; 3/50; 0/50) in males and hepatocellular neoplasms (9/48; 5/16; 2/49) in females.

Genetic Toxicology:

Vinyl toluene did not induce gene mutations in S. typhimurium strains TA98, TA100, TA1535, or TA1537 with or without exogenous metabolic activation (S9). Vinyl toluene was positive in the mouse lymphoma assay for induction of trifluorothymidine resistance in L5178Y/TK cells in the absence of S9; it was not tested with S9. Vinyl toluene did not induce sister chromatid exchanges or chromosomal aberrations in CHO cells with or without S9.

Conclusions:

Under the conditions of these 2-year inhalation studies, there was no evidence of carcinogenic activity for male or female F344/N rats exposed to 100 or 300 ppm vinyl toluene and no evidence of carcinogenic activity for male or female B6C3F1 mice exposed to 10 or 25 ppm.

There was evidence of chemical-related toxicity to the nasal passage in both rats and mice.

Synonyms: 3-vinyl toluene and 4-vinyl toluene (mixed isomers)


Report Date: March 1990

Pathology Tables, Survival and Growth Curves from NTP 2-year Studies

Target Organs & Incidences from 2-year Studies


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