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Abstract for TR-498 - p-Nitrotoluene (CASRN 99-99-0)

Abstract

Toxicology and Carcinogenesis Studies of p-Nitrotoluene (CAS No. 99-99-0) in F344/N Rats and B6C3F1 Mice (Feed Studies)

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Chemical Formula: C7H7NO2

p-Nitrotoluene is used to synthesize agricultural and rubber chemicals, azo and sulfur dyes, and dyes for cotton, wool, silk, leather, and paper. p-Nitrotoluene was nominated by the National Institute for Occupational Safety and Health and the NTP based on its considerable human exposure as well as the absence of long-term studies of carcinogenicity in rodents. Male and female F344/N rats and B6C3F1 mice were exposed to p-nitrotoluene (greater than 99% pure) in feed for 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, L5178Y mouse lymphoma cells, cultured Chinese hamster ovary cells, and rat and mouse bone marrow cells.

2-YEAR STUDY IN RATS

Groups of 50 male and 50 female rats were fed diets containing 0, 1,250, 2,500, or 5,000 ppm p-nitrotoluene (equivalent to average daily doses of approximately 55, 110, or 240 mg p-nitrotoluene/kg body weight to males and 60, 125, or 265 mg/kg to females) for 105 or 106 weeks.

Survival, Body Weights, and Feed Consumption

Survival of all exposed groups of rats was similar to that of the control groups. Mean body weights of 5,000 ppm male and 2,500 and 5,000 ppm female rats were less than those of the controls during most of the study; mean body weights of 1,250 ppm females were less during the second year of the study. Feed consumption by 5,000 ppm females was less than that by the controls during year 2 of the study.

Biomarkers of Exposure

Two urinary metabolites were followed during the study as biomarkers of exposure. The ratios of p-nitrobenzoic acid to creatinine and of p-acetamidobenzoic acid to creatinine determined at 2 weeks and at 3, 12, and 18 months were linearly related to exposure in males and females.

Pathology Findings

The incidence of clitoral gland adenoma or carcinoma (combined) was significantly greater in 2,500 ppm females than that in the controls and exceeded the historical control ranges. The incidence of clitoral gland neoplasms was not increased in 5,000 ppm females, possibly because of the lower body weights in this group. The incidences of subcutaneous fibroma and of subcutaneous fibroma or fibrosarcoma (combined) in 2,500 ppm male rats were significantly increased and exceeded the historical control ranges.

The incidences of several nonneoplastic kidney lesions were significantly increased in exposed groups of rats, and the severities of these lesions generally increased males and endometrial cystic hyperplasia of the uterus in 2,500 and 5,000 ppm females were significantly increased.

The incidences of mononuclear cell leukemia were significantly decreased in all exposed groups except 1,250 ppm females. The incidence of interstitial cell adenoma of the testis in 5,000 ppm males was significantly decreased.

2-YEAR STUDY IN MICE

Groups of 50 male and 50 female mice were fed diets containing 0, 1,250, 2,500, or 5,000 ppm p-nitrotoluene (equivalent to average daily doses of approximately 170, 345, or 690 mg/kg to males and 155, 315, or 660 mg/kg to females) for 105 or 106 weeks.

Survival, Body Weights,and Feed Consumption

Survival of all exposed groups of male and female mice was similar to that of the control groups. Mean body weights of 5,000 ppm males and females were less than those of the control groups during most of the study. Mean body weights of 2,500 ppm males were less than those of the controls after week 92. Feed consumption by all exposed groups of mice was similar to that by the control groups.

Pathology Findings

The incidence of alveolar/bronchiolar adenoma or carcinoma (combined) was significantly greater in 5,000 ppm male mice than that in the controls, as was the incidence of alveolar epithelial hyperplasia in this group. The incidences of alveolar epithelial bronchiolization were significantly increased in all exposed groups of males and females.

GENETIC TOXICOLOGY

p-nitrotoluene was not mutagenic in any of several strains of S. typhimurium, with or without metabolic activation enzymes (S9) . A positive response was observed with p-nitrotoluene in the L5178Y mouse lymphoma cell assay in trials with S9. Significantly increased sister chromatid exchange frequencies were observed in cultured Chinese hamster ovary cells treated with p-nitrotoluene with and without S9. Chromosomal aberrations were also induced in Chinese hamster ovary cells treated with p-nitrotoluene in the presence of S9; no increased aberrations were seen without S9. p-nitrotoluene did not induce a significant reproducible increase in the frequency of micronuclei in bone marrow polychromatic erythrocytes of male rats or male mice when administered by intraperitoneal injection.

CONCLUSIONS

Under the conditions of these 2-year feed studies there was equivocal evidence of carcinogenic activity of p-nitrotoluene in male F344/N rats based on increased incidences of subcutaneous skin neoplasms. There was some evidence of carcinogenic activity of p-nitrotoluene in female F344/N rats based on increased incidences of clitoral gland neoplasms. There was equivocal evidence of carcinogenic activity of p-nitrotoluene in male B6C3F1 mice based on increased incidences of alveolar/bronchiolar neoplasms. There was no evidence of carcinogenic activity of p-nitrotoluene in female B6C3F1 mice exposed to 1,250, 2,500, or 5,000 ppm.

Exposure to p-nitrotoluene caused increased incidences of nonneoplastic lesions of the kidney, spleen, and liver in male and female rats, testis in male rats, and lung in male and female mice.

Decreased incidences of mononuclear cell leukemia in male and female rats and testicular interstitial cell adenoma in male rats were attributed to exposure to p-nitrotoluene.

Synonyms: Methyl nitrobenzene; 1-methyl-4-nitrobenzene; 4-methylnitrobenzene; p-methylnitrobenzene; p-nitrophenylmethane; 4-nitrotoluol; 4-nitrotoluene; PNT


Summary of the 2-Year Carcinogenesis and Genetic Toxicology Studies of p-Nitrotoluene
 

Male
F344/N Rats

Female
F344/N Rats

Male
B6C3F1 Mice

Female
B6C3F1 Mice

Concentrations
in feed

0, 1,250, 2,500, or 5,000 ppm

0, 1,250, 2,500, or 5,000 ppm

0, 1,250, 2,500, or 5,000 ppm

0, 1,250, 2,500, or 5,000 ppm

Body weights

5,000 ppm group less than the control group

Exposed groups less than the control group

2,500 and 5,000 ppm
groups less than the
control group

5,000 ppm group less than the control group

Survival rates

31/50, 38/50, 38/50, 40/50

39/50, 37/50, 39/50, 41/50

46/50, 46/50, 45/50, 42/50

46/50, 47/50, 43/50, 49/50

Nonneoplastic effects

Kidney: renal tubule hyaline droplet (2/50, 23/50,27/50,18/50); renal tubule pigmentation (10/50, 28/50, 47/50, 46/50)

Spleen: hematopoietic cell proliferation (9/50, 13/50, 19/50, 25/50); pigmentation (10/50, 12/50, 24/50, 38/50)

Liver: basophilic focus (31/50, 39/50, 42/50, 45/50); clear cell focus (20/50, 27/50, 30/50, 32/50); eosinophilic focus (5/50, 5/50, 5/50, 19/50)

Testis: germinal epithelial atrophy (7/50, 11/50, 8/50, 30/50)

Kidney: renal tubule hyaline droplet (8/50, 41/50, 49/50, 46/50); renal tubule pigmentation (9/50, 43/50, 49/50, 50/50); mineralization (15/50, 21/50, 32/50, 40/50); oncocytic renal tubule hyperplasia (0/50, 2/50, 4/50, 6/50)

Spleen: hematopoietic cell proliferation (26/50, 26/50, 45/50, 43/50); pigmentation (24/50, 32/50, 45/50, 48/50)

Liver: eosinophilic focus (1/50, 2/50, 7/50, 9/50)

Lung: alveolar epithelial bronchiolization (0/50, 20/50, 30/50, 48/50); alveolar epithelial hyperplasia (1/50, 1/50, 4/50, 6/50)

Lung: alveolar epithelial bronchiolization (0/50, 33/50, 41/50, 49/50)

Neoplastic effects

None

Clitoral gland: adenoma or carcinoma (8/50, 12/50, 20/50, 8/49)

None

None

Equivocal findings

Skin (subcutaneous): fibroma (1/50, 2/50, 7/50, 1/50); fibroma or fibrosarcoma (1/50, 2/50, 9/50, 1/50)

None

Lung: alveolar/bronchiolar adenoma or carcinoma (8/50, 14/50, 12/50, 19/50)

None

Decreased incidences

Mononuclear cell leukemia: (24/50, 12/50, 5/50, 4/50)

Testis: interstitial cell adenoma (49/50, 46/50, 45/50, 34/50)

Mononuclear cell leukemia: (13/50, 12/50
3/50, 1/50)

None

None

Level of evidence of carcinogenic activity

Equivocal evidence

Some evidence

Equivocal evidence

No evidence

Genetic Toxicology of Butyl Benzyl Phthalate
Assay Test System Results
Bacterial Mutagenicity Salmonella typhimurium gene mutations: Negative in strains TA98, TA100, TA 1535, and TA1537 with and without S9
Mammalian Cell Mutagenicity Mouse lymphoma gene mutations: Positive with S9, negative without S9
Sister chromatid exchanges Cultured Chinese hamster ovary cells in vitro: Positive with and without S9
Chromosomal aberrations Cultured Chinese hamster ovary cells in vitro: Positive with S9, negative without S9
Micronucleated erythrocytes Rat bone marrow in vivo: Negative when administered by intraperitoneal injection
Micronucleated erythrocytes Mouse bone marrow in vivo: Negative when administered by intrapentoneal injection

Report Date: May 2002

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

Target Organs & Incidences from 2-year Studies

 


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