National Toxicology Program

National Toxicology Program

Abstract for TR-418 - p-Nitroaniline (CASRN 100-01-6)

Toxicology and Carcinogenesis Studies of p-Nitroaniline (CAS No. 100-01-6) in B6C3F1Mice (GavageStudies)

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Chemical Formula:C6H6N2O2

p-Nitroaniline is an intermediate in the preparation of several azodyes usedfor coloring consumer products. Toxicology and carcinogenicity studies wereconducted by administering p-nitroaniline (>99% pure) in corn oil bygavageto groups of male and female B6C3F1 mice for 14 days, 13 weeks, and 2years.Genetic toxicology studies were conducted in Salmonella typhimurium,Chinesehamster ovary cells, mouse Iymphoma cells, and Drosophilamelanogaster.


Groups of five male and five female B6C3F1 micereceivedp-nitroaniline in corn oil by gavage at doses of 0, 10, 30, 100, 300, or1,000mg/kg body weight 5 days per week for 2 weeks. All mice that received 1,000mg/kg died from chemical-related toxicity by day 4 of the studies. Final meanbody weights of mice receiving 300 mg/kg or less were similar to those of thecontrols. Hematology results were consistent with chemical-relatedmethemoglobinemia and regenerative anemia. Met hemoglobinconcentrations in allgroups of dosed mice were significantly higher than those in controls.Hematocrit values in mice that received 300 mg/kg and total erythrocytecountsin mice that received 100 or 300 mg/kg were significantly lower than those incontrols. Reticulocyte counts in 300 mg/kg male mice and in 100 or 300 mg/kgfemales were significantly higher than controls. Heinz bodies were observed inerythrocytes of all 300 mg/kg mice and in two 100 mg/kg male mice. Theabsoluteand relative spleen weights of 100 and 300 mg/kg mice were significantlygreater than those of the controls. Hematopoiesis and pigment (hemosiderin)accumulation were observed in the splenic red pulp of males and femalesreceiving 300 mg/kg; pigment (hemosiderin) accumulation in Kupffer cells oftheliver was also seen in male mice at this dose level.


Groups of 20 male and 20 female B6C3F1 micereceivedp-nitroaniline in corn oil by gavage at doses of 0, 1, 3, 10, 30, or 100mg/kgbody weight 5 days per week for up to 13 weeks. Eight or nine mice in eachgroup were evaluated at 7 weeks. There were no deaths associated withexposureto p-nitroaniline, and final mean body weights of dosed mice weresimilar tothose of the controls. Hematologic and pathologic findings at 7 and 13 weekswere similar to those seen in the 14-day studies and occurred primarily in the30 and 100 mg/kg groups. Met hemoglobin concentrations were increasedandhematocrit levels and erythrocyte counts were decreased relative to those ofthe controls. Heinz bodies were observed in erythrocytes and nucleatederythrocytes and reticulocytes were increased in number.

Absolute and relative spleen weights of male and female mice receiving30 and100 mg/kg were significantly greater than those of controls at 7 and 13 weeks.Absolute and relative liver weights of female mice necropsied at 7 weeks weresignificantly greater in the 30 and 100 mg/kg groups; by 13 weeks, bothabsolute and relative liver weights were similar to control values. Theincidence or severity of splenic hematopoiesis and pigmentation(hemosiderin)increased with dose at the 7-week interim evaluations and at the end of thestudies. Pigment (hemosiderin) was also present in Kupffer cells of the liverin dosed male mice.


Groups of 70 male and 70 female B6C3F1 micereceivedp-nitroaniline in corn oil by gavage at doses of 0, 3, 30, or 100 mg/kgbodyweight for 5 days per week for up to 103 weeks. The dose selection was basedonthe hematologic and pathologic findings of the 13-week studies. Nine or tenmice from each group were evaluated at 9 and 15 months for the presence ofchemical-related lesions.

Body Weights, Clinical Findings, Survival, and Hematology: Mean bodyweightsof male and female mice that received p-nitroaniline were similar tothose ofcontrol mice throughout the 2-year studies. There were no clinical findingsassociated with chemical exposure, and survival of dosed mice was similar tothat of controls. The hematology findings at the 9 and 15-month interimevaluations were similar to those in the 14-day and 13-week studies. The methemoglobin concentrations were significantly higher in all 30 or 100 mg/kgmice; sulfhemoglobin concentrations were significantly higher at 9 months inall 30 or 100 mg/kg female mice and at 15 months in 100 mg/kg females.Hematocrit and erythrocyte counts in 100 mg/kg mice were significantly lowerthan those in controls. By 9 months, reticulocyte counts were significantlyhigher in all 30 or 100 mg/kg mice. At 15 months, only the 100 mg/kg miceexhibited significantly higher reticulocyte counts.

Neoplasms and Nonneoplastic Lesions: Lesions related to theadministration ofp-nitroaniline occurred in the spleen, liver, and bone marrow, primarilyinmice receiving 30 or 100 mg/kg; these were observed at the 9- and 15-monthinterim evaluations and at the end of the studies. There were increases in theincidence or severity of splenic congestion, hematopoiesis, pigment(hemosiderin) accumulation, Kupffer cell pigmentation in the liver, and bonemarrow hypercellularity (hyperplasia).

The incidences of hemangiosarcoma of the liver (0 ppm, 0/50; 3 ppm,1/50; 30ppm, 2/50; 100 ppm, 4/50) and hemangioma or hemangiosarcoma(combined) at allsites (5/50, 3/50, 4/50, 10/50) were marginally increased in 100 mg/kg malemice. The incidence of hepatocellular adenoma or carcinoma (combined) wassignificantly decreased (25/50, 26/50, 25/50, 13/50) in 100 mg/kg malemice.


p-Nitroaniline is mutagenic in vitro. Itwas tested intwo laboratories for induction of gene mutations in several strains ofSalmonella typhimurium. Both studies showed positive results in strain TA98,with and without S9 activation; results were negative for all other strains.p-Nitroaniline was tested in two laboratories for induction of sistercrematedexchanges and chromosomal aberrations in Chinese hamster ovary cells. Inthesister cremated exchange study, one laboratory reported negative resultswithout S9 and positive results with S9; the second laboratory reportedequivocal results without S9 and negative results with S9. In the chromosomalaberrations study, both laboratories found positive results with S9. WithoutS9, one laboratory reported weakly positive results while the other reportednegative results. p-Nitroaniline induced trifluorothymidine resistance inL5178Y mouse Iymphoma cells in the absence of S9; no induction oftrifluorothymidine resistance was noted with S9. In contrast to the positiveresults in the previous tests, p-nitroaniline did not induce sex-linkedrecessive lethal mutations in germ cells of male Drosophila melanogasterwhenadministered by feeding or injection to adult males or by feeding to larvae.


Under the conditions of these 2-year gavage studiesthere wasequivocal evidence of carcinogenic activity of p-nitroaniline inmaleB6C3F1 mice based on the increased incidences of hemangiosarcoma of theliverand hemangioma or hemangiosarcoma (combined) at all sites. There wasnoevidence of carcinogenic activity of p-nitroaniline in female B6C3F1micereceiving doses of 3, 30, or 100 mg/kg.

Report Date: May 1993

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

Target Organs & Incidences from 2-year Studies

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