Nitroethane

Carcinogenicity

Key value for chemical safety assessment

Carcinogenicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

circa 1986

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was not conducted according to guidelines but was conducted according to GLPs and the report contains sufficient data for interpretation of study results.

Principles of method if other than guideline:

Similar to OECD Guideline Number 453 Combined Chronic Tox/Carcinogenicity Study Male and female Long-Evans rats were exposed by inhalation to vapors of nitroethane (NE) at either 100 ppm or 200 ppm, seven hours per day, five days per week for two years. General observations were made daily and body weights were obtained weekly or biweekly. During the study any rats that were found dead or sacrificed moribund were given a thorough gross examination and tissues retained for microscopic examination. After two years of inhalation of NE, all surviving rats were sacrificed. Blood samples were obtained from selected individuals for hematology and serum chemistry studies. All rats were examined histopathologically.

GLP compliance:

yes

Species:

rat

Strain:

Long-Evans

Sex:

male/female

Details on test animals or test system and environmental conditions:

The laboratory animals selected for this investigation were Long-Evans rats having the strain designation of BLU:(LE)BR and were obtained from the Blue Spruce Farms, Altamont, N.Y. After arrival at the laboratory, the animals were quarantined and acclimated to the laboratory conditions,During the investigation all animals were individually housed in stainless steel wire mesh cages and were maintained in air-conditioned quarters except during the periods of exposure. A standard laboratory animal diet and water were freely available to the animals except during the daily exposure period. During exposure, food and water were removed from the cages of all animals including controls in order to reduce alimentary exposure to NE,

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

Vapors of NE were generated by bubbling purified nitrogen through liquid NE in an all-glass vessel maintained in a thermostatted water bath at a temperature of 45C. Sufficient liquid NE to maintain a constant liquid level in the generator was added automatically.The exposure chambers were 5 ft. wide, 5 ft. high and 5 ft. deep with tapering conical sections above and below. Chamber contents were exhausted from the lower section. The effluent from the NE vapor generators were conducted to a vortex part of the upper conical section where it was mixed with filtered air-conditioned air. The chambers were operated in the open dynamic mode.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of NE within the chamber was monitored using a MIRAN IA infra-red gas analyzer. Concentrations were monitored at least three and usually four times each day.

Duration of treatment / exposure:

7 hours/day

Frequency of treatment:

5 days/week for 2 years

Post exposure period:

Not applicable

Remarks:

Doses / Concentrations:0, 100 or 200 ppm NEBasis:nominal conc.

No. of animals per sex per dose:

40 males and 40 females/concentration (high concentration had 41 males and 39 females)

Control animals:

yes, concurrent no treatment

Details on study design:

One hundred twenty one (121) male and one hundred nineteen (119) female rats were randomly assigned to the following groups:Group - Male Female NE conc. (ppm)CONTROL (I) 40 40 0EXPOSED (II) 40 40 100EXPOSED (III) 41 39 200The intent was to assign 40 animals of each sex to each group, but after exposure was begun, it was determined that one animal assigned to group III - female was actually a male. The rats assigned to exposure groups (II and III) were exposed to appropriate concentrations of NE for seven hours daily, five days each week, for two years.

Positive control:

No positive control was used.

Observations and examinations performed and frequency:

The animals were observed daily for general appearance and for signs of pharmacologic, behavioral or other toxic effects of exposure to NE. Moribund animals were sacrificed and these and any animals found dead were subjected to the pathological examination described below.The animals were weighed weekly during the first six months of the study and at two-week intervals thereafter.

Sacrifice and pathology:

At the time of the terminal sacrifice, blood samples were obtained from 10 male and 10 female rats for clinical laboratory studies of hematology and serum chemistry. Hematologic parameters examined included:Erythrocyte Count (RBC) - xl0(6)/mm(30 via Royco Cell Crit 921 cell counterLeucocyte Count (WBC) - xl0(6)/mm(3) via Royco Cell Crit 921 cell counterMean Corpuscular Volume (MCV) - fL via Royco Cell Crit 921 cell counterPacked Cell Volume (HCT) - % via Royco Cell Crit 921 cell counterHemoglobin (HGB) - g% via Cyanmethemoglobin Colorimetric Method using Chemetrics Analyzer IISerum chemistry parameters included:Serum glutamic-Oxaloacetic transaminase, also known as serum aspartite aminotransferase, (SGOT) - U/L measured with Modified Amador and Wacker Method using Chemetrics Analyzer IISerum Glutamic-Pyruvic transaminase, also known as alanine aminotransferase, (SGPT) - U/L measured with Modified Henry Procedure using Chemetrics Analyzer IITotal Bilirubin (BILI) - mg/dl measured with Diazo Method using Chemetrics Analyzer IITotal Protein (PROT) - g/dl measured with Biuret Method using .Chemetrics Analyzer I1Blood Urea Nitrogen (BUN) - mg/dl measured with Modified Urease Technique using Chemetrics Analyzer IICreatinine (CREAT) - mg/dl measured with Modified Fabini and Ertingshausen using Chemetrics Analyzer IISodium (NA) - meq/l measured with Flame photometrypotassium (K) - meq/l measured with Flame photometryPathology: Full necropsies were performed on all animals found dead or sacrificed moribund and on all remaining animals surviving two years. Each of the animals was given a thorough gross examination and the following organs were weighed: brain (including cerebellum and medulla), liver, kidneys, lungs and heart.The following organs and tissues were examined, removed and fixed in 10% buffered formalin for processing and preparation ofslides for microscopic examination:liver, heart, lung, artery or aorta, lymph nodes, thymus, spleen, salivary gland, pancreas, kidneys, urinary bladder, mammary glands, trachea, thyroid, esophagus, stomach, colon, intestine, adrenals, eye, pituitary, brain (including cerebrum, cerebellum and medulla), muscle, nerve, bone, bone marrow, skin and subcutis, spinal cord. For males: testes, prostate, epididymas, seminal vesicles. For females: ovaries, uterus, cervix, oviduct.

Other examinations:

No additional information available.

Statistics:

a) Chamber concentrations - the daily concentration of NE in each chamber was calculated as the arithmetic mean of the individual concentration measurements. Concentrations for each week of the study were calculated as the mean of the daily concentrations.b) Body weights - means and standard deviations of the weekly (or bi-weekly) body weights of each sex and group were calculated, Comparisons were made between the control and exposed groups using Student's "t" test, c) Organ weights and clinical laboratory data - organ weights were expressed as both absolute weight (grams) and weight relative to the whole body weight (% of body weight), Means and standard deviations of each of these parameters and the parameters of clinical chemistry and hematology were calculated, Variances were tested for homogeneity using Bartlett's test, and in cases where the variances proved to be homogeneous, an analysis of variance (ANOVA) was performed. If the ANOVA indicated statistical significance between means at p=,05, Duncan's Multiple Range test was used to determine which pairs of means-were.significantly different.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

very slight reduction in body weight which may or may not be treatment related

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

Conditions of Exposure: The grand average of the weekly means of the chamber operated at a nominal level of 100 ppm (Group II) was 99.8 ppm, and of the chamber operated at 200 ppm (Group III) was 199.2 ppm. The altitude of the site of the experiment (Alamogordo, New Mexico) is 1350 meters, and at 25C, a concentration of 99.8 ppm is equivalent to 263 mg of NE per cubic meter of air. Similarly, a concentration of 199.2 ppm is equivalent to 525 of NE per cubic meter of air.General Observations: During the two years of exposure to NE, the rats tolerated the exposures well and did not display pharrnacologic or other overt effects of exposure to the nitroparaffin. The number of animals surviving the full two years of exposure to NE was approximately the same among the various control and exposed groups, although the largest number (and percent) of surviving animals was among both male and female rats exposed to NE at 200 ppm. Survival is shown in Table 1.Body Weights: Generally, after exposure was initiated, the mean body weights of exposed groups of rats was less than the mean body weights ofthe control groups, although the difference was small. At the selected probability (p) value of 0.05, the "t" test indicated statistical significance throughout the study between Group I (control) and Group II (exposed - 100 ppm) males, although, surprisingly, statistical significance between Group I and Group III (exposed - 200 ppm) males occurred only during weeks 6-15 and occassionally thereafter, Among the females, statisticallysignificant differences were observed throughout the entire study between Group I and Group III but only occassionally between Group I and Group II animals. The lack of a well-defined relationship between body weight and exposure concentration of NE, at least among the males, suggests that factors other than exposure to NE may have been involved, Although every attempt was made to duplicate conditions between exposed and control groups, including removal of food during exposure periods, the control animals were not housed in an exposure chamber during the exposure periods. This small difference in treatment of the groups may have influenced the body weights.During weeks 80-82, a small decrease in mean body weights was observed among all groups, including controls. Clinical signs observed among the animals, and among other rats in the colony concurrently but not assigned to this study, were consistant with an intercurrent infection of sialodacryoadenitis virus. This condition causes swelling of salivary glands among some individuals, as well as reduced food consumption and weight loss, but is otherwise a mild and self-limiting infection. Mortality is very low and did not appear to influence mortality rates in the present study.Hematology: At the termination of the investigation, blood samples were obtained from selected animals for studies of hematology. At the selected probability level of 0.05, there was no effect of exposure of male or female rats to 100 ppm or 200 ppm of NE on erythrocyte count, packed cell volume, mean corpuscular volume, or hemoglobin. Heterogeneous variances precluded ANOVA calculations of male leucocyte count data if all values were included, but an inspection of the data showed that one outlying value in Group I caused the heterogeneity. If this value is eliminated, the ANOVA calculation is permitted and no significant differences between any pairs of means is indicated. Similarly, a single outlying value in a Group III animal prevented ANOVA calculation of the female leucocyte count data, but if eliminated, allowed the ANOVA calculation which showed no statistically different means.Serum Chemistry: There was no effect of exposure of male or female rats to either 100 ppm or 200 ppm of NE on glutamic-oxaloacetic transaminase (SGOT), glutamic-pyruvic transaminase (SGPT), total bilirubin, sodium or potassium. In the case of SGOT and SGPT calculations of ANOVA among females, a single outlying value was eliminated from Group III. There was no significant difference between means of total protein among male rats, but at p=0.05, there was a slight but significant elevation of total protein among Group III (200 ppm) females as compared to Group I (controls). Elevations of blood urea nitrogen (BUN) of two male rats in Group II (100 ppm) prevented ANOVA calculations, but there was no difference between Group I (controls) and Group III (200 pprn). There was a statistically significant difference in BUN between Group I (control) females and Group III (200 ppm) females, but not between Group I and Group II (100 ppm). Two males in Group II with elevated-creatinine levels prevented ANOVA calculation but an examination of the means does not suggest an effect of NE. There was no significant difference between means of creatinine levels among females.Organ Weights: Statistical calculations were performed on the organ weight data from animals surviving to the terminal sacrifice. This included determination of mean, standard deviation, a test for homogeneity of variance and ANOVA where applicable. An examination of the data does not suggest any biologically significant effect of NE on weights of the major organs. Although heterogeneous variances restricted ANOVA calculations of most liver data, there was no evidence of an effect on liver weights, and it can be said with certainty that there was no enlargement or increase in liver weight resulting from inhalation of NE. There was no statistically significant effect on absolute or relative kidney weights of male rats nor of absolute kidney weights of female rats. With regard to relative kidney weights of the females, at p=0.05 there was a statistically significant difference betweenGroup I (controls) and Group II (100 ppm exposed) but not between other groups. However, the difference between the two means is very small; there was no correlation with exposure level, and the finding is considered spurious. Among males, absolute brain weights but not relative brain weights displayed a statistically significant difference between Group I between other groups. However, the difference between the two means is very small; there was no correlation with exposure level, and the finding is considered spurious. Among males, absolute brain weights but not relative brain weights displayed a statistically significant difference between Group I (controls) and Group II (100 ppm exposed). Among females there were no significant differences in absolute weights, but between Group I (controls) and both exposed groups, there were statistically significant differences at p=0.05, Since brain weights are very constant within similar groups of animals, the relative brain weight differences among females may be a reflection of the previously noted differences in total body weight. There were no significant differences in absolute or relative weights of heart or lungs among animals of either sex.Pathology: At the completion of two years of exposure to NE, all surviving rats were sacrificed and a complete necropsy was performed on each. Complete necropsies were also performed on all rats that were either found dead or sacrificed moribund. Tissues were examined microscopically. Theexpected incidence of age-related degenerative diseases was seen in approximately equal frequencies in all groups. The incidence of nodular hyperplasia and adenomas of the pituitary gland associated with the endocrine target organ response was similar in all groups.There was an increased incidence of bronchopneumonia in Group I (controls) as compared to Group II (100 ppm exposed) and III (200 ppm exposed).The total number of tumors in the control group was 46 in males and 46 in females. In treated Group II there were 44 tumors in males and 56 tumors in females, which in treated Group III there were 33 tumors in males and 45 tumors in females. These results indicated that in all treated groups, except Group II females, there were fewer tumors than in the control groups. This increase in tumors in the females of Group II appeared to be related to the increased frequency of pituitary adenoma-endocrine complex related tumors. In the control rats there were foci of hyperplasia in the liver manifested by compact, small hepatocytes frequently with amphoteric cytoplasm. In other control animals, there were foci of nodular hyperplasia in which increased number of hepatocytes, frequently with larger hyperchromatic nuclei and prominent nucleoli, were found. Both of these types of focal lesions were multicentric and microscopic and therefore did not present a gross mass lesion. In the control male rats, there were eight (8) instances of focal hyperplasia and four (4) instances of focal nodular hyperplasia of the liver. In the control female rats there was one (1) instance of focal hyperplasia and one (1) instance of nodular hyperplasia (with gross) of the liver.In Group II there was one (1) male instance of nodular hyperplasia of the liver and no malignancies. In Group III there were two (2) male rats with nodular hyperplasia of the liver and one (1) hepatocarcinoma in a female rat.These data do not indicate any significant hepatic pathologic difference between the control and exposed (NE) rat groups, but they do indicate a normal spontaneous risk of hepatic nodules in aged rats.

Relevance of carcinogenic effects / potential:

Nitroethane was not carcinogenic in a two year bioassay with rats

Dose descriptor:

NOAEC

Effect level:

200 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Based on lack of a significant effect noted in rats exposed to 200 ppm for 7 hours/day, 5 days/week for 2 years.

Remarks on result:

not determinable

Remarks:

no NOAEC identified. Effect type:toxicity (migrated information)

Dose descriptor:

NOAEC

Effect level:

200 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Based on lack of a significant effect noted in rats exposed to 200 ppm for 7 hours/day, 5 days/week for 2 years.

Remarks on result:

not determinable

Remarks:

no NOAEC identified. Effect type:carcinogenicity (migrated information)

Table 1 Survival following two years exposure to Nitroethane

Sex	Group	Initial Number	Number Surviving	Per Cent Surviving
Males	I	40	20	50.0
	II	40	19	47.5
	III	41	24	58.5
Females	I	40	17	42.5
	II	40	17	42.5
	III	39	25	64.1

Conclusions:

Exposure of the rats to NE had no pharmacologic effects nor were there any effects on mortality of rats of either sex at either level of exposure. Body weights of both sexes of both exposed groups were slightly less than controls, but lack of a well-defined dose-response relationship suggested the involvement of factors other than just exposure to NE. There were no effects of.exposure to NE on hematology. There were no biologically significant effects of exposure to NE on clinical chemistry or on organ weights. There was no significant difference in the non-neoplastic or neoplastic pathology related to exposure to NE.

Executive summary:

Male and female Long-Evans rats were exposed by inhalation to vapors of nitroethane (NE) at either 100 ppm or 200 ppm, seven hours per day, five days per week for two years. General observations were made daily and body weights were obtained weekly or biweekly.

During the study any rats that were found dead or sacrificed moribund were given a thorough gross examination and tissues retained for microscopic examination. After two years of inhalation of NE, all surviving rats were sacrificed. Blood samples were obtained from selected individuals for hematology and serum chemistry studies. All rats were examined histopathologically.

Exposure of the rats to NE had no pharmacologic effects nor were there any effects on mortality of rats of either sex at either level of exposure. Body weights of both sexes of both exposed groups were slightly less than controls, but lack of a well-defined dose-response relationship suggested the involvement of factors other than just exposure to NE. There were no effects of.exposure to NE on hematology. There were no biologically significant effects of exposure to NE on clinical chemistry or on organ weights. There was no significant difference in the non-neoplastic or neoplastic pathology related to exposure to NE.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

614 mg/m³

Study duration:

chronic

Species:

rat

Quality of whole database:

Good

Justification for classification or non-classification

A two year inhalation study in long-evans rats failed to show any gross or histopathological evidence for tumor formation. Therefore, nitroethane is not classifiable under GHS.

Additional information

Male and female Long-Evans rats were exposed by inhalation to vapors of nitroethane (NE) at either 100 ppm or 200 ppm, seven hours per day, five days per week for two years. General observations were made daily and body weights were obtained weekly or biweekly.

During the study any rats that were found dead or sacrificed moribund were given a thorough gross examination and tissues retained for microscopic examination. After two years of inhalation of NE, all surviving rats were sacrificed. Blood samples were obtained from selected individuals for hematology and serum chemistry studies. All rats were examined histopathologically.

Exposure of the rats to NE had no pharmacologic effects nor were there any effects on mortality of rats of either sex at either level of exposure. Body weights of both sexes of both exposed groups were slightly less than controls, but lack of a well-defined dose-response relationship suggested the involvement of factors other than just exposure to NE. There were no effects of.exposure to NE on hematology. There were no biologically significant effects of exposure to NE on clinical chemistry or on organ weights. There was no significant difference in the non-neoplastic or neoplastic pathology related to exposure to NE.

Justification for selection of carcinogenicity via inhalation route endpoint:
The study was not conducted according to guidelines but was conducted according to GLPs and the report contains sufficient data for interpretation of study results.