2-nitropropane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1977

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Not GLP, some biochemical and histological analyses that are performed in guideline studies were not conducted. Some of the test material may have been ingested. Animals may have been exposed to a decomposition product. Weights of high dose animals were significantly less than controls. Animals were group housed during inhalation exposures.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1977

Reference 2

Reference Type:

publication

Title:

Subchronic inhalation toxicity of nitromethane and 2-nitropropane

Author:

Lewis TR, Ulrich CE and Busey WM.

Year:

1977

Bibliographic source:

J Environmen Pathol Toxicol 2:233-249

Materials and methods

Test guideline

Qualifier:

no guideline followed

GLP compliance:

no

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-nitropropane

EC Number:

201-209-1

EC Name:

2-nitropropane

Cas Number:

79-46-9

Molecular formula:

C3H7NO2

IUPAC Name:

2-nitropropane

Details on test material:

Purity of the test material was 94.45 % (by weight). It also contained 3.07% 1-nitropropane, 1.96% nitroethane, 0.42% 2-nitro-2-methylpropane, 0.03% 2-nitrobutane and < 0.01% water. Other minor impurities were not listed.

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

Two hundred fifty male, Sprague-Dawley rats (100 g) were acclimated for 14 days. All animals were allowed food and tap water ad libitum. The animals were randomly allocated to 25 groups of 10 animals each.

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

Generation of vapor: Test material was pumped at a constant flowrate to the vaporization apparatus. Vaporization was accomplished by utlizing a counter-current flow of heated air. The temperatures at the top and bottom of the column were 75 and 120 degrees C, respectively. Air flows were within 18-25 l/min. The concentrated vapor-air mixture was piped to the exposure chamber inlet and diliuted with air flowing at approximately 1000 l/min. The volume of the exposure chambers was 6 cubic meters. Air was supplied by an air conditioning system separate from the general laboratory system. It was controlled for both temperature (21.5 degrees C) and relative humidity (50%). Chamber flowrate was monitored as the pressure drop across a sharp-edged orifice.

Rats were housed in the chambers 24 hours/day. They were caged (10/cage) in wire mesh stainless steel cages, with a dropping pan beneath. Once per day (just prior to exposure) animals were removed from the chambers and all pans and the chamber interiors were hosed down with hot water and a disinfectant. All cages were exchanged for clean ones once per week.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Each chamber was autosampled approximately every hour for concentration of test material. The samples were analyzed using a calibrated Wilks MIRAN I infrared absorption spectrophotometer (at a wavelength of 3.4 microns). Chamber concentrations were read from the charts twice daily. Nominal concentrations were obtained by noting the volume of compound used during the each day.

Duration of treatment / exposure:

Groups of 10 animals were daily exposed to 25 or 200 ppm (nominal) test material and euthanized at 2 days, 10 days, 1 month, 3 months or 6 months.

Frequency of treatment:

7 hours/day, 5 days/week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 25 or 200 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0, 27.2 +/- 3.1 ppm and 207 +/- 15 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

10 male rats/dose/group

Control animals:

yes

Details on study design:

Groups of 10 animals were exposed to 25 or 200 ppm (nominal) test material and euthanized at 2 days, 10 days, 1 month, 3 months or 6 months. Animals were weighed at unlisted intervals. Average weights of controls and rats exposed to 27 ppm were 171 g at time of exposure. Blood for hematolgic (hematocrit, hemoglobin, erythrocyte count, prothrombin time and methemoglobin) and biochemical (serum glutamic-pyruvic transaminase, ornithine carbamyl transferase and thyroxin) analyses was obtained from the abdominal aorta at each termination. All animals that died or survived to termination were given complete necropsies. The liver, kidney, thyroid, lungs plus trachea (both wet and dry) and brain (both wet and dry) were weighed. The lungs, adrenals, bronchi, cerebellum, cerebral hemispheres, eyes, kidneys, liver, spleen, thyroid and trachea were processed and evaluated microscopically.

Examinations

Observations and examinations performed and frequency:

Animals were weighed at unlisted intervals.

Sacrifice and pathology:

Blood for hematolgic (hematocrit, hemoglobin, erythrocyte count, prothrombin time and methemoglobin) and biochemical (serum glutamic-pyruvic transaminase, ornithine carbamyl transferase and thyroxin) analyses was obtained from the abdominal aorta at each termination. All animals that died or survived to termination were given complete necropsies. The liver, kidney, thyroid, lungs plus trachea (both wet and dry) and brain (both wet and dry) were weighed. The lungs, adrenals, bronchi, cerebellum, cerebral hemispheres, eyes, kidneys, liver, spleen, thyroid and trachea were processed and evaluated microscopically.

Statistics:

Data were first evaluated for homogeneity using Bartlett's test, with the rejection level set at p = 0.01. A one-way analysis of variance was then conducted (with the critical value set at p = 0.10). Data that were significantly different were then analyzed with the Student's t-test to determine which means were significantly different from control. The critical value for these analyses was P = 0.05.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

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:

effects observed, treatment-related

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

Effects at 207 ppm: There was no effect of treatment on body weight. Hematocrit, hemoglobin, red blood cells and prothrombin time were decreased at 10 days and 1 month in rats exposed to 207 ppm. At three months, the prothrombin time of rats exposed to 207 ppm was decreased and red blood cells were increased. Methemoglobin concentrations were increased at 6 months. None of the hematologic changes were considered by the authors to be related to exposure. Serum glutamic-pyruvic transaminase was increased in rats exposed to 207 ppm at 10 days and 1 and 6 months. Serum throxin was increased in rats exposed to 207 ppm at 3 months. Wet/dry weights of lungs were increased in rats exposed to 207 ppm for 1, 3 or 6 months. Relative lung and liver weights of animals exposed to 207 ppm test material were elevated at 3 and 6 months. At 1, 3 and 6 months, rats exposed to 207 ppm had an increased incidence dark hemorrhagic foci in the lungs. The livers of rats exposed to 207 ppm for 3 months had areas of necrosis and surface lesions and were paler in color than controls. After 6 months of exposure to 207 ppm, the livers were enlarged and pale with numerous masses and lesions.

No exposure-related microscopic alterations were seen in any of the tissues of rats exposed for 2 or 10 days, or 1 month. In all 9 rats euthanized after exposure to 207 ppm test material for 3 months, numerous focal areas of hepatocellular hypertrophy were noted. The hepatocytes in these foci were more eosinophilic than the surrounding cells and usually contained large, vesiculated nuclei. In 4 of the 9 rats, basophilic foci containing hyperplastic, small hepatocytes with hyperchromatic nuclei were observed. Occasionally, mitotic figures were present.

Multiple hepatocellular carcinomas and numerous neoplastic nodules were present in the livers of all 10 rats exposed to 207 ppm test material for 6 months. In many cases, the normal hepatic parenchyma was destroyed. The neoplasms were composed of anaplastic hepatocytes, sometimes forming broad sheets or trabeculae several cells thick. Blood-filled cysts were occasionally seen in the neoplasm. Mitotic figures were commonly observed. The carcinomas appeared to be rapidly growing. However, no metastatic hepatocellular carcinomas were seen in any of the other tissues examined.

Effects at 27 ppm : There was no effect of treatment on body weight. Hematocrit and red blood cells were decreased and methemoglobin was increased at 10 days in rats exposed to 27 ppm. Hematocrit also was decreased at 1 month in rats exposed to 27 ppm. Rats exposed to 27 ppm for 3 months had increased hematocrit, hemoglobin and red blood cells. Methemoglobin concentrations were increased at 6 months. None of the hematologic changes were considered by the authors to be related to exposure. Wet/dry weights of lungs were increased in rats exposed to 27 ppm for 3 months. No exposure-related macroscopic or microscopic changes were observed in any organ that was examined.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

27 ppm (analytical)

Sex:

male

2

Dose descriptor:

LOAEL

Effect level:

207 ppm (analytical)

Sex:

male

Basis for effect level:

other: Liver effects

3

Dose descriptor:

other: 6-hour LC50

Effect level:

400 ppm

Sex:

male

4

Dose descriptor:

other: 6 hour LC50

Effect level:

> 580 ppm

Sex:

female

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

The study was conducted at the Huntingdon Research Center under NIOSH contract No. 210-75-0039.

The material nitromethane was tested concurrently (at 98 and 745 ppm) in this study.  This material had no effect on the pathology of the liver. 2-nitropropane also was tested in rabbits at the same concentrations.  Rabbits and rats were exposed in the same chambers.  The results for the rabbit study are described in a different summary.

The 6-hr LC50 value also was determined, using rats of both sexes. In males, this value was approximately 400 ppm.  Females were less sensitive, as none died after exposure to a concentration that killed all of the males (580 ppm).

The high dose for the study was originally 400 ppm (instead of 200 ppm).  However, since excessive mortality occurred within 3 days, the exposure was stopped.  New groups of rats with average weights of 96 g were then exposed to 200 ppm (nominal).  These animals weighed less than controls or rats exposed to 27 ppm (avg. weight 171 g).  Therefore, results for rats exposed to 207 ppm were compared to those of controls that had significantly higher weights.  A new control group comprised of rats with weights approximating those of rats exposed to 207 ppm should have been added when animals were exposed to 207 ppm.

The authors noted that some of the material may have decomposed during the vaporization process, which was conducted at 75-120 degrees C.  Therefore, the possibility exists that a decomposition product contributed to the toxicity.

Since food and water were not withdrawn during exposure, it is possible that some of the material was ingested.

The NOAEL for this study was 27 ppm. Increased wet/dry lung weights that occurred at 3 months were not supported by histologic evidence of edema.

Applicant's summary and conclusion

Conclusions:

The NOAEL is 27 ppm and the LOAEL is 207 ppm.