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Toxicological information

Carcinogenicity

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Administrative data

Endpoint:
carcinogenicity: 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 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.

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
1977
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

Test material

Reference
Name:
Unnamed
Type:
Constituent
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 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.

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.

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Vehicle:
unchanged (no vehicle)
Details on exposure:
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.
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:
7 hours/day
Frequency of treatment:
up to 5 days/week, animals were euthanized at 2 days, 10 days, 1 month, 3 months or 6 months
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 25 or 200 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
0, 27.2 +/- 3.1 ppm and 207 +/- 15 ppm
Basis:
analytical conc.
No. of animals per sex per dose:
10/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. 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:
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:
no effects observed
Urinalysis findings:
no effects observed
Behaviour (functional findings):
no effects observed
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:
The average (+/- SD) concentrations of test material in the exposure chambers were 27.2 +/- 3.1 ppm and 207 +/- 15 ppm for the nominal concentrations of 25 and 200 ppm, respectively.

Effects at 207 ppm: There was no effect of treatment on body weight. 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. No exposure-related macroscopic or microscopic changes were observed in any organ that was examined.

Any other information on results incl. tables

This study is described in detail in section 7.5.3.  Only the methods and results pertaining to histopathology are presented in this summary.

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.

Applicant's summary and conclusion

Conclusions:
2-Nitropropane was positive in this carcinogenicity study.