N-hexane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1980

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable with restrictions because there was no GLP statement provided, and limited data on methods were reported, but the study seemed to be well-conducted.

Data source

Reference

Reference Type:

publication

Title:

A comparative study on the neurotoxicity of n-pentane, n-hexane, and n-heptane in the rat

Author:

Takeuchi, Y, Ono, Y, Hisanaga, N, Kitoh, J, and Sugiura, Y

Year:

1980

Bibliographic source:

British Journal of Industrial Medicine, 37, 241-247

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

7 rats were exposed to 3000 ppm of hexane vapors for 12 hrs a day for 16 weeks. Body weights and conduction velocity of the peripheral nerve of the tail was measured at 0, 4, 8, 12 and 16 weeks. At the end of the exposure period, two animals were sacrificed and the nerve tissue examined.

GLP compliance:

not specified

Limit test:

yes

Test material

Reference

Name:

Unnamed

Type:

Constituent

Details on test material:

- Name of test material (as cited in study report): n-hexane
- Analytical purity: 99%

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 308 +/- 18 g

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23.5-24.5

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

not specified

Vehicle:

not specified

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Temperature, humidity, pressure in air chamber: 23.5-24.5 degree C, 41-61% humidity


TEST ATMOSPHERE
- Brief description of analytical method used: gas detector measurements were taken daily, liquid chromatography measurements were taken twice weekly

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

gas detector measurements were taken daily, liquid chromatography measurements were taken twice weekly

Duration of treatment / exposure:

16 weeks

Frequency of treatment:

daily, 12 hrs per day

Doses / concentrations

Remarks:

Doses / Concentrations:
3000 ppm
Basis:
no data

No. of animals per sex per dose:

7

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale: not provided
- Rationale for animal assignment (if not random): not provided
- Rationale for selecting satellite groups: not provided
- Post-exposure recovery period in satellite groups: not provided
- Section schedule rationale (if not random): not provided

Examinations

Observations and examinations performed and frequency:

BODY WEIGHT: Yes
- Time schedule for examinations: 0, 4, 8, 12, and 16 weeks after start of exposure

OTHER: The conduction velocity of the peripheral nerve of the tail was measured at 0, 4, 8, 12 and 16 weeks

Sacrifice and pathology:

HISTOPATHOLOGY: Yes, 2 rats were sacrificed at the end of 16 weeks, and their gastrocnemius and soleus muscles, dorsal trunk of the tail nerve, and the tibial nerve examined.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
Two animals died during the study. One animal died 1 day before the end of the exposure period, and one animal died three days before the end of the exposure period.

BODY WEIGHT AND WEIGHT GAIN
Body weight gain was significantly reduced at 4 weeks after start of exposure, and remained depressed for the rest of the experiment.

NEUROBEHAVIOUR
Unsteady gait was observed in one animal at 10 weeks exposure, and in 4 animals at 12 weeks. 2 animals at this time point also showed foot drop. At 16 weeks exposure, the five surviving rats had unsteady gait, and two had foot drop. All animals had muscular atrophy at this time point.

HISTOPATHOLOGY: NON-NEOPLASTIC
There were paranodal swellings in the myelinated fibers of the tibial nerve and dorsal trunk of the tail nerve. There were an excessive number of neurofilaments, vesicles, multivesicular bodies, mitochondria, myelin figures, and dense bodies in the paranodal axoplasm and no neurotubules. Denervated neuromuscular junctions in the muscles were observed. Muscle fibers were of irregular shape and size, and had an increased number of nuclei, and had disordered myofilaments, zig-zagging of the z-band, and invaginations of the plasma membrane.


OTHER FINDINGS
The motor nerve conduction velocity (MCV) was significantly less than controls by 4 weeks of exposure. MCVs could not be measured in 2 animals after 16 weeks due to nerve damage. Distal latencies (DL) were signficantly prolonged after 4 weeks of exposure, and could not be measured in 2 aminals at 16 weeks of exposure.

Effect levels

Dose descriptor:

LOAEC

Effect level:

3 000 ppm

Sex:

male

Basis for effect level:

other: neurotoxicology

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

The LOAEC for sub-chronic exposure to hexane vapors was 3000 ppm based on reduced body weight gain, mortality and neurological effects.

Executive summary:

In this study, 7 rats were exposed to 3000 ppm of hexane vapors for 12 hrs a day for 16 weeks. Body weights and conduction velocity of the peripheral nerve of the tail was measured at 0, 4, 8, 12 and 16 weeks. At the end of the exposure period, two animals were sacrificed and the nerve tissue examined. Two animals died before the end of the exposure period. All animals showed reduced weight gain after 4 weeks of exposure. Neurological effects were seen beginning at 10 weeks exposure. Motor nerve conduction velocity and distal latency were significantly affected after 4 weeks exposure. Examination of neural tissue showed damage to the tibial nerve and dorsal trunk of the tail nerve. The LOAEC for sub-chronic exposure was 3000 ppm.