Registration Dossier

Administrative data

Endpoint:
sub-chronic toxicity: oral
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:
The Relative Neurotoxicity of methyl-n-butyl ketone, n-hexane, and their metabolites
Author:
Krasavage, WJ, O'Donoghue, JL, DiVincenzo, GD, and Terhaar, CJ
Year:
1980
Bibliographic source:
Toxicology and Applied Pharmacology, 52, 433-441

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
5 male rats were exposed to concentrations of 6.60, 13.2, and 46.2 mmol/kg bw (568, 1135, 3973 mg/kg) by oral gavage for 90 to 120 days. During the exposure, the rats were examined for body weight, clinical signs, mortality, and neurological effects. Animals were sacrificed after exhibiting hindlimb paralysis, or the end of the exposure period. After sacrifice, a histopathological examination was done on the testes, epididymis, and nerve tissue of the animals.
GLP compliance:
no

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:
other: CD (SD) BR
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River COBS
- Weight at study initiation: 214.5 +/- 17.1 g
- Housing: singly in wire cages
- Diet (e.g. ad libitum): Purina Laboratory Chow, ad libitum
- Water (e.g. ad libitum): ad libitum

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
not specified
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
once daily for 90 days, except for animals at the 46.2 mmol/kg dose which were treated for 120 days
Frequency of treatment:
5 days/week
Doses / concentrations
Remarks:
Doses / Concentrations:
6.6, 13.2, and 46.2 mmol/kg (568, 1135, 3973 mg/kg)
Basis:

No. of animals per sex per dose:
5 males
Control animals:
yes, sham-exposed

Examinations

Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily
- Cage side observations: toxicity and general condition changes in posture, gait, and toe pinch


DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:


BODY WEIGHT: Yes
- Time schedule for examinations: twice weekly


FOOD CONSUMPTION:
- Food consumption: Yes
- Time schedule for examinations: twice weekly

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes / No / No data
- Time schedule for examinations:

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: daily
- Battery of functions tested: changes in posture, gait, and toe pinch


Sacrifice and pathology:
HISTOPATHOLOGY: Yes, testes, epididymis, and nerve tissue were 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 specified
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 rats in the 13.2 mmol/kg group and one in the 46.2 mmol/kg group died immediately after intubation. Only the 46.2 mmol/kg dose produced hindlimb paralysis in 90 days.

BODY WEIGHT AND WEIGHT GAIN
Body weight gain was reduced after 3 weeks of exposure at all dose levels. This reduction in body weight followed a reduction in food consumption. Significant and dose dependant weight reduction was seen in the 13.2 and 46.2 mmol/kg groups.

NEUROBEHAVIOUR
Hindlimb paralysis was seen in the 46.2 mmol/kg dose animals an average of 101.3 +/- 9. 4 days after start of exposure.

HISTOPATHOLOGY: NON-NEOPLASTIC
The 46.2 mmol/kg dose produced multifocal axonal swellings, adaxonal myelin infolding, and paranodal myelin retraction. Atrophy of the germinal epithelium was also seen in the testes of animals at this dose level.

Effect levels

open allclose all
Dose descriptor:
NOAEL
Effect level:
6.6 other: mmol/kg bw
Sex:
male
Dose descriptor:
NOAEL
Effect level:
13.2 other: mmol/kg bw
Sex:
male
Basis for effect level:
other: neurological effects
Dose descriptor:
LOAEL
Effect level:
46.2 other: mmol/kg bw
Sex:
male
Basis for effect level:
other: neurological effects

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
Neurological effects were only seen at the highest dose level after an average of 101.3 days of exposure. The LOAEL for neurological effects is 46.2 mmol/kg bw (37973 mg/kg), and the NOAEL is 13.2 mmol/kg bw (1135 mg/kg). Reduced body weight gain was seen at all three dose levels, however was only considered treatment related in the 13.2 and 46.2 mmol/kg bw groups. The NOAEL is therefore 6.60 mmol/kg bw.
Executive summary:

This study examined the effect of oral exposure to the test substance n-hexane. 5 male rats were exposed to concentrations of 6.60, 13.2, and 46.2 mmol/kg bw (568, 1135, 3973 mg/kg) by oral gavage for 90 to 120 days. During the exposure, the rats were examined for body weight, clinical signs, mortality, and neurological effects. Animals were sacrificed after exhibiting hindlimb paralysis, or the end of the exposure period. After sacrifice, a histopathological examination was done on the testes, epididymis, and nerve tissue of the animals. Neurological effects were only seen at the highest dose level after an average of 101.3 days of exposure. The LOAEL for neurological effects is 46.2 mmol/kg bw (37973 mg/kg), and the NOAEL is 13.2 mmol/kg bw (1135 mg/kg). Reduced body weight gain was seen at all three dose levels, however was only considered treatment related in the 13.2 and 46.2 mmol/kg bw groups. The NOAEL is therefore 6.60 mmol/kg bw.