2,2-dimethylbutane

Neurotoxicity

Description of key information

No studies are available for the registered substance 2,2 -Dimethylbutane. Based on the read-across approach, information on n-hexane is used.

One read across key neurotoxicity study of commercial hexane was found (API, 1990e; Klimisch = 2). Results showed no effects to behavior or evidence of toxicity.

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

neurotoxicity: sub-chronic inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989-04-03 to 1989-07-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restrictions because it is well documented and follows OECD Guideline 424.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Deviations:

yes

Remarks:

On a single occasion a control group female and high exposure female were mis-dosed. Due to it being a single instance, it is not considered to have affected the outcome of the study.

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Canada, Inc.
- Age at study initiation: 7-8 weeks of age
- Weight at study initiation: 233-271 g male, 185-239 g female
- Housing: individually in stainless steel wire mesh cages, identified by ear notching
- Diet (e.g. ad libitum): Purina Rodent Laboratory Chow, ad libitum
- Water (e.g. ad libitum): reverse osmosis sterilized water, ad libitum
- Acclimation period: 2 weeks male, 3 weeks female


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-24
- Humidity (%): 25-79
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark


IN-LIFE DATES: From: April 3, 1989 To: July 14, 1989

Route of administration:

inhalation: vapour

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: cylindrical stainless steel and glass whole-body chambers, 410 l
- Method of holding animals in test chamber: cages
- Method of conditioning air: Test substance was metered into a glass column that was wrapped with a heating element and filled with glass beads. Dry compressed air moved through the column where it mixed with the test substance before entering the exposure chamber.
- Temperature, humidity, pressure in air chamber: 20-24 degree C, 30-70% humidity,
- Air change rate: 12-15 per hour


TEST ATMOSPHERE
- Brief description of analytical method used: pre-study, samples were taken from sampling points in the breathing zone and analyzed using GC. Samples were also analyzed with GC daily during the first exposure week, and weekly thereafter. During exposure, samples were taken every 30 min. and analyzed using an infrared gas analyzer.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

896 ppm
2,996 ppm
9,006 ppm

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

6 hrs/day, 5 days/week

Remarks:

Doses / Concentrations:
0, 900, 3000, 9000 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

12 male, 12 female

Control animals:

yes, sham-exposed

Observations and clinical examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations: mortality and clinical signs

BODY WEIGHT: Yes
- Time schedule for examinations: weekly, on behavioral testing days

FOOD CONSUMPTION: Yes
Weekly

Neurobehavioural examinations performed and frequency:

FUNCTIONAL OBSERVATIONAL BATTERY: Yes
- Parameters checked: body position, locomotor activity, bizarre behavior, tremors, piloerection, respiratory rate, defecation, vocalization, pupil size, lacrimation, salivation, urinary staining, diarrhea, body tone, abdominal tone, pinna reflex, extensor thrust, tail pinch, toe pinch, auricular startle, gait, limb rotation, visual placing, air righting reflex, pupillary reflex, positional passivity, urination, grip strength, hindlimb splay,
- Description of procedures:
- Minimization of bias:
- Technicians were blind to treatment status of animals: Yes
- Site of testing: 2' square of plexiglass
- Time schedule for examinations: day 0, 1, 7, 14, 35, 63, and 91
- Description of equipment where required: Both hindlimb and forelimb grip strength was tested using a Chatilon strain gauge.

LOCOMOTOR ACTIVITY: Yes
- Type of equipment used: figure 8 activity monitor
- Length of session, number and length of subsessions: 1 hr, 6 10 min sessions
- Time schedule for examinations: pre-study and days 34, 62, and 90

Sacrifice and (histo)pathology:

- Number of animals sacrificed: 8 per group
- Parameters measured:
- Brain weight: yes
- Length and width of brain: yes
- Procedures for perfusion: Ringer's solution with heparin and sodium nitrate, then gluteraldehyde, formaldehyde, calcium chloride, picric acid, and cacodylate buffer.
- Number of animals perfused: 8
- Tissues evaluated: peripheral nervous system, sciatic nerve, lumbar dorsal root ganglion, lumbar dorsal root, lumbar ventral root, cervical dorsal root ganglion, cervical dorsal root, cervical ventral root, sural nerve, tibial nerve, Gasserian ganglion, lumbar spinal cord at swelling, cervical spinal cord at swelling, center of cerebrum, midbrain, cerebellum, pons, medulla oblongota
- Type of staining: uranyl acetate
- Methodology of preparation of sections:
- Thickness: 0.5 micron
- Embedding media: epoxy
- Number of animals evaulated from each sex and treatment group: 6

Statistics:

Body weights and food consumption were analyzed using Bartlett's test, and the Kruskal-Wallis test if needed. Motor activity testing was analyzed using a repeated measures analysis in Snedecor and Cochran (1980). Two-Way Classifications. In Statistical Methods, Iowa State University Press (14) 255-273.

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 examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Clinical biochemistry findings:

not examined

Behaviour (functional findings):

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
One animal died due to a fracture of the muzzle/nares on day 22. No other animals died during the study. Males and females in treatment groups had more staining of the muzzle/head or periorbital region. No other significant differences between control groups and treatment groups were noted.

BODY WEIGHT AND WEIGHT GAIN
Body weight was unaffected by treatment.

FOOD CONSUMPTION
No adverse effects to food consumption were noted.

NEUROBEHAVIOUR
The motor activity results showed no significant differences between control groups and treatments groups. The results of the hindlimb splay and grip strength studies showed no significant differences between control groups and treatment groups.

GROSS PATHOLOGY
No treatment related effects were found.

NEUROPATHOLOGY
No treatment related finding were noted.

Key result

Dose descriptor:

NOAEC

Effect level:

9 000 ppm

Sex:

male/female

Basis for effect level:

other: Neurotoxicity

Key result

Critical effects observed:

no

Conclusions:

Exposure to the test substance had no effect on the behavior of rats. The NOAEC for sub-chronic neurological effects is 9000 ppm in rats.

Executive summary:

This study examined the neurological effects of inhalation exposure to commercial hexane to rats. Rats were exposed to nominal concentrations of 0, 900, 3000, or 9000 ppm for 6 hrs/day, 5 days/week, for 13 weeks. Rats were tested monthly throughout the exposure for hindlimb splay and grip strength. A functional observational battery was also performed regularly. Animals were also examined for clinical signs, body weight, and food consumption.

Results showed no effects to behavior or evidence of toxicity. The NOAEC for sub-chronic neurological effects in rats is 9000 ppm (31680 mg/m³).

Reference 2

Endpoint:

neurotoxicity: sub-chronic inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

1989-04-03 to 1989-07-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restrictions because it is well documented and follows OECD Guideline 424.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Deviations:

yes

Remarks:

On a single occasion a control group female and high exposure female were mis-dosed. Due to it being a single instance, it is not considered to have affected the outcome of the study.

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Canada, Inc.
- Age at study initiation: 7-8 weeks of age
- Weight at study initiation: 233-271 g male, 185-239 g female
- Housing: individually in stainless steel wire mesh cages, identified by ear notching
- Diet (e.g. ad libitum): Purina Rodent Laboratory Chow, ad libitum
- Water (e.g. ad libitum): reverse osmosis sterilized water, ad libitum
- Acclimation period: 2 weeks male, 3 weeks female


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-24
- Humidity (%): 25-79
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark


IN-LIFE DATES: From: April 3, 1989 To: July 14, 1989

Route of administration:

inhalation: vapour

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: cylindrical stainless steel and glass whole-body chambers, 410 l
- Method of holding animals in test chamber: cages
- Method of conditioning air: Test substance was metered into a glass column that was wrapped with a heating element and filled with glass beads. Dry compressed air moved through the column where it mixed with the test substance before entering the exposure chamber.
- Temperature, humidity, pressure in air chamber: 20-24 degree C, 30-70% humidity,
- Air change rate: 12-15 per hour


TEST ATMOSPHERE
- Brief description of analytical method used: pre-study, samples were taken from sampling points in the breathing zone and analyzed using GC. Samples were also analyzed with GC daily during the first exposure week, and weekly thereafter. During exposure, samples were taken every 30 min. and analyzed using an infrared gas analyzer.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

896 ppm
2,996 ppm
9,006 ppm

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

6 hrs/day, 5 days/week

Remarks:

Doses / Concentrations:
0, 900, 3000, 9000 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

12 male, 12 female

Control animals:

yes, sham-exposed

Observations and clinical examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations: mortality and clinical signs

BODY WEIGHT: Yes
- Time schedule for examinations: weekly, on behavioral testing days

FOOD CONSUMPTION: Yes
Weekly

Neurobehavioural examinations performed and frequency:

FUNCTIONAL OBSERVATIONAL BATTERY: Yes
- Parameters checked: body position, locomotor activity, bizarre behavior, tremors, piloerection, respiratory rate, defecation, vocalization, pupil size, lacrimation, salivation, urinary staining, diarrhea, body tone, abdominal tone, pinna reflex, extensor thrust, tail pinch, toe pinch, auricular startle, gait, limb rotation, visual placing, air righting reflex, pupillary reflex, positional passivity, urination, grip strength, hindlimb splay,
- Description of procedures:
- Minimization of bias:
- Technicians were blind to treatment status of animals: Yes
- Site of testing: 2' square of plexiglass
- Time schedule for examinations: day 0, 1, 7, 14, 35, 63, and 91
- Description of equipment where required: Both hindlimb and forelimb grip strength was tested using a Chatilon strain gauge.

LOCOMOTOR ACTIVITY: Yes
- Type of equipment used: figure 8 activity monitor
- Length of session, number and length of subsessions: 1 hr, 6 10 min sessions
- Time schedule for examinations: pre-study and days 34, 62, and 90

Sacrifice and (histo)pathology:

- Number of animals sacrificed: 8 per group
- Parameters measured:
- Brain weight: yes
- Length and width of brain: yes
- Procedures for perfusion: Ringer's solution with heparin and sodium nitrate, then gluteraldehyde, formaldehyde, calcium chloride, picric acid, and cacodylate buffer.
- Number of animals perfused: 8
- Tissues evaluated: peripheral nervous system, sciatic nerve, lumbar dorsal root ganglion, lumbar dorsal root, lumbar ventral root, cervical dorsal root ganglion, cervical dorsal root, cervical ventral root, sural nerve, tibial nerve, Gasserian ganglion, lumbar spinal cord at swelling, cervical spinal cord at swelling, center of cerebrum, midbrain, cerebellum, pons, medulla oblongota
- Type of staining: uranyl acetate
- Methodology of preparation of sections:
- Thickness: 0.5 micron
- Embedding media: epoxy
- Number of animals evaulated from each sex and treatment group: 6

Statistics:

Body weights and food consumption were analyzed using Bartlett's test, and the Kruskal-Wallis test if needed. Motor activity testing was analyzed using a repeated measures analysis in Snedecor and Cochran (1980). Two-Way Classifications. In Statistical Methods, Iowa State University Press (14) 255-273.

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 examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Clinical biochemistry findings:

not examined

Behaviour (functional findings):

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
One animal died due to a fracture of the muzzle/nares on day 22. No other animals died during the study. Males and females in treatment groups had more staining of the muzzle/head or periorbital region. No other significant differences between control groups and treatment groups were noted.

BODY WEIGHT AND WEIGHT GAIN
Body weight was unaffected by treatment.

FOOD CONSUMPTION
No adverse effects to food consumption were noted.

NEUROBEHAVIOUR
The motor activity results showed no significant differences between control groups and treatments groups. The results of the hindlimb splay and grip strength studies showed no significant differences between control groups and treatment groups.

GROSS PATHOLOGY
No treatment related effects were found.

NEUROPATHOLOGY
No treatment related finding were noted.

Key result

Dose descriptor:

NOAEC

Effect level:

9 000 ppm

Sex:

male/female

Basis for effect level:

other: Neurotoxicity

Key result

Critical effects observed:

no

Conclusions:

Exposure to the test substance had no effect on the behavior of rats. The NOAEC for sub-chronic neurological effects is 9000 ppm in rats.

Executive summary:

This study examined the neurological effects of inhalation exposure to commercial hexane to rats. Rats were exposed to nominal concentrations of 0, 900, 3000, or 9000 ppm for 6 hrs/day, 5 days/week, for 13 weeks. Rats were tested monthly throughout the exposure for hindlimb splay and grip strength. A functional observational battery was also performed regularly. Animals were also examined for clinical signs, body weight, and food consumption.

Results showed no effects to behavior or evidence of toxicity. The NOAEC for sub-chronic neurological effects in rats is 9000 ppm (31680 mg/m³).

Endpoint conclusion

Endpoint conclusion:

no study available

Effect on neurotoxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

31 680 mg/m³

Study duration:

subchronic

Species:

rat

Effect on neurotoxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

There is no data available for 2,2 -Dimethylbutane. Based on an analogue approach data are read-across to n-Hexane.

In a key study, the neurological effects of inhalation exposure to commercial hexane (53% n-hexane) in rats was examined (API, 1990e; Klimisch score = 2). Rats were exposed to nominal concentrations of 0, 900, 3000, or 9000 ppm for 6 hrs/day, 5 days/week, for 13 weeks. Rats were tested monthly throughout the exposure for hindlimb splay and grip strength. A functional observational battery was also performed regularly. Animals were also examined for clinical signs, body weight, and food consumption. Results showed no effects to behavior or evidence of toxicity. The NOAEC for sub-chronic neurological effects in rats was 9000 ppm (31680 mg/m³).

This study directly informs the DNEL.

Justification for classification or non-classification

No studies are available for the registered substance 2,2 -Dimethylbutane. Based on the read-across approach, information on n-hexane is used. Based on available read across data, 2,2 -Dimethylbutane does not warrant classification for neurotoxicity under the Regulation (EC) 1272/2008 on classification, labelling and packaging of substances and mixtures (CLP).