2,3-dimethylbutane

Endpoint summary

Description of key information

Repeated Dose Inhalation 90d – NOAEC = 10504 mg/m³ (2984 ppm) for rats (similar to OECD TG 413)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: oral

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

a short-term toxicity study does not need to be conducted because a reliable sub-chronic (90 days) or chronic toxicity study is available, conducted with an appropriate species, dosage, solvent and route of administration

Reference 2

Endpoint:

sub-chronic toxicity: oral

Data waiving:

other justification

Justification for data waiving:

other:

Justification for type of information:

The ‘justification for the read across’ is provided in the ‘Attached justification’ section below.

Species:

rat

Endpoint conclusion

Endpoint conclusion:

no study available

Quality of whole database:

One supporting short-term read across study from a structural analogue available for assessment.

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

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

Adequacy of study:

key study

Study period:

1989-04-10 to 1989-07-12

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 413.

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 413 (Subchronic Inhalation Toxicity: 90-Day Study)

GLP compliance:

yes

Limit test:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Raleigh, NC
- Age at study initiation: 8 weeks
- Weight at study initiation: approx. 181 g male, approx. 123 g female
- Housing: individually in stainless steel wire mesh cages, identified by tail tattoo
- Diet (e.g. ad libitum): Purina Rodent Chow Brand Animal Diet#5002, ad libitum
- Water (e.g. ad libitum): ad libitum, Elizabethtown Water Company
- Acclimation period: 20 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 68-75 degree F
- Humidity (%): 40-60
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark


IN-LIFE DATES: From: April 10, 1989 To: July 12, 1989

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: Particle size measurements showed that there was no measurable amount of test substance present as aerosol.

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 1000 l glass and stainless steel exposure chamber
- Method of holding animals in test chamber: individual cages
- Source and rate of air: chamber supplied air, 200-216 lpm
- Method of conditioning air: Test substance in a 5-gallon drum passed through a fluid metering pump into teflon tubing to a coiled glass rod in the volatilization chamber. Nitrogen was also fed into the volitization chamber. A heating element was positioned in the center of the glass coil to aid volatilization. The nitrogen and test substance mixture, then entered the exposure chamber.
- Air flow rate: 200-216 lpm
- Air change rate: 4.6-5.0 min.

TEST ATMOSPHERE
- Brief description of analytical method used: GC
- Samples taken from breathing zone: yes, once per week

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Air samples were drawn from the chamber via teflon tubing into charcoal tubes.

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

6 hrs/day, 5 days/week

Remarks:

Doses / Concentrations:
0, 900, 3,000, 9000 ppm
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0, 904, 2,984, 8,992 ppm (0, 3182, 10504, 31652 mg/m3)
Basis:
analytical conc.

No. of animals per sex per dose:

10 animals of each sex per dose

Control animals:

yes, sham-exposed

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations: mortality, toxicological and pharmacological effects


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: prior to test and week during the test


BODY WEIGHT: Yes
- Time schedule for examinations: twice prior to test, weekly during test and at termination


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
Weekly beginning one week prior to test

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: prior to test and prior to sacrifice


HAEMATOLOGY: Yes
- Time schedule for collection of blood: prior to test on 10 animals per sex, and at sacrifice
- Animals fasted: Yes
- Anaesthetic used for blood collection: Yes, ether
- Parameters checked: erythrocyte count, hemoglobin count, hematocrit, total and differential leucocyte count, platelet count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: prior to test on 10 animals per sex, and at sacrifice
- Animals fasted: Yes
- Parameters checked: glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, creatinine, blood urea nitrogen, fasting glucose, total protein, alkaline phosphatase, albumin, potassium, sodium, calcium, chloride, inorganic phophorus, gamma glutamyl transpeptidase, total bilirubin, creatine phosphokinase, lactic acid dehydrogenase

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
all orifices, cranial cavity, brain, spinal cord, nasal cavity, thoracic, abdominal, and pelvic cavities

ORGAN WEIGHTS: Yes
adrenals, ovaries, testes with epididymides, kidneys, liver, brain, lungs, heart, spleen


HISTOPATHOLOGY: Yes
abdominal aorta, adrenals, bone, bone marrow, brain, esophagus, eyes, optic nerve, larynx, ovaries, testes with epididymus, heart, kidneys, liver, intestine, gall bladder, lungs, lymph nodes, nerve, skeletal muscle, trachea, nasopharyngeal tissues, pancreas, pituitary, prostate, salivary gland, thymus, spinal cord, seminal vesicles, spleen, skin, stomach, thyroid, urinary bladder, uterus, exorbital lacrimal glands, Zymbal gland

Statistics:

Statistical analysis was done on body weight, body weight gain, change in body weight, food consumption, change in food consumption, hematology, clinical chemistry, organ weights, organ/body and organ/brain weight ratios.

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):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No rats died during the study. Transient excess lacrimation was observed in the female rats. No other effects attibutable to exposure were noted.

BODY WEIGHT AND WEIGHT GAIN
Females in the high exposure group had sporadic reduced weight gain. As there was no consistant overall effect, this was not considered treatment related.

FOOD CONSUMPTION
There was no effect on food consumption.


OPHTHALMOSCOPIC EXAMINATION
Two males in the high exposure group showed corneal dystrophy. As this is not uncommon in males of this strain of rat, it is not considered treatment related.

HAEMATOLOGY
There were increased platelets in high exposure males. High and medium exposure males also had increased mean corpuscular volume. The significance of these changes are uncertain.

CLINICAL CHEMISTRY
High exposure males had increased creatinine, total protein, and albumin. They had decreased serum chloride. The significance of these changes are also uncertain.

ORGAN WEIGHTS
High exposure males had increased organ/body and organ/brain weight ratios. High exposure males and females had increased relative spleen weights. Liver weights were also increased in high exposure males. The liver effects appeared to be treatment related.

GROSS PATHOLOGY
No treatment related effects were noted.

HISTOPATHOLOGY: NON-NEOPLASTIC
There was hemorrhage and inflammation in male rat livers at the high dose level. There was also inflammation in the kidneys of males in the high and middle exposure groups. The significance of these effects are uncertain.

Key result

Dose descriptor:

NOAEC

Effect level:

2 984 ppm

Sex:

male

Basis for effect level:

other: 10504 mg/m3

Key result

Dose descriptor:

LOAEC

Effect level:

8 992 ppm

Sex:

male

Basis for effect level:

other: 31652 mg/m3; liver and kidney effects

Key result

Dose descriptor:

NOAEC

Effect level:

8 992 ppm

Sex:

female

Basis for effect level:

other: 31652 mg/m3

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

8 992 ppm

System:

other: Hepatobiliary and urinary

Organ:

kidney

liver

Treatment related:

yes

Dose response relationship:

not specified

Relevant for humans:

not specified

Conclusions:

The NOAEC for male rats exposed via inhalation was 2984 ppm based on liver and kidney effects. The LOAEC for male rats was 8992 ppm. The NOAEC for female rats was 8992 ppm.

Executive summary:

The purpose of this study was to determine the sub-chronic toxicity of commercial hexane via inhalation. Groups of 10 male and 10 female rats were exposed to concentrations of 0, 904, 2,984, and 8,992 ppm of test substance for 6 hrs/day, 5 days/week, for 13 weeks. During the exposure period, animals were examined for mortality, body weight, clinical signs, opthamological effects, and food consumption. At the end of the exposure period, the animals were sacrificed and examined for hematological parameters, clinical chemistry, gross pathology, organ weights, and histopathology.

There was no mortality among the exposed groups, and no treatment related effects to body weight gain. At sacrifice, the only possible treatment related effects were hemorrhage and inflammation in high dose male livers. The significance of this effect is uncertain. The NOAEC for male rats in 2984 ppm (10504 mg/m³), and the LOAEC is 8992 ppm (31652 mg/m³). The NOAEC for female rats in 8992 ppm (31652 mg/m³).

Reference 2

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

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

Adequacy of study:

key study

Study period:

1989-04-11 to 1989-07-13

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 413.

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 413 (Subchronic Inhalation Toxicity: 90-Day Study)

GLP compliance:

yes

Limit test:

yes

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Raleigh, NC
- Age at study initiation: 8 weeks
- Weight at study initiation: approx. 25 g male, approx. 19 g female
- Housing: individually in stainless steel wire mesh cages, identified by tail tattoo or cage card
- Diet (e.g. ad libitum): Purina Rodent Chow Brand Animal Diet#5002, ad libitum
- Water (e.g. ad libitum): ad libitum, Elizabethtown Water Company
- Acclimation period: 22 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 68-75 degree F
- Humidity (%): 40-60
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark


IN-LIFE DATES: From: April 11, 1989 To: July 13, 1989

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: Particle size measurements showed that there was no measurable amount of test substance present as aerosol.

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 1000 l glass and stainless steel exposure chamber
- Method of holding animals in test chamber: individual cages
- Source and rate of air: chamber supplied air, 200-216 lpm
- Method of conditioning air: Test substance in a 5-gallon drum passed through a fluid metering pump into teflon tubing to a coiled glass rod in the volatilization chamber. Nitrogen was also fed into the volitization chamber. A heating element was positioned in the center of the glass coil to aid volatilization. The nitrogen and test substance mixture, then entered the exposure chamber.
- Air flow rate: 200-216 lpm
- Air change rate: 4.6-5.0 min.

TEST ATMOSPHERE
- Brief description of analytical method used: GC
- Samples taken from breathing zone: yes, once per week

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Air samples were drawn from the chamber via teflon tubing into charcoal tubes.

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

6 hrs/day, 5 days/week

Remarks:

Doses / Concentrations:
0, 900, 3,000, 9000 ppm
Basis:
other: target concentrations

Remarks:

Doses / Concentrations:
904, 2,984, 8,992 ppm (0, 3182, 10504, 31652 mg/m3)
Basis:
analytical conc.

No. of animals per sex per dose:

10 animals of each sex per dose

Control animals:

yes, sham-exposed

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations: mortality, toxicological and pharmacological effects


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: prior to test and week during the test


BODY WEIGHT: Yes
- Time schedule for examinations: twice prior to test, weekly during test and at termination


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
Weekly beginning one week prior to test

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: prior to test and prior to sacrifice


HAEMATOLOGY: Yes
- Time schedule for collection of blood: prior to test on 10 animals per sex, and at sacrifice
- Animals fasted: Yes
- Anaesthetic used for blood collection: Yes, ether
- Parameters checked: erythrocyte count, hemoglobin count, hematocrit, total and differential leucocyte count, platelet count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: prior to test on 10 animals per sex, and at sacrifice
- Animals fasted: Yes
- Parameters checked: glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, creatinine, blood urea nitrogen, fasting glucose, total protein, alkaline phosphatase, albumin, potassium, sodium, calcium, chloride, inorganic phophorus, gamma glutamyl transpeptidase, total bilirubin, creatine phosphokinase, lactic acid dehydrogenase

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
all orifices, cranial cavity, brain, spinal cord, nasal cavity, thoracic, abdominal, and pelvic cavities

ORGAN WEIGHTS: Yes
adrenals, ovaries, testes with epididymides, kidneys, liver, brain, lungs, heart, spleen


HISTOPATHOLOGY: Yes
abdominal aorta, adrenals, bone, bone marrow, brain, esophagus, eyes, optic nerve, larynx, ovaries, testes with epididymus, heart, kidneys, liver, intestine, gall bladder, lungs, lymph nodes, nerve, skeletal muscle, trachea, nasopharyngeal tissues, pancreas, pituitary, prostate, salivary gland, thymus, spinal cord, seminal vesicles, spleen, skin, stomach, thyroid, urinary bladder, uterus, exorbital lacrimal glands, Zymbal gland

Statistics:

Statistical analysis was done on body weight, body weight gain, change in body weight, food consumption, change in food consumption, hematology, clinical chemistry, organ weights, organ/body and organ/brain weight ratios.

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):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
Seven mice died during the study, 3 from drawing blood, and 4 others died accidently. None of these deaths were attributed to treatment. There was sporadic excessive lacrimation due to exposure, no other clinical signs were considered treatment related.

BODY WEIGHT AND WEIGHT GAIN
There was no effect on body weight observed.

FOOD CONSUMPTION
There was no effect on food consumption.


OPHTHALMOSCOPIC EXAMINATION
No effects were observed.

HAEMATOLOGY
High exposure males had increased mean corpuscular volume. The significance of these changes are uncertain.

CLINICAL CHEMISTRY
No treatment related effects were observed.

ORGAN WEIGHTS
No effects to organ weights were noted.

GROSS PATHOLOGY
No treatment related effects were noted.

HISTOPATHOLOGY: NON-NEOPLASTIC
No treatment related effects were noted.

Key result

Dose descriptor:

NOAEC

Effect level:

>= 8 992 ppm

Sex:

male/female

Basis for effect level:

other: 31652 mg/m3

Key result

Critical effects observed:

no

Conclusions:

The NOAEC for male and female mice exposed via inhalation is 8992 ppm (31652 mg/m3).

Executive summary:

The purpose of this study was to determine the sub-chronic toxicity of commercial hexane via inhalation. Groups of 10 male and 10 female mice were exposed to concentrations of 0, 904, 2,984, and 8,992 ppm of test substance for 6 hrs/day, 5 days/week, for 13 weeks. During the exposure period, animals were examined for mortality, body weight, clinical signs, opthamological effects, and food consumption. At the end of the exposure period, the animals were sacrificed and examined for hematological parameters, clinical chemistry, gross pathology, organ weights, and histopathology.

Seven animals died during the study, however, all deaths were accidental and not considered treatment related. The NOAEC for mice is 8992 ppm (31652 mg/m³).

Reference 3

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

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

Adequacy of study:

key study

Study period:

17 April 1978 - 30 March 1979

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study with acceptable restrictions. Limited documentation on animal housing, only 2 concentrations tested, exposure duration 84 days, no ophthalmological examination.

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 413 (Subchronic Inhalation Toxicity: 90-Day Study)

GLP compliance:

no

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Wilmington, Mass. 01887
- Age at study initiation: males 6 wks, females 7 wks
- Weight at study initiation: males 185 g mean (range 165-217 g); females 162 g mean (range 138-189)
- Fasting period before study: no
- Housing: paired in chamber, individual out of chamber
- Diet (e.g. ad libitum): Standard laboratory pellet diet (Purina Laboratory Chow) ad libitum (out of chamber only)
- Water (e.g. ad libitum): ad libitum (out of chamber only)
- Acclimation period: 13 days

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: not applicable, vapour

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass chambers with 1 cubic meter total volume (760 L effective volume)
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols:
- Temperature, humidity, pressure in air chamber:
- Air flow rate: 134 L/min
- Air change rate: 8 per hour
- Method of particle size determination: not applicable, vapour


TEST ATMOSPHERE
- Brief description of analytical method used: Atmospheric sampling was performed using a Wilks Scientific Corp., Miran 1A Ambient Air Analyzer (long pathlength infrared). A calibration curve relating the absorption to the airborne concentration of the test material was prepared. On each exposure day, three samples were drawn from each exposure chamber (at about 1, 3, and 5 hours) and the exposure concentration calculated by comparing the absorption of this sample to the standard curve.
In addition, the composition of the test atmosphere was analyzed for homogeneity by gas chromatographic analysis of several charcoal-trapped vapour samples collected from each chamber during the 12-wk exposure period

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The test atmosphere was analysed for concentration and homogeneity by measurement of the infrared spectrum and by gas chromatographic analysis, respectively. Based on the infrared analysis the animals were exposed to cumulative mean concentrations of 385 and 1200 ppm, respectively. Gas chromatographic analysis of the chamber atmosphere demonstrated that the test material composition was representative of the initial sample.

Duration of treatment / exposure:

12 weeks

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
400, 1200 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

35

Control animals:

yes, sham-exposed

Details on study design:

- Rationale for animal assignment (if not random): assigned to group by weight

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily
- Cage side observations included: incidence of abnormal signs


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly (full recorded physical assessment)


BODY WEIGHT: Yes
- Time schedule for examinations: weekly, from 5 days prior to exposure through termination


WATER CONSUMPTION: No


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes (retro-orbital sinus)
- Time schedule for collection of blood: 4, 8, 12 weeks
- Anaesthetic used for blood collection: Yes (exsanguination under ether anesthesia)
- Animals fasted: Yes (fasted overnight prior to bleeding)
- How many animals: 10/sex/group (4 and 8 weeks), 15/sex/group (12 weeks, all survivors)
- Parameters examined: hemoblobin, hematocrit, erythrocyte count, clotting time, total and differential leukocytes


CLINICAL CHEMISTRY: Yes (retro-orbital sinus)
- Time schedule for collection of blood: 4, 8, 12 weeks
- Animals fasted: Yes (exsanguination under ether anesthesia)
- How many animals: 10/sex/group (4 and 8 weeks), 15/sex/group (12 weeks, all survivors)
- Parameters examined: blood urea nitrogen, serum glutamic pyruvic transaminase (SGPT), glucose, alkaline phosphatase


OTHER:
Organ weights and organ/body weight ratios determined in animals sacrificed at 4, 8 and 12 weeks (adrenals, brain (sans pituitary), gonads, kidneys, liver, lungs)

Sacrifice and pathology:

GROSS PATHOLOGY: Yes: adrenals, brain (without pituitary), gonads, kidneys, liver, lungs
HISTOPATHOLOGY: Yes (control and 1200 ppm group): adrenals (2), bone marrow (sternal), brain (2 sections), eye, gonad, heart (with coronary vessels) intestine, colon, duodenum, ileum, kidneys (2), liver (2 sections), lung (2 sections), lymph node (mesenteric), mammary gland, pancreas, pituitary, salivary gland, skeletal muscle, skin, spinal cord (cervical), spleen, stomach, thyroid, trachea, urinary bladder, uterus/prostate, gross lesions, tissue masses

Statistics:

Body weight, hematology and clinical chemistry parameters, organ weights and organ/body weight ratios were statistically evaluated. Mean values for all treatment groups were compared to the control group at each time interval (4, 8, and 12 weeks). Hematology and clinical chemistry parameters were compared by the F-test and Student's t-test. When variances differed significantly (F-test), Student's t-test was appropriately modified using Cochran's approximation (t'). Body weight, organ weight and organ/body weight ratios were compared to control according to Dunnett.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

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:

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:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No treatment-related mortality occured (1 male of the 1200 ppm group was accidentally killed).
Several animals in all groups exhibited dry rales and red and mucoid nasal discharge (more numerous in the treated groups, but not clearly treatment-related), moist rales, excessive lacrimation, hair loss and chromodacryorrhea were found in a limited number of animals in all groups (not treatment-related)
1200 ppm: singular occurrences of excessive salivation, laboured, irregular breathing; yellow staining of the anogenital fur in 6 males and 35 females from wk 3 through 12
400 ppm: yellow staining of the anogenital fur in 2 females
Control: singular occurrences of excessive salivation and bleeding inside the ear; a limited number of animals with brown staining of the ano-genital region and soft stool; three observations (in one animal) of an abnormally dark red or red and yellow eye

BODY WEIGHT AND WEIGHT GAIN
1200 ppm: mean body weights in males significantly higher at wk 2 and significantly lower (p?0.05) from wk 8 through 11 than in controls
400 ppm: mean body weight and weight gains in males similar to control throughout the study, except wk 2 (significantly higher, p?0.01), in females mean body weights significantly depressed (p?0.01 and p?0.05) at wk 5 through 8.

HAEMATOLOGY
Several statistically significant (p < 0.05 and p < 0.01) decreases in mean hematocrit values of males and females of both treated groups at wk 4 and 8, statistically significant decreases (p?0.05) in mean hemoglobin values at wk 8 in the males of both treated groups and the females of the 400 ppm group at wk 4. Mean red blood cell values were significantly decreased in 1200 ppm males at wk 8 and 400 ppm females at wk 12. Since all values were within normal biological limits, these findings were not considered to be treatment-related.

CLINICAL CHEMISTRY
Mean SGPT levels were significantly (p?0.01) depressed in 1200 ppm males at wk 4, 400 and 1200 ppm males at wk 8, and in 1200 ppm females at wk 12. Mean blood urea nitrogen levels were significantly increased in the males of both treated groups at wk 8. Mean glucose levels were significantly (p?0.01 or p?0.05) increased in 400 ppm males at wk 8, decreased in 1200 ppm males at wk 12, and decreased in 1200 ppm females at wk 4 and 12. The observed effects were not considered to be treatment-related.

ORGAN WEIGHTS
Mean kidney weights and kidney/body weight ratios were significantly (p?0.05) higher in the 1200 ppm males at wk 8. In the 400 ppm males these values were also elevated, but not statistically significant. At wk 12, mean kidney weights and kidney/body weight ratios for 400 and 1200 ppm males were significantly (p?0.01) elevated, indicating a treatment-related response. The only other statistically significant (p?0.05) findings were elevated mean adrenal/body weight ratios for the 1200 ppm males at wk 4 and the 400 ppm females at wk 12.

GROSS PATHOLOGY
Microscopic evaluation of organs and tissues from the control and high level exposure groups revealed a mild tubular injury in the kidneys of some exposed male rats sacrificed after exposure for 8 and 12 wk. Other changes were unrelated to group or sex and were considered to be spontaneous.

HISTOPATHOLOGY: NON-NEOPLASTIC
See Gross Pathology

Key result

Dose descriptor:

NOAEC

Effect level:

1 200 ppm (nominal)

Sex:

male

Basis for effect level:

other: overall effects

Critical effects observed:

not specified

Significantly increased mean kidney weights and kidney/body weight ratios were observed in males at 400 ppm, which were considered to be treatment-related by the authors of the study.

The kidney was confirmed as potential target organ for the test material-induced toxicity by the observation of mild tubular injury found in the histopathological examination of high dose males.

The fact, that these effects were strictly limited to male rats and that the test substance belongs to a category of substances which are known for their ability to induce nephropathy in male rats due to their exclusive expression of alpha-2u-globulin, the protein known to play the crucial role in the onset of this disease, the observed effects in the kidney have to be regarded as species-specific and therefore not relevant for risk assessment in humans. Therefore, these effects were not considered for the determination of the NOAEC.

Conclusions:

In a 12 -week inhalation study with rats the test substance hydrocarbons, C7 -C9, isoalkanes was tested. Significantly increased mean kidney weights and kidney/body weight ratios were observed in males at 400 ppm, which were considered to be treatment-related by the authors of the study.

The kidney was confirmed as potential target organ for the test material-induced toxicity by the observation of mild tubular injury found in the histopathological examination of high dose males.

The fact, that these effects were strictly limited to male rats and that the test substance belongs to a category of substances which are known for their ability to induce nephropathy in male rats due to their exclusive expression of alpha-2u-globulin, the protein known to play the crucial role in the onset of this disease, the observed effects in the kidney have to be regarded as species-specific and therefore not relevant for risk assessment in humans. Therefore, these effects were not considered for the determination of the NOAEC.

Renal effects were strictly limited to males, therefore the authors concluded an alpha-2u-globulin-related mechanism for the observed nephropathy. The observation was not considered for determination of the NOAEC.

Executive summary:

In a 12 -week inhalation study with rats the test substance hydrocarbons, C7 -C9, isoalkanes was tested. Significantly increased mean kidney weights and kidney/body weight ratios were observed in males at 400 ppm, which were considered to be treatment-related by the authors of the study. The kidney was confirmed as potential target organ for the test material-induced toxicity by the observation of mild tubular injury found in the histopathological examination of high dose males. The fact, that these effects were strictly limited to male rats and that the test substance belongs to a category of substances which are known for their ability to induce nephropathy in male rats due to their exclusive expression of alpha-2u-globulin, the protein known to play the crucial role in the onset of this disease, the observed effects in the kidney have to be regarded as species-specific and therefore not relevant for risk assessment in humans. Therefore, these effects were not considered for the determination of the NOAEC. Renal effects were strictly limited to males, therefore the authors concluded an alpha-2u-globulin-related mechanism for the observed nephropathy. The observation was not considered for determination of the NOAEC.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

10 504 mg/m³

Study duration:

subchronic

Experimental exposure time per week (hours/week):

30

Species:

rat

Quality of whole database:

One supporting short-term; three key sub-chronic; and two supporting chronic read across toxicity studies from structural analogues available for assessment.

System:

other: Hepatobiliary and Urinary

Organ:

kidney

liver

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: dermal

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

a short-term toxicity study does not need to be conducted because a reliable sub-chronic (90 days) or chronic toxicity study is available, conducted with an appropriate species, dosage, solvent and route of administration

Reference 2

Endpoint:

sub-chronic toxicity: dermal

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Critical effects observed:

not specified

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

There is no repeated dose toxicity data available for 2,3-Dimethylbutane. However, data is available for structural analogues, 2-methylbutane; commercial hexane; mixed hexanes; and Hydrocarbons, C7-C9, isoalkanes. This data is read across to 2,3-Dimethylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

 

Oral

 

2-methylbutane

The nephrotoxicity of 2-methylbutane was evaluated in male F344 rats over 4 weeks after oral gavage doses of 0.5 g/kg/day and 2.0 g/kg/day (Halder et al., 1985). Clinical examinations were conducted twice daily throughout the study, and nephrotoxicity and histopathology of the kidney were evaluated at termination. The results were compared to positive and negative controls. Statistical methods used were appropriate. Mortality occurred in 90% of high-dose rats and 10% of low-dose rats. Kidney weights for surviving animals were comparable to controls. 2-methylbutane's ability to cause hydrocarbon nephropathy was comparable to the saline control (not significantly different).

 

The study’s goal was to examine nephrotoxicity, not systemic toxicity as outlined in OECD guideline 407. Study methods are well-documented and scientifically sound. However, several study limitations are noted when comparing the study’s methods to OECD 407. First, female rates were not used in the study. Second, the selected dose levels did not cover an appropriate range (only two dose groups were used, and both were at fairly high doses for a substance that can be aspirated). Third, the substance was administered 5 days/week instead of 7. Fourth, body weight measurements were only taken twice during the experiment (prior to dosing and at the scheduled sacrifice). Fifth, the only post-necropsy examinations were of the kidney. Finally, functional observations, haematology analysis, urinalysis and other post-necropsy examinations were not conducted. Consequently, these studies were not considered key. 

 

An OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents) test is proposed for structural analogue, Hydrocarbons, C7-C9, isoalkanes. This data is read across to based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13. This endpoint will be updated subsequent to ECHA's approval of the testing proposal and availability of data upon completion of the study.

 

Inhalation

 

2-methylbutane

In a supporting 3-day inhalation toxicity study, 2 -methylbutane was administered to 8WAG/RijCrlBR male rats per dose groupat concentrations of 0, 2, 6.5, or 20 g/m3 for 8 hours per day for 3 consecutive days (CEFIC, 2000). Behavioural effects in rats were assessed through two experiments. The first experiment evaluated rats by the standardized functional observational battery assessment and automated motor activity assessment; the second experiment evaluated cognitive behaviour through the visual discrimination task. For both experiments, general intoxication was not induced. There were no treatment-related changes in body weight for either experiment. For experiment I, there was a significant increase in foot splay at 2 g/m3 after the first 8 -hour exposure period; however, this effect was not considered treatment-related because it was only observed at the low dose. Consequently, no statistically significant dose-related neurobehavioral effects observed in the rats in either experiment.

This study received a Klimisch score of 1 and is classified as reliable without restrictions because it is compliant with OECD GLPs. It was selected as a supporting study because the duration of exposure was only 3 days, instead of 28 days, and focused on neurobehavioural effects.

 

Commercial hexane

In a sub-chronic toxicity study of commercial hexane (40-55% hexane), groups of 10 male and 10 female rats were exposed to concentrations of 0, 904, 2984, and 8992 ppm of test substance for 6 hrs/day, 5 days/week, for 13 weeks via the inhalation route (API, 1990b). There was no mortality among the exposed groups, and no treatment related effects to body weight gain. At sacrifice hemorrhage and inflammation in high dose male livers were considered the only possible treatment related effects. The significance of this effect is uncertain. The NOAEC for male rats in 2984 ppm (10504 mg/m³), and the LOAEC is 8992 ppm (31652 mg/m³). The NOAEC for female rats in 8992 ppm (31652 mg/m³).

In a similar sub-chronic toxicity study of commercial hexane (40-55% hexane), groups of 10 male and 10 female mice were exposed to concentrations of 0, 904, 2,984, and 8,992 ppm of test substance for 6 hrs/day, 5 days/week, for 13 weeks, via inhalation (API, 1990c). Seven animals died during the study; however, all deaths were accidental and not considered treatment related. The NOAEC for mice is 8992 ppm (31652 mg/m³).

Hydrocarbons, C7-C9, isoalkanes

Systemic toxicity of hydrocarbons, C7-C9, iso-alkanes was assessed in a 12-week inhalation toxicity study in rats (ExxonMobil Chemical,1979). In this study, repeated exposure to 400 or 1200 ppm of the test substance for 6 hours/day, 5 days/week, for 12 weeks resulted in male rat kidney effects consistent with the alpha-2µ-globulin-induced nephropathy in male rats. There was no treatment-related mortality and clinical findings were unremarkable. Under the test conditions, the NOAEC (excluding male rat nephropathy) was determined to be >1200ppm.

 

The fact that alpha-2µ-globulin-induced nephropathy was strictly limited to male rats and that the test substance belongs to a category of substances which are known for their ability to induce nephropathy in male rats due to their exclusive expression of alpha-2µ -globulin, the protein known to play the crucial role in the onset of this disease, the observed effects in the kidney have to be regarded as species-specific and are not relevant for risk assessment in humans.

 

Mixed hexanes

In a chronic inhalation toxicity study (API, 1983a,b), mixed hexanes was administered to 40 Sprague-Dawley, rats by dynamic whole body exposure at concentrations of 500 ppm for 22 hours per day, 7 days per week for a total of 168 days. The only significant pharmacotoxic sign was abnormal gait in the positive control group and in a group being exposed to 500 ppm of mixed hexanes. Abnormal gait increased in incidence and severity over time in these groups. The average body weights in these same groups were 25 to 30 percent less than that of the negative controls. Six months following continuous inhalation of either n-hexane, mixed hexanes, or a combination of both, all rats were sacrificed and necropsied. Tissues were weighed and a full set of tissues was preserved for future microscopic examination. No toxicologically significant lesions were observed macroscopically in mixed hexane treated and n-hexane treated rats, however, microscopic lesions were observed. A trace to mild level of atrophy was observed in skeletal muscle. A slight increase in the incidence and severity of chronic nephritis and kidney weight was observed. One death occurred early in the study and did not appear to be related to exposure to test materials.

Justification for classification or non-classification

Based on available read across data, 2,3-Dimethylbutane does not meet the criteria for classification for repeated dose toxicity (STOT-RE) under the new Regulation (EC) 1272/2008 on classification, labeling and packaging of substances and mixtures (CLP).