Registration Dossier

Administrative data

Description of key information

Oral
Rat: LD50 = >2830 mg/kg bw (males)/ 3350 mg/kg bw (females; GLP, OECD 401; Union Carbide Corporation 1993)
Mouse: LD50 = 3500 mg/kg bw (Kushneva et al. 1983, Val. 4)
Rabbit: LD50 = ca. 3000 mg/kg bw (Munch 1972).
Inhalation
Rat, 6 h: LC0 >= 18.2 mg/L (GLP, neurotoxicity guideline, CMA 1994)
Rat, 4 h: LC50 = 24.6 mg/L (standardized test; Smyth et al. 1954)
Rat, 4 h: LC50 = 19.6 mg/L; irritation of the respiratory tract (Kushneva et al. 1983, Val. 4)
Mouse, 4 h: LC50 = 15.5 mg/L (Kushneva et al. 1983, Val. 4)
Rabbit, 4 h: LC50 = 26.3 mg/L (Kushneva et al. 1983, Val. 4)
Guinea pig, 4 h: LC50 = 19.9 mg/L (Kushneva et al. 1983, Val. 4)
Dermal
Rabbit: LD50 = > 2000 mg/kg bw (males); 2460 mg/kg bw (females; GLP, OECD 402; Union Carbide Corporation 1993)
Rabbit: LD 50 = 3392 mg/kg bw (males; standardized test; Smyth et al. 1954)

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records
Reference
Endpoint:
acute toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
December 22, 1992 to January 21, 1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EPA OTS 798.1175 (Acute Oral Toxicity)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 401 (Acute Oral Toxicity)
Deviations:
no
GLP compliance:
yes
Test type:
standard acute method
Limit test:
no
Specific details on test material used for the study:
A of isobutanol, Lot No. TS3370114 was used. The test substance was a colorless, transparent, low viscosity liquid.

NMR spectral data and mass spectral fragmentation data show that this sample is isobutanol. Sample purity, measured by capillary GC, is = 99.9%.
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
Male and female Sprague Dawley* albino rats were received from Harlan Sprague Dawley, Inc. (Indianapolis, IN). The strain and species were selected because of their availability and existing historical data. Male rats were ordered to be approximately 195 to 215 g (designated by the supplier to be approximately 7 to 8 weeks of age). Female rats were ordered to be approximately 220 to 240 g (approximately 11 to 12 weeks of age). The females were ordered to be nulliparous and nonpregnant. Occasionally, male and female rats that were ordered in at 6 weeks of age (initially received for other acute testing) were used as long as weight requirements were met on the day of dosing.

Once a month, 5 rats/sex received for acute testing and housed in Room 109 were subjected to a quality control evaluation, including gross pathology, parasitology and viral serology testing. Periodically, a Clinical Veterinarian examined the rats housed in Room 109 for any signs of health deficiencies. All animals were assigned a unique number and identified by cage cards. Animals were also identified by an ear tagging procedure during the week of receipt.

The animals were separated by se (up to 5/cage) in stainless steel, wire mesh cages (approximately 23.5 x 40.0 x 18.0 cm.). DACBQ (Deotized Animal Cage Board; Shepherd Specialty Papers, Inc.) was placed under each cage and changed regularly. An automatic timer was set to provide fluorescent lighting for a 12-hour photoperiod (approximately 0500 to 1700 hours for the light phase). Temperature and relative humidity were recorded (Cole-Parmer HygrothermographQ Seven-Day Continuous Recorder, Model No. 8368-00, Cole-Parmer Instrument Co., Chicago, IL). Temperature was routinely maintained at 66-77OF during the test period; relative humidity was routinely maintained at 40-70%. Any minor exceptions to these specified ranges can be found in the raw data.

Tap water (Municipal Authority of Westmoreland County, Greensburg, PA) was available ad libitum except during dosing and was delivered by an automatic watering system with demand control valves mounted on each rack. Water analyses were provided by the supplier, Halliburton NUS Environmental Laboratories, Materials Engineering & Testing Company, and Lancaster Laboratories, Inc. at regular intervals. EPA standards for maximum levels of contaminants were not exceeded. Pelleted, certified AGWAY@ PROLAB@ Animal Diet Rat, Mouse, Hamster 3000 (Agway Inc,) was available ad libitum. For the peroral test, the feed was removed the day before dose administration. After dosing, feed was again made available ad libitum. Analyses for chemical composition and possible contaminants of each feed lot were performed by Agway Inc. and the results are included in BRRC files. Feed and water analysis reports were reviewed by the Study Director as they were available.

Animal Acclimation
The animals were acclimated for at least 5 days before dosing. Detailed clinical observations were conducted twice, at the time of receipt and during animal identification and/or dosing. Cage-side observations and mortality checks were conducted at least once daily. Animals considered unacceptable for the study, based on the clinical signs or body weights (rabbits), were rejected for use on this study.

Study Organization
The animals were weighed and inspected for health on the day of the test. Only those exhibiting a healthy state were used. Healthy animals appeared lert, active and well groomed, with no evidence of discharge, diarrhea, breathing difficulties or locomotor abnormalities. A BRRC veterinarian was available for consultation regarding any animal health concerns. Animals were randomly assigned to cages and were designated for dosing according to need and availability.

Rat body weights were within 20% of the group mean for each sex. For the peroral test, the body weight range on the day of dosing was 281 to 292 g for males and 210 to 259 g for females (including those used for preliminary testing). A total of 3 male and 20 female rats were used for the definitive peroral test.
Route of administration:
oral: gavage
Vehicle:
other: 0.25% w/v aqueous methyl cellulose solution
Details on oral exposure:
Each dosing mixture was prepared just prior to administration by diluting the appropriate amount of isobutanol with 0.25% w/v aqueous methyl cellulose solution (CAS No. for water is 7732-18-5; CAS No. for methyl cellulose, Sigma Chemical, is 9004-67-5). All resulting emulsions were mixed for approximately 15 to 30 minutes on a magnetic stirrer. Doses were administered by stomach intubation through a commercial 16-gauge (3-inch) ba11-end stainless steel needle attached to a disposable syringe. The exact amounts of test substance and emulsion given to each rat were recorded on the raw data form.



Doses:
1000, 2000, 2830 and 4000 mg/kg (females)
2830 mg/kg (males)
No. of animals per sex per dose:
5 females/dose level
3 males at 2830 mg/kg
Control animals:
not specified
Details on study design:
The rats were fasted overnight before dosing. Five female rats were included on each of several dose levels in order to determine an LD50. Three male rats were included on an intermediate dose level for comparison. An additional 2 female rats were used for preliminary peroral toxicity testing. For individual animals, the dosing volume was adjusted according to body weight. Dosed rats were observed frequently for signs of toxicity on the first day of the test and twice a day thereafter (except on weekends or holidays when they were examined for death alone). Weights were recorded on the day of dosing and at 7 and 14 days after dosing or at death.

After 14 days, all survivors were sacrificed by CO2 overdose. Necropsies were performed on all animals that died or were sacrificed. Unless tissues were judged to be excessively autolyzed, the following tissues were collected from selected animals and retained in 10% neutral buffered formalin: kidneys, urinary bladder, liver, sciatic nerve, stomach, intestines and spleen. Lungs were also saved because of possible lung damage, based on clinical signs.

During the acute peroral toxicity test, several animals (including survivors) had varying amounts of blood present in the urine. Therefore, the Sponsor requested that histology evaluation be performed on all saved kidney and urinary bladder tissues. One female rat appeared to be pregnant at necropsy and the uterus was saved in order to verify this condition (since the animals are ordered to be nonpregnant).
Statistics:
An LD50 was calculated for female rats, based on the 14-day observation period. It was calculated by the moving average method (Thompson, 1947). An estimate of the slope was made by the formula developed by Weil (1983).

Reference
Thompson, W. R. (1947). Use of moving averages and interpolation to estimate medium-effective dose. Bacteriological Rev. 11, 115-145.

Weil, C. S. (1983). Economical LD50 and slope determination. Drug and Chemical Toxicology 6(6), 595-603.
Preliminary study:
Not applicable.
Key result
Sex:
female
Dose descriptor:
LD50
Effect level:
3 350 mg/kg bw
Based on:
test mat.
95% CL:
2 860 - 3 920
Key result
Sex:
male
Dose descriptor:
LD50
Effect level:
> 2 830 mg/kg bw
Based on:
test mat.
Mortality:
In preliminary testing, 1 female rat was dosed with 2000 mg/kg of isobutanol and 1 female rat was dosed with 8000 mg/kg (20% w/v emulsions in 0.25% aqueous methyl cellulose solution). The rat receiving 8000 mg/kg died. In the definitive test, the peroral LDs0 for female rats dosed with the test substance (emulsions in 0.25% aqueous methyl cellulose solution) was 3350 mg/kg. None of 3 male rats died after receiving peroral doses of 2830 mg/kg of isobutanol (a comparison dose that produced 0 of 5 female deaths), although signs were apparent.

Deaths occurred within 2 hours to 1 day. Survivors recovered within 0.5 hour to 6 days.
Clinical signs:
Signs of toxicity included sluggishness, unsteady gait, lacrimation, piloerection, slow breathing, prostration and a trace to large amount of blood -
in urine (positive by HEMASTIX" Reagent Strips).
Body weight:
Several females exhibited a slight weight loss within 7 to 14 days.
Gross pathology:
Necropsy of animals that died revealed discolored and/or mottled lungs (bright to dark red), tan to dark maroon and/or mottled livers (in 2), discolored stomachs (gray and/or yellow), 1 liquid-filled stomach, dark red and/or gray areas on the intestines, red to brown kidneys (in 1) and a large amount of blood in the urine of 1 (positive by HEMASTIX" Reagent Strips). There were no gross lesions apparent in any survivor at necropsy. One female survivor dosed with 2830 mg/kg of isobutanol appeared pregnant at necropsy (determined to be a pseudopregnancy during microscopic evaluation).

The kidneys and urinary bladders from 1 or 2 rats from each dose group (except 1000 mg/kg) were saved and examined microscopically. The only kidney lesions evident were single instances of tubular proteinosis, tubular basophilia, mineralization and congestion which were not considered to be attributable to the test substance. There were no lesions observed in the urinary bladders. In the uterus of the 1 female rat (2830 mg/kg) that appeared pregnant at necropsy, deciduoma of pseudopregnancy were apparent. This condition is somewhat unusual for animals of this age group and was, therefore, possibly related to the treatment.
Other findings:
No additional information available.

No additional information available.

Interpretation of results:
Category 5 based on GHS criteria
Conclusions:
The acute oral toxicity was examined. The LD50 in female rats was 3350 mg/kg and in male rats was >2830 mg/kg. Kidney lesions were apparent microscopically but were not considered to be treatment-related.
Executive summary:

The acute oral toxicity of isobutanol was examined. The LD50 in female rats was 3350 mg/kg and in male rats was >2830 mg/kg. Kidney lesions were apparent microscopically but were not considered to be treatment-related.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
3 350 mg/kg bw

Acute toxicity: via inhalation route

Link to relevant study records
Reference
Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
other: 40 CFR 799 Multi-Substance Rule for the Testing of Neurotoxicity; 40 CFR Part 798.1150 Inhalation Test Guidelines; Test Guidelines 798.6050 & 798.6200 updated by Neurotoxicity Guideline 81-8, Subdivision F
Principles of method if other than guideline:
Male and female rats (10/sex) were exposed by inhalation for 6 hours to a vapor of isobutanol at 0, 1500, 3000 and 6000 ppm. The animals were observed for 14 days.
GLP compliance:
yes
Test type:
standard acute method
Specific details on test material used for the study:
- Name of test material (as cited in study report): Isobutanol
- Physical state: liquid
- Analytical purity: > 99.9 %
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Raleigh, NC, USA
- Age at study initiation: 8 weeks
- Weight at study initiation: males: 288-388 g; females: 187-290 g
- Housing: individually
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 5 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-24 °C
- Humidity (%): 40-60 %
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
air
Details on inhalation exposure:
- Exposure Chambers: Four 2000-liter stainless steel and glass Hazelton H-2000 chambers
- Animal Housing during Exposure: Individual stainless steel wire mesh cages, positioned in one tier in the chamber
Exposure Duration: 6 hours
- Test Atmosphere Generation System: Test material was fed into a Laskin-type nebulizer mounted in a filtered supply air inlet at top of the inhalation chamber. Exposure concentrations were controlled by using an adjustable-flow valveless pump to regulate the
rate at which isobutanol was delivered to the nebulizer.
- Test Atmosphere Sampling Method: Six test atmosphere samples were drawn through a Miran 1A infrared detector calibrated for isobutanol.
Sampling Location: In the animal breathing area from a port halfway down on the chamber door
- Chamber Atmosphere Distributions: Chamber atmospheres were sampled in 2 different locations for all 3 exposure concentrations.
- Gas Chromatography Analysis: Samples of the chamber atmospheres were collected in two impingers, in series, containing methanol. The solutions were analyzed for isobutanol content using gas chromatography with a flame ionization detector.
Analytical verification of test atmosphere concentrations:
yes
Duration of exposure:
6 h
Concentrations:
0, 1500, 3000, 6000 ppm (0, 4.54, 9.09, 18.18 mg/l)
No. of animals per sex per dose:
10
Control animals:
yes
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Checks for mortality and moribundity and noteworthy signs of toxicity were made daily from the day of
randomization until the day of sacrifice; weighing: day 0, day 7 and day 14.
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight
Statistics:
A two-way ANCOVA and Duncan’s multiple comparison test was used to determine statistical significance. The FOB evaluation was similar to methods published by Mosher (1991).
Key result
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 18.18 mg/L air
Exp. duration:
6 h
Remarks on result:
other: original data: 6000 ppm
Mortality:
1/10 male animals died at 6000 ppm. This death was attributed to an ophthalmic examination where atropine drops were applied to its eyes.
All other animals survived.
Clinical signs:
during exposure: There was clear evidence of generalized depression of the central nervous system (animals were non-responsive to tapping on side
of inhalation chambers) and labored respiration in rats during the 6 hours of exposure to 6000 and 3000 ppm of isobutanol. One male amimal at the 6000 ppm concentration was prostrate at the end of his exposure, and another male animal at the same concentration level was lacrimating at the end of the exposure. The 6000 ppm concentration animals were affected to a greater extent than the 3000 ppm concentration rats. Minimal effects
(hypoactivity) were seen in rats at die 1500 ppm level.
Body weight:
Body weights of male rats in the 3000 and 6000 ppm groups were significantly lower than the male controls throughout the study. These statistically
significant results are due to pretest differences and not because of exposure to the chemical.
Gross pathology:
There were no treatment-related lesions or other gross changes in the tissues and organs examined during necropsy. Enlarged, dilated, distended
uteri were observed at necropsy in the low, mid, and high groups at incidences of 3/10, 1/10, and 1/10, respectively. This finding was not observed in the control group. The severity was minimal in all instances. This is a common observation and usually reflects physiologic changes related to the
estrus cycle. This is further substantiated by the inverse dose response. Therefore, although histologic examination was not conducted, it appears that these observations are unassociated with treatment and reflect the normal variation expected with different stages of the estrus cycle.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
discriminating conc.
18 200 mg/m³

Acute toxicity: via dermal route

Link to relevant study records
Reference
Endpoint:
acute toxicity: dermal
Type of information:
experimental study
Adequacy of study:
key study
Study period:
6 Jan - 9 March 1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EPA OTS 798.1100 (Acute Dermal Toxicity)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 402 (Acute Dermal Toxicity)
Deviations:
no
GLP compliance:
yes
Test type:
standard acute method
Limit test:
no
Specific details on test material used for the study:
A sample of isobutanol, Lot No. TS3370114, CAS No. 78-83-1, was used. The test substance was a colorless, transparent, low viscosity liquid.
Gas chromatography-mass spectrometry (GC/MS) and nuclear magnetic resonance spectroscopy (NMR) techniques were independently used to confirm the sample's identity. Sample purity, measured by capillary GC, is ~ 99.9%.
Species:
rabbit
Strain:
New Zealand White
Sex:
male/female
Details on test animals and environmental conditions:
Male and female New Zealand White rabbits were received from Hazleton Research Products, Inc. (Denver, PA). The strain and species were selected because of their availability and existing historical data. Rabbits were ordered to be between 2.0 and 2.3 kg (designated by the supplier to be approximately 12 to 14 weeks of age). The females were nulliparous and nonpregnant.

Periodically, a Clinical Veterinarian examined rabbits for any signs of health deficiencies. Within 1 or 2 days of receipt, all animals were assigned a unique number which was marked on the animal cage card. The rabbit number was also marked in indelible ink on 1 ear at the time of dosing.

The rabbits were housed individually in cages with wire floors (approximately 61.0 x 46.0 x 36.0 cm.). DACBQ (Deotized Animal Cage Board; Shepherd Specialty Papers, Inc.) was placed under each cage and changed regularly. An automatic timer was set to provide fluorescent lighting for a 12-hour photoperiod (approximately 0500 to 1700 hours for the light phase). Temperature and relative humidity were recorded (Cole-Parmer Hygrothermograph Seven-Day Continuous Recorder, Model No. 8368-00, Cole-Parmer Instrument Co., Chicago, IL). Temperature was routinely maintained at 61-70°F during the test period; relative humidity was routinely maintained at 40-70%. Any minor exceptions to these specified ranges were noted in the raw data.

Tap water (Municipal Authority of Westmoreland County, Greensburg, PA) was available ad libitum (except during dosing) and was delivered by an automatic watering system with demand control valves mounted on each rack. Water analyses were provided by the supplier, Halliburton NUS Environmental Laboratories, Materials Engineering & Testing Company, and Lancaster Laboratories, Inc. at regular intervals. EPA standards for maximum levels of contaminants were not exceeded. As available, water analysis reports were reviewed by the Study Director. AGWAYe PROLABe Animal Diet High Fiber Rabbit (Agway Inc.) was available ad libitum except during the actual dosing period. No analyses of chemical composition and possible contaminants of the feed were conducted by the supplier.

Animal Acclimation
The animals were acclimated for at least 5 days before dosing. Detailed clinical observations were conducted twice, at the time of receipt and during animal identification and/or dosing. In addition, rabbits were examined and weighed twice prior to dosing. Cage-side observations and mortality checks were conducted at least once daily. Animals considered unacceptable for the study, based on the clinical signs or body weights (rabbits), were rejected for use on this study.

Study Organization
The animals were weighed and inspected for health on the day of the test. Only those exhibiting a healthy state were used. Healthy animals appeared alert, active and well groomed, with no evidence of discharge, diarrhea, breathing difficulties or locomotor abnormalities. A BRRC veterinarian was available for consultation regarding any animal health concerns. Animals were randomly assigned to cages and were designated for dosing according to need and availability.
Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Details on dermal exposure:
The fur was removed from the entire trunk of each rabbit using veterinary clippers at least 1 day before application of the test substance. As necessary, the rabbit skin was carefully trimmed (to remove excess regrowth of fur) up to the day before dosing. Only animals with an intact and normal epidermis were used in the study. A double layer of gauze sheeting was wrapped around the trunk and secured with adhesive tape. Polyethylene sheeting was then wrapped around the trunk over the gauze. To secure the polyethylene, plastic ties or rubber bands were added (at the ends of the trunk). The test substance had a tendency to adhere to the inside of the syringe during dosing causing the plunger to stick. Therefore, in order to minimize the potential for exposure by spraying, the undiluted test substance was applied under the plastic wraps for most animals, covering as large a skin area as possible. The area of skin covered/dose level could not be measured except for 1 rabbit at 1.0 g/kg for which the dose was applied directly to the skin prior to wrapping. The amount of test substance applied was recorded for each animal. The sheeting was then protected from removal or tearing by wrapping the rabbit trunk with VETRAP" bandaging tape. The ends of the VETRAP" were secured. After the 24-hour contact period, all coverings were removed.

Duration of exposure:
24 hours
Doses:
Probe study
8000 mg/kg (female)

Definitive study
1000, 2000 and 4000 mg/kg (females)
2000 mg/kg (males)
No. of animals per sex per dose:
Probe study
1 female

Definitive study
5 females/dose
3 males/dose
Control animals:
no
Details on study design:
In the definitive percutaneous toxicity test, 5 female rabbits were included on each of several dose levels in order to determine an LD50. Three male rabbits were included on an intermediate dose level for comparison. One female rabbit was used for preliminary percutaneous toxicity testing. For individual animals, the dose volume was adjusted according to body weight. Treated rabbits wera observed frequently for signs of toxic effect on the first day of the test and twice a day thereafter (except on weekends or holidays when they were examined for death alone). Weights were recorded on the day of dosing and at 7 and 14 days after dosing or at death.

After 14 days, all survivors were sacrificed by ear vein injection using Euthanasia-6 Solution (Veterinarian Laboratories Inc., Lenexa, KS). Necropsies were performed on all animals that died or were sacrificed. The following tissues (unless excessively autolyzed) were collected and retained in 10% neutral buffered formalin: kidneys, urinary bladder, liver, sciatic nerve and spleen. Because of possible lung damage as based on clinical signs, these tissues were also saved from selected animals.
Statistics:
LD50 value, along with evaluations of 95% confidence limits, were calculated by the moving average method (Thompson, 1947). Estimates of the slope will use the method of Weil (1983).

References
Thompson, W. R. (1947). Use of moving averages and interpolation to estimate median effective dose. Bact. Rev. 2, 115-145.
Weil, C. (5. (1983). Economical LD50 and slope determination. Druq Chem. Toxicol 595-603.
Sex:
female
Dose descriptor:
LD50
Effect level:
2 460 mg/kg bw
Based on:
test mat.
95% CL:
1 790 - 3 390
Sex:
male
Dose descriptor:
LD50
Effect level:
> 2 000 mg/kg bw
Based on:
test mat.
Remarks on result:
other: 0 of 3 died at 2000 mg/kg
Mortality:
One rabbit was dosed with 8.0 g/kg of isobutanol in preliminary percutaneous toxicity testing (24-hour occluded contact) and died.

Of the 5 female rabbits/group dosed with 1000, 2000 or 4000 mg/kg, there were 0, 1 and 5 animals that died, respectively. One animal from the 2000 and the 4000 mg/kg groups died on the after exposure. All other deaths occurred on the day of exposure. The earliest death occurred 3 hours after test material was applied to the skin.

None of 3 male rabbits died following application of 2000 mg/kg.
Clinical signs:
Dermal reactions included erythema, edema, necrosis, ecchymoses (on 2), fissuring, ulceration (on l), desquamation, scabs and alopecia. Signs of
toxicity observed included sluggishness, lacrimation (in l), transient tremors (in I), prostration, an unsteady gait (in l), abnormal breathing (slow and/or labored), red eyes (conjunctivae, iris and/or nictitating membrane) and wetness of the periurogenital fur (of 1). For 1 to 2 days, 1 rabbit held its head abnormally low with its eyes directed upward; this animal eventually returned to normal.
Body weight:
Several animals exhibited a weight loss by 7 days, but most recovered by 14 days.
Gross pathology:
Gross pathologic evaluation of animals that died revealed red patches or areas on the lungs, dark red lungs (in l), discolored and/or mottled livers (tan or darkened), gas-filled (characterized by bubbles) intestines (in 2), darkened spleens (in 2), dark red foci on 1 spleen, enlarged adrenals (in l), kidneys with a pitted surface (in 1) and a trace amount of blood in the urine of 1 (positive by HEMASTIX@ Reagent Strips). Necropsy of survivors revealed red to dark red patches or areas on the lungs (in 2 ) , gas-filled intestines (in l), 1 mottled dark maroon and light tan spleen, kidneys with a pitted surface (in 1) and tan kidneys (in 2).
Other findings:
No additional information available.

No additional information available.

Interpretation of results:
Category 5 based on GHS criteria
Conclusions:
The dermal LD50 in male and female rabbits is >2000 and 2460 mg/kg, respectively.
Executive summary:

The acute dermal toxicity was examined. The dermal LD50 in male and female rabbits is >2000 and 2460 mg/kg, respectively.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
2 460 mg/kg bw

Additional information

There are valid data available for the assessment of the acute toxicity of isobutanol.

 

Oral

The most reliable data were provided from a GLP conform study according to OECD TG 401(Union Carbide Corporation 1993). Here, groups of 5 female Sprague-Dawley rats received 1000, 2000, 2830 or 4000 mg isobutanol (purity 99.9%) /kg bw in aqueous methyl cellulose solution per gavage; additionally, 2830 mg isobutanol/ kg bw was similiarily administered to a group of 3 male Sprague-Dawley rats. The animals were observed at least twice per day for 14 d, weights were recorded on days 0, 7 and 14 and necropsies were performed on all animals that died or were sacrificed. After 14 days, the LD50 for females was calculated to be 3350 mg/kg bw for female rats and >2830 mg/kg bw for male rats. In the 4000 mg/kg bw group, female animals died within one day. Clinical signs consisted of sluggishness, unsteady gait, lacrimation, piloerection, slow breathing, prostration and a trace to large amount of blood in urine and were reversible within 0.5 hours to 6 days. Necropsy of animals that died revealed discolored and/or mottled lungs (bright to dark red), tan to dark maroon and/or mottled livers (in 2), discolored stomachs (gray and/or yellow), 1 liquid-filled stomach, dark red and/or gray areas on the intestines, red to brown kidneys (in 1) and a large amount of blood in the urine of 1. Kidney lesions were apparent microscopically but were not considered to be treatment-related. In the uterus of the 1 female rat (2830 mg/kg) that appeared pregnant at necropsy, deciduoma of pseudopregnancy were apparent. This condition is somewhat unusual for animals of this age group and was, therefore, possibly related to the treatment.

In a follow-up study, the potential for pseudopregnancy following single peroral doses of isobutanol to female rats was evaluated (UCC 1993). Here, 1 of 5 rats dosed with 2830 mg/kg of isobutanol died in a probe study, and in the definitive study, 6 of 15 rats dosed with 2830 mg/kg of the test substance died within 2 days following dose administration, indicating a LD50 level of > 2830 mg/kg bw for female rats.

LD50 values for other common laboratory species were 3500 mg/kg bw in mice (Kushneva et al. 1983, Val. 4) and ca. 3000 mg/kg bw in rabbits (Munch 1972).

 

Inhalation

CMA (1994) studied the acute neurotoxicity after inhalative exposure in rats in a GLP conform study according to US guideline 81 -8, F. Groups of 10 male and 10 female rats were exposed to 0, 1500, 3000 and 6000 ppm for 6 hours (corresponding to 4.5, 9.1 and 18.2 mg/L) and were observed for 14 days. No treatment-related mortality was observed. Clinical signs were narcosis, labored respiration, prostration and lacrimation in the mid and high dose during exposure. Body weight gains were not affected by the test substance. At necropsy, no treatment related effects were observed. Decreases in motor activity were detected after exposure, but not after 7 and 14 days of observation. Results of the FOB were not affected by treatment. The LC0 for rats is considered to be >18.2 mg/L after 6 hours.

Additionally, in a study following a standardized test procedure, six rats were exposed to atmospheric vapor levels of 8000 ppm (corresponding to ca. 24.6 mg/l) for four hours (Smyth et al. 1954). After exposure, animals were observed for 14 days before a necropsy was performed with all test animals. The LD50 is approx. 24.6 mg/L since 2/6 animals died during the observation period. No further data were given.

In a GLP conform inhalation hazard test similar to OECD TG 403, a group of 5 male and 5 female rats was exposed to a saturated vapor of isobutanol (purity: 99.9%) in air for 6 hours under static conditions (UCC 1993). The vapor concentration in the course of the exposure period was not determined; however, it is considered that concentrations of 6000 ppm (ca. 18 mg/L) were attainable. Survivors were observed for 14 days and weighed on days 7 and 14 post-exposure. All rats were subjected to a gross necropsy examination. No deaths were observed. During exposure, animals showed hypoactivity, lacrimation, narcosis, prostration, abnormal breathing (short, shallow breaths) and wetness of the periocular fur. Prostration, narcosis and negative reflexes (surface righting and toe and tail pinch) were observed following exposure and recovered within one day. One female rat appeared to be pregnant or exhibit pseudopregnancy at necropsy. Microscopic evaluation of the uteri from this animal revealed the presence of deciduoma resulting from pseudopregnancy.

In a further standardized inhalation hazard test with a saturated vapour atmosphere, 0/12 animals died within 3 h under dynamic conditions (nominal conc. = 27.7 mg/L), but 1/6 animals died after 7 h (nom. conc. 21.1 mg/L; BASF 1978). In another inhalation hazard test under dynamic conditions, a comparable result was produced (i.e. LC0 > 37.7 mg/L/ 7h, BASF 1979).

In a non-guideline study, mice were exposed to different vapour concentrations of 2 -methylpropanol in air. 1818ppm (app. 5.45 mg/L) caused a reduction in breathing rate by 50% (De Ceaurriz, 1981).

 

Dermal

The most reliable data were provided from a GLP conform guideline study according to OECD TG 402 (Union Carbide Corporation 1993). Here, groups of five female New Zealand White rabbits were treated with 1000, 2000 or 4000 mg isobutanol (purity 99.9%)/kg bw for 24 hours under occlusive conditions. Additionally, 3 males were comparably treated with 2000 mg/kg bw. Treated rabbits were observed frequently for signs of toxic effect on the first day of the test and twice a day thereafter. Weights were recorded on the day of dosing and at 7 and 14 days after dosing or at death. After 14 days, all survivors were sacrificed. Following the moving average method of Thompson, the LD50 value for female rabbits was calculated to be 2460 mg/kg bw. One female of the mid and all five animals of the high dose group died on the day of exposure or during the following day. None of the male rabbits died, indicating a LD50 > 2000 mg/kg bw for male rabbits. Signs of systemic toxicity observed included sluggishness, lacrimation, transient tremors, prostration, an unsteady gait, abnormal breathing (slow and/or labored), red eyes (conjunctivae, iris and/or nictitating membrane) and wetness of the periurogenital fur. Local reactions included erythema, edema, necrosis, ecchymoses, fissuring, ulceration, desquamation, scabs and alopecia. Several animals exhibited a weight loss by 7 days, but most recovered by 14 days. Gross pathologic evaluation of animals that died revealed red patches or areas on the lungs, dark red lungs, discolored and/or mottled livers (tan or darkened), gas-filled (characterized by bubbles) intestines, darkened spleens, dark red foci on 1 spleen, enlarged adrenals, kidneys with a pitted surface and a trace amount of blood in the urine. Necropsy of survivors revealed red to dark red patches or areas on the lungs, gas-filled intestines, mottled dark maroon and light tan spleen, kidneys with a pitted surface and tan kidneys.

Additionally, four male New Zealand White rabbits were exposed for 24 hours to the test substance under occlusive conditions following a standardized test procedure (Smyth et al. 1954). After exposure, animals were observed for 14 days before a necropsy was performed with all test animals. The LD50 was 3392 mg/kg bw.

Justification for classification or non-classification

The available data for isobutanol indicate a relative low potential for acute toxicity.

Based on the oral LD50 of >2830 mg/kg bw for male rats/ 3350 mg/kg bw for female rats, the substance has not to be classified according to 1272/2008/EC (CLP) requirements.

Based on the inhalation LC0 of >18.2 mg/L for rats after 6 h exposition, the substance has not to be classified according to 1272/2008/EC (CLP) requirements.

Based on the dermal LD50 of >2000 mg/kg bw for male rabbits and 2460 mg/kg bw for female rabbits, the substance has not to be classified according to 1272/2008/EC (CLP) requirements.