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Description of key information

The oral LD50 of butyric anhydride was determined to be 7700  mg/kg bw in rats.  Supporting data from the acid hydrolysis product confirmed an LD50 > 2 g/kg in 2 reliable studies.  A third study reporting an LD50 value an order of magnitude lower for the acid is available, but it is of lower quality than the other studies and does not provide the full experimental results or study data.
In an Inhalation Hazard Test similar to OECD TG 403, mortality was observed in a saturated atmosphere (~ 4.21 mg/l) at both 3 and 7 hours of exposure. The LC50 was 4.21 mg/l.
No dermal toxicity data was available for isobutyric anhydride. The dermal LD50 of isobutyric acid was determined to be 474 mg/kg in male rabbits (Smyth, 1962). As excess water is required for full hydrolysis to the acid, the results for the acid should be considered a worst-case.

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:
1978
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Basic data given: comparable to guidelines/standards
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 401 (Acute Oral Toxicity)
Deviations:
yes
Remarks:
reporting details
GLP compliance:
no
Test type:
standard acute method
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Weight at study initiation: mean: male: 318g; female: 223g
Route of administration:
oral: gavage
Vehicle:
olive oil
Details on oral exposure:
VEHICLE
- Concentration in vehicle: 50 - 31.6%

MAXIMUM DOSE VOLUME APPLIED: 20 mL/kg
Doses:
10000, 6810, 4640, 3160 mg/kg bw
No. of animals per sex per dose:
5
Control animals:
no
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: weighing: before substance application and on day 4 and day 7 after application. Observations: daily
- Necropsy of survivors performed: yes
Sex:
male/female
Dose descriptor:
LD50
Effect level:
ca. 7 700 mg/kg bw
Based on:
test mat.
Remarks on result:
other: Mortalities were seen at all doses except for the low dose group
Mortality:
At the highest dose (10000mg/kg) all animals died within 48 hours. At 6810 mg/kg 3 of 5 female rats died within 24 hours and 1 male rat died after 7 days of application. At 4640 mg/kg 1 of 5 female rat died after 7 days. At the lowest dose no animal died within the observation time of 14 days.
Clinical signs:
In all dose groups in the first hours after treatment were dyspnae, apathy and staggering found. In the higher dose groups (except lowest dose group) abdominal position, tremor, opisthotonus, diarrhoe, exsiccose, lacrimation and salivation were found.
Body weight:
At the lowest dose animals showed normal body weight gain at all time points. In the other groups at the beginning of the study a body weight reduction was seen which normalised during the further study.
Gross pathology:
animals found dead: heart: acute dilatation and hyperemia; stomach: dilated, strong intravascular injection, substance induced mucosal malacia as well as bloody ulceration in the glandular stomach; intestine: partly atonic
scheduled sacrificed animals: stomach: agglutination of the gastro-oesophageal vestibule.
Interpretation of results:
practically nontoxic
Remarks:
Migrated information Criteria used for interpretation of results: EU
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
LD50
Value:
7 700 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
Study period:
1978
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non standard test design, with little reporting detail
Qualifier:
no guideline followed
Principles of method if other than guideline:
Inhalation-Risk-Test was performed in principle as described in OECD Guideline 403 (adopted 1981). It demonstrates the toxicity of an atmosphere saturated with vapors of the volatile components of a test substance at the temperature chosen for vapor generation (20°C).
GLP compliance:
no
Test type:
standard acute method
Limit test:
yes
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Weight at study initiation: mean: male: 228 g; female: 196 g
Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
air
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Source and rate of air: 200L air/h
- System of generating particulates/aerosols: Vapor is generated by bubbling 200 L/h air at 20°C through a substance column of about 5 cm above a fritted glass disc in a glass cylinder for 1, 3 and 7 hours.
- Pressure in air chamber: 755 mm/Hg
Analytical verification of test atmosphere concentrations:
no
Duration of exposure:
7 h
Concentrations:
mean: 7 hours: 4.21 mg/L; 3 hours: 4.18 mg/L; 1 hours: 4.27 mg/L
No. of animals per sex per dose:
3
Control animals:
no
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: daily, weighing at beginning and at the end of the study
- Necropsy of survivors performed: yes
Sex:
male/female
Dose descriptor:
LC50
Effect level:
ca. 4.21 mg/L air
Based on:
test mat.
Exp. duration:
7 h
Mortality:
1 male rat died after 3 h exposure on day one after exposure.
1 male rat died after 7 h exposure on day one after exposure further 3 animals died on day 2.
In the 1 hour exposure test no animal died.
Clinical signs:
other: Eyelid closure, clear and bloody discharge (nose), piloerection and dyspnea were seen as long as the animals were under exposure. At the 7 hour exposure dyspnea and crust formation at the nose were seen until day 6.
Body weight:
Normal body weight gain.
Gross pathology:
All dead animals showed in the heart an acute dilation (right) and an acute congestion. One animal showed a blood filled lung after infarct. In sacrificed animals were no abnormalities detected.
Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LC50
Value:
4 210 mg/m³

Acute toxicity: via dermal route

Link to relevant study records
Reference
Endpoint:
acute toxicity: dermal
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline study with acceptable restrictions (only 4 animals per group, occlusive wrapping, limited reporting)
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 402 (Acute Dermal Toxicity)
Deviations:
yes
Remarks:
: only 4 animals per group, occlusive wrapping, limited reporting
Principles of method if other than guideline:
Pre-guideline test, but method similar to OECD TG 402
GLP compliance:
no
Remarks:
pre-GLP study
Test type:
standard acute method
Limit test:
no
Species:
rabbit
Strain:
New Zealand White
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 2.5 - 3.5 kg
Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Details on dermal exposure:
TEST SITE
- Area of exposure: part of the trunk
- % coverage: no data
- Type of wrap if used: impervious plastic film

REMOVAL OF TEST SUBSTANCE
- Washing (if done): no data
- Time after start of exposure: 24 hours

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): graduate doses were applied, but individual doses are not specified
Duration of exposure:
24 hours
Doses:
no individual doses specified
No. of animals per sex per dose:
4
Control animals:
no
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: no data
- Necropsy of survivors performed: no data
- Other examinations performed: clinical signs, body weight,organ weights, histopathology, other: no data
Statistics:
LD50 values were calculated by the method of Thompson (1947, Bacteriol. Rev. 11, 115) using the tables of Weil (1952, Biometrics 8, 249. The limits of ± 1.96 standard deviations are presented.
Sex:
male
Dose descriptor:
LD50
Effect level:
0.5 mL/kg bw
Remarks on result:
other: corresponds to 474 mg/kg
Mortality:
no data

Fiducial range of LD50 value (presented as ± 1.96 S.D.) was from 0.37 - 0.67 mL/kg.

Values converted to mg/kg are (substance density = 0.949): 474 mg/kg (351 - 636 mg/kg).

There is no information on local effects reported.

Interpretation of results:
harmful
Remarks:
Migrated information Criteria used for interpretation of results: EU
Conclusions:
The acute dermal LD50 for isobutyric acid was 474 mg/kg bw in male rabbits requiring the classification as harmful according to EU legislation.
Executive summary:

The acute dermal toxicity of isobutyric acid was determined in groups of 4 male albino New Zealand rabbits receiving graduate single doses of test substance per group. Number and quantity of indivual doses are not specified. The exposure time was 24 hours followed by an observation period of 14 days. From mortality data, the LD50 and a range of ± 1.96 SD was calculated according to the method of Thomson (1947).

Overall the study was conducted similar to OECD test guideline 403 with some restrictions (only 4 animals per group, occlusive wrapping, limited reporting).

 

The acute dermal LD50 was 474 mg/kg bw in rabbits (Smyth, 1962).

 

Based on this LD50 value, isobutyric acid requires classification as harmful according to EU regulations.
Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
Value:
474 mg/kg bw

Additional information

Justification for selection of acute toxicity – oral endpoint
The isobutyric anhydride study was selected as the key study, as it is the only study available for the test substance. Data from that study and studies from isobutyric acid (the hydrolysis product) place the LD50 at greater than 2 g/kg BW. Considering that the anhydride will immediately hydrolyze to the acid upon contact with water, the reason for the difference in values is not readily apparent. The Smyth study from 1962 for isobutyric acid gives an LD50 an order of magnitude lower than the other acid studies. The body of work for Smyth and Carpenter in general for reporting LD50 values in the literature are considered to be reliable. However, as the Smyth article is much less documented than the more modern studies and the LD50 value is based on a calculation over log order dose differences, the study is considered to be less reliable than the anhydride or other acid studies.

Justification for selection of acute toxicity – inhalation endpoint
The study selected was the key study for isobutyric anhydride, which was the only test-article specific study available.

Justification for selection of acute toxicity – dermal endpoint
No data is available for isobutyric anhydride. As the substance is considered to be corrosive to skin, a new study is not required. Data from the hydrolysis product, isobutyric acid, is provided as read-across. While read-across to the acid has issues, as hydrolysis can not be confirmed, the highly irritating to corrosive nature of the chemical does not warrant further testing, and thus the classification used may be considered a worst-case.

Justification for classification or non-classification

Acute toxicity: oral

 

The acute LD50 of 7700 mg/kg bw in rats exceeds clearly the EU cut-off value for classification as toxic, i.e. 2000 mg/kg bw. Read-across to the hydrolysis product, isobutyric acid, also has LD50 values > 2 g/kg. A single older acid study has an LD50 value an order of magnitude lower than the other studies, but those values were from a poorly documented journal article, and the data could not be verified. No classification for acute oral toxicity is required.

 

Acute toxicity: inhalation

 

A saturated atmosphere of isobutyric anhydride (~ 4.1 mg/l) resulted in deaths at 7 and 3 hours of exposure. The LC50 was 4.21 mg/l. This result requires a category 3 acute inhalation classification.

 

Acute toxicity: dermal

 

No anhydride data was available, and as the substance is corrosive, new data is not required. The hydrolysis product, isobutyric acid, was used for read-across. Normally, read-across is valid in a system that has excess water present, such as any sort of oral administration. For dermal studies, significant hydrolysis of the anhydride to the acid can not be assumed. With this in mind, the category 3 classifcation from the acid is used, however, it should be considered a worst-case for the anhydride unless excess water is present. Based on these results a category 3 acute dermal classification is required.