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Description of key information

The oral LD50 of butyric acid was determined to be 2230 mg/kg bw in rats (Hüls AG, 1985).
In an Inhalation Hazard Test similar to OECD TG 403, no mortality was observed in rats exposed to a saturated vapor concentration for 8 hours (nominal saturated vapor concentration 7,2 mg/L at 20°C).
The dermal LD50 of butyric acid was determined to be 474 mg/kg in male rabbits (Smyth, 1962).

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:
20.08.1985 - 10.09.1985
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study
Qualifier:
according to
Guideline:
OECD Guideline 401 (Acute Oral Toxicity)
Version / remarks:
1981
GLP compliance:
no
Test type:
standard acute method
Limit test:
no
Species:
rat
Strain:
other: WISW (SPF THO)
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: F. Winkelmann, 4799 Borchen, Germany
- Weight at study initiation: male: 124 g; female: 107 g
- Fasting period before study: 16 hrs
- Housing: 1 -5 animals each cage (Makrolon Typ III)
- Diet (e.g. ad libitum): R10 Alleindiät für Ratten, Ssniff Spezialfutter GmbH, 4770 Soest, ad libidum
- Water (e.g. ad libitum): tap water, ad libidum
- Acclimation period: 4-8 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 +/- 1
- Humidity (%): 60 +/- 5
- Air changes (per hr): 15x
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
oral: gavage
Vehicle:
unchanged (no vehicle)
Details on oral exposure:
MAXIMUM DOSE VOLUME APPLIED: 2.09 - 3.33 cm3/kg
Doses:
1990, 2510, 2835, 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
- Animals were weighed before treatment and on day 1, 7 and 14; observations were recorded up to 6 hrs following treatment and daily thereafter.
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, histopathology
Statistics:
Determination of LD50 according to Litchfield and Wilcoxon (J. Pharmacol. Exp. Ther. 96, 1949, p. 99)
Sex:
male/female
Dose descriptor:
LD50
Effect level:
2 230 mg/kg bw
95% CL:
2 009 - 2 475
Mortality:
1990 mg/kg bw: 2/5 (male), 1/5 (female) within 4 days; 2510 mg/kg bw: 3/5 (male), 5/5 (female) within 11 days
2835 mg/kg bw: 5/5 (male), 4/5 (female) within 11 days; 3160 mg/kg bw: 3/5 (male), 5/5 (female) within 4 hours
Clinical signs:
5 - 30 min after treatment, the animals showed slight to severe sedation and ataxia, lateral and prone position, labored breathing, staggering. Later
on hypothermia, ruffled fur, trembling, bloody noses and snouts, and blood in the urine. Signs persisted in some animals until the end of the 14-day observation period, i.e.sedation, ataxia, ruffled fur, hypothermia, staggering were noted, along with a clear body weight reduction.
Body weight:
Body weight was decreased in all treated animal groups (-7% to -25%) at the end of the observation period.
Gross pathology:
Animals that died: hyperemia and distension was noted in the stomach, small intestine, and the bladder, and bloody contents were noted in these organs. Corrosion of the stomach wall was noted in some of the animals.
Animals sacrificed at termination: hyperemia, discoloring of the instestinal mucosa, swelling of the stomach mucosa was noted in some instances. Adhesions of the stomach, liver and spleen were noted in 3 survivors.
Interpretation of results:
Category 4 based on GHS criteria
Remarks:
Migrated information Criteria used for interpretation of results: EU
Conclusions:
The acute oral LD50 was 2230 mg/kg bw in male and female rats in an OECD 401 study.
Executive summary:

The acute oral toxicity was determined in a valid OECD 401 study in groups of 5 male and female rats, receiving a dose of 1990, 2510, 2835, 3160 mg/kg bw by oral gavage.

The clinical signs. i.e. sedation, ataxia, ruffled fur, hypothermia and staggering, persisted in some animals until the end of the 14-day observation period. Dead animals suffered from gastro-intestinal hemorrhage as result of the corrosive activity of the isobutyric acid.

The oral LD50 was 2230 (2009 - 2475) mg/kg bw (Hüls AG, 1985).

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
Value:
2 230 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:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
Version / remarks:
: Inhalation hazard test as described in the Annex
GLP compliance:
no
Test type:
other: Inhalation hazard test
Limit test:
no
Species:
rat
Strain:
not specified
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Weight at study initiation: 213 g (mean)
Route of administration:
inhalation: vapour
Vehicle:
other: unchanged (no vehicle)
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
Rats exposed for 3 h, 8 h, respectively, to a vapour saturated atmosphere. Vapour was generated by bubbling 200 l/h dry air (no CO2) through the liquid substance column (volume ca. 50 ml) of about 5 cm above a fritted glass disc in a glass cylinder. The glas cylinder was heated in a water bath. The air pressure was 754 mm Hg. Temperature in the exposure chamber was 20°C.

Duration of exposure:
8 h
Concentrations:
9.59 mg/l
No. of animals per sex per dose:
6
Control animals:
yes
Details on study design:
- Duration of observation period following administration:7 days
- Other examinations performed: clinical signs
Sex:
male/female
Dose descriptor:
LC0
Effect level:
9.59 mg/L air
Exp. duration:
8 h
Remarks on result:
other: Inhalation Hazard Tests
Mortality:
No Mortality was observed.
Clinical signs:
other: severe mucosal irritation at exposure, day 1 dyspnea (1/12)
Body weight:
Body weight development was positive and with in the normal range
Gross pathology:
nothing abnormal was detected
Interpretation of results:
GHS criteria not met
Remarks:
Criteria used for interpretation of results: other: OECD TG 403
Conclusions:
Isobutyric acid did not cause any mortality within 7 days after exposure of six male and six female rats for 8 hours to an approximately vapor saturated atmosphere (ca. 9.59 mg/L).
Executive summary:

This acute inhalation toxicity test was performed as Inhalation Hazard Test. Six male and six female rats were exposed for 8 hr to an atmosphere saturated or close to saturation with vapors of isobutyric acid. Breathing atmosphere concentrations are reported as 9.59 mg/L air.

 

Under the conditions of this test, no mortality was observed for the extended exposure period of 8 hr (BASF AG, 1974).

 

The test concentration of 9.59 mg/L air of this test exceeds the limit concentration (5 mg/L) of OECD TG 403 for a limit test but not the limit concentration for vapors (20 mg/L) of EU TG B.2. According to the criteria of OECD test guideline 403 (Acute Inhalation Toxicity), it can be assumed that there is no likely inhalation hazard for isobutyric acid under normal conditions of exposure.

 

Standards of the OECD test guideline 403 (Acute Inhalation Toxicity) are only met with restrictions by this investigation (observation period 7 days). A LC50 was not determined. Nevertheless, the results of the study are regarded as being valuable. Deviations from the test guideline are considered not to influence the results in a way that the reported results could not be relied on.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

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
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:
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 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:
Category 3 based on GHS criteria
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

Acute toxicity: oral

 

For assessment of the acute oral toxicity of isobutyric acid, three studies are available.

 

Study

RL

LD50
[mg/kg bw]

Hüls AG 1985

1

2230 (m/f)

BASF AG 1989

2

2510 (m/f)

Smyth 1962

2

266 (m)

 

 

The study by Hüls AG is performed according to OECD test guideline 401 without restrictions. The observation period in the BASF study is only 7 days but otherwise it follows OECD TG 401. The Smyth study is a toxicity screen performed as part of a program for the toxicity testing of numerous chemicals. It was conducted before 1962. Only results and a general description of the test method are reported. There is no further specification of the test substance. It is considered the least reliable of the three studies.

 

Thus, the study of Hüls AG (1985) is chosen as key study for the following reasons

 

- The study was performed according to OECD test guideline 401.

- The test substance is sufficiently characterized.

- Documentation follows the requirements of the test guideline.

 

The result of the BASF study confirms the LD50 value determined in the Hüls study. Both studies are assessed to be reliable. The low result of Smyth is considered to be an outlier and not to represent the true toxicity of isobutyric acid.

 

This finding is further confirmed by the LD50 values of other structurally related carboxylic acids which are in the same order of magnitude

LD50 values of structurally related short chain carboxylic acids (data are taken from the respective SIDS/IUCLID datasets)

 

  Substance

LD50 [mg/kg bw]

Reference

  Butyric acid

1632 (m/f)

BASF1978

2940 (m)

Smyth (et al) 1951

8790 (f)

Smyth (et al) 1954

  Isovaleric acid

≥ 2000 (m/f, limit tests)

Hoechst AG 1988

  Valeric acid

1720 (f)

Hoechst AG 1988

1040 (m)

Smyth (et al) 1962

 

.

 

Hüls AG (1985), key study, RL 1

 

The acute oral toxicity was determined in a valid OECD 401 study in groups of 5 male and female rats, receiving doses of 1990, 2510, 2835, 3160 mg/kg bw by oral gavage.

 

The clinical signs i.e. sedation, ataxia, ruffled fur, hypothermia and staggering, persisted in some animals until the end of the 14-day observation period. Dead animals suffered from gastro-intestinal hemorrhage as result of the corrosive activity of the isobutyric acid.

 

The oral LD50 was 2230 (2009 - 2475) mg/kg bw in rats (Hüls AG, 1985).

 

BASF AG (1974), supporting study RL 2

 

In an acute oral toxicity study similar to OECD TG 401, groups of 5 male and 5 female Gassner rats were given a single oral dose of isobutyric acid (purity 99%) in water containing carboxymethylcellulose at doses of 190, 1516, 2370, 2650, 3030.and 6060 mg/kg bw. Then animals were observed for 7 days.

 

Clinical signs were abdominal position, apathy, dyspnea, and cyanosis.

 

The acute oral LD50 was determined to be ca. 2510 mg/kg bw in rats (BASF, 1974).

 

Smyth (1962)

 

The acute oral toxicity of isobutyric acid was determined in groups of 5 male Carworth-Wistar rats receiving a single oral dose of the test substance by gavage each. The dosages were spaced by a factor of 2 (logarithmically). The observation period was 14 days. 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 the recently replaced OECD test guideline 401.

 

The acute oral LD50 was 266 mg/kg bw in rats (Smyth, 1962).

 

Acute toxicity: inhalation

 

For assessment of the acute inhalation toxicity of isobutyric acid two studies are available. Both are conducted as Inhalation Hazard Test similar to OECD test guideline 403. In both studies, no mortality was observed at saturated vapor concentrations for exposure periods of up to 8 h. The LC0 can be assessed to be saturated vapor concentration (7.2 mg/L at 20°C).

 

LC50 for isobutyric acid will be > 7.2 mg/L.

 

BASF AG (1974)

 

Six male and six female rats were exposed for 3 and for 8 h to an atmosphere saturated or close to saturation with vapors of isobutyric acid. Concentration is reported to be 9.59 mg/L (no information if concentration is nominal or measured).

 

Under the conditions of the test, no mortality was observed even for the longest exposure period of 8 hr (BASF AG, 1974).

 

Standards of the OECD test guideline 403 (Acute Inhalation Toxicity) are only met with restrictions (no information if concentration was measured).

 

Smyth (1962)

 

Six albino rats were exposed for various time periods up to 8 hr to an atmosphere saturated or close to saturation with vapors of isobutyric acid. Actual atmosphere concentrations were not measured but can be estimated to be saturated or close to saturation by the method the atmosphere was generated. Saturated vapor concentration of isobutyric acid in air is 7.2 mg/L at 20°C (Auer Technikum, Edition 12, Auergesellschaft GmbH, Berlin, 1988).

 

Under the conditions of the test, no mortality was observed even for the longest exposure period of 8 hr (Smyth, 1962).

 

Standards of the OECD test guideline 403 (Acute Inhalation Toxicity) are only met with restrictions by this investigation (only 6 rats, only male animals, no concentrations measured, deficiencies in reporting). Results may be of limited validity (compare with results for oral toxicity).

 

Acute toxicity: dermal

 

For assessment of the acute dermal toxicity of isobutyric acid, only one study is available.

 

Smyth (1962)

 

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 individual 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 determined to be 474 mg/kg bw in rabbits (Smyth, 1962).

Justification for classification or non-classification

Acute toxicity: oral

 

The acute LD50 of 2230 mg/kg bw in rats exceeds clearly the EU cut-off value for classification as toxic, i.e. 2000 mg/kg bw.

 

Acute toxicity: inhalation

 

The nominal saturation concentration of this test exceeds the limit concentration (5 mg/L) of OECD TG 403 for a limit test but not the limit concentration for vapors (20 mg/L) of EU TG B.2. According to the criteria of OECD test guideline 403 (Acute Inhalation Toxicity), it can be assumed that there is no likely inhalation hazard for isobutyric acid under normal conditions of exposure.

 

A LC50 value as basis for the classification according to EU regulations is not available.

 

Acute toxicity: dermal

 

Based on an LD50 value of 474 mg/kg bw in rabbits, isobutyric acid requires classification in toxicity category 3 according to EU regulations (Regulation (EC) No 1272/2008) .