Isovaleric acid

Endpoint summary

Additional information

Valid experimental data are available for the endpoints 6.1.1 - Short-term toxicity to fish, 6.1.3 - Short-term toxicity to aquatic invertebrates, 6.1.5 - Toxicity to aquatic algae and cyanobacteria, and 6.1.7 - Toxicity to microorganisms. For the other endpoints, no data could be identified. For substances registered under provisions of Article 12(1)(c) of REACH, data for these endpoints are not required.

In case endpoints for aquatic toxicity are not covered by data collected for isovaleric acid, results for other short-chain saturated aliphatic carboxylic acids (valeric acid, isobutyric acid) will be used for reading across. The use of these acids as supporting substances is justified based on following reasons.

All three acids are closely related. The length of the carbon chain is the same or it differs only in one carbon atom. Physical and physico-chemical properties as well as chemical reactivity will be quite similar. Main structural feature is the carboxylic acid group, which will have a major impact on the effects of all three acids in aquatic systems. Thus, it is justified to use valeric acid as well as isobutyric acid as supporting substance in the evaluation of the short-term toxicity of isovaleric acid to fish.

In the tests selected as key studies, carboxylic acids are used as they are without neutralisation.

 

Short-term-toxicity to fish

For isovaleric acid, valid data regarding the short-term toxicity to fish are not available. To compensate for this lack of data, information resulting from valeric acid and isobutyric acid as supporting substances is used.

Supporting substances

Four valid short-term toxicity tests to fish have been located. All four have minor shortcomings and are assigned a reliability of 2. All are considered suited for assessment.

Valeric acid: 96-h LC50 for fathead minnows (Pimephales promelas) = 77 mg/L (Mattson, 1976)

Isobutyric acid: 96-h LC50 for golden orfe (Leuciscus idus) = 146.6 mg/L (BASF AG, 1989)

Isobutyric acid: 96-h LC50 for rainbow trout (Oncorhynchus mykiss) = 286 mg/L (Hoechst AG, 1979)

Isobutyric acid: 96-h LC50 for pumpkinseed (Lepomis gibbosus) = 435 mg/L (Hoechst AG, 1979)

For determination of the short term toxicity to fish and as key study, the test with the lowest LC50 value (77 mg/L) was selected (Mattson, 1976)

Isovaleric acid: short-term toxicity to fish

As molecular weights of valeric acid and isovaleric acid are the same, the LC50 of 77 mg/L applies also for isovaleric acid.

Remark

Results of tests with neat acids (reported above) and neutralized acids (IUCLID Sect. 6.1.1 - RAC isobutyric acid BASF AG 1989, RAC 2 -methybutyric acid Hoechst 1997) are quite different (LC50 of neat acids between 435 and < 100 mg/L, LC50 of neutralized acids > 1000 mg/L - limit test). The higher toxicity of neat acids may be related to the lowered pH in test solutions (pH < 5) after addition of the neat acid.

 

Long-term toxicity to fish

Data are not required as only Annex VII data requirements have to be fulfilled.

 

Short-term toxicity to aquatic invertebrates

No valid data could be located regarding the short-term toxicity of isovaleric acid to aquatic invertebrates.

To compensate for this lack of data, information resulting from isobutyric acid as supporting substance is used.

Supporting substance isobutyric acid:

In a valid Daphnia acute immobilization test similar to OECD TG 202, the EC50 of isobutyric acid was determined to be 51.25 mg/L (BASF AG, 1989).

Isovaleric acid: short-term toxicity to aquatic invertebrates

Taking into account the molecular weights of isovaleric acid (102.13) and isobutyric acid (88.11), an EC50 of 59.4 mg/L for isovaleric acid is calculated.

 

Long-term toxicity to aquatic invertebrates

Data are not required as only Annex VII data requirements have to be fulfilled.

 

Toxicity to aquatic algae and cyanobacteria

Valid data regarding the toxicity of isovaleric acid to aquatic algae and cyanobacteria are not available. To compensate for this lack of data, information resulting from valeric acid as supporting substance is used.

Supporting substance valeric acid:

In a valid growth inhibition test with green algae according to OECD TG 201, the EC50 of valeric acid was determined to be 29.3 mg/L (ACC, 2002).

Isovaleric acid: Toxicity to aquatic algae and cyanobacteria

As molecular weights of valeric acid and isovaleric acid are the same, the EC50 of 29.3 mg/L applies also for isovaleric acid.

 

Toxicity to aquatic plants other than algae

Data are not required as only Annex VII data requirements have to be fulfilled.

 

Toxicity to microorganisms

Tests were performed with isovaleric acid as test substance. One test out of the two is valid (Schulz, 2006).

In a valid 40 hour growth inhibition study, test cultures of the cilliate Tetrahymena pyriformis were exposed to graduate concentrations of isovaleric acid. The IC50 value based on cell density was determined to be 224 mg/L indicating low to moderate toxicity of isovaleric acid to aqueous microorganisms.