Isovaleric acid

Toxicity to aquatic algae and cyanobacteria

Description of key information

No valid data could be located regarding the toxicity of isovaleric acid to aquatic algae and cyanobacteria. 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). As molecular weights of valeric acid and isovaleric acid are the same, the EC50 of 29.3 mg/L applies also for isovaleric acid.

Key value for chemical safety assessment

EC50 for freshwater algae:

29.3 mg/L

Additional information

For the toxicity assessment of isovaleric acid to aquatic algae, valid data could not be identified. Data for valeric acid and isobutyric acid as supporting substances will be used based on following reasons.

 

All three acids are closely related. The length of the carbons 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 toxicity of isovaleric acid to aquatic algae and cyanobacteria.

 

Supporting substance valeric acid

ACC 2002 (according to OECD TG 201, Reliability 1)

In a 72-h toxicity study, cultures of Selenastrum capricornutum (new name: Pseudokirchnerella subcapitata) were exposed to valeric acid at nominal concentrations of 0 (controls), 0.50, 1.1, 2.4, 5.3, 12, 26, and 57 mg/L under static conditions. Cell concentrations were determined at scheduled time points by light microscope and a hemacytometer.

The 72-h ErC50 was determined to be 29.3 mg/L based on measured(init.) concentrations (ACC, 2002)

 

Supporting substance isobutyric acid

BASF 1990 (according to German test guideline DIN 38412, part 9 which is comparable to OECD TG 201, Reliability 2)

In a 72-h toxicity study, cultures of Scenedesmus subspicatus (new name Desmodesmus subspicatus), strain SAG 86.81, were exposed to isobutyric acid at nominal concentrations of 0 (controls), 3.9, 7.8, 15.6, 31.25, 62.5, 125, 250, and 500 mg/L under static conditions. Cell density was recorded at 0, 24, 48, and 72 h by fluorescence measurement.

The 72-h ErC50 was determined to be 45.1 mg/L (BASF AG, 1990)

 

Isovaleric acid: toxicity to aquatic algae and cyanobacteria

To represent the toxicity of isovaleric acid to aquatic algae and cyanobacteria, the study results with valeric acid will be used. The study follows the OECD TG 201 is performed under GLP and has the higher reliability. In addition, the resulting EC50 value is lower.

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

Thus, data from two related acids may be used for read across. Taking into account the molecular weights of isovaleric acid (102.13) and isobutyric acid (88.11), an EC50 of 52.3 mg/L for isovaleric acid can be calculated. As molecular weights of valeric acid and isovaleric acid are identical, the EC50 of 29.3 mg/L applies also for isovaleric acid. It is proposed to use the lower value for risk considerations.