Isovaleric acid

Short-term toxicity to fish

Description of key information

No valid data could be located regarding the short-term toxicity of isovaleric acid to fish.
To compensate for this lack of data, information resulting from valeric acid as supporting substance is used.
Supporting substance valeric acid: in a valid short-term toxicity fish test similar to OECD TG 203, the LC50 of valeric acid was determined to be 77 mg/L (Mattson, 1976).
As molecular weights of valeric acid and isovaleric acid are the same, the LC50 of 77 mg/L applies also for isovaleric acid.
Toxicity of valeric acid may be related to the lowered pH of test solutions (≤ 5.9)

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

77 mg/L

Additional information

As valid data for isovaleric acid are not available, 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 short-term toxicity of isovaleric acid to fish.

 

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 suitable 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 was selected.

Mattson, 1976

Valeric acid was tested on fathead minnows (Pimephales promelas) in a 96-h static study. No specific guideline was reported, but documentation is sufficient to assign validity and adequate reliability. The test design is similar to OECD TG 203. An unspecified number of test concentrations and one control were set up. Two test chamber with 10 fish each was used per test concentration.

Based on nominal concentrations, the 96-h LC50 was 77 mg/L (Mattson, 1976).

 

Valeric 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

Addition of neat carboxylic acids to dilution water results in a drop of pH in test solutions. Within the concentration range tested, pH values in test solutions were as low as 4.5 to 5. This is clearly outside the range given in the OECD TG 203 for good quality dilution water (pH 6 to 8.5).

Toxicity in these tests appear closely related to the low pH of the test solution as toxicity test with neutralized acids (pH in test solution adjusted to the pH of dilution water) yield much lower toxicity with LC50 values > 1000 mg/L (2-methylbutyric acid - Zok/Hoechst 1997; isobutyric acid - BASF 1989). Thus, it may be discussed if the toxicity observed in tests with straight acids represents the intrinsic long term toxicity of the test substance and not just a side effect of low pH.