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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

The key study for this endpoint is from a study on the registered substance, isobutyric anhydride, while the remaining suporting studies were conducted on the hydrolysis substance, isobutryic acid.  The results from the key study was the most sensitive.  Three different fish species were tested in these short term toxicity fish tests.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
26 mg/L

Additional information

The key study for this endpoint was conducted on the registered substance, isobutyric anhydride. The key study using isobutyric anhydride in a 96 -hour test with golden orfe (Leuciscus idus) resulted in a LC50 range of 22 -32 mg/L. The value utilized for the hazard/risk assessment from this study is 26 mg/L.

However, hydrolysis studies show that isobutyric anhydride added to water rapidly converts to isobutyric acid. Isobutyric acid data is being used by read across as supporting data for this endpoint. In three individual short term (96 hr) tests, the toxicity of isobutyric acid to three fish species was tested. All tests were performed using the same method (similar to OECD TG 203). Although there are some restrictions (test substance concentration not measured, only four concentrations tested) the studies are assessed as acceptable.


There was no adjustment of pH. In two tests (Hoechst AG), pH-values were measured after addition of the test substance to the dilution water. Values in the test medium declined in a concentration dependent manner within 24 hours to a pH as low as 4.6.


The 96 -h LC50 for golden orfe (Leuciscus idus) was 146.6 mg/L (BASF AG, 1989).

The 96-h LC50 for rainbow trout (Oncorhynchus mykiss) was 286 mg/L (Hoechst AG, 1979).

The 96-h LC50 for pumpkinseed (Lepomis gibbosus) was 435 mg/L (Hoechst AG, 1979).


Sublethal effects were discoloration, imbalance, uncoordinated movements, and dorsal and lateral position. Fish of the three highest dose groups were narcotized. In sacrificed pumpkinseed (dose group 315 and 500 mg/L), light discoloration of livers were observed.


For high test substance concentrations, the observed toxicity may have been influenced by the acidic conditions of the test medium.