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Short-term toxicity to aquatic invertebrates

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Description of key information

A Daphnia sp. Acute Immobilization Test in accordance with OECD Testing Guideline 202 and GLP principles was designed to assess the potential effects of methyl 2-hydroxyisobutyrate to the freshwater cladoceran, Daphnia magna. The study was conducted as a limit test with four replicate vessels of five daphnids per test level exposed to nominal test concentrations of 0 (water control) and 100 mg methyl 2-hydroxyisobutyrate/L, over a 48-hour static exposure period. Observations were made at 24 and 48 hours (±1 hour from test initiation) for daphnid immobility (inability to swim within approximately 15 seconds after gentle agitation of the test vessel) and any changes in behavior or appearance.

The acute toxicity values for daphnid (D. magna) exposed to methyl 2-hydroxyisobutyrate over a 48-hour exposure period and based on nominal concentrations were as follows: 24- and 48-hour EC50 : >100 mg/L (limit concentration tested); 48-hour NOEC: 100 mg/L (limit concentration tested)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
100 mg/L

Additional information

Temperatures during the exposure period ranged from 20-21°C. Dissolved oxygen levels ranged from 8.6-8.8 mg/L (97-101% air saturation). The pH ranged from 7.7-7.8 and the light intensity ranged from 354-414 lux. Test solutions were analyzed for methyl 2-hydroxyisobutyrate concentrations at test initiation and exposure termination by gas chromatography with selected ion monitoring (GC/SIM).

None of the analyses of the water control exhibited a concentration exceeding the lower limit of quantitation (LLQ) equivalent to 0.125 mg methyl 2-hydroxyisobutyrate/L. Measured concentrations of methyl 2-hydroxyisobutyrate at the limit test level ranged from 82.1 to 92.6% of the nominal concentration over the course of the exposure period. The resulting mean measured concentration was 87.4 mg methyl 2-hydroxyisobutyrate/L, equating to 87.4% of the nominal concentration. Because the mean measured concentration was within ± 20% of the nominal target concentration, results were based on the nominal (limit) concentration.

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