Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Algae: 72h-ErC50 (Pseudokirchneriella subcapitata, growth rate) = 73.2 mg/L, NOErC (Pseudokirchneriella subcapitata, growth rate) = 54.4 mg/L (mean measured)

Daphnia: 48h-EC50 (Daphnia magna, mobility) = 88.1 mg/L (mean measured)

Fish: 96-LC50 (Brachydanio rerio) > 1000 mg/L (nominal)

Additional information

Toxicity to algae

A reliable key study is available for the assessment on aquatic toxicity to green algae (RL1; read-across from isopentanoic acid). The study was performed according to OECD 201 (1984) and in compliance with GLP. The freshwater alga Pseudokirchneriella subcapitata was exposed to seven nominal test concentrations of 1.56, 3.13, 6.25, 12.5, 25.0, 50.0, 100 mg/L and a medium control over a 96-hour period in static test conditions. Test concentrations were analytically verified. Deviation from nominal concentrations was <20%. Nonetheless, effect concentrations were based on mean measured values.

The pH values in the test solutions ranged from 4.8 to 7.7 at test initiation, from 4.7 to 9.6 in replicates with algae at test termination, and from 4.7 to 7.5 in blank replicates without algae at test termination. The low pH was related to the test substance itself, which is an acid. Therefore, observed growth inhibition may be related to pH-effects rather than inherent toxicity of the test substance. The derived effect concentrations were: 72h-ErC50 (Pseudokirchneriella subcapitata, growth rate) = 73.2 mg/L, NOErC (Pseudokirchneriella subcapitata, growth rate) = 54.4 mg/L.

The study fulfilled the validity criteria of the guideline (OECD 201 adopted 1984 and 2011). The study was considered reliable and adequate for the environmental hazard assessment for aquatic organisms.

Acute toxicity to aquatic invertebrates

A reliable key study is available on acute toxicity to aquatic invertebrates (RL1; read-across from isopentanoic acid). The study was conducted according to OECD 202 (1984) and in compliance with GLP. Daphnids were exposed to nominal test concentrations of 0 (water control) and 7.78, 13.0, 21.6, 36.0, 60.0, and 100 mg/L test substance over a time period of 48 hours in a static test system. Test concentrations were confirmed on days 0 (from bulk solutions) and 2 (from each test vessel). Deviation from nominal concentrations was <20%. Nonetheless, effect concentrations were based on mean measured values.

Observed adverse effects (immobility) were in part pH-related rather than to inherent toxicity of the test compound: In the preliminary study, pH of the test solutions was not adjusted, and no immobility occurred up to the highest concentration at 100 mg/L. The definitive study was conducted with no pH adjustment, and therefore represented a more conservative estimate of toxicity by including pH-effects. The derived test concentrations were: 48h-EC50 = 88.1 mg/L (mean measured), with a 95% confidence interval of 82.9–93.7 mg/L; 48h-NOEC = 65.2 mg/L (mean measured).

The study fulfilled the validity criteria of the guideline (OECD 202 adopted 1984 and 2004). The study was considered reliable and adequate for the environmental hazard assessment for aquatic organisms.

Acute toxicity to fish

A reliable supproting study is available for the submission substance (RL1). 2-Methylbutyric acid (2 -MBA)was tested in zebra fish (Brachydanio rerio) over 96 hours in a static system. The study was performed acc. to OECD 203 and in compliance with GLP. The concentration tested was 1000 mg/L (limit test) and a negative control (0 mg/L). After adding the substance, the pH fell to a value of 4.0. It was then adjusted to the pH of the test water with 10 molar NaOH. The test concentration was analytically verified. Fish exposed to 2 -MBA showed changes in behaviour, swimming behaviour and respiration rate. The effects were reversible from 48 hours after exposure. No mortality occurred. Therefore, the 96-LC50 was > 1000 mg/L.

The validity criteria of the test guideline were fulfilled. The study was reliable and adequate for the environmental hazard assessment for aquatic organisms.