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Short-term toxicity to fish

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Description of key information

The substance is with probability acutely not harmful to fish. 

Key value for chemical safety assessment

Additional information

Experimental data are available from a study conducted equivalently to OECD 203 using O. latipes (MOE, Japan, 2017). In this study the pH was not adjusted. Therefore, the pH of the test upper limit concentration deviated from the ideal test conditions. The pH of the test liquid at the upper limit concentration (100 mg/L) was 5.4 - 5.7 throughout the exposure period. According to the Chemical Substances Control Law Test Guidelines, an additional test with pH-adjusted test concentrations should be carried out, if the pH is not in the recommended range of 6 - 8.5.

However, the pKa of this test substance is 4.69 (estimated value; SPARC on-line calculator, http://sparc.chem.uga.edu/sparc/). The substance was, therefore, considered to be dissociated to an amount of ca. 90% at the pH of 5.4 – 5.7. If adjusted to a pH of 7.8 - 8.0, it would be 100% dissociated. The study results indicate 0% mortality at the upper limit concentration (100 mg/L), with an inappropriate pH and when the test substance is ca. 90% dissociated. Therefore, it was assumed that raising the pH of the test liquid in order to give 100% dissociation would not affect the mortality rate. Consequently, and in terms of animal welfare, it was decided not to carry out an additional study with adjustment of the pH.

In addition, the acute toxicity of propanoic acid, 2,2 -dimethyl- (CAS 75-98-9) to fish was investigated in a static test conducted equivalently to OECD 203 using O. mykiss as test organism (Hexion, 1997). Based on nominal test concentrations the 96-h LC50 was considered to be >300 mg/L as no mortality was observed within the exposure period of 96-h at the highest test concentration of 300 mg/L (96-h NOEC = 300 mg/L); in this study the pH of test solutions was adjusted. These data were selected as key data in terms of the chemical safety assessment.

Propanoic acid, 2,2 -dimethyl- (CAS 75 -98 -9) is concluded to be with high probability acutely not harmful to fish.