2-ethylhexanoic acid

Toxicity to aquatic algae and cyanobacteria

Description of key information

2-ethylhexanoic acid is with high probability acutely not harmful to aquatic algae

Key value for chemical safety assessment

EC50 for freshwater algae:

485 mg/L

EC10 or NOEC for freshwater algae:

231 mg/L

Additional information

In a non-GLP, 96-h static test with the green alga Desmodesmus subspicatus according to German Industrial Standard DIN 38412 part 9, the algae toxicity of 2-ethylhexanoic acid was investigated. The test concentrations were not analytically verified. As the test substance causes a pH-shift to more acidic conditions with increasing test substance concentrations, the highest test solution (500 mg/L) was tested in parallel after pH-adjustment. Statistical evaluation of the endpoint growth rate revealed an 72 -h ErC50 of 49.3 mg/L (95% CL: 37.9 - 64.1 mg/L, nominal; pH not adjusted) and an 72 -h ErC10 of 31.9 mg/L (95% CL: 22.9 - 44.6 mg/L, nominal; pH not adjusted; BASF AG, 1988, report no.: 2/0949/88).

The algae toxicity of the test substance was influenced by pH effects due to the acidity of the test substance. The toxicity in the pH-adjusted treatment (pH 8) after 72 h was lower (Algae growth inhibition: 40.3 %) compared to the 500 mg/l treatment (Inhibition: 100 %) without buffering the pH (pH < 4). Therefore, the 72 -h ErC50 was determined to be higher than the highest tested concentration (500 mg/L) under pH-adjusted test conditions.

 

 

The Japanese Ministry of the Environment performed a growth inhibition test on the green algae Pseudokirchneriella subcapitata according to OECD 201 and under GLP and with analytical determiation of the test item concentrations (NITE 2002, report no.: A010465-1). The test concentrations were analytically verified and deviated less than 20% from the nominal concentrations. Moreover, the study was performed with the salt of 2-ethylhxanoic acid (Sodium 2-ethylhexanoate, CAS 19766-89-3) which resembles the acid after neutralization. Therefore, pH effects on the observed toxicity can be excluded. This study was selected as the key study for the assessment of the algal toxicity of 2-ethylhexanoic acid.

The data of the original report were re-evaluated using ToxRat v3.3 in order to obtain an EC10, which is not originally reported (BASF SE, 2020). According to REACH Guidance document chapter R.10 Table R.10-1 (Overview of toxicity test endpoints and guidance on derivation of L(E)C50 and NOEC values) an EC10 for a long-term test which is obtained using an appropriate statistical method (usually regression analysis) will be used preferentially. There has been a recommendation within OECD in 1996 to phase out the use of the NOEC, in particular as it can correspond to large and potentially biologically important magnitudes of effect. The advantage of regression method for the estimation of ECx is that information from the whole concentration-effect relationship is taken into account and that confidence intervals can be calculated. These methods result in an ECx, where x is a low effect percentile (e.g. 5-20%). It makes results from different experiments more comparable than NOECs. The recalculation fulfills the required validity criteria.

The 72 -h ErC50 was 485 mg/L (95% CL: 465 – 506 mg/L; nominal, recalculated, BASF SE, 2020). The 72 -h ErC10 was determined to be 231 mg/L (95% CL: 209 – 251 mg/L; nominal, recalculated, BASF SE, 2020).

Overall, based on the available experimental data for the acid and the salt of the acid, it can be concluded that 2-ethylhexanoic acid is with high probability acutely not harmful to aquatic algae.