2-ethylhexanoic acid, manganese salt

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Data from reliablesource. Though no test report is available at present the data from this source are known to be well documented and the test are performed according to GLP and OECD guidelines.

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

GLP compliance:

not specified

Remarks:

probably: yes

Analytical monitoring:

yes

Vehicle:

not specified

Test organisms (species):

Daphnia magna

Details on test organisms:

Test organism
The recommended species is Daphnia magna, but other Daphnia species such as Daphnia pulexs may also be used.
Use organisms that are 24 hr old or younger at the beginning of the exposure. To reduce variation, do not use the first offsprings of the parents. The test organisms must be obtained from healthy parents (i.e., showing no sign of stress under the culture conditions such as a high mortality, the appearance of males or oostegites, a prolonged period before the first offsprings and discoloration) of the same strain.
The parent organisms must be cultured under conditions (light, temperature and water) as same as those employed in the test. When performing the test using water different from that usually used for culturing Daphnia spp., establish an acclimatization period before beginning the exposure. The acclimatization can be performed by culturing the organisms in the material water at the test temperature for at least 48 hr before beginning the exposure. Use the offsprings obtained from acclimatized parents for the test.

Test type:

not specified

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Details on test conditions:

The following test vessel and equipment are used for the study.

Test vessel
The test vessel or other instrument that contacts the test solution must be made of glass or other chemically inert materials. Cap the vessel loosely to prevent evaporation and dust contamination.
If the test substance is volatile, perform the test in a sealed system. Use a sufficiently large vessel to prevent shortage of dissolved oxygen.

Instrument
Use a dissolved oxygen meter (a microelectrode or other instrument suitable for measuring the dissolved oxygen concentration with a small amount of sample), a pH meter, an appropriate instrument for controlling temperature, etc., for the test.


Material water
Use water suitable for culturing and testing Daphnia spp. It can be natural water (surface water or groundwater), dechlorinated tap water or artificially prepared water (e.g., Appendix Table 1), but must satisfy the conditions listed in Appendix Table 2.
Do not use Elendt M4 or M7 media or water containing chelating agents for testing metal-containing substances. The water hardness should be 250 mg/L or smaller in terms of calcium carbonate concentration, and the pH should be 6-9.
Aerate the material water before using it for the test.


Test solution
To prepare a test solution of each concentration, directly dissolve the required amount of the test substance in the material water, or prepare a stock solution of the test substance at an appropriate concentration and dilute it with the material water. Follow the descriptions in "Preparation of the test solution" under "III. General rules".
Perform the test without adjusting the pH. If the pH of the material water is not within the range of 6-9, it is recommended to perform an additional test after adjusting the pH to that observed prior to the addition of the test substance. Perform the pH adjustment through a method causing no change in the concentration, chemical reaction or precipitation of the test substance. Preferably, use HCl or NaOH for the pH adjustment.


Test method
The test can be performed under a static, semi-static or flow-through condition. If the test substance concentration is unstable, a semi-static or flow-through test is recommended.

Exposure period
Perform the exposure period for 48 hr.

Volume and number of test organisms

Volume: Use at least 2 mL or the test solution per organism.
Number of test organisms: Use at least 20 organisms for each of the test concentrations and the control. Preferably, divide the organisms into 4 groups of 5 organisms.

Test concentrations
Adopt a concentration range comprising at least 5 concentrations that are setup in a geometric progression, preferably at a geometric ratio of within 2.2. The highest test concentration preferably induces 100% immobilization, but concentrations of 100 mg/L or higher do not need to be tested. Preferably, no effect is observed at the lowest concentration.
Perform a control, and additionally an auxiliary control if using any auxiliary.

Culture method

Illumination: The photoperiod is preferably set to 16 hr light and 8 hr dark. The test can be conducted in dark if the test substance is unstable against light.
Temperature: The temperature is set within the range of 18°C - 22°C, with variations among the test vessels of ± 1.0°C.
Dissolved oxygen concentration: It must be kept at 3 mg/L or higher. In principle, do not perform aeration during the exposure period.
Feeding: Do not feed the organisms.

Beginning of the exposure to the test substance
Start the exposure by transferring a specified number of organisms established in 5-3. to each test vessel.

Observation
Observe the mobility of the organisms at least twice, i.e., at 24 and 48 hr after the beginning of the exposure. The organisms are considered as being immobilized when they do not move for 15 sec after the test vessel is gently shaken. During observation, record any anomaly in behavior or appearance besides immobilization.

Reference substance (positive control):

not specified

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

910 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

mobility

Description of key information

The substance is with high probability acutely not harmful to aquatic invertebrates.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

913 mg/L

Additional information

The acute toxicity of 2-ethylhexanoic acid (CAS 149-57-5) to aquatic invertebrates was investigated in a non GLP acute test according to Directive 79/831/EEC using Daphnia magna. The determinate 48-h EC50 value in this study was 85.4 mg/L, related to the nominal concentration (BASF SE 1988). However, the test substance caused a pH-shift to more acidic conditions in the higher concentrations (250 mg/L = 4.92 (0h) - 5.21 (48h); 125 mg/L = 5.79 (0h), 7.09 (48h); 62.5 mg/L = 6.95 (0h) - 7.85 (48h)). In the concentration 125 mg/L all animals are immobile after 48 hours whereas in the concentration 62.5 mg/L only one daphnid was immobile at the test end. The acceptable pH range for daphnia given in the OECD TG 202 (6.0 to 9.0) was determined after 48 hours of exposure. No test solutions were pH-adjusted. Therefore, it can be considered that the observed toxicity is likely due to the pH-shift.

Another test according to OECD guideline 202 using Daphnia magna as test organism was performed (NITE, Japan 2002). The test was conducted under supervision of the Japanese Ministry of the Environment. In opposite to the study with the acid, this study was conducted under GLP and the test concentrations were analytically verified. The test concentrations were analytically verified and deviated less than 20% from the nominal concentrations. Moreover, the study was performed with the salt of the acid (Sodium 2-ethylhexanoate, CAS 19766-89-3) which resembles the acid after neutralization. By that, in this study, the toxicity of the test substance was not influenced by acidic pH effects. Therefore, the study was used as a key study for the assessment of the acute toxicity of CAS 149-57-5 to aquatic invertebrates.

After 48 hours an EC50 of 913 mg/L was estimated (nominal, analytically verified, NITE 2002, report no.: A010465-4).

In addition, another acute test performed with 2-ethylhexanoic acid (CAS 149-57-5) by DOW (1993) revealed a 48-h EC50 of 109 mg/L. However, the study doesn’t have sufficient details on the acidity of the test conditions and analytical measurements of the test substance treatments.

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