2-ethylhexanoic acid, manganese salt

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Test procedure according to National Standard with acceptable restrictions (e.g. exposure concentrations in the test and the stability of test item were not confirmed by chemical analysis)

Qualifier:

according to guideline

Guideline:

other: Method: other: German Industrial Standard DIN 38412, Part 9

GLP compliance:

no

Analytical monitoring:

no

Vehicle:

not specified

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

pH:

3.82 - 7.98

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 500 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: pH adjusted

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

49.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95%: 37.9 - 64.1 mg/L

Remarks:

not pH-adjusted

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

32 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95 % = 22.9 - 44.6 mg/L

Remarks:

not pH-adjusted

Results related to nominal concentrations
-----------------------------------------

Effect values based on growth rate:
EµC10 (72 h) = 31.94 mg/l (CI 95 % = 22.90 - 44.56)
EµC10 (96 h) = 27.94 mg/l (CI 95 % = 17.81 - 43.83)
EµC50 (72 h) = 49.28 mg/l (CI 95 % = 37.91 - 64.06)
EµC50 (96 h) = 44.39 mg/l (CI 95 % = 31.42 - 62.71)

Effect values based on biomass:
EbC10 (72 h) = 32.54 mg/l (CI 95 % = 16.85 - 62.86)
EbC10 (96 h) = 24.50 mg/l (CI 95 % = 11.10 - 54.05)
EbC50 (72 h) = 60.51 mg/l (CI 95 % = 36.74 - 99.65)
EbC50 (96 h) = 40.62 mg/l (CI 95 % = 22.50 - 73.33)


Cell density values (cells * 10^3/ml):

Concentration (mg/l)    0 h   24 h   48 h   72 h   96 h
  0 (Control)           12     28     56    140    415 
 25                     12     28     55    128    290 
 50                     12     27     42     50     70
100                     12     17     17     13     13
250                     11     10     10      4      4
500                     12      8      4      4      4
500 (pH control)        12     23     31     52     75


Inhibition of growth rate and biomass after 72 and 96 h:

                                Inhibition (%)
                        Growth rate            Biomass
Concentration (mg/l)   72 h     96 h        72 h     96 h
  0 (Control)           --       --          --       -- 
 25                     3.6     10.1         4.4     16.5 
 50                    41.9     50.2        41.1     69.4
100                    96.7     97.7        84.7     95.4
250                   100.0    100.0        97.5    100.0
500                   100.0    100.0       100.0    100.0
500 (pH control)       40.3     48.3        55.0     71.0  


Physico-chemical parameters:
  
                                  pH
Concentration (mg/l)        0 h        96 h
 0 (Control)               7.83        7.92
 25                        7.52        7.77
 50                        7.19        7.45
100                        5.48        5.59
250                        4.25        4.30
500                        3.82        3.85
500 (pH control)           7.84        7.98

- the temperature was 24.8 °C in all test concentrations

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:

500 mg/L

EC10 or NOEC for freshwater algae:

130 mg/L

Additional information

In a non-GLP, 72-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.

In addition, under supervision of the Japanese Ministry of the Environment a test on the green algae Pseudokirchneriella subcapitata according to OECD 201 and under GLP was conducted and published in 2002. 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 algae 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 algal toxicity of CAS 149-57-5.

In the original study report the 24-h-72 -h NOEC (growth rate) was 130 mg/L, the 24-h-72 -h ErC50 was 500 mg/L (nominal, NITE 2002, report no.: A010465-1).

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.