2-butyloctanoic acid

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: A QSAR model, ECOSAR was used to estimate algae toxicity.

Justification for type of information:

QSAR prediction

Qualifier:

no guideline required

Principles of method if other than guideline:

The QSAR model, Ecological Structure Activity Relationships (ECOSAR) Class Program was used to estimate the short-term toxicity to algae.

GLP compliance:

no

Analytical monitoring:

not required

Test organisms (species):

other: algae

Water media type:

freshwater

Key result

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

16.975 mg/L

Basis for effect:

growth rate

Duration:

96 h

Dose descriptor:

other: ChV

Effect conc.:

7.178 mg/L

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

5.076 mg/L

Validity criteria fulfilled:

not applicable

Conclusions:

Using a reliable QSAR model, Ecological Structure Activity Relationships (ECOSAR) Class Program was used to estimate the 96hr EC50 for algae to be 16.975 mg/L. In addition, the 96 hr ChV was calculated to be 7.178 mg/L.

Executive summary:

Using a reliable QSAR model, Ecological Structure Activity Relationships (ECOSAR) Class Program was used to estimate the 96hr EC50 for algae to be 16.975 mg/L. In addition, the 96 hr ChV was calculated to be 7.178 mg/L. As per REACH Guidance Ch 10, a NOEC can be calculated from the chronic value. Therefore, the calculated NOEC is 5.076 mg/L.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Justification for type of information:

ISOCARB are aliphatic branched carboxylic acids and include substances with carbon chain lengths of C11 to C24. Their only functional group is the carboxyl group, which they share in common. All ISOCARB have a single branching at the C2 position, where the branches differ in chain length from methyl to decyl. Common physical and biological pathways result in structurally similar breakdown products and are responsible for similar environmental behaviour. The structural similarities result in the same mode of ecotoxicological action. (Please see Category Approach)

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

2.7 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% CL: 2.0 - 3.5 mg/L

Duration:

72 h

Dose descriptor:

EC20

Effect conc.:

4.6 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% CL: 3.7 - 5.6 mg/L

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

13 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% CL: 11 - 15 mg/L

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

1.3 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): no
- Unusual cell shape: no
- Colour differences: no
- Flocculation: no
- Adherence to test vessels: no
- Aggregation of algal cells: no
- Other: no
- Any stimulation of growth found in any treatment: no
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: no
- Effect concentrations exceeding solubility of substance in test medium: no

Reported statistics and error estimates:

Parameters of probit analysis (growth rate)
---------------------------------------
Computation runs: 7
Slope b: 1.9166
Intercept a: -2.11697
Variance of b: 1.4806
Goodness of Fit
Chi²: 0.1046
Degrees of freedom: 10
p(Chi²): 1.0000
Log EC50: 1.1046
SE Log EC50: 0.2642
g-Criterion: 0.0209
Residual Variance (Chi²/df): 0.0105
r²: 0.9600
F: 237.1530
p(F) (df: 1;10): 0.0000

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the present study with Pseudokirchneriella subcapitata, Reaction mass of n-undecanoic-acid and 2-methyl-decanoic-acid and 2-ethyl-nonanoic-acid and 2-propyl-octanoic-acid and 2-butyl-heptanoic-acid inhibited growth rate and yield of this fresh water algae species significantly at a time weighted average concentration of 4.2 mg/L.
The EC50 for growth rate inhibition (72h-ErC50) was 13 mg/L (95% confidence interval ranging from 11 to 15 mg/l).
The EC50 for yield inhibition (72h-EyC50) was 3.1 mg/L (95% confidence interval ranging from 2.0 to 3.3 mg/L).
The 72h-NOEC for growth rate inhibition was 1.3 mg/L. The 72h-EC10 for yield inhibiton was 1.2 mg/L.

Executive summary:

Pseudokirchneriella subcapitata, Fresh Water Algal Growth Inhibition Test with Reaction mass of n-undecanoic-acid and 2-methyl-decanoic-acid and 2-ethyl-nonanoic-acid and 2-propyl-octanoic-acid and 2-butyl-heptanoic-acid.

The study procedures described in this report were based on the OECD guideline No. 201, 2006; Annex 5 corrected 28 July 2011. In addition, the procedures were designed to meet the test methods of the Commission Regulation (EC) No 440/2008, Part C.3, 2008; Amended by EC No. 761/2009 and the ISO International Standard 8692, 2012.

The batch of Reaction mass of n-undecanoic-acid and 2-methyl-decanoic-acid and 2-ethyl-nonanoic-acid and 2-propyl-octanoic-acid and 2-butyl-heptanoic-acid tested was a clear yellowish liquid with a purity of 97.6 % and not completely soluble at the loading rate initially prepared.

A final test was performed based on the results of a preceding combined limit/range-finding test. Preparation of test solutions started with a nominal concentration of 100 mg/l applying a 2 -day period of magnetic stirring followed by an one-hour settlement period. The aqueous Water Soluble Fraction (WSF) was siphoned off. The pH of the WSF was adjusted from 5.8 to 6.5 using 1 M NaOH. This solution was used as the highest test concentration. The lower test concentrations were prepared by subsequent dilutions of the WSF in test medium. The final test solutions were all clear and colourless.

Six replicates of exponentially growing algal cultures were exposed to a control, whereas three replicates per concentration were exposed to nominally 0.10, 0.32, 1.0, 3.2, 10, 32 and 100% of the WSF. The initial cell density was 10E4 cells/ml and the total exposure period was 72 hours. Samples for analytical confirmation of actual exposure concentrations were taken at the start, after 24 and 72 hours of exposure.

The concentrations measured in the samples taken from the solutions containing 0.10 and 0.32% of the WSF prepared at 100 mg/l were below the Limit Of Quantification (LOQ was 0.5 mg/l) at all sample occasions. The actual concentration at the start of the test in the vessels containing 1.0, 3.2, 10, 32 and 100% of the WSF prepared at 100 mg/l were 0.74, 2.9, 9.7, 32 and 111 mg/l, respectively. These concentrations did not remain stable during the exposure period (21 -52% of the initial at the end of the rest). The Time Weighted Average (TWA) exposure concentrations were calculated to correspond to 0.42, 1.3, 4.2, 23 and 93 mg/l. The two lowest test concentrations that were below LOQ and the 0.42 mg/l concentration were not needed for determination of the effect parameters.

The study met the acceptability criteria prescribed by the protocol and was considered valid.

Effect parameters based on growth rate:

NOErC 1.3 mg/L

ErC10 2.7 mg/L (95% confidence interval 2.0 - 3.5 mg/L)

ErC20 4.6 mg/L (95% confidence interval 3.7 - 5.6 mg/L)

ErC50 13 mg/L (95% confidence interval 11 - 15 mg/L)

Effect parameters based on yield:

NOEyC 1.3 mg/L

EyC10 1.2 mg/L (95% confidence interval 1.0 - 1.3 mg/L)

EyC20 1.6 mg/L (95% confidence interval 1.5 - 1.8 mg/L)

EyC50 3.1 mg/L (95% confidence interval 2.0 - 3.3 mg/L)

Description of key information

An algae test with 2-butyl octanoic acid is not available but an ecosar calculation. The toxicity of the similar substance Reaction mass of n-undecanoic-acid and 2-methyl-decanoic-acid and 2-ethyl-nonanoic-acid and 2-propyl-octanoic-acid and 2-butyl-heptanoic-acid was assessed in a fresh water algal groth inhibition test with Pseudokirchnerella subcapitata according to OECD guideline 201. The ErC10 of 2.7 mg/L (95% CL 2.0 – 3.5 mg/L), NOErC of 1.3 mg/L and the  ErC50 of 13 mg/L (95% CL 11 – 15 mg/L) after 72 hours of exposure can be considered reliable without restrictions. The ECOSAR calculation of the test substance 2-butyl octanoic acid confirms that range of acute toxicity with a value of 16.975 mg/L and chronic toxicity with a calculated NOEC of 5.076 mg/L..

Key value for chemical safety assessment

EC50 for freshwater algae:

13 mg/L

EC10 or NOEC for freshwater algae:

1.3 mg/L

Additional information

An algae test with Reaction mass of 2-methyl-decanoic-acid and 2-ethyl-nonanoic-acid and 2-propyl-octanoic-acid and 2-butyl-heptanoic-acid is not available. Toxicity in freshwater algae Pseudokirchneriella subcapitata with the similar substance Reaction mass of n-undecanoic-acid and 2-methyl-decanoic-acid and 2-ethyl-nonanoic-acid and 2-propyl-octanoic-acid and 2-butyl-heptanoic-acid was tested according to OECD guideline No. 201. The study met the acceptability criteria and was conducted GLP compliant, therefore considered reliable without restrictions. The ECOSAR calculation of the test substance 2-butyl octanoic acid also predicts that range of toxicity with a value of 16.975 mg/L.