Octanoic acid

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

fish, juvenile growth test

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well documented publication which meets basic scientific principles.

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 305 E (Bioaccumulation: Flow-through Fish Test)

Deviations:

yes

Remarks:

depuration phase was not determined; fish were only sampled at the end of exposure

Principles of method if other than guideline:

28-day flow-though test in fish on mortality, growth rate and bioconcentration

GLP compliance:

no

Analytical monitoring:

yes

Details on sampling:

Sampling intervals/frequency for test medium samples: Concentrations of laurate in all the test media were determined frequently throughout the test (n = 21; one sample per test concentration on each sampling occasion) using liquid scintillation counting method (LSC).

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Stocks of sodium laurate were prepared daily by warming (above the Kraft point of 35–40°C) equimolar quantities of sodium hydroxide and lauric acid in distilled water in a water bath to keep the soap in solution (stock solutions of 5.7, 3.2, 1.82, 1.03 and 0.57 g/L). Radiolabeled lauric acid in dimethyl sulfoxide (DMSO) was added to each stock (final concentration, 0.5 ml DMSO/L) to give specific activities of 0.57, 1.02, 1.79, 3.16, and 5.71 mCi/g, respectively.
- Controls: yes, only vehicle control
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): dimethyl sulfoxide (DMSO)
- Concentration of vehicle in test medium(final test solution(s): final concentration 0.5 mL/L
- Evidence of undissolved material (e.g. precipitate, surface film, etc): No undissolved material observed in the stocks

Test organisms (species):

Danio rerio (previous name: Brachydanio rerio)

Details on test organisms:

TEST ORGANISM
- Common name: zebrafish
- Age at study initiation (mean and range, SD): approx. 2 months old
- Weight at study initiation (mean and range, SD): 68.9 mg ± 9.8 mg
- Weight at termination (mean and range, SD): 111.3±7.8 mg
- Method of breeding: feeding based on body weight, before feeding, surface scum (precipitated calcium laurate) was removed to minimize uptake of laurate via dietary sources
- Health status: healthy
- Feeding during test: yes, Fish were fed during the week and on weekends. Feeding levels were adjusted for mortalities that occurred during the test. To recalculate the food ratio for each exposure vessel, fish were not fed on day 13, as well not on day 27 (a day before the test termination).
- Food type: Tetramint and Artemia
- Amount: 2% of wet weight during the week, 4% of wet weight in weekends
- Frequency: during the week the fish was feed once daily with each type of food, respectively, at weekend once only with Tetramint.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

28 d

Post exposure observation period:

no

Hardness:

96.5 ± 4.5 mg/L CaCO3

Test temperature:

21.5 ± 0.5 ℃

pH:

7.6 ± 0.2

Dissolved oxygen:

8 ± 0.7

Salinity:

no data

Nominal and measured concentrations:

nominal laurate concentrations: 0, 2.0, 3.6, 6.4, 11.2 and 20.0 mg/L
measured laurate concentrations: 0, 2.2, 3.7, 6.6, 12.9 and 20.1 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 5 Liter
- Type (delete if not applicable): open
- Type of flow-through (e.g. peristaltic or proportional diluter): proportional diluter
- Renewal rate of test solution (frequency/flow rate): 170 -180 mL/min.
- No. of organisms per vessel: 16
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap water

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 16 h light/8 h dark
- Light intensity: no data

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : mortality

Reference substance (positive control):

no

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

6.4 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

9.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Details on results:

- Fish weights (individual and mean values) on day 0, 14 (if measured) and 28: see Table [1]
- Pseudo-specific growth rates for periods 0-28 or 0-14 and 0-28: see Table [1]
- Type of and number with morphological abnormalities: not observed
- Type of and number with behavioural abnormalities: not observed
- Other biological observations: not observed
- Effect concentrations exceeding solubility of substance in test medium: no
- Incidents in the course of the test which might have influenced the results:

1) Exposure concentrations and the estimated water solubility of laurate in the test media

 

Recovery of laurate concentration in media: 100 to 115% of nominal concentrations. At concentrations of 2, 3.6, and 6.4 mg/L, there was little difference between total and soluble laurate, but approximate 8.6 mg/L and 8.0 mg/L of soluble laurate were measured in the 11.2 and 20 mg/L test media, corresponding to 80 and 40% of the total laurate, respectively. Therefore, an approximate solubility limit for laurate in the test medium was 8 to 9 mg/L.

During the test, precipitates were visible, particularly at the higher concentrations (11.2 and 20.0 mg/L).

 

No shorter-chain carboxylic acids (<12 carbons) were observed by GC–FID, indicating that the test substance in aqueous media was present as intact sodium laurate throughout the exposure period.

2) Effects on survival and growth

Exposure to sodium laurate caused mortalities at total concentrations of 3.6 (6%), 6.4 (14%), 11 (75%), and 20 mg/L

(75%). The estimated 4-, 8-, 15-, and 28-d median lethal concentrations (LC50s) were 20, 12, 9.9, and 9.8 mg/L, respectively. Based on soluble concentrations of laurate, LC50 values for the above time intervals were 10, 7.6, 7.6, and 7.6 mg/L. The 28-d NOEC for mortality was 2 mg/L.

 

Control fish increased in weight by 18 and 47% after 14 and 28 d, respectively. Fish exposed to the lower concentrations (2–6.4 mg/L) all increased in weight, and this increase was greater than that seen in control animals. It is known that fattyacids formed de novo and those originating from dietary lipids are easily esterified into neutral lipids and phospholipids.Once absorbed, laurate could perhaps be used as an additional food source by these fish, resulting in slightly enhanced growth compared to that of the control fish. The 28-d NOEC for growth was 6.4 mg/L.

Table1. Pseudospecific growth rates for zebrafish exposed to increasing concentrations of sodium laurate

Time period of exposure	Pseudospecific growth rate ± SD
	control	2 mg/L	3.6 mg/L	6.4 mg/L
0 - 14	1.14 ± 1.10	1.75 ± 1.31	2.04 ± 0.89	1.50 ± 1.26
0 - 28	1.36 ± 0.54	1.72 ± 0.79	1.99 ± 0.46	1.70 ± 0.50
14 - 28	1.57 ± 1.08	1.69 ± 1.58	1.94 ± 0.92	1.90 ± 0.99

Reference 2

Endpoint:

fish, juvenile growth test

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please refer to the category justification provided in IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: Source CAS 629-25-4

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

6.4 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: Source CAS 629-25-4

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

9.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks on result:

other: Source CAS 629-25-4

Description of key information

NOEC (28 d) = 6.4 mg/L (nominal), based on growth rate of Danio rerio (OECD 305 E); RA CAS 629-25-4

NOEC (28 d) = 2 mg/L (nominal), based on mortality of Danio rerio (OECD 305 E); RA CAS 629-25-4

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

6.4 mg/L

Additional information

No studies are available reviewing the toxicity of octanoic acid to fish. Therefore, a read across was conducted to the analogue substance sodium laurate. The study by Egmond et al. (1999) performed with the read across substance was conducted according to OECD 305 E (bioaccumulation: flow-through fish test). Danio rerio was exposed to nominal 0, 2.0, 3.6, 6.4, 11.2 and 20.0 mg/L test item concentrations for 28 d. The test item concentrations were monitored by GC-FID. NOEC values were determined based on growth rate and mortality and were 6.4 mg/L and 2 mg/L, respectively. In addition an LC50 (28 d) of 9.8 mg/L was reported.