Hexanoic acid

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

key study

Study period:

03 September - 06 September 2002

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Remarks:

The concentration of the substance during test was not maintained within ± 20% of the nominal concentration. Neverthelss, the result of the test was analysed with nominal concentration.

GLP compliance:

yes

Remarks:

according to Japanese GLP standard

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
PHYSICO-CHEMICAL PROPERTIES
- Melting point: -10/-7 °C
- Boiling point: 223 °C
- Vapour pressure: 1 mmHg at 78 °C, 10 mmHg at 113.2 °C, 100 mmHg at 160 °C
- Water solubility (under test conditions): 2410 mg/L at 15 °C

Analytical monitoring:

yes

Details on sampling:

- Sampling method: 2 mL of test water was directly sampled by each vessel before study initiation. After exposure, test water was sampled and centrifuged to remove algae (3000 rpm, 10 min).

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Test item was dissoved in dilution water. The concentration of stock solution was 100 mg/L. Each concentration was prepared by diluting stock solution.
- Controls: Blank control
- Evidence of undissolved material (e.g. precipitate, surface film, etc): Apperance of test water was clear colorless in all concetration.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Common name: Algae
- Strain: ATCC22662
- Source (laboratory, culture collection): American Type Culture Collection
- Age of inoculum (at test initiation): Within 4 days
- Method of cultivation:

ACCLIMATION
- Acclimation period: 2002-08-30 to 2002-09-03
- Culturing media and conditions (same as test or not): same as test

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

23.5 - 24.2 °C

pH:

5.7 - 9.8

Nominal and measured concentrations:

Nominal concentration: control, 10, 15, 22, 32, 46, 68 and 100 mg/L
Measured concentration: (0 hour and 72 hours): - ; 10.7 and 7.9; 14.7 and 13.5; 21.1 and 19.2; 31.0 and 27.5; 48.4 and 39.9; 70.4 and 62.6; 108 and 86.6 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 300 mL Erlenmeyer flask
- Type: Capped with air-permeable stopper
- Material, fill volume: Glass, 100 mL
- Initial cells density: 10000 cells/mL
- Control end cells density: 2436100 ± 597200 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3

GROWTH MEDIUM
- Standard medium used: yes

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Photoperiod: continuously
- Light intensity and quality: 4000 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: electronic particle counter;

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.5
- Range finding study: Performed twice
- Test concentrations: (1) 1, 10 and 100 mg/L, (2) 5 and 10 mg/L
- Results used to determine the conditions for the definitive study:
(1) Growth rate after 72 hours was 100% in control group, 87% in 1 mg/L group, 88% in 10 mg/L group and 0% in 100 mg/L group.
(2) Growth rate after 72 hours was 100 %in control group, 85% in 5 mg/L group and 91% in 10 mg/L group.

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

52.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

32 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

56.4 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 36.9 - 86.4 mg/L

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

32 mg/L

Nominal / measured:

nominal

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 abnormality was observed

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- EC50: 0.473 mg/L

Reported statistics and error estimates:

The NOEC were determined by an analysis of variance (ANOVA), Dunnett test, subsequent to Bartlett test for homogeneity of variances. Statistical analyses were performed using Yukms Statlight # 4 software.

Table 1. Percent growth inhibition

Nominal Concentration (mg/L)	Biomass	Growth rate (24-72 h)
	Inhibition (%) *1	Inhibition (%) *1
Control	-	-
10	- 17.2	- 3.7
15	- 23.6 +	- 2.7
22	- 29.4 ++	- 1.2
32	-30.3 ++	- 2.3
46	27.6 *	11.6 **
68	95.9 +++	87.2 **
100	99.8 +++	99.7 **

*1 Values are the percent inhibition relative to the control.

* Indicates a significant difference (α = 0.05) from the control.

** Indicates a significant difference (α = 0.01) from the control.

+++ Statistical comparison test could not be performed for this concentration. However, it was concluded that this concentration level showed adverse effect on Algal growth.

+, ++ This concentration level showed a significant difference (+: α= 0.05, ++: α = 0.01), but it was concluded that this concentration level did not show adverse effect on Algal growth.

Description of key information

ErC50 (72 h, growth rate) = 56.4 mg/L (nominal, OECD 201)
NOErC (72 h, growth rate) = 32 mg/L (nominal, OECD 201)

Key value for chemical safety assessment

EC50 for freshwater algae:

56.4 mg/L

EC10 or NOEC for freshwater algae:

32 mg/L

Additional information

No data on toxicity to algae are available for hexanoic acid C6 (CAS 142-62-1).

Therefore ecotoxicological effects are predicted from adequate and reliable data for a source substance by read-across to the target substance within the group applying the group concept in accordance with Annex XI, Item 1.5, of Regulation (EC) No 1907/2006.

Due to an increasing toxicity with increasing chain length from hexanoic acid C6 to decanoic acid C10 for aquatic organisms read across is performed to heptanoic acid C7 (CAS 111-14-8) since this substance is the most structurally related one in comparison to hexanoic acid.

In the study provided from the Ministry of the Environment, Government of Japan (2002), heptanoic acid C7 was tested according to OECD 201 under GLP-conditions. Selenastrum capricornutum was exposed to 0, 10, 15, 22, 32, 46, 68 and 100 mg/L (nominal, measured values in the range of 80 - 120% of nominal concentrations). The ECr50 (72 h) and NOErC were stated as 56.4 mg/L and 32 mg/L, respectively.