Decyl laurate

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:

key study

Study period:

17 - 21 Oct 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Version / remarks:

23 Mar 2006

GLP compliance:

yes (incl. QA statement)

Remarks:

The Department of Health of the Government of the United Kingdom, GLP Monitoring Authority (15 Nov 2016)

Analytical monitoring:

yes

Remarks:

GC-MS

Details on sampling:

- Concentrations: All test concentrations and the controls for dilution water (culture medium) and solvent were sampled.
- Sampling method: 100 mL samples were taken from excess test solutions at test start (0 h) and from test vessesl at the test end (72 h).

Vehicle:

yes

Remarks:

tetrahydrofuran (THF)

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A clear and colorless stock solution with a nominal concentration of 20 g/L was prepared by adding 0.2 g test item to 10 mL tetrahydrofuran. Test solutions were prepared by dilution of this stock solution by the addition of appropriate amounts of stock solution to dilution water.
- Controls: A solvent control was prepared by addition of an appropriate amount of solvent (without test item) to dilution water. The dilution water control consisted of culture medium only.
- Chemical name of vehicle: Tetrahydrofuran (THF)
- Concentration of vehicle in test medium: max 0.01% (v/v) (stock solution: 20 g/L; highest test concentration: 2 mg/L; final test solution volume: 100 mL)
- Evidence of undissolved material: The test solutions were clear and colourless and contained globules of test substance on the surface of the media in 1.0 and 2.0 mg/L.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: Unicellular freshwater green microalga
- Strain: CCAP 278/4
- Source: In-house laboratory cultures maintained under axenic conditions.
- Age of inoculum: 4 d
- Method of cultivation: The culture was grown in the same medium and conditions used for the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

22.2 - 22.7 °C (test incubator)

pH:

0 h: 6.98 (control), 7.11 - 7.29 (treatments)
72 h: 7.55 (control), 7.72 - 8.00 (treatments)

Nominal and measured concentrations:

Culture medium control, solvent control, 0.125, 0.25, 0.50, 1.00, and 2.00 mg/L (nominal)
< LOQ, < LOQ, 0.075, 0.15, 0.27, 0.75, and 1.30 mg/L (mean measured)

Details on test conditions:

TEST SYSTEM
- Test vessel: Conical glass flasks of 250 mL nominal capacity filled with 100 mL test solution and closed with foam bungs
- Initial cell density: 0.526E+04 cells/mL (0.158 mL inoculum)
- Control end cell density: 23.30E+04 cells/mL (culture medium control), 21.38E+04 cells/mL (solvent control)
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- No. of vessels per vehicle control (replicates): 6

GROWTH MEDIUM
- Standard medium used: Yes, AAP medium

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: AAP medium according to guideline
- Culture medium different from test medium: Culture medium same as test medium
- Intervals of water quality measurement: pH values were measured at 0 h in excess test solution and at 72 h in one replicate test vessel from each test concentration containing algae. The temperature of the test incubator was measured daily. Light intensity was measured once during the study in each of four representative positions.

OTHER TEST CONDITIONS
- Photoperiod: Continuous
- Light intensity and quality: cool-white, approximately 6133 lux ± 15%
- Other: The test vessels were placed on an orbital shaker (160 rpm) in the incubator and their positions were randomised daily.

EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: Electronic particle counter (Coulter counter, between equivalent spherical diameters of 2.3 - 5.0 µm) after 0, 24, 48, and 72 h
- Other: Microscopic observation of cells at the end of the test.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
- Range finding study: Yes, non-GLP
- Test concentrations: 0.0625, 0.125, 0.25, 0.50, and 1.0 mg/L
- Results used to determine the conditions for the definitive study: Yes. The highest test concentration and the solvent were selected based on the results of a non-GLP range-finding test.

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 1.3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 1.3 mg/L

Nominal / measured:

meas. (arithm. mean)

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: No
- Any observations that might cause a difference between measured and nominal values: The test solutions were clear and colourless with globules of the item on the surface of the media in 1.0 and 2.0 mg/L.
- Effect concentrations exceeding solubility of substance in test medium: Yes

Reported statistics and error estimates:

One-way analysis of variation and t-test (p < 0.05).

VALIDITY CRITERIA

The study fulfilled the validity criteria laid down by the guideline (Table 1).

 

Table 1: Validity criteria for OECD 201.

Criterion from the guideline	Outcome	Validity criterion fulfilled
The biomass in the control cultures should have increased exponentially by a factor of at least 16 within the 72-hour test period.	Cell density increased by 44.3 and 40.6 over 72 h in the control and solvent control, respectively.	Yes
The mean coefficient of variation for section-by-section specific growth rates (days 0-1, 1-2 and 2-3, for 72-hour tests) in the control cultures must not exceed 35%	The mean coefficient of variation was 25% for the control and 29% for the solvent control.	Yes
The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures must not exceed 7% in tests with Pseudokirchneriella subcapitata and Desmodesmus subspicatus.	The coefficient of variation of average specific growth rates was 3.5% for the control and 2.3% for the solvent control.	Yes

 

 

ANALYTICAL RESULTS

Analytical data are summarized in Table 2. Based on the analytical results, the mean measured total concentrations were used for the calculation and reporting of results.

Table 2. Analytical results.

nominal concentration of test item [mg/L]	measured concentration of test item				mean measured total concentration [mg/L]	mean measured total concentration [%]
culture medium control	< LOQ	-	< LOQ	-	0	-
solvent control	< LOQ	-	< LOQ	-	0	-
0.125	0.15	120	< LOQ	0	0.075	60
0.25	0.29^a	116	< LOQ^b	0	0.15	58
0.5	0.53	106	< LOQ	0	0.27	53
1.0	1.5	150	< LOQ	0	0.75	75
2.0	2.5	125	0.023	1	1.3	63

^a            triplicate analyses: 0.33, 0.27, and 0.27 mg/L

^b            duplicate analyses: < LOQ and < LOQ mg/L

LOQ     = 0.01 mg/L

 

BIOLOGICAL RESULTS

No significant differences (p < 0.05) were found and less than 50% growth rate (Table 3) and yield (Table 4) inhibition were found for all tested concentrations. Therefore, the ErC50 (72 h) and EyC50 (72 h) were considered to be greater than the highest tested concentration. The microscopic observations of the control, solvent control and all test concentrations showed that cells appeared normal. The reported effect concentrations are summarized in Table 5.

Table 3. Mean growth rates over the test period.

Nominal concentration of test item [mg/L]	Mean measured total concentration of test item [mg/L]	Mean growth rate/day (0-72 hours)	Mean growth rate/day 95% Cl	Percentage of solvent control (%)
Culture medium control	0	1.26	1.2 - 1.31	102
Solvent control	0	1.23	1.20 - 1.26	-
0.125	0.075	1.26	1.16 - 1.35	102
0.25	0.15	1.25	1.13 - 1.38	101
0.5	0.27	1.24	1.10 - 1.38	100
1.0	0.75	1.28	1.21 - 1.35	104
2.0	1.3	1.30	1.29 - 1.31	105

No significant differences (p <0.05) from the solvent control

All biological measurements are quoted to 3 significant figures and percentages to the nearest integer

 

Table 4. Mean yields over the test period.

Nominal concentration of test item [mg/L]	Mean measured total concentration of test item [mg/L]	Mean yield (0-72 hours) [10^4 cells/ml]	Percentage of solvent control [%]
Culture medium control	0	22.8	109
Solvent control	0	20.9	-
0.125	0.075	22.3	107
0.25	0.15	22.2	106
0.5	0.27	21.4	102
1.0	0.75	23.9	114
2.0	1.3	25.5	122

No significant differences (p <0.05) from the solvent control

Mean yield values are quoted to 3 significant figures and percentages to the nearest integer.

 

Table 5. Results based on mean measured total concentrations of the test item.

Growth rate	test item [mg/L]	Yield	test item [mg/L]
NOEC	> 1.3	NOEC	> 1.3
LOEC	> 1.3	LOEC	> 1.3
ErC50	> 1.3	EyC50	> 1.3
ErC10	> 1.3	EyC10	> 1.3

 

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Description of key information

ErC10 (72 h) > 1.30 mg/L (arithmetic mean measured, OECD 201, P. subcapitata)

ErC50 (72 h) > 1.30 mg/L (arithmetic mean measured, OECD 201, P. subcapitata)

Additional information

There is one experimental study available, in which the toxicity of decyl laurate (CAS 36528-28-6) to aquatic algae was assessed according to OECD guideline 201 and GLP.

In a static test, Pseudokirchneriella subcapitata was exposed to the five nominal test item concentrations of 0.125, 0.25, 0.5, 1.0 and 2.0 mg/L for 72 h. Since the test item was poorly soluble, a primary test item stock solution with a nominal concentration of 20 g/L was prepared in the solvent tetrahydrofuran. The final test solutions were prepared by dilution of this stock solution with culture medium. Therefore, solvent and dilution water controls were run in parallel. Test item concentrations in all the test solutions including controls were analytically verified by GC-MS at test start (0 h) and end (72 h) of the test. Algal cell densities were determined by electronic particle counting with a Coulter counter after 0, 24, 48, and 72 h.

The measured test item concentrations were 106 – 120% of the nominal concentrations at the beginning of the test (0 h) and 0 – 1% at the end of the test (72 h), indicating that the test item was not stable for the duration of the test. Effect values were determined and reported on the basis of the mean measured total concentrations, which were 0.075, 0.15, 0.27, 0.75, and 1.3 mg/L (53 – 75% of nominal concentrations). After 72 h, inhibition was less than 50% in both cases and no significant growth rate and yield inhibition was observed. Therefore, the ErC50 (72 h) and EyC50 (72 h) is considered to be greater than the highest concentration tested and is reported as > 1.3 mg/L. The reported NOEC is 1.3 mg/L for growth rate and yield inhibition and the ErC10 (72 h) and EyC10 (72 h) are both > 1.3 mg/L, respectively.