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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
No purity; Limited information on test design
according to guideline
OECD Guideline 201 (Alga, Growth Inhibition Test)
according to guideline
other: ISO 14442 norm: Water quality - guidelines for algae growth inhibition tests with poorly soluble materials, volatile compounds, metals and waste water
GLP compliance:
Non-GLP testing facility.
Analytical monitoring:
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Test solutions are prepared in accordance with the ISO 14442 norm. The preparation consists of 68 hours of gentle agitation by magnetic stirring to obtain a vortex of about 1/3 (or less in some conditions) of the height between the top and the bottom of the flask, followed by 4 hours of phase separation. The aqueous phase, containing the soluble substances (Water Accommodated Fraction) is taken to perform the test. The test solution is identified according to its loading rate (massic proportions of substance to be tested / test medium mass introduced into the diphasic reactor) while operating the ‘WAF’.
Test organisms (species):
Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)
Details on test organisms:
- Common name: green algae
- Source: Microbiotests Inc., Venecoweg 19, 9810 Nazareth, Belgium
- Batch number: SC110511 – R11 (21 Oct 2011)
Test type:
Water media type:
Limit test:
Total exposure duration:
72 h
Test temperature:
23 ± 2 °C
8.1 ± 0.2
Nominal and measured concentrations:
nominal: 0.104 g/1000 g (loading ratio: massic proportions of substance to be tested / test medium mass introduced into the diphasic reactor) which will be determined as 0.104 g/L
Details on test conditions:
- Test vessel: culture vials, placed onto a rotative stirrer (60 mvt/s) for incubation)
- Initial cells density: 5000 - 10000 cells/mL
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

- Source/preparation of dilution water: OECD medium
- Culture medium different from test medium: no
- Intervals of water quality measurement: The pH of the control and test solution are measured at the beginning and the pH of one vial of each lot is measured at the end of the test.

- Adjustment of pH: no
- Photoperiod: continuous
- Light intensity and quality during incubation: white continued light, with spectra from 400 – 700 nm and intensity about 6000 Lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: Every 24 h using a spectrophotometer (670 nm wavelength).
Reference substance (positive control):
72 h
Dose descriptor:
Effect conc.:
> 0.104 g/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
growth rate

The value of inhibition rate of charge of the test substance is the relative difference of the specific growth rate compared to the control group (see the table below).


Table 1: Inhibition of cell growth at 72 hours

0.10 (g/1000 g)*

Inhibition (%)

Test item R1

- 7.5

Test item R2

- 5.2

Test item R3

- 2.7

Test item R4

- 4.3

Test item R5

- 5.8

Test item R6

- 6.8


- 5.4

Standard deviation


* This test concentration is stated as 0.104 g/L.

Description of key information

No effects up to the limit of water solubility (OECD 201, P. subcapitata)

Key value for chemical safety assessment

Additional information

Two studies are available, in which the toxicity of the target substance Fatty acids, C18-unsaturated, 2-hexyldecyl ester to aquatic algae was investigated according to internationally accepted testing guidelines. The key study was conducted with the target substance and the supporting study was conducted with the structurally related source substance 2-octyldodecyl isooctadecanoate (CAS 93803-87-3). The source substance is characterized by similar fatty acid and alcohol components and is therefore considered a suitable representative for the assessment of the toxicity of the target substance to aquatic algae. Read-across was conducted in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5 and a detailed justification of the analogue approach is provided in IUCLID section 13.

In the key study, P. subcapitata was exposed to a water accommodated fraction (WAF) with a nominal loading rate of 0.104 g/L test item in a static limit test for 72 h according to OECD guideline 201. After 72 h the observed mean inhibition of the specific growth rate was -5.4%, resulting in an EL50 (72 h) of > 0.104 g/L (nominal).

In the supporting GLP-study, P. subcapitata was exposed to two WAFs with nominal loading rates of 10 and 100 mg/L test item, respectively, in a static test according to OECD guideline 201. The detection of test item concentrations in the test media was not possible with the available analytical techniques due to the very low solubility of the test item.

After 72 h, an inhibition of cell growth by 31.2% was recorded at the nominal concentration level of 100 mg/L whereas no effects on cell growth were observed at the nominal concentration level of 10 mg/L. The significant inhibition of growth was suspected to result from the turbidity of the test solution caused by undissolved test material, which may have absorbed a fraction of the light required for proper algal cell growth. The reported effect concentrations are an EL50 (72 h) > 100 mg/L (nominal) and a NOELR (72 h) of ≥ 100 mg/L (nominal). Since both test loading rates were clearly above the water solubility, it can be concluded that both effect loading rates exceed the water solubility of the test item.

In summary, the available key study showed that the target substance Fatty acids, C18-unsaturated, 2-hexyldecyl ester does not cause any effects on aquatic algae up to the limit of water solubility (< 0.56 mg/L). This finding is confirmed by the supporting study with source substance2-octyldodecyl isooctadecanoate (CAS 93803-87-3). Based on the structural and chemical similarity of the target and source substances, the target substance is expected to exhibit a similar ecotoxicological profile as the source substance.