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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reason / purpose:
read-across source
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: Water Accommodated Fraction (WAF)
Basis for effect:
growth rate
Remarks on result:
other:
Remarks:
Source: CAS 93803-87-3 Croda, 1998, S. capricornutum, 72 h
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
>= 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: Water Accommodated Fraction (WAF)
Basis for effect:
growth rate
Remarks on result:
other:
Remarks:
Source: CAS 93803-87-3 Croda, 1998, S. capricornutum, 72 h
Conclusions:
No effects up to the limit of water solubility (< 0.05 mg/L, S. capricornutum, OECD 201); read-across
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
21 Apr - 24 Apr 1998
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The highest test concentration was slightly turbid which probably has affected the outcome of this study).
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Qualifier:
according to
Guideline:
ISO 8692 (Water Quality - Fresh Water Algal Growth Inhibition Test with Scenedesmus subspicatus and Selenastrum capricornutum)
Qualifier:
according to
Guideline:
EU Method C.3 (Algal Inhibition test)
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Two solutions were prepared at nominal concentrations of 10 and 100 mL respectively in order to achieve maximum exposure concentrations. These solutions were stirred for approx. 21 h, stabilized for 4 h and separated using a separation funnel afterwards. After preparation, volumes of 50 mL were added to each replicate of the respective test concentration.
- Eluate: no
- Differential loading: no
- Controls: yes, test medium control
- Evidence of undissolved material: The separated solutions were slightly turbid.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: green algae
- Strain: CCAP 278/4
- Source: Laboratory culture
- Method of cultivation: Algae stock cultures were started by inoculating growth medium with algal cells from pure culture on agar. The suspensions were continuously aerated and exposed to light (4000-9000 lux) in a climate room at a temperature of 23 ± 2 °C.

ACCLIMATION
- Acclimation period: 4 d before the start of the test, cells from the algal stock culture were inoculated in a culture medium at a cell density of 2x10^4 cells/mL.
- 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
Hardness:
24 mg CaCO3/L
Test temperature:
20 - 22 °C
pH:
8.3 - 8.5
Nominal and measured concentrations:
nominal: 0, 10 and 100 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Material, size: all-glass, 100 mL
- Aeration: continuously shaking
- Initial cells density: 1x10^4 cells/mL
- Control end cells density: 47.5 x 10^4 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- Other: One vessel of each test concentration without algae.

GROWTH MEDIUM
- Standard medium used: yes (according to ISO guideline)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap water purified by reverse osmosis and then passed over activated carbon and ion-exchange cartridges.
- Culture medium different from test medium: no

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: continuously illuminated
- Light intensity and quality: TLD-lamps of 18 Watt yielding 6000 - 6500 lux.

EFFECT PARAMETERS MEASURED: growth rate (every 24 h)
- Determination of cell concentrations: At the beginning of the test, cells were counted by microscope using a counting chamber. Thereafter, cell densities were determined by spectrophotometric measurement of samples at 720 nm using a Lambda Spectrophotometer (Perkin-Elmer, Illinois, USA), with a cuvette of 5 cm path-length. Algal medium was used as blank and the extra replicates as background for the treated solutions.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10x
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: Water Accommodated Fraction (WAF)
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
>= 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: Water Accommodated Fraction (WAF)
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): yes
- Any stimulation of growth found in any treatment: no
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Test solution at nominal 100 mg/L was slightly turbid.
Results with reference substance (positive control):
- Results with reference substance valid? yes
- EC50: 1.7 mg/L based on growth rate reduction (95% CL: 1.1 - 2.8 mg/L)

Cell growth was inhibited significantly (31.2%) at nominal 100 mg/L, while cell growth was not affected at nominal 10 mg/L. This significant effect is probably related to the turbid test solution which adsorbed a fraction of light needed for algal cell growth. Since both test concentrations are above water solubility it can be concluded that both the EC 50 and the NOEC exceed the maximum possible water solubility of the test substance.

Table 1: Percentage reduction of growth rate at different time intervals.

Concentration of test substance:

Cell growth inhibition (0-72 h):

Growth rate [cells/mL/h-1]

Area (mean)

Inhibition [%]

mean µ1

Reduction [%]

blank

894.41

--

0.05360

--

10 mg/L

855.12

4.4

0.05204

2.9

100 mg/L

615.50

31.2

0.05140

4.1

Description of key information

No effects up to the limit of water solubility (1.39 µg/L, 20 °C, S. capricornutum, OECD 201); read-across

Key value for chemical safety assessment

Additional information

There is no study available assessing the toxicity of the target substance Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) to aquatic algae. Therefore, read-across to the structurally related source substance 2-octyldodecyl isooctadecanoate (CAS 93803-87-3) was conducted in accordance with Regulation (EC) No 1907/2006, Annex XI, 1.5. The source substance is characterized by similar fatty acid chain lengths as well as alcohol components and is therefore considered suitable representative for the assessment of the toxicity of the target substance to aquatic algae. A detailed justification of the analogue approach is provided in IUCLID section 13.

The available study with the source substance was conducted according to OECD guideline 201 and GLP (Croda, 1998). In a static test design, Selenastrum capricornutum was exposed to Water Accommodated Fractions (WAF) with nominal loading rates of 10 and 100 mg/L test item for 72 h. A chemical analysis of the test substance concentrations in the test vessels was not possible since no applicable method could be established to detect test item concentrations due to the very low water solubility. After 72 h, an inhibition of cell growth (31.2%) was observed after 72 h in the WAF test solution of 100 mg/L, whereas no inhibition was observed in the WAF test solution of 10 mg/L. It was reported that this effect is probably related to insoluble particles which might have adsorbed fractions of light needed for algal cell growth. However, the growth rate was not inhibited resulting in an EL50 (72 h) of > 100 mg/L and a NOELR (72 h) of ≥ 100 mg/L. Based on this result it can be concluded that no toxicological effects on aquatic algae occurred up to the limit of water solubility of the source substance.

Based on the structural and chemical similarity of the target and source substance, the target substance is expected to exhibit a similar ecotoxicological profile. Therefore, it can be concluded that the target substance Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) does not cause toxic effects to aquatic algae up to the limit of water solubility.