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Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1992/09/29 to 1992/11/26
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study not performed under GLP; Deviations from the updated OECD-guideline (adopted 2006): No analysis of test material concentration in solution; surfactant used as vehicle; exposure above the water solubility of the substance
Qualifier:
according to guideline
Guideline:
other: Directive 87/302/EEC, Part C, page 89-94 Algal inhibition test
Deviations:
no
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 2.0 g test substance and 18 g water containing 0.4 % Tween 80 were mixed together using a marble mill for 24 hours. A portion of this blend (1 mL) was mixed and made up to 1000 mL with water. This stock solution contained 100 mg/L test substance and 3.6 mg/L vehicle. Calculated amounts of the stock solution to produce the desired test concentrations were added to the test water and were homogeneously distributed. The algae were then transferred into the flasks.
- Controls: Blank - water; vehicle - 3.6 mg/L Tween 80
- Chemical name of vehicle (dispersant): Tween 80
- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): 3.6 mg/L in stock solution and vehicle control
- Evidence of undissolved material (e.g. precipitate, surface film, etc): No evidence of precipitation or surface film.
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Common name: Green algae
- Source (laboratory, culture collection): Ciba-Geigt Ltd, testing facility
- Method of cultivation: according to guideline

ACCLIMATION
- Acclimation period: preculture period = 3 days
- Culturing media and conditions: same as test
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
24+/-1 deg C
pH:
7.9-9.5
Nominal and measured concentrations:
1.23, 3.7, 11, 33 or 100 mg/L (nominal)
Details on test conditions:
TEST SYSTEM
- Type: closed
- Material, size, headspace, fill volume: 100 mL Erlenmyer flask, 50 mL test solution per flask
- Aeration: no
- Initial cells density: 11000 cells/mL
- Control end cells density: Blank - 1084000 cells/mL; vehicle - 850000 cells/mL
- No. of organisms per vessel:
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- No. of vessels per vehicle control (replicates): 3

GROWTH MEDIUM
- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: composition according to guideline
- Culture medium different from test medium: no

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: continuous illumination
- Light intensity and quality: cold white fluorescent light, approx 8000 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: TOA cell counter at 24, 48 and 72 hours

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
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: no
19 % growth inhibition was observed at 100 mg/L (nominal). It is considered that the growth inhibition observed is likely to be a consequence of the physical effect of undissolved substance reducing the light intensity.

Description of key information

With high probability acutely not harmful to aquatic algae and cyanobacteria. No toxic effects in the range of water solubility. 

Key value for chemical safety assessment

Additional information

In a 72 hour acute toxicity study, the cultures of Scenedesmus subspicatus were exposed to the test item at nominal concentrations of 0, 1.23, 3.77, 11, 33 and 100 mg/L under static conditions in accordance with the EEC guideline 302/87 (1987). The EbC50 values after 72 hours of exposure based on cell number were > 100 mg/L and the NOEbC values after 72 hours of exposure based on cell number were 100 mg/L. 

This toxicity study is classified as acceptable and satisfies the guideline requirements for OECD 201 toxicity study.