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Ecotoxicological information

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
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)
Deviations:
yes
Remarks:
minor pH change in controls not considered to have affected study integrity
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
IDENTIFICATION AND QUANTIFICATION OF TEST SUBSTANCE/PRODUCT
- Separation method (e.g. HPLC, GC): HPLC
- Conditions (column, mobile phase, etc.): Eclipse plus C18, 1.8 µm, 4.6 mm i.d. x 50 mm. Eluant was ultra pure water and acetonitrile.
- Detection method (e.g. ECD, UV, MS, ICP-AES, ICP-MS): Photodiode array detector
- Detection limits (LOD, LOQ) (indicate method of determination/calculation): LOD 0.001 mg/L
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: A stock solution was initially prepared at 100 mg/L. This was stirred for 48 hours and then filtered. The resulting solution was then further diluted to provide the test substance concentrations.
- Controls: Dilution water
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): None observed in final test solutions.
Test organisms (species):
Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Unicellular green algae
- Strain: ATCC22662
- Source (laboratory, culture collection): America Type Culture Collection
- Age of inoculum (at test initiation): Original strain at lab over 10 years old. This is periodically tested to ensure the algae is not comtaminated. Algae was subcultured up to 4 days ahead of use in test conditions.
- Method of cultivation: Under the same conditions as that during the test. No modified or unusual cells were observed.

Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22 +/- 2°C (in culturing apparatus)
pH:
Beginning in test vessels: 7.8 to 7.9
End in test vessels: 8.1 to 10.4

The pH of the control vessels increased by more than 1.5 units over the course of the test which is outside the guideline requirements. Generally, the concentration of the bicarbonate ion decreases by carbon dioxide assimilation in algae. If there is little air exchange (supply of CO2) in a closed system the pH would increase. Since the algae grew exponentially in the control group, it was considered that the pH increase did not affect the integrity of the study.
Nominal and measured concentrations:
Nominal: 0.1, 0.32, 1.0, 3.2 and 10 mg/L
Measured (time weighted mean): 0.0222, 0.0697, 0.211, 0.604 and 1.45 mg/L.
Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.42 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence limits 0.409 to 0.432 mg/L
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.07 mg/L
Nominal / measured:
meas. (TWA)
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): None
- Unusual cell shape: None
- Colour differences: In the controls and the first three test concentrations, the test cultures appeared to be green. The colour in the highest two test concentrations was unchanged.
- Flocculation: none
- Adherence to test vessels: Not observed
- Aggregation of algal cells: None
- Any stimulation of growth found in any treatment: None
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: None observed
Results with reference substance (positive control):
- Results with reference substance valid? Results were within the range of historical laboratory data
- EC50: 0.793 mg/L
Reported statistics and error estimates:
The NOEC was determined by analysis of variance (ANOVA), Williams's test subsequent to Bartlett's test for homogeniety of variances.
The EC50 value and 95% confidence limits were determined by least squares regression analysis of the logarithm of test concentration against the growth inhibition (%) relative to the control.
Validity criteria fulfilled:
yes
Remarks:
The biomass of the controls increased exponentially (above 16 fold). The Coefficient of Variation parameters set in the OECD guideline were also not exceeded.
Conclusions:
An OECD guideline, GLP study assessing algal growth inhibition provided a 72 hour ErC50 value of 0.42 mg/L and a NOEC of 0.0697 mg/L.

Description of key information

A reliable OECD guideline and GLP study is available assessing algal growth inhibition of the substance. No data is available assessing the toxicity of the substance to marine algae.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.42 mg/L
EC10 or NOEC for freshwater algae:
0.07 mg/L

Additional information