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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
not specified
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
- Sample storage conditions before analysis: Samples were diluted with isopropanol to a total volume of 50 mL. Aliquots were filtered and used for GC/MS-analysis
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: 22.21 mg test item were dissolved in 2 L of test medium and stirring for approximately 10 min at 20 ± 2 °C. The stock solution was prepared at 111% of the nominal concentration to compensate for the dilution by the later addition of algal inoculum
- Differential loading: yes
- Controls: Medium without test item
- Evidence of undissolved material (e.g. precipitate, surface film, etc): no, the stock as well as the test solutions were visibly clear
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Common name: unicellular green algae
- Strain: SAG 86.81
- Source (laboratory, culture collection): A stock algal culture is maintained continuously at the test facility. The culture was originally obtained from the Collection of algal cultures in the University of Göttingen, Germany
- Method of cultivation: An inoculum culture in exponential growth was prepared with an aliquot of the stock algal culture added to sterile test media to provide an initial cell density of 0.5 x 10E4 cells/mL. The inoculum culture is incubated under test conditions for 3 days prior to test initiation.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.7 - 22.9 °C
pH:
7.9 - 8.2
Nominal and measured concentrations:
Nominal: control, 0.1, 0.32, 1.0, 3.2, 10 mg/L
Geometrical mean measured: -, 0.06 (estimated), 0.194 (estimated), 0.546, 1.95, 6.62 mg/L
Initially measured: -, -, -, 0.8109, 3.15, 9.49 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL Erlenmeyer flasks
- Type (delete if not applicable): closed, plugged with gas permeable silicone sponge caps
- Material, size, headspace, fill volume: glass, test volume = 100 mL
- Initial cells density: 0.5 x 10E4 cells/mL
- Control end cells density:49.6 x 10E4 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

OTHER TEST CONDITIONS
- Photoperiod: permanent illumination
- Light intensity and quality: Artificial light, type universal white (OSRAM L 25). To minimize the potential effect of slight variations in illumination, the test vessels were rearranged daily. The light intensity was 5183 lux in average (± 15% variability) at a wave length of 400 - 700 nm

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Chlorophyll measurement: in vivo chlorophyll-a fluorescence (pulsed excitation with light flashes having a wavelength of 432 nm)

TEST CONCENTRATIONS
- Spacing factor for test concentrations: approximately 3.2
- Range finding study: yes
- Results used to determine the conditions for the definitive study: ErC50 = 3.02 mg/L
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.95 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.629 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.194 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.02 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: yield
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.295 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: yield
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.061 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: yield
Results with reference substance (positive control):
- Results with reference substance valid? yes
- EC50: 0.71 - 0.97 mg/L after 72 hour (growth rate)
Validity criteria fulfilled:
yes
Conclusions:
The test subtance is chronically toxic to aquatic algae.
Executive summary:

In this guidleine (OECD 201) study conducted with GLP certification, the 72 hour EC50 of the test material EC 231-272-0 to algae ( Desmodesmus subspicatus) was determined to be 1.95 mg/l. The test was conducted in freshwater, static, conditions. Test concentrations ranged from 0.1 to 10 mg/l (nominal). As the 72 hour EC50 is >1 mg/l and <10 mg/l, this result would normally trigger classification of the test material as hazardous to the aquatic environment according to CLP 1272/2008 Chronic Category 2. However, as the substance is readily biodegradable, the classification is not triggered.

Description of key information

Study conducted to recognised training guidelines with GLP certification

Key value for chemical safety assessment

EC50 for freshwater algae:
1.95 mg/L
EC10 or NOEC for freshwater algae:
0.194 mg/L

Additional information

The key study for the determination of the inhibition of algal growth was conducted according to OECD guideline 201 including analytical test item concentration verification (BASF SE, 2010). The ErC50 (72 h) was 1.95 mg/L based on the geometrical mean measured test item concentration. The ErC10 was determined to be 0.629 mg/L. Therefore, the test susbstance is acutely toxic to aquatic algae.

A supporting study was conducted (ABC Laboratories, Inc., 1993).

The algae toxicity test followed only standard procedures used in the testing laboratory, no official guideline is mentioned. However, as indicated by the test design, the test procedure may be considered similar to a OECD 201 test. Nevertheless, the test was conducted without analytical monitoring and the section-by-section specific growth rates are not given. The EC50 after 72 h based on cell counts was determined to be 0.64 mg/L. Due to the deficiencies the values are not used in the risk assessment.