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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:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
not specified
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
not specified
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
Analytical verification of all test concentrations at 0 and 72 hours.
Concentration of the stock solution also determined
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Stock solution 0.1 g/L prepared in deionised water.
- Controls: Blank control
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): None used
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM

- Strain: Desmodesmus subspicatus (CHODAT (86.81 SAG))
- Source (laboratory, culture collection): University of Gottingen, Germany.
- Age of inoculum (at test initiation): A preculture was taken from a stock culture 3 days prior to the test. Test cultures were innoculated at 20,000 cells/mL from the preculture
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
Not stated
Test temperature:
23.4 - 23.5°C
pH:
pH 7.4 - 8.0 at start of test.
pH 7.9 - 9.6 at end of test
Nominal and measured concentrations:
Nominal 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, 1.2 and 2.4 mg/L
Measured concentrations at 0h: 0.03, 0.03, 0.06, 0.11, 0.22, 0.48, 0.9, 1.85 mg/L
Measured concentrations at 72h: <0.01 mg/L (calculated 0.01 mg/L), <0.01 mg/L (calculated 0.01 mg/L), <0.01 mg/L (calculated 0.02 mg/L), 0.06, 0.11, 0.25, 0.39, 0.45 mg/L
Geometrical mean measured concentrations: 0.019, 0.019, 0.037, 0.079, 0.158, 0.346, 0.593, 0.910 mg/L
It was not possible to calculate geometric mean measured concentrations for the three lowest test concentrations as measured concentrations after 72 h were <0.01 mg/L, therefore for these samples the 72 hour concentrations were calculated based on calculation of the mean value of % deviation from the 0 hour to 72 hour concentrations for the other test concentrations and using this to calculate the 72 concentrations for the other test concentrations.
Details on test conditions:
Culture vessels: Sterile, aerated Erlenmeyer flasks
Initial cell density: 20,000 cells/ml
Growth medium: As described in EU method C2 and OECD guideline 201
Number of replicates per concentration: 3
Photoperiod: constant light
Light intensity:6000 - 1000 lux, white
Determination of cell concentration: spectrophotometer.
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.88 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.12 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 0.91 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.:
0.26 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.:
0.037 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass
Reported statistics and error estimates:
Expected probits for each concentration calculated by probit transformation of the percentage inhibition rates over the regression line. NOEC determined on the basis of the area under the growth curve during the whole exposure time using the student t-test.
Validity criteria fulfilled:
yes
Remarks:
Control cell concentration increased by a factor of at least 16 within 3 days. Measured test concentrations after 72 h deviated by >20% therefore geometric mean measured concentrations used.
Conclusions:
The 72-hour EC50 and EC10 based on growth rate were >0.91 and 0.26 mg/L, respectively. The 72-hour EC50 and EC10 based on biomass were 0.88 and 0.12 mg/L, respectively. The 72-hour NOEC based on cell growth was 0.037 mg/L.
Executive summary:

Enste-Diefenbach (2003) is a GLP compliant algal toxicity study following OECD guideline 201. Analytical verification of test concentrations was conducted and as concentrations at 72 hours were outside 20% of nominal, mean measured concentrations were used for reporting of results. Three replicates were included for each test concentration and the validity criteria given in the study report were met. There are some limitations with the reporting of the study, therefore it is assigned a Klimisch score of 2 (reliable with restrictions) and is used for assessment of this endpoint.

The 72-hour EC50 and EC10 based on growth rate were >0.91 and 0.26 mg/L, respectively. The 72-hour EC50 and EC10 based on biomass were 0.88 and 0.12 mg/L, respectively. The 72-hour NOEC based on cell growth was 0.037 mg/L.

Description of key information

The 72-hour EC50 and EC10 based on growth rate were >0.91 and 0.26 mg/L, respectively. The 72-hour EC50 and EC10 based on biomass were 0.88 and 0.12 mg/L, respectively. The 72-hour NOEC based on cell growth was 0.037 mg/L. 

Key value for chemical safety assessment

Additional information

Enste-Diefenbach (2003) is a GLP compliant algal toxicity study following OECD guideline 201. Analytical verification of test concentrations was conducted and as concentrations at 72 hours were outside 20% of nominal, mean measured concentrations were used for reporting of results. Three replicates were included for each test concentration. The validity criteria given in the study report were met. There are some limitations with the reporting of the study, therefore it is assigned a Klimisch score of 2 (reliable with restrictions), however it is suitable for use for assessment of this endpoint.

The 72-hour EC50 and EC10 based on growth rate were >0.91 and 0.26 mg/L, respectively. The 72-hour EC50 and EC10 based on biomass were 0.88 and 0.12 mg/L, respectively. The 72-hour NOEC based on cell growth was 0.037 mg/L.