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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:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Qualifier:
according to
Guideline:
EU Method C.3 (Algal Inhibition test)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Vehicle:
no
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
20.9 – 23.3 °C
pH:
7.3 - 8.5
Nominal and measured concentrations:
Nominal concentrations [mg/L]: 0, 1, 3.2, 10, 32, 100
At the beginning and at the end of the test, the content of the test item in the test solutions was determined using HPLC-UV. The measured concentrations lay between 95 % and 104 % of the nominal concentrations at the beginning of the test and between 97 % and 103 % of the nominal concentrations at the end of the test. Therefore, the biological results were based on the nominal concentrations
Details on test conditions:
For each treatment, 200 mL of the respective test item solution was mixed with the necessary amount of algal pre-culture (0.297 mL) to achieve a cell concentration of 2.4 *103 cells/mL. For the blank control, 350 mL nutrient medium was used instead of test item solution and mixed with the necessary amount of algal pre-culture (0.519 mL). In this mix-ture, the pH-value was measured.
The real cell concentration at the beginning of the test was measured with an electronic particle counter in the blank control solution. This measured value was used as start cell concentration for all replicates.
The test vessels were filled with 45 ± 1 mL of the respective test solution and incubated open (covered with perforated plastic foil acting as a stopper) for 72 hours, shaken on an orbital shaker to keep the algae in suspension. Before the start of incubation and every 24 hours, the cell number was determined with an electronic particle counter. After the test the pH value in treatments and blank control was measured again.
At the end of the test, the treatments were examined microscopically in order to assess the appearance of the algae and detect abnormalities (e.g. caused by the exposure to the test item).
The concentration of the test item in the test vessels was measured at the start and at the end of the test.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
cell number
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
79.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
cell number
Validity criteria fulfilled:
yes
Conclusions:
Based on the test results the NOEC, 72 h can be stated to be 10.00 mg/L and the EC50, 72 h can be stated to be > 100 mg/L, respectively.
Due to the results of the study, the test material does not meet the criteria for a classification as acute or chronic aquatic toxic.
Executive summary:

One valid experiment was performed.

The study was performed using 5 concentrations ranging from 1.0 to 100 mg/L (nominal). Incubation time (test system Desmodesmus subspicatus) was 72 hours. The cell concentration of each replicate was determined by measuring the cell numbers every 24 hours with an electronic particle counter. Growth rate µ and the yield were determined from the cell number at the respective observation times.

Significant inhibition of algal growth was observed at the following concentrations:

32 – 100 mg/L (nominal)

At the start and at the end of the test, the content of the test item in the test solutions was determined using HPLC.

The measured concentrations lay between 95 % and 104 % of the nominal concentrations at the beginning of the test and between 97 % and 103 % of the nominal concentrations at the end of the test. Therefore, the biological results were based on the nominal concentrations (see Guidance Doc. No. 23 §176).

Due to the low inhibition levels no EC50 could be determined for growth rate. Therefore, this value is given as a range. 

The 72h-EC50values of potassium dichromate (K2Cr2O7, CAS No. 7778-50-9) were determined in a separate reference test. The values lay within the range of the laboratory (growth rate 0.65 - 1.10 mg/L, yield 0.21 – 0.66 mg/L).

Description of key information

One study was performed according to OECD 201.

Based on the test results the NOEC, 72 h can be stated to be 10.00 mg/L and the EC50, 72 h can be stated to be > 100 mg/L, respectively.

Due to the results of the study, the test material does not meet the criteria for a classification as acute or chronic aquatic toxic.

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC50 for marine water algae:
100 mg/L
EC10 or NOEC for freshwater algae:
10 mg/L
EC10 or NOEC for marine water algae:
10 mg/L

Additional information