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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:
Experimental dates: 14 to 17 August 2018
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:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: Control, 4.6, 10, 22, 46 and 100 mg/L (test substance as received)
- Sampling method: All samples were diluted with dilution water to within calibration range
- Sample storage conditions before analysis: No data
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Water-accommodated fraction (WAF). Nominal amounts of test item, corresponding to nominal 100 mg/L, was mixed with algal medium and shaken vigorously for 24 hours. After shaking the test solution was put in an ultrasonic bath for 30 mins, then centrifuged at 4500 rpm for 10 mins. The pH of the overlying phase was adjusted to pH 7.4. Lower test solutions were prepared by diluting the nominal 100 mg/L test solution with algal medium
- Eluate: Algal medium
- Differential loading: No
- Controls: Algal medium only
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): Not applicable
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Common name: Desmodesmus subspicatus
- Strain: 86.81
- Source (laboratory, culture collection): MBM Sciencebridge GmbH, maintained as laboratory culture since 2016
- Age of inoculum (at test initiation): 96h

ACCLIMATION
- Acclimation period: Not applicable
- Culturing media and conditions (same as test or not): Yes
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
No data
Test temperature:
21.6 - 23.7oC
pH:
7.3 - 9.6
Dissolved oxygen:
No data
Salinity:
No data
Conductivity:
No data
Nominal and measured concentrations:
Nominal test concentrations: 4.6, 10, 22 46 and 100 mg/L
Geometric mean measured concentrations (DEG-2ECL): 1.1, 3.3, 11.5, 31.0 and 71.1 mg/L
Goemetric mean measured concentrations (DEB-3ECL): 0.39, 0.90, 2.1, 6.2 and 13.2 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: glass flasks, total volume 65 mL
- Material, size, headspace, fill volume: Glass flasks, total volume 65 mL
- Aeration: No
- Initial cells density: 2.2 *10^3 cells/mL
- Control end cells density: 5.8 *10^5 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
- Sterile test conditions: No
- Adjustment of pH: No
- Photoperiod: Continuous light
- Light intensity and quality: 5000 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: Electronic particle counter
- Chlorophyll measurement: Not applicable
- Other: No

TEST CONCENTRATIONS
- Spacing factor for test concentrations:
- Justification for using less concentrations than requested by guideline: Not applicable
- Range finding study: Yes
- Test concentrations:
- Results used to determine the conditions for the definitive study:
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
33.14 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: Based on component DEG-2ECL
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
6.29 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: Based on component DEG-3ECL
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
3.21 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: Based on component DEG-2ECL
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.71 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: Based on component DEG-3ECL

Nominal concc (mg/L)

Mean cell numbers/mL

Growth rate

(0-72h)

% inhibition

Yield

(cells/conc/mL)

% inhibition

 

0h

24h

48h

72h

Control

2200

16873

85170

586823

1.86

-

584623

-

4.6

2200

11007

56193

456300

1.77

4.7

454100

22.3

10

2200

11920

43360

421313

1.75

6.0

419113

28.3

22

2200

9193

15160

121553

1.34

28.2

119353

79.6

46

2200

6907

12460

30560

0.87

53.2

28360

95.1

100

2200

6887

9993

18187

0.70

62.5

15987

97.3

Validity criteria fulfilled:
yes
Conclusions:
A 72-hour toxicity study with the green alga, Desmodesmus subspicatus, also known as Scenedesmus subspicatus, was conducted in accordance with the OECD test guideline 201 and in compliance with GLP. The test was performed at nominal concentrations of 4.6, 10, 22 46 and 100 mg/l water accommodated fraction (WAF) under static conditions. The test substance is UVCB and is unstable in the test medium. Two components (DEG-2ECL and DEG-3ECL) were measured analytically. Results are reported based on both analysed components.
Acute toxicity (EC50) values for growth rate inhibition are 33.14 mg/l and 6.29 mg/l based on geometric mean measured concentrations of two components.
Executive summary:

A 72-hour toxicity study with the green alga, Desmodesmus subspicatus, also known as Scenedesmus subspicatus, was conducted in accordance with the OECD test guideline 201 and in compliance with GLP. The test was performed at nominal concentrations of 4.6, 10, 22 46 and 100 mg/L water accommodated fraction (WAF), under static conditions. The test substance is UVCB and two components (DEG-2ECL and DEG-3ECL) were measured analytically. Results are reported based on both analysed components. Based on geometric mean measured concentrations of the two measured components (DEG-2ECL and DEG-3ECL) the 72-hour EC50 (growth rate) was determined to be 33.14 mg/l and 6.29 mg/l. Under the conditions of the test the EC50 for growth rate inhibition was 6.29 mg/l and is relied upon for PNEC development.

Inhibition of growth rate was low with the laboratory reporting <10% adverse effects on growth rate for the two measured components at the geometric mean measured concentration of 1.07 mg/l (4.6 mg/l nominal). Growth rate inhibition was not considered to biologically relevant because the inhibition was below 10%. The EC10 based on both measured components was determined to be 3.21 and 0.71 mg/l, although is not relied upon in the assessment due to low biological relevance of the growth response.

Description of key information

Acute toxicity (EC50) values for growth rate inhibition for the green alga Desmodesmus subspicatus, also known as Scenedesmus subspicatus, are 33.14 mg/l and 6.29 mg/l based on geometric mean measured concentrations of two components. The test substance is unstable in the test medium and reported as two components. The lower value of 6.29 mg/l is relied upon to be precautionary in PNEC development.

The laboratory reported <10% adverse effects on growth rate for the two components with calculated geometric mean 72-hour EC10 values of 3.21 mg/l and 0.71 mg/l (4.6 mg/l nominal concentration). Both values are not biologically relevant for adverse effects on algal growth with a mean inhibition of growth at 4.7%. A mean reduced growth rate of only 6% was seen at the next highest nominal concentration of 10 mg/l. Substance stability in the test medium is low and the algal EC10 results for the two components of the test substance are not considered to be adequate for classification. The substance is rapidly biodegradable (meets the 10-day window) and not considered to pose a long-term hazard to aquatic organisms.

Key value for chemical safety assessment

EC50 for freshwater algae:
6.29 mg/L
EC10 or NOEC for freshwater algae:
0.71 mg/L

Additional information

A reliable 72-hour toxicity study with the green alga, Desmodesmus subspicatus, also known as Scenedesmus subspicatus, was conducted in accordance with the OECD test guideline 201 and in compliance with GLP. The test was performed at nominal concentrations of 4.6, 10, 22 46 and 100 mg/L water-accommodated fraction (WAF), under static conditions. The test substance is UVCB and two components (DEG-2ECL and DEG-3ECL) were measured analytically. Results are reported based on both analysed components.