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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
28 April - 21 May 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to the OECD 201 Guideline and complied with the principles of GLP.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2015
Report Date:
2015

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Version / remarks:
(2006, Annex 5 corrected 28 July 2011)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
no
Qualifier:
according to
Guideline:
ISO 8692 (Water Quality - Fresh Water Algal Growth Inhibition Test with Scenedesmus subspicatus and Selenastrum capricornutum)
Deviations:
no
Qualifier:
according to
Guideline:
other: Guidance document on aquatic toxicity testing of difficult substances and mixtures, OECD series on testing and assessment number 23, December 14, 2000
Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Remarks:
migrated information: powder
Details on test material:
- Name of test material (as cited in study report): Strontium tartrate (anhydrous)
- Appearance: Off-white powder

Sampling and analysis

Analytical monitoring:
yes
Details on sampling:
Samples of 4.8 mL for possible analysis were taken from all test concentrations and the control at t=0 h and t=72 h and stored in a freezer until analysis.
At the end of the exposure period, the replicates with algae were pooled at each concentration before sampling.
On the day of analysis, the test samples were defrosted at room temperature. The samples were diluted in a 25:1 (v:v) ratio with HNO3 and analysed. If necessary, the samples were further diluted with 4% HNO3 in M2-medium to obtain concentrations within the calibration range.

Test solutions

Vehicle:
no
Details on test solutions:
Preparation of test solutions started with the highest test concentration of 100 mg/L. Half an hour of magnetic stirring resulted in a clear and colourless solution that was used as highest test group and used to prepare the lower test groups by subsequent dilution in test medium. All final test solutions were clear and colourless.
After preparation, volumes of 50 mL were added to each replicate of the respective test concentration. Subsequently, 1 mL of an algal suspension was added to each replicate providing a cell density of 10^4 cells/mL.

Test organisms

Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: NIVA CHL 1
- Source (laboratory, culture collection): In-house laboratory culture.
- Age of inoculum (at test initiation):
- Method of cultivation: Algae stock cultures were started by inoculating growth medium with algal cells from a pure culture on agar. The suspensions were continuously aerated and exposed to light in a climate room at a temperature of 21-24°C. 3 days before the start of the test, cells from the algal stock culture were inoculated in culture medium at a cell density of 1 x 10^4 cells/mL. The pre-culture was maintained under the same conditions as used in the test. The cell density was measured immediately before use.

ACCLIMATION
- Culturing media and conditions (same as test or not): Pre-culture medium is same as test (M2)

Study design

Test type:
static
Water media type:
freshwater
Total exposure duration:
72 h
Post exposure observation period:
None

Test conditions

Hardness:
24 mg CaCO3/L
Test temperature:
21-23 ºC
pH:
8.2-8.5
Dissolved oxygen:
Not measured
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 1.0, 3.2, 10, 32 and 100 mg/L
Analyses of the samples taken during the final test showed that measured concentrations were stable and in agreement with nominal during the 72-hour test period (94-108% relative to nominal).

Details on test conditions:
TEST SYSTEM
- Test vessel: 100 mL, all-glass, containing 50 mL of test solution
- Aeration: no
- Initial cells density: 1x 10^4 cells/mL
- Control end cells density: 139x 10^4 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes (M2)

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuously
- Light intensity and quality: TLD-lamps with a light intensity within the range of 78 to 81 µE.m-2.s-1.

EFFECT PARAMETERS MEASURED :
- Algal density at t = 0 , 24, 48 and 72h. At the beginning of the test, cells were counted using a microscope and a counting chamber. Thereafter cell densities were determined by spectrophotometric measurement of samples at 720 nm using a spectrophotometer with immersion probe (pathlength =20 mm). Algal medium was used as blank.

TEST CONCENTRATIONS
- combined limit/range-finding test: nominal concentrations 0.1, 1.0, 10 and 100 mg/L (analytically confirmed, except for 0.1 mg/L which was not analysed).
- Definitive test: nominal concentrations: 1.0, 3.2, 10, 32 and 100 mg/L (analytically confirmed)
Reference substance (positive control):
yes
Remarks:
potassium dichromate

Results and discussion

Effect concentrationsopen allclose all
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: The nominal concentrations were analytically confirmed (recovery > 80%)
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: The nominal concentrations were analytically confirmed (recovery > 80%)
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: The nominal concentrations were analytically confirmed (recovery > 80%)
Details on results:
Growth rates were in the range of the controls at the concentrations of 1.0 to 10 mg/L during the 72-hour test period, whereas the growth rate of algae exposed to 32 and 100 mg/L were slightly reduced.
Statistically significant inhibition of growth rate was found at concentrations of 32 mg/L and higher. It should however be considered that the effects of 3.1 and 6.6% can be considered as not biologically relevant as they were below 10%. Therefore, the NOEC was determined to be 100 mg/L.

Microscopic observations at the end of the test revealed a normal and healthy appearance of the exposed cells when compared to the control.

Acceptability of the test:
- In the controls, cell density increased by an average factor of >16 during the 72h testing period (i.e. 139).
- The mean coefficient of variation for section-by-section specific growth rates in the control cultures did not exceed 35% (i.e. 13%).
- The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures did not exceed 7% (i.e. 2.2%).
Results with reference substance (positive control):
The EC50 for growth rate inhibition (72h-ERC50) was 1.3 mg/L with a 95% confidence interval ranging from 1.1 to 1.5 mg/L. The historical ranges for growth rate inhibition lie between 0.82 and 2.3 mg/L. Hence, the 72h-ERC50 for the algal culture tested corresponds with this range.

Any other information on results incl. tables

Table 1     Percentage inhibition of growth rate (total test period) during the final test

Strontium tartrate (anhydrous) concentration (mg/l)

Mean

Std. Dev.

n

%Inhibition

Control

1.643

0.0365

6

0.0

1.0

1.647

0.0355

3

-0.3

3.2

1.638

0.0326

3

0.3

10

1.674

0.0280

3

-1.9

32

1.591

0.0376

3

3.1*#

100

1.533

0.0067

3

6.6*#

* - effect was statistically significant

#- effect not biologically relevant

 

Table 2     Percentage inhibition of growth rate at different time intervals during the final test

Test substance1concentration (mg/l)

n

0 – 24 h

24 – 48 h

48 – 72h

Mean

%Inhibition

Mean

%Inhibition

Mean

%Inhibition

Control

6

1.865

0.0

1.616

0.0

1.447

0.0

1.0

3

1.746

6.4

1.743

-7.9

1.452

-0.4

3.2

3

1.830

1.9

1.608

0.4

1.475

-1.9

10

3

2.026

-8.6

1.491

7.7

1.504

-4.0

32

3

1.788

4.1

1.547

4.3

1.438

0.6

100

3

1.802

3.4

1.444

10.6

1.354

6.4

1.Strontium tartrate (anhydrous)

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the present study with Pseudokirchneriella subcapitata, 72h-ErC50 was >100 mg/L, the 72h-ErC10 was >100 mg/L and the NOErC was 100 mg/L.
Executive summary:

A 72-h algae growth inhibition test was performed with the substance according to OECD 201 and in compliance with GLP principles. Nominal concentrations of 1.0, 3.2, 10, 32 and 100 mg/L were tested. Analyses of the samples taken during the final test showed that measured concentrations were stable and in agreement with nominal during the 72-hour test period (94-108% relative to nominal).

Growth rates were in the range of the controls at the concentrations of 1.0 to 10 mg/L during the 72-hour test period, whereas the growth rate of algae exposed to 32 and 100 mg/L were slightly reduced.

Statistically significant inhibition of growth rate was found at concentrations of 32 mg/L and higher. It should however be considered that the effects of 3.1 and 6.6% can be considered as not biologically relevant as they were below 10%. Therefore, the NOEC was determined to be 100 mg/L.

The 72h-ErC50 was >100 mg/L and the 72h-ErC10 was >100 mg/L.