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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:
29-08-2015 to 15-12-2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study performed under GLP. All relevant validity criteria were met.
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
inspected June 2013; signature: November 2013
Analytical monitoring:
yes
Details on sampling:
- Concentrations: All relevant concentration levels and the control were analytically verified via GC-MS at the start (0 hours), 24 hours and at the end of the exposure (72 hours). Nominal: 0 (control), 0.50, 1.00, 2.00, 4.00, 8.00 mg/L with corresponding geometric mean measured concentrations: 0 (control), 0.341, 0.625, 1.32, 2.66, 5.42 mg/L.
- Sampling method: Analytical evaluation of the concentrations of the test item were carried out via GC-MS from freshly prepared media after 0 hours (with algae), 24 hours (with algae) and old test media after 72 hours (with algae) of exposure. Three replicates per concentration and six for the control (without test item) were prepared. Separate replicates for each measuring time were prepared. All samples for the test item analysis were taken from additionally prepared replicates with algae. The method was validated prior to this study according to SANCO 3029/99 rev.4 (2000).
- Sample storage conditions before analysis: All original samples were stored at 6 ± 2 °C if necessary. Prepared samples were stored in an autosampler at room temperature until analysis.
Vehicle:
no
Test organisms (species):
Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata
- Strain: HINDÁK, SAG 61.81
- Source (laboratory, culture collection): Sammlung von Algenkulturen (SAG), Pflanzenphysiologisches Institut der Universität Göttingen, Nikolausberger Weg 18, D-37073 Göttingen, Germany
- Method of cultivation: Fresh stocks are prepared every month on Z-Agar. Light intensity amounted to 35-70 µE·m-2·s-1 for 24 hours per day.

ACCLIMATION
- Acclimation period: No. However, a three days old preculture, prepared in dilution water, was used as inoculum.
- Culturing media and conditions (same as test or not): No. Culture Medium: Nutrient medium Z according to LÜTTGE et al. (1994) Botanica Acta, Journal of the German Botanical Society, No. 3 Volume 107 page 111-186 (June 1994), THIEME-VERLAG.
Dilution water: (mg/L) - NH4Cl 15 ; MgCl2.6 H2O: 12 ; CaCl2.2 H2O: 18 ; MgSO4.7H2O: 15 ; KH2PO4: 1.6 ; FeCl3.6H2O: 0.064 ; Na2EDTA.2H2O: 0.1 ; H3BO3: 0.185 ; MnCl2.4H2O: 0.415 ; ZnCl2: 3x10-3 ; Na2MoO4.2H2O: 7x10-3 ; CoCl2.6H2O: 1.5x10-3 ; CuCl2.2H2O: 1x10-5 ; NaHCO3: 50 ; NaHCO3* : 250 ; MES monohydrate*: 2665.6 ; pH 8.1 +/- 0.2. This medium has a nominal hardness of 0.24 mmol Ca+Mg/L.
* additional compounds were added to enable sufficient growth under conditions without headspace.
- Any deformed or abnormal cells observed: None reported.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Remarks on exposure duration:
In accordance with the OECD TG 201 guideline.
Hardness:
Ca+Mg: 0.24 mmol/L
Test temperature:
Nominal range: 21 - 24 °C, controlled at ± 2°C - measured room temperature values were min: 21.5 ; max 22.5 and mean 22.0 °C
pH:
0 hours: pH 8.01 ± 0.2 (and 8.07 in control); 72 hours: pH 8.57-9.07 (definitive test concentrations) and pH 9.17 (controls). pH did not vary more than 1.5 units.
Nominal and measured concentrations:
Preliminary test: 0 (control), 0.12, 1.2, and 12 mg/L as a nominal test item concentration (non-GLP range finding test)
Final test: Nominal: 0 (control), 0.50, 1.00, 2.00, 4.00, 8.00 mg/L
with corresponding geometric mean measured concentrations: 0 (control), 0.341, 0.625, 1.32, 2.66, 5.42 mg/L.
See table 3 for nominal and measured concentrations at initial exposure and during the course of the test.
Details on test conditions:
TEST SYSTEM
- Test vessel: Glass.
- Type: Closed - Static. Sterile headspace flasks
- Material, size, headspace, fill volume: , volume: 119 mL, with aluminium tops with PFTE seals. Minimum headspace.
- Aeration: Vessel shaken continuously. Test containers were placed on a rotary shaker and oscillated at approximately 70 rpm.
- Initial cells density: nominal: 5 x 10^3 - 10^4 and current: 6153 cells/ml
- Control end cells density: Mean (of replicates after 72 hours) 502809 cells/ml (or ca. x81 increase in cell density)
- No. of vessels per concentration (replicates): 3 replicates of each test concentration; 1 extra replicate of each test group for sampling purposes
- No. of vessels per control (replicates): 6 replicates of the control
- No. of vessels per vehicle control (replicates): Not applicable.

GROWTH MEDIUM
- Standard medium used: Yes. adjusted-Medium M2.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Prepared according to guidelines (see 'Details on test organisms' field for more details on composition).
- Culture medium different from test medium: Yes. (see 'Details on test organisms' field)
- Intervals of water quality measurement: Start and end of the test period.

OTHER TEST CONDITIONS
- Sterile test conditions: No.
- Adjustment of pH: No.
- Photoperiod: 24 hours ; continuous
- Light intensity and quality: 60 - 120 µE/m2/s ; within ± 15 % over incubation area
- Salinity (for marine algae): Not applicable.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: The cell density was measured daily via Chlorophyll a-fluorescence, excitation at 436 nm, emission at 685 nm. Dilution water was used as background signal. No self-fluorescence was found at the concentration level of 12.00 mg/L in the range finding test.
- Other: Initial cell density: Microscopic evaluation of the cells was carried out at the start and end of the exposure. The cells were checked for any unusual cell shapes, colour differences, differences in chloroplast morphology, flocculation and adherence of algae to test containers or aggregation of algae cells.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2.0. In definitive test justified from the results of the range finding study.
- Justification for using less concentrations than requested by guideline: Not applicable.
- Range finding study: Yes. 0 (control), 0.12, 1.2, and 12 mg/L as a nominal test item concentration (non-GLP range finding test)
- Test concentrations: Three replicates per concentration were exposed to dilutions representing 0.12, 1.2, 12 mg/L based on nominal test item concentration in a preliminary test.
- Results used to determine the conditions for the definitive study: Yes.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.51 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% C.I.: 1.34 - 2.19 mg/L
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.11 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: yield
Remarks on result:
other: 95% C.I.: 0.929 - 1.38 mg/L
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
1.26 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% C.I.: 0.923 - 1.32 mg/L
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.434 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: yield
Remarks on result:
other: 95% C.I.: <0.341 - 0.566 mg/L
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.341 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): Yes.
- Observation of abnormalities (for algal test): Microscopic evaluation of the cells at the start of the incubation period and at test end revealed no morphological abnormalities in the test item concentration or control.
- Unusual cell shape: No.
- Colour differences: None.
- Flocculation: Not reported.
- Adherence to test vessels:
- Aggregation of algal cells: No.
- Other:
- Any stimulation of growth found in any treatment: Yes. At low concentrations 0.341 mg/L geometric mean measured concentration a growth rate and yield inhibition negative at 72h was observed. This was low dose stimulation and was limited and was taken into account in the data analysis and effect level calculations.
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Not applicable. The measured concentrations of the test item at the start of exposure were in the range of 63- 77% and after 24 and 48 hours in the range of 65 - 70% of the nominal values. At the end of exposure (72 h) the measured concentrations were in the range of 63 - 72% of the nominal values of all concentrations. Therefore, the geometric mean concentrations was used for calculations.
- Effect concentrations exceeding solubility of substance in test medium: No.
Results with reference substance (positive control):
- Results with reference substance valid?: Yes.
- EC50: The EC50 for growth rate reduction (ERC50: 0-72h) was 0.774 mg/L with a 95% confidence interval ranging from 0.711 to 1.088 mg/L without headspace. The EC50 for yield inhibition (EYC50: 0-72h) was 0.502 mg/L with a 95% confidence interval ranging from 0.4.00 to 0.583 mg/L without headspace.
The results with headspace and without headspace were within the test facility SOPs (historic values).
- Other: The sensitivity of the test system was in agreement with the historical data..
Reported statistics and error estimates:
EC10-, EC20- and EC50-values with confidence intervals of growth rate and yield inhibition after 72 hours were calculated by sigmoidal dose-response regression. The NOEC/LOEC were determined by calculation of statistically significant differences of growth rate and yield inhibition. Using Williams Sequential t-test Procedure. A Shapiro-Wilk's Normality test and a Levene's Equal Variance test were done first. P-values for both Normality and Equal Variance tests are 0.05. The alpha-value (acceptable probability of incorrectly concluding that there is a difference) is alpha = 0.01.

Table 1. Results of the Preliminary Range Finding Test (non GLP, 0 - 72 hours)

Nominal test item concentration [mg/L]

Growth Rate Inhibition [%]

Yield Inhibition [%]

12.0

100

100

1.20

10

36

0.12

0

-2

Negative values = growth stimulation

 

Table 2. Percentage reduction in growth rate and inhibition of yield in the definitive test

Statistically significant differences of growth rates and yield compared to control values are marked (+), not significant differences are marked (-)

Geometric mean measured test item concentration

Replicate

 

Growth Rate

Inhibition of Growth Rate

 

Yield

Inhibition of Yield

[mg/L]

 

 

[d-1]

[%]

 

[Cells/mL]

[%]

5.42

1

 

< LOQ

100

 

< LOQ

100

 

2

 

< LOQ

100

 

< LOQ

100

 

3

 

< LOQ

100

 

< LOQ

100

 

Mean

(+)

N.A.

100

(+)

N.A.

100

2.66

1

 

< LOQ

100

 

< LOQ

100

 

2

 

< LOQ

100

 

< LOQ

100

 

3

 

< LOQ

100

 

< LOQ

100

 

Mean

(+)

N.A.

100

(+)

N.A.

100

1.32

1

 

1.38

15

 

384800

53

 

2

 

1.42

13

 

435415

46

 

3

 

1.32

19

 

313111

53

 

Mean

(+)

1.05

29

(+)

136778

72

0.625

1

 

1.51

7

 

562611

31

 

2

 

1.52

7

 

583434

28

 

3

 

1.50

8

 

540220

33

 

Mean

(+)

1.51

7

(+)

562088

31

0.341

1

 

1.61

1

 

774667

4

 

2

 

1.66

-2

 

887751

-10

 

3

 

1.63

0

 

801825

1

 

Mean

(-)

1.63

0

(-)

821414

-1

Control

1

 

1.62

 

 

788591

 

 

2

 

1.61

 

 

766576

 

 

3

 

1.65

 

 

860845

 

 

4

 

1.62

 

 

791727

 

 

5

 

1.63

 

 

813240

 

 

6

 

1.64

 

 

842154

 

 

Mean

 

1.63

 

 

810522

 

 

Table 3. Measured Concentrations and Percentage of the nominal Concentration of the Test Item

Nominal test item concentration

[mg/L]

Measured concentration

[mg/L]

%

Measured concentration

[mg/L]

%

Measured concentration

[mg/L]

%

8.00

6.12

77

5.46

68

5.43

68

4.00

2.88

72

2.65

66

2.74

69

2.00

1.42

71

1.31

66

1.28

64

1.00

0.632

63

0.647

65

0.634

63

0.50

0.360

72

0.352

70

0.359

72

Control

< LOQ

< LOQ

< LOQ

< LOQ

< LOQ

< LOQ

Meas. Conc = Measured concentration of the test item (dilution factor taken into account)

% = Percent of the initial measured concentration of the test item

LOQ = Limit of Quantification of the analytical method (0.005 mg/L test item)

Validity criteria fulfilled:
yes
Conclusions:
The test substance 72h-EC50 (growth rate reduction) was 1.51 (C.I. 1.34 – 2.19) mg/L. The corresponding EC10 was 1.26 (C.I. 0.923 – 1.32) mg/L and the NOEC was 0.341 mg/L.
Executive summary:

The algal growth inhibition to Pseudokirchneriella subcapitata, was carried out according to OECD TG 201 Freshwater Alga and Cyanobacteria, Growth Inhibition Test and EU Method C.3 guidelines under GLP. The aim of the study was to assess the effects on growth rate and yield over a period of 72 hours. The study was conducted under static conditions with an initial cell density of 6153 cells/mL. With regard to the volatility of the test item, glass flasks without headspace were used to reduce losses of the test item. Five test item solutions with a dilution factor of 2 (nominal) and concentrations of 0.50, 1.00, 2.00, 4.00 and 8.00 mg/L were freshly prepared with dilution water at 30°C and stirred for 24 hours with 1100 rpm at room temperature. Thereafter the stock solution was stirred for a further 24 hours at 1100 rpm. Prior to the start of the the test item solutions were clear (negative Tyndall effect) and tested without further dilution. Three replicates were tested for each test item concentration and six replicates for the control. The environmental conditions were within the acceptable limits. The concentrations of the test item were analytically verified via GC-MS at test start (0 hours), after 24 hours and 48 hours and at the end (72 hours) of the exposure. The recovery rates of the test item at the start were in the range of 63 - 77%. After 24 hours and 48 hours, the recovery ranges were 65 - 70% and 59 – 64% respectively. At the end of the exposure test item concentrations were in the range of 63 - 72 % of the nominal test item concentrations. On this basis the effect levels were based on geometric mean measured concentrations which were: 0 (control), 0.341, 0.625, 1.32, 2.66, 5.42 mg/L. The validity criteria of the test guideline were fulfilled. The EC50 for growth rate reduction (72h-ErC50) was 1.51 (C.I. 1.34 – 2.19) mg/L. The corresponding EC10 was 1.26 (C.I. 0.923 – 1.32) mg/L and the NOEC was 0.341 mg/L.

Description of key information

ErC50 (algae; growth rate) = 1.51 (C.I. 1.34 - 2.19) mg/L based on geometric mean measured concentrations, 72hour-freshwater, OECD TG 201, 2015

ErC10 (algae; growth rate) = 1.26 (C.I. 0.923 – 1.32 ) mg/L based on geometric mean measured concentrations, 72hour-freshwater, OECD TG 201, 2015

NOEC (algae; growth rate) = 0.341 mg/L based on geometric mean measured concentrations, 72hour-freshwater, OECD TG 201, 2015

Key value for chemical safety assessment

EC50 for freshwater algae:
1.51 mg/L
EC10 or NOEC for freshwater algae:
0.341 mg/L

Additional information

Key Study : OECD TG 201, 2015 : The algal growth inhibition to Pseudokirchneriella subcapitata, was carried out according to OECD TG 201 Freshwater Alga and Cyanobacteria, Growth Inhibition Test and EU Method C.3 guidelines under GLP. The aim of the study was to assess the effects on growth rate and yield over a period of 72 hours. The study was conducted under static conditions with an initial cell density of 6153 cells/mL. With regard to the volatility of the test item, glass flasks without headspace were used to reduce losses of the test item. Five test item solutions with a dilution factor of 2 (nominal) and concentrations of 0.50, 1.00, 2.00, 4.00 and 8.00 mg/L were freshly prepared with dilution water at 30°C and stirred for 24 hours with 1100 rpm at room temperature. Thereafter the stock solution was stirred for a further 24 hours at 1100 rpm. Prior to the start of the the test item solutions were clear (negative Tyndall effect) and tested without further dilution. Three replicates were tested for each test item concentration and six replicates for the control. The environmental conditions were within the acceptable limits. The concentrations of the test item were analytically verified via GC-MS at test start (0 hours), after 24 hours and 48 hours and at the end (72 hours) of the exposure. The recovery rates of the test item at the start were in the range of 63 - 77%. After 24 hours and 48 hours, the recovery ranges were 65 - 70% and 59 – 64% respectively. At the end of the exposure test item concentrations were in the range of 63 - 72 % of the nominal test item concentrations. On this basis the effect levels were based on geometric mean measured concentrations which were: 0 (control), 0.341, 0.625, 1.32, 2.66, 5.42 mg/L. The validity criteria of the test guideline were fulfilled. The EC50 for growth rate reduction (72h-ErC50) was 1.51 (C.I. 1.34 – 2.19) mg/L. The corresponding EC10 was 1.26 (C.I. 0.923 – 1.32) mg/L and the NOEC was 0.341 mg/L.