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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:
05 Dec 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Vehicle:
yes
Remarks:
water
Details on test solutions:
A stock preparation with a test item concentration of 100 mg/L was freshly prepared.
Out of the stock solution 5 concentration levels were tested in a geometrical series with a dilution factor of 1.25, 2.5, 5.0, 10.0 and 20.0 mg/L (nominal), corresponding to the geometric mean measured concentrations 1.07, 2.15, 4.88, 10.1 and 19.9 mg/L.The concentration levels are based on the results of a preliminary range finding test.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
Test organism: Pseudokirchneriella subcapitata HINDAK, SAG 61.81
Origin:
Sammlung von Algenkulturen (SAG), Pflanzenphysiologisches Institut der Universität Göttingen, Göttingen, Germany
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.0-23.5 °C
pH:
7.80 - 9.32
Nominal and measured concentrations:
nominal: 1.25, 2.50, 5.00, 10.00, 20.00 mg/L
geometric mean measured: 1.07, 2.15, 4.88, 10.1, 19.9 mg/L
Details on test conditions:
The study was performed as a static test in open vessels under culture conditions. The flasks contained 100 mL either reconstituted water or test medium (test item group).
The duration of exposure was 72 hours. The algal biomass in each flask was determined daily during the exposure period via Chlorophyll a-fluorescence. Microscopic evaluation of the cells at the start and at the end of the incubation period was carried out.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
9.32 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
3.06 mg/L
Nominal / measured:
nominal
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 revealed no morphological abnormalities. At the end rounded cells (no typical sickle shape) were found at concentration levels 19.9 - 4.88 mg/L.
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- EC50: 72-h EC50 = 0.559 mg/L based on growth rate

Table 1:NOEC, LOEC, ECx-values and 95%Confidence lntervals of the test item

(0-72 hours)

based on geometrie mean measured test item eoneentrations [mg/L]

 

 

Growth Rate Inhibition

Geometrie mean measured test item eoncentration [mg/L]

NOEC

1.07

LOEC

2.15

ErC10

3.06 (2.80 - 3.33)

ErC20

4.60 (4.34 -4.87)

ErC50

9.32 (8.97 - 9.70)

 

Yield Inhibition

Geometrie mean measured test item eoncentration rma/Ll

NOEC

1.07

LOEC

2.15

EyC10

1.30(<1.07 - 1.60)

EyC20

1.84 (1.57 - 2.16)

EyC50

3.34 (2.98 - 3.72)

Validity criteria fulfilled:
yes
Conclusions:
The 72 h EC50 for growth rate and yield were 9.32 and 3.34 mg/L. The EC10 value for inhibition of growth rate after 72 h was 3.06 mg/L.
Executive summary:

The toxicity of the test item to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined according to the principles of OECD 201 and Council Regulation (EC) No. 266/2016 C.3. The aim of the study was the determination of NOEC, LOEC, EC10, EC20- and EC50-values of growth rate and yield over a period of 72 hours.

The study was conducted under static conditions with an initial cell density of 6839 cells/ml. A stock solution with a nominal test item concentration of 100 mg/L was freshly prepared with dilution water one day prior to the start of exposure. The stock solution was stirred for 24 hours at room temperature, 1100 rpm. Undissolved particles were removed by membrane filtration (membrane filter 0.45 µm, RC, MACHEREY-NAGEL). The filter was saturated in order to avoid adsorption during the filtration. The first 25 mL of the filtrate were discarded. The filtration was interrupted for 10 minutes to allow adsorption and saturation of the filter material with dissolved test item.Thereafter, the filtration was continued. The next 25 ml were discarded. The following filtrate was used in the test. During filtration, the filter was always be kept covered.The solution was checked via laser beam (Tyndall effect) for undissolved test item, which was negative.

Out of the stock solution five concentration levels were tested in a geometrical series with a factor of 2: 1.25 - 2.50 - 5.00 - 10.0 - 20.0 mg/L, corresponding to the geometric mean measured test item concentrations 1.07 - 2.15 - 4.88 - 10.1 - 19.9 mg/L. 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 determined at the start of the exposure (0 hours) and at the end of the exposure (72 hours) of all tested solutions and the control via HPLC-DAD.

The measured concentrations of the test item were between 101% and 103% at the start of the exposure (0 hours) and between 72 and 102% at the end of the exposure (72 hours). Since the measured test item concentrations were not within the range of ± 20% of the nominal concentrations, the geometric mean measured concentrations were calculated.

All effect values given are based on the geometric mean measured test item concentrations of the test item.

The EC50-value with 95% confidence interval for inhibition of growth rate (ErC50) after 72 hours was 9.32 (8.97 - 9.70) mg/L. The EC10-value with 95% confidence interval for inhibition of growth rate (ErC10) after 72 hours was 3.06 (2.80 – 3.33) mg/L.

 

Description of key information

OECD 201: 72 -h ErC50 = 9.32 mg/L; 72 -h ErC10 = 3.06 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
9.32 mg/L
EC10 or NOEC for freshwater algae:
3.06 mg/L

Additional information

The toxicity of the test item to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined according to the principles of OECD 201 and Council Regulation (EC) No. 266/2016 C.3. The aim of the study was the determination of NOEC, LOEC, EC10, EC20- and EC50-values of growth rate and yield over a period of 72 hours.

The study was conducted under static conditions with an initial cell density of 6839 cells/ml. A stock solution with a nominal test item concentration of 100 mg/L was freshly prepared with dilution water one day prior to the start of exposure. The stock solution was stirred for 24 hours at room temperature, 1100 rpm. Undissolved particles were removed by membrane filtration (membrane filter 0.45 µm, RC, MACHEREY-NAGEL). The filter was saturated in order to avoid adsorption during the filtration. The first 25 mL of the filtrate were discarded. The filtration was interrupted for 10 minutes to allow adsorption and saturation of the filter material with dissolved test item.Thereafter, the filtration was continued. The next 25 ml were discarded. The following filtrate was used in the test. During filtration, the filter was always be kept covered.The solution was checked via laser beam (Tyndall effect) for undissolved test item, which was negative.

Out of the stock solution five concentration levels were tested in a geometrical series with a factor of 2: 1.25 - 2.50 - 5.00 - 10.0 - 20.0 mg/L, corresponding to the geometric mean measured test item concentrations 1.07 - 2.15 - 4.88 - 10.1 - 19.9 mg/L. 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 determined at the start of the exposure (0 hours) and at the end of the exposure (72 hours) of all tested solutions and the control via HPLC-DAD.

The measured concentrations of the test item were between 101% and 103% at the start of the exposure (0 hours) and between 72 and 102% at the end of the exposure (72 hours). Since the measured test item concentrations were not within the range of ± 20% of the nominal concentrations, the geometric mean measured concentrations were calculated.

All effect values given are based on the geometric mean measured test item concentrations of the test item.

The EC50-value with 95% confidence interval for inhibition of growth rate (ErC50) after 72 hours was 9.32 (8.97 - 9.70) mg/L. The EC10-value with 95% confidence interval for inhibition of growth rate (ErC10) after 72 hours was 3.06 (2.80 – 3.33) mg/L.