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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
Study period:
13 April 2020 - 01 January 2021
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Version / remarks:
2011
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures, OECD Series on Testing and Assessment no. 23
Version / remarks:
2019
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0.0 (control) and 100.0 (nominal) mg/L.
- Sampling method: samples of 10 mL were collected from all test concentrations in duplicates at 0 and 72 hours. Samples of 15 mL were collected from further replicates at 0, 24 and 72 hours.
- Sample storage conditions before analysis: all samples were analysed on the same day of collection from the respective test vessels.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Stock solution was prepared by weighing required quantity of test item in a beaker; to this, a small volume of OECD alga medium was added and stirred well using a glass rod; after complete solubility of test item, test formulation was transferred to measuring cylinder, beaker was rinsed with OECD alga medium and transferred again to measuring cylinder. Rinsing process was repeated until the complete transfer of test contents.
The required test concentrations were prepared by adding appropriate amount of stock solutions and made up to required volume using OECD alga medium. A homogeneous distribution of the test item within the stock solution was achieved by stirring using magnetic stirrer shortly before preparation of the test vessels, no filtration or other separation methods were used (measurements account for both the soluble and non-soluble fractions).
- Evidence of undissolved material: at 24, 48, and 72 hours, fine particles were observed at the bottom of conical flask at the test concentration of 100.0 mg/L.
Test organisms (species):
Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: green algae
- Strain: ATCC 22662
- Source (laboratory, culture collection): American Type Culture Collection

ACCLIMATION
- Acclimation period: 3 days (pre-culture)
- Culturing media and conditions (same as test or not): Inoculum was pre-cultured (in two flasks containing 100 mL of culture medium) during 3 days prior to each test. The algal cell density of pre-cultures was 44325 and 42825 cells/mL at the start of the dose range-finding and main tests, respectively. The biomass increased by a factor of 8.4 (day 2) and 21.7 (day 3) for the dose range-finding and by a factor of 8.6 (day 2) and 21.6 (day 3) for the main test.
- Any deformed or abnormal cells observed: no.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Test temperature:
22.3 to 22.8°C
pH:
8.05 to 8.32 (0 h) and 8.01 to 8.24 (72 h)
Nominal and measured concentrations:
Nominal concentrations: 0 (control), 100 mg/L.
Measured concentrations: Since measured values by ICP-MS were within ± 20 % of the initial values, nominal concentrations are reported. However, at tested concentration of 100 mg/L, the limit of saturation was found to be, 9.13 to 11.80 mg test item/L in filtered sample and 10.17 to 13.44 mg test item/L in the centrifuged sample, respectively.
Details on test conditions:
TEST SYSTEM
- Test vessel: sterilised Erlenmeyer flasks with air permeable stoppers
- Material, size, headspace, fill volume: glass, 250 mL capacity, the minimum volume of the test solution at the initiation of the test in the test vessel was 100 mL and in order to shorten the light path the test volume was made to 25 mL in each flask.
- Initial cells density: 5544 cells/mL (average)
- Control end cells density: 894208.3 cells/mL (average)
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

GROWTH MEDIUM / WATER PARAMETERS
- Standard medium used: yes (OECD medium as per TG 201)
- Source/preparation of dilution water: sterilized deionized water
- Culture medium different from test medium: no

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Photoperiod: constant illumination
- Light intensity and quality: 8331 to 8974 Lux, white fluorescent lamps (irradiation was above 120 µE/m2sec as recommended per OECD GD 23 for coloured substances).

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: counting chamber; samples collected were loaded on a haemocytometer and the cells were counted manually using microscope.Cell density is obtained by calculating the average cell count [average cell counts calculated by summating the number of cells in all the four large corner squares (squares 1 to 4) and dividing the sum by 4] and multiplied with chamber conversion factor (CCF).
Cell Density (cells/mL) = Average cell count × 10000 (CCF) × Dilution factor
- Chlorophyll measurement: no

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 0 (control), 0.01, 0.1, 1.0, 10.0, 50.0 and 100.0 mg/L
- Results used to determine the conditions for the definitive study: Under test conditions, average inhibition growth rates were 0.05, 1.36, 3.39, 3.69, 4.70 and 8.34, respectively. No toxic effects were observed up to the highest concentration tested. Therefore a limit test was performed.
Reference substance (positive control):
yes
Remarks:
(3,5-dichlorophenol 97%)
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
9.13 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: No effects were observed up to the limit of saturation of the test item in test media.
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 9.13 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: No effects were observed up to the limit of saturation of the test item in test media.
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): no.
- Any stimulation of growth found in any treatment: no
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: during the main test, fine particles were observed at the bottom of the flasks after 24, 48 and 72h. On analytical verification at tested concentration of 100 mg/L, the limit of saturation was found to be, 9.13 to 11.80 mg test item/L in filtered sample and 10.17 to 13.44 mg test item/L in the centrifuged sample, respectively.
- Effect concentrations exceeding solubility of substance in test medium: yes.
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- ErC50 (0-72h) = 1.07 mg/L (0.91 – 1.27)
Reported statistics and error estimates:
The 72 hours EC10, EC20 and EC50 values were not calculated for growth rate and yield as it was a limit test.

Table 1. Mean cell density after exposure during main study (limit test).
































































































Group



Test Conc.
 (mg/L)



Replicate



Mean Cell Density (104Cells/mL)



Observation Periods



24 hour



48 hour



72 hour



G1



0.0



1



4.40



25.30



86.63



2



4.40



28.88



86.90



3



4.95



23.38



91.03



4



4.68



22.55



90.20



5



4.13



26.13



91.30



6



4.40



25.03



90.48



G2



100.0



1



4.40



23.10



82.50



2



4.68



24.20



81.95



3



4.13



24.75



83.60



4



4.95



25.85



84.15



5



4.40



25.30



87.45



6



4.40



25.03



84.43



Table 2: Average specific growth rate during main study (limit test).


























































































































































Group



Test Conc.
(mg/L)



Replicate



Growth Rate



Mean Growth
Rate



Observation Intervals (Days)



0 to 1



1 to 2



2 to 3



0 to 3



G1



0.0



1



2.07



1.75



1.23



1.68



1.69



2



2.07



1.88



1.10



1.68



3



2.19



1.55



1.36



1.70



4



2.13



1.57



1.39



1.70



5



2.01



1.85



1.25



1.70



6



2.07



1.74



1.29



1.70



Mean



2.09



1.72



1.27



1.69



±SD



0.06



0.14



0.10



0.01



CV (%)



2.99



7.90



8.03



0.46



G2



100.0



1



2.07



1.66



1.27



1.67



1.68



2



2.13



1.64



1.22



1.67



3



2.01



1.79



1.22



1.67



4



2.19



1.65



1.18



1.67



5



2.07



1.75



1.24



1.69



6



2.07



1.74



1.22



1.68



Mean



2.11



1.71



1.21



1.68



±SD



0.07



0.05



0.03



0.01



CV (%)



3.22



3.08



2.49



0.42



±SD: Standard deviation; CV: Coefficient of Variation.


Table 3. Yield of alga during main study (limit test).





















































































































Group



Test Conc.
(mg/L)



Replicate



Cell density (Cells/mL)



Yield
(72 hours)



0 hour



72 hour



G1



0.0



1



5544



866250.00



860706.00



2



5544



869000.00



863456.00



3



5544



910250.00



904706.00



4



5544



902000.00



896456.00



5



5544



913000.00



907456.00



6



5544



904750.00



899206.00


 

Mean



894208.33



888664.33


 

±SD



20973.45



20973.45



G2



100.0



1



5544



825000.00



819456.00



2



5544



819500.00



813956.00



3



5544



836000.00



830456.00



4



5544



841500.00



835956.00



5



5544



874500.00



868956.00



6



5544



844250.00



838706.00


 

Mean



840125.00



834581.00


 

±SD



19347.97



19347.97



±SD: Standard deviation.


Table 4. Percent inhibition in yield, cell density and growth rate during main study (limit test)



























Group



Test Conc. (mg/L)



% inhibition in Yield



% inhibition in Cell Density



% inhibition in Growth Rate



G1



0



-



-



-



G2



100.0



6.09



6.05



0.91



 


Table 5. Acceptance criteria for control during main study (limit test).

















































Daily average growth rate



±SD



% CV out of the daily growth rates



1.68



0.42



25.19



1.68



0.51



30.50



1.70



0.43



25.54



1.70



0.39



22.86



1.70



0.40



23.39



1.70



0.39



23.24



Mean % of CV 0 – 72 hours



25.12



Mean % CV of specific growth rate 0-72 hours



0.46



The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures was 0.46 during limit test (validity criterion: should not exceed 7%).


 


Table 6. Biomass increase during the whole test period



































































Initial biomass (cells/mL)



 Cell density on day 3 (cells/mL)



Biomass increase Factor


   

5544



156.25


 

5544



869000



156.75


   

5544



910250



164.19


   

5544



902000



162.70


   

5544



913000



164.68


   

5544



904750



163.19


   

Mean



894208.33



161.29


   

±SD: Standard deviation.


Table 7. Summary of test concentration analysis during the 72-hour alga growth inhibition test






































Group



0 hour Fresh Solution



72 hour Spent Solution



 



Nominal Concentration


(mg/L)



 Conc. Obtained                        


(mg/L)



(%)


Recovery



Nominal Concentration


(mg/L)



 Conc. Obtained                        


 (mg/L)



(%)


Recovery



G1



0.0



-



-



0.0



-



-



G2



100.0



109.96



109.96



100.0



117.38



117.38



Table 8. Temperature and light intensity during pre-culture and exposure - main study

























































































































Day



Temperature of the surrogate


(°C)



Light intensity (Lux)



Revolutions per minute (rpm)



1



2



3



4



 



During Acclimatization (pre-culture and exposure period)



Pre-culture



0



22.5



8534



8765



8471



8356



100



1



22.3



8711



8653



8728



8557



100



2



22.2



8751



8545



8471



8562



100



 


Exposure



3



22.4



8637



8789



8654



8765



100



4



22.9



8615



8839



8559



8569



100



5



22.5



8719



8926



8639



8721



100



6



22.3



8549



8929



8729



8621



100



 



Mean



22.4



8645



8778



8607



8593



-



 



±SD



0.2



85.2



140.6



109.6



132.8



-



 



Min



22.2



8356



 



 



Max



22.9



8929



 



-: Not applicable; SD: Standard deviation; Min: Minimum; Max: Maximum.


Table 9. pH of test medium during main study









































































Group 



Test Conc. (mg/L)



pH



0 hours



72 hours



R1



R2



R3



R4



R5



R6



R1



R2



R3



R4



R5



R6



G1



0.0



8.26



8.28



8.31



8.30



8.29



8.34



8.35



8.39



8.33



8.34



8.34



8.31



G2



100.0



8.32



8.30



8.27



8.34



8.35



8.29



8.30



8.24



8.36



8.28



8.32



8.39



 



Min



8.26



8.24



 



Max



8.35



8.39



 

Validity criteria fulfilled:
yes
Remarks:
(increase of biomass in control during 72h>16 fold; coefficient of variation of the mean specific growth rate among replicates in control (t0-t72)<7%; the mean of the replicate coefficients of variation in section-by-section growth rate in control < 35%)
Conclusions:
In an Alga Growth Inhibition Test with Pseudokirchneriella subcapitata green algae, the 72h-ErC50 and NOEC of the test item based on growth rate were found to be above the saturation limit of the test item.
Executive summary:

An Algae Growth Inhibition Test was performed with Pseudokirchneriella subcapitata green algae on the test item, over a period of 72 h in static conditions, according to OECD TG 201, under GLP conditions. 


Based on an in-house solubility test, the test item was found to be soluble up to 100 mg/L. Based on the performed preliminary range-finding test performed at 0 (control), 0.01, 0.1, 1.0, 10.0, 50.0 and 100.0 mg/L, where no toxic effects were observed at any dose tested, a Limit Test was carried out using only one test concentration of 100 mg/L (nominal) and one control group. OECD medium was used for algal culturing. The test design included six replicates at test concentration and six replicates for the untreated control. Test medium alone and 3,5-dichlorophenol 97% were used as negative and positive controls, respectively. 


A validated analytical method based on ICP-MS was used to monitor the concentration and stability of the active ingredient in the test solution. The test
item was considered as stable in the testing conditions after 72 hours of exposure as the measured concentrations in samples were maintained within ± 20 percent of the nominal concentrations. However, during the main test, fine particles were observed at the bottom of the conical flask at the test concentration of 100.0 mg/L after 24, 48 and 72 hours. Therefore, additional replicates were prepared for analytical monitoring. On analytical verification at the concentration of 100 mg/L, the limit of saturation was found to be, 9.13 to 11.80 mg test item/L in the filtered sample and 10.17 to 13.44 mg test item/L in the centrifuged sample, respectively.


Under test conditions and based on nominal concentrations, the 72-hour No Observed Effect Concentration (NOEC) was determined to be 100.0 mg/L, and the Lowest Observed Effect Concentration (LOEC) was >100.0 mg/L. The 72 hours EC50 value for growth rate (ErC50) and yield (EyC50) were determined to be >100.0 mg/L. All validity criteria were met.


Therefore, no effects were observed up to the limit of saturation of the test item in test media.

Description of key information

Key study: Method according to OECD 201, GLP study. Under test conditions and based on nominal concentrations, the 72-hour No Observed Effect Concentration (NOEC) was determined to be 100.0 mg/L, and the Lowest Observed Effect Concentration (LOEC) was >100.0 mg/L. The 72 hours EC50 value for growth rate (ErC50) and yield (EyC50) were determined to be >100.0 mg/L. All validity criteria were met. Based on analytical verification, no effects were observed up to the limit of saturation (9.13 to 11.80 mg test item/L) of the test item in test media.

Key value for chemical safety assessment

EC50 for freshwater algae:
9.13 mg/L
EC10 or NOEC for freshwater algae:
9.13 mg/L

Additional information