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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
From 2017-06-28 to 2017-06-29
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Remarks:
This calculation method predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following the Guideline for Testing of Chemicals No. 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test", referenced as Method C.3 of Commission Regulation No. 440/2008. This approach uses a thermodynamically based module to calculate the water concentrations and the individual toxicity of each constituent is first derived from a QSAR model validated to be compliant with the OECD recommandations for QSAR modeling (OECD, 2004). Then, the effective loading rate of the mixture to the test organisms (i.e. Pseudokirchneriella subcapitata) is determined as a Water Accommodated Fraction (WAF) test (OECD, 2000).
Justification for type of information:
1. SOFTWARE
iSafeRat® HA-QSAR toolbox v2.3

2. MODEL (incl. version number)
iSafeRat® holistic HA-QSAR v1.7

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
See attached report

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached QMRF

5. APPLICABILITY DOMAIN
See attached report

6. ADEQUACY OF THE RESULT
See attached report
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
not applicable
Remarks:
(QSAR model)
Principles of method if other than guideline:
This calculation method predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following OECD Guideline 201 adapted for testing as a mixture using the WAF method. The criterion measured was the median effective loading rate of the mixture ErL50 (Median Effective Loading for specific growth rate), a statistically derived loading rate which is expected to cause 50% inhibition of intrinsic rate of growth of the test system within a period of 72 hours. This approach uses a thermodynamically based module to calculate the water concentrations and the individual toxicity of each constituent is first derived from a QSAR model validated to be compliant with the OECD recommandations for QSAR modeling (OECD, 2004). Then, the effective loading rate of the mixture to the test organisms (i.e. Pseudokirchneriella subcapitata) is determined as a Water Accommodated Fraction (WAF) test (OECD, 2000).
GLP compliance:
no
Specific details on test material used for the study:
No additional information
Analytical monitoring:
no
Details on sampling:
Not applicable
Vehicle:
no
Details on test solutions:
Not applicable
Test organisms (species):
other: algae sp.
Details on test organisms:
Not applicable
Test type:
other: QSAR method
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Remarks on exposure duration:
none
Post exposure observation period:
Not applicable
Hardness:
Not applicable
Test temperature:
Not applicable
pH:
Not applicable
Dissolved oxygen:
Not applicable
Salinity:
Not applicable
Nominal and measured concentrations:
Not applicable
Details on test conditions:
Not applicable
Reference substance (positive control):
no
Remarks:
QSAR model
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
6 mg/L
Nominal / measured:
estimated
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
The 72h-ErL50 is predicted at 6.0 mg/L. At this 72h-ErL50, the expected concentrations of each constituent in the mixture (based on thermodynamic calculation) are specify in the attached report.
This method has previously been validated in an internal publication (Bicherel & Thomas, 2014, available in "Attached background material") and will be made available to the Competent Authorities upon request.
Results with reference substance (positive control):
Not applicable
Reported statistics and error estimates:
Not applicable

No additional information

Validity criteria fulfilled:
not applicable
Conclusions:
The 72-h ErL50 based on growth rate was determined to be 6.0 mg/L.
Executive summary:

A calculation method was used to predict the inhibition of algal growth exposed the test substance, a Natural Complex Substance, using the WAF method. This calculation method predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following the Guideline for Testing of Chemicals No. 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test", referenced as Method C.3 of Commission Regulation No. 440/2008 adapted for testing of a mixture using the WAF method. The criterion measured was the median effective loading rate of the mixture ErL50 (Median Effective Loading for specific growth rate), a statistically derived loading rate which is expected to cause 50% inhibition of intrinsic rate of growth of the test system within a period of 72 hours.

 

The growth inhibition of algae was determined using a validated calculation method for the Mode of Action (MOA) in question (non-polar narcosis). been validated in an internal publication for MOA 1 (non-polar narcosis) and acute exposure (Bicherel and Thomas, 2014). The algorithm is based on a QSAR model which has been validated to be compliant with the OECD recommandations for QSAR modeling (OECD, 2004). The QSAR model is based on validated data from a training set of 40 chemicals derived from 72-hour test on algae, for which the concentrations of the test item had been determined by chemical analyses over the test period. Further to this the effective loading rate of the WAF is determined by using a series of calculation steps using phase equilibrium thermodynamics and excluding the non-bioavailable fraction, this approach is based on validated data derived from 72-hour ErL50 tests on algae, for which the concentrations of the test item had been determined by chemical analyses over the test period.

The 72-h ErL50 based on growth rate was determined to be 6.0 mg/L.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
07-20 November 2008
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
This GLP study was performed according to OECD Guideline 201 with the following deficiencies: old WAF method - dispersions were stirred for 3 hours and then filtered.
Qualifier:
according to
Guideline:
OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
no
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. certificate)
Remarks:
The Swiss GLP Monitoring Authorities (inspected on 05-09 & 26-30 November 2007 / signed on 12 November 2008)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Appearance: Pale yellow liquid
Analytical monitoring:
yes
Details on sampling:
Analysis of the test Item concentrations:
For measurement of the actual concentrations of the test item, duplicate samples were taken from the test media of all test concentrations at the start of the test (without algae) and at the end of the test (containing algae). At the same sampling times, duplicate samples were also taken from the control.
For sampling at the end of the test, the test medium of the treatment replicates was pooled.
The samples were analyzed immediately after sampling. Immediately after sampling, acetone was added to each sample (1% of acetone per sample volume).
The concentrations of the test item were determined in the duplicate test medium samples from all test concentrations. From the control samples, one of the duplicate samples was analyzed from the corresponding sampling times.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: For preparation of the WAFs, individual dispersions of the test item with the loading rates as mentioned above were prepared (table 6.1.5/1).
The dispersions were stirred for 3 hours at room temperature in the dark to dissolve a maximum amount of the different compounds of the test item in the dispersion. Then, the dispersions were filtered through membrane filters (Schleicher & Schuell, Type NC45, pore size 0.45 μm) and the undiluted filtrates were tested as WAFs. The negative pressure of the filtration unit was reduced as much as possible to avoid losses of volatile components of the test item during filtration.
The stirring period of 3 hours was chosen based on the results of a pre-experiment (non-GLP) in which the maximum concentration of the different compounds in the test media was reached after the stirring period of 3 hours.
The test media were prepared just before the start of the test.
- Controls: Test water without test item
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: Strain No. 61.81 SAG
- Source (laboratory, culture collection): Strain No. 61.81 SAG, supplied by the Collection of Algal Cultures (SAG, Institute for Plant Physiology, University of Göttingen, Göttingen/Germany). The algae were cultivated at Harlan Laboratories under standardized conditions according to the test guidelines.
- Age of inoculum (at test initiation): An inoculum culture was set up four days before the start of the exposure.
- Method of cultivation: The algae were cultivated under the test conditions. The inoculum culture was diluted threefold one day before the start of the test to ensure that the algae were in the exponential growth phase when used to inoculate the test solutions.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Post exposure observation period:
None
Hardness:
Water hardness (calculated) of the test water was 0.24 mmol/L (= 24 mg/L as CaCO3).
Test temperature:
Water temperature during the test was 22 °C
pH:
At the start of the test, the pH measured in the treatments was between 8.0 and 8.1. At the end of the test, pH values of 8.8 to 8.9 were measured (Table 6). The increase of the pH during the test was caused by the uptake of CO2 by the algae due to their rapid growth despite the test media were stirred during the test.
Dissolved oxygen:
No data
Salinity:
No data
Nominal and measured concentrations:
Water accommodated fractions (WAFs) with the loading rates 0.10, 0.33, 1.0, 3.3 and 10 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 50-mL Erlenmeyer flasks
- Type: closed; test flasks were made tight with glass stoppers to avoid losses of the volatile substance.
- Material, size, headspace, fill volume: Since the test item was determined to be volatile (according to the results of a pre-experiment, non-GLP), the test was performed in 50-mL Erlenmeyer flasks completely filled with about 50 mL test medium.
- Aeration: During the test, the test solutions were continuously stirred by magnetic stirrers.
- Initial cells density: At the start of the test, 10000 cells/mL were inoculated; the algal cell density in the pre-culture was determined by an electronic particle counter (Coulter Counter®, Model ZM).
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Algae were cultivated and tested in synthetic test water, prepared according to the test guidelines, but modified according to the International Standard ISO 14442 as the test was performed in a closed test system. The concentration of NaHCO3 was increased by 200 mg/L to 250 mg/L (as carbon source for the algal growth), and 6 mmol/L HEPES-buffer were added to keep the pH in the test media as constant as possible.

OTHER TEST CONDITIONS
- The test flasks were incubated in a temperature-controlled water bath at a temperature of 22 °C and illuminated by fluorescent tubes (Philips TLD 36W/840), installed above the test flasks. The mean measured light intensity at the level of the test solutions was approximately 7300 Lux (range: 6600 to 7800 Lux, measured at nine places in the experimental area).

EFFECT PARAMETERS MEASURED:
Determination of Algal Biomass:
- A small volume of the algal suspension was daily withdrawn from each test flask for the measurement of the biomass, and was not replaced.
- The algal biomass in the samples was determined by fluorescence measurement (BIO-TEK® Multi-Detection Microplate Reader, Model FLx800). The measurements were performed in duplicate.
- At the end of the test, a sample was taken from the control and from the loading rate of nominal 3.3 mg/L. The shape and size of the algal cells were visually inspected. This loading rate was chosen since, at the highest nominal loading rate of 10 mg/L, the algal cell density was too low for a reliable examination.
- Water Quality Criteria: The pH was measured and recorded in each treatment at the start and at the end of the test. The water temperature was measured and recorded daily in an Erlenmeyer flask filled with water and incubated under the same conditions as the test flasks. The appearance of the test media was also recorded daily.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2
- The selection of the loading rates was based on the results of a range-finding test and on results of a pre-experiment to determine the solubility of the test item in the test water (non-GLP). The enlarged spacing factor of 3.2 between the test concentrations was chosen, because according to the results of the range-finding test the concentration-effect relationship was rather flat and, thus, a large concentration range had to be tested.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EL10
Effect conc.:
4.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence interval: 3.8 – 4.5 mg/L
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
9.1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence interval: 8.9 – 9.4 mg/L
Duration:
72 h
Dose descriptor:
other: The highest tested loading rate without observed effect
Effect conc.:
3.3 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
- The test item had a significant inhibitory effect on the average growth rate of the algae after the test period of 72 hours at the concentration of 10 mg/L and on yield at the concentration of 3.3 mg/L and at all higher test concentrations (results of Williams-tests, one-sided, α = 0.05). Thus, the concentration of 3.3 mg/L was determined to be the 72-hour LOEC.
- The 72-hour NOEC was determined to be 1.0 mg/L, since up to and including this test concentration the growth rate and yield of the algae after 72 hours were not significantly lower than in the control.
- The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 3.3 mg/L and the algal cells in the control. The shape and size of the algal cells were obviously not affected by the test item up to at least this concentration.
- No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the test period
Results with reference substance (positive control):
For evaluation of the algal quality and experimental conditions, potassium dichromate is tested as a positive control twice a year to demonstrate satisfactory test conditions. The result of the latest positive control test performed in 2008 showed that the sensitivity of the test system was within the historical range of Harlan Laboratories (72-hour EC50 for the growth rate: 1.20 mg/L (RCC Study No. B83755), range of the 72-hour EC50 for the growth rate from 2000 to 2008: 0.71–1.74 mg/L).
Reported statistics and error estimates:
The 72-hour ELC10, EL20 and EL50 values for the inhibition of average growth rate and yield and their 95% confidence intervals were calculated by Probit Analysis.
For the determination of the LOEC and NOEC, average growth rate and yield at the test concentrations were compared to the control values by Williams tests.

Analysis of concentrations: At the start of the test, the measured test item concentrations (based on the sum of four peaks) in the test media with the loading rates of 0.10, 0.33, 1.0, 3.3 and 10 mg/L were between 0.006 and 0.69 mg/L. At the end of the test, the measured concentrations in the test media were between < LOQ and 0.31 mg/L. Since water accommodated fractions of the test item were tested, all reported biological results were based on the loading rates of the test item.

 

Table 6.1.5/2: Average Growth Rates (μ)

Loading rate (mg/L)

 

Average growth rate μ (day-1) and inhibition of μ (Ir)

0-24 h

0-48 h

0-72 h

μ

 

Ir(%)

 

μ

 

Ir(%)

 

μ

 

Ir(%)

 

Control 

1.098

0.0

1.695

0.0

1.737

0.0

0.10

1.255

-14.3

1.697

-0.1

1.727

0.6

0.33

1.262

-15.0

1.714

-1.1

1.724

0.8

1.0

1.181

-7.5

1.706

-0.6

1.733

0.2

3.3

1.088

0.9

1.644*

3.0

1.655

4.7

10

0.642*

41.5

0.751*

55.7

0.762*

56.1

*: mean value significantly lower than in the control (according to Williams-tests, one-sided, α = 0.05)

 

Table 6.1.5/3: Yield (Y)

 

Loading rate (mg/L)

 

Yield Y (x 103) and inhibition of Y (Iy)

 

0-24 h

0-48 h

0-72 h

Y

Iy(%)

Y

Iy(%)

Y

Iy(%)

Control 

1.893

0.0

28.491

0.0

168.431

0.0

0.10

2.316

-22.3

28.623

-0.5

164.261

2.5

0.33

2.365

-24.9

29.624

-4.0

168.594

-0.1

1.0

2.094

-10.6

29.138

-2.3

166.160

1.3

3.3

1.830

3.4

25.527*

10.4

133.721*

20.6

10

0.859*

54.6

3.357*

88.2

8.360*

95.0

*: mean value significantly lower than in the control (according to Williams-tests, one-sided, α = 0.05)

 

Validity criteria:

In the control the biomass increased by a factor of 184 over 72 hours. The validity criterion of increase of biomass by at least a factor of 16 within three days was fulfilled.

The mean coefficient of variation of the daily growth rates in the control (section-by-section growth rates) during 72 hours was 34%. According to the OECD test guideline, the mean coefficient of variation must not be higher than 35%. Thus, the validity criterion was fulfilled.

The coefficient of variation of the average specific growth rates in the replicates of the control after 72 hours was 1.5%. According to the OECD test guideline, the coefficient of variation must not be higher than 7%. Thus, the validity criterion was fulfilled.

Validity criteria fulfilled:
yes
Conclusions:
Under the test conditions and based on the loading rates, the ErL10 and ErL50 values were calculated to be 4.2 mg/L (95% CI: 3.8-4.5 mg/L) and 9.1 mg/L (95% CI: 8.9-9.4 mg/L), based on growth rate, respectively.
Executive summary:

The influence of the test item on the growth of the freshwater green algal species Pseudokirchneriella subcapitata (formerly Selenastrum capricornutum) was investigated in a 72-hour static test according to OECD Guideline 201/ EU method C.3 and in compliance with GLP.

 

In order to test the toxicity of the multi-component test item to the algae, water accommodated fractions (WAFs) with different loading rates of the test item were prepared and tested. WAFs with the following loading rates of the test item were tested: 0.10, 0.33, 1.0, 3.3 and 10 mg/L. A control was run in parallel.

For preparation of the WAFs, individual dispersions of the test item with the loading rates as mentioned above were prepared. The dispersions were stirred for 3 hours at room temperature in the dark to dissolve a maximum amount of the different compounds of the test item in the dispersion. Then, the dispersions were filtered through membrane filters and the undiluted filtrates were tested as WAFs. The negative pressure of the filtration unit was reduced as much as possible to avoid losses of volatile components of the test item during filtration. The stirring period of 3 hours was chosen based on the results of a pre-experiment (non-GLP) in which the maximum concentration of the different compounds in the test media was reached after the stirring period of 3 hours.

 

At the start of the test, the measured test item concentrations (based on the sum of four peaks) in the test media with the loading rates of 0.10, 0.33, 1.0, 3.3 and 10 mg/L were between 0.006 and 0.69 mg/L. At the end of the test, the measured concentrations in the test media were between < LOQ and 0.31 mg/L. Since water accommodated fractions of the test item were tested, all reported biological results were based on the loading rates of the test item.

 

The test item had a significant inhibitory effect on the average growth rate of the algae after the test period of 72 hours at the concentration of 10 mg/L. The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 3.3 mg/L and the algal cells in the control. The shape and size of the algal cells were obviously not affected by the test item up to at least this concentration. No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the test period.

 

Under the test conditions and based on the loading rates, the ErL10 and ErL50 values were calculated to be 4.2 mg/L (95% CI: 3.8-4.5 mg/L) and 9.1 mg/L (95% CI: 8.9-9.4 mg/L), based on growth rate, respectively.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
[further information is included as attachment to Iuclid section 13]

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This read-across is based on the hypothesis that source and target substances have similar physico-chemical, environmental fate and (eco)toxicological properties because of their structural and composition similarity.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See Read-across justification document in Section 13 of IUCLID.

3. ANALOGUE APPROACH JUSTIFICATION
In addition to the structural/composition similarity, physico-chemical and environmental fate properties, both substances have been shown to be toxic to aquatic organisms (all EL50 values are comprised between 1 and 10 mg/L, except the EL50 value on the aquatic invertebrates Daphnia magna for the source substance at 15 mg/L). No experimental study is available for the target substance. The acute toxicity of the target substance to the aquatic invertebrates and algae was determined using QSAR results (iSafeRat® Holistic HA-QSAR v1.7). The QSAR results supports the experimental studies performed on the source substance with EL50 values more conservative but in the same order of magnitude. The common main components of both substances have the same mode of action (MoA 1, non-polar narcosis) with similar log Kow values. The ecotoxicological properties between the target and source substances are pronounced.
Therefore, it’s considered suitable and scientifically justified to read-across the data between the two substances to fill the short-term toxicity to aquatic invertebrates and the toxicity to aquatic algae endpoints in the present dossier.

4. DATA MATRIX
See Read-across justification document in Section 13 of IUCLID.
Reason / purpose:
read-across source
Reason / purpose:
read-across: supporting information
Key result
Duration:
72 h
Dose descriptor:
EL10
Effect conc.:
4.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence interval: 3.8 – 4.5 mg/L
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
9.1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% confidence interval: 8.9 – 9.4 mg/L
Duration:
72 h
Dose descriptor:
other: The highest tested loading rate without observed effect
Effect conc.:
3.3 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Validity criteria fulfilled:
not applicable
Conclusions:
According to the experimental study performed on the source substance, the ErL10 and ErL50 values (based on nominal loading rates) for the target substance can be determined at 4.2 mg/L (95% CI: 3.8-4.5 mg/L) and 9.1 mg/L (95% CI: 8.9-9.4 mg/L), based on growth rate, respectively.
Executive summary:

No experimental study is available on the target substance to assess the toxicity to aquatic algae. However, a study was performed according to OECD Guideline 201 with GLP statement, to assess the influence of the read-across (source) substance on the growth of the freshwater green algal species Pseudokirchneriella subcapitata in a 72-hour static test.

Both substances (the target and the source substances) are UVCB substances with very similar compositions.

In the experimental study performed on the source substance, Water Accommodated Fractions (WAFs) with different loading rates (0.10, 0.33, 1.0, 3.3 and 10 mg/L) of the test item were prepared and tested. A control was run in parallel.

At the start of the test, the measured test item concentrations (based on the sum of four peaks) in the test media with the loading rates of 0.10, 0.33, 1.0, 3.3 and 10 mg/L were between 0.006 and 0.69 mg/L. At the end of the test, the measured concentrations in the test media were between < LOQ and 0.31 mg/L. Since water accommodated fractions of the test item were tested, all reported biological results were based on the loading rates of the test item.

The test item had a significant inhibitory effect on the average growth rate of the algae after the test period of 72 hours at the concentration of 10 mg/L. The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 3.3 mg/L and the algal cells in the control. The shape and size of the algal cells were obviously not affected by the test item up to at least this concentration. No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the test period.

Under the test conditions and based on the loading rates, the ErL10 and ErL50 values were calculated to be 4.2 mg/L (95% CI: 3.8-4.5 mg/L) and 9.1 mg/L (95% CI: 8.9-9.4 mg/L), based on growth rate, respectively.

Description of key information

QSAR, iSafeRat® Holistic HA-QSAR v1.7, calculation method, WAF, key study, validity 1:

72h-ErL50 = 6.0 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
6 mg/L

Additional information

To assess the toxicity of the registered substance to aquatic algae, a set of two data are available.

The first data (KREATiS, 2017), assessed as a key datapoint, is a QSAR. This QSAR used a calculation method to predict the acute toxicity of the registered substance, an UVCB substance, to aquatic algae (72h-ErL50 value). This calculation method predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following OECD Guideline 201 adapted for testing as a mixture using the WAF method. This method has previously been validated in an internal publication (Bicheral and Thomas, 2014; available in the Endpoint Study Record). This algorithm is based on a QSAR model (iSafeRat® Holistic HA-QSAR v1.7) which has been validated to be compliant with the OECD recommendations for QSAR modelling (OECD, 2004). The QSAR is based on validated data for a training set of 40 chemicals derived from 72h test on algae, for which the concentrations of the test item had been determined by chemical analyses over the test period. Further to this, the effective loading rate of the WAF is determined by using a series of calculation steps using phase equilibrium thermodynamics and excluding the non-bioavailable fraction. The 72h-ErL50 value based on growth rate was determined to be 6.0 mg/L.

To support this prediction and reinforce the correct order of magnitude, a second data was provided in the dossier. This data is an experimental study (Harlan, 2009) performed on a source substance, according to OECD Guideline 201 with GLP statement. The 72h toxicity of this substance to the growth of the freshwater green algae species Pseudokirchneriella subcapitata, under static conditions, was assessed using WAF method. Both substances (the target and the source substances) are UVCB substances with very similar compositions. The main components of both substances have the same mode of action (MoA 1, non-polar narcosis) with similar log Kow values. In this experimental study, the 72-hour ErL50 of the test item was calculated to be 9.1 mg/L (95% confidence limits of 8.9 and 9.4 mg/L). This experimental result on the source substance supports the QSAR key result performed on the target substance, with a predicted EL50 value slightly more conservative.

In conclusion, according to the key data, the retained 72h-ErL50 value for the registered substance on algae is 6.0 mg/L.