Lorenox™

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

August 01st, 2019 to August 13th, 2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
iSafeRat® toolbox – in Silico Algorithms For Environmental Risk And Toxicity version 2.4

2. MODEL (incl. version number)
iSafeRat® holistic HA-QSAR v1.8

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
isomer 1: CC1C(OC)CCC(C)=CCCC=C(C)CC1
isomer 2: CC1C(OC)CCC(C)=CCCC(C)=CCC1
isomer 3: CC1C(OC)CCC=C(C)CCC(C)=CCC1
isomer 4: CC1CCC(C)=CCCC(C)=CCCC1OC
The toxicity of the test item was predicted using the iSafeRat® Ecotox module providing the Subcooled Liquid Water Solubility (SLWS) as the input. TThe SLWS has been predicted using the iSafeRat® Water Solubility module providing the experimental log KOW value as the input. Water Solubility of the test item = 2.09 mg/L (or -5.053 in log (mol/L).

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

5. APPLICABILITY DOMAIN
See attached QPRF

6. ADEQUACY OF THE RESULT
See attached QPRF

Reason / purpose for cross-reference:

reference to other study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

not applicable

Remarks:

QSAR model

Principles of method if other than guideline:

The purpose of this QSAR model is to accurately predict the toxicity to algae as would be expected in a laboratory experiment following the OECD Guideline 201 and EC method C.3 for specific, named mechanisms of action. The model provides an in silico prediction for the 72-hour ErC50 value that can effectively be used in place of an experimentally derived 72-hour ErC50 value. The regression is method used to achieve this has been fully validated following the OECD (2004) recommendations.

GLP compliance:

no

Specific details on test material used for the study:

Water Solubility: 2.09 mg/L (KREATiS, 2019)

Analytical monitoring:

no

Details on sampling:

not applicable

Vehicle:

no

Details on test solutions:

not applicable

Test organisms (species):

other: Pseudokirchneriella subcapitata, Desmodesmus subspicatus, Scenedesmus quadricauda

Details on test organisms:

No difference in terms of toxic mechanism of action between algae (or indeed other) aquatic species is expected. Any observed differences may be attributed to lifestyle related parameters and relative duration of study versus cell size rather than to a
specific toxic mechanism causing species differences.

Test type:

other: QSAR

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Remarks on exposure duration:

Results from a test duration of 72 hours only were used for this algorithm.

Post exposure observation period:

None

Hardness:

The QSAR is based on data from studies performed at acceptable hardness to ensure control survival.

Test temperature:

The temperatures varied from approximately 20 to 25 °C depending on the species used to construct the algorithm. This small difference is not expected to contribute to the variability of the ErC50 values found in experimental data.

pH:

Test results were preferably taken from studies with measured pHs between 6 - 9. However it is recognized that in some cases (due to high luminosity) the pH may increase in the control and lower concentrations (which do not cause significant effect over the study period). This pH increase did not generally disqualify the study from being used in the test and validation set for non-polar chemicals.

Dissolved oxygen:

The QSAR is based on data from reliable studies performed at acceptable oxygen concentrations.

Salinity:

Not applicable

Conductivity:

No data

Nominal and measured concentrations:

Studies were used only where sufficient evidence was presented to determine that the stubstance was stable under test conditions (i.e. maintened within ± 20 % of the nominal or measured initial concentration throughout the test) or, if not, the result was based on measured concentrations as geometric mean.

Details on test conditions:

Following the guideline OECD 201, all studies were from a static test design. For suspected volatile substances only tests performed in closed vessels were accepted unless accompanying analytical monitoring proved such a design was not necessary.

Reference substance (positive control):

no

Remarks:

QSAR model

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

0.73 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95%CL: 0.26 - 2.09 mg/L

Details on results:

The test item falls within the applicability domain of the model and was therefore reliably predicted for its toxicity (72h-ErC50) to algae. Therefore, this endpoint value can be considered valid for use in risk assessment and classification and labelling.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

95% confidence interval (α = 0.05): 2.3 – 3.4 mg/L
QSAR statistical parameters are given in the QMRF and the QPRF

Analysis of the Applicability Domain of the model

Descriptor domain

The Subcooled Liquid Water Solubility value (-5.053 in log (mol/L)) given as the input to the Ecotox module of the iSafeRat® Holistic HA-QSAR falls within the intermediate domain of the model between a log water solubility (in log (mol/L)) of - 9.34 to - 4.38 where baseline toxicity cannot be experimentally measured accurately. Moreover the toxicity may be greater than the water solubility limit. Based on a statistical k-NN approach (k = 3), the toxicity of the test item is estimated as the geometric mean between the toxicity value predicted using the regression line and the solubility cut-off line (with the confidence intervals being placed at these limits).

Structural fragment domain

All chemical groups within the molecular structure are taken into account by the model.

Mechanistic domain

Currently, the ecotoxicity module of the iSafeRat® Holistic HA-QSAR can reliably predict the aquatic toxicity for chemicals with the following mechanisms of action of toxicity (MechoA):

• non-polar narcosis (MechoA 1.1)

• polar narcosis of alkyl-/alkoxy-phenols (MechoA 1.2)

• polar narcosis of aliphatic amines (MechoA 1.2)

• cationic narcosis of quaternary ammoniums (MechoA 1.3)

• mono-/poly-esters whose hydrolysis products are narcotics (MechoA 2.1)

• hard electrophile reactivity (MechoA 3.1)

• RedOx cycling of primary thiols (MechoA 4.4)

• Proton release of carboxylic acids (MechoA 5.2)

The MechoA of molecules is predicted directly from the structure. The test item as an aliphatic ether is expected to exert a MechoA 1.1 and can be taken into account by the model.

Validity criteria fulfilled:

yes

Remarks:

partially

Conclusions:

The test item falls within the applicability domain of the model except for the descriptor domain. From a descriptor domain point of view, the test item falls within the intermediate domain where baseline toxicity cannot be experimentally measured accurately. Moreover, the toxicity may be greater than the water solubility limit. Based on a statistical k-NN approach (k = 3), the toxicity of the test item is estimated as the geometric mean between the toxicity value predicted using the regression line and the solubility cut-off line (with the confidence intervals being placed at these limits).

The 72h-ErC50 of the test item to algae was predicted as 0.73 mg/L.
95% confidence interval (α = 0.05): 0.26 – 2.09 mg/L

Executive summary:

A Quantitative Structure-Activity Relationship (QSAR) was used to calculate the inhibition of growth to algae of the test item. This QSAR model has been validated to be compliant with the OECD recommendations for QSAR modeling (OECD, 2004) and 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" (OECD, 2006), referenced as Method C.3 of Commission Regulation No. 440/2008 (European Commission, 2008). The criterion predicted was the ErC50 (Median Effective Concentration for specific growth rate), a statistically derived concentration 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 validated QSAR model for the Mechanism of Action (MechoA) in question (MechoA 1.1, i.e. non-polar narcosis) (Bauer et al., 2018). The QSAR model is based on validated data for a training set of 40 chemicals derived from 72-hour ErC50 test on algae, for which the concentrations of the test item had been determined by chemical analyses over the test period.

The test item falls within the applicability domain of the model except for the descriptor domain. From a descriptor domain point of view, the test item falls within the intermediate domain where baseline toxicity cannot be experimentally measured accurately. Moreover, the toxicity may be greater than the water solubility limit. Based on a statistical k-NN approach (k = 3), the toxicity of the test item is estimated as the geometric mean between the toxicity value predicted using the regression line and the solubility cut-off line (with the confidence intervals being placed at these limits).

The 72h-ErC₅₀of the test item to algae was predicted as 0.73 mg/L.

95% confidence interval (α = 0.05): 0.26 – 2.09 mg/L

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

disregarded due to major methodological deficiencies

Study period:

11 September to 06 November 2009

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Remarks:

This study was performed according to OECD Guideline 201 with GLP certificate. All validity criteria were fulfilled. The substance is adequately identified, but some data on composition is missing. This study is considered not assignable due to insufficient information provided on the semi-static methodology used. A validation study should be provided to validate this method and, at the time being, a semi-static system is not accepted as an adaptation of the OECD Guideline. With this method, parent and degradation products are present simultaneously, so interactions can occured. In addition, acetone was used as solvent in this study. Because of the potential for interaction with the test chemical resulting in an altered response in the test, solvent use should be restricted to situations where no other acceptable method of test solution preparation is available. The use of solvent is not the best method at the time being. Furthermore, solvents are generally not appropriate for multiconstituent substances, like the test substance (which is a mixture of isomers), where the use of the solvent can preferentially dissolve one or more components and thereby affect the toxicity. Then, the concentration/quantity of solvent used in the treatment solutions was 0.5 mL/L, corresponding to 395 mg/L (with a density of 0.79), which is 5 times higher than the recommended maximum level of solvent (below 0.1 mL/L; OECD No. 23) but is below the NOEC of acetone (which was reported in the ECHA disseminated dossier at 530 mg/L). No Range-finding test was performed. No table with % inhibition of growth rate was reported in the study report. Effects results were based on nominal concentrations instead of measured concentrations (the test substance was not stable: the test concentration did not long for more than a few hours).

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

yes

Remarks:

semi-static methodology used; the study was conducted directly as a limit test at the limit of solubility of the test item in water without previous range-finding test.

Principles of method if other than guideline:

Not applicable

GLP compliance:

yes (incl. QA statement)

Remarks:

Dates of inspection: 23-24 July 2008 / Date of signature: 19 October 2009

Specific details on test material used for the study:

- Physical state: Pale yellow translucent liquid
- Storage condition of test material: Stored at room temperature protected from direct sun light

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Analytical verification of the test item was performed at the concentrations of 1.5 mg/L

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Chemical name of vehicle: Acetone
- Method: The treatment solutions were prepared in acetone: 76.2 mg of the test item were weighed and the volume was made to 25 mL with acetone. The test item treated units received 50 μL of the resulting solution at test initiation. The test concentration was maintained during the test period using the same treatment solution:
- T0+6 h: +40 μL
- T0+24 h: +50 μL
- T0+30 h: +40 μL
- T0+48 h: +50 μL
- T0+54 h: +30 μL
- Controls: Another set of solvent control units were prepared which received the same successive volumes of acetone during the test period.
- Concentration of vehicle in test medium: 0.5 mL/L

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Source (laboratory, culture collection): Strain was provided in December 2007 by the Museum National d'Histoire Naturelle (Paris, France) and regularly sub-cultured in the OECD medium at the Phytosafe site.
- Method of cultivation: The inoculum culture was prepared 2-4 days before the start of the test and incubated under the same conditions as the test cultures such to adapt the test algae to test conditions and ensure that the algae were in the exponential growth phase when used to inoculate the test solutions.

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Post exposure observation period:

None

Hardness:

No data

Test temperature:

21-24 °C

pH:

Start of the test: 9.2
End of the test: 8.1-9.1

Dissolved oxygen:

No data

Salinity:

No data

Conductivity:

No data

Nominal and measured concentrations:

Nominal concentration: 1.5 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: Glass Erlenmeyer flasks (250 mL) filled with 100 mL of culture served as test vessels.
- Type: The test vessels were capped with air-permeable stoppers.
- Initial cells density: The initial biomass in the test cultures was the same in all test cultures and sufficiently low to allow exponential growth throughout the incubation period without any risk of nutrient depletion. Historical data at Phytosafe site show that 2 to 5 X 10^3 cells/mL is an appropriate number.
- No. of vessels per concentration (replicates): 6 replicate units for the 1.5 mg/L test item treatment
- No. of vessels per control (replicates): 6 replicate units for the water control
- No. of vessels per vehicle control (replicates): 6 replicate units for the solvent control

GROWTH MEDIUM
- Standard medium used: OECD medium (OECD TG 201, according to ISO 8692) was freshly reconstituted by dilution of mineral stock solutions in water.

OTHER TEST CONDITIONS
- The test vessels were continuously shaken in a culture apparatus (Innova shaker 44R) so as to keep the algae in suspension and to facilitate the transfer of CO2.
- Light intensity and quality: The surface of the cultures received continuous, uniform fluorescent illumination of 4440 - 8880 lux, which is said to correspond approximately to the recommended light intensity 60-120 μE/m^2/S. The light intensity did not deviate by more than 15 % from the average light intensity over the incubation area.

EFFECT PARAMETERS MEASURED
Algal biomass: The algal biomass in each flask was determined daily over the test period using small volumes removed from the test solution by pipette. These volumes were not replaced. The numeration was done using an electronic cell counter (Coulter Counter ZM). The results were expressed as cells per liter of solution.
pH values: The pH of the solutions was measured at the beginning and at end of test. The pH of the control medium was not to increase by more than 1.5 units during the test.
Other observations: The inoculum culture was examined microscopically to verify that it was normal and healthy in appearance and to detect any abnormal appearance of the algae (as may be caused by exposure to the test substance) at the end of the test.

Reference substance (positive control):

yes

Remarks:

Potassium dichromate at 0.2, 0.6, 0.75 and 1.0 mg/L

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: yield

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 4.3% inhibition at 1.5 mg/L, significant vs controls at the 5% confidence level

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: yield

Remarks on result:

other: 19.6% inhibition at 1.5 mg/L, significant vs controls at the 5% confidence level

Details on results:

Daily numerations:
The control cultures showed exponential growth throughout the test period. The multiplication rate was approximately 146 (mean value).
The multiplication rate was slightly decreased in the test item treated units as compared with the control even though the growth rate appeared to remain exponential throughout the test period: the final cell density represented only approximately 120 times the initial value (mean value).

Specific growth rate:
The specific growth rate was regular in the control group throughout the test period, and the standard deviation between the three replicate units corresponded to less than 35 % of the mean value at each sampling time point as required. The standard deviation for the average specific growth rates throughout the entire test period in the replicate control cultures did not exceed 7 %, as required.
F-variance analysis at a 5% confidence level was used to detect any significant differences in mean specific growth rates (section-by-section and total values) as compared to the water control. The threshold value for F at the 5 % confidence level was calculated to be 4.96.
The solvent control was considered as similar to the water control.
For the test item treatment, the difference vs. control was significant for the last day of testing and for the overall testing period.
Calculation showed that the difference represented 4.3 % inhibition only for the entire period.

Yield:
The yield of biomass in the solvent control was considered as similar to that in the water control (5% confidence level).
In the test item treatment, the yield of biomass was significantly reduced. Calculation showed that the difference represented 19.6 % inhibition only for the entire period.

Results with reference substance (positive control):

The EC50-72 h for Potassium dichromate was 0.75 mg/L for the specific growth rate and 0.45 mg/L for the yield. The EC50-72 h for Potassium dichromate was between 0.6 and 1.0 mg/L for the specific growth rate and between 0.2 and 0.75 mg/L for the yield. The results fulfilled the validity criteria based on Phytosafe historical data.

Reported statistics and error estimates:

Statistical determination of the NOEC: The NOEC was derived from the F-variance analysis at a 5%-confidence level of the response variable (specific growth rate or yield) for each test item treatment compared to the controls. The NOEC corresponds to the highest tested concentration that failed to induce significant effects.
EC50 calculations: Consistently with the classical approach, EC50 values and the related 95% confidence intervals were derived from regression analysis of the concentration response-curves. In this case where no dose-related effect was observed, the EC50 values were not calculated.

Control of the treatment concentrations

Test initiation: the measured concentrations represented 90.5% of the nominal value.

During the test period, the test concentration regularly decreased to less than 80% of the nominal value even though the test concentration was restored twice per day.

The measured concentrations are reported below on a per cent basis as compared to the nominal value.

The results showed that the nominal treatment concentration was not stable for more than a few hours.

T0+6 h, old medium: 35.3 %

T0+6 h, new medium: 102.1 %

T0+24 h, old medium: 15.5 %

T0+24 h, new medium: 108.6 %

T0+30 h, old medium: 38.2 %

T0+30 h, new medium: 132.7 %

T0+48 h, old medium: 8.6%

T0+48 h, new medium: 120.7 %

T0+54 h, old medium: 45.2 %

T0+54 h, new medium: 111.5 %

End of test: 6.3%

Table 6.1.5/1: Limit test - Measured specific growth rates per day (section-by-section and total)

 

Groups	0 to 24 h	24 to 48 h	48 to 72 h	Total period
Control - Mean ± S.D.	1.77 ± 0.003	1.51 ± 0.06	1.70 ± 0.07	1.66 ± 0.03
Solvent - Mean ± S.D.	1.76 ± 0.02	1.50 ± 0.06	1.67 ± 0.06	1.64 ± 0.02
Test item 1.5 mg/L - Mean ± S.D.	1.76 ± 0.04	1.51 ± 0.04	1.50 ± 0.07	1.59 ± 0.01
Statistical analysis (Threshold value for F = 4.96)	F = 0.18	F = 0.00	F = 27.75	F= 23.19

 

TABLE 6.1.5/2: Limit test - Yield of biomass throughout the 72-hour incubation period

 

Groups	Yield
Control - Mean ± S.D.	4.83E+08 ± 4.61E+07
Solvent - Mean ± S.D.	4.61E+08 ± 3.03E+07
Test item 1.5 mg/L - Mean ± S.D.	3.88E+08 ± 1.67E+07
Statistical analysis (Threshold value for F = 4.96)	F = 22.31

 

VALIDITY OF THE TEST RESULTS

The test was considered as valid in the light of the following criteria:

- The biomass in the control cultures increased exponentially by a factor of at least 16 over the 72-hour test period.

- The mean coefficient of variation for section-by-section specific growth rates in the control cultures did not exceed 35 % (this criterion applies to the mean value of the coefficients of variation calculated for replicate control cultures).

- The coefficient of variation for average specific growth rates over the entire test period in replicate control cultures did not exceed 7 %.

Additionally, the EC₅₀-72 h for Potassium dichromate was between 0.6 and 1.0 mg/L for the specific growth rate and between 0.2 and 0.75 mg/L for the yield. The results fulfilled the validity criteria based on Phytosafe historical data.

The test item treatment was restored twice per day but this was not sufficient for that the test concentration was maintained at more than 80% of the nominal value. Analytical assessment showed that the test concentration did not long for more than a few hours.

Validity criteria fulfilled:

yes

Conclusions:

Under the test conditions, the ErC50 (growth rate) and EyC50 (yield) of the test item to Desmodesmus subspicatus was > 1.5 mg/L. The NOEC was < 1.5 mg/L based on specific growth rate (4.3% inhibition at 1.5 mg/L) and yield (19.6% inhibition at 1.5 mg/L).
However, this study is considered not assignable due to insufficient information provided on the semi-static methodology used.

Executive summary:

In an algal growth inhibition study performed according to OECD Guideline 201 and in compliance with GLP, the freshwater green algae species Desmodesmus subspicatus was exposed to test item at the nominal concentration of 1.5 mg/L (six replicates per concentration) for 72 hours, under semi-static conditions and constant illumination, shaking at a temperature of 21-24 °C. Water and solvent controls were included. The percent inhibition for growth rate and yield was determined.

 

At test initiation, the measured concentrations represented 90.5% of the nominal value. During the test period, the test concentration regularly decreased to less than 80% of the nominal value even though the test concentration was restored twice per day.

 

The specific growth rate was regular in the control group throughout the test period, and the standard deviation between the three replicate units corresponded to less than 35 % of the mean value at each sampling time point as required. The standard deviation for the average specific growth rates throughout the entire test period in the replicate control cultures did not exceed 7 %, as required. The solvent control was considered as similar to the water control. The specific growth rate was slightly affected throughout the test period (4.3 % inhibition for the entire test period) and the difference vs. control was considered as significant at the 5% confidence level.

 

The yield of biomass in the solvent control was considered as similar to that in the water control (5% confidence level). The yield of biomass after 72 h of testing was reduced by 19.6 % and the difference vs. control was considered as significant at the 5% confidence level.

 

Under the test conditions, the E_rC50 (growth rate) and E_yC50 (yield) of the test item to Desmodesmus subspicatus was > 1.5 mg/L. The NOEC was <1.5 mg/L based on specific growth rate (4.3% inhibition at 1.5 mg/L) and yield (19.6% inhibition at 1.5 mg/L).

All validity criteria were fulfilled. However, this study is considered not assignable due to insufficient information provided on the semi-static methodology used. A validation study should be provided to validate this method and, currently, a semi-static system is not accepted as an adaptation of the OECD Guideline. Using the method described here, parent and degradation products are present simultaneously, so interactions can occur. In addition, acetone was used as solvent in this study, adding unnecessary complication to the test design given the relatively high water solubility of the test item at approximately 44 mg/L. Because of the potential for interaction with the test chemical resulting in an altered response in the test, solvent use should be restricted to situations where no other acceptable method of test solution preparation is available. Furthermore, solvents are generally not appropriate for multiconstituent substances, such as this test substance (which is a mixture of isomers), where the use of the solvent can preferentially dissolve one or more components and thereby affect the toxicity. Furthermore, the concentration/quantity of solvent used in the treatment solutions was 0.5 mL/L, corresponding to 395 mg/L (with a density of 0.79), which is 5 times higher than the recommended maximum level of solvent (below 0.1 mL/L; OECD No. 23) but is below the NOEC of acetone (which was reported in the ECHA disseminated dossier at 530 mg/L). No Range-finding test was performed. No table with % inhibition of growth rate was reported in the study report. Effects results were based on nominal concentrations instead of measured concentrations (the test substance was lost unde rthe test conditions: the test concentration did not remain stable for more than a few hours).

Description of key information

iSafeRat® High-Accuracy-Quantitative Structure-Activity Relationship, KREATiS, 2019 :

72h-ErC50 = 0.73 mg/L (95% confidence interval: 0.26 – 2.09 mg/L)

Key value for chemical safety assessment

EC50 for freshwater algae:

0.73 mg/L

Additional information

One experimental study and one QSAR prediction are available to assess the toxicity of the registered substance to aquatic algae.

 

The experimental study (Phytosafe, 2009) was disregarded and considered as not assignable due to insufficient information provided on the semi-static methodology used. A validation study should be provided to validate this method and, currently, a semi-static system is not accepted as an adaptation of the OECD Guideline. With this method, parent and degradation products are present simultaneously, so interactions can occur. In addition, acetone was used as solvent in this study which was an unnecessary complication given the relatively high solubility of approximately 44 mg/L. Because of the potential for interaction with the test chemical resulting in an altered response in the test, solvent use should be restricted to situations where no other acceptable method of test solution preparation is available. Furthermore, solvents are generally not appropriate for multiconstituent substances, which is the case for this test substance (which is a mixture of isomers), where the use of the solvent can preferentially dissolve one or more components and thereby affect the toxicity. Furthermore, the concentration/quantity of solvent used in the treatment solutions was 0.5 mL/L, corresponding to 395 mg/L (with a density of 0.79), which is 5 times higher than the recommended maximum level of solvent (below 0.1 mL/L; OECD No. 23) but is below the NOEC of acetone (which was reported in the ECHA disseminated dossier at 530 mg/L).

Under the test conditions, the 72h-ErC50 value of the test substance to Desmodesmus subspicatus, based on growth rate, was greater than 1.5 mg/L, the limit test concentration. The NOEC was lower than 1.5 mg/L based on specific growth rate (4.3% inhibition at 1.5 mg/L). Effects results were based on nominal concentrations instead of measured concentrations (the test substance was lost during the study: the test concentration did not remain stable for more than a few hours). No Range-finding test was performed and no table with inhibition percentage of growth rate was reported in the study report. Therefore, these results cannot be used and the study was disregarded.

 

The QSAR prediction (KREATiS, 2019) was considered as reliable and was used as key data. The QSAR model has been validated to be compliant with the OECD recommendations for QSAR modeling (OECD, 2004) and predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following the OECD Guideline 201. The growth inhibition of algae was determined using validated QSAR model for the Mechanism of Action (MechoA) in question (MechoA 1.1, i.e. non-polar narcosis) (Bauer et al., 2018). The QSAR model is based on validated data for a training set of 40 chemicals derived from 72-hour ErC50 test on algae, for which the concentrations of the test item had been determined by chemical analyses over the test period. The test item falls within the applicability domain of the model except for the descriptor domain. From a descriptor domain point of view, the test item falls within the intermediate domain where baseline toxicity cannot be experimentally measured accurately. Moreover, the toxicity may be greater than the water solubility limit. Based on a statistical k-NN approach (k = 3), the toxicity of the test item is estimated as the geometric mean between the toxicity value predicted using the regression line and the solubility cut-off line (with the confidence intervals being placed at these limits).

The 72h-ErC50 of the test item to algae was predicted at 0.73 mg/L (95% confidence interval: 0.26 – 2.09 mg/L)