1,4-bis[(2,6-diethyl-4-methylphenyl)amino]anthraquinone

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

06 April 2022 to 07 April 2022

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

Remarks:

The test item falls within the applicability domain of the models except for the descriptor domain. Therefore, both predicted TOXICITY TO ALGAE (72-HOUR ErC50) and TOXICITY TO ALGAE (72-HOUR NOECr) are considered as extrapolations. These results can be considered as reliable with restrictions (descriptor domain).

Justification for type of information:

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

2. MODEL (incl. version number)
iSafeRat® algErC50 v1.9
iSafeRat® algNOEC v1.2

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
CCc1cc(C)cc(CC)c1Nc2ccc(Nc3c(CC)cc(C)cc3CC)c4C(=O)c5ccccc5C(=O)c24

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

5. APPLICABILITY DOMAIN
See attached Study Report and QPRF in Annex

6. ADEQUACY OF THE RESULT
See attached Study Report and QPRF in Annex

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 TOXICITY TO ALGAE (72-HOUR ErC50 and NOECr) was determined using iSafeRat® algEC50 and iSafeRat® algNOEC, two validated QSAR models for the Mechanism of Action (MechoA) in question (MechoA 1.1, i.e. non-polar narcosis) (Bauer et al., 2018). The QSAR models provide in silico predictions for the 72-hour ErC50 and NOECr values that can effectively be used in place of an experimentally derived results. The QSAR models are based on validated data for a training set of 40 chemicals derived from 72-hour ErC50 and 32 chemicals derived from 72-hour NOECr test on algae, for which the concentrations of the test item had been determined by chemical analyses over the test period.

GLP compliance:

no

Remarks:

QSAR model

Analytical monitoring:

no

Remarks:

QSAR model

Details on sampling:

not applicable

Vehicle:

no

Remarks:

QSAR model

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 model

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:

not applicable

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 models. This small difference is not expected to significantly contribute to the variability of the 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 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 toxic values found in experimental data.

Salinity:

not applicable

Conductivity:

not applicable

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):

not required

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 0.003 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other:

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 0.003 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other:

Details on results:

The test item falls within the applicability domain of the models except for the descriptor domain. Therefore, both predicted TOXICITY TO ALGAE (72-HOUR ErC50) and TOXICITY TO ALGAE (72-HOUR NOECr) are considered as extrapolations. These results can be considered as reliable with restrictions (descriptor domain).

Results with reference substance (positive control):

not applicable

Reported statistics and error estimates:

95% confidence interval (α = 0.05) for 72h-ErC50: not applicable
95% confidence interval (α = 0.05) for 72h-NOECr: not applicable

Applicability Domain

Descriptor domain

The Subcooled Liquid Water Solubility value (< -6.594 in log10 (mol/L)) given as the input to the iSafeRat® algErC50 model falls within the intermediate domain of the model between a Subcooled Liquid Water Solubility of -9.34 to -4.38 in log10 (mol/L) where baseline toxicity cannot be experimentally measured accurately. In this intermediate domain, the toxicity may to be greater than the water solubility limit. For confirmation, a statistical k-NN approach (k = 3) is performed on the data of substances found to be in the intermediate domain of the model. The toxicity of the three closest neighbours based on the solubility are considered. Based on these data, either the toxicity of the test item is expected to be greater than the limit of solubility, or the toxicity is estimated by the geometric mean between the toxicity value predicted using the regression line and the solubility cut-off line. According to this analysis, the toxicity of the test item is estimated as greater than the water solubility limit.

 

The Subcooled Liquid Water Solubility value (< -6.594 in log10 (mol/L)) given as the input to the iSafeRat® algNOECr model does not fall within the descriptor domain of the model between a Subcooled Liquid Water Solubility of -5.154 to 0.490. Therefore, the prediction is considered as an extrapolation.

Structural fragment domain

The variability of structure in the training set is not considered as a relevant domain since the model is based on a mechanistic approach (mechanism of action). Since the MechoA is related to the molecular structure, the following list of chemical moieties can give an overview of the structural domain:

• Alcohol


• Alkane


• Alkene


• Anthraquinones


• Aromatic hydrocarbons and polycyclic aromatic hydrocarbon


• Ester


• Ether


• Halogenated hydrocarbons


• Ketone

The test item as an anthraquinone can be taken into account by the model.

Mechanistic domain
The iSafeRat® algErC50 model 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 iSafeRat® algNOECr model can only reliably predict the aquatic toxicity for chemicals with the mechanism of action of non-polar narcosis (MechoA 1.1).

The MechoA of molecules is predicted directly from the structure. The test item as an  aminoanthraquinone is expected to exert a MechoA 1.1 & m4.3: Non-polar narcosis for all species & metabolisation into nitroso generating protein and DNA adducts, oxidative stress, DNA adducts, cancer development for mammals only (Bauer et al., 2018). Therefore, the test item can be taken into account by the model in order to predict toxicity to non-mammal aquatic organisms.

Validity criteria fulfilled:

yes

Conclusions:

The test item falls within the applicability domain of the models except for the descriptor domain. Therefore, both predicted TOXICITY TO ALGAE (72-HOUR ErC50) and TOXICITY TO ALGAE (72-HOUR NOECr) are considered as extrapolations. These results can be considered as reliable with restrictions (descriptor domain).
The TOXICITY TO ALGAE (72-HOUR ErC50 and NOECr) of the test item was both predicted as greater than the water solubility value within the exposure period of the test.
95% confidence interval (α = 0.05) for 72h-ErC50: not applicable
95% confidence interval (α = 0.05) for 72h-NOECr: not applicable

Executive summary:

Two Quantitative Structure-Activity Relationship (QSAR) models were used to calculate the TOXICITY TO ALGAE (72-HOUR ErC50 and NOECr) of the test item. These QSAR models have been validated to be compliant with the OECD  recommendations for QSAR modeling (OECD, 2004) and predict the endpoint values 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 criterions predicted were the Median Effective Concentration (ErC50), a statistically derived concentration which is expected to cause 50% inhibition of intrinsic rate of growth of the test system and the No Observed Effect Concentration (NOECr), a tested concentration which is expected to cause no effect on intrinsic rate of growth of the test system. Both criterions were determined for a period exposure of 72 hours.

 

The TOXICITY TO ALGAE (72-HOUR ErC50 and NOECr) was determined using iSafeRat® algEC50 and iSafeRat® algNOEC, two validated QSAR models for the Mechanism of Action (MechoA) in question (MechoA 1.1, i.e. non-polar narcosis) (Bauer et al., 2018). The QSAR models provide in silico predictions for the 72-hour ErC50 and NOECr values that can effectively be used in place of an experimentally derived results. The QSAR models are based on validated data for a training set of 40 chemicals derived from 72-hour ErC50 and 32 chemicals derived from 72-hour NOECr 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 models except for the descriptor domain. Therefore, both predicted TOXICITY TO ALGAE (72-HOUR ErC50) and TOXICITY TO ALGAE (72-HOUR NOECr) are considered as extrapolations. These results can be considered as reliable with restrictions (descriptor domain).

The TOXICITY TO ALGAE (72-HOUR ErC50 and NOECr) of the test item was both predicted as greater than the water solubility value within the exposure period of the test.
95% confidence interval (α = 0.05) for 72h-ErC50: not applicable
95% confidence interval (α = 0.05) for 72h-NOECr: not applicable

Description of key information

72h-NOECr and ErC50 (algae) > solubility limit; iSafeRat® High-Accuracy-Quantitative Structure-Activity Relationship; KREATiS (2022).

To be confirmed with the new experimental study planned on the registered substance. 

Additional information

To strengthen the reliability of the HA-QSAR prediction and the category approach, experimental algae studies are available on the source substances, Reinblau RLW (CAS No 41611-76-1), Solvent Violet 36 (CAS No 82-16-6) and Solvent Green 28 (CAS No 4851-50-7). Both substances are members of the category. See the category approach justification document, attached in section 13, for further details.

Furthermore, an experimental algae OECD TG 201 study will be performed on the registered substance, Reinblau BLW. The dossier will be updated with the new study as soon at it becomes available.

Global overview of the category approach for the endpoint:

	Solvent Violet 36	Solvent Green 3	Reinblau RLW	Reinblau BLW	Solvent Blue 104^#	Solvent Green 28
Toxicity to aquatic algae	72h-ErC10 and ErC50 (D.subspicatus) > 100 mg/L (nominal) or > 0.16 mg/L (measured)^$   72h-NOECr and ErC50 (algae) > solubility limit*	72h-NOECr and ErC50 (algae) > solubility limit*   Other Lead Registrant data available but not considered key	72h-ErC10 and ErC50 (D.subspicatus) > 100 mg/L (nominal)^$   72h-NOECr and ErC50 (algae) > solubility limit*	Study planned (OECD TG 201)   72h-NOECr and ErC50 (algae) > solubility limit*	72h-NOECr and ErC50 (algae) > solubility limit*	72h-ErC10 and ErC50 (D.subspicatus) > 100 mg/L (nominal)^$

^# not registered by LANXESS

* iSafeRat® High Accuracy QSAR predictions (KREATiS, 2022)

^$ experimental studies