[No public or meaningful name is available]

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

10 August 2022

Reliability:

2 (reliable with restrictions)

Justification for type of information:

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.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2022

Report date:

2022

Materials and methods

Principles of method if other than guideline:

The TOXICITY TO ALGAE (72-HOUR ErC50 and NOECr) was determined using iSafeRat® algEC50 and iSafeRat® algNOEC. The purpose of this study is to accurately predict the toxicity to algae as would be expected in a laboratory experiment following the OECD Guideline 201 (OECD, 2006) and EC method C.3 (European Commission, 2008) for specific, named mechanisms of action. 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 models are based on a simple linear regression line between Subcooled Liquid Solubility Water (SLWS) and the growth rate inhibition to algae (ErC50 or NOECr) following the methodology outlined in ECETOC (2013) and Thomas et al. (2015). In brief, the algorithm used was an updated and improved version of that used by ECETOC for nonpolar narcotic compounds which was then validated using an external test set. The general equation used by the model is:

log ErC50 (or NOECr) = a x log SLWS + b

The water solubility values are corrected to take into account the Subcooled Liquid Water Solubility (SLWS) which is
an expression of the chemical activity of a pure compound within a given medium. The choice of the SLWS is justified in order to compare liquids and solids within the same dataset. Indeed, the solids have an entropy of fusion different to liquids as demonstrated by Yalkowsky (1979). Consequently, the water solubility of the solids is corrected using their melting point according to the following equation:
SLWS solid = WS solid/e (6.79(1-MP/298))x(ml/L)



SLWS solid: Subcooled Liquid Water Solubility (SLWS) of a given compound with solid state at 25°C.
WS solid: Water Solubility (WS) of a given compound with solid state at 25°C (as measured).
MP: Melting Point of the given compound (K).

Species: Results from the following species were used in the regression:
Raphidocelis subcapitata (formerly known as Pseudokirchneriella subcapitata),
Desmodesmus subspicatus, Scenedesmus quadricauda
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 duration: Results from a test duration of 72 hours only were used for the models.
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.
Test type: 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.
Chemical analysis: Studies were used for QSAR model development only where sufficient evidence was
presented to determine that the substance was stable under test conditions (i.e.
maintained 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.
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.
Klimisch score: The studies used in the dataset were considered valid under the OECD guideline
and REACH regulation (European Parliament and European Union Council, 2006)
(i.e. Klimisch score 1 or 2) by registrants of the substances included in the training
and test sets were revalidated by KREATiS and the critical parameters of the study
were considered to be within acceptable limits.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Reaction products of 2,3; 2,4; 2,5 and 2,6 mixed xylidenes, C7 and C8 linear substituted naphthols and diazonium salts

Molecular formula:

Not available: variable

IUPAC Name:

Reaction products of 2,3; 2,4; 2,5 and 2,6 mixed xylidenes, C7 and C8 linear substituted naphthols and diazonium salts

Details on test material:

CAS No 92257-31-3
EC-No. 296-120-8
Composition SR164:1 is a mixture of compounds with octyl, heptyl, ethyl and methyl groups of
variable numbers and positions. For the purpose of this study, only the smallest and
biggest constituents of SR164:1 were investigated.

Specific details on test material used for the study:

SR 164:1 smallest constituent Oc1c(CCCCCCC)cc2ccccc2c1N=Nc(cc3CC)ccc3N=Nc4ccccc4
SR 164:1 biggest constituent Oc1c(CCCCCCCC)cc2ccccc2c1N=Nc(cc3C)c(C)cc3N=Nc4c(C)cc(C)cc4

Results and discussion

Effect concentrations

Key result

Duration:

72 h

Dose descriptor:

EC50

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: ErC50 > solubility limit for both the smallest and largest constituents of the test substance

Applicant's summary and conclusion

Conclusions:

The QSAR models used to achieve the study have been fully validated following the OECD recommendations (OECD, 2004). For both constituents, the test item falls partially within the applicability domain of the model.
Therefore, the predicted TOXICITY TO ALGAE (72-HOUR ErC50) is considered as an extrapolation” because the solubility of the substance is so low that it falls beyond the point at which toxicity data crosses the solubility regression line. As no toxicity can be observed beyond the solubility limit (and any effect concentrations can only be related to physical interaction which is not environmentally relevant), it is no longer possible to construct a regression line beyond the solubility limit. However, the lack of statistical fit does not indicate that the conclusion
“toxicity >solubility limit” is erroneous.
No algae data are available in our dataset for substances with a solubility as low as that of the test items, and strictly speaking the results should be considered as an extrapolation. However, because any substance with a solubility lower than the solubility limit regression line used in this QSAR will not meet the criteria of toxicity examined in this endpoint. The endpoint can be considered as falling under the domain >solubility limit.
This result should be considered as reliable with restrictions (descriptor domain, structural domain). The 72-hour NOEC was not determined because the QSAR model iSafeRat® algNOEC is only applicable for chemicals with the mechanism of action of non-polar narcosis (MechoA 1.1).
The TOXICITY TO ALGAE (72-HOUR ErC50) of both constituents of the test item was greater than their subcooled liquid water solubility.
95% confidence interval (α = 0.05) for 72h-ErC50: not applicable

Executive summary:

Introduction. 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.
Methods. 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 1.2, i.e. polar narcosis of alkyl-/alkoxy-phenols) (Bauer et al., 2018). The QSAR models are based on validated data for a training set of 8 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 72-hour NOEC was not determined because the QSAR model iSafeRat® algNOEC is only applicable for chemicals with the mechanism of action of non-polar narcosis (MechoA 1.1).

Results. The results below are the toxicity values anticipated during a 72-hour study on algae based on measured
concentrations.

Constituents	Constituents 72h-ErC50 (mg test item/L)	72h-NOECr (mg test item/L)
SR 164:1 smallest constituent	> solubility limit	Not Determined
SR 164:1 biggest constituent	> solubility limit	Not Determined