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Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Study period:
From 2018-08-24 to 2018-08-30
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
Principles of method if other than guideline:
The acute toxicity to aquatic algae was determined using a validated QSAR for the Mode of Action in question. The first step of the iSafeRat mixture toxicity calculation employs phase equilibrium thermodynamics in order to determine the concentrations of each constituent within the WAF. This fraction equates to the analysable fraction of a WAF study.
Within the WAF, the constituents also partition between themselves further reducing the bioavailable fraction and thus the toxicity of the mixture compared to the individual constituents. In the calculation the second step is to remove this non-bioavailable fraction.
The final step is to determine the truly bioavailable fraction of the WAF per constituent. The ErC50s of each constituent are already known from literature or calculated using the iSafeRat QSAR model. An additivity approach (based on Chemical Activity of each constituent) is used in order to calculate the Effective Loading rate of the WAF.
The method has been validated using data derived from 72-hour ErC50 tests on aquatic 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.
GLP compliance:
no
Specific details on test material used for the study:
Not applicable.
Analytical monitoring:
not required
Details on sampling:
Not applicable.
Vehicle:
no
Details on test solutions:
Not applicable.
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
Not applicable.
Test type:
other: Calculatio method
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Remarks on exposure duration:
72h-ErL50 (effective loading rate of WAF)
Post exposure observation period:
Not appliable.
Hardness:
Hardness is not a necessary component of the WAF calculation.
Test temperature:
The Temperature is not a necessary component of the WAF calculation.
pH:
The pH is not a necessary component of the WAF calculation .
Dissolved oxygen:
The oxygen concentration is not a necessary component of the WAF calculation.
Salinity:
Salinity is not a necessary component of the WAF calculation.
Nominal and measured concentrations:
The calculation determines measured concentrations.
Details on test conditions:
Calculation method.
Reference substance (positive control):
not required
Duration:
72 h
Dose descriptor:
other: ErL50
Remarks:
effective loading rate
Effect conc.:
7.7 mg/L
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: Based on the typical composition provided by the supplier
Details on results:
Not applicable.
Results with reference substance (positive control):
Not applicable.
Reported statistics and error estimates:
Not applicable.

Analytically Measured Aqueous Phase (AMAP) calculated at the predicted EL50:

constituents concentration in the WAF (mg.L-1)
Constituent 1 1.1
Constituent 2 0.98
Constituent 3 0.88
Constituent 4 0.87
Constituent 5 0.47
Constituent 6 0.37
Constituent 7 0.22
Constituent 8 0.32
Constituent 9 0.18
Constituent 10 0.23
Constituent 11 0.19
Constituent 12 0.15
Constituent 13 0.14
Constituent 14 0.12
Constituent 15 0.12
Constituent 16 0.12
Constituent 17 0.11
Constituent 18 0.1
Constituent 19 0.085
Validity criteria fulfilled:
yes
Conclusions:
72h-ErL50 for typical composition of Thuja Oil is of 7.7 mg test item/L.
Executive summary:

Thuja Oil is a Natural Complex Substance (UVCB) with a well-defined composition (92.1%).

Its acute toxicity to aquatic algae has been investigated using an in-house calculation method that replaces an OECD 201 study and guideline for Testing of Chemicals No. 23 (i.e. WAF conditions). The “typical” composition proposed by the supplier of the substance has been investigated.

The first step of the iSafeRat mixture toxicity calculation employs phase equilibrium thermodynamics in order to determine the concentrations of each constituent within the WAF. This fraction equates to the analyzable fraction of a WAF study.

Within the WAF, the constituents also partition between themselves further reducing the bioavailable fraction and thus the toxicity of the mixture compared to the individual constituents. In the calculation the second step is to remove this non-bioavailable fraction.

The final step is to determine the truly bioavailable fraction of the WAF per constituent. The ErC50s of each constituent are already known from literature or predicted using the iSafeRat QSAR model. Each value has been included as a supporting study in the IUCLID. An additivity approach (based on Chemical Activity of each constituent) is used in order to calculate the Effective Loading rate of the WAF.

Using this approach, the 72-h ErL50 was 7.7 mg test material/L for the typical composition of Thuja Oil. ErL50 was based on growth rate.

Based on the results of this study, Thuja Oil would not be classified as acute 1 to aquatic organisms in accordance with the classification of the CLP.

This toxicity study is acceptable and can be used for that endpoint.

 

Results Synopsis

Test Type: Calculation method

ErL50: 7.7 mg test material/L for typical composition

Description of key information

A calculation methodthat replaces an OECD 201 study and guideline for Testing of Chemicals No. 23 (i.e. WAF conditions) has been used to assess the acute toxicity of Thuja Oil to algae.

A 72h-ErL50 of 7.7 mg/L has been estimated.

Based on the results of this study, Thuja oil would not be classified as acute 1 to aquatic organisms in accordance with the classification of the CLP.

Key value for chemical safety assessment

EC50 for freshwater algae:
7.7 mg/L

Additional information

The acute toxicity to aquatic algae of the UVCB Thuja Oil has been investigated using a reliable in-house calculation method that replaces an OECD 201 study and guideline for Testing of Chemicals No. 23 (i.e. WAF conditions). The “typical” composition proposed by the supplier of the substance has been investigated.

The first step of the iSafeRat mixture toxicity calculation employs phase equilibrium thermodynamics in order to determine the concentrations of each constituent within the WAF. This fraction equates to the analyzable fraction of a WAF study.

Within the WAF, the constituents also partition between themselves further reducing the bioavailable fraction and thus the toxicity of the mixture compared to the individual constituents. In the calculation the second step is to remove this non-bioavailable fraction.

The final step is to determine the truly bioavailable fraction of the WAF per constituent. The ErC50s of each constituent are already known from literature or predicted using the iSafeRat QSAR model. Each value has been included as a supporting study in the IUCLID. An additivity approach (based on Chemical Activity of each constituent) is used in order to calculate the Effective Loading rate of the WAF.