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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:
(Q)SAR
Adequacy of study:
key study
Study period:
22 August 2017
Reliability:
2 (reliable with restrictions)
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
Justification for type of information:
Cedarwood Virginia oil is an UVCB substance. Regarding the different solubility of its constituents that make the testing difficult and a known fraction 82.55%, calculation from the ecotoxicity of the known constituent appears as an acceptable approach.
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 the Guideline for Testing of Chemicals No. 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test", (1) referenced as Method C.3 of Commission Regulation No. 440/2008 (2) 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). It has been validated in an internal publication for MOA 1 (non-polar narcosis) and acute exposure (Bicherel and Thomas, 2014) (3). The algorithm is based on a QSAR model which has been validated to be compliant with the OECD recommandations for QSAR modeling (OECD, 2004) (4). 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.

(1) OECD Guideline for testing of chemicals No. 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test", adopted March 23, 2006; Annex 5 corrected July 28, 2011.
(2) Commission Regulation (EC) No. 761/2009 amending Regulation (EC) No. 440/2008, Part C, C.3.: "Algal Inhibition Test", p. 36-56, Official Journal of the European Union (EN), dated August 24, 2009, L 220:1-94.
(3) Bicherel P and Thomas PC (2014) iSafeRat® WAF calculation method to predict acute aquatic toxicity. Position paper prepared by KREATiS.
(4) OECD (2004) Principles for the validation, for regulatory purposes, of (Quantitative) Structure Activity-Relationship Models, http://www.oecd.org/env/ehs/risk-assessment/oecdquantitativestructure-activityrelationshipsprojectqsars.htm.
GLP compliance:
no
Remarks:
Not required for a calculation based on multiple QSARs method.
Specific details on test material used for the study:
Typical legal entity composition provided by the registrant of the substance, REACH NCS Sesquiterpenes HC / Alc consortium. Composition is as agreed in the Substance Identification Profile version-8 dated 12 Sept. 2017.

constituents mass fraction (%) within typical composition
α-cedrene: 29.72
cedrol: 20.30
thujopsene: 16.04
β-cedrene: 5.46
widdrol: 4.15
β-chamigrene: 1.19
β-caryophyllene: 1.09
cuparene: 0.93
β-himachalene: 0.93
α-duprezianene: 0.90
α-chamigrene: 0.71
α-bisabolol: 0.67
α-himachalene: 0.46
TOTAL: 82.55
Analytical monitoring:
no
Remarks:
Not relevant for a calculation based on multiple QSARs method
Details on sampling:
Not relevant.
Test organisms (species):
other: green algae
Water media type:
freshwater
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
2.9 mg/L
Nominal / measured:
nominal
Conc. based on:
other: Water Accomodated Fraction
Basis for effect:
growth rate
Remarks on result:
other: Calculation based on QSARs.
Remarks:
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.

At the loading rate the expected concentrations of each constituent in the mixture (based on thermodynamic calculation) are as follows:

constituents

concentration in the WAF (mg.L-1)

α-cedrene

0.012

cedrol

0.59

thujopsene

0.011

β-cedrene

0.005

widdrol

0.12

β-chamigrene

0.034

β-caryophyllene

0.0013

cuparene

0.0014

β-himachalene

0.0013

α-duprezianene

0.00055

α-chamigrene

0.015

α-bisabolol

0.019

α-himachalene

0.015

Validity criteria fulfilled:
yes
Remarks:
QSAR model validated to be compliant with the OECD recommandations for QSAR modeling (OECD, 2004). The validated training set consists of 40 chemicals.
Conclusions:
The 72h ErL50 (mg test item.L-1) = 2.9 mg/L

Executive summary:

A calculation method was used to predict the inhibition of algal growth exposed the test item Cedarwood Virginia oil. 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", (1) referenced as Method C.3 of Commission Regulation No. 440/2008 (2) adapted for testing of a mixture using the WAF method.

By using a "known constituents approach" based on non-polar-narcosis MOA-1 QSARs and WAF "adapted water solubilities”, the algae 72h-ErL50 is estimated 2.9 mg/L.

Description of key information

A calculation method was used to predict the inhibition of algal growth exposed the test item Cedarwood Virginia oil. 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", (1) referenced as Method C.3 of Commission Regulation No. 440/2008 (2) adapted for testing of a mixture using the WAF method.

By using a "known constituents approach" based on non-polar-narcosis MOA-1 QSARs and WAF "adapted water solubilities”, the algae 72h-ErL50 is estimated 2.9 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
2.9 mg/L

Additional information