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Ecotoxicological information

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:
supporting study
Study period:
November 30th 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:
Ylang Ylang oil III is an UVCB substance. Regarding the different solubility of its constituents that make the testing difficult and a known fraction 89.95 %, 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-3 dated 5 october 2017. See test material information Ylang Ylang oil III: (QSAR)

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
Total exposure duration:
72 h
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
7.1 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.

Analytically Measured Aqueous Phase (AMAP) calculated at the predicted ErL50.

constituents

concentration in the WAF (mg.L-1)

germacrene D

0.026

farnesene

0.0071

β-caryophyllene

0.013

benzyl benzoate

0.43

Δ-cadinene

0.0040

α-humulene

0.0021

farnesyl acetate

0.0041

geranyl acetate

0.19

benzyl salicylate

0.18

farnesol

0.14

α-cadinol

0.14

α-copaene

0.00053

linalool

0.089

γ-muurolene

0.0029

cinnamyl acetate

0.060

benzyl acetate

0.043

methyl benzoate

0.036

geraniol

0.029

4-methylanisole

0.022

prenyl acetate

0.0071

Validity criteria fulfilled:
yes
Remarks:
QSAR model validated to be compliant with the OECD recommendation for QSAR modelling (OECD, 2004) described within the QMRF.
Conclusions:
The 72h ErL50 (mg test item.L-1) = 7.1 mg/L

Executive summary:

A calculation method was used to predict the inhibition of algal growth exposed to the test item Ylang Ylang oil III . 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 determined to be 7.1 mg/L.

Description of key information

An OECDTG 201 GLP test was performed with Raphidocelis subcapitata(formerly known as Pseudokirchneriella subcapitata).Water Accommodated Fractions (WAFs) were prepared and used as test concentrations. Six exponentially growing algal cultures were exposed to an untreated control, whereas three replicates per group were exposed to WAFs prepared at loading rate of  0.16, 0.80, 4.0, 20 and 100 mg Ylang Ylang III per litre under static conditions. In addition, two lower concentrations were prepared by adding 4% and 20% of the WAF at 0.16 mg/L, respectively, to the test medium.  The initial algal cell density was 10^4 cells/mL and the total exposure period was 72 hours. Samples for Total Organic Carbon (TOC) analyses were taken from WAFs at 0.80 mg/L and higher at the start and at the end of the test. Due to the potential volatile nature of the test item, the exposure was performed in airtight closed vessels with headspace reduced to a minimum.TOC-analysis is a non-specific method and the test substance is a UVCB, therefore the effect parameters were reported in terms of loading rates initially prepared.A flat dose response curve for the inhibition of growth rate was obtained with the loading rates of Ylang Ylang III resulting in 39% inhibition at the highest loading rate of 100 mg/L. Statistically significant inhibition of growth rate was found at all loading rates tested. However, only the inhibition found at loading rates of 0.16 mg/L and higher was found to be biologically relevant, i.e. was >10%.A flat dose response curve for the inhibition of yield was obtained with the loading rates of Ylang Ylang III resulting in 87% inhibition at the highest loading rate of 100 mg/L. Statistically significant inhibition of yield was found at all loading rates tested. The study met the acceptability criteria prescribed by the study plan and was considered valid.

In conclusion, under the conditions of this study with Raphidocelis subcapitata, the EL50 of Ylang Ylang III for growth rate inhibition (72h-ERL50) and yield inhibition (72h-EYL50) was >100 mg/L and 1.9 mg/L. While the EL10 for growth rate inhibition (72h-ERL10) and yield inhibition (72h-EYL10) was 0.73 mg/L and <0.0064 mg/L, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
0.73 mg/L

Additional information

An additional study is available to predict the ErL50 for algae by means of QSAR (Kreatis, 2017). In this study the algae 72h-ErL50 was concluded to be 7.1 mg/L. The experimental value is preferred over the predicted value, as the study was fully valid and resulted in an ErL50 and concrete ErL10 value, the QSAR only resulted in an ErL50.