3,7-dimethylocta-1,3,6-triene

Endpoint summary

Description of key information

For Ocimene the following results were derived:

Guideline	Test species	Endpoint	Result	Remark
OECD TG 202, under GLP conditions	Daphnia magna	48-h EC50	1.47 mg/L	Data derived from read-across to Myrcene (CAS# 123-35-3). Semi-static conditions and measured concentrations were used. Key study.
OECD TG 201, under GLP conditions	Pseudokirchneriella subcapitata	48-h* ErC50 48-h* ErC10	0.342 mg/L 0.274 mg/L	Data derived from read-across to Myrcene (CAS# 123-35-3). Static conditions and measured concentrations were used. Key study.

* The test was terminated after 48 hours due to significant loss in the flasks. However, as test substance still remained in the flasks at 48 hours and all validity criteria were met, following the OECD Guideline, it was considered acceptable to base the test results on the 48 h values.

Additional information

The aquatic toxicity of Ocimene is based on read-across from Myrcene. The read-across documentation is for Daphnia and algae and is included in the study records of the respective endpoints. The read-across justification is also presented below:

Aquatic toxicity ofOcimene (CAS #13877-91-3) based on read-across from data available for Myrcene (CAS #123-35-3)

 

Introduction and hypothesis for the analogue approach

Ocimene has a poly-unsaturated alkene backbone consisting of 8 carbon atoms containing 3 double bonds and methyl substituents on the third and seventh position.For this substance no aquatic toxicity information is available.For assessing the aquatic toxicity of Ocimene the analogue approach is selected because for a closely related analogue, Myrcene,aquatic toxicityinformation is available which can be used for read-across.

Hypothesis: Ocimene has the same aquatic toxicity potential as Myrcene asboth substances are very similar in structures and related properties.

Available information:For the source chemical Myrcenedata are available from GLP guideline studies with aquatic invertebrates and aquatic algae. The EC50 for Daphnia and algae and the EC10 for algae were1.47 mg/L, 0.342 mg/L and 0.274 mg/L, respectively. The data are reliable without restrictions (Klimisch 1).

Target and source chemical

Chemical structures of the target chemical and the source chemical are shown in the data matrix, including physico-chemical properties and available ecotoxicological information.

Purity / Impurities

Ocimene is a multi-constituent consisting of two isomers E (66%, CAS 3779-61-1) and Z (29%, CAS 3338-55-4) and an impurity1-methylidene-4-(prop-1-en-2-yl)cyclohexane
Analogue approach justification
According to Annex XI section 1.5, read-across can be used to replace testing when the similarity can be based on a common backbone and a common functional group.

Analogue selection: Myrcene was considered the closest analogue considering molecular weight and chemical structure for which adequate algae and Daphnia information was available.
Structural similarities and differences:Ocimene and Myrcene have the same alkene backbone, with 3 double bonds which can be conjugated and are branched with a methyl group on two positions. The one difference is that Ocimene (trans) has the double bond in the long alkene chain, while Myrcene has the double bond attached to the methyl group branching from the alkene chain. For both substances this results in a conjugated bond with the primary double bond (at the top of the structure, see data matrix).
Bioavailability:Ocimene and Myrcene have similar bioavailability based on similarities in being liquids, molecular weight and physico-chemical properties: e.g. Log Kows are 5.4 and 4.8, respectively. The differences in log Kow are expected to be due to experimental variability, because the structural features are very similar and also the calculated log Kow values (ECOSAR) are very similar 4.8 and 4.9, for Ocimene and Myrcene, respectively.
Reactivity: BothOcimene and Myrcene contain a conjugated double bond and therefore the reactivity is expected to be similar. This conjugated double bond is not presenting reactivity beyond the neutral organic mode of action as both substances are similarly categorized in ECOSAR and OECD Toolbox.
Uncertainty of the prediction:There is no remaining uncertainty in view of the arguments above. There is no need to convert the Myrcene toxicity data towards Ocimene, because of the similarities in molecular weight and log Kows (the differences in measured log Kow are thought to be due to experimental error).
Conclusions for hazard assessment and environmental classification
Hazard assessment:For Ocimene no experimental aquatic toxicity information is available. Read-across is performed from the structural analogue Myrcene. The lowest acute value of Myrcene is the EC50 for algae: 0.34 mg/L; the one available EC10 is 0.27 mg/L. A conversion is not considered necessary, therefore the same values will be used for Ocimene.
Final conclusion on hazard and C&L: The lowest EC50 for Ocimene is the ErC50 for algae being 0.34 mg/L and the one long-term for algae is 0.27 mg/L. These values will be taken forward to the C&L section.

 

Data matrix presenting the information to read-across for Ocimene from Myrcene

Common name	Ocimene	Myrcene
Chemical name	(3E)-3,7-dimethylocta-1,3,6-triene, (3Z)-3,7-dimethylocta-1,3,6-triene	1,6-Octadiene, 7-methyl-3-methylene-
Chemical structures	3E3Z
Cas no	3779-61-1 and 3338-55-4
CAS no generic	13877-91-3	123-35-3
REACH registered	2018	Registered
EINECS	237-641-2	204-622-5
Empirical formula	C10H16	C10H16
Molecular weight	136.24	136.24
Physical state	Liquid	Liquid
Melting point	<-20 °C (IFF measured)	<-80 °C (ECHA dissemination site)
Boiling point	184.1 °C (IFF measured)	165oC (ECHA dissemination site)
Vapour pressure	220.7 Pa (at 24 °C) (IFF measured)	267 Pa (ECHA dissemination site)
Water solubility	14.5 (at 24 °C) (IFF measured)	5.1 (ECHA dissemination site)
Log Kow	5.4 (at 25 °C) (IFF measured) 4.8 (EpiSuite prediction)	4.8 (ECHA dissemination site) 4.9 (EpiSuite prediction)
Aquatic toxicity
Acute Daphnia EC50 in mg/L	Read-across	1.47 mg/L
Acute aquatic algae 72-h ErC50 in mg/L	Read-across	0.342 mg/L
Long-term algae 72-h ErC10 in mg/L	Read-across	0.274 mg/L