2-hexylcyclopentan-1-one

Short-term toxicity to aquatic invertebrates

Description of key information

Jasmatone (2-hexylcyclopentanone) was predicted to have a 48-hr Daphnid LC50 of 3.99 mg/L using the ECOSAR (v1.11) neutral organics SAR. A closely structurally-related compound, Projasmon P (2-heptylcyclopentanone), was found in a guideline and GLP study to have an EC50 (48 hr) of 1.85 mg/L.  The latter is considered a worst-case conservative estimate based on the relative log Kow  values of the registration substance (3.9, measured value) and analogue substance (4.0, measured value).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

3.99 mg/L

Additional information

A weight-of-evidence approach has been used to assess the short-term aquatic toxicity to aquatic invertebrates based on a QSAR prediction for the registration substance, 2-hexylcyclopentanone (tradename: Jasmatone), and a valid study for the analogue substance, 2-heptylcyclopentanone (tradename: Projasmon P).

A QSAR prediction on the registration substance was undertaken using ECOSAR v1.11 (Neutral Organics ECOSAR class). The 48-hour daphnid LC50 was predicted to be 3.99 mg/L. The predicted value is considered reliable taking into account that the QSAR model is scientifically valid and Jasmatone falls within its applicability domain. The reliability is also supported by predicted and experimental data for analogues in the ECOSAR database (closest neighbours in the log Kow descriptor space) and the structural analogue, 2-heptylcyclopentanone which has an experimental value of 1.85 mg/L (see next paragraph) and which is predicted by ECOSAR v1.11 to have a daphnid LC50 of 1.639 mg/L.

A valid study is available for the analogue substance, 2 -heptylcyclopentanone (tradename: Projasmon P). The daphnid EC50 was determined to be 1.85 mg/L in a guideline, GLP study. The read-across is considered reliable on the basis of structural similarities (both substances are 2 -alkyl substituted cyclopentanones), the same aquatic toxicity mode of action class (neutral organic) and similar physicochemical properties. Moreover, given that aquatic toxicity increases with log Kow, the read-cross substance is expected to be more toxic than the registration substance (see table below) and hence the analogue value of 1.85mg/L is considered a worst-case conservative estimate for the aquatic toxicity of Jasmatone.

	REGISTRATION SUBSTANCE Jasmatone (2-hexylcyclopentanone) CAS No. 13074-65-2	ANALOGUE SUBSTANCE Projasmon P (2-heptylcyclopentanone) CAS No.137-03-1
Measured log Kow	3.91^1	4.4^2
Estimated log Kow (EPISuite/Kowwin v1.68)	3.508	3.999
Measured Daphnia 48hr LC50	-	1.85 mg/L
Estimated Daphnia 48hr LC50 (ECOSAR v1.11)	3.991 mg/L	1.639 mg/L

¹Measured value presented in this dossier
² Measured value taken from internal study report 14-E016 owned by the Lead Registrant

Both the QSAR predicted value of 3.99 mg/L and the read-across experimental value of 1.85 mg/L fall within the same acute aquatic hazard classification criterion range: E(L)C50 > 1 mg/L and <= 10 mg/L. Thus the above weight-of-evidence approach is considered suitable for regulatory purposes.

Given that the read-across value is a conservative estimate (see discussion and table above), the reliable QSAR predicted value of 3.99 mg/L is considered a more realistic estimate of the aquatic toxicity of Jasmtone and as such has been selected as the key value.