Registration Dossier

Ecotoxicological information

Short-term toxicity to fish

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Description of key information

Based on a valid short-term fish study for the closely related substance Isoraldeine 70, the fish 96 hour LC50 for (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2 -one is estimated to be 10.9 mg/L.The read-across is justified and considered adequate for the purposes of classification and risk assessment.

Key value for chemical safety assessment

LC50 for freshwater fish:
10.9 mg/L

Additional information

A study to assess the short-term toxicity to fish is not available for the registration substance. However, a valid short-term fish study does exist for the related substance; Isoraldeine 70. Read-across from this source substance is considered to give a reliable estimate of the short-term toxicity of (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one to fish and is justified based on the hypothesis that the target substance and source substance will have similar ecotoxicological properties as a result of structural similarity (both the target and source substance consist of isomers), the same mode of action and similar physicochemical properties. A detailed justification for the proposed read-across in-line with the ECHA RAAF guidelines is provided in the target endpoint record.

The study performed on Isoraldeine 70 (Study Report Number: B-161751, Schlienger 1992) employed a static design. It is GLP compliant, conducted to OECD guideline 203 and using test material (approximately 60% iso-alpha-methyl ionone, 91.4% total of all isomers) which is representative of the source substance. The study design covered the required exposure duration of 96 hours and included sufficient dose levels to enable the relevant determination of potency. Analytical confirmation was not performed and results were based on nominal concentrations. However, give the stability of other related methyl ionone source substances in both daphnia and algae studies (see IUCLID endpoints 6.1.3. and 6.1.5 respectively), the study was considered reliable with restrictions (reliability 2). The 96 hr EC50 was determined to be 10.9 mg/L by plotting the log of the various test concentrations against percentile mortality.