Reaction mass of (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one and (E) -1-(2,6,6-trimethylcyclohex-2-en-1-yl)pent-1-en-3-one and (E) -1-(2,6,6-trimethylcyclohex-1-en-1-yl)pent-1-en-3-one

Short-term toxicity to aquatic invertebrates

Description of key information

Based on valid short-term daphnia studies for two closely related structural analogues, the daphnid 48 hour EC50 for the registered substance is estimated to be => 2.05 and < 4.1 mg/L. The determined value of 2.65 mg/L from the most reliable study has been selected as the key value for chemical safety assessment.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

2.65 mg/L

Additional information

A study to assess the short-term toxicity to aquatic invertebrates is not available for the registration substance. However, valid short-term daphnia studies exist for two analogue substances; Methyl Ionone Alpha Iso 60 (CAS 127-51-5) and Methyl Ionone (CAS 1335-46-2; trade quality Raldeine A GD). Both studies are GLP compliant, conducted to OECD 202 guidelines, covered the required exposure duration of 48 hours and included sufficient dose levels to enable the relevant determination of potency. The EC50 value from each study was determined to be  =>2.05 and < 4.1 mg/L (Methyl Ionone Alpha Iso 60 , study reliability 2) and 2.65 mg/L (Raldeine A GD , study reliability 1).

A detailed justification for the proposed read-across in-line with the ECHA RAAF guidelines is provided in the target endpoint record. This shows that the aquatic toxicity of the target substance and the two source substances, which consist of the same isomers but in different ratios, are expected to be similar on the basis that all individual isomers present in these substances will exhibit similar aquatic toxicity due to their structural similarity, same mode of action and similar lipophilicity and that, therefore, any variation in the ratio of isomers between substances will not significantly influence their aquatic toxicity properties.  This is supported by the above daphnia 48h EC50 results for both source substances and also the similar toxicity to green algae (see endpoint 6.1.5).

Therefore, used in a weight-of-evidence approach the above daphnia 48h EC50 results are considered to give a reliable estimate of the 48h EC50 for Reaction mass of (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one and (E)-1-(2,6,6-trimethylcyclohex-2-en-1-yl)pent-1-en-3-one and (E)-1-(2,6,6-trimethylcyclohex-1-en-1-yl)pent-1-en-3-one. Furthermore, the EC50 values obtained from both source studies are within the same environmental classification band and as such are considered adequate for regulatory purposes. The value of 2.65mg/L, obtained from the most reliable study, has been selected as key value for the purposes of classification and labelling.