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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

Based on valid short-term daphnia studies for two closely related structural analogues, the daphnid 48 hour EC50 for (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2 -one 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

EC50/LC50 for freshwater invertebrates:
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 and Raldeine A GD. Read-across from these two analogue substances 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 aquatic invertebrates and is justified based on the hypothesis that the target substance and two source substances 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 Methyl Ionone Alpha Iso 60 (Study No AT/N51/02) employed a static design. It is GLP compliant, conducted to OECD guideline 202 and using test material (53 -58% main isomer) which is represenative of the source substance. The study design covered the required exposure duration of 48 hours and included sufficient dose levels to enable the relevant determination of potency. Analysis of the test solutions was performed at the start of the test (0 hours) and at the end of the exposure period (48 hours). Based on TOC analysis, the amount of test item present was shown to relatively stable throughout the test period. The study was considered reliable with restrictions (reliability 2). The 48 hr EC50 was reported to be 3.7 mg/L (95% confidence interval 3.0 to 4.5 mg/L) based on calculated concentrations of test substance from mean measured TOC concentrations. These calculated concentrations were corrected for an alpha-iso-isomer purity of 55.5%. Given that the other components present in the test item are isomers of the major constituent and will contribute to the overall toxicity of the test item, this correction is not justified. Therefore the EC50 based on the assumption of 100% active test item has been estimated by the registrant. Two approaches were used giving a value of 2.05 mg/L and a range of > 2.2 and < 4.1 mg/L.

The study performed on Methyl Ionone (Study No 2469 -FF) was conducted under semi-static design with test medium renewal after 24 hours. It is GLP compliant, conducted according to OECD guideline 202 and using test material (94.4% sum of isomers, 78% n-isomers of methyl ionone) which is representative of the source substance. The study design covered the required exposure duration of 48 hours and included sufficient dose levels to enable the relevant determination of potency. Analytical confirmation of the test substance using GLC analysis was performed at 0 hours, 24 hours (before media renewal), 24 hours (after media renewal) and 48 hours. The measured concentrations, the means of which ranged from 80 to 89% of nominal concentrations, were steady throughout the exposure period. The study is considered reliable without restrictions (reliability 1). The 48 hr EC50 was determined to be 2.65 mg/L (95 confidence interval 1.82 to 5.32mg/L) and the 48 hr LC50 to be 3.11 mg/L (95% confidence interval of 1.82 to 5.32 mg/L) based on mean measured concentrations.

The 48h EC50 results for the two source substances are similar and within the same environmental classification band. Used in a weight of evidence approach, they are considered to give a reliable estimate of the 48h EC50 for (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one, which is a value of => 2.05 and <4.1 mg/L. The read-across is justified and considered adequate for the purposes of classification and risk assessment.