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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Based on a valid algal inhibition study for a closely related analogue substance, the 96h EC50 for 2,6,6-trimethylcyclohexa-1,3-dienecarbaldehyde was estimated to be 13 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
13 mg/L

Additional information

In the absence of experimental data on the registered substance, the toxicity to aqautic algae and cyanobacteria has been assessed based on read-across. The analogue approach has been used which is based on the hypothesis that the source substance (Shisolia) and target substance (Safranal P) are expected to have similar ecotoxicological properties as a result of structural similarity, the same expected mode of action for aquatic toxicity and similar hydrophobicity (as modelled by log Kow). A detailed justification for the proposed read-across in-line with the ECHA RAAF guidelines is provided in the target endpoint record.

The effect of the source substance on the growth of the green alga Pseudokirchneriella subcapitata was determined according to OECD guideline 201. It is a GLP compliant study conducted with a test material representative of the source substance and in compliance with agreed protocols, with no or minor deviations from the standard test. The study was considered valid.

As the test item is a volatile substance, the test was performed using flasks completely filled with test medium and tightly sealed with glass stoppers to avoid losses of test item. In order to evaluate the influence of the presence of light and algae on the stability of the test item, additional flasks containing the test medium were set up in a closed system. Three different incubation conditions, “Light with algae”, “Light without algae”, and “Darkness without algae”, were applied.

Over the test period of 96 hours the test item concentrations in the test media decreased. In the parallel stability study the main loss of test substance in the test water was attributed to adsorption to the growing algal biomass which accounted for approximately 13% decrease of the starting concentration over the period of 48 hours, 27% over 72 hours, and, 72% over 96 hours. This loss was considered in the calculation of the study endpoints, as the algal cells were, in effect, exposed to this complimentary fraction of test substance. Losses due to aqueous photolysis were only in the order of 5%. The study design covered the required exposure duration of 72/96 hours and included sufficient dose levels to enable the relevant determination of potency. Therefore, the study results are adequate for the purpose of classification and labelling and/or risk assessment.


The biological test results (based on mean measured test item concentrations) were as follows: 

The 72 hr ErC50 and ErC10 were determined to be 18 mg/L and 12 mg/L respectively.

The 96 hr ErC50 and ErC10 were determined to be 21 mg/L and 13 mg/L respectively.


The measured log Kow of the target substance (2,6,6-trimethylcyclohexa-1,3-dienecarbaldehyde, tradename Safranal, log Kow 2.7) is slightly higher than that for the source substance (Shisolia, log Kow 2.4). Thus, if aquatic toxicity tests were conducted on Safranal the determined response values might be slightly lower than those obtained for Shisolia. This is supported by experimental fish LC50 values of 4.3 and 9.2 mg/L respectively (see the short-term toxicity to fish endpoint for details). ECOSAR vinyl/allyl aldehyde estimates for the algal endpoint using the measured log Kow values as input give a 96-hr EC50 value of 22.7 mg/L for the target substance and a value of 15.9 mg/L for the source substance. These estimates are considered reliable given that the experimental data for the source substance (21 mg/L) is in close agreement with the ECOSAR prediction (22.7 mg/L). By comparing the ECOSAR estimates for the target and source substance, the log Kow difference results in a predicted algal 96h E50 value for Safranal that is 1.4 times lower than that for Shisolia. Applying this correction factor to the Shisolia measured values of 21mg/L (96h) and 18mg/L (72h), leads to corrected read-across estimates of 15 mg/L(96h) and 13mg/L (72h) for Safranal. The latter value has been selected as the key result for the purpose of the chemical safety assessment.