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Short-term toxicity to aquatic invertebrates

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The acute toxicity of L-Menthol (CAS no. 2216-51-5) to invertebrates (Daphnia magna) was determined in a static immobilisation test according to EU Method C.2 (Acute Toxicity for Daphnia) which is similar to the OECD Guideline 202. After 48 hours of exposure an EC50 of 26.6 mg/L (measured) is obtained (Haarmann & Reimer, 2002).

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Additional information

Hypothesis for the read-across approach:

REACH regulation (Corrigendum) EC 1907/2006 on page L 136/120: “Substances whose physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be considered as a group, or ‘category’ of substances. Application of the group concept requires that physicochemical properties, human health effects and environmental effects or environmental fate may be predicted from data for reference substance(s) within the group by interpolation

to other substances in the group (read-across approach).”

Further, ECHA guidance document “Guidance on information requirements and chemical safety assessment – Chapter R.6: QSARs and grouping of chemicals (May, 2008)” provides information on the use of read-across (page 78) as follows: “In the read-across technique, endpoint information for one chemical is used to predict the same endpoint for another chemical, which is considered to be similar in some way (usually on the basis of structural similarity). In principle, read-across can be applied to characterise physico-chemical properties, environmental fate, human health effects and ecotoxicity.”

It can be stated that menthols act as a prime example of substances that are suitable for read-across since menthols are (stereo)isomeres and, thus, ideally fulfill the recommended criteria of structural similarity. Further, the OECD SIDS report on menthols (2003) assessed data of the isomers L-menthol (CAS no. 2216-51-5), D-menthol (CAS no. 15356-60-2), the racemate and menthol (unspecified isomers; CAS no. 1490-04-6). The report concludes on page 4 that “the menthols can be considered as a category because of their similarity in physico-chemical, toxicological, ecotoxicological and environmental fate properties” which is another requirement to justify the application of the read-across approach.

Comparing the details on physico-chemical properties for menthol (CAS no. 1490-04-6) in the endpoint entries and L-menthol (2216-51-5) in “Details on properties of test surrogate or analogue material” of this endpoint entry highligth that the menthols can be considered as a category, as was concluded by the OECD SIDS report (2003). There are no functional groups that are different between the source and target chemical which could affect the anticipated toxicity.

In the OECD SIDS report (2003) the endpoint “short-term toxicity to aquatic invertebrates” of the menthol (CAS no. 1490-04-6), that is read-across in this chapter, is given with an effect range for Daphnia magna of: 24 h EC50 = 37.7 - 71 mg/L and 48 h EC50 = 26.6 mg/L for all menthols that are given above. The study providing the latter effect concentration (48 h EC50 = 26.6 mg/L) investigated on L menthol (CAS no. 2216-51-5) and was selected for read-across.