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Description of key information

Short-term toxicity

Data on acute aquatic toxicity covering all three trophic levels are available for cyclohexanone.

The most reliable study on short-term toxicity to fish was performed under flow through conditions using a method comparable to OECD 203. In this study a LC50 (96h) of 527 mg/l for Pimephales promelas was determined (based on measured concentrations; Brooke et al. 1984).

Results from two publications by Bringmann and Kuehn (1982, 1977) indicate that cyclohexanone is acutely not harmful to Daphnia m. The 24h-EC50 values are 800 mg/L and 820 mg/L, respectively. Both studies were performed according to German industrial standard, with a test period of 24 h and without analytical controls. Despite these limitations the studies were considered as valid with restrictions in the framework of the OECD SIDS Initial Assessment Report on Cyclohexanone (UNEP Publications, 2006).

The very low acute toxicity of cyclohexanone to aquatic invertebrates is confirmed by the results of an estimation conducted with the QSAR Toolbox (v4.3.1) using trend analysis within category members. The estimated EC50 of 207 mg/L is considered reliable and is taken, as a worst case, as key value for the chemical safety assessment.

A further indication of the low acute toxicity of cyclohexanone to aquatic invertebrates is supplied by the result of an investigation on acute toxicity to Daphnia m. conducted with the very similar substance cyclopentanone (CAS No. 120 -92 -3) according to OECD Guideline 202 (Rhodia, 2003). In this test no immobilisation was observed at a test concentration of 100 mg/l at time 0; 24 and 48 hours (analytical monitoring was performed).

The lowest effect value of cyclohexanone on algae is described in a publication by Brack and Rottler (1994). A 72h-EC50 of 32.9 mg/L and a 72 h-EC10 of 3.56 mg/L, both based on biomass, were determined. The study was not conducted according an official guideline and the test organism used, the unicellular freshwater green alga Chlamydomonas reinhardtii, is not a standard organism according to OECD guideline 201 as well. Moreover, Chlamydomonas reinhardtii showed in the study a higher sensitivity to organic compounds than Scenedesmus subspicatus. Therefore the results of the study were used, as a worst case, for chemical safety assessment and PNEC derivation but not taken into account for classification.

For the standard test organism Scenedesmus subspicatus Bringmann and Kühn (1978) determined a TT (Threshold Toxicity, comparable to EC10) of 370 mg/L after 192 h exposition. 

These results, although determined in an old study conducted not according to current guideline, are supported by the data on algal toxicity of the structural analogue substance cyclopentanone (CAS No. 120 -92 -3). For cyclopentanone a GLP guideline study on growth-inhibition with analytical controls is available for the green alga Desmodesmus s. (L'Haridon, 2003). At the end of the test duration 72 h EC50 and 72 h NOEC of respectively >100 mg/L and 100 mg/L were determined. 


Long-term toxicity

No experimental data on long-term toxicity on fish and aquatic invertebrates are available.

A NOEC (21 d) of 26.6 mg/L for reproduction in Daphnia magna was estimated using the QSAR Toolbox v4.3.1. The prediction is based on trend analysis within 26 values from similar chemicals (category approach).

The result is derived from a valid QSAR model and falls into its applicability domain. It is considered therefore reliable to cover the endpoint and is taken as key value for the chemical safety assessment.

Additional information