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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

With high probability acute not harmful to aquatic algae

Key value for chemical safety assessment

EC50 for freshwater algae:
32.9 mg/L
EC10 or NOEC for freshwater algae:
3.56 mg/L

Additional information

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, 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 a higher sensitivity to organic compounds than Scenedesmus subspicatus. Therefore the results of the study were used for chemical safety assessment and PNEC derivation but not taken into account for classification.


Brack and Rottler compared the effect of cyclohexanone and other organic chemicals on Chlamydomonas reinhardtii with the effect caused on standard algae Scenedesmus subspicatus reported in a publication of Bringmann and Kühn (1978). 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. The study was considered as valid with restrictions, since no analytical measurements conducted. Furthermore the test duration of 8 days is unusual long, with the consequence that exponential growth at the end of the test is unlikely. Nevertheless the obtained result may be considered as supportive information for determining the low toxicity of cyclohexanone on algae.

Finally, a further indication of the low acute toxicity of cyclohexanone to green algae is supplied by the result of an investigation conducted with the very similar substance cyclopentanone (CAS No. 120 -92 -3).

Both substances are saturated alicyclic ketones, whose only difference consists in a methylene group.The relevant physico-chemical properties are quite similar as well.

For cyclopentanone a GLP guideline study with analytical controls is available (L'Haridon, 2003). At the end of the test duration the recovery rate of the test item was > 80 %. Therefore volatilisation can be excluded under this test conditions. After 72 hours exposition to cyclopentanone no effect on Scenedesmus subspicatus was observed up to the highest test concentration of 100 mg/L.