2-isopropyl-5-methyl-cyclohexanone

Biodegradation in water: screening tests

Description of key information

Based on weight of evidence evaluation from two valid studies, both DL-Menthone enantiomers and DL-Isomenthone enantiomers can be considered as readily biodegradable in various mixed compositions. 

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Ready biodegradability tests for the read-across substances DL-Menthone enantiomers and DL-Isomenthone enantiomers are available, which show that both are readily biodegradable (refer to read across justification).

In the study of Müller (1999) test item DL-Isomenthone (CAS 491-07-6) was investigated in a Closed Bottle test according to EU method C.4-E (1992). The test item was mainly (64.5 %) composed of the two cis-enantiomers (2S,5S)- and (2R,5R)-2-isopropyl-5-methylcyclohexanone (CAS 18309-28-9 and 1196-31-2).

The test micro-organism inoculum was taken from a municipal sewage water treatment plant. The parameter followed in duplicate for biodegradation estimation was the oxygen consumption measured as the reduction of dissolved oxygen measured at days 0, 7, 14, 21 and at the test end day 28. Degradation started after day 7, when mean 9 % degradation was measured, and was completed at day 21, when mean 60 % were reached. The test item was degraded by 63 % until day 28. The test item can be considered readily biodegradable as in accordance with the guidance the 14 day window was clearly met.

As the test item consisted to 64.5 % of the two cis-enantiomers and furthermore to 35.2 % of trans-isomers DL-Menthone (CAS 89-80-5, enantiomer ratio 1:1), the test item composition equals the composition of "reaction mass of isomenthone and trans-menthone 32/65" as given in chapter 1.2, which provides direct evidence for the ready biodegradability of this reaction mass composition.

In the study of King (1996) the test item consisting of mainly (82%) DL-Menthone (trans-Menthone CAS 89-80-5) was investigated for its biodegradation potential in a study according to the OECD TG 301 B protocol (1992). The test was performed under GLP conditions and a summary report with sufficient level of detail is available. The test system used is not fully applicable to volatile substances and the study is therefore of lesser reliability.

The inoculum was derived from the secondary effluent from a non-adapted activated sludge plant and the biodegradation was measured on the basis of DIC in the test vessels considering the control level in days 4, 8, 14, 22, 24, and 28. The percentage biodegradation of the test item was -2.7, 56.2, 91.7, 91.7, 91.6 and 99.5 % respectively. Thus the 10 days window starts at day 8 and the pass level (of 70 %) is reached at days 14, which indicates rapid and ready biodegradation. In conclusion rapid and thus ready biodegradation of test item mainly (82%) DL-Menthone was indicated by this study. The test item composition is similar to the composition of "reaction mass of isomenthone and trans-menthone 70/30" as well as of "reaction mass of isomenthone and trans-menthone 95/5" (as given in chapter 1.2). Despite the limited reliability of the study, evidence is provided for the ready biodegradability of these two reaction mass compositions.