Cyclohexanone oxime

Biodegradation in water: screening tests

Description of key information

In a valid study performed according to international ISO guideline 9439 close to OECD 301B (reliability category 2) the test item cyclohexanone oxime was assessed to be readily biodegradable meeting the 10-day window requirement. 

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

In a valid study performed according to international ISO guideline 9439 close to OECD 301B (reliability category 2) the test item cyclohexanone oxime was assessed to be readily biodegradable meeting the 10-day window requirement. An initial test item concentration of nominal 63 mg/L was applied, corresponding to 40 mg/L DOC/TOC. Non-adapted activated sludge from laboratory sewage treatment plant receiving sewage of domestic and synthetic origin was used in a final solids concentration of 5 mg/L. Validity criteria of the guidelines were fulfilled. Based on CO2 evolution, within 28 days a mean degradation (2 replicates) of 79% was reached. Elimination deduced from DOC reduction amounted to 100% within 28 days.

This result is supported by a test on inherent biodegradability (Zahn-Wellens test) performed according to EU method C.9 (equivalent to OECD 302B; reliability category 2). An initial test item concentration of nominal 656 mg/L was applied, corresponding to 400 mg/L DOC (nominal). Non-adapted sludge from a STP receiving industrial and domestic sewage was applied with a final concentration of solids of 0.5 g/L.

Adsorption (3 -hours value) was determined to be negligible (2.7%). Adaption phase was very short, as already between day 1 and 3 degradation phase began and at day 3 already 50.2% of the test item were degraded. The final degradation level at the end of the test amounted to 96.5%. Reported degradation is exclusive of elimination, i.e. the DOC determined after 3 hours was taken as the reference value according to the EU-guideline.

Conclusions:

- Cyclohexanone oxime is inherently biodegradable, fulfilling specific criteria (≥70 % mineralisation (DOC removal) within 7 d; log phase no longer than 3d; removal before degradation occurs was below 15%, namely 2.7% and inoculum was not pre-adapted).

- Elimination due to adsorption was negligible (2.7% within 3 hours).

- Inoculum toxicity can safely be excluded at the initial nominal concentration of cyclohexanone oxime of 656 mg/L.

The Zahn-Wellens test will be used as key study for hazard assessment for STP microorganisms. In line with REACH guidance on Information Requirements and Chemical Safety Assessment part R.10 the initial nominal concentration of cyclohexanone oxime of 656 mg/L will be regarded as a NOEC STP-microorganisms.