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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

As the biodegradation in OECD 301D did not reach 60% of the ThOD within a 10-d window the test substance is classified as not readily biodegradable. Nevertheless, significant biodegradation (59 % of the ThOD) was observed within 28 days. 

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Additional information

Ready biodegradability of 3,3,5-trimethylcyclohexanone was determined in OECD 301D (Closed Bottle Test) at an initial concentration of 2 mg/L. As inoculum freshly collected sewage from a predominately domestic sewage treatment plant (adaption not specified) was used. The O2consumption was followed for biodegradation estimation over a time period of 28 days at a mean temperature of 20.44 °C. Benzoic acid, sodium salt, was used as reference substance.

The test substance 3,3,5-trimethylcyclohexanone showed 59 % degradation within 28 days. The activity of the inoculum was confirmed by 94 % degradation of the reference substance within 28 days.

As the biodegradation did not reach 60% of the theoretical oxygen demand (ThOD) within a 10-d window the test substance is classified as not readily biodegradable. Nevertheless, significant biodegradation was observed.

A second test was conducted according to OECD 302B (Inherent biodegradability: Zahn-Wellens/EMPA Test). This study is not regarded in the assessment of 3,3,5-trimethylcyclohexanone biodegradability because the high degree of elimination in the abiotic control indicates that elimination is dominated by physico-chemical processes. Thus DOC analysis and consequently the test system is unsuitable for this substance.