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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Cyclohexane is readily biodegradable, showing 77% biodegradation in 28 days.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Two biodegradation studies are available for cyclohexane. The Exxon (1995) study is GLP compliant and follows OECD guideline 301F (Manometric Respiration Test). Non-adapted activated sludge from a domestic sewage treatment plant was exposed to 34 mg/L cyclohexane for 29 days. Biodegradation reached 10% on day 13 and 60% on day 21, with 77% biodegradation by day 29. The Exxon (1995) is the key study in the EU RAR (2004) for cyclohexane; it follows standard guidelines, fulfils the validity criteria and is GLP compliant. There are conflicting results from other studies reported in the EU RAR, however these studies were found to be unreliable for various reasons. Following OECD 301F, 77% degradation of the test material was observed after 28 days with the 10 day window met and therefore cyclohexane is considered to be readily biodegradable.

The BASF (2002) study is a biodegradability in the CO2 headspace test following ISO 14593, though no information is available on whether it was conducted under GLP. Non-adapted activated sludge from a laboratory wastewater treatment plant treating municipal sewage was exposed to 23 mg/L cyclohexane for 49 days. The BASF study (2002) reports a biodegradation of < 10 % after 28 days and 60 to 70 % after 49 days, indicating that cyclohexane was biodegradable under the test conditions but did not fulfil the OECD criteria for ready biodegradability.