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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Fatty acids, C16-18 and C18-unsatd., branched and linear, is readily biodegradable according to OECD criteria.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

One study investigating the biodegradability of Fatty acids, C16-18 and C18-unsatd., branched and linear is available. Based on the result of this study the test substance is determined as readily biodegradable (Sewell, 1994). The test conducted was comparable to OECD guideline 301B using domestic activated sludge and a test substance concentration of 20 mg/L. The test substance attained 67 % degradation after 29 days, however a 10d window was not met. This test is supported by a read across substance in the sub-category 1, Isooctadecanoic acid, CAS No. 30399-84-9. This supporting study reported an observed degradation of 88 % after 28 days for the nominal test concentration of 10 mg/L and a degradation of 62 % after 28 days for the nominal test concentration of 20 mg/L, again not meeting the 10d window (Coenen, 1990). Since fatty acids C16 -C18 and C18 unsaturated, branched and linear, and all other members of sub-category 1 are UVCB substances and thus consist of constituents with different chain-lengths and different degrees of branching, sequential (instead of concurrent) biodegradation can take place but all can be considered as readily biodegradable.

Thus, referring to Annex I to the OECD Guideline for Testing of Chemicals ‘Revised introduction to the OECD guidelines for testing of chemicals, section 3’ (OECD, March 2006), the 10-day window should not be considered for this UVCB substance and due to a degradation of >60 % within 28 days the monomeric acids of sub-category 1 can be regarded as readily biodegradable.