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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Isooctadecanoic acid is determined to be readily biodegradable.

Key value for chemical safety assessment

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

Additional information

Two guideline studies investigating the ready biodegradability of the test substance according to OECD 301B are available for Isooctadecanoic acid. Both studies used domestic activated sludge as inoculum. In the key study (Coenen 1990) a degradation of 88% after 28 days was observed 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. In the second study (Bogers 1988) a degradation of < 30% of the test substance was observed, however this result can be disregarded as (Coenen, 1990) has clearly shown that the substance degrades by more than 60% after 28 d. This conclusion is supported by a further study investigating the ready biodegradability of a dimerised fatty acids and its derivatives sub-category 1 member, Fatty Acids, C16-C18 and C18 unsatd., branched and linear (CAS No. 68955-98-6). The test was conducted 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.

In both tests the 10 day window was not met however 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 2 can be regarded as readily biodegradable.