Isooctadecanoic acid

Endpoint summary

Additional information

As summarized in the category justification, the members of the fatty acids are divided into two sub-categories on the basis of their environmental fate. The first sub-category covers three monomeric (by-) products of the dimerization process (readily biodegradable substances). The second sub-category covers the predominately oligomers (dimeric and trimeric products) of dimerization based on their lack of ready biodegradability and the environmental fate.Based on the results of the screening tests for biodegradation in water for Isooctadecanoic acid, the test substance is determined as readily biodegradable (Coenen, 1990). 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. The 10 day window was not met . 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 Unsaturated, 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 (Sewell, 1994). The 10 day window was not met. As both Isooctadecanoic acid 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.