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Environmental fate & pathways

Endpoint summary

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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 properties. 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 their environmental fate. Based on the results of the screening tests for biodegradation in water for Fatty acids, C16-18 and C18-unsatd., branched and linear, 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 the 10 day window was not met. This test is supported by a read across substance in the sub-category 1, Isooctadecanoic acid. This acid contains the highest amount of C18 branched Fatty acids and has the highest level of saturation. 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 (Coenen, 1990). Again here the 10d window was not met.

Since Fatty acids, C16-18 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.