Octadecanoic acid, branched and linear

Endpoint summary

Additional information

As summarized in the category justification, the members of the dimerised fatty acids and its derivatives 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 or biodegradable substances). The second sub-category covers the predominately oligomers (dimeric and trimeric products) of dimerization based on their lack of biodegradability and the environmental fate. Secondary source data is available for Octadecanoic acid indicating inherent biodegradability, however, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 1.2. Weight of evidence, data from several independent sources of information of monomeric fatty acids C16-18 saturated and unsaturated indicate that the substance is likely to be readily biodegradable as well. As summarized in the category justification, the members of the dimerised fatty acids and its derivatives subcategory 1 (predominantly monomers) will biodegrade. Individual degradation rates reported may vary to some degree depending on their physico chemical properties (e.g. water solubility), bioavailability and test methods employed.

As aforementioned two screening tests for biodegradation in water are available for 2 sub-category 1 members; Fatty acids, C16-18 and C18-unsatd., branched and linear, and Isooctadecanoic acid, respectively. Both the test substances were determined as readily biodegradable (Sewell, 1994, Coenen, 1990). A biodegradation screening test conducted similar to OECD guideline 301B using domestic activated sludge and a test substance concentration of 20 mg/L was carried out for Fatty acids, C16-18 and C18-unsatd., branched and linear. The test substance attained 67 % degradation after 29 days, however the 10 day window was not met. This test is supported by a further 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. The biodegradation study reported an observed degradation of 88% of Isooctandecanoic 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). Here again, the 10 day window was not met. Since Octadecanoic acid, 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. Two further studies on analogue substances were included as part of a weight of evidence. Stearic acid, saturated was tested by Bogers (1989) for ready biodegradability according to OECD 301B and GLP. At concentrations of 10 and 20 mg/L the degradation values were 72 % and 71 %, respectively at test termination (28 d). The pass criterion for ready biodegradability (60 % degradation within 10 days once exceeded 10 % degradation) was barely missed. However, the sampling interval was not as narrow as recommended by the OECD guideline (sampling every second day, followed by sampling every fifth day) which might have led to the barely missing of the 10-day window. The failure of the 10-day window in biodegradation tests due to the low water solubility/bioavailability as well as to the inappropriate sampling intervals were already recognized and discussed within the framework of the SIDS Initial Assessment Report for the Category “Aliphatic Acids” (OECD, 2009) and judged not to preclude the ready biodegradability of the fatty acids. For second analogue substance, octadec-9-anoic acid a GLP study according to OECD 301B was conducted (Coenen, 1991). After 28 days 93 % and 75 % of octadec-9 -enoic acid was biodegraded at concentrations of 10 mg/L and 20 mg/L, respectively und thus passed the 60 % degradation level. Furthermore, the degradation value at the lower test concentration of 10 mg/L met the 10-day window. According to the criteria for ready biodegradation 9-Octadecenoic acid, (Z)- is readily biodegradable. Since the reference substance itself failed the pass criterion for validity (60 % degradation was not reached within 14 d), the study should had been repeated.

The consistent test results regarding ready biodegradability from both sub-category 1 members; Fatty acids, C16-18 and C18-unsaturated, branched and linear and Isooctadecanoic acid respectively, in addition to two further analogue substances: octadec-9-enoic acid and stearic acid, supersede the low biodegradation rate as reported in the HPV documentation (EPA, 2009) and Octadecanoic acid, branched and linear can be considered to be readily biodegradable. Additionally, given that Isooctadecanoic acid is also highly branched and has a lower water solubility than the Octadecanoic acid, branched and linear, one can conclude that Octadecanoic acid , branched and linear is also readily biodegradable as it should have a higher bioavailability.

Thus, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 1.2. Weight of evidence, there is sufficient data from several independent sources of information of monomeric fatty acids C16-18 saturated and unsaturated leading to the conclusion that Octadecanoic acid, branched and linear is readily biodegradable. Considering that this substance is readily biodegradable in accordance to Regulation (EC) No 1907/2006 Annex IX, 9.2.1.2, 9.2.1.3 and 9.2.1.4 column 2 to further simulation testing on ultimate degradation in surface water, sediment or soil does not need to be conducted.