Octadecanoic acid, C16-20-branched alkyl esters

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 69.9% after 28 d (OECD 301B) and 75.3% after 28 d (OECD 301C); read-across

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Since no studies investigating the ready biodegradability of Octadecanoic acid, C16-20-branched alkyl esters (CAS 85203-92-5) are available for this endpoint, in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5 a read-across to the structurally related source substances Fatty acids C20-22 (even numbered), C18-22 (even numbered)-alkyl esters (CAS 17671-27-1) and 2-octyldodecyl isooctanoate (CAS 93803-87-3) was conducted. The read-across substances are representative to evaluate the biodegradation of Octadecanoic acid, C16-20-branched alkyl esters. The source substance Fatty acids C20-22 (even numbered), C18-22 (even numbered)-alkyl esters (CAS 17671-27-1) is characterized as an ester of C20/C22 fatty acids and C20/C22 alcohols. The second source substance 2-octyldodecyl isooctanoate (CAS 93803-87-3) is an ester of isooctanoate (C18 iso) and 2-octyldodecanol (C20 branched). This read-across is justified in detail in the overall summary (IUCLID Section 6.1) and within the analogue justification in IUCLID Section 13.

The study with the source substance Fatty acids C20-22 (even numbered), C18-22 (even numbered)-alkyl esters (CAS 17671-27-1) was performed according to OECD 301C (GLP) under aerobic conditions using a mixture of activated sludge from STP with freshwater from rivers and lakes, marine water and marine sediment as inoculum. The test substance was applied at a concentration of 100 mg/L. A biodegradation of 75.3% (BOD) was observed after 28 d. Since the substance reached the pass level for OECD 301C (biodegradation is > 60% after 28 d, no 10-day window required) Fatty acids C20-22 (even numbered), C18-22 (even numbered)-alkyl esters is readily biodegradable according to the OECD criteria.

The study with the second source substance 2-octyldodecyl isooctadecanoate was performed according to OECD 301B under aerobic conditions using domestic activated sludge as inoculum. A test substance concentration of approx. 14.5 mg/L was degraded to an extent of 68.1 - 71.7% (mean: 69.9%) after 29 d. Since 2-octyldodecyl isooctadecanoate is an UVCB substance and consists of structurally similar constituents with e.g. different chain-lengths, degree and/or site of branching or stereo-isomers, sequential (instead of concurrent) biodegradation of the individual structures can take place, but all can be considered as readily biodegradable. Thus, referring to Annex I of 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 substance can be regarded as readily biodegradable. Moreover, the read-across substance is assumed to be not inhibitory to activated sludge microorganisms based on a biodegradation of > 25% in the toxicity control after 14 d.

In addition to the experimental studies from structurally similar source substances, (Q)SAR calculations using VEGA 1.1.3 were used to assess the ready biodegradability of the target substance. The model is based on the OECD TG 301C - modified MITI -I test data and provides a qualitative evaluation (binary classification) of ready biodegradability properties. The calculations were performed for four representative structural components of the UVCB substance. Ready biodegradability was estimated for each component. All components were within the applicability domain of the model and the results are considered to be reliable for environmental risk assessment.

Based on the results from two structurally similar source substances and reliable (Q)SAR calculations (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5) it can be concluded that Octadecanoic acid, C16-20-branched alkyl esters (CAS 85203-92-5) is readily biodegradable according to the OECD criteria.