Fatty acids, C18-22

Biodegradation in water: screening tests

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

No study on ready biodegradability is available for fatty acids, C18-22. Therefore, read across from the key studies of the main constituents of the blend was performed. According to the Substance Identity Profile stearic acid (C18), eicosanoic acid (C20) and docosanoic acid (C22) are the most representative structures for fatty acids, C18-22.
Therefore the available experimental data as well as the QSAR prediction on ready biodegradability for stearic acid (CAS 57-11-4), eicosanoic acid (CAS 506-30-9) and docosanoic acid (CAS 112-85-6) were considered to deduce the biodegradability of fatty acids, C18-22.

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 determined degradation values were 72% and 71%, respectively at test termination (28 d). The pass criterion for ready biodegradability (60% degradation reached within 10 days once exceeded 10% degradation) was barely missed. However, the sampling interval was not as small as recommended by the OECD guideline which might have led to the barely missing of the 10-day window.
The failure of the 10-day window in biodegradation tests with fatty acids 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.

 

Reliable results of the QSAR model BIOWIN v.4.10 (EPI Suite, 2010) predict ready biodegradability for eicosanoic acid. This method is based on the application of Bayesian analysis to ready biodegradation data for chemicals, derived collectively from all six OECD301 test methods plus OECD310.

 

Ready and inherent biodegradability of docosanoic acid were tested by the Japanese Ministry for the Environment (MOE, 1997). At a concentration of 100 mg/L the substance biodegrades up to 48 - 56% (BOD) after 28 days according to OECD 301C. In the inherent biodegradation test according to OECD 302C, the substance was tested at a concentration of 30 mg/L resulting in biodegradation rates of docosanoic acid up to 79 - 96% (BOD) after 28 days.
Results of the QSAR model BIOWIN v.4.10 (EPI Suite, 2013) predict ready biodegradability for docosanoic acid. This method is based on the application of Bayesian analysis to readily biodegradation data for chemicals, derived collectively from all six OECD301 test methods plus OECD310.
Finally, the unsaturated fatty acid docosenoic acid with a chain length of C22 was found to be readily biodegradable in a biodegradation test similar to OECD 301 D (Closed Bottle Test) (Richterich and Mühlberg, 2001). The read across substance docosenoic acid (C22:1, CAS 112-86-7) was inoculated with suspended garden mould for 30 days. Based on the oxygen consumption biodegradation on day 5, 15 and 30 was 40 %, 77 % and 90 %, respectively. Therefore, it can be concluded, that docosenoic acid, a C22:1 fatty acid, is readily biodegradable.

Based on the substance identity profile of fatty acids, C18-22 and on the presented data of the main constituents / read across substances it is justified to conclude that the substance is readily biodegradable.