Fatty acids, soya, conjugated

Biodegradation in water: screening tests

Description of key information

readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

No study on ready biodegradability is available for fatty acids, soybean oil conj. Therefore, read across from experimental data of the constituents is done (palmitic acid (C16, saturated); oleic acid (C18, 1 double bond, 9-Octadecenoic acid, (Z)-)) as well as a mixture containing linoleic acid (C18, 2 double bonds). These experimental data are supported by QSAR predictions on ready biodegradability of linoleic acid.

Palmitic acid (CAS 57-10-3) was tested according to the ISO 10708 (BODIS test) which is apparently similar to the “closed bottle test”, OECD 301 D and was designed for insoluble substances. Three replicates with palmitic acid at concentrations of 100 mg/L COD were incubated with non-adapted activated sludge. The oxygen consumption was monitored during the 28 day test period. The results clearly showed that palmitic acid was degraded by 65% in average at day 28 (Börner, 1994).

Coenen (1991) conducted a GLP study according to OECD 301B. After 28 d 93% and 75% of oleic acid (CAS 112-80-1) were biodegraded at concentrations of 10 mg/L and 20 mg/L, respectively und thus pass the 60% degradation level. Furthermore, of the lower test concentration (10 mg/L) the 10 day window was met. According to the criteria for ready biodegradation oleic acid (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.

In addition, oleic acid was tested in a study provided by the Japanese Ministry of the Environment. The GLP-study was conducted according to OECD 301C (2003) under GLP conditions. At a test concentration of 100 mg/L the degradation was determined to be 78% based on BOD/ThOD measurements. According to that result, the substance is characterised as ready biodegradable.

Results of a further BODIS test (Küster, 2000) showed ready biodegradability for a test material containing 60% linoleic acid, CAS 60-33-3 (further constituent: 25% oleic acid, CAS 112-80-1; residues: linolenic acid (C18’’’), palmitic acid (C16), myristic acid (C14), stearic acid (C18)). The average degradation obtained after the 28 day exposure period was determined to be 71%. Since the tested material consists of structurally similar constituents with different chain-lengths, sequential biodegradation of the individual structures can take place, but all can be considered as readily biodegradable. 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 thus should be evaluated as readily biodegradable.

Results of the QSAR model BIOWIN v.4.10 (EPI Suite, 2012) predict ready biodegradability for linoleic 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.

Overall, the fatty acids, soybean oil conjugated is regarded as readily biodegradable. This judgment is consistent with the hazard assessment presented in the OECD SIDS (2009) for the category “Aliphatic Acids Category” where aliphatic fatty acids with a carbon chain length in the range of C16 – C18 were evaluated to be readily biodegradable.