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Environmental fate & pathways

Biodegradation in water: screening tests

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Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

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The ready biodegradability of fatty acids, hydrogenated tallow, distn. residues is assessed in a weight of evidence approach based on the results of the fatty acid structures contained in the substance. According to the Substance Identity Profile palmitic acid (C16, CAS no. 57-10-3), stearic acid (C18, CAS no. 57-11-4) and oleic acid (C18’, CAS no. 112-80-1) are the most representative structures for fatty acids, hydrogenated tallow, distn. residues.
Experimental data as well as QSAR predictions on ready biodegradability were considered to deduce the biodegradability.

Palmitic acid was tested according to the ISO 10708 (BODIS test) which is apparently similar to the “closed bottle test”, OECD 301 D. 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).
According to the opinion of the SCIENTIFIC COMMITTEE ON HEALTH AND ENVIRONMENTAL RISKS on “Compatibility of the ISO standard 10708 (biodegradability test method) with the ultimate biodegradability requirements imposed through Annex III of Regulation 648/2004 of Parliament and of the Council”, the BODIS-Test/ISO 10708 shows the same variability and biodegradation results obtained with other OECD screening tests (SCHER, 2005). Since the pass criterion of 60% degradation within 28 days of the ISO 10708 is consistent with those obtained with the OECD ready biodegradability methods, palmitic acid can be regarded as readily biodegradable.

Stearic acid, saturated was tested by Bogers (1989) for its 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 has to be reached within 10 days once exceeded 10% degradation) was barely missed. Since the sampling interval was not as narrow as recommended by the OECD guideline (sampling every second day, followed by sampling every fifth day) this might have led to the barely missing of the 10-day window.
Reliable results of the QSAR model BIOWIN V.4.10 (EPI Suite, 2010) predicts ready biodegradability for stearic acid.

Coenen (1991) conducted a GLP study according to OECD 301B. After 28 d 93% and 75% of oleic acid were biodegraded at concentrations of 10 mg/L and 20 mg/L, respectively und thus pass the 60% degradation level. Furthermore, at the lower test concentration of 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.
Reliable results of the QSAR model BIOWIN V.4.10 (EPI Suite, 2010) predicts ready biodegradability for oleic acid.

Overall, fatty acids, hydrogenated tallow, distn. residues 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 C8 – C22 were judged to be readily biodegradable.