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Biodegradation in water: screening tests

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Description of key information

Readily biodegradable, but failing 10d window: 60.5% (O2 consumption) after 28 d. The time window is consequently not considered applicable (OECD, 2006; guidance on the
application of CLP* criteria, version 5.0: II.2.1.2, page 564)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window
Type of water:
freshwater

Additional information

A GLP study was perform to assess biodegradation in water of 2 -Hydroxyethyl palmitate. The substance is considered as readily biodegradable but failing the 10day window (biodegradation of 60.5% after 28 d). The biodegradation kinetics (lag period, growth rate, and yield) of the individual chemicals in a multi-constituent chemical are not necessarily the same. The biodegradation of a substance consisting of many constituents is therefore an addition of different biodegradation curves. It is thus possible that individual compounds meet the time window criterion whereas the biodegradability curve of the multi-constituent suggests that the test substance is not readily biodegradable. The time window is consequently not considered applicable (OECD, 2006; guidance on the application of CLP* criteria, version 5.0: II.2.1.2, page 564) for 2-hydroxyethyl palmitate. The test item should therefore be classified as readily biodegradable.


 


Three studies are available investigating the ready biodegradability of Fatty acids, C16 -18, esters with ethylene glycol (CAS 91031 -31 -1), structurally very close to 2 -Hydroxyethyl palmitate.The key study performed with fatty acids, C16-18, esters with ethylene glycol according to ISO 10708 (GLP) resulted in a biodegradation of 61% after 28 d and 85% after 56 d, respectively (Richterich, 1998). This study was conducted using sewage from a municipal wastewater treatment plant as inoculum. For substances with different chain lengths the 10-day window should not be used for the interpretation of results. It is possible that a sequential biodegradation occurred which might have resulted in a prolonged lag-Phase and therefore a slower biodegradation period, although the test substance was biodegraded in a large amount after the test duration. In this case the pass level can be applied after 28 days and therefore the test substance is considered to be readily biodegradable.To support this result, a read-across to the structurally related category member ethylene distearate (CAS 627-83-8) was conducted in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5. The read-across substance is characterized by the same alcohol component (ethylene glycol) diesterified with similar fatty acid (stearic acid (source) compared to stearic/palmitic acid (target)) and can therefore be used for read-across. The first step of biodegradation is the enzyme-catalysed cleavage of the ester bond by lipase or esterase which are synthesized by a wide range of microorganisms (Boczar et al., 2001). The free fatty acids (C4 to C24 incl. C18 unsatd.) are known to be degraded rapidly and utilized as substrates by activated sludge microorganisms (Kangala & Medrzycka, 2008). The first study (Ministry of Economy, Trade and Industry, Japan, 1998) was conducted with the read-across substance ethylene distearate according to the OECD Guideline 301C (GLP) under aerobic conditions using a mixture of activated sludge from sewage treatment plants, freshwater from rivers and lakes, marine water and marine sediment as inoculum. A mean biodegradation of 73% 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) the test substance is readily biodegradable according to the OECD criteria. This result is supported by a second GLP-Guideline study with the read-across substance ethylene distearate according to OECD 301B using non-adapted activated sludge as inoculum (Mead, 1996). 70% biodegradation and the fulfilment of the 10-day window criterion classify the substance to be readily biodegradable. Based on the results available results for the target and the source substance (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5) it can be concluded that fatty acids, C16-18, esters with ethylene glycol is readily biodegradable according to the OECD criteria.


 


For a detailed reference list please refer to the CSR or IUCLID section 13.

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