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Environmental fate & pathways

Biodegradation in water: screening tests

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Fatty acids, C16-18 and C18-unsaturated, dimerized (CAS No. 71808-39-4) does not meet the OECD criteria for ready biodegradability (<10 %)

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The biodegradation of Fatty acids, C16-18 and C18-unsaturated, dimerized was tested in a CO2 evolution test according to OECD guideline 301B, using domestic activated sludge as inoculum. At test termination (28 days) the substance was degraded to 29.3 % (Kelly, 2004).

Three further studies investigating the biodegradation in water (screening tests) for the sub-category 2 members, i.e. Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4), Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5), and Fatty acids, C18-unsaturated, trimers (CAS No. 68937-90-6) are available and were used as read-across. The first study, investigating the ready biodegradability of Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4), was conducted as a CO2 evolution test according to OECD guideline 301B using domestic activated sludge as inoculum. As was the case for the hydrogenated form of the Dimer acid, the unsaturated form also recorded a biodegradation of < 10 % at test termination (28 days) (Bogers, 1988). Another CO2 evolution test for Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5) was conducted according to OECD guideline 301B using domestic activated sludge as inoculum (Kelly, 2002). At test termination (28 days) the substance was degraded to 9.5 %.  Similarly, for Fatty acids, C18-unsaturated, trimers (CAS No. 68937-90-6) a study was conducted according to the "ASTM D 5864-95 Standard Test Method for Determining Aerobic Aquatic Biodegradation of Lubricants or Their Components" (Batch Processing Sturm Test) using activated sludge which was pre-adapted to the test substance. Due to the use of pre-adapted sludge the test cannot fulfil the OECD criteria for readily biodegradability. Nevertheless, as the biodegradation of the test substance was < 10 % at test termination after 28 days, Fatty acids, C18-unsaturated, trimers (CAS No. 68937-90-6) is in any case determined to be not readily biodegradable under test conditions according to OECD criteria (O'Leary, 1999).

Since all available study reports for biodegradation in water (screening tests) for the sub-category 2 members determined a degradation of < 10 % within 28 days (not readily biodegradable), it can be concluded that Fatty acids, C16-18 and C18-unsaturated, dimerized (CAS No. 71808-39-4) does not meet the OECD criteria for ready biodegradability.