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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

 Super Muguet should be regarded as readily biodegradable based on the results of two standard ready screening tests. Super Muguet underwent 74% and 85% degradation after 28 days.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The Ready Biodegradability of Super Muguet has been determined in two ready biodegradability tests (Rudio 2003, Linjun 2014). Both are GLP studies, performed according to international accepted guidelines and using the Manometric Respirometry Test conditions. The level of biodegradation achieved after 28 days was 74% and 85% respectively, which exceeds the pass level of 60% theoretical oxygen demand.

The 10 day window criterion was not met in one study (Rudio, 2003); biodegradation exceeded 10% on day 7 and reached only 45% at the end of the 10-day window (days 7 to 17). The 10-day time window criterion was developed on the assumption that a test substance is degraded according to a “standard” growth curve in ready biodegradability tests. Super Muguet is a mixture of three isomers. The degradation curve will therefore be the sum of three growth curves. The OECD Guidelines for Testing of Chemicals, Section 3. Part 1: Principles and strategies related to the testing of degradation of organic chemicals (adopted 23 March 2006), states that if a substance consists of “constituents with different chain-lengths, degree and/or site of branching or stereo-isomers, even in their most purified commercial forms” and “it is anticipated that a sequential biodegradation of the individual structures is taking place, then the 10-day window should not be applied to interpret the results of the test.” The 10-day time-window should therefore be ignored as a pass / fail criterion for Super Muguet. Thus, Super Muguet should be regarded as readily biodegradable according to this test based only on the biodegradation percentage of 74% at day 28.

In the more recent test (Linjun, 2014) where the two replicates were performed at a lower test item concentration of 22 and 23.5 mg/L as opposed to 100mg/L in the 2003 test, the 10 day window was met. Biodegradation at the end of the 10 day window was 77.8% (day 9 = 23.1%, day 19 = 77.8%). The substance was regarded as readily biodegradable according to this study, exceeding the pass level of 60% ThOD (85.2% achieved) and meeting the 10-day window criterion.