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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

FAV-ES was found to biodegrade under the conditions of the modified Sturm test. After 49 days, a biodegradation of 63% was observed. 
The substance is not considered readily biodegradable as the test substance did not yield 60% degradation in 28 days (only 55%).

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

The biodegradation of FAV-ES is determined according to test method OECD 301 B (modified sturm test). The test is carried out at room temperature (23°C ± 2), and in parallel two positive controls are also tested: cellulose microcrystalline Avicell®(Merck) (insoluble) and sodium acetate (CH3COONa, soluble).

The used inoculum is active, in fact the positive controls reached a biodegradation of about 87% after 49 days. The biodegradation of FAV-ES and sodium acetate started immediately, while the cellulose showed a “lag” phase of 3 days. The test fulfilled the validity criteria reported in OECD 301 B.

In accordance with the guideline, FAV-ES cannot be claimed “Ready Biodegradable” in fact it did not reach a 60% biodegradation within the 28 days. As it concerns a UVCB substance, the 10 days window criterion does not apply.

Nevertheless, the product is showing a significant biodegradation: after 28 days the absolute biodegradation of FAV-ES is 55.7%. Therefore, it is concluded that while FAV-ES cannot be considered readily biodegradable, it does biodegrade to a significant extent. With this respect, the Guidance on the Application of the CLP criteria (section II.3.1) mentions that borderline degradation might indicate that some of the individual constituents of UVCB substances may be rapidly degradable and others may not be rapidly degradable. In this case, a more detailed assessment of the degradability of the individual constituents in the UVCB may be required. When the constituents that are not-rapidly degradable constitute a significant part of the complex substance, e.g. more than 20% - or for a hazardous constituent even lower - the substance should be regarded as not rapidly degradable.

As no further test data on the UVCB are available in the current case, the biodegradability of each individual constituent in the UVCB is estimated using EpiSuite. The QSAR results demonstrate that all but one of the FAV-ES constituents are predicted to be readily biodegradable. The one constituent that was predicted to not be readily biodegradable is present in FAV-ES as a typical concentration of only 5.23%.

The difference between the outcome of the QSAR model (all but one constituents readily biodegradable) and the actual biodegradation test (not fulfilling criteria for readily biodegradable), is related to the water solubility of the FAV-ES constituents. According to the QSAR results, the vast majority of the FAV-ES constituents has a water solubility below 10 µg/L. As a consequence, due to the relatively high substance loading in ready biodegradation tests, part of the test substance will not be dissolved, which slows down the degradation rate. With effect is acknowledged in the Guidance on the Application of the CLP criteria (section II.3.2).


[Type of water: freshwater]