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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Within 28 days, a degradation rate of 2 % was determined. The test item is considered to be "Not Readily Biodegradtion". The reference compound sodium benzoate showed 79 % degradation after 14 days.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The existing study on ready biodegradation (Currenta, 2010) reported 2% degradation and, thus, indicates that ditolyl ether is not readily biodegradable. However, revising the dossier and this study it got obvious that the study result might be flawed. This GLP and OECD 301F conform study was conducted with a test concentration of 100 mg/L, which is in accordance with the OECD guideline. However, the water solubility of the substance is 2.83 mg/L and, therefore, the test concentration could have been too high, and only parts of the substance might have been available to bacteria and to biodegradation.

Furthermore, there is another study (Kanne, 1986) which is somehow difficult to interpret as the method refers to a ready biodegradation but as adapted sludge was used the study finally investigated on inherent biodegradation. The study result, therefore, has to be questioned and was scored with Klimisch 3.

Thus, the available data on biodegradation might not be appropriate to conclude on the persistence of ditolyl ether (based on screening tests), and the registrant decided to conduct new GLP and OECD conform studies on:

1) ready biodegradation (OECD 301D) and

2) inherent biodegradation (OECD 302C).

In contrast to the assumption that the existing data on biodegradation might have been flawed, the new studies confirmed that ready and inherent biodegradation of ditolyl ether are low with 2-3% after 28 days.

Concluding, existing and new studies on ready and inherent biodegradation reported only 2-3% degradation. Based on these screening studies ditolyl ether is not rated as biodegradable.