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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

under test conditions no biodegradation observed

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The substance under registration (CAS 67786-25-8) was tested for the ready biodegradability, according to modified OECD screening test OECD 301E and a degradation of about 11 % in 28 days was reported (Ellgehausen H., 1986). The result is supported by the outcomes from the BOD:COD ratio study available (Ciba-Geigy Ltd., 1992), thus the CAS 67786-25-8 can be considered as non ready biodegradable. In fact, according to the endpoint specific ECHA guidance[1], the 5-day biochemical oxygen demand (BOD5) can be used for classification purposes about the readily biodegradation potential.

Furthermore, the conclusion about ready biodegradability is consistent with the Zahn Wellens test results, in which a degradation of 3 % in 28 days was observed (Ciba Geigy Ltd., 1992). The studies presented suggest that the substance is neither readily nor inherently biodegradable.

The same behaviour was observed for the similar substance belonging to the Stilbene Fluorescent Whitening Agents CAS 16470-24-9; it is he analogue dihydroxyethylamino derivative tetrasulphonated. The substance under registration and the analogous share the same functional groups, with the difference that CAS 67786-25-8 is the dihydroxyisopropylamino derivative, while CAS 16470-24-9 is the dihydroxyethylamino derivative; the difference has no impact on the biodegradation potential, as well as quantity and chemical identity of the impurities have no influence on the possibility of Read Across for this end point. Both substances are tetrasulphoned sodium salts and both are very soluble in water (1000 g/l Vs 650 g/l, respectively). For further details refer to the Category Justification Report to the section 13 of the dossier.

In the ready biodegradability test, performed according to OECD guideline 301A, a DOC removal of 1.2 % was observed (Ciba-Geigy Ltd., 1992), demonstrating a non-ready biodegradation potential.

Also in the case of the inherent biodegradability the CAS 16470-24-9 behaviour observed in the two Zahn Wellens tests is similar to that observed in the same test for CAS 67786-25-8: in one case a biodegradation of 24 % after 28 days was indicated (Ciba-Geigy Ltd., 1992). This value is obtained at about the fifth day, afterwards the degradation process seems to stop. The slope of the 28 days curve and the second test of inherent biodegradation (Novartis Services AG., 1997) reported suggest that the 24 % of DOC removal recorded in the first test can still be related to a slow adsorption process more than a biological degradation..

In conclusion, the substance can be considered as neither readily nor inherently biodegradable.

[1]Guidance on information requirements and Chemical Safety Assessment, Chapter R.7b: Endpoint specific guidance (Version 1.1, May 2008).