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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

No ready biodegradation has been tested on the substance, but some information is existing in the form of summaries reporting data about BOD5 and inherent biodegradation (Ciba-Geigy 1995 - Zahn Wellens OECD 302B). The Zahn Wellens study reports a variation in the DOC in the first 5 days of about 76 %, afterwards no or negligible degradation is observed. The existing BOD5 measurements (Whitehead M. 1990 and Ciba-Geigy 1995) indicate respectively no oxygen consumption and 10% oxygen consumption in the first 5 days, supporting the hypothesis that the DOC removal in the first 5 days is not related to biodegradation process, but to a slow adsorption process.

The same behaviour has been observed for the similar substance of the Stlbene Fluorescent Whitening Agents CAS 16470-24-9, the analogue dihydroxyethylamino derivative tetrasulphonated, for which the related data are reported here.

In a ready biodegradability test according to OECD guideline 301A (key study) a DOC removal of 1.2 % was observed. Hence, the substance CAS 16470-24-9 is considered not readily biodegradable. Three BOD5 tests, in which no oxygen consumption was measured, confirm the non rapid biodegradability of the test substance. Additional information is given from two Zahn Wellens tests (OECD 302B). One of the two indicates a biodegradation of 24% after 28 days. This value is reach at about the fifth day; afterwards the degradation process seems to stop. The slope of the 28 days curve, the second test of inherent biodegradation and the BOD5/COD reported suggest that this 28% DOC removal 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.