Disodium [2,4-dihydro-4-[(2-hydroxy-5-nitrophenyl)azo]-5-methyl-2-phenyl-3H-pyrazol-3-onato(2-)][3-hydroxy-4-[(2-hydroxy-1-naphthyl)azo]-7-nitronaphthalene-1-sulphonato(3-)]chromate(2-)

Biodegradation in water: screening tests

Description of key information

Inherent primary biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

The biodegradation of Acid Brown 282 (ABr282) was evaluated following the Zahn-Wellens/EMPA test procedures, adopted as OECD Guideline 302 B for determining inherent biodegradability. In both the reliable available studies, it was recorded an elimination of ABr282 higher than 20 %, but less than 70 % degradation after 28 days of contact time: 24 % in the Archroma study (Archroma Germany GmbH, 2005) and 32 % in the Huntsman study (Huntsman Textile Effects (Germany), 1995). Therefore ABr282 can be termed as inherent, primary biodegradable under the conditions of the OECD guideline no. 302 B.

A third Zahn/Wellens test is available (Huntsman Textile Effects (Germany), 1989), but it has been disregarded on the basis of the lot composition tested: the dye concentration was just of 26 % and the remaining components are all ready biodegradable. This may explains why a complete degradation was observed after 16 days.

Inherent biodegradability data may be used for extrapolation to a rate constant in models for estimation of the elimination of chemicals in the STP, nevertheless, this extrapolation is only allowed if the pass level of 70 % degradation in the Zahn-Wellens/EMPA has been reached. Therefore in this case the results cannot be used for the estimation of the substance elimination in STP.

The substance is not expected to be ready biodegradable. The QSAR based screening criterion for identifying substances for persistency (P and vP) confirmed that the substance is expected to be persistent and this estimated behaviour is supported by the results obtained from the BOD5:COD studies available.

In conclusion, ABr282 undergoes a primary degradation in the first days of the test, when it reaches a percentage of degradation that remains similar for the following days, up to the 28th day. It is clear that ABr282 is not ready biodegradable, nevertheless the test results do not provide sufficient information to clearly confirm the substance to be persistent.