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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Not readily biodegradable (according to OECD criteria).

Key value for chemical safety assessment

Additional information

Data on the ready biodegradability of the described 'red disazo pigment' are not available. However, two model calculations were conducted to assess the biodegradability in a weight of evidence. The EPI Suite v4.11 (BIOWIN Program v4.10) calculation resulted in "not readily biodegradable". Additionally, the biodegradation was calculated by using CATALOGIC v5.13.1 (BOD 28 days MITI (OECD 301C) v11.15). It resulted in ca. 0 % biodegradation after 28 d. Even though the structural domain was correct with only 84.62 % (15.38 % unknown) the results support the overall conclusion in the weight of evidence.

Moreover, the 'red disazo pigment' is practically insoluble and therefore considered to be essentially not bioavailable. Due to the large molecular size, cellular uptake of the pigment is unlikely. Hence intracellular biodegradation, which is the main degradation route of bacteria, is probably low. It can be concluded that the substance is likely to persist in the environment.

The dispersion stability (see chapter 5.6) of Pigment Brown 23 was strongly depended on water hardness. Dissolution was excluded as the main cause of the apparent stability. Only in soft water with 0 mM Ca(NO3)2 at pH 7 or 9 the dispersion stability was intermediate, at all other conditions the stability was low.

Nanomaterials do not reach a thermodynamical equilibrium between dispersed and dissolved phase. Nevertheless, the amount of the dissolved part is negligible due to the low solubility. The majority of the compound will be in its dispersed form which is still accessible for microorganisms.

For this reason no ready or inherent degradation studies are proposed.