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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The test substance is not readily biodegradable according OECD criteria.

Key value for chemical safety assessment

Additional information

In Article 13 of Regulation (EC) No 1907/2006, it is laid down that information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI (of the same Regulation) are met. Furthermore according to Article 25 of the same Regulation testing on vertebrate animals shall be undertaken only as a last resort.

According to Annex XI of Regulation (EC) No 1907/2006 (Q)SAR results can be used if (1) the scientific validity of the (Q)SAR model has been established, (2) the substance falls within the applicability domain of the (Q)SAR model, (3) the results are adequate for the purpose of classification and labeling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

For the assessment of the test substance (Q)SAR results were used for aerobic biodegradability in water.The criteria listed in Annex XI of Regulation (EC) No 1907/2006 are considered to be adequately fulfilled and therefore the endpoint(s) sufficiently covered and suitable for risk assessment.

Therefore, further experimental studies on aerobic biodegradability in water are not provided.

Both QSAR models show that the test substance is not readily biodegradable according OECD criteria. The EPI Suite v4.10 (BIOWIN Program v4.10) calculation resulted in "not readily biodegradable". The test substance was within the applicability domain of the model. Additionally, the biodegradation was calculated by using CATALOGIC v5.11.16 (BOD 28 days MITI (OECD 301C) v08.11). It resulted in 9 % biodegradation after 28 d. Even though the structural domain was correct with only 50 % (50 % unknown) the results support the overall conclusion in the weight of evidence.

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

Additionally, the weight-of-evidence is supported by the estimation of the BOD5 (CIBA-GEIGY Limited 1981). It was tested according to the German Guideline H-5. In this study concentrations of 1, 2, 3, 4 and 5 mg/L of test substance, a negative and a positive control (sodium benzoate) were tested. No biodegradation was observed during the exposure period of 5 days. The BOD5 for the test substance was 0 mg O2/mg test substance, and the TOD was 0.384 mg O2/mg test substance. The BOD5 for the reference substance was measured at 1.275 mg O2/mg which is equal to 95.8% biodegradation.

In overall conclusion, further tests on biodegradation are scientifically not justified.