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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The test substance attained 91% oxidation at day 28 in the modified CO2 evolution test. > 60% oxidation was achieved within the 10 day time window. The substance can therefore  be classified as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

In order to assess the biotic degradation, four biodegradation screening tests were performed. Three tests assessed the biodegradability in aerobic aqueous media, whereas one test was performed under anaerobic conditions.

Aerobic degradation

One study (Lebertz, 1992) was disregarded because of the lack of COD method explanation and insufficient correction of nitrification. The two other aerobic degradation studies were performed according to OECD TG 301B (CO2 evolution test) and both studies were considered reliable with restrictions due to the lack of substance identification data. 

The key study (Clarke, 2003) was performed to assess the ready biodegradability of the test material in an aerobic aqueous medium. The method followed that described in the OECD TG 301B under GLP conditions (reliability 2). The test material was exposed to activated sewage sludge micro-organsims with culture medium in sealed culture vessels in the dark at 21 ° C for 28 days. The degradation of the test material was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the standard material, sodium benzoate, together with a toxicity control were used for validation purposes. The test material attained 91% oxidation after 28 days. By inspection of the degradation curve the test material achieved 10% oxidation between days 4 and 5 and 60% oxidation between days 13 and 14 thereby satisfying the 10 -day window validation criterion whereby 60% oxidation must be attained within 10 days of the degradation exceeding 10%.The test material can therefore be considered to be readily biodegradable meeting the 10-day window criterium.

The results of the key study are supported by the other aerobic degradation study (OECD 301B, GLP, reliability 2) where an oxidation percentage of 78% was reported at a test concentration of 5 ppm after 28 days (Danneberg, 1993).

 

Anaerobic degradation

The study was performed to assess the anaerobic biodegradability of the test material in an anaerobic aqueous medium.The study followed the method described in ECETOC Technical Report No. 28 "Evaluation of anaerobic biodegradation" and ISO Guideline No 11734 "Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in digested sludge - Method by measurement of the biogas production". The study was considered reliable with restrictions due to the lack of information on the substance identification (reliability 2). The test material was exposed to anaerobic sewage sludge micro-organsims at a concentration of 50 mg C/L with culture medium in sealed culture vessels in the dark at 35 °C for 56 days. The degradation of the test material was assessed by the production of gas and formation of dissolved inorganic carbon. Control solutions with inoculum and the standard material, sodium benzoate, together with a toxicity control were used for validation purposes. The test material attained 53% mineralisation after 56 days calculated from the volume of gas produced and 50% mineralisation from dissolved inorganic carbon formation.

Conclusion

Based on the key study (OECD 301B, GLP, reliability 2) it can be concluded that the substance fulfills the criterion for readily biodegradability meeting the 10 day window criterion. The substance is also likely to degrade under anaerobic conditions although at a slower rate compared to aerobic conditions.