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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The ready biodegradation of the test substance, TM 11-213, was 0 % at 21°C after 28 days according to OECD Test Guideline 301B using the CO2 Evolution method. Before this test was carried out pre-study solubility work was performed in order to determine the most suitable method of preparation.  From the pre-study solubility work and following the recommendations of the International Standards Organisation (ISO, 1995) it was concluded that the optmal dispersion was obtained when the test item was ultrasonicated in approximately 400 mL mineral media for 15 minutes prior to addition to the test vessel. The test item, at a concentration of 10 mg Carbon/L, was exposed to activated sewage sludge micro-organisms with mineral medium in sealed culture vessels in the dark at approximately 21°C for 28 days. The biodegradation of the test item was assessed by the determination of carbon dioxide produced.  The test item attained 0 % biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No. 301B. In the toxicity control (sodium benzoate plus test substance the biodegradation of the control exceeded the 25% limit which according to the test criteria confirmed that the test substance wasnot inhibitory to the sludge micro-organisms.. Value used for CSA: Biodegradation in water: under test conditions no biodegradation observed

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Two studies were performed to investigate the ready biodegradabilityof the test item in the presence of unacclimatized sewage sludge micro-organisms. In he first study no measurable biodegradation was observed. This result was somewhat unexpected because some biodegradation was anticipated based on BIOWIN 5 and 6 predictions, which showed a probability between 0.7 and 0.8. The computer models may have overpredicted since the fused rings are considered to be hindering biodegradation even though the alkyl side chain was expected to be biodegradable. The biodegradation may also be hindered because of limited water solubility which would decrease bioavailability to the sludge microorganisms. Therefore a second test was performed.

The first ready biodegradability study was performed according to OECD Test Guideline 301F - Manometric Respirometry Test method. Unacclimatised sewage microorganisms were used and the amount of oxygen consumed was measured over a28-day test period. The test item was adsorbed onto a glass fibre filter and then added to the inoculated medium in test vessel at a level of 33.2 mg/L, equivalent to 95.5 mg ThOD/L (n=2). The percentage degradation of TM 11-213 after 28 days averaged 0.5 % (n = 2). 

In view of the anticipated difficulties associated with the evaluation of the biodegradability of organic compounds with low water solubility, a modification to the standard method of preparation of the test concentration was included in a second study assess the ready biodegradabilityof the test item in an aerobic system.. The method followed was compatible with the OECD Test Guideline 301B-CO2 Evolution test method, described at the key information.