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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The test item attained 82% degradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60% degradation must be attained within 10 days of the degradation exceeding 10%.  The test item can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301B.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Introduction.

A study was performed to assess the ready biodegradability of the test item in an aerobic aqueous medium. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (1992) No 301B, "Ready Biodegradability; CO2Evolution Test" referenced as Method C.4-C of Commission Regulation (EC) No. 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OPPTS 835.3110 (Paragraph (M)).

Methods.

The test item, at a concentration of 10 mg Carbon/l, was exposed to activated sewage sludge micro-organisms with culture medium in sealed culture vessels in the dark at approximately 21°C for 28 days.

Following the recommendations of the International Standards Organisation (ISO 1995) and the published literature (Handley et al, 2002), the test item was adsorbed onto granular silica gel prior to dispersion in the test medium to aid dispersion of the test item in the test medium and to increase the surface area of the test item exposed to the test organisms.

The degradation of the test item was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the reference item, sodium benzoate, together with a toxicity control were used for validation purposes.

Results

The test item attained 82% degradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60% degradation must be attained within 10 days of the degradation exceeding 10%. The test item can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301B.

The toxicity control attained 72% degradation after 14 days thereby confirming that the test item was not toxic to the sewage treatment micro-organisms used in the test. 

Sodium benzoate attained 67% degradation after 14 days and 81% degradation after 28 days thereby confirming the suitability of the inoculum and test conditions. 

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