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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Two guideline-conform studies on biodegradation are available. The 1996 study on ready biodegradability via the manostatic respirometry method (OCED 301F) revealed only 9% degradation after 28 days, thus clearly failing the ready biodegradability criteria. The 1989 Zahn-Wellens-Test (OECD 302 B) revealed a degree of degradation of 70% after 28 days, indicating that the test item can be considered as inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

Zahn-Wellens-Test, BASF 1989:

A mixture containing the test substance, mineral nutrients and a relatively large amount of activated sludge in aqueous medium is agitated and aerated at 20-25°C in the dark or in diffuse light for up to 28 days. Blank controls, containing activated sludge and mineral nutrients but no test substance, are run in parallel. The biodegradation process is monitored by determination of DOC in filtered samples taken at certain time intervals. The ratio of eliminated DOC, corrected for the blank, after each time interval, to the initial DOC value is expressed as the percentage biodegradation at the sampling time. The percentage biodegradation is plotted against time to give the biodegradation curve. This valid study which followed OECD Guideline 302 B revealed a degree of degradation of 70% after 28 days indicating that the test item can be considered as inherently biodegradable.

Manostatic respirometer study, BASF 1996:

A measured volume of inoculated mineral medium, containing a known concentration of test substance as the nominal sole source of organic carbon, is stirred in a closed flask at a constant temperature. The consumption of oxygen is determined by measuring the quantity of oxygen (produced via electrolysis of a copper sulfate solution) required to maintain constant gas volume in the respirometer flask. Evolved carbon dioxide is absorbed in a solution of potassium hydroxide. The amount of oxygen taken up by the microbial population during biodegradation of the test substance (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of ThOD. In a valid study conducted under GLP which followed OECD Guideline 301 F, after 28 days a degree of degradation of 9% was observed. The test item therefore is not readily biodegradable.