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Determination of ‘ready’ biodegradability: carbon dioxide (CO2) evolution test (modified Sturm test) with Thioanisole.

The study procedures described in this report were based on the OECD guideline No. 301B, 1992. In addition, the procedures were designed to meet the test methods of the Commission Regulation (EC) No. 440/2008 of 30 May 2008, Publication No. L142, Part C. 4-C and the ISO International Standard 9439, 1999.

Thioanisole was a colourless to slightly yellowish liquid with a purity of at least 99 %. The test substance was tested in duplicate at approximately 17.5 mg/L, corresponding to 12 mg TOC/L. The organic carbon content was based on the molecular formula. The theoretical CO2 production (ThCO2) of Thioanisole was calculated to be 2.48 mg CO2/mg. Preparation was as much as possible performed under yellow light and/or dimmed light conditions.

The study consisted of six bottles:

-2 inoculum blanks (no test substance)

- 2 test bottles (Thioanisole)

- 1 positive control (sodium acetate) and

- 1 toxicity control (Thioanisole plus sodium acetate).

Since Thioanisole was not sufficiently soluble to allow preparation of an aqueous solution at a concentration of 1 g/L, weighed amounts were added to the 2 litres test bottles containing medium with microbial organisms and mineral components. To this end, 10 mL of Milli-RO water was added to each weighing bottle containing he test substance. After vigorous mixing (vortex) the resulting suspension was added quantitativel to the test medium. The test solutions were continuously stired during the test, to ensure optimal contact between the test substance and the test organisms. Test duration was 28 days (last CO2-measurement on the 29thday).

The relative biodegradation values calculated from the measurements performed during the test revealed no significant biodegradation of Thioanisole. In the toxicity control, Thioanisole was found not to inhibit microbial activity.

Since all criteria for acceptability of the test were met, this study was considered to be valid.


In conclusion, Thioanisole is designated as not readily biodegradable.