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Biodegradation in water: screening tests

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Description of key information

not readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

In the Klimisch 1 study from Soeter (2015) the biodegradability of SMPO Heavy ends was determined according to the ‘ready’ biodegradability: carbon dioxide (CO2) evolution test (modified Sturm test). The study procedures were based on the OECD guideline No. 301 B, 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, ISO 9439, 1999 and ISO 10634, 1995.

SMPO Heavy ends was a brown liquid. Since the organic carbon content could not be calculated, a sample of SMPO Heavy ends was taken for determination of the Total Organic Carbon (TOC) content. The TOC content of SMPO Heavy ends was determined to be 88%. The test substance was tested in duplicate at approximately 14 mg/l, corresponding to 12 mg TOC/l. Based on the TOC content the ThCO2 of SMPO Heavy ends was calculated to be 3.22 mg CO2/mg.

The study consisted of six bottles:

- 2 inoculum blanks (no test substance),

- 2 test bottles (SMPO Heavy ends),

- 1 positive control (sodium acetate) and

- 1 toxicity control (SMPO Heavy ends plus sodium acetate).

SMPO Heavy ends was not sufficiently soluble to allow the test substance to dissolve at the tested concentration. Therefore, SMPO Heavy ends was coated on an inert carrier (granular silica gel). For each replica 10 ml Milli-RO water was added to approximately 27 mg SMPO Heavy ends After vigorous mixing (vortex) the resulting suspensions were added to the individual test bottles containing 10 gram silica. 300 ml Milli-RO water was added to the coated silica and thoroughly mixing was applied for approximately 15 minutes to ensure homogenous distribution of the test substance.

The final test media were made up to 2 litres by adding inoculated medium and Milli-RO water. The test solutions were continuously stirred during the test, to ensure optimal contact between the test substance and the test organisms. Test duration was 28 days (last CO2-measurement on day 29).

The relative biodegradation values calculated from the measurements performed during the test period revealed 16% and 25% biodegradation of SMPO Heavy ends (based on ThCO2), for the duplicate bottles tested.

In the toxicity control, SMPO Heavy ends 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, SMPO Heavy ends was designated as not readily biodegradable.