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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Biodegradation in water: screening tests: 0.14% in 28d (OECD 310)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

A biodegradation rate of 0.14% in 28d, i.e. no biodegradation observed under test conditions, was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Itrich and Federle (2007) conducted a study to investigate the biodegradation of D5 by activated sludge microorganisms. The D5 used in the study was 14C-labelled on the methyl groups. The activated sludge sample used in the experiment was taken from a primarily domestic waste-water treatment plant in Ohio, USA (solids content 2228 mg/l).

The test method used was optimised to account for the volatile and adsorptive behaviour of D5. A stock solution of the test substance was prepared in tetrahydrofuran and then mixed with a concentrated solution of surfactant (a C45 alkyl sulfate) prior to dispersion in water. This dosing system was chosen to simulate domestic ‘grey water’.

The test flasks were sealed.

The final concentrations of D5 and the surfactant in the test vessel were 7.2 μg/l and 3 mg/l, respectively, and the pH of the solution was 7.1

The test vessels were incubated at 22°C for 28 days. During the test the headspace was continuously purged with CO2- free air, and the sludge was continuously mixed using a stirrer.

Traps were used to collect volatiles and CO2 evolved. Samples of the sludge solids were also collected and analysed for both 14C and the parent compound.

Overall recovery of 14C from the test chambers was good (average 102.1% in biotic vessels and 99.2% in abiotic vessels over the 28 days).

No significant formation of 14CO2 was observed during the study.

Some of the tetrahydrofuran extracts from the sludge solids (where most of the radioactivity was found to be distributed) were also analysed for the parent compound. These showed that the majority (88-99%) of the radioactivity in these extracts from both the biotic treatment and the abiotic controls was parent compound. No evidence for metabolites was apparent in these analyses.

Overall the results of this study show that no significant biodegradation or other transformation (e.g. hydrolysis) or loss process (e.g. volatilisation) occurred under the conditions of this study. This supports the result of the key study.

Itrich N R and Federle T W, 2007, Biotransformation of Decamethylcyclopentasiloxane (D5)

in Activated Sludge Waste Water Treatment. Experimental Summary, Environmental Science

Laboratory. Cincinnati, OH: Miami Valley Laboratories.