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Diss Factsheets

Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The test material is readily biodegradable but fails the 10 day window.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

This endpoint was addressed using a read across approach to structural analogues of the registered substance. Two key studies are provided, one on tall oil and one on ethanolamine. In this respect it is considered that the data submitted provides an adequate reflection of the test material.

 

The biodegradability of the read across substance distilled tall oil was investigated in accordance with the standardised guideline OECD 301D under GLP conditions. The study was assigned a reliability score of 2 in accordance with the criteria of Klimisch (1997).

The biodegradation of the organic compounds in the test material by inoculum obtained from a domestic waste water treatment plant, at an initial concentration of 1.96 mg/L, was determined by measuring the oxygen consumption in BOD test bottles. The measured oxygen consumption was compared to the theoretical oxygen demand for a complete degradation of the test material. The theoretical oxygen demand was expressed as the chemical oxygen demand (COD). Sodium benzoate was used as a reference material to evaluate the suitability of the inoculum.

The test material did not inhibit the respiratory activity in the inoculum. The secondary effluent used as inoculum was found to have a satisfactory activity as sodium benzoate was degraded more than 60 % within the first 7 days of the test period.

The biological oxygen demand for the test material was 43 and 60 % of the theoretical oxygen demand after 7 and 28 days respectively. These results indicate that the test material is dominated by readily biodegradable compounds and contains recalcitrant chemicals as well.

Under the conditions of this study, a biodegradation value of 60 % was obtained for the test material after 28 days. It is therefore considered to be readily biodegradable but failing the 10 day window.

 

The second key ready biodegradability study investigates the read across substance ethanolamine in accordance with the standardised guideline OECD 301A. The study was assigned a reliability score of 2 in accordance with the criteria of Klimisch (1997).

From an initial concentration of the test material of 20 mg/L, DOC removal over 21 days was monitored to form an estimate of the percentage biodegradation of the test material by activated sewage sludge from a domestic source. After 21 days, it was determined that more than 90 % of the test material had been degraded.

Under the conditions of this study, the test material was determined to be readily biodegradable.

 

Under the conditions of these studies, both the tall oil and ethanolamine components of the test material are considered to be readily biodegradable; however the distilled tall oil failed the 10 day window. On this basis, and as a precautionary measure, the overall determination that will be carried forward for risk assessment of the registered substance will be readily biodegradable but failing the 10 day window.