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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

In an OECD TG 306, the test material attained 87% degradation after 28 days and therefore can be considered to have the potential for biodegradation in the marine environment.

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Justification for Read Across

Attached at section 13 is a category justification that explains the rationale for using data on a mixture of Dimethyl Esters (DBE), and Dimethyl Glutarate, to supplement the available data on Dimethyl Adipate.

One reliable key study (Mead, 2001) on the marine biodegradability is available. The method followed that described in the OECD TDG 306, (1992) "Biodegradability in Sea Water; Closed Bottle Test" and US EPA Fate, Transport, and Transformation Test Guidelines OPPTS 835.3160.

The test material, at a concentration of 2.0 mg/L, was exposed to marine micro- organisms with test medium in sealed culture vessels in the dark at 20 °C for 28 days. The degradation of the test material was assessed by the determination of the amount of oxygen consumed. Control solutions containing the standard material, sodium benzoate, together with a toxicity control were used for validation purposes.

For the purpose of the definitive study the test material was dissolved directly in test medium. An amount of test material (100 mg) was dissolved in test medium with the aid of ultrasonication (approximately 20 minutes) and the volume adjusted to 100 mL to give a 1000 mg/L stock solution. An aliquot (12 mL) of this stock solution was dispersed in a final volume of 6 litres of test medium to give a concentration of 2.0 mg/L. The volumetric flask containing the stock solution was inverted several times to ensure homogeneity of the solution.

A test concentration of 2.0 mg/L was employed in the study as the Theoretical Oxygen Demand (ThOD) of the test material was calculated to be 1.60 mg O2/mg. Hence if complete degradation of the test material occurred, the oxygen depletion in the test vessels would be 3.20mg O2/L and as such deoxygenation of the test media would not occur. Analysis of the concentration, homogeneity and stability of the test material in the test solutions were not appropriate to the Test Guideline.

The oxygen depletion in the control vessels was 17% of the initial dissolved oxygen concentration and the residual oxygen concentration remained at 1.55mg O2/L or greater in all test vessels, thereby satisfying the validation criteria for oxygen depletion.

The toxicity control attained 67% degradation after 28 days. The degradation rate in the toxicity control was lower than that expected based on the sum of the oxygen depletion values for the test and standard material. This effect is considered to be due to the marine micro-organisms present in the test medium being unable to degrade both the sodium benzoate and test material present simultaneously and hence the low degradation rate. However, the results of this and the test material vessels clearly show that the test material is not toxic to the micro-organisms present. The standard material, sodium benzoate, attained 71% degradation after 28 days thereby confirming the suitability of the test method and culture conditions.

The test material attained 87% degradation after 28 days and, therefore, can be considered to have the potential for biodegradation in the marine environment under the terms and conditions of OECD Guideline No 306.