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Environmental fate & pathways

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As Benzyl acetate is a sparingly soluble compound, the CO2 production method is deemed beneficial. A new method based on OECD 301B was developed. The method used infra-red analysis to precisely determine carbon dioxide in both aqueous and gaseous samples thus allowing the test system to be scaled down considerably. In addition a 'cleaner' inoculum of similar activity to that recommended by the OECD guideline was obtained by using the secondary effluent from an activated sludge plant. This resulted in very much lowered CO2 production in the controls. The method was proven to be accurate and reliable by testing the four compounds used in the 1988 OECD ring testing together with a further eight reference compounds.

Benzyl acetate in a dilute mineral salts solution is incubated in sealed vessels with appropriate micro-organisms for 28 days. Only two thirds of the volume of the vessel is filled with liquid. At the test concentrations used only about 15% of the available oxygen in the headspace gas is required for the complete oxidation of all test compound carbon to carbon dioxide. Any carbon dioxide produced by the breakdown of the test material is distributed between the liquid and gaseous phases. Periodically a vessel is taken, a sample of the headspace gas withdrawn using a gas syringe and the concentration of carbon dioxide in the headspace gas determined. The seal is then broken and the concentration of dissolved inorganic carbon (DIC) in the solution is measured. Similar determinations are made for a control vessel which does not contain the test substance. The difference in the total inorganic carbon found in the test and control vessels allows the quantity of carbon dioxide produced from the test compound to be ascertained. From knowledge of the quantity of test material added and its carbon content the extent of mineralisation was calculated.

Benzyl acetate was found to biodegrade 100.9% over 28 days proving that the test substance is readily biodegradable.

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