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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 Periodically a vessel is taken, a sample of the headspace gas withdrawn using a gas syringe and the concentration of carbon dioxide in the headspace gas determined.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 a 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.

Although no further testing is required according to the REACH Annex III column 2, a soil adsorption study was commissioned and a BCF was calculated.

Soil Adsorption, HLS, 2010:

A study was performed according to OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)). The purpose of the study was to estimate the adsorption coefficient (Koc) of Benzyl acetate by HPLC. Benzyl acetate was determined to have a log10 Koc value of 2.4 (equivalent Koc = 250).

Therefore, Benzyl acetate has a medium potential for soil mobility.

Bioaccumulation calculations:

The log Kow value of Benzyl acetate was found to be 1.96 (Sangster, 1989). The log Kow is below the trigger of 3 therefore the substance is not expected to bioaccumulate in living organisms. According to Column 2 of Annex IX of the REACH regulation, no bioaccumulation study is required if the log Kow is below the trigger of 3.

However, data was taken from the Handbook of Chemical Property Estimation Methods which describes the methods used for estimating bioconcentration factors in aquatic organisms. These methods are based on data from laboratory experiments that were designed to maintain relatively constant amounts of the chemical in the water environment, and where equilibrium concentrations of the chemical could be ascertained.

Using the above log Kow figure, a BCF was derived using the Handbook of Chemical Property Estimation Methods. The BCF was found to be 8. According to the guidance on information requirements and chemical safety assessment part B, Benzyl acetate is not considered to be hazardous as the BCF is below 10.

As Benzyl Acetate is readily biodegradable it can safely be assumed that there are no breakdown products of concern and no further testing to determine environmental pathways is required.

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