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Environmental fate & pathways

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On the basis of experimental data in the form of a biodegradability screening study (OECD 301B), Diurea 8 is not considered readily biodegradable (Harlan 2012). Due to the very low predicted water solubility of Diurea 8 (Dawick 2012), the hydrolysis and degradation in surface water endpoints have been waived. The sediment and soil simulation testing have been waived on the basis that the Chemical Safety Assessment has not indicated a need to further investigate these endpoints. Diurea 8 only ever occurs within a base oil grease designed to minimise leaching and the log octanol-water partition coefficients for constituents are estimated to be above 6 (Dawick 2012) which indicates Diurea 8 is likely to reside within the hydrophobic base oil grease matrix. The predicted physical-chemical properties (water solubility, vapour pressure and octanol-water partition coefficient), coupled with the fact that Diurea 8 is only ever manufactured within a base oil grease indicate that environmental exposures of Diurea 8 to air, soil and water compartments will be severely limited. In the event that constituents of Diurea 8 leached out of the base oil grease matrix, environmental partitioning would be primarily to soil or sediment. However, this process is considered highly unlikely and the exposure concentrations of Diurea 8 which would be available for bioaccumulation are extremely limited.

The reactions to form Diurea 8 occur in-situ during the grease manufacturing process and consequently Diurea 8 only ever exists within the base oil grease matrix. The matrix effect, as recognised by the OECD Lubricant Emission Scenario document (OECD 2004), needs to be taken into account as the process of manufacturing the thickener in an inert base oil is likely to influence factors such as the exposure levels and availability of Diurea 8 to man and the environment. In the grease manufacturing process unique interactions, more appropriately defined as intermolecular interactions (rather than chemical bonding), occur between the hydrocarbons within the base oil and the Diurea 8 thickener constituents. The chemistry is complex and the intermolecular interactions between the thickener and hydrocarbons within the base oil do not strictly fall under the definitions of a reaction product nor do they act as a simple mixture of components. In realistic use scenarios, the Diurea 8 thickener constituents will be contained within base oil, with the formulated greases specifically designed to minimise the leaching of the thickener to the external environment.

Reference

OECD (2004) OECD Series on emission scenario documents, Number 10: Emission scenario document on lubricants and lubricant additives. Environment directorate: Joint meeting of the chemicals committee and the working part on chemicals, pesticides and biotechnology. ENV/JM/MONO(2004)21