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EC number: 807-113-1 | CAS number: 3709-71-5
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The logarithm of the organic carbon normalized adsorption coefficient (log Koc) for HFP kinetic dimer could not be determined by an HPLC method according to OECD TG121. The log Koc value was instead calculated using the experimental log Kow value and the equation specified for 'Predominantly hydrophobics' in Chapter 4 of the Technical Guidance Document on Risk Assessment. The log Koc value so calculated was 3.4.
The Henry’s Law constant (HLC) for HFP kinetic dimer was measured directly using concentrations in a water-air system. The dimensionless HLC was 5690 at 22 °C, 760 mmHg (HLC in unit-specific values: 1.40E+07 Pa∙m³/mol, or 138 atm∙m³/mole). Koa was determined by combining dimensionless Kow reported as an intermediate result in the partition coefficient study report with the dimensionless HLC. The overall Koa value for HFP kinetic dimer is 2.46 (log Koa, 0.39). Considering the HLC, Koa and the Koc values, the majority of HFP kinetic dimer is expected to volatilize from soil or aqueous solution in open systems. Only a very small amount of HFP kinetic dimer is expected to dissolve and subsequently be available for leaching in soil. Adsorption to soil or suspended particles is not an important fate for HFP kinetic dimer in environment.
Distribution in the environment was modeled using a Level III fugacity model, EQC model V1.01. The EQC model was developed for use with highly volatile and poorly water soluble compounds and was validated against data for decamethylcyclopentasiloxane, i.e. D5.(1) Two cases were examined: 100% release to the atmospheric compartment and 100% to the soil compartment. In the atmospheric-release case, 99.996% of HFP kinetic dimer was predicted to be in gas phase in the air compartment, whereas 0.0036% was predicted to be in the gas-filled pore spaces in the soil, and 0.00020% sorbed to soil solids. The half-time for transport from soil to air was predicted to be 1.47 hours, which is several orders of magnitude shorter than transport from air to soils or from air to water. In the soil-release case, 2.11% was predicted to be retained in the soil, of which 2.00% is in the gas-filled pore spaces and 0.11% is sorbed to soil solids. Only negligible amounts of HFP kinetic dimer are expected to be present in aquatic systems or soils.
1) Hughes, L.; Mackay, D.; Powell, D. E.; Kim, J. An updated state of the science EQC model for evaluating chemical fate in the environment: Application to D5 (decamethylcyclopentasiloxane). 2012, Chemosphere, 87, 118-124. The model was downloaded from the Canadian Centre for Environmental Modelling and Chemistry, http://www.trentu.ca/academic/aminss/envmodel/models/NewEQCv101.html .
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