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EC number: 807-113-1
CAS number: 3709-71-5
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
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,
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