Registration Dossier

Environmental fate & pathways

Endpoint summary

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HFP kinetic dimer is used as a process aid for polymer manufacture. HFP kinetic dimer is a liquid at room temperature with a vapor pressure of 34.7 kPa at 20°C. The water solubility is 649 µg/L at 22.3 °C. The measured Henry’s Law constant (HLC) is 1.40E+07 Pa·m³/mol (138 atm·m³/mole). The vapor pressure, low water solubility and high Henry’s law constant combine to move HFP kinetic dimer from any terrestrial compartment into the atmosphere. Evaporation of HFP kinetic dimer from surfaces is rapid. Fugacity modeling indicates that distribution from soil to air dominates over all other processes, and therefore that release to soils would result in rapid volatilization to the atmospheric compartment. Because articles containing the substance are only used indoors, the substance is not exposed to weathering; essentially all releases are to the atmospheric compartment. Assuming 100% release to the atmospheric compartment, 99.996% of substance remains in the gas phase of the air compartment, with 0.0036% in gas-filled pore paces, and 0.00020% sorbed to soil solids. Therefore, this compound will remain in the atmosphere when released from industrial applications. However, disposal of articles at the end of their service life may be by landfill. In the worst case, with 100% of HFP kinetic dimer emission directed to the soil compartment, 97.9% of HFP kinetic dimer was predicted to be in the gas phase in the air compartment, whereas 2.0% was predicted to be in the gas-filled pore spaces in the soil, and 0.11% sorbed to soil solid. It is not biodegradable, and hydrolysis is not expected to contribute to environmental degradation. Degradation in the environment is by indirect photolysis, with a half-life of approximately 0.57 years (overall atmospheric lifetime, 0.82 years). The pathway for decay is expected to be analogous to that for perfluorobutene (1), i.e., addition of hydroxyl radical to the unsaturated group followed by scission to form a carboxylate moiety from each of the two unsaturated carbons. The ultimate degradation products are expected to be perfluoroisobutyric acid (i-PFBA, CAS# 335-10-4), trifluoroacetic acid (TFA, CAS# 76-05-1) and hydrofluoric acid (HF, CAS# 7664-39-3). These acids are miscible in water and are completely ionized in rainwater. They are expected to undergo wet deposition with no further significant transformation. Please note that a published environmental risk assessment on TFA is available in the literature (2).

USEPA states flatly that fluorocarbons do not deplete ozone because they lack chlorine or bromine. Fluorine radicals do not contribute to ozone depletion because of fast quenching of F* by water or hydrogen donors, slow reaction of FO* radicals with oxygen, and obligate reformation of F* in the pathway (3). F* radicals are rapidly and irreversibly removed from the atmosphere after quenching as HF. Therefore, neither HFP kinetic dimer nor any of its acidic photodegradation products contribute to ozone depletion.

HFP kinetic dimer is not expected to partition to moist soils or surface waters. Upon accidental, direct release to the aquatic compartment, the chemical is expected to volatilize rapidly. In closed-bottle (OECD301D) assays, ≤12% biodegradation was observed. HFP kinetic dimer has a measured n-octanol: water partition coefficient of 4.1 and is expected to have little potential to bioaccumulate. The calculated log Koa of HFP kinetic dimer is 0.39. This log Koa value indicates that HFP kinetic dimer has a low potential to partition from air to the lipid rich tissues of air-breathing organisms. Given its extremely short half-life due to volatilization, it would not remain in aquatic environments or organisms for a sufficient time to allow partitioning into lipid tissues or to permit meaningful testing of bioconcentration.

Partitioning of i-PFBA, TFA, and HF in the environment is driven by the fact that these acids are completely ionized at environmental pH values, are miscible in water, and are not likely to bind with organic matter based on low Koc values and low log Kow values. i-PFBA, TFA, and HF will be associated with the aqueous phase of any environment where they are released, and will be highly mobile in soils. i-PFBA, TFA, and HF that have deposited in aquatic compartments are expected to remain in the aquatic compartment.

The registrant is not aware of information on biodegradation of i-PFBA. The registrant has assessed perfluoropropanoic acid (PFPA) in ready biodegradation tests and demonstrated that essentially no biodegradation occurs. TFA (see below) is similarly not biodegraded. Based on results from other internally-conducted studies of longer chain perfluorinated chemicals, it is anticipated that microorganisms will not be capable of utilizing i-PFBA as a carbon source. It has been shown from studies with many other perfluorinated moieties that fluorochemicals are oxidatively recalcitrant and resistant to most conventional waste treatment technologies (4). It can be assumed that i-PFBA will remain as i-PFBA and not degrade further under environmental biotic conditions. Therefore, i-PFBA is not expected to biodegrade in surface waters, sediments or soils. i-PFBA is a strong acid which is expected to be entirely deprotonated at environmental pH, with an estimated logD less than -0.34 at pH > 5.5 as predicted by QSAR software (Advanced Chemistry Development, Inc. (ACD/Labs) Toronto, Ontario, Canada. Version 12). The registrant has completed a bioconcentration study of n-PFBA in carp. The BCF at steady state was found to be <3 - 6. Based on readacross of the n-PFBA result and the modeled partition coefficient, i-PFBA is not expected to bioaccumulate in aquatic organisms.

A review of available literature indicates that TFA is not readily biodegradable and would be considered very persistent in the environment (2). TFA is very water soluble, with a lower solubility limit > 10 g/mL (2). As a water soluble anion, it is not expected to bioconcentrate in aquatic organisms. A calculated log Kow value of -2.1 has been proposed (2). BCF data was available only for terrestrial plants. At concentrations at or below the no effect level of 1 mg/L, literature bioconcentration factors ranged from 5.4 to 27 (2).

HF is an inorganic mineral acid. It is not subject to biodegradation or bioconcentration.

References:

1) C.J. Young, M.D. Hurley, T.J. Wallington, S.A. Maybury. 2009. Atmospheric chemistry of perfluorobutenes (CF3CF=CFCF3 and CF3CF2CF=CF2); kinetics and mechanisms of reactions with OH radicals and chlorine atoms, IR spectra, global warming potentials, and oxidation to perfluorocarboxylic acids. Atmospheric Environment: Vol. 43, pp. 3717-3724.

2) Boutonnet (Ed.), 1999. Environmental Risk Assessment of Trifluoroacetic Acid. Human and Ecological Risk Assessment: Vol. 5, No. 1, pp. 59-124.

3) A.J. Colussi, M.A. Crela. 1994. Rate of the reaction between oxygen monofluoride and ozone. Implications for the atmospheric role of fluorine. Chem. Phys. Lett. Vol. 229, pp. 134-138.

4) C. D. Vecitis, H. Park, J. Cheng, B. T. Mader, M. R. Hoffman.  2009.  Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA).  Front. Environ. Sci. Engin. China.  Vol. 3, No. 2, pp. 129-151.