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Environmental fate & pathways

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CAS# 297730-93-9 is a segregated ether with a completely fluorinated region and a hydrocarbon region.  The substance is a liquid at room temperature with a vapor pressure of 0.847 kPa at 20°C.  The water solubility of CAS# 297730-93-9 is 21.3 µg/L at 23 °C.  The measured Henry’s Law constant (HLC) is 4.7 x 107Pa m³/mol (464 atm m³/mol). Releases of CAS# 297730-93-9 are expected to be to the atmosphere based upon its intended uses.  Fugitive emissions may occur at transfer points.  During routine use, there is no anticipated release to water or wastewater in the EU.  Therefore, this compound will remain in the atmosphere when released from industrial applications.  The molecule contains no hydrolysable groups and is not biodegradable.  Degradation in the environment is initiated by indirect photolysis of the hydrocarbon region, with formation of segregated C7-perfluoroalkyl ester intermediates.  Initial phototransformation has a half-life of approximately 1.5 years.  The segregated esters are subject to direct and indirect photolysis.  No information on direct phototransformation rate is currently available.  Based on the available data, the esters appear to be longer lived in the atmosphere than the parent compound.  The ultimate degradation products are hydrofluoric acid (HF, CAS# 7664-39-3), trifluoroacetic acid (TFA, CAS# 76-05-1) and perfluorobutyric acid (PFBA, CAS# 375-22-4). Perfluoropropionic acid (PFPA, CAS# 422-64-0) may also occur in limited (<1% of PFBA yield) amounts.  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 (1).


As CAS# 297730-93-9 is a highly fluorinated chemical, global warming and ozone depletion potentials may be of interest.  USEPA states flatly that hydrofluorocarbons 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 (2). F* radicals are rapidly and irreversibly removed from the atmosphere after quenching as HF.  Therefore, neither CAS# 297730-93-9 nor any of its acidic photodegradation products contribute to ozone depletion. Global warming potential depends on three factors: absorption of infrared radiation, area of the spectrum the absorption occurs and lifetime of the material in the atmosphere.  CAS# 297730-93-9 has an estimated GWP of 100 over a 100-year integrated time horizon (calculation based on reported GWP relative to CFC-11)(3). Although the integrated absorption cross section of CAS# 297730-93-9 is large, the short atmospheric lifetime makes the global warming potential of the compound negligible.


In closed-bottle (OECD301D) assays, no biodegradation of CAS# 297730-93-9 was observed.  In an OECD 308 biodegradation simulation study in sediments done under aerobic and anaerobic condition, CAS# 297730-93-9 was determined to degrade very slowly (half life of 91 to 224 years in aerobic sediments and between 189 and 415 years in anaerobic sediments). Trace levels of PFBA formation was observed in both anaerobic and aerobic conditions. HFC-227 was also consistently detected at trace levels in the bioactive cultures of the anaerobic study. In the aerobic study, HFC-227 was occasionally detected but without a clear trend with time and later timepoints were also affected by an increase in limit of quantitation due to the oxygen replenishment procedure. However, CAS# 297730-93-9 is not expected to partition to moist soils or surface waters.  Upon accidental, direct release of CAS# 297730-93-9 to the aquatic compartment, the chemical is expected to volatilize rapidly.  Given its extremely short half-life due to volatilization, it will not exist in aquatic environments or organisms for a sufficient time to allow partitioning into lipid tissues or testing of bioconcentration meaningfully. Accordingly, CAS# 297730-93-9 is expected to have little potential to bioaccumulate.  Biodegradation and bioaccumulation can therefore be discussed in the context of the degradation products, predominantly acids resulting from photolysis in the atmosphere. 


Partitioning of HF, TFA and PFBA 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.  HF, TFA and PFBA will be associated with the aqueous phase of any environment where they are released, and will be highly mobile in soils.  HF, TFA and PFBA that have deposited in aquatic compartments are expected to remain in the aquatic compartment. 


A review of available information indicates that perfluorocarboxylic acids under aerobic conditions are not readily or inherently biodegradable. In addition, it has been shown from studies with many other longer chain perfluorinated moieties that fluorochemicals are oxidatively recalcitrant and resistant to most conventional waste treatment technologies (4). TFA (see below) is similarly not biodegraded.  Therefore, PFBA is not expected to biodegrade in surface waters, sediments or soils.  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).  A bioconcentration study of PFPA in carp has been completed.  The BCF at steady state was found to be 1.2 and < 4.8 at the two exposure concentrations.  Based on the available evidence, 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 (1).  TFA is very water soluble (> 10 g/mL(1)).  As a water soluble anion, it is not expected to bioconcentrate in aquatic organisms.  A calculated log Kow value of -2.1 (1) has been proposed.  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 (1).




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


2)   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.


3)    Goto, M., Inoue, Y., Kawasaki, M., Guschin, A. G., Molina, L. T., Molina, M. J., Wallington, T. J., Hurley, M. D.  2002.  Atmospheric Chemistry of HFE-7500 [n-C3F7CF(OC2H5)CF(CF3)2]: Reaction with OH Radicals and Cl Atoms and Atmospheric Fate of n-C3F7CF(OCHO∙)CF(CF3)2 and n-C3F7CF(OCH2CH2O∙)CF(CF3)2 Radicals.  Environ. Sci. Technol. Vol. 36, No. 11, pp. 2395-2402.


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.