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Environmental fate & pathways

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Description of key information

Novec 7700 is a segregated hydrofluoroether. It is a liquid at room temperature with a vapor pressure of 150 Pa (1.1 mm Hg) at 25 °C. Novec 7700 water solubility is 0.407 µg/L at 22.6 °C. Its measured Henry’s law constant is 982 atm∙m³/mol at 23.4 °C. Releases of Novec 7700 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. The vapor pressure, low water solubility and high Henry’s law constant combine to move Novec 7700 from any terrestrial compartment into the atmosphere. Once in the atmospheric compartment, this compound will not partition to terrestrial or aquatic compartments based on the same properties. Therefore, this compound will remain in the atmosphere when released from industrial or professional applications. Information on Novec 7700 biodegradability is provided by readacross from the ethoxylated analogue Novec 7800. Novec 7800 was not degraded in an OECD301C test done with modifications for a volatile substance.

As explained in the justification for readacross, the structural difference between Novec 7700 and Novec 7800 is unlikely to lead to a difference in biodegradation potential. No biodegradation of Novec 7700 is expected under environmental conditions based on the Novec 7800 result. Degradation of Novec 7700 in the environment is expected to be by indirect photolysis in the troposphere, for which an overall half-life of 3.9 years was measured.  A short-lived diketone intermediate subject to rapid (t½ of 0.9 days) direct photolysis was detected in this experiment. Major degradation product was carbonyl difluoride for both Novec 7700 and the diketone intermediate; carbonyl difluoride hydrolyzes spontaneously under environmental conditions. Carbonyl difluoride detection may have been confounded with acetyl fluoride, as the two are difficult to distinguish spectrographically and branching along the substance backbone would lead to acetyl fluoride production. The  expected final degradation products are hydrofluoric acid (HF, CAS# 7664-39-3), trifluoroacetic acid (TFA, CAS# 76-05-1) and carbon dioxide. These materials are miscible in water and are completely ionized in rainwater. They are expected to undergo wet deposition with no further significant transformation upon return to the troposphere. Novec 7700 has a measured log Kow of 6.6.  However, Novec 7700 is expected to have little potential to bioaccumulate. Given its extremely short half-life in the aquatic compartment 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 under relevant conditions.

As Novec 7700 is a highly fluorinated substance, 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 (1). F* radicals are rapidly and irreversibly removed from the atmosphere after quenching as HF. Therefore, neither Novec 7700 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. Novec 7700 has an estimated GWP of 420 over a 100-year integrated time horizon.

Reference:

1) 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.

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