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Environmental fate & pathways

Phototransformation in air

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Description of key information

By weight of evidence, FC-770 is expected to have an atmospheric lifetime in the range of 1600 – 4000 years. 

Key value for chemical safety assessment

Half-life in air:
1 100 yr

Additional information

FC-770 is expected to reside in the atmosphere. Given its uses, any releases will be solely to the atmospheric compartment. No releases to aquatic or terrestrial compartments are expected. Due to its high vapor pressure, high Henry’s Law constant, and low water solubility, FC-770 will not partition from the atmosphere to other compartments. Therefore, phototransformation processes will control FC-770 fate. The susceptibility of FC-770 to phototransformation in the atmosphere has not been directly assessed. However, perfluorinated chemicals are generally considered to be stable in the atmosphere. Specifically, the structural analog perfluoro-N-methylmorpholine (PNMM) was resistant to direct photolysis under medium pressure mercury lamp irradiation, as well as indirect photolysis by hydroxyl radical and O(1D) (singlet oxygen atoms). PNMM differs from FC-770 solely in the alkyl chain(s) attached to the morpholinic nitrogen. Comparison of UV spectra for FC-770 and PNMM reveals very little difference in absorption cross sections. As such, it is expected to have similar susceptibility to direct photolysis. As perfluoroalkyl chains are essentially inert to oxidative processes, FC-770 is expected to have similar reactivity to PNMM with regard to transformation by oxidizing species. PNMM showed potential reactivity with O(1D) at the limit of experimental error and no detectable reactivity with hydroxyl radical. Maximum rate constants for phototransfomation reactions are < 1.4E-17 cm³ molecule-1 s-1 [hydroxyl radical] and < 1.5E-11 cm³ molecule-1 s-1 [O(¹D)]. These correspond to minimum atmospheric lifetimes of 5570 years and 2000 years, respectively, and were lumped to provide an estimated atmospheric lifetime for PNMM greater than 1600 years by indirect processes. This minimum lifetime is read across directly to FC-770. The stability of the carbon-fluorine bond indicates that an upper limit for photochemical destruction can be made by analogy with simple perfluorocarbons (PFCs). The only important sinks for PFCs are photolysis or ion reactions in the mesosphere(1). Medium-chain perfluoroalkanes such as perfluoropentane and perfluorohexane have atmospheric lifetimes in the range of 3000 - 4000 years(2). Presence of oxygen and nitrogen in FC-770 does not stabilize the molecule, therefore a maximum atmospheric lifetime of 4000 years can be established by read-across from medium chain perfluoroalkanes. FC-770 is expected to undergo scission of carbon-carbon bonds on exposure to light in the vacuum UV range at high altitudes, with no stable degradation products formed once photoinitiation occurs(3). Ultimate degradation products are CO2, HF and NOx compounds.

 

1) D. Ehhalt, M. Prather, F. Dentener, R. Derwent, E. Dlugokencky, E. Holland, I. Isaksen, J. Katima, V. Kirchhoff, P. Matson, P. Midgley, M. Wang, 2001: Atmospheric Chemistry and Greenhouse Gases. In: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer,P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881 pp.

 

2) Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

 

3) C.J. Young, M.D. Hurley, T.J. Wallington, S. A. Mabury, 2006. Atmospheric lifetime and Global Warming Potential of a perfluoropolyether. Environ. Sci. Technol. Vol 40, pp. 2242-2246.