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Environmental fate & pathways

Phototransformation in air

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Description of key information

By weight of evidence, Perfluoro-N-methylmorpholine (PMM) is expected to have an atmospheric lifetime in the range of 1600 – 4000 years.

Key value for chemical safety assessment

Additional information

PMM 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, PMM will not partition from the atmosphere to other compartments. Therefore, phototransformation processes will control its fate. The susceptibility of PMM to phototransformation in the atmosphere was assessed in a single study. PMM was resistant to direct photolysis under medium pressure mercury lamp irradiation, as well as indirect photolysis by hydroxyl radical. PMM 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 greater than 1600 years by indirect processes. 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 (1). Presence of oxygen and nitrogen in PMM does not stabilize the molecule, therefore a maximum atmospheric lifetime of 4000 years can be established by analogy with medium chain perfluoroalkanes. PMM 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 (2). Ultimate degradation products are expected to be CO2, HF and NOx compounds.

1) 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.

2) 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.