Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment

Abstract

Following the introduction of hydrochlorofluorocarbon (HCFCs) and hydrofluorocarbon (HFCs) gases as replacements for the ozone-destroying chlorofluorocarbons (CFCs), it has been discovered that HCFCs/HFCs can degrade in the atmosphere to produce trifluoroacetic acid1, a compound with no known loss mechanisms in the environment2,3, and higher concentrations in natural waters4 have been shown to be mildly phytotoxic5. Present environmental levels of trifluooracetic acid are not accounted by HCFC/HFC degradation alone8,9,10. Here we report that thermolysis of fluorinated polymers, such as the commercial polymers Teflon and Kel-F, can also produce trifluoroacetate and the similar compound chlorodifluoroacetate. This can occur either directly, or indirectly via products that are known to degrade to these haloacetates in the atmosphere11. The environmental significance of these findings is confirmed by modelling, which indicates that the thermolysis of fluoropolymers in industrial and consumer high-temperature applications (ovens, non-stick cooking utensils and combustion engines) is likely to be a significant source of trifluoroacetate in urban rain water (25 ng l-1, as estimated for Toronto). Thermolysis also leads to longer chain polyfluoro- and/or polychlorofluoro- (C3–C14) carboxylic acids which may be equally persistent. Some of these products have recently been linked with possible adverse health6 and environmental impacts and are being phased out of the US market7. Furthermore, we detected CFCs and fluorocarbons—groups that can destroy ozone and act as greenhouse gases, respectively—among the other thermal degradation products, suggesting that continued use of fluoropolymers may also exacerbate stratospheric ozone-depletion and global warming.

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Figure 1: Proposed significant pathways in the thermal decomposition of fluoropolymers.
Figure 2: Proposed environmental reaction pathways for the thermal degradation of fluoro- and chlorofluoropolymers.

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Acknowledgements

We thank H. Sun, I. Manners, M. Ginzburg, D. McIntosh., D. Mathers, W. Yoo and F. Noventa for assistance with experimental procedures and the use of equipment, and F. Wania for assistance in environmental modelling. This work was supported by a Strategic Project Grant from the Natural Science and Engineering Research Council of Canada (NSERC); we thank Perkin Elmer for their equipment donation to the University of Toronto ANALEST facility.

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Correspondence to Scott A. Mabury.

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Ellis, D., Mabury, S., Martin, J. et al. Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment. Nature 412, 321–324 (2001). https://doi.org/10.1038/35085548

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