Theoretical investigation into the atmospheric reactions of fluorotelomer alcohols (FTOHs), with OH radicals
The scientific community has been investigating a new category of polyfluorinated compounds termed as perfluorinated carboxylic acids (PFCAs;CnF2n+1COOH). Focus has been on their origins, health impacts as well as environmental transformation and occurrence. PFCAs are cause severe health problems. For instance, they are believed to induce propensity to liver cancer. A great deal of research in recent years has given insightful information on human exposure, environmental occurrence and potential sources. Longer chains of PFCAs (i.e., n > 7) are particularly toxic and bioaccumulative. They have a tendency to accumulate in living tissues and to resist bio- and chemical degradation under conditions prevailing in abiotic and biotic systems in the environment. PFCAs are emitted to the environment through direct and indirect sources. The former relate to the use and manufacture of PFCAs. The later arise as a consequence of the atmospheric degradation of potent precursors into PFCAs. However, detailed accounting of indirect sources still remains a subject of ongoing scrutiny. One of the most discussed precursors candidates for the atmospheric formation of PFCAs are fluorotelomer alcohols (FTOHs;CF3(CF2)nCH2CH2OH). The environmental persistency of FTOHs enables them to undergo long-range atmospheric transport, which in turn increases their potential as direct precursors for the atmospheric generation of PFCAs. Formation of PFCAs from the atmospheric oxidation of FTOHs occurs only in the presence of excess NOx. Parallel reactions involving HO2 have also been suggested to account for the formation of PFCAs.
To provide an atomic-based understanding for the atmospheric chemistry of FTOHs, we report in this study a density functional theory (DFT) investigation into the initial reaction of OH radicals with CF3(CF2)nCH2CH2OH where n = 2-6. As the OH radicals are the sole initiators for the atmospheric oxidation of hydrocarbons in the atmosphere, calculated rate constants will be applied to estimate atmospheric half-lives of FTOHs. Our results are discussed in view of the available experimental observations. The effect of the size of the (CF2)n on the energetics and the kinetics of the abstraction process is also discussed.
|Publication Type:||Journal Article|
|Notes:||Paper presented at the 32nd International Symposium on Halogenated Persistent organic Pollutants - dioxin, 26 - 31 August, Cairns, Qld, Australia|
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