Understanding long-range transport mechanisms of perfluoroalkyl substances

Pickard, Heidi (2017) Understanding long-range transport mechanisms of perfluoroalkyl substances. Masters thesis, Memorial University of Newfoundland.

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Abstract

Perfluoroalkyl acids (PFAAs) are persistent, bioaccumulative compounds found ubiquitously within the environment. They can be formed from the atmospheric oxidation of volatile precursor compounds and undergo long-range transport (LRT) through the atmosphere and ocean to remote locations. Ice caps preserve a temporal record of PFAA deposition making them useful in studying the atmospheric trends in LRT of PFAAs as well as understanding major pollutant sources and production changes over time. A 15 m ice core representing 38 years of deposition (1977 – 2015) was collected from the Devon Ice Cap in Nunavut and analyzed for PFAAs. Samples were concentrated by solid phase extraction and analyzed by UPLC-MS/MS, IC, and ICP-OES. Both shortand long-chain perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs) were detected in the samples, with fluxes ranging from <LOD to 4.44×10⁴ ng m ⁻² yr⁻¹. In this work I assess temporal trends in deposition, homologue profiles, ion tracers, air mass transport models, and production and regulation trends to characterize the PFAA depositional profile on the Devon Ice Cap and to further understand the LRT mechanisms of these persistent pollutants. In Chapter 3 my results demonstrate that the PFCAs and perflurooctane sulfonate (PFOS) have continuous and increasing deposition on Devon Ice Cap, despite recent North American regulations and phase-outs. I propose that this is the result of on-going emission and use of these compounds, their precursors and other newly unidentified compounds in regions outside of North America. Through modelling air mass transport densities, and comparing temporal trends in deposition with production changes of possible sources, I find that Eurasian sources, particularly from Continental Asia are large contributors to the global pollutants impacting Devon Ice Cap. By comparing PFAAs to their precursors and correlating pairs of PFCAs, I determine that deposition of PFAAs is dominated by atmospheric formation from volatile precursor sources, and major ion analysis provides new information regarding the transport of PFAAs, confirming that marine aerosol inputs are unimportant to the LRT mechanisms of these compounds. In Chapter 4 my results from the Arctic ice core analysis show a tenfold increase in short-chain PFCA (scPFCA) deposition between 1986 and 2014, which coincides with increased production and atmospheric burden of chlorofluorocarbon (CFC)- replacement compounds. This is the first multi-decadal temporal record of scPFCA deposition and indicates that Montreal Protocol-mandated introduction of CFC-replacement compounds for the heat-transfer industry is the dominant source of scPFCAs to remote regions.

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