Perfluoroalkyl substances (PFASs) describe a class of extremely persistent and bioaccumulative compounds that are distributed ubiquitously in the environment. These compounds can be formed from the atmospheric oxidation of volatile precursor compounds or exist in their anionic form, where they can be subsequently removed by wet or dry deposition processes. In the current study, large-volume precipitation samples were collected across four (4) locations across a latitudinal transect in Newfoundland and Labrador, Canada (NL-BELT). The sampling sites were experimental forests within the watersheds of Grand Codroy (47.893° N, 59.174° W), Humber River (49.070° N, 57.643° W), Salmon River (51.256° N, 56.138° W), and Eagle River (53.550° N, 56.987° W). The sample collection was done monthly from October 2013 to August 2016, using an open polyvinylchloride (PVC) pipe or high-density polyethylene (HDPE) total deposition samplers and custom-built HDPE automated deposition samplers. Samples were concentrated using solid-phase extraction (SPE) and analyzed by liquid chromatography-tandem mass spectrometry.

Perfluoroalkylcarboxylic acids (PFCAs) and Perfluoroalkylsulfonic acids (PFSAs) were detected consistently in precipitation samples. The concentration of PFCAs ranged from <LOD to 9851 pg L^-1, with the short-chain compound PFBA showing the highest concentration and a detection frequency of 82%. PFOA (C8) was detected in all samples with a mean concentration of 729 pg L^-1 across the sampling sites. The other PFCAs (C6 - C11) were detected in <74% of samples. The PFSA concentrations were generally lower than the corresponding PFCA with an average concentration of 400 pg L^-1 across the sampling sites. Concentrations (pg L^-1) were converted to annual flux (ng m^-2 a^-1). The average PFCA flux was 500 ng m^-2 a^-1, while the PFSA flux across the sampling sites was 13 ng m^-2 a^-1.

Our results from homologue correlations, molar concentration ratios and model comparisons suggest that most PFCAs are formed through oxidation of precursor compounds. A trend of increasing influence of precursor oxidation as latitude increases was observed. Air mass trajectory analysis suggests a continental input as winds predominantly move from east to west. Correlations with major ions suggest multiple sources, including marine aerosols. This is one of the first studies that explicitly estimates the contribution of dry deposition to overall PFAA deposition. We found that dry deposition of gases and particles can be the dominant deposition pathway for select PFAAs. These observations highlight the complex mechanisms responsible for the transport and deposition of PFAAs along the remote NL-BELT.

¹ Department of Chemistry, York University, Toronto, ON, Canada

² Natural Resources Canada, Climate Change Impacts and Adaptation Division, Lands and Minerals Sector, Ottawa, ON, Canada

³ Department of Earth Science, Memorial University, St. John's, NL, Canada

⁴ Environment and Climate Change Canada, Aquatic Contaminants Research Division, Burlington, Ontario, Canada

* Corresponding Author: danielp@yorku.ca