The occurrence of legacy per- and polyfluoroalkyl substances (PFAS) deposited along a latitudinal transect in Newfoundland and Labrador, Canada.

Atmospheric deposition samples were collected across four sites of the Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT) to better understand the sources and fate of per- and polyfluoroalkyl substances (PFAS). Both total and wet deposition samples were collected between October 2013 and August 2016. Perfluoroalkylcarboxylic acids (PFCAs) and perfluoroalkylsulfonic acids (PFSAs) were detected consistently in deposition samples. The median PFCA homologue concentration across the sampling sites was 300 pg L-1, with concentration values ranging from <LOD to 10 000 pg L-1. The PFSAs were two orders of magnitude lower than PFCAs, with a median concentration of 3 pg L-1. Concentrations (pg L-1) were converted to annual flux using volume, sampler area, and duration (ng m-2 a-1). The median PFCA flux was 170 ng m-2 a-1, while the PFSA flux across the sampling sites was 33 ng m-2 a-1. Our measurements are among the first to separate the roles of wet and dry deposition, which could be quantified for perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and perfluorononanoic acid (PFNA). We found that dry deposition was variable and could be an important contributor to the total deposition flux for the three PFCAs assessed. Our analysis of homologue correlations, molar concentration ratios, and model comparisons suggests that most PFCAs are formed indirectly through the oxidation of precursor compounds. Air mass back trajectory and major ion analysis, conversely, indicate that direct transport and/or marine aerosol are minor contributors in this region. These observations highlight the complex mechanisms responsible for the transport and deposition of PFAAs along the remote NL-BELT.