Spatial Distribution and Load of Per- and Polyfluoroalkyl Substances (Pfass) in Background Soils in Sweden

Abstract

Per- and polyfluoroalkyl substances (PFASs) are known to be persistent, bioaccumulative, and have adverse health effects, but very little is known about PFASs in the terrestrial environment and factors influencing their distribution. This paper presents one of the first comprehensive studies investigating PFASs ( n = 28) in background forest soils ( n = 27) on national scale across Sweden. The results showed that 16 of 28 target PFASs were present and all sites contained at least three types of PFASs, with total concentrations ranging between 0.40 ng/g dry weight (dw) and 6.6 ng/g dw. Perfluorooctanesulfonic acid (PFOS) showed the highest prevalence, with 89% detection frequency and a median concentration of 0.39 ng/g dw. The PFOS loads (ng/m 3 ) showed a distinct spatial distribution, with a significant exponential increase from north to south ( R 2 = 0.55; p <0.001) and west to east ( R 2 = 0.35; p <0.01). The compound 6:2 fluorotelomer sulfonate (6:2 FTSA) had a higher median concentration (1.4 ng/g dw), but was more impacted by local sources. Partial least squares discriminant analysis (PLS-DA) showed regional clustering of PFAS compositional profiles, indicating that PFAS soil background concentrations are functions of spatial variations at local, regional, and countrywide scale. Such spatial trends have not been observed previously and it could not be deduced whether they are indicative of trends on a global scale, or country-specific and better explained by proximity to densely populated urban areas. An interpolation and extrapolation raster map created from the results was used to calculate the average total PFAS load on Swedish soils. Estimated total load in the top 10-cm soil layer was 2.7 ± 2.4 tons for PFOS and 16 ± 14 tons for ∑PFASs, indicating that soil carries a considerable legacy of past PFAS release.

Keywords: PFAS, PFOS, Soil, deposition