Per- and Polyfluoroalkyl Substances (PFAS): Concentrations and Deposition in Precipitation

An increasing body of evidence documents measurable levels of a broad range of PFAS compounds in precipitation - which translate into substantial deposition loads to terrestrial and aquatic resources. In many environments these atmospheric deposition fluxes can represent the dominant source of PFAS – however, very large gaps in our understanding of atmospheric sources and processing, and deposition fluxes of PFAS remain. 

To address these issues the University of Wisconsin-Madison Wisconsin State Laboratory of Hygiene (WSLH) and the WSLH managed National Atmospheric Deposition Program (NADP), initiated a program to evaluate the efficacy of the US NADP National Trends Network (NTN) for assessment of wet-deposition of PFAS and provide novel new data on levels of PFAS in precipitation across the US.  Dedicated experiments with a diverse suite of 34 PFAS compounds addressed system blanks and stability of the PFAS species in the NTN precipitation collectors. A robust standardized protocol was promulgated for PFAS wet-deposition measurements using the NADP-NTN infrastructure and analytical tools at the WSLH.

We have now applied this protocol in several studies, including in an intensive 5-month study in 2020 at NTN sites across Wisconsin, USA (Pfotenhauer et al., 2022), and in an on-going large-scale nationwide monitoring effort at 10 NTN sites initiated in 2020 and supported by the US Environmental Protection Agency-Office of Research & Development (EPA-ORD).  In the Wisconsin study, 91 precipitation samples, along with an array of QA/QC samples were collected from 8 NTN sites across Wisconsin, and analyzed for 34 PFAS compounds. Concentrations of individual PFAS compounds were generally less than 1 ng/L, however, summed PFAS concentrations ranged from 0.7 to 6.1 ng/L with a median of 1.5 ng/L. Perfluoro carboxylates (PFCAs) were detected most frequently and constituted an average of 83% of the total PFAS mass. Daily flux values ranged from 1.3 to 47.4 ng/m²/day with a median of 5.7 ng/m²/day. Differences in the PFAS fingerprints were observed among the 8 sampling sites, reflecting local sources.