Per- and polyfluoroalkyl substances along the St Louis River and in the Duluth, MN area 2019-2021

Tree swallow nest boxes were deployed at sites proximal to two putative aqueous film forming foam (AFFF) sources in the Duluth, MN area, as well as along the St. Louis River and a reference lake for comparative purposes. The two AFFF sites were the current Duluth Air National Guard Base (ANG) and the Lake Superior College Emergency Response Training Center. Concentrations of between 13 and 40 per- and polyfluoroalkyl substances (PFAS), depending on year, were quantified in tree swallow egg, nestling carcasses, and stomach contents. Assessments were made for oxidative stress and ethoxyresorufin-O-dealkylase biomarker responses in liver tissue, thyroid hormone levels in plasma and thyroid glands, DNA damage in red blood cells, and two measures of immune response (haptoglobin-like activity and immunoglobulin) in plasma of the nestlings. Additionally, other contaminants such as polychlorinated biphenyls, other legacy organochlorine pesticides, and trace elements were assessed at sites with no previous data. Total egg PFAS concentrations at the ANG site and north of there were 30 – 40 times higher than at the reference lake while nestling PFAS concentrations were 10 – 15 times higher than at the reference lake. In contrast, although the St. Louis River sites had slightly elevated egg and nestling PFAS concentrations relative to the reference lake (2 – 5 times higher), although those concentrations were not significantly higher. One PFAS, perfluorohexane sulfonate (PFHxS), was proportionately higher, as a proportion of total PFAS, at sites with a known AFFF source compared to the reference lake, but also compared to sites along the St. Louis River with mainly urban and industrial sources of PFAS. The ratio of total carboxylates to total sulfonates also distinguished between PFAS sources. There were few to no differences in biomarker responses among sites, and no association with PFAS exposure.