Temporal and spatial variability of per- and polyfluoroalkyl substances (PFAS) in otters (Lutra lutra) from Sweden

Per- and polyfluoroalkyl substances (PFAS) are a large class of highly persistent chemicals, some of which are bioaccumulative, hormone disrupting and toxic. As a result, PFAS pose considerable risks to both humans and wildlife (particularly top predators), which experience elevated PFAS exposure due to biomagnification through the food chain. This study investigates temporal and spatial variability of 15 PFAS in 447 liver samples collected over five-decades (1970-2020) from Eurasian otters (Lutra lutra), an aquatic top predator which serves as an effective sentinel of environmental contamination. Perfluorooctane sulfonate (PFOS) was found in the highest concentrations, up to 15,300 ng/g ww and was the dominant compound in most otters. Among perfluoroalkyl carboxylic acids (PFCAs), concentrations generally decreased with increasing chain length from C9 to C15. Among all PFAS, temporal trends of perfluorooctane sulfonamide (FOSA; a PFOS-precursor) peaked earliest (beginning of the 1990s), followed by perfluoroalkyl sulfonic acids (PFSAs; mid-late 1990s) and then PFCAs (C11-C15; late 2000s-early 2010s). However, perfluorooctanoic acid (PFOA; C8) and perfluorononanoic acid (PFNA; C9) have continued to increase over the entire period, resulting in overall stable total PFAS concentrations (as PFOA-equivalents). Spatially, PFSAs were elevated in southern, more populous regions, whereas PFNA dominated in the rural northwest, suggesting differing source profiles (possibly a combination of local emissions and/or differences in atmospheric deposition). Overall, these findings indicate that while targeted regulations have reduced certain PFAS in the environment, total PFAS exposure in Swedish otters has not declined significantly over the past decade. The results highlight the continued need for long-term monitoring of apex predators to evaluate regulatory effectiveness.