Using a Multi-Tracer Approach to Examine Perfluoroalkyl Substance Sources and Dietary Exposure Pathways in Pacific Bald Eagles

Perfluoroalkyl substances (PFAS) are globally distributed contaminants that bioaccumulate in avian apex predators, yet species-specific bioaccumulation processes and links to dietary sources remain poorly resolved. Using an integrative, multi-habitat sampling framework, we blood sampled 89 bald eagle (<i>Haliaeetus leucocephalus</i>) nestlings across eight regions from the Pacific coast of British Columbia (BC), Canada and quantified 17 PFAS. We paired contaminant data with stable isotope analyses (δ¹⁵N, δ¹³C, δ³⁴S) to characterize trophic position and habitat use, and fatty acid (FA) profiling to partition aquatic vs terrestrial prey sources, while modeling biological covariates. Our most parsimonious model describing spatial variation in PFAS exposure included region and nestling age. PFAS profiles were dominated by PFOS (mean = 23.5; range 2.1-159 ng/mL), comprising 33-72% of ∑₁₇ PFAS, with remaining burdens composed of PFNA, PFDA, PFUdA, and PFTrDA. Stable isotopes did not uniformly predict PFAS concentrations; however, PFUdA and PFTrDA were positively correlated with δ¹³C and ∑ Omega-3 FAs, consistent with marine-derived diets. PFOS and PFHxS were negatively correlated with ∑ Omega-6 FAs, suggesting greater biomagnification in nestlings feeding within terrestrial or mammalian food webs. To our knowledge, this work represents the first comprehensive assessment of PFAS exposure in Pacific bald eagles and is also one of the first attempts to apply a multi-dietary tracer approach to contextualize habitat use and dietary pathways of PFAS in a regional apex predator.