Bald eagles as bio-sentinels: Monitoring and fingerprinting PFAS contamination

The present study assessed bald eagle (Haliaeetus leucocephalus) nestlings as a sentinel species for per- and polyfluoroalkyl substances (PFAS) fingerprinting tools due to their high trophic position, well-characterized life history, and restricted foraging ranges during nesting. From 2023 to 2025, we sampled 115 bald eagle nestlings across seven regions in Wisconsin, Lake Superior, and Lake Michigan to quantify plasma PFAS concentrations and evaluate regional contamination fingerprints. Total PFAS levels were highest in the Middle Wisconsin River and Apostle Islands, and lowest in the Upper Wisconsin River. Regional compositional profiles revealed distinct patterns: Middle Wisconsin River nestlings showed elevated PFOS and precursor compounds, while Apostle Islands nestlings exhibited elevated short chain and legacy compounds such as PFBS, PFNA and PFUnA. Principal component analyses and correlation structures further distinguished sites, suggesting both point-source contamination and diffuse inputs. These findings underscore the utility of bald eagles as biomonitors for spatially explicit PFAS contamination and demonstrate how fingerprinting approaches can improve source attribution and risk assessment in Great Lakes ecosystems.