Diet-Driven Rapid and Selective Accumulation of Per- and Polyfluoroalkyl Substances in Black-Tailed Gull Nestlings

Poorly characterized dietary exposure in predators often leads to inconsistent field-based bioaccumulation metrics for per- and polyfluoroalkyl substances (PFAS). This study evaluated PFAS accumulation in the plasma of black-tailed gull ( Larus crassirostris ) nestlings subjected to contrasting marine (wild; n = 26) and freshwater (captive; n = 30) diets. Stable isotope mixing models (δ 13 C and δ 15 N) were employed to reconstruct wild nestling diets and calculate mixed-diet biomagnification factors (BMFs). Nestlings on freshwater diets exhibited higher concentrations of most PFAS groups than those on marine diets (ΣPFAS = 265 and 124 ng/g ww, respectively), except for sulfonamide-based precursors (FASAs). This pattern suggests a higher contamination risk in freshwater systems, likely from agricultural runoff, as indicated by elevated PFAS levels and δ 15 N in freshwater prey. Despite contrasting prey PFAS profiles, both nestling groups preferentially accumulated greater proportions of C 7 –C 9 perfluoroalkyl sulfonic acids (PFSAs) and 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA). Mixed-diet BMFs were consistently below one for FASAs, C 4 –C 6 perfluoroalkyl carboxylic acids (PFCAs), and PFDS, while exceeding one for C 9 –C 14 PFCAs, C 7 –C 9 PFSAs, and 6:2 Cl-PFESA. Observed discrepancies in PFOA, PFBS, and PFHxS biomagnification between nestling groups further implicate the role of in vivo precursor transformation. These findings emphasize the need for further monitoring within freshwater ecosystems, and integrating mixed-diet approaches to assess PFAS bioaccumulation in field studies.