Early Life Uptake and Elimination of Per- and Polyfluoroalkyl Substances in a Seasonally Invertivorous Bird.

Exposure to per- and polyfluoroalkyl substances (PFAS) impairs avian reproduction and development, yet uptake and elimination pathways in birds remain poorly resolved. To better understand these processes, we quantified PFAS in whole blood (n = 124) from adult and juvenile house sparrows (Passer domesticus) at 16 urban-industrial sites. Dietary pathways were traced using stable isotopes of carbon and nitrogen from feathers (n = 66). At our most contaminated site, we recaptured individuals across eight months to assess seasonal trends in PFAS burdens. We found that exposure to perfluorosulfonic acids (PFSAs) was highest near fire training areas, while perfluorocarboxylic acids (PFCAs) were highest near oil production facilities. PFOS, PFDoA, and PFTeDA were higher in juveniles than adults, and females exhibited lower PFNA, PFUdA, and PFTeDA than males, consistent with maternal transfer of PFAS into eggs. Young fledglings showed tightly clustered, depleted δ13C values (-22.9 ± 0.8‰) compared to adults (-18.9 ± 3.6‰), indicating selective invertebrate provisioning as another source of early life exposure. In recaptured juveniles, ∑PFCAs and ∑PFSAs declined throughout development (0.43-1.25% per day). This enabled estimation of compound-specific elimination half-lives, which ranged from 29 days (PFBS) to 91 days (PFNA). Adults showed slower elimination rates. Our findings indicate pronounced early life vulnerability to PFAS exposure in terrestrial birds.