Influence of perfluoroalkyl acids and other parameters on circulating thyroid hormones and immune-related microRNA expression in free-ranging nestling peregrine falcons

Exposure to certain perfluoroalkyl acids (PFAAs) can have considerable effects on the endocrine and immune systems, although such remain largely uncharacterized in wildlife. Using an apex avian predator, we investigated possible relationships of thyroid hormones (THs), specifically free (F) total (T) thyroxine (FT4; TT4) triiodothyronine (FT3; TT3), expression immune-related microRNA biomarker (i.e., miR-155), with concentrations 11 PFAAs nestling peregrine falcons (Falco peregrinus). Nestling peregrines (n = 56; usually two chicks each sex per nest) were blood sampled when 23 ± 4 days old urban rural regions Laurentian Great Lakes Basin (Ontario, Canada) 2016 2018. The circulating several significantly associated THs estimated gland activity (TT3:TT4; FT3:FT4), including PFHxS PFDS (TT3; TT3:TT4), PFOA (TT4; PFTeDA PFHxDA TT3:TT4) ΣPFCAs (TT4). Our novel evaluation miR-155 nestlings identified negative plasma counts concentrations, indicating potential down-regulation impaired immunity. Several PFAA homologues predicted variation conjunction year (e.g., inter-annual differences weather, ambient temperature, rainfall), region (urban/rural), age, and/or diet (trophic position; δ15N), which suggests that multiple environmental biological stressors, exposure, influenced function these nestlings. Further research is warranted identify mechanisms additional impacts PFAA-related disruption growth, development, health risks developing birds.