Stress hormones in relation to per- and poly-fluoroalkyl substances (PFAS) and rodenticide exposure in an avian top predator.

Apex predators are excellent indicators of environmental pollution given their long lifespan, high trophic position, and sensitivity to disturbance. However, little is known about how exposure to multiple contaminants may relate to long-term activity of the hypothalamic-pituitary-adrenal axis (HPA) in terrestrial raptors. We therefore investigated concentrations of 37 per- and polyfluoroalkyl substances (PFAS) and 7 first- and second-generation anticoagulant rodenticides in tawny owls (Strix aluco) collected in central Norway 2009-2022 and examined their associations with corticosterone (CORT) concentrations measured in feathers. Total PFAS concentrations in the liver samples (n = 27) ranged from 17 to 1341 ng/g dry weight (dw), with a median of 85 ng/g dw. We detected 2-16 different PFAS, with 7 PFAS in >50% of the samples. Total rodenticide concentrations in the liver samples ranged from <0.2 to 6743 ng/g dw, with a median of 398 ng/g dw (125 ng/g ww) and three specific rodenticides were detected: brodifacoum (74%), bromadiolone (26%), and flocoumafen (15%). Brodifacoum was detected in three-fourths of the sampled owls, with 60% exhibiting hepatic concentrations >100 ng/g ww and 40% > 200 ng/g ww, concentrations previously associated with health effects and increased mortality in predatory birds, respectively. PFTriDA and brodifacoum, as well as PFTDA and brodifacoum, interacted additively with CORT concentrations in feathers. Our findings underscore the critical need for continuous monitoring of organic pollutants, such as PFAS and anticoagulant rodenticides, and their effects on terrestrial ecosystems.