Mercury in white-tailed eagle nestlings from northern Norway (2013–2018): Toxicity risk and dietary drivers of exposure

Mercury (Hg) pollution is a global environmental problem. Hg exposure is linked to adverse health effects such as neurotoxicity and reproductive impairments, making monitoring crucial for assessing toxicity risks to humans and wildlife. Top predators, such as the white-tailed eagle (Haliaeetus albicilla), are excellent biomonitors of environmental contamination due to their susceptibility of accumulating high levels of biomagnifying pollutants like Hg. In this study, body feathers of white-tailed eagle nestlings (n = 217) were sampled in northern Norway in 2013-2018. Feathers were analyzed for total Hg (THg) concentrations and stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) to explore the influence of dietary ecology on Hg exposure. THg concentrations ranged between 0.96 and 4.85 μg g^-1, with approximately 11 % of the chicks exceeding 3.9 μg g^-1, the threshold value considered moderate risk for toxic effects. THg concentrations were similar across years, except for 2015, which had significantly higher levels; however, isotope values did not differ between years, suggesting this was not driven by dietary shifts. We found a significant and positive relationship between THg concentrations and δ¹⁵N, supporting the biomagnifying property of Hg. Similarly, we detected a significant positive THg-δ¹³C relationship, indicating higher Hg exposure with a more marine diet. We also found a significant and negative relationship between THg and wing length (age proxy), suggesting younger chicks have higher Hg concentrations than older chicks, likely due to mass dilution during chick growth. This study improves our understanding of Hg exposure and risk in a top predator along the Norwegian coast.