Environmental forensics: an innovative technique using bone to identify mercury and stable isotope levels in internal tissues of wildlife in a changing western Alaska environment

Abstract

We evaluated if total mercury (THg) concentrations of keratin-based and bone-based tissues can predict THg concentrations in skeletal muscle, renal medulla, renal cortex, and liver. The THg concentration in matched tissues of 65 red foxes, Vulpes vulpes, from western Alaska was determined. Hair THg concentration had a significant positive correlation with liver, renal medulla, renal cortex, and muscle. The THg concentration is moderately predictive of THg concentration in the renal cortex and liver for these foxes based on R² values (R² = 0.61 and 0.63, respectively), but was not moderately predictive of THg for renal medulla R² = 0.50 and muscle R² = 0.39. Bone is weakly predictive of THg concentration in muscle (R² = 0.40), but not a reliable tissue to predict THg concentration in liver (R² = 0.24), renal cortex (R² = 0.35), or renal medulla (R² = 0.25).These results confirm the potential use of trapped animals, specifically foxes, as useful Arctic sentinel species to inform researchers about patterns in THg levels over time as industrialization of the Arctic continues. Stable isotope analysis was also performed on the same red fox tissues from the first study. We examined stable carbon (δ¹³C) and nitrogen isotopes (δ¹⁵N) to 1) examine the lipid extraction process, 2) evaluate carbon and nitrogen correlations among tissues to establish stable isotope values for modern northern wild fox populations, 3) describe the C:N ratios in males and females, 4) establish trophic positions of freeranging northern red foxes, and 5) to relate the wild red fox trophic level to potential mercury biomagnifications reported in a previous study. Hair, bone, muscle, liver, renal cortex and medulla tissues of the red fox were isotopically significantly different from each other. We found evidence that the Western Alaska red fox was eating a different diet based upon a lower trophic position than red foxes from other northern areas. We concluded that stable isotope data can help explain mercury concentration levels influenced by seasonal diet changes of the Alaska red fox. In our third study, we took a forensic approach to look at the health and dietary indicators in museum preserved bone of red (Vulpes vulpes) and Arctic foxes (Vulpes lagopus) from the Yukon Territory in Canada. This study attempts to 1) measure the mercury (THg) concentration levels, 2) estimate a diet using carbon stable isotopes (δ¹³C) and 3) establish a trophic level using nitrogen stable isotopes (δ¹⁵N), from bones of these sentinel species. This study examines two Arctic foxes and three red foxes of unknown age and origin. Yukon Territory Arctic foxes THg concentrations were 0.017 and 0.025 mg/kg. The red foxes THg concentrations were 0.010, 0.036 and 0.073 mg/kg. The δ¹³C levels were -21.13‰ and -21.36‰ for Arctic foxes and -20.05‰, -20.08‰, and -23.12‰ for red foxes. Their δ¹⁵N levels were 5.59‰ and 7.22‰ for the Arctic foxes and 6.10‰, 6.57‰ and 6.66‰ for red foxes. These Arctic and red Yukon Territory foxes indicate a trophic level similar to Arctic terrestrial omnivores.