New insights into trace element offloading and bioaccumulation in endangered Hawaiian monk seal bones

Hawaiian monk seals (HMS) Neomonachus schauinslandi are endangered pinnipeds endemic to the Hawaiian Archipelago, but during the 21st century, seals began to establish residency within the Main Hawaiian Islands (MHI). This habitat shift may be increasing their exposure to greater anthropogenic (urbanization, agricultural practices, and military activity) rather than just natural (volcanic activity, rock weathering, soil erosion, and dissolution of salts) trace element contaminants. HMS skeletal bones from both MHI and the Northwest Hawaiian Islands (NWHI) were analyzed by inductively coupled plasma mass spectroscopy for 16 trace elements. Zn (67.8–269 μg g^–1) and Fe (14.6–494 μg g^–1), both structurally contained within bone, had the highest concentrations. Surprisingly, the more urbanized MHI seals had significantly lower concentrations of As, Cd, Cr, Cu, and Se compared to seals from the remote NWHI. These differences could be attributed to the HMS diet at different locations, proximity of prey from shore, or volcanic rock weathering. Higher concentrations of Cu, Fe, Ni, and Sn were found in HMS pups compared to adults and juveniles, which could imply contaminant offloading to the pups, while adults had highest Cd and Hg concentrations, indicating age bioaccumulation and biomagnification. This study provides the first inorganic measure of trace elements in the endangered endemic HMS.