Bering Sea | Mammals
Evidence of adverse effects of mercury on pinnipeds? Presenter: Todd O’Hara , tmohara@tamu.edu, Texas A&M University Lorrie Rea , ldrea@alaska.edu, University of Alaska - Fairbanks
Many use One Health approaches to assess mercury (Hg) exposure and adverse effects on pinnipeds. We synthesize approximately eight recent in vivo & in vitro studies to assess potential adverse effects of Hg. We used toxicological “thresholds” in a risk assessment approach and investigate increasing Hg concentrations ([Hg]) in some locations. We focus on free ranging Steller sea lions (SSL, conservation concern), and harbor seal pups (rehabilitation). Toxicosis potential includes immune, oxidative stress, and neurologic impacts. Decreasing total selenium concentrations ([TSe]; essential element) with increasing Hg concentrations highlighted as an important interaction. Published upper and lower toxicological thresholds (20 & 30 ppm THg) for pinniped hair are used. We propose upper and lower toxicological thresholds for blood as they provide better insight for some in vitro approaches and diagnostics. Blood [THg] > 0.2 to 0.5 μg/ml may affect immune status. A decrease in serum haptoglobin (immune marker) associated with blood > 0.11 THg mg/kg ww was noted. At relevant concentrations in vitro Hg exposure alters mitogen-induced lymphocyte proliferation and cytokine expression in SSL pups. Exploring immune status more broadly concluded concern for population health, but not suitable for assessing Hg adverse effects due to confounding variables. In vitro approaches control for some whole animal confounding variables. Exposure to Hg is linked to in vitro and in vivo immunotoxicity (North Sea pinnipeds) for both innate and adaptive immune systems. In SSL pups interactions of high Hg with potentially inadequate Se results in higher oxidative stress (lipid peroxidation). Often assessed as TSe:THg molar ratio in whole blood and other tissues. Decreasing TSe:THg molar ratio provides potential for Hg-induced Se deficiency. Harbor seal pups of Central CA provide a pinniped model in proximity of San Francisco Bay (known Hg contamination). We developed a harbor seal pup specific neurological exam study with detailed assessments showing decreased response to tactile stimulation, decreased movement, and longer rehabilitation time relative to Hg concentrations. In summary, 1) Proposed thresholds of concern for Hg appear relevant, 2) In vivo & in vitro approaches to assess immune system status indicate responses to Hg, 3) Serial neurological exams in harbor seal pups shows promise to determine adverse effects, & 4) One Health and conservation perspectives are important.
Alaska Marine Science Symposium 2023 55
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