Tissue-specific trace element accumulation, mercury and arsenic speciation in Atlantic walrus (Odobenus rosmarus rosmarus)

Walruses (Odobenus rosmarus) are long-lived Arctic marine mammals and play an important ecological and cultural role in northern communities. We quantified and compared concentrations of 34 elements in blubber, liver, and muscle tissues from 97 Atlantic walruses (Odobenus r. rosmarus) harvested between 2019 and 2021 from two management stocks in the eastern Canadian Arctic (Foxe Basin and Hudson Bay-Davis Strait). Trace element profiles differed strongly among tissues, reflecting physiological roles in exposure and detoxification. Stock-level differences were evident for select elements, including cadmium, selenium, arsenic, and mercury. Based on the elevated arsenic and mercury concentrations, we prioritised these two elements for speciation analyses in a small subset of samples. While arsenic concentrations were relatively high, arsenic speciation in blubber was dominated by arsenolipid (82%) whose toxicity to marine mammals remains unknown, followed by low toxic organic forms, particularly dimethylarsinic acid (6.6-8.9%). Mercury (Hg) forms varied among tissues, with methylmercury present at higher levels in muscle (mean 82.7%), lower levels in liver (mean 9.9%), and high but variable levels in blubber (mean 72.2%). Hg:Selenium molar ratios were approximately 21-fold higher in liver than in blubber and were higher in the Hudson Bay-Davis Strait stock. Elevated concentrations of cadmium and methylmercury in liver relative to other tissues highlight tissue-specific accumulation patterns and warrant further investigation of their ecological and physiological implications.