What is it about?

Bluefin tuna (BFT), highly prized among consumers, accumulate high levels of mercury (Hg) as neurotoxic methylmercury (MeHg). However, how Hg bioaccumulation varies among globally distributed BFT populations is not understood. Here we show mercury accumulation rates (MARs) in BFT are highest in the Mediterranean Sea and decrease as North Pacific Ocean > Indian Ocean > North Atlantic Ocean. Moreover, MARs increase in proportion to the concentrations of MeHg in regional seawater and zooplankton, linking MeHg accumulation in BFT to MeHg bioavailability at the base of each sub-basin's food web. Observed global patterns correspond to levels of Hg in each ocean sub-basin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. Mercury accumulation rate in bluefin tuna as a global pollution index reflects natural and human sources and global thermohaline circulation.

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Why is it important?

Bluefin tuna (BFT) is an apex predatory, long-lived, migratory pelagic fish that is widely distributed throughout the world's oceans. These fish have very high concentrations of neurotoxic methylmercury (MeHg) in their tissues, which increase with age. Our study shows that Hg accumulation rates (MARs) in BFT as a global pollution index can reveal global patterns of Hg pollution and bioavailability in the oceans and further reflect both natural and anthropogenic emissions and regional environmental features. Overall, MARs provide a means to compare Hg bioavailability among geographically distinct populations of upper trophic level marine fish across ocean subbasins, to investigate trophic dynamics of Hg in marine food webs, and furthermore, to improve public health risk assessments of Hg exposure from seafood.


This paper provides a standard basis of comparison to examine spatial and temporal trends of Hg pollution across the world's oceans using tuna fish as a biological indicator. The authors’ investigations strongly support the idea that Hg bioaccumulation in tuna varies with levels of MeHg across ocean basins. This is an important scientific breakthrough.

Chun-Mao Tseng
Institute of Oceanography, National Taiwan University

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This page is a summary of: Bluefin tuna reveal global patterns of mercury pollution and bioavailability in the world's oceans, Proceedings of the National Academy of Sciences, September 2021, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2111205118.
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