Bluefin tuna reveal global patterns of mercury pollution and bioavailability in the world's oceans

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 subbasin's food web. Observed global patterns correspond to levels of Hg in each ocean subbasin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. MAR in BFT as a global pollution index reflects natural and human sources and global thermohaline circulation.

Automated summary

Research shows that the mercury accumulation rate in bluefin tuna is highest in the Mediterranean Sea, decreases in the North Pacific, Indian Ocean, and North Atlantic Ocean, correlating with the concentrations of MeHg in regional seawater and zooplankton. These differences are related to the levels of mercury in each ocean subbasin, geogenic enrichment, and anthropogenic contamination.