Photo by: Pixabay user Astama81.

Harvard researchers have traced the major sources of methylmercury, a poisonous form of metal, in the U.S. diet. Although most of that exposure comes from eating seafood, the geographic origins of the mercury hasn’t been well understood until now.


Why it matters: The organic form of mercury, methylmercury (MeHg), can cause long-term cognitive problems in children, and harm cardiovascular health in adults.

  • Mercury is released into the atmosphere by coal combustion and gold mining, and can work its way into the land, air, and water. It can be spread around the world through major atmospheric and ocean currents.
  • One of the largest sources of mercury emissions to the air in the U.S. and globally are coal-fired power plants. Most coal contains trace amounts of mercury that is released when the coal is burned.
  • Mercury exposure in the U.S. occurs mostly through the consumption of contaminated fish including those sold in grocery stores. Tuna consumption alone may account for more than 90% of methylmercury intake by the U.S. population.

The background: A global treaty called the Minamata Convention was put into place in 2017 to reduce human-created mercury emissions. In order to understand how it may affect humans’ exposure to mercury in the environment, the study’s authors reasoned, it was essential to know where the bulk of each nations’ seafood comes from.

“Seafood is one of the last wild foods consumed by humans and an essential source of protein and micronutrients for many populations. This work shows that global environmental quality and the health of the oceans affects the food we eat,” says Harvard Chan School’s Elsie Sunderland, senior author of the study.

The Upshot: This work confirms that the largest fraction of methylmercury in the U.S. diet comes from open ocean fisheries (45%), mainly those in the equatorial and South Pacific Ocean. Knowing this will help reduce future mercury exposure for the U.S. population, as well as other populations worldwide that rely on those fisheries.

Climate Connection: In addition to winding up in fisheries, mercury emissions released into the atmosphere by coal combustion and gold mining can also be pushed into Arctic air by prevailing winds. During rain or snow events, mercury can fall onto land, where it becomes frozen into Arctic permafrost. As global temperatures warm, that land can thaw, releasing the mercury back into the environment.


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Dr. Aaron Bernstein

Aaron Bernstein MD, MPH

Aaron examines the human health effects of global environmental changes with the aim of promoting a deeper understanding of these subjects among students, educators, policy makers, and the public.

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