Originally published on FoodUnfolded.com in December 2023. Header image by Cait Mack for FoodUnfolded.

With its low melting point, high density, and excellent conductivity, mercury has several industrial and scientific applications. But the unsafe use of this metal can result in severe health and environmental implications, especially through bioaccumulation in seafood.

Mercury enters the atmosphere and water bodies through a number of human activities and natural processes, such as mining, fossil fuel combustion, volcanic eruptions, and gradual discharge from the earth’s crust.¹ Once released, mercury interacts with its environment to form various chemical compounds that can be severely toxic to humans and wildlife.

Why is there mercury in seafood?

Mercury that enters water bodies, particularly oceans, turns into a compound called methylmercury because of biogeochemical conditions in marine water and the action of microorganisms living in water and soil.1 Unlike mercury, methylmercury can bioaccumulate because the organs, tissues, and muscles of living organisms can absorb it. This, in turn, causes biomagnification, meaning that the concentration of methylmercury in an organism increases along with its level in the food chain. With this, higher trophic-level fish such as sharks, swordfish, and some varieties of tuna from contaminated waters often have a high concentration of methylmercury in their bodies. If consumed, this toxic compound is passed on to humans and can cause adverse health effects, including neurological and cardiovascular problems.² Pregnant women and infants are particularly vulnerable to mercury poisoning from consuming such seafood.² However, not all populations around the world are at equal risk.

Communities that harvest their own fish from contaminated waters are more likely to suffer from the adverse health effects of methylmercury poisoning. Without the rigorous safety checks that internationally traded seafood often goes through, locally caught mercury-contaminated fish may end up on the plates of unsuspecting consumers, causing them grave harm over their lifetimes.