Mercury has always been in our oceans – and it always will be. Mercury is a naturally occurring element in the earth’s crust. In nature, mercury is emitted into the atmosphere through soil erosion, volcanoes and forest fires. Volcanoes and oceans vents are the main source of naturally occurring mercury in our oceans.  

According to scientific estimates, the majority of the mercury released into the environment comes from natural sources.

So, in fact, mercury has always been in fish, including tuna, in trace amounts – and it always will be.

Some mercury also enters the atmosphere as a result of human pollution. Mercury is found in many rocks, including coal, which is burned for energy generation. When coal is burned, mercury is released into the environment. Coal-burning power plants are the largest human-caused source of mercury emissions to the air in the United States. Also, burning hazardous wastes, producing chlorine, breaking mercury products, spilling mercury and improperly disposing of mercury products can also release it into the environment.

When people talk about exposure to ‘mercury’ in fish, they’re actually referring to methylmercury.  Methylmercury is formed when mercury gets into water bodies – whether by natural processes or pollution – where it is converted into an organic compound through the actions of bacteria. Fish ingest and absorb methylmercury in minute quantities by feeding on organisms living in water where it is present.

Toxic methylmercury exposure is extremely rare, however. It has only happened in four recorded incidents in human history – and none at all for the past 30 years. Each of the cases (two of which occurred in Japan and two in Iraq) was the result of extraordinary circumstances involving widespread, accidental industrial contamination.  

Put simply, normal fish consumption carries virtually no risk of methylmercury toxicity or danger. And there is no evidence documenting that even one person in the United State has ever experienced mercury poisoning from eating fish.