The small amounts of mercury absorbed by the human body due to diet and amalgam fillings may be harmless, but mercury spills due to large industrial accidents are a different story. Industrial (and natural) release of large amounts of elemental mercury into the ocean has had disastrous effects. Metallic mercury can be altered by aquatic plants and animals to forms known as "ethyl" and "methyl mercury".
These forms of mercury--known collectively as organic mercury--are soluble and well absorbed in the digestive tract. In cultures that eat a lot of fish, such as in Japan, people living in areas where the fish are caught in contaminated waters can be subject to real mercury poisoning. This is because the soluble mercury compounds (produced by aquatic plants metabolizing metallic mercury) are concentrated as they progress up the food chain from plant grazing sea animals to larger and larger fish. This is exactly what happened in Minamata, Japan in the early 1970's. (Click here to read more about the tragedy in Minamata. Click the image to read a second essay. Note that this tragedy was confined to the area immediately surrounding Minamata Japan. Other areas were not affected.
Seafood---Is it Safe to eat?
Is eating seafood dangerous because of the amount of mercury found in fish? Even though the amount of mercury found in fish is vastly more than that released by a mouthful of dental amalgams, it still takes a lot of fish eaten weekly for a lifetime to accumulate enough mercury to cause health problems.
In order for any toxic material to have negative effects on the human body, that material must accumulate in the system in spite of the fact that the body naturally eliminates it through the liver or kidneys on a daily basis. (Mercury is eliminated through the kidneys.)
Even though seafood contains much more mercury than is released by a mouthful of amalgam fillings, it still takes quite a lot of seafood eaten over a long period of time to have toxic effects on the human body. If the amount of mercury consumed does not exceed the body's ability to excrete it over time, then there is no toxic effect. The human body is simply very good at eliminating mercury.
The amount of fish eaten in the United States is tiny when compared to the amount eaten by other populations such as the Scandinavians, Japanese, Indonesians, Chinese and large numbers of island populations. Even so, none of these populations suffers any ill effects from their diet. On average, people in the Seychelles Islands eat between 12 and 14 fish meals every week, and the mercury serum levels measured from the island natives are approximately ten times higher than those measured in the United States. Yet none of the studied Seychelles natives suffered any ill effects from mercury in fish, and they received the significant health benefits of fish consumption. Furthermore, there is no evidence that there is any more mercury in seafood today than there was 100 years ago. There may even be less. The Smithsonian Institution tested tuna samples that were archived between 1878 and 1909, and compared them with similar fish tissue from 1971 and 1993. They found significantly less mercury in the more recently caught fish. In some cases, the difference was more than 50 percent. To learn more about this subject, please visit this site.