Information About Mercury

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Information About Mercury

Seafood should be an important part of everyone’s diet. Leading health authorities, including the American Heart Association,USDA Dietary Guidelines for Americans, American Medical Association and American Diabetes Association, recommend consumers eat fish at least twice a week. We encourage you to watch the videos hyperlinked below to learn more about mercury and the importance of eating fish as a regular part of your diet.

Science-Based Evidence: The Benefits of a Fish-Rich Diet During Pregnancy
Seafood Deficiency in the American Diet: How it Hurts Our Hearts and Brains
Fish During Pregnancy: Science Calls for Updated Advice

What is mercury?

Mercury is a metal that occurs naturally in air and water and is also a by-product of industrial activity. It's released into the atmosphere both by nature through mercury vapor that is emitted from the Earth's crust and through the burning of household and industrial wastes, including fossil fuels.

Mercury in seawater arises mostly from natural processes, including underwater volcanoes.

How does methylmercury enter our food?

Mercury finds it way into seafood from naturally occurring mercury found in oceanic underwater volcanoes. Ocean-going species swim in deep oceans far from human industrial sources of mercury.

Mercury enters freshwater species from natural sources as well as from anthropogenic (man-made) sources such as air pollutants (thanks to rain) deposited into rivers and lakes.

In the water, bacteria transform the mercury into methylmercury, a process called methylation. Larger, migratory species, such as shark and swordfish, absorb methylmercury from the water and ingest it when eating algae and other smaller species of fish. In the deep ocean, it would take thousands of years for anthropogenic mercury to reach the bottom sediment, be methylated and rise through the food chain.

Who monitors the levels of methylmercury in our food supply?

In the United States, the responsibility for regulating mercury is shared by two federal agencies: the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA). The FDA regulates commercially sold fish and seafood and provides consumption advice for consumers, while the EPA regulates the amount of mercury released into the environment. The EPA additionally works with state governments to develop fresh water fish advisories.

Do fish contain methylmercury?

Nearly all fish contain some methylmercury. Large predator species such as shark, swordfish, king mackerel and tilefish contain the most methylmercury. In general, the larger and older a fish is, the more it will contain. This is due to the fact that methylmercury accumulates over time.

How much methylmercury is found in fish?

Levels of methylmercury vary greatly, largely based upon the species, size and age of the fish.

According to the FDA, in general, methylmercury levels for most fish range from less than 0.01 parts per million (ppm) to 0.5 ppm. The average concentration for commercially important species is less than 0.3 ppm. In a few species, methylmercury levels can reach 1 ppm, which is the limit allowed by the FDA in fish intended for human consumption. This level is found most often in large predator fish, including shark, swordfish, king mackerel and tilefish. Fresh-water species -- such as pike and walleye (which are also predator fish) -- sometimes have methylmercury levels in the 1 ppm range, if they swim in waters polluted with high mercury levels.

What are the health effects associated with methylmercury consumption?

Excess exposure to methylmercury can result in adverse health effects. The most severe effects have been seen following high-dose mercury poisoning situations not from average fish consumption.

A current study of children in the Seychelles Islands (in the Indian Ocean) shows that continuous low-level exposure does not cause any neurodevelopmental problems.

Why does the FDA recommend a limit for methylmercury consumption?

The FDA is conservative in protecting the health of American consumers. As such, it has set consumption advice at the 1 ppm level, which is the limit allowed by the FDA for fish intended for human consumption. The level is purposely set 10 times lower than the lowest level associated with health problems (specifically mercury poisoning). This conservative level allows for the greater protection of everyone - adults, children and even unborn babies.

Are Americans at risk for methylmercury poisoning from eating fish?

No. Only a very small number of pregnant women and women of childbearing age who may become pregnant who eat exceedingly large quantities of predator fish (shark, swordfish, tilefish and king mackerel) need to be aware of certain concerns. The FDA says that it is all right to eat other fish, "as long as you select a variety of fish while you are pregnant or may become pregnant, you can safely enjoy eating them as part of a healthful diet. You can safely eat 12 ounces per week of cooked fish. You can choose shellfish, canned fish, smaller ocean fish or farm-raised fish - just pick a variety of different species."

Are people who eat extraordinarily large quantities of fish at risk?

Pregnant women who eat large predator species of fish (swordfish, tilefish, king mackerel or shark) may put their unborn children at risk. This is because the developing nervous system of a fetus is especially susceptible to effects of high methylmercury levels. The Environmental Protection Agency provides current advice on fish consumption from fresh water lakes and streams. Check with your state or local health department to see if there are special advisories on fish caught from waters in your local area.

What precautions should women take to reduce these risks?

The FDA recommends that pregnant women and women of childbearing age who may become pregnant should not eat shark, swordfish, king mackerel or tilefish. FDA advises that pregnant women and women of childbearing age who may become pregnant "can safely eat 12 ounces per week of cooked fish. A typical serving size of fish is from 3 to 6 ounces. Of course, if your serving sizes are smaller, you can eat fish more frequently. You can choose shellfish, canned fish, smaller ocean fish or farm-raised fish-just pick a variety of different species." The EPA recommends that pregnant women or who may become pregnant, nursing mothers and young children should limit their consumption of fish caught by family and friends to one meal per week. Of course, all consumers and especially pregnant women should follow the basic nutritional guidelines.

Are children at increased risk?

No. However, the FDA advises "it is prudent for nursing mothers and young children not to eat these fish" (swordfish, shark, tilefish, and king mackerel). The EPA recommends young children limit their consumption of fish caught by family and friends to one meal per week.

Should Americans eliminate fish from their diets because of methylmercury?

No. Fish is an excellent source of lean protein, vitamins and minerals. In addition, research has shown that omega-3 fatty acids found naturally in certain species of fish help lower the risk of heart disease and ease the pain of arthritis, among other things. There are ways to decrease one's risk of methylmercury without denying oneself the good taste and health benefits of fish. What's more, FDA acknowledges that seafood is an important part of a balanced diet for pregnant women and those of childbearing age who may become pregnant. According to a recent report authored by a committee from the National Academy of Sciences' National Research Council (NAS/NRC) for the EPA, "Because of the beneficial effects of fish consumption, the long-term goal needs to be a reduction in the concentrations of methylmercury in fish rather than a replacement of fish in the diet by other foods. Eliminating an entire type of food or food group from the diet is generally unwise from a nutritional standpoint."

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