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Risks of Mercury in Fish

Fish is an excellent low-fat food and a great source of protein, vitamins and minerals. In Washington State, fish not only offer a tremendous source of nutrition, but catching, cooking and eating fish are important cultural and family practices. However, some fish contain high levels of a form of mercury, called methyl mercury that can be harmful to pregnant women, women of childbearing age and children under six.

Mercury occurs naturally in the environment. It can be released into the air as a result of volcanic activity. Mercury also comes from industrial pollution, especially burning of coal and other fossil fuels and from burning household or industrial wastes. Mercury compounds settle into sediments of lakes, rivers and oceans, where bacteria convert the inorganic mercury compound to methyl mercury. Fish absorb methyl mercury from water as it passes over their gills. Fish primarily absorb methyl mercury from the prey they eat.

Health problems caused by mercury are most severe for the developing fetus and for young children. Pregnant women who eat fish contaminated with large amounts of methyl mercury run the risk that their babies will have unhealthful changes in their central nervous system and possible in their heart or blood vessels. Nervous system changes can affect the baby’s ability to learn. In adults, methyl mercury can lead to problems of the central nervous system and possible adverse effects on the cardiovascular system.

The Food and Drug Administration has issued a “consumer advisory” to women of childbearing age, to avoid certain kinds of fish. The Centers of Disease Control and Prevention (CDC) and the Washington State Department of Health also support this advisory.

The advisory suggests to pregnant women, women of childbearing age and children under six:

  • Not to eat any shark, swordfish, tilefish, king mackerel or either fresh caught or frozen tuna steaks.
  • Most species of salmon tend to have very low levels of mercury and are safe to eat. Chinook have higher levels of mercury than other salmon, but these levels are still below those found in fish named in this advisory.
  • Fish sticks are fineas long as they aren’t made from shark, swordfish, tilefish, king mackerel or tuna, which most don’t appear to be. Be sure to check the package to make sure the processed fish you are buying is not made from any of the fish mentioned.
  • Women of childbearing age should limit the amount of canned tuna they eat to about one can per week (six ounces)
  • Children under six should eat less than one half a can of tuna (three ounces) per week. Specific weekly limits of children under six range from one ounce for a child who weighs about 20 pounds, to three ounces for a child who weighs about 60 pounds.
  • The type of tuna can make a difference. Read the label on canned tuna and choose “Chunk Light” or “Chunk” tuna. They have less mercury than the “Solid White” or “chunk White” canned tuna. Canned tuna composed of smaller species of tuna such as skipjack and albacore has much lower levels than most tuna steaks.

To learn more about the statewide advisory check out the “Fish Facts For Healthy Nutrition” from The Department of Health website at