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About Mercury in Seafood

Early in your pregnancy, you probably received advice from your midwife to avoid eating certain kinds of fish. You might wonder: why these fish and not others? How does mercury get into fish? What effects does mercury have on humans? Are any fish or seafood safe to eat?

The fish you've been warned against include king mackerel, shark, swordfish, tilefish, and fresh or frozen tuna. They are the ones most likely to be contaminated with mercury because they are very large and have long life spans.

Mercury enters the environment from power plants that burn fossil fuels like coal. Rain, snow and runoff send the mercury into bodies of water where it is transformed into methylmercury. Small fish absorb methylmercury as they feed. These smaller fish are prey for the large varieties above. The larger ones eat lots of small fish over many years, thus increasing the amount of mercury they contain.

Methylmercury is a problem because it affects brain functions. The rapidly growing brains of fetuses, infants and young children are most susceptible to the effects of mercury.

That said, it's also true that seafood is an excellent source of protein for you and your growing baby. Many widely available fish have relatively low mercury levels and thus are safe to eat in moderate amounts. The FDA recommends a limit of 12 oz per week for women of childbearing age and nursing mothers. The EPA's guidelines are more stringent: no more than 8 oz uncooked (6 oz cooked) or one meal of fish per week for pregnant or nursing women.

Canned tuna is acceptable because it comes from a smaller species of tuna. Light tuna is preferable to white. Other types of fish and seafood that can be safely consumed are catfish, crab, flounder, sole, grouper, haddock, herring, lobster, ocean perch, oysters, rainbow trout, salmon, sardines, scallops, shrimp, spiny lobster, tilapia, and farmed trout. Be sure not to exceed the recommended maximum of one meal per week.

To learn more, visit:
www.cfsan.fda.gov The FDA food safety site
www.epa.gov/mercury The EPA mercury site
The National Academy of Science's report on Toxicological Effects of Methylmercury is online at
www4.nas.edu/news.nsf/isbn/0309071402


Disclaimer: The above represents the author’s opinion and is intended for the use of clients of the Midwives at Mount Auburn. It should not substitute for the advice of your own care provider.