All About Mercury
Mercury is a well-known neurological and kidney toxin. It exists naturally in the environment, but more is released into the air, land, and water when we burn trash, dump sewage on cropland, and when our factories burn fossil fuel. Mercury has made its way into the fish part of the food chain because it is found in water. The bigger fish, such as pike, bass, and very large tuna, seem to contain more mercury because they eat smaller fish and almost immediately inherit those fish's mercury stores.
The bad news: Because eating fish that contains mercury can damage the nervous systems of unborn babies and may pose a risk to young children, The FDA has written an advisory for pregnant women. Pregnant women can safely eat 12 ounces of cooked fish per week, as long as it's from the lower-mercury species. Which fish have the most mercury? Shark, tilefish, king mackerel, and swordfish tend to top the list.
The good news: One of our most popular fishes -- canned tuna -- contains lower levels of mercury than other types. But that's where the good news ends. The Environmental Working Group advises pregnant women to eat no more than 6 ounces (about one can's worth) of tuna per month -- mainly because this fish is eaten so frequently in America.