From the Blog

Mercury Toxicity: Fish Eaters Beware

Mercury is one of the most toxic substances known. Everyone is exposed to small amounts of mercury.

It is a metal found naturally in the environment, but humans increase the amount of mercury in the air, water, and soil by farming, burning coal, and using it in manufacturing. In water, mercury is absorbed by fish. People ingest mercury by eating fish, and at high levels, it can be harmful, especially to the developing fetus, infants, and small children.

Nearly all fish and shellfish contain traces of mercury. Large, long-lived, predatory ocean fish have the highest levels. Consumption of these fish and shellfish can result in high levels of mercury in the human body. For most people, the level of mercury absorbed by eating fish is not a concern. However, the U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) recommend that women who are trying to conceive, pregnant women, nursing mothers, and young children should strictly adhere to the following guidelines:

• Do not eat shark, swordfish, king mackerel, or tile fish because they contain the highest levels of mercury.

• Eat no more than 6 oz (170g) per week of canned albacore ("white") tuna, tuna steaks, lobster, halibut, and orange roughy.

• Eat no more than 12 oz (340g) per week of fish and shellfish lower in mercury, such as shrimp, canned light tuna (not albacore tuna), salmon, pollock, and catfish.

• And, if no advice is available about the fish or shellfish you eat, consume no more than 6 oz (170g) per week, and don’t eat any other fish or shellfish during that week.

• Also, fish sticks and fish-sandwiches sold at fast-food restaurants are generally lower in mercury.

Mercury accumulates in blood and is excreted slowly overtime. When a woman consumes a large amount of fish high in mercury, it may take up to a year for the mercury levels to drop after she stops eating the fish.

In the developing brain, mercury interferes with the organization of brain cells and causes direct destruction. Typically, infants that were exposed to mercury as fetuses appear normal at birth. Developmental delay, blindness, deafness, and seizures can develop over time.

The most important treatment involves identifying the mercury source and stopping the exposure. To reduce environmental exposure, many mercury compounds are no longer sold in the United States. However, pesticides, vaccines, and anti-septic agents may not be regulated in other countries.

Overall, fish and shellfish are part of a healthy, balanced diet. They contain protein and essential nutrients, such as omega-3 fatty acids, which can contribute to heart health and optimal growth and development. Following these, as well as other important nutritional guidelines, will contribute to healthier children today and tomorrow.

For more information:

• Local health departments or environmental agencies

• The EPA fish Web site at http://www.epa.gov/ost/fish

• The EPA mercury Web site at http://www.epa.gov/mercury

• The FDA seafood Web site at http://www.cfsan.fda.gov/seafood1.html

Dr. Abdul Cader is a pediatrician. She was a co-founder of the UMMA Clinic while a medical student at UCLA.