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Mercury in Fish

  1. Is mercury a risk for everyone or only pregnant women?

    Mercury poses the greatest risk to developing fetuses, infants and young children because their brains and nervous systems are still developing. As a result, women of childbearing age should minimize their intake of fish, as mercury accumulates in the blood and can take more than year to be significantly purged from their bodies. Mercury exposure, especially high levels, can also harm all adults.

  2. Is all fish equally contaminated? And if so, should I eliminate fish from my diet completely?

    Nearly all fish and shellfish contain traces of mercury. Larger fish species have higher levels, as they live longer and have more time to accumulate mercury. Large fish, such as king mackerels,mercury droplet swordfish, tilefish, and shark have the highest levels and should be avoided. Crab, tuna and freshwater trout possess the next highest levels. The best solution is to moderate the intake of long-lived fish. Eat a variety of smaller fish.

  3. Why be concerned?

    Mercury is a highly poisonous metal that attacks the nervous system and kidneys. Developing fetuses, babies and children can develop brain damage and learning disabilities as a result with neurological symptoms similar to cerebral palsy. In adults, high mercury intake can cause numbness, burning or tingling of the extremities (lips, fingers, toes); fatigue; weakness; irritability; shyness; loss of memory and coordination; tremors; and changes in hearing and blurred vision. Extremely high mercury levels can permanently damage an adult’s brain and kidneys, or even lead to circulatory failure.

  4. How do fish become contaminated?

    Mercury is a naturally occurring toxic metal that exists at low levels throughout the environment, and it never entirely breaks down or disappears. Industrial sources of mercury include coal-fired power plants, waste incinerators, certain factories, and mining operations that significantly increase the threat of contamination. Mercury enters streams, rivers, lakes, and oceans primarily through rain and surface water runoff. Bacteria then converts it to an organic form called methylmercury – the form that is dangerous to people.

    The concentration of methylmercury increases as it goes up the food chain. When bigger fish eat small fish with low mercury levels, the amount of mercury increases in the bigger fish.

  5. Are there rules regulating the levels of contamination in seafood?

    No. The U.S. Food and Drug Administration warns that pregnant women and young children should not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury. However, there are efforts for the FDA to weaken even that warning.

Food & Water Watch joins many other environmental groups in recommending a more cautious diet. For example, no man, woman or child should eat bluefish, striped bass or blue marlin. Only men should have one serving a month of swordfish. Men and woman can have one serving a month of bluefin tuna and children only half a serving. Overall, to decrease mercury contamination, eat few servings of big, long-lived fish. Have a variety of smaller fish.