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Mercury in seafood

Mercury is a toxic metal that poses a serious health risk to developing fetuses, babies and children, who can suffer brain damage and learning disabilities from prolonged or repeated exposure to even small amounts of mercury. Although the metal occurs naturally in the environment, mercury levels in our air, land and water have increased dramatically since the rise of industrialization in the late 19th century.

What is Mercury and Where Does It Come From?

Mercury is a naturally occurring toxic metal that exists at low levels throughout the environment, and as an element it never breaks down or disappears. Mercury cycles through the environment, passing between the air, land and water, and affects plants and animals.

According to the EDF report Out of Control and Close to Home [PDF], local sources of mercury—such as coal-fired power plants, waste incinerators, and certain factories and mining operations—can create hot spots of pollution that impact local communities. Mercury emissions are a global problem as well, since mercury can be carried through the atmosphere over large distances.

Mercury enters streams, rivers, lakes and oceans primarily through rain and surface water runoff. Bacteria can then convert it to an organic form called methylmercury -- the form that is dangerous to people.


All fish have some mercury. When small fish with low mercury levels get eaten by bigger fish, the amount of mercury biomagnifies. For this reason, long-lived fish and top-level predators like swordfish and shark often have the highest mercury levels. According to EPA, mercury concentrations in fish can be 1 to 10 million times the mercury concentration in the water.

The problem of mercury-contaminated fish is widespread. According to the EPA's National Listing of Fish Advisories:

  • Mercury advisories increased 95% between 2003 and 2010 (from 2,362 to 4,598). This is largely due to greater monitoring, not necessarily greater pollution.
  • All 50 states currently issue mercury advisories.
  • As of 2010, almost 18 million lake acres and approximately 1.4 million river miles were covered by some type of consumption advisory.
  • Currently, 28 states have statewide mercury advisories in freshwater lakes or rivers, and 19 states have statewide advisories for mercury in their coastal waters.

Statewide advisories urge people to limit their consumption of all fish and shellfish from freshwater or coastal areas. Visit the EPA fish advisory website for more information on adviseries in your area.

What Are the Health Risks of eating Mercury-Contaminated Fish?

Mercury targets the nervous system and kidneys. Developing fetuses, infants and young children are at the highest risk from mercury exposure, since their brains and nervous systems are still forming. Fetuses can absorb mercury directly across the placenta, and nursing infants can get it from their mother's breast milk. This is why it is so important for women of childbearing age to minimize their consumption of fish with high mercury levels. It can take 12-18 months for a women's body to significantly rid itself methylmercury.

Children exposed to excessive mercury before birth may exhibit problems with mental development and coordination, including how they think, learn and problem-solve later in life. Developmental and neurological damage can be irreversible for fetuses and young children, but as children get older, the risk associated with mercury exposure decreases.

Mercury exposure can also harm adults. Symptoms can include 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.

How Can I Reduce the Risks of Eating Seafood Contaminated With Mercury?

Since methylmercury binds to proteins, it is found throughout fish tissue, including the muscle that makes up fish steaks and fillets. Therefore, cleaning and cooking methods that can reduce amounts of other contaminants (like trimming fat and removing skin and organs) are not successful in reducing mercury levels in fish.

The best way to reduce exposure to methylmercury is to reduce your consumption of predatory or long-lived fish (such as swordfishsharkorange roughy and tuna). Be especially conservative if you are a woman of childbearing age or are feeding young children.

Where CAN I find more information on mercury levels in SEAFOOD?

EDF marine scientist Tim Fitzgerald recently co-authored an unparalleled collection of mercury levels in commercial seafood, in partnership with Stony Brook University. This study is the basis for the mercury advice found throughout the Seafood Selector.