Mercury in Fish: Should you be concerned?

by Scott Middleton on February 21, 2014

Containing protein, essential nutrients, and omega-3 fatty acids, fish are a key component to a healthy and balanced diet. Fish have even been shown to improve heart health (Water: Outreach and communication, 2013). However, fish and shellfish consumption in excess can be dangerous. This is because fish and shellfish almost always contain a toxin: mercury. This liquid metal has been used for at least 2,500 years in numerous ways (Nadakavukaren, 2011). Recent uss of mercury include use in fluorescent light bulbs, as a slime retardant in paper making, as an ingredient in medicinal products, in the manufacture of scientific instruments, and so on (Nadakavukaren, 2011). Despite its many uses, mercury can be dangerous for women who might become pregnant, women who are pregnant, nursing mothers, and young children. Higher levels of mercury, which may be ingested by eating too much of certain fish or shellfish, can damage the developing nervous system of a young child or an unborn fetus (Water: Outreach and communication, 2013).

Mercury comes in two forms: inorganic mercury and organic mercury, the latter being the far more toxic of the two. Inorganic mercury often attacks the kidneys or the liver. It can either diffuse into the body through inhalation in the lungs or by absorption through the skin with prolonged contact. This can cause neurological problems, such as the tremors and mental aberrations expressed by hatmakers in France in the 1500s, which became known as “Mad Hatters’ Disease” (Nadakavukaren, 2011). Inhalation is more common than skin absorption, and it is estimated that as many as 70,000 American workers are exposed to mercury vapors. Interestingly, while inhaling mercury vapors poses a serious threat, swallowing mercury poses no threat at all. This could occur if a child was to bite down on a thermometer containing mercury, but the mercury would simply be excreted in the feces (Nadakavukaren, 2011).

Organic mercury is far more toxic than the inorganic form. A common form of organic mercury is methyl mercury. Organic mercury enters the bloodstream and, over time, diffuses into the brain. Often this may take a couple months to have any effect on the body. The first sign of organic mercury poisoning is numbness in the lips, tongue, and fingertips. This escalates gradually, negatively effecting speech, swallowing, and walking before deafness and vision problems occur, often causing the victim to lose touch with his or her surroundings. In the past, these symptoms were often mistakenly thought to be those of a mental illness (Nadakavukaren, 2011).

Although mercury occurs in the environment naturally in trace amounts, the current primary source of mercury is atmospheric fallout. This atmospheric mercury enters the atmosphere via coal combustion, mining and smelting, and incineration of mercury wastes (Nadakavukaren, 2011). Once it enters the environment, it enters the food chain at the lowest level and works its way up the food chain, increasing in concentration as it passes from one fish to the next predator in the chain. According to an experiment conducted by the U.S. Geological Survey from 1998 to 2005, detectable levels of mercury were found in fish from all 291 streams tested (Nadakavukaren, 2011). This prominence of mercury in fish, together with its harmful effects as a toxin, are why certain populations must be especially careful about what species of fish they eat as well as the quantity consumed.



The United States Environmental Protection Agency, or EPA, summarizes the guidelines for women and young children to follow regarding the consumption of fish and shellfish in three general recommendations:

1. Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.
2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.
3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don’t consume any other fish during that week. (Water: Outreach and communication, 2013)

For a complete list of fish and their respective mercury levels, visit the National Resources Defense Council’s website at:


Works Cited

Nadakavukaren, A. (2011). Our global environment: A health perspective. Prospect Heights, IL: Waveland Press, Inc

Protect yourself and your family: Consumer guide to mercury in fish. (n.d.). Retrieved from

Water: Outreach and communication:what you need to know about mercury in fish and shellfish . (2013, November 20). Retrieved from

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