By Diana Barnes-Brown for Medtech1
In the last several years, scientists and medical experts have begun voicing new concern about a growing health risk in fish and shellfish: mercury.
Mercury is found in nature, but when it occurs in toxic levels it is most often a form of the metal mercury which occurs when emissions from coal-burning power plants and other industrial sources enter the ecosystem as smoke, which then contaminates rain as it falls to the ground, and eventually drains into rivers, lakes, and the ocean.
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Fish and shellfish are an important part of a healthy diet. Yet, some fish and shellfish contain higher levels of mercury that may harm an unborn baby or young child's developing nervous system.
Pregnant women, nursing women and young children can change their diets to reduce their risk:
Buy “light tuna” as opposed to only buying albacore “chunk tuna”
Do not eat shark, swordfish, king mackerel and tilefish
Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury such as shrimp, salmon, pollock, and catfish
Get more specific information about fish and merucury levels at the FDA’s report on Mercury Levels in Commercial Fish and Shellfish
Recent reports on mercury levels in canned tuna sold in the United States have raised new speculation about whether the metal, known to cause serious birth defects and brain deterioration at toxic levels, is present in canned tuna in amounts that render the fish unsafe for human consumption.
At the end of December, the FDA announced plans to investigate the possibility of the presence of yellowfin tuna, a species particularly vulnerable to high mercury levels, in some brands of “light tuna” or “chunk light tuna.”
Typically, the larger the organism, the higher the potential toxin levels. This is because larger organisms are closer to the top of the food chain, meaning that they have eaten more “links” in the food chain and therefore accumulated more toxins in a process called biological magnification.
Because of this, FDA guidelines currently suggest that people select light tuna over white tuna, because cans of light tuna mostly contain skipjack tuna, a smaller and therefore less potentially toxic species than the larger albacore tuna that is used for canned white tuna.
However, in a three-part series published by the Chicago Tribune in December, it was reported that yellowfin tuna, another large species with a resultantly larger capacity for mercury toxicity, was being packaged as “light” tuna in up to 180 million cans of tuna sold around the nation.
Despite a statement from the U.S. Tuna Foundation’s executive director David Burney, who said that yellowfin was a “non-issue,” the FDA maintains plans to follow up with an inquiry.
Mercury poisoning has been long recognized as a risk by the medical community for decades, and can cause learning disabilities, motor impairment, and memory loss; in some cases it can even cause seizures and death. It is also responsible for the Alice in Wonderland character the Mad Hatter, because many hatters in author Lewis Carroll’s day used mercury to cure the fabric they worked with, and were often victims of chronic mercury poisoning as a result.
In the 1950s, the global scientific community became more acutely aware of the risks posed by industrial pollution when the villagers of Japan’s Minemata Bay, a community that relied heavily on local fishermen’s hauls for food, began to grow ill in great numbers with the symptoms of mercury poisoning.
It was discovered that a power plant was leaking toxic levels of mercury into the sea. Once in the ecosystem, the mercury had been broken down into methylmercury, an easily absorbed form of the toxin, by microbes. Then it had leeched from the water into insects and small marine organisms, which were then eaten by larger organisms, until it was consumed in its biologically magnified form by fish that were sources of human food. People who ate the fish became ill, and their children did as well. The discovery prompted the FDA to place limits on mercury toxicity in fish products.
In 2004 the FDA issued a formal recommendation that pregnant and nursing women limit their fish intake, and take special care to avoid shark, swordfish, king mackerel, tilefish and albacore tuna, where the toxin is known to exist in greater concentration.
While there are not currently any many other government-level warnings against mercury in human food sources, many environmentalists and nutritional experts decry the FDA and other nutrition policy makers guidelines as overly lax, citing examples of illness that resembles mercury toxicity in people with much lower levels of mercury in their systems. There has also been rising concern among medical experts at the use of mercury amalgams in dentistry, with some advising their patients to seek removal of old amalgam fillings and have them replaced with gold.