Mercury is an extremely toxic element found in nature and as a pollutant in the environment. It is particularly dangerous because mercury contamination can exist without our realizing that it’s there. For example, fish or shellfish can be contaminated with the most toxic form of mercury, called methylmercury, and you cannot taste or smell it.

Almost all fish and shellfish contain traces of mercury. Fish become contaminated because industrial waste has been dumped into streams or the ocean or released into the air and fallen into streams and oceans. Fish absorb the mercury as they feed in the water.

Fortunately, the risk of mercury poisoning from eating fish and shellfish is generally not a health concern. Fish and shellfish are important components of a healthy diet, because they contain high-quality protein, are low in saturated fat, and are good sources of omega-3 fatty acids. However, it is particularly dangerous for a developing fetus to be exposed to methylmercury. Fetuses are 5 to 10 times more sensitive to the substance than adults are. Methylmercury can affect the immune system, alter genetic and enzyme systems, and damage the nervous system, including coordination and the senses of touch, taste, and sight.

Pregnant women, women who may become pregnant, nursing women, and young children should avoid types of fish that tend to have higher levels of mercury, such as king mackerel, shark, swordfish, and tilefish. People in these high-risk categories should also have no more than 12 ounces a week of other kinds of fish and shellfish. Young children should consume even less than 12 ounces of fish and shellfish per week.

ADDITIONAL FACTS

  1. Another form of mercury, called elemental mercury, can be released from a broken thermometer. Though it is less toxic than methylmercury, elemental mercury causes tremors, gingivitis, and excitability when it is inhaled over a long period. If elemental mercury is ingested, it usually passes though the digestive system without causing harm.
  2. The larger and older a fish is, the higher the level of methylmercury it contains. This is because larger fish have had more time to accumulate the substance from contaminated water.