Mercury: Health EffectsPrint Friendly Page
The general public is exposed to mercury's toxic effects primarily by ingesting fish that have been contaminated with methylmercury. Approximately 95 percent of the mercury found in fish is in the form of methylmercury, a particularly toxic form of mercury that is easily absorbed when ingested. It affects the immune system, alters genetic and enzyme systems, and damages the nervous system, including coordination and the senses of touch, taste, and sight. Potential effects from exposures to mercury are shown in Table 1.
Because methylmercury is toxic to the developing nervous system, unborn fetuses and young children are especially susceptible. Therefore, the population at highest risk is the offspring of women that consume large amounts of fish and seafood. A 2000 National Academy of Sciences report concluded that "available consumption data and current population and fertility rates indicate that over 60,000 newborns annually might be at risk for adverse neuro-developmental effects from in-utero exposure to methylmercury." In March 2001, based on data from the Centers for Disease Control, the US EPA estimated that 10 percent of US women of child-bearing age have levels of mercury that double their risk of having babies born with mental or neurological problems.
Mercury may pose a risk to some adult populations whose diets consist primarily of large amounts of fish and seafood that may be contaminated with mercury. For example, a study conducted by Finnish scientists suggested that an increased intake of methylmercury (from eating fish) increased the risk of cardiovascular disease. Other studies have found no connection and some suggest that the benefits from the omega-3 fatty acids in seafood, such as reducing high blood pressure, outweigh the risks associated with methylmercury in certain groups. A 2007 National Academy of Sciences report suggested that "increased methylmercury exposure might be a risk factor for adult cardiovascular toxicity; evidence for additional benefits of seafood consumption to those at risk for heart disease is too weak to warrant special advice."
Exposure to humans can also occur by inhalation of or bodily contact with elemental mercury from a broken product (e.g., mercury fever thermometer) or manufacturing process. In either case, mercury can be in its elemental form or combined with an inorganic element or compound.
Mercury also poses health risks to wildlife that eat contaminated fish. Adverse effects in exposed wildlife may include death, reduced reproductive success, impaired growth and development, and behavioral abnormalities. Reproductive effects are of particular concern because these may occur at levels of exposure well below those associated with symptoms of overt toxicity. Species that are more likely to be at risk from exposure to mercury in fish include top-level avian and mammalian predators, such as eagles, loons, osprey, mink, and otters.
Sources: National Academy of Sciences, "Toxicological Effects of Methylmercury," 2000: http://books.nap.edu/catalog.php?record_id=9899
Last Updated: 11/06/08