Mercury Contamination of Food

The chemical element mercury is a shiny metallic liquid which occurs in only trace amounts in igneous and sedimentary rocks. Mercury is found principally in the form of the ore cinnabar (mercury sulfide), but can also be found in the uncombined state (1). Mercury will dissolve numerous metals to form amalgams and is thus used to extract gold dust from rocks by dissolving the gold and then boiling off the mercury. The amalgam used in dental fillings contains tin and silver (and sometimes gold) dissolved in mercury (1). The use of this amalgam in "silver fillings" is a highly debated issue. If you are interested in more information please see the external links below.

Mercury is emitted to the ambient air from a variety of fuel combustion, incineration and industrial processes and natural sources. While atmospheric concentrations are generally very low, mercury is deposited by wet and dry processes to forest ecosystems, from which it can ultimately be transported to and bioaccumulate in highly toxic forms in the food chain of aquatic ecosystems (2). Here it can cause adverse effects on aquatic organisms and ultimately human health (2). Mercury exposure via food most often occurs when seafood containing mercury is eaten, or when mercury containing plants, such as rice, are consumed.

There are two types of mercury poisoning, acute and chronic. Acute mercury poisoning results from the ingestion of soluble mercury salts, which violently corrode skin and mucous membranes. Although cases have occurred in which persons have ingested elemental mercury without suffering permanent damage, mercury vapor aspirated into the lungs can cause severe pneumonia and death. Chronic mercury poisoning occurs through the regular absorption of small amounts of mercury. This condition is often a disease of workers in mercury mines, laboratories, and industries that use mercury. The most toxic mercury compounds are those that are fat soluble, because this property assists in their distribution throughout the body. Methyl mercury compounds, such as dimethyl mercury, are among the most dangerous. Mercury salts released into the environment may frequently be converted by anaerobic bacteria into such compounds, which can then be carried through the food chain to humans as in the disaster at Minamata Bay, Japan Other microorganisms can convert methyl mercury compounds into the insoluble, and therefore harmless, mercury sulfide(1).

The federal government has developed regulations, guidelines, and standards to protect people from the possible health effects of exposure to mercury (3).

• The Environmental Protection Agency (EPA) has limited the level of inorganic mercury in rivers, lakes, and streams to 144 parts per trillion parts of water (ppt) (144 ng/L). EPA requires that all releases of more than 1 pound of mercury metal to the environment be reported. EPA estimates that for an adult of average weight, exposure to 0.021 milligrams (mg) of inorganic or organic mercury per day in food or water will probably not result in any harm to health.
• The Food and Drug Administration (FDA) limits levels of mercury to no more than 2 parts per billion (ppb) (0.002 milligrams of mercury per liter of water [mg/L]) in bottled water.
• The Occupational Safety and Health Administration (OSHA) has set a limit of 1.2 ppb of organic mercury in workroom air (equal to 0.01 milligrams of mercury per cubic meter of air [mg/m3]) and 6.1 ppb (0.05 mg/m3) for inorganic mercury vapor to protect workers during an 8-hour shift. The National Institute for Occupational Safety and Health (NIOSH) recommends that the amount of inorganic mercury be limited to 6.1 ppb (0.05 mg/m3) averaged over a 10-hour workshift.

Here are some very informative external links that pertain to Mercury in food:

• UC Davis - Mercury in Seafood
• FDA/CFSAN - Mercury In Fish: Cause for Concern?
• 1995 National Listing of Fish Consumption Advisories
• Minamata Disaster
• American Dental Association Topical Index: Amalgam

References

1. Banfield, J. Mercury, URL: http://www.geology.wisc.edu/~jill/hg.html

2. Allison Bush and Frank B. DuRoss Mercury Monitoring. May 19, 1995, Vermont Monitoring Cooperative. URL: http://www.uvm.edu/~snrdept/vmc/hg.html

3. Agency for Toxic Substances and Disease Registry, Public Health Statement, Mercury - ATSDR Public Health Statement, December 1990 URL: http://atsdr1.atsdr.cdc.gov:8080/ToxProfiles/phs8916.html

This Page prepared by B.T. Johnson, December 1997 UCD EXTOXNET FAQ Team.