Methylmercury poisoning is brain and nervous system damage from the chemical methylmercury.
Methylmercury is a type of mercury ("quicksilver"), a metal that is liquid at room temperature. Most compounds containing mercury are poisonous. Methylmercury has been used to preserve seed grain, which is fed to animals. Methylmercury may also form in water when other forms of mercury in the water react with certain bacteria.
Methylmercury poisoning has occurred after people have eaten meat from animals fed seed grain or fish from waters contaminated with methylmercury (such as Minamata Bay in Japan). Because of many industrial uses, including the manufacture of fluorescent lights, batteries, polyvinyl chloride, and latex paint, mercury is a common pollutant of air and water.
Unborn babies and infants are very sensitive to methylmercury's effects. Methylmercury causes central nervous system (brain and spinal cord) damage. How bad the damage is depends on how much poison gets into the body. Many of the symptoms of mercury poisoning are similar to those seen in cerebral palsy. In fact, methylmercury is thought to cause a form of cerebral palsy.
The FDA recommends that women who are pregnant or may become pregnant, and nursing mothers avoid fish that may contain unsafe levels of methylmercury. Such fish include swordfish, king mackerel, shark, or tilefish. (Infants should not be given these fish, either.) You should not eat any of these fish caught by friends and family. Check with your local or state health department for warnings against locally caught, noncommercial fish.
Some health care providers have raised concerns about ethyl mercury (thiomersal), a chemical used in some vaccines. However, research shows that childhood vaccines do not lead to dangerous mercury levels in the body. Vaccines used in children today only contain trace amounts of thiomersal. Thiomersal-free vaccines are available.
Exams and Tests
Tests will vary depending on the symptoms that occur.
Methylmercury damage is irreversible. Treatment is determined by the severity of the condition and is similar to that given for cerebral palsy. The patient should be removed from the source of exposure. Treatment may involve:
- Activated charcoal (if mercury is swallowed)
- Administration of intravenous fluids and electrolytes
- Breathing support, including a breathing machine (ventilator)
- Dialysis (kidney machine)
The symptoms are irreversible; however, they do not usually worsen unless there is a new exposure to methylmercury.
When to Contact a Medical Professional
The National Poison Control Center (1-800-222-1222) can be called from anywhere in the United States. This national hotline number will let you talk to experts in poisoning. They will give you further instructions.
This is a free and confidential service. All local poison control centers in the United States use this national number. You should call if you have any questions about poisoning or poison prevention. It does NOT need to be an emergency. You can call for any reason, 24 hours a day, 7 days a week.
Take the container with you to the hospital, if possible.
Avoiding any foods contaminated with methylmercury will prevent poisoning. Because of manufacturing, mercury has become so common in the environment that trace amounts of methylmercury are present in many foods from the ocean, including deep-sea tuna. Fortunately, the levels are low enough that most of these foods remain safe.
Avoid contact with mercury-containing industrial products. Contact poison control if you believe you may have been exposed.
Minamata Bay disease; Basra poison grain poisoning
Long H, Nelson LS. Metals and metalloids. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York, NY: McGraw-Hill; 2004:chap 184.
Velez LI, O'Connell EJ. Heavy metals. In: Marx JA, Hockberger RS, Walls RM, et al., eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Elsevier Mosby; 2013:chap 157.
Update Date 1/15/2014
Updated by: Jacob L. Heller, MD, MHA, Emergency Medicine, Virginia Mason Medical Center, Seattle, Washington. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.