Methylmercury poisoning is brain and nervous system damage from the chemical methylmercury.
This article is for information only. DO NOT use it to treat or manage an actual poison exposure. If you or someone you are with has an exposure, call your local emergency number (such as 911), or your local poison center can be reached directly by calling the national toll-free Poison Help hotline (1-800-222-1222) from anywhere in the United States.
Methylmercury is a type of mercury, a metal that is liquid at room temperature. A nickname for mercury is quicksilver. Most compounds containing mercury are poisonous. Methylmercury is a very poisonous form of mercury. It forms when bacteria react with mercury in water, soil, or plants. It was used to preserve grain fed to animals.
Methylmercury poisoning has occurred in people who have eaten meat from animals that ate grain that was treated with this form of mercury. Poisoning from eating fish from water that is contaminated with methylmercury has also occurred. One such body of water is Minamata Bay in Japan.
Methylmercury is used in fluorescent lights, batteries, and polyvinyl chloride. It 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 severe the damage is depends on how much poison gets into the body. Many of the symptoms of mercury poisoning are similar to symptoms of 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. This includes swordfish, king mackerel, shark, and tilefish. Infants should not eat these fish, either. No one should 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.
Symptoms of methylmercury poisoning include:
- Cerebral palsy (movement and coordination problems, and other complications)
- Growth problems
- Impaired mental functioning
- Lung function impairment
- Small head (microcephaly)
Tests will vary, depending on a person’s symptoms.
Methylmercury damage cannot be reversed. Treatment will depend on how severe a person’s condition is. It is similar to treatment for cerebral palsy. The person should be moved away from the source of exposure to methylmercury. Treatment may involve:
- Activated charcoal by mouth or tube through the nose into the stomach, if mercury is swallowed
- Blood and urine tests
- Breathing support, including oxygen, tube through the mouth into the throat, and breathing machine
- Chest x-ray
- Dialysis (kidney machine)
- ECG (electrocardiogram, or heart tracing)
- Fluids through a vein (by IV)
- Medicine to treat symptoms
The symptoms cannot be reversed. However, they do not usually get worse unless there is a new exposure to methylmercury, or the person is still exposed to the original source.
Methylmercury poisoning has been linked to an increased heart attack rate.
If you feel you or someone you know has symptoms of methylmercury poisoning, seek medical care right away.
Take the container with you to the hospital, if possible.
Your local poison control center can be reached directly by calling the national toll-free Poison Help hotline (1-800-222-1222) from anywhere in the United States. This national hotline 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.
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. However, the levels are low enough that most of these foods remain safe.
Avoid contact with industrial products that contain mercury. Contact poison control if you believe you may have been exposed.
Smith SA. Acquired peripheral neuropathies. In: Swaiman KF, Ashwal S, Ferriero DM, et al, eds. Swaiman’s Pediatric Neurology: Principles and Practice. 6th ed. Philadelphia, PA: Elsevier; 2017:chap 142.
Theobald JL, Mycyk MB. Iron and heavy metals. In: Walls RM, Hockberger RS, Gausche-Hill M, eds. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier; 2018:chap 151.