Definition

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 the 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.

Alternative Names

Minamata Bay disease; Basra poison grain poisoning

Poisonous Ingredient

Methylmercury

Where Found

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.

Poisoning from eating fish from water that is contaminated with methylmercury has occurred. One famous incident occurred in Minamata Bay in Japan in the 1940s. Methylmercury poisoning has also occurred in people who have eaten meat from animals fed with grain that was treated with this form of mercury. Rare cases have occurred in children who ate bread made from grain contaminated with methylmercury.

Methylmercury is used in fluorescent lights, batteries, and polyvinyl chloride. It is a common pollutant of air and water.

Symptoms

Symptoms of methylmercury poisoning include:

• Blindness
• Cerebral palsy (in the child of a pregnant woman exposed to methylmercury)
• Deafness
• Growth problems
• Impaired mental functioning
• Lung function impairment
• Movement or coordination problems
• Seizures
• Small head (microcephaly)

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.

Before Calling Emergency

Have this information ready:

• Person's age, weight, and condition (for example, is the person awake and alert?)
• Source of the mercury
• Time it was swallowed, inhaled, or touched
• Amount swallowed, inhaled, or touched

Do not delay calling for help if you do not know the above information.

Poison Control

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.

What to Expect at the Emergency Room

The provider will measure and monitor the person's vital signs, including temperature, pulse, breathing rate, and blood pressure.

Tests that may be done include:

• Blood and urine tests
• Chest x-ray
• ECG (electrocardiogram) or heart tracing

Treatment may include:

• Activated charcoal by mouth or tube through the nose into the stomach, if mercury is swallowed
• Dialysis (kidney machine)
• Fluids through a vein (by IV)
• Medicine to treat symptoms

Outlook (Prognosis)

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. Prevention of continued exposure to mercury is the most important part of treatment.

Complications depend on how severe a person's condition is, and what their specific symptoms are (such as blindness or deafness).

References

Pizzorno JE, Crinnion W. Environmental medicine. In: Pizzorno JE, Murray MT, eds. Textbook of Natural Medicine. 5th ed. St Louis, MO: Elsevier; 2021:chap 35.

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, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 146.

U.S. Food and Drug Administration website. Mercury in Food and Dietary Supplements. Last updated March 1, 2023. Accessed May 19, 2023.