Mercury Poisoning

The three forms of mercury

Ethylmercury in the vaccine preservative thimerosal is cleared quickly and is not a cause of mercury poisoning. Most US vaccines for children no longer contain it.

Symptoms

Mercury vapor (elemental)

Short-term high exposure (heating or vacuuming mercury in an enclosed space) causes cough, chest tightness, shortness of breath, fever, a metallic taste, vomiting and, in severe cases, lung inflammation.

Long-term lower exposure causes the classic picture:

• Tremor: fine shaking of the hands, eyelids and tongue that worsens with intended movement
• Erethism: shyness, irritability, anxiety, mood swings, insomnia and memory loss (the source of the "mad hatter" phrase, from hat makers exposed to mercury)
• gum inflammation, excess saliva and loose teeth
• headache, tiredness and weakness
• kidney damage

Mercury salts (inorganic)

Swallowing a mercury salt causes a corrosive injury: burning mouth and throat, vomiting, bloody diarrhea, and shock, followed by acute kidney failure. Long-term skin absorption from creams typically causes nephrotic syndrome (leg swelling, foamy urine) and nerve symptoms such as numbness and tingling, anxiety and tiredness.

Methylmercury

Symptoms appear weeks to months after exposure and can be permanent:

• numbness and pins and needles around the mouth, in the fingers and toes
• poor coordination and an unsteady walk
• narrowing of the visual field (tunnel vision)
• hearing loss and slurred speech
• muscle weakness and memory problems

In pregnancy, methylmercury crosses the placenta. The fetal brain is far more sensitive than an adult's, so exposure can affect a child's development even when the mother has no symptoms.

Children: acrodynia

Children exposed to mercury vapor or salts can develop acrodynia (pink disease): pink, painful, peeling hands and feet, sweating, irritability, light sensitivity, high blood pressure and a fast heartbeat.

Testing for mercury

• Urine mercury (spot corrected for creatinine or 24-hour collection): best for elemental and inorganic exposure.
• Whole blood mercury: best for recent exposure and for methylmercury.
• Hair analysis: reflects methylmercury exposure over months, used in research and fish-consumption studies. Commercial hair tests for "heavy metals" are unreliable for diagnosis.
• Kidney function tests and urine protein, plus nerve tests where needed.

Avoid "provoked" urine tests, where a chelating drug is given before the sample. They produce misleadingly high results and are not recommended by toxicology societies.

Treatment

1. Stop the exposure: leave the contaminated area, stop using the product, or change the diet. For low-level exposure this may be all that is needed, as mercury levels fall over weeks to months.
2. Supportive care: oxygen and breathing support for lung injury after vapor inhalation; fluids and kidney support after swallowing salts; dialysis for kidney failure.
3. Chelation therapy: medicines that bind mercury so it can be excreted. Options include oral succimer (DMSA), DMPS, and injected dimercaprol (BAL) for severe inorganic poisoning. Chelation helps most with inorganic and elemental mercury and is less effective once methylmercury is in the brain.

Treatment should be guided by a medical toxicologist or Poison Control. Over-the-counter "detox" products and unsupervised chelation are unsafe.

What to do after a broken mercury thermometer

A fever thermometer holds less than a gram of mercury, which is a small risk if cleaned up properly.

• Open windows, turn off heating and air conditioning, and keep children and pets out.
• Wear gloves. Use stiff paper to push droplets together and an eyedropper or sticky tape to collect them.
• Put everything in a sealable jar or bag and contact your local waste authority.
• Never vacuum or sweep mercury: it spreads vapor into the air.
• Do not pour mercury down a drain or wash contaminated clothing in a machine.

Call Poison Control or your local environmental agency for larger spills.

Prevention

• Follow FDA and EPA fish advice: choose lower-mercury fish such as salmon, sardines, shrimp, cod, canned light tuna and tilapia. During pregnancy and for young children, avoid shark, swordfish, king mackerel, marlin, orange roughy, bigeye tuna and Gulf of Mexico tilefish.
• Check local advisories before eating fish you catch.
• Avoid unlabeled imported skin-lightening, anti-aging or acne creams. Check labels for "mercurous chloride", "calomel", "mercuric", "mercurio" or "mercury".
• Replace old mercury thermometers with digital ones and dispose of them through hazardous waste programs.
• Follow workplace safety rules in dentistry, mining, and chemical or lamp manufacturing.

Frequently asked questions

What are the first signs of mercury poisoning?

It depends on the form. Mercury vapor may first cause tremor, irritability, poor sleep and a metallic taste. Methylmercury often starts with numbness and tingling around the mouth, fingers and toes. Swallowed mercury salts cause immediate burning pain, vomiting and diarrhea.

Can you get mercury poisoning from eating fish?

Yes, but it is rare from normal diets. Large predatory fish such as swordfish, shark and king mackerel contain the most methylmercury. Eating them frequently can raise levels. Most fish are safe in recommended amounts, and fish provides important nutrients, especially in pregnancy.

Is a broken thermometer dangerous?

A single broken fever thermometer is a small risk if handled correctly. Ventilate the room, collect the beads with paper and tape, seal them in a container and never vacuum. Call Poison Control if you are unsure or if someone has symptoms.

Can mercury fillings cause mercury poisoning?

Dental amalgam fillings release very small amounts of mercury vapor. Health agencies have not found that intact fillings cause poisoning in the general population. The FDA suggests alternatives for new fillings in some higher-risk groups, such as pregnant women, but does not advise removing intact fillings, which can increase exposure.

Is mercury poisoning reversible?

Some effects improve when exposure stops, especially tremor and mood changes from vapor and kidney damage from salts. Damage from methylmercury, especially to the developing brain, and from severe poisoning can be permanent. Early recognition and removing the source give the best chance of recovery.