Mercury Poisoning

Mercury poisoning is toxicity from elemental (metallic), inorganic or organic mercury. The three forms differ in route, target organ and treatment.

• Elemental mercury (thermometers, barometers, dental amalgam, gold mining, fluorescent lamps, folk remedies): liquid is poorly absorbed from the gut, but vapor is readily absorbed from the lungs (about 80%) and crosses the blood-brain barrier. Heated or spilled mercury vaporizes at room temperature.
• Inorganic salts (mercuric chloride, mercuric cyanide, calomel, skin-lightening creams, batteries, some antiseptics): corrosive to the gut and kidney.
• Organic mercury: methylmercury (contaminated fish, Minamata disease, fungicide-treated grain in Iraq) is absorbed 90 to 100% from the gut and accumulates in the brain, and dimethylmercury is lethal in tiny amounts through skin or vapor, with a delay of weeks to months before symptoms.

Mechanisms: mercury binds sulfhydryl groups of enzymes and structural proteins, impairing neuronal, renal tubular and cellular function. Blood levels over 10 micrograms/L and urine over 20 micrograms/L (24 hours) are the usual markers of excess exposure.

Complications: chemical pneumonitis and pulmonary edema (acute vapor inhalation), erethism, tremor and neuropsychiatric damage, acrodynia (pink disease) in children, nephrotic syndrome and acute tubular necrosis, corrosive gastroenteritis with shock, and permanent visual field loss and ataxia (methylmercury). Methylmercury crosses the placenta and causes severe congenital neurological damage.

• Acute elemental vapor inhalation: cough, dyspnea, metallic taste, fever, chest pain, tachypnea, pneumonitis, pulmonary edema over hours to days
• Chronic elemental: tremor of the hands, eyelids and tongue, erethism (irritability, shyness, insomnia, memory loss), gingivitis, hypersalivation, metallic taste, proteinuria
• Acrodynia in children: pink, painful, peeling hands and feet, irritability, photophobia, sweating, hypertension, tachycardia
• Inorganic salts: metallic taste, burning mouth and throat, bloody vomiting and diarrhea, shock, then oliguric kidney failure over 1 to 2 days
• Methylmercury: paresthesias of the lips and extremities, ataxia, dysarthria, constricted visual fields, hearing loss, tremor, progressive encephalopathy
• Red flags: respiratory distress, oliguria, bloody diarrhea, ataxia with visual field loss, pregnancy and exposure in children

1. Exposure history: type, route, quantity and duration, with an inspection of the home, workplace, remedies and diet.
2. 24-hour urine mercury (best for elemental and inorganic exposure): over 20 micrograms/L is elevated, and over 100 micrograms/L is associated with symptoms. Use a mercury-free container, and avoid collecting after contrast agents or chelation.
3. Whole blood mercury: over 10 micrograms/L is elevated (most useful for methylmercury, and for recent acute exposure). Hair mercury reflects methylmercury exposure over months.
4. Renal function, urine protein, electrolytes, liver tests and full blood count.
5. Chest radiograph (and oxygen saturation) after inhalation, and abdominal radiograph (radio-opaque mercury in the gut, after swallowing or in the appendix).
6. Neurological examination, visual field testing and neuropsychological assessment for chronic exposure.

Differentials: hyperthyroidism, Parkinson disease, essential tremor, other heavy metal poisoning, pheochromocytoma (acrodynia), Kawasaki disease, other causes of nephrotic syndrome.

1. Stop exposure: evacuate the room, ventilate the area, remove contaminated clothing and wash skin and hair with soap and water. Clean spills with a mercury spill kit (never a household vacuum or broom) and remove pooled mercury with a card, syringe or amalgamating powder.
2. Respiratory support: oxygen, humidified air, bronchodilators for bronchospasm, and positive pressure ventilation for pulmonary edema. Steroids have no proven value.
3. Elemental mercury swallowed: no treatment in most, because it is inert in the intact gut. Remove from the appendix or diverticulum surgically if retained and symptomatic.
4. Inorganic mercury ingestion:
   • IV crystalloid and early resuscitation, nil by mouth, and analgesia.
   • Early chelation: dimercaprol 3 to 5 mg/kg IM every 4 hours for 2 days, then every 6 hours on day 3, then every 12 hours for up to 10 days, as long as the patient has normal or recovering renal function. Do not give to patients with peanut allergy.
   • Switch to succimer 10 mg/kg orally every 8 hours for 5 days, then every 12 hours for 14 days, when the gut is working. Alternative: unithiol (DMPS) 3 to 5 mg/kg IV every 4 hours initially, then 100 to 200 mg orally three times a day.
   • Haemodialysis, with or without chelation, for oliguric kidney failure.
5. Chronic elemental mercury poisoning: remove from exposure, then succimer 10 mg/kg orally every 8 hours for 5 days, then every 12 hours for 14 days if symptomatic with an elevated urine level. Monitor liver enzymes and blood count weekly.
6. Organic mercury (methylmercury): dimercaprol is contraindicated because it redistributes mercury to the brain. Use succimer 10 mg/kg orally every 8 hours for 5 days, then every 12 hours for 14 days, and whole blood exchange in severe cases. Cessation of fish intake and avoidance of high-mercury species (shark, swordfish, king mackerel, tilefish).
7. Acrodynia: remove the source (calomel, teething powders, remedy), succimer, and supportive care for pain.
8. Pregnancy and children: avoid exposure, and maternal blood and cord blood measurement. Chelation only for symptomatic severe poisoning after expert advice.

Follow-up: urine and blood mercury at 2 to 4 weeks after chelation and then every 3 months until normal. Neurological and renal review, and environmental clean-up confirmed by air monitoring. Counsel on safe disposal of mercury devices and on fish consumption in pregnancy.