Mercury poisoning occurs as a result of inhalation, ingestion, injection, or skin absorption of mercury or mercuric compounds. Mercury occurs in 3 distinct forms: elemental mercury, inorganic salts, and organic compounds. Toxic exposures to mercury are decreasing in frequency due to increased awareness of the dangers of this compound. Toxic complications vary depending on the form of mercury, dose, and rate of exposure. Clinical manifestations may include organ damage or further disease development (acrodynia, Hunter-Russell syndrome, Minamata disease).

Elemental mercury is usually only harmful when inhaled and is usually harmless when touched or swallowed. Occupational exposure is most common, including workers at medical device manufacturing plants (most commonly thermometers), gold miners, and dental workers exposed to amalgam tooth fillings. In some cultural practices and other forms of alternative medicine, mercury is injected intravenously or consumed in high doses and can lead to mercury poisoning. Patients with acute toxicity may present with interstitial pneumonitis, cough, chest pain, stomatitis, excessive salivation, conjunctivitis, dermatitis, nausea, vomiting, and diarrhea. The classic triad of chronic toxicity is neuropsychiatric disturbances, tremor, and gingivostomatitis. Treatment for inhaled elemental mercury poisoning includes supportive care with supplemental oxygen, bronchodilators, intravenous (IV) hydration, and monitoring of serum and urine mercury concentrations. Chelating agents can be used in selected patients with elevated mercury concentrations.

Inorganic mercury is typically poisonous when ingested or absorbed through skin and mucosa. Occupational exposure can occur in workers in the chlor-alkali, electroplating, and chemical research industries. Acute ingestion can cause gastroenteritis, which manifests as abdominal pain, vomiting, diarrhea, gastrointestinal hemorrhage, and shock. Chronic exposure can cause gingivitis, stomatitis, erethism, excessive salivation, neuropsychiatric symptoms, and nephrotic syndrome with renal tubular dysfunction. Treatment for ingested inorganic mercury poisoning is supportive and may include IV fluids, chelators, and rarely hemodialysis.

Organic mercury is harmful when inhaled, ingested (most common route), or absorbed through the skin. The most common organic mercuries are methyl and dimethyl mercury, which can be found in fresh- and saltwater fish. Being exposed to organic mercury for a chronic period of time may result in paresthesias, headaches, ataxia, dysarthria, visual field constriction, blindness, and hearing impairment. Prenatal exposure can cause cerebral palsy. Treatment consists of chelators typically given to the patient over a period of weeks to months.

Acrodynia is a syndrome that affects young children who are exposed to elemental mercury, inorganic salts, and organic phenylmercury. Symptoms include rash, edema, skin desquamation of palms and soles, fever, and irritability.