Toxicology – Mercury Poisoning

Sources

Mercury exists in several forms, and toxicity depends strongly on the form and route of exposure.

• Elemental mercury: thermometers, some older thermostats, dental amalgam, industrial processes, and gold extraction
• Inorganic mercury salts: some industrial chemicals, older disinfectants, pigments, and manufacturing processes
• Organic mercury compounds: especially methylmercury, which can accumulate in large predatory fish

Typical Presentation

A person with chronic occupational mercury exposure may develop:

• Tremor
• Irritability or personality change
• Memory problems
• Excessive sweating
• Gingivitis or inflammation of the mouth

Clinical Features

Elemental mercury vapor inhalation

• Cough
• Dyspnea
• Chemical pneumonitis
• Noncardiogenic pulmonary edema in severe exposure

Chronic vapor exposure can produce the classic combination of:

• Neuropsychiatric changes
• Tremor
• Gingivostomatitis

Neuropsychiatric symptoms may include irritability, insomnia, poor concentration, memory impairment, and emotional instability.

Inorganic mercury salts

Ingestion can cause:

• Severe nausea and vomiting
• Abdominal pain
• Hemorrhagic gastroenteritis
• Acute tubular injury
• Acute kidney failure

Chronic exposure can also produce neurologic abnormalities.

Organic mercury

Methylmercury primarily damages the nervous system and may cause:

• Paresthesias
• Ataxia
• Tremor or other movement abnormalities
• Visual impairment
• Hearing impairment
• Hyperreflexia
• Cognitive dysfunction

Developing fetuses and young children are particularly vulnerable to the neurologic effects of methylmercury.

Mechanism of Action

Mercury binds strongly to sulfhydryl groups in proteins.

This interferes with:

• Enzyme activity
• Cellular metabolism
• Membrane function
• Antioxidant defenses

The nervous system and kidneys are major targets of toxicity.

Management

Treatment includes:

• Immediate removal from the exposure source
• Supportive care
• Respiratory support for severe inhalational injury
• Renal monitoring after significant inorganic mercury exposure

Chelation may be considered in clinically significant poisoning, commonly with agents such as:

• Succimer (DMSA)
• DMPS

Choice of therapy depends on the mercury compound, exposure severity, symptoms, and specialist guidance.

Key Points

• Mercury toxicity differs markedly between elemental, inorganic, and organic forms.
• Swallowed liquid elemental mercury is poorly absorbed from an intact GI tract, whereas inhaled mercury vapor can be highly toxic.
• Chronic elemental mercury exposure classically causes tremor + neuropsychiatric changes + gingivostomatitis.
• Inorganic mercury mainly causes severe GI and renal toxicity.
• Methylmercury predominantly causes neurologic toxicity.
• Significant suspected mercury poisoning should be discussed with a medical toxicologist or poison center.