MERCURY POISONING

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Mercury poisoning occurs due to exposure to mercury, a heavy metal with toxic effects on multiple systems of the human body. Mercury exists in three forms—elemental (metallic), inorganic, and organic—each with distinct toxicological properties. The toxicity results from its ability to bind sulfhydryl groups, inhibiting enzymes, and disrupting cellular processes, particularly in the nervous and renal systems.

Types of Mercury and Sources:

1. Elemental Mercury:
   • Found in thermometers, barometers, dental amalgams, and certain industrial applications.
   • Inhalation is the primary route of exposure. It is poorly absorbed through ingestion or skin contact.
2. Inorganic Mercury:
   • Found in industrial processes, certain antiseptics, batteries, and pigments.
   • Exposure occurs through ingestion or dermal contact.
3. Organic Mercury (Methylmercury):
   • Found in contaminated fish (e.g., large predatory fish like swordfish, shark) and seafood.
   • Ingested via contaminated food.

Pathophysiology

Mercury primarily exerts its toxic effects by binding to thiol (sulfhydryl) groups in proteins, which leads to the inhibition of essential enzymes and disruption of cellular processes. This affects the central and peripheral nervous systems, the kidneys, and other organs. Mercury can cross the blood-brain barrier and the placenta, leading to neurological damage in both adults and fetuses.

Clinical Features:

1. Acute Mercury Poisoning:
   • Elemental Mercury:
     • Inhalation: Pneumonitis, cough, dyspnea, fever, metallic taste, and acute respiratory distress syndrome (ARDS).
     • CNS: Tremors, irritability, mood changes, confusion, and headache.
   • Inorganic Mercury:
     • Gastrointestinal: Severe abdominal pain, vomiting, diarrhea (possibly bloody), and stomatitis.
     • Renal: Acute renal failure with oliguria, proteinuria, and hematuria.

1. Chronic Mercury Poisoning (Mercurialism):
   • CNS Symptoms: Tremors, anxiety, depression, irritability, memory problems, fatigue, insomnia.
   • Erethism: A constellation of mood changes including excitability, timidity, and emotional instability, historically associated with “mad hatter syndrome.”
   • Peripheral Neuropathy: Numbness, paresthesias, and muscle weakness.
   • Renal: Chronic glomerulonephritis, nephrotic syndrome.
   • Oral Cavity: Gingivitis, excessive salivation, and metallic taste.
   • Skin: Acrodynia (painful erythema and desquamation of palms and soles), rashes, and itching.

Diagnosis:

• History of exposure is crucial (occupational, environmental, or dietary).
• Blood Mercury Levels:
  • Normal: < 5 μg/L for total mercury.
  • Elevated in acute poisoning.
• Urine Mercury Levels:
  • Chronic exposure can lead to elevated urine mercury.
  • 10 μg/g creatinine indicates significant exposure.
• Neuropsychological Tests: To assess cognitive and neurological dysfunction in chronic poisoning.
• Renal Function Tests: To assess renal involvement in cases of both acute and chronic poisoning.

Management:

1. Acute Mercury Poisoning:
   • Removal from the source of exposure.
   • Supportive Care: Airway management, oxygen therapy, and mechanical ventilation if necessary.
   • Chelation Therapy:
     • Dimercaprol (BAL): Effective in acute inorganic mercury poisoning but contraindicated in methylmercury poisoning.
     • Succimer (DMSA): Used in both elemental and organic mercury poisoning.
     • Unithiol: An alternative chelator for chronic mercury poisoning.
2. Chronic Mercury Poisoning:
   • Chelation Therapy (DMSA or DMPS).
   • Symptomatic Treatment: Managing neuropsychiatric symptoms and renal complications.
   • Dietary Recommendations: Reducing the consumption of fish high in methylmercury.

Prevention:

• Workplace safety: Proper ventilation, protective equipment, and regular monitoring in industries involving mercury.
• Public health education: About the risks of mercury exposure from contaminated fish and household items.
• Monitoring: Regular monitoring of mercury levels in high-risk populations (e.g., industrial workers, pregnant women, people living in contaminated areas).

Prognosis:

• Acute exposure can lead to life-threatening complications, but early treatment often leads to full recovery.
• Chronic exposure can cause irreversible neurological damage, especially in children and fetuses.