Mercury toxicity is a systemic toxicological emergency caused by exposure to elemental, inorganic, or organic mercury compounds. Mercury is a heavy metal that has no physiological role in the human body and is toxic at very low concentrations.

Exposure may occur through:

• Inhalation of mercury vapour

• Ingestion of contaminated food or chemicals

• Percutaneous absorption through skin

• Injection (rare but reported)

• Occupational exposure

Mercury distributes widely and accumulates particularly in:

• Brain (central nervous system)

• Kidneys

• Liver

• Peripheral nerves

• Fetus (crosses placenta)

• Breast milk

The toxicity depends on the chemical form, because each form targets different organs.

2. Types and Toxicokinetics

Absorption

Distribution

Mercury binds sulfhydryl groups → enzyme inhibition → mitochondrial failure → neuronal death.

Organic mercury crosses:

• Blood-brain barrier

• Placenta

Elimination

• Urine

• Feces

• Breast milk

• Hair and nails (chronic exposure marker)

Half-life:

• Elemental: 40–60 days

• Organic: up to 3 months

3. Risk Factors

Occupational

• Gold mining

• Dentistry

• Battery manufacturing

• Fluorescent bulb handling

• Laboratory workers

Environmental

• Fish from contaminated waters

• Industrial pollution

• Improper waste disposal

• Broken thermometers in enclosed rooms

Patient-related

• Children (hand-to-mouth exposure)

• Pregnant women

• Chronic kidney disease

• Malnutrition

• Poor ventilation housing

4. Pathophysiology

Mercury causes toxicity by:

1. Binding sulfhydryl (-SH) groups

2. Inhibiting enzymes

3. Increasing oxidative stress

4. Damaging neuronal microtubules

5. Causing mitochondrial dysfunction

5. Clinical Manifestations

Symptoms vary according to mercury type.

A. Inorganic Mercury Poisoning

Gastrointestinal (corrosive phase)

• Ash-gray mucous membranes

• Severe abdominal pain

• Haematochesia

• Vomiting

• Metallic taste

• Foul breath

Oral cavity

• Stomatitis

• Gingivitis

• Loosening of teeth

• Excess salivation

Systemic

• Hypovolaemic shock

• Acute kidney injury

• Renal tubular necrosis

B. Organic Mercury Poisoning (Neurotoxic phase)

Early neurological signs

• Paresthesias

• Peripheral neuropathy

• Fatigue

• Irritability

Progressive neurological syndrome

• Scotomata

• Visual field constriction (tunnel vision)

• Ataxia

• Hearing loss

• Dysarthria

• Tremor

• Movement disorders

Advanced toxicity

• Mental deterioration

• Paralysis

• Coma

• Death

6. Diagnostic Criteria

Suspect mercury poisoning if:

• Neurological deterioration + fish exposure

• Gingivitis + kidney injury

• Occupational exposure history

• Unexplained neuropathy

• Concentric visual field loss

7. Investigations

Laboratory tests

• Blood mercury level (recent exposure)

• Urine mercury level (chronic exposure)

• FBC

• Renal function tests

• Electrolytes

Specialized tests

• Hair mercury level (chronic methylmercury)

• Toenail mercury level

• CSF mercury level (severe neurotoxicity)

Imaging

• Abdominal X-ray (ingested mercury visible)

• Brain MRI (chronic poisoning → cortical atrophy)

8. Management

Treat immediately once suspected — do NOT wait for laboratory confirmation.

8.1 Initial Stabilization (ABC)

• Secure airway

• Give oxygen

• IV access

• Treat shock

8.2 Non-Pharmacological Treatment

Decontamination

• Remove patient from exposure

• Remove contaminated clothing

• Copious skin irrigation

Gastrointestinal management

• Gastric lavage (only if visible mercury on X-ray)

• Activated charcoal

• Whole bowel irrigation (selected cases)

Supportive care

• IV fluids

• Electrolyte correction

• Dialysis if renal failure

Surgical intervention

Remove mercury lodged in intestine/colon if persistent source.

8.3 Chelation Therapy

Chelation binds mercury → increases urinary excretion.

First line: Succimer (DMSA)

Dose:

• 10 mg/kg PO every 8 hrs for 5 days

• Then 10 mg/kg every 12 hrs for 14 days(Max 500 mg per dose)

Preferred because:

• Oral

• Safer

• Effective for children

Acute Inorganic Mercury: Dimercaprol (BAL)

Dose:

• Day 1: 5 mg/kg IM once

• Day 2–11: 2.5 mg/kg IM every 12 hrs

Additional options (specialist use)

• DMPS

• Penicillamine (rare)

8.4 Dialysis

Indicated when:

• Renal failure

• Very high mercury levels

• Severe electrolyte imbalance

9. Complications

• Chronic kidney disease

• Peripheral neuropathy

• Blindness

• Cerebellar degeneration

• Developmental delay (children)

• Fetal malformations

• Death

10. Special Populations

Pregnancy

Mercury crosses placenta → fetal brain injury

Children

More severe neurological damage

Chronic exposure

May present as psychiatric illness:

• Memory loss

• Personality change

• Depression

• Tremor (erethism)

11. Prognosis

12. Prevention

Do’s

• Keep medicines and poisons secured

• Child-resistant containers

• Keep original containers

• Read labels carefully

Don’ts

• Leave containers open

• Transfer chemicals

• Remove labels

• Store tablets in purse/envelope

• Refer to medicine as sweets

• Take medicine in front of children

13. Public Health Prevention

• Avoid contaminated fish

• Occupational protective equipment

• Proper disposal of industrial waste

• Ventilate indoor spills

• Avoid mercury-containing cosmetics