Mercury Poisoning - A Comprehensive Forensic Examination Answer

I. MECHANISM OF ACTION (Toxicodynamics)

General

• Inhaled as vapor
• Applied to skin or mucous membranes in finely divided state
• Absorbed through any route other than the intact GI lumen

Molecular Mechanism

1. Sulfhydryl (–SH) group binding: The mercuric ion has a high affinity for sulfhydryl groups of enzymes, cellular proteins, and nucleic acids. This binding inactivates essential cellular enzymes and interferes with all vital cellular transport functions.
2. Interference with mitotic apparatus: Mercury binds to the spindle apparatus, disrupting cell division.
3. Rapid conversion in blood: Inorganic mercury is rapidly converted to mercuric ions in the blood, leading to direct renal tubular damage.
4. CNS targeting: In the central nervous system, mercury acts predominantly on the:
   • Cerebellum
   • Temporal lobe
   • Basal ganglia
   • Corpus callosum
5. Organic mercury (methylmercury, ethylmercury, phenyl mercury) is even more toxic because it is lipid-soluble, crosses the blood-brain barrier readily, and accumulates in neural tissue. It also undergoes enterohepatic circulation (absorbed → liver → bile → intestine → reabsorbed).
6. Kidney: Mercury is selectively nephrotoxic - it causes acute tubular necrosis and glomerulonephritis by binding to renal tubular cell proteins.
7. Fate and excretion: After absorption, mercuric ions are distributed between blood cells and plasma, then diffuse into tissues binding to protein sulfhydryl groups. Mercury accumulates in liver, kidneys, spleen, and CNS. It is excreted via saliva, urine, feces, milk, and perspiration. It undergoes significant enterohepatic circulation.

II. SIGNS AND SYMPTOMS

Acute Poisoning - Biphasic Presentation

• Acrid metallic taste in the mouth
• Sensation of constriction in the throat; hoarseness; dyspnea
• Mouth, tongue, and fauces become corroded, swollen with a greyish-white coating/eschar
• Burning pain extending from mouth to stomach and abdomen
• Nausea, retching, and vomiting - vomit contains greyish, slimy mucoid material with blood and shreds of mucous membrane
• Diarrhea with bloodstained stools and tenesmus
• Circulatory collapse: cold clammy skin, pale anxious face, sunken eyes, dilated pupils, rapid feeble pulse, sighing respirations
• Syncope, convulsions, and general insensibility
• Inhalation of fumes: ataxia, restriction of visual field, paresis, and delirium

• Glossitis and ulcerative gingivitis within 24-36 hours
• Severe infection, loosening of teeth, necrosis of the jaw
• In 2-3 days: renal tubular necrosis with transient polyuria, albuminuria, cylindruria, uremia, and acidosis
• Recovery may occur in 10-14 days; otherwise, death from uremia
• After many days: membranous colitis with dysentery, ulceration of colonic mucosa, and hemorrhage

III. MANAGEMENT

A. Immediate / First Aid

1. Gastric lavage with:
   • 5% sodium formaldehyde sulfoxylate solution (250 mL) - this reduces mercuric chloride to the less soluble, less toxic mercurous compound; leave ~100 mL in the stomach
   • Alternatively: 2-5% sodium bicarbonate, milk, or egg-white to bind mercury
   • Note: Sodium formaldehyde sulfoxylate is NOT recommended in some recent guidelines; activated charcoal is of uncertain benefit
2. Egg albumin - forms insoluble mercuric albuminate; must be removed promptly by emetics or gastric lavage (soluble in excess albumin)
3. Cathartics should NOT be given; whole bowel irrigation may be beneficial
4. Activated charcoal with magnesium sulfate (increases adsorptive power and hastens removal)

B. Chelation Therapy (Antidotes)

C. Supportive Measures

• Urine alkalinization - keep urine alkaline
• High colonic lavage with 1:1000 sulfoxylate solution twice daily (to flush mercury re-excreted into large bowel)
• Hemodialysis / peritoneal dialysis - indicated in significant renal failure
• Treatment of shock and cardiovascular collapse
• Symptomatic treatment as indicated

IV. AUTOPSY FINDINGS (Postmortem Appearances)

Acute Poisoning

• Evidence of corrosive action around the lips and mouth
• Features of shock and dehydration

• Tongue: white and sodden in appearance
• Mouth: diffuse greyish-white escharotic appearance (eschar = hard crust over a raw surface)
• Mucous membrane of the entire GI tract: inflamed and corroded
• Muscular coats of the GI tract are so softened that organs are difficult to remove without rupture

• Mercury has a selective action on the cecum and large intestine
• Cecum and large intestine show: intense inflammation, ulceration, and even gangrene
• This is due to re-excretion of mercury into the large bowel
• If person survives a few days: large intestine shows necrosis due to re-excretion

• Acute tubular degeneration/necrosis
• Hemorrhagic glomerular nephritis
• Toxic nephritis (tubular nephritis)

• Congested
• Cloudy swelling (hydropic degeneration)
• Fatty change/degeneration

• Fatty degeneration of cardiac muscle
• Subendocardial hemorrhages

Chronic Poisoning (Postmortem)

• Changes in the large intestine are often very striking - necrosis may spread to involve practically the whole of the lower bowel
• Kidney damage: tubular nephritis
• Fatty degeneration of liver and cardiac muscle
• In chronic cases: features of stomatitis, gingivitis

Histology / Chemical Analysis

• Mercury may be detected in bones in acute poisoning
• Maximum mercury concentration found in: kidney, nails, scalp hair, and skin (detected by neutron activation analysis)

V. MEDICO-LEGAL IMPORTANCE

1. Non-poisonous metallic form: Pure metallic mercury is NOT considered poisonous as it is not absorbed by gastric juice. 1-2 pounds can be taken to cure constipation without harmful effects. This is of importance when assessing whether ingested mercury is the cause of death.
2. Mercury vapor is toxic: Concentration of 0.5 mg/m³ is sufficient to cause poisoning. This is important in occupational exposure cases.
3. Transdermal absorption: Mercury is absorbed through the skin; rubbing mercury ointment has caused deaths - three deaths reported after application of mercury ointment for itching. Relevant in cases of non-oral poisoning.
4. Subcutaneous injection: Produces local abscess formation. IV injection causes mercurialism with thrombophlebitis, granuloma formation, pulmonary embolism, and hemoptysis.
5. Mercury embolism: Reported when blood is collected from arteries under mercury seal. Important in iatrogenic injury cases.
6. Amalgam/dental use: Amalgams used for filling carious teeth can sometimes cause poisoning. Mercury used widely in medicine (antiseptics, diuretics) - detection in small quantities alone does not necessarily indicate poisonous cause of death.
7. Differential toxicity of compounds: Mercuric salts are more poisonous than mercurous salts; trivalent salts more toxic than bivalent. Organic compounds (methyl/ethyl mercury) are more toxic than inorganic counterparts - relevant for differential diagnosis.
8. Occupational/industrial exposure:
   • Workers in: thermometer/barometer manufacture, mirror industry, hat and fur industries, fingerprint detection (police officers), ultraviolet apparatus manufacture, gold/silver industries
   • Relevant to industrial compensation and negligence cases
   • Hatters show the "hatter's shake" (coarse intentional tremor) and "erethism" (personality disturbance with shyness, irritability, loss of memory, insomnia)
9. Mercuria lentis: Discolouration of the anterior lens capsule seen on slit-lamp examination - an early sign of chronic mercury poisoning. Bilateral; no effect on visual acuity. Useful in diagnosing chronic industrial exposure.
10. Acrodynia (Pink Disease): An idiosyncratic hypersensitivity reaction in children due to chronic mercury exposure in any form. Characterized by anorexia, insomnia, sweating, generalized skin rash, and puffy pinkish painful hands and feet.
11. Not a normal body constituent: Mercury is not normally present in the human body; therefore its presence in tissues indicates that it must have been introduced into the system. However, 5-150 mg/100g may normally be found in liver and kidney.
12. Excretion pathways: Eliminated via saliva, urine, feces, milk, and perspiration. Urine and blood mercury levels assist in medico-legal decision-making: Blood >35 µg/L and Urine >150 µg/L indicate chronic exposure.
13. Minamata Disease: Organic mercurial poisoning from consuming fish contaminated with mercury - occurred as a disaster in Japan in 1956 (Minamata Bay). Relevant in environmental poisoning, mass casualty events, and public health negligence.
14. Mode of poisoning: Mercuric chloride is easily obtainable (used as antiseptic, disinfectant, contraceptive tablets). Accidental poisoning may occur from ingestion of antiseptic solutions or tablets (perchloride/iodide). Suicide and homicide also possible.
15. Detection and analysis: Mercury can be detected by Marsh's test (modified), Reinsch's test, and neutron activation analysis. Chemical analysis of kidney, nails, hair, and scalp tissue is most rewarding in suspected cases.