mercury toxicity (hydrargyria, mercurialism)

Etiology

• environmental exposure (see epidemiology)
  • elemental mercury (Hg)
    • barometers, batteries, bronzing, calibration instruments, chlor-alkali production, dental amalgams, electroplating, fingerprinting products, fluorescent & mercury lamps, infrared detectors, the jewelry industry, manometers, neon lamps, paints, paper pulp production, photography, silver & gold production, semiconductor cells, thermometers
  • inorganic mercury
    • antisyphilitic agents, acetaldehyde production, chemical laboratory work, cosmetics, disinfectants, explosives, embalming, fur hat processing, ink manufacturing, mercury vapor lamps, mirror silvering, perfume industry, photography, spermicidal jellies, tattooing inks, taxidermy production, vinyl chloride production, wood preservation
  • organic mercury
    • antiseptics, bactericidals, embalming agents, farming, fungicides, germicidal agents, insecticides, laundry products, diaper products, paper manufacturing, pathology products, histology products, seed preservation, wood preservatives
• eating contaminated fish (larger fish)
• dental amalgam appears not to be a risk
• thimerosal (a mercury-containing preservative in vaccines) appears not to be a risk

Epidemiology

• 2400 single exposures in USA (2008), no deaths
• mercury poisoning can result from vapor inhalation, ingestion, injection, or absorption through the skin
• elemental mercury (Hg)
  • liquid at room temperature, vaporizes & is well absorbed (80%) through inhalation
  • its lipid-soluble property allows passage through the alveoli into the bloodstream
  • mostly converted to inorganic Hg+ or Hg+2 by catalase in erythrocytes
• inorganic mercury
  • found mostly in the mercuric salt form (batteries)
  • ingestion: 10% is absorbed
  • accumulates mostly in the kidney
  • CNS penetration is limited due to low lipid solubility
  • long-term skin exposure may also result in toxicity
  • elimination occur largely through the feces
  • renal elimination is poor
• organic mercury (also see methylmercury)
  • aryl & short- & long-chain alkyl compounds
  • found in antiseptics, fungicides, & industrial run-off
  • absorbed more completely from the GI tract than inorganic salts (90-95%)
  • accumulates in brain, kidney, liver, hair, & skin
  • elimination occur largely through the feces
  • renal elimination is poor

Pathology

• neurologic, gastrointestinal, & renal pathology
• organic mercury
  • most toxic to the CNS
  • short-chained (methylmercury) - affects the CNS
  • long-chained - subacute/chronic effects similar to that of inorganic mercury exposure
  • may lead to acetylcholine deficiency
• elemental mercury - primary neurologic toxicity
• inorganic mercury salts
  • acute
    • severe corrosive gastroenteritis
    • acute tubular necrosis
  • subacute or chronic - GI, neurologic, & renal dysfunction
• higher brain mercury levels associated with weekly seafood consumption not associated with cognitive impairment

Clinical manifestations

• acute exposure caused by inhaled elemental
  • fever, chills
  • shortness of breath, pleuritic chest pain
  • metallic taste, stomatitis
  • lethargy, confusion
  • vomiting
• chronic & intense acute exposure
  • classic triad found in chronic toxicity
    • tremors
    • gingivitis
    • erethism
  • headache
  • visual disturbance (eg, tunnel vision)
  • peripheral neuropathy, salivation
  • insomnia
  • ataxia

Laboratory

• blood mercury: < 10 ug/L is normal
• urine mercury: < 20 ug/L is normal
• complete blood count (CBC) to assess anemia
• chem7 to assess renal function & electrolyte imbalance
• consider sending environmental samples to FDA or NIOSH

Radiology

• plain radiograph of the abdomen to visualize ingested elemental mercury, which appears radiopaque

Complications

• pulmonary complications of inhaled toxicity
  • interstitial emphysema, pneumatocele, pneumothorax, pneumomediastinum, interstitial fibrosis
  • fatal ARDS has been reported
• injected elemental mercury can cause pulmonary embolism

Differential diagnosis

• metal fume fever
• in elderly
  • Parkinson's disease
  • metabolic encephalopathy
  • depression
  • Alzheimer's disease

Management

• general
  • remove from contamination
  • oxygen
  • IV access
• do not induce emesis if exposure to inorganic mercury
• gastric lavage for exposure to organic mercury, especially if seen on abdominal X-ray
• activated charcoal binds organic & inorganic mercury
• whole bowel irrigation of questionable utility
• chelation therapy
  • symptomatic patient
  • blood mercury &/or urine mercury elevated
• hemodialysis with L-cystein as a chelator in severe cases
• neostigmine may help motor function in chronic methylmercury toxicity
• polythiol is a nonabsorbable resin that may facilitate removal of methylmercury (or short chain alkyl organic mercury), via excretion in the bile after enterohepatic circulation
• consults:
  • consult regional poison control center &/or a toxicologist
• prognosis:
  • recovery is usually without sequela

More general terms

• heavy metal toxicity

Additional terms

• mercury [Hg]