Mercury toxicity

Background

Common Exposures

  • Industrial
    • Batteries, fungicide
  • Seafood consumption
    • Mostly methylmercury

Exists as three major forms

  • All disrupt sulfhydryl ezymes leading to impaired cellular function

Elemental

  • Liquid metal at room temperature (Think of the Terminator recongealing)
  • 14x more dense than water
  • Volatile and lipid soluble, therefore rapidly absorbed through lungs (approximately 70-80%)
  • Oxidized rapidly to inorganic form
  • Poorly absorbed from GI tract
    • Therefor most ingestions are non-toxic

Organic

  • Exists in three major forms:
  1. Long chain
  2. Short chain
  3. Aryl
  • Long chain and Aryl forms are rapidly converted to inorganic forms
  • Short chain forms are highly lipophilic and cross the blood-brain barrier and placenta
    • Metabolized in the liver to N-acetyl-homocysteine-methylmercury which undergoes enterohepatic recirculation

Inorganic

  • Exists as monovalent and divalent
  • Corrosive
  • Chronic exposures lead to accumulation in brain and CNS
  • Found in many batteries, little risk of toxicity from the mercury components s/p ingestion
    • Other dangers exist though!!!
  • The California Department of Public Health issued a health alert on May, 2014 noting mercury poisoning linked to use of skin-lightening or acne Creams from Mexico[1]

Historical Exposures

Atomic symbol of Hg from latin name hydrargyros which means silver water

  • Hat felters (Elemental)
    • "Mad as a hatter"
  • Anti-syphilitic agents (Inorganic)
    • "A night in the arms of venus lead to a lifetime on mercury"
  • Calomel (Inorganic)
    • Mercurous Chloride sold as a teething powder
    • Causes "pink disease"
      • pain and erythema of the palms and soles, irritability, insomnia, anorexia, diaphoresis, photophobia, and skin rash
  • Minamata Bay, Japan (Organic)
    • Massive exposure to methylmercury from contaminated seafood secondary to industrial dumping of mercury containing compounds
  • Iraq 1971 (Organic)
    • 95,000 tons of methylmercury coated grain sold for human consumption
  • Miners and smelters (Elemental)
    • Mostly secondary to exposure to Cinnabar (HgS)
  • Dental workers through amalgams (Elemental)
    • Clinical effects secondary to exposure to mercury through amalgams is controversial

Clinical Features

  • Clinical presentation highly dependent on form, concentration and duration of exposure
    • Inhalation of elemental mercury and ingestion of inorganic can cause acute or subacute toxicity
    • Organic mercury more likely causes chronic toxicity

Elemental Mercury

Acute Exposure

  • Metal fume fever
    • Usually self limited course of fever, chills, shortness of breath, metallic taste in throat, lethargy, confusion, vomiting, renal tubular necrosis
      • Rarely may progress to respiratory compromise and death
  • Worse presentation in children
    • May develop pneumothorax, pneumomediastinum and interstitial emphysema
  • Small airway obstruction secondary to desquamation

Chronic Exposure

  • Classic Triad:
  1. Tremor
  2. Gingivitis/stomatitis
  3. Hyperexcitable state/emotional lability
  • Other findings
    • Headache, visual disturbances, peripheral neuropathy, ataxia

Inorganic Mercury

Acute Exposure

  • Primarily toxic through oral route
  • Causes caustic burns
    • Severity dependent on type [Hg(2)Cl vs Hg(1)Cl] and concentration of mercurial salts
      • Mercuric forms [Hg(2)] more toxic
    • Other symptoms include pain, nausea, hematemesis, hypovolemia, acute tubular necrosis
    • Sequelae include renal failure

Chronic Exposure

  • Chronic exposures usually secondary to inhalation exposure
  • Symptoms include renal failure, dementia, acrodynia
    • Acrodynia (AKA pink disease) = painful erythema and edema of hands and feet, rash, tachycardia, hypertension and irritability.
  • Neuropsychiatric disturbances

Organic Mercury

  • Acute and chronic exposures present similarly
    • Acute presentations usually show signs days to weeks after exposure
  • Neuro symptoms predominate
    • Tremor, ataxia, paresthesias, memory difficulties, visual disturbances, hearing loss
  • May also cause thrombocytopenia and agranulocytosis
  • Highly fetotoxic
    • Easily crosses placenta
    • May lead to severe mental retardation (like those with Minamata disease), developmental delay, ataxia and seizures in offspring
    • Controversy exists over exposure from regular diet
      • Albacore tuna may contain up to 0.34ppm of organic mercury
      • Please see Faroe Island and Seychelles studies
    • Thimerosal (mercury containing preservative found in many vaccines) has NOT been linked to developmental delays or autism

Differential Diagnosis

Heavy metal toxicity

Evaluation

Work-Up

  • Urine and blood Hg levels
  • CBC
  • Chem 7
  • Type and screen
  • Radiographs

Evaluation

  • Urine Hg levels (>25μg/L is elevated) for elemental and organic mercury
    • Levels >300μg/L usually symptomatic
    • Organic mercury poorly excreted
  • Blood levels for organic mercury
  • Hair analysis is not sufficient

Management

  • ABC's
  • Decontaminate

Inhalation injuries

Caustic injuries

  • May consider milk or egg whites
    • Thought to bind Hg
  • WBI

Chelation therapy

  • Penicillamine 250mg PO QID x 1-2wks
    • Avoid in renal failure
  • Dimercaprol (BAL) 2.5-5mg IM Q6-12hr
  • DMSA 10mg/kg TID x 5days then 10mg/kg BID x 14days

Disposition

See Also

External Links

References

Authors:

Ross Donaldson