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:
- Long chain
- Short chain
- 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 flu-like illness; fever, chills, shortness of breath, metallic taste in throat, lethargy, confusion, vomiting, renal tubular necrosis
- Rarely may progress to respiratory compromise and death
- Usually self limited course of flu-like illness; fever, chills, shortness of breath, metallic taste in throat, lethargy, confusion, vomiting, renal tubular necrosis
- Worse presentation in children
- May develop pneumothorax, pneumomediastinum and interstitial emphysema
- Small airway obstruction secondary to desquamation
Chronic Exposure
- Classic Triad:
- Tremor
- Gingivitis/stomatitis
- 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
- Severity dependent on type [Hg(2)Cl vs Hg(1)Cl] and concentration of mercurial salts
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 intellectual disability (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
Background
Heavy metal toxicity results from exposure to metals like lead, mercury, arsenic, or cadmium, which interfere with cellular function. Exposure may occur occupationally, environmentally, through ingestion, or from alternative medicines. Chronic toxicity can present insidiously, while acute toxicity may mimic sepsis or encephalopathy. Diagnosis is often delayed due to nonspecific symptoms.
Clinical Features
Symptoms depend on the metal and exposure duration but may include:
Neurologic: Peripheral neuropathy, confusion, tremor, encephalopathy
GI: Abdominal pain, nausea, vomiting, diarrhea, anorexia
Heme: Anemia (especially microcytic or hemolytic), basophilic stippling (lead)
Renal: Tubular dysfunction, proteinuria, Fanconi syndrome
Dermatologic: Mees’ lines (arsenic), hyperpigmentation, hair loss
Others: Fatigue, weight loss, hypertension (cadmium), immunosuppression
Differential Diagnosis
Sepsis or systemic inflammatory response
Drug toxicity or overdose
Metabolic disorders (e.g., porphyria, uremia)
Psychiatric illness (if symptoms are vague or bizarre)
Neurologic diseases (e.g., Guillain-Barré, MS, Parkinson’s)
Vitamin deficiencies (e.g., B12, thiamine)
Evaluation
Workup
History: Occupational exposures, home remedies, hobbies (e.g., jewelry making, battery recycling), diet, water source, imported goods
Labs:
- CBC, CMP, urinalysis
- Blood lead level, serum/urine arsenic, mercury, or cadmium (based on suspicion)
- Urine heavy metal screen (note: spot testing may require creatinine correction)
Imaging: Abdominal X-ray (radiopaque material in GI tract, especially with lead)
EKG: Evaluate for QT prolongation or arrhythmias in severe cases
Diagnosis
Confirmed by elevated blood or urine levels of the specific metal in the context of clinical findings. Hair and nail testing are unreliable for acute toxicity. Interpret results with toxicologist input if possible.
Management
Remove the source of exposure (e.g., occupational control, GI decontamination if recent ingestion)
Supportive care: IV fluids, seizure control, electrolyte repletion
Chelation therapy (in consultation with toxicology or Poison Control):
Lead: EDTA, dimercaprol (BAL), succimer
Mercury/arsenic: Dimercaprol or DMSA
Cadmium: No effective chelation—focus on supportive care
Notify local public health authorities if exposure source is environmental or occupational
Disposition
Admit if symptomatic, unstable, or requiring chelation
Discharge may be appropriate for asymptomatic patients with low-level exposure and outpatient follow-up
Arrange toxicology or environmental medicine follow-up for source control and serial testing
See Also
- Aluminum toxicity
- Antimony toxicity
- Arsenic toxicity
- Barium toxicity
- Bismuth toxicity
- Cadmium toxicity
- Chromium toxicity
- Cobalt toxicity
- Copper toxicity
- Gold toxicity
- Iron toxicity
- Lead toxicity
- Lithium toxicity
- Manganese toxicity
- Mercury toxicity
- Nickel toxicity
- Phosphorus toxicity
- Platinum toxicity
- Selenium toxicity
- Silver toxicity
- Thallium toxicity
- Tin toxicity
- Zinc toxicity
Evaluation
Work-Up
- Urine and blood mercury levels
- CBC
- Chem 7
- Type and screen
- Radiographs
Evaluation
- Urine mercury 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
- Of note, mercury can penetrate through latex and nitrile gloves
Inhalation injuries
- Oxygen
- May require intubation
Caustic injuries
- May consider milk or egg whites
- Thought to bind mercury
- WBI
Chelation therapy
The choice of chelating agent is dependent of the type of mercury poisoning.
- Penicillamine 250mg PO QID x 1-2wks
- Avoid in renal failure
- Dimercaprol (BAL) 2.5-5mg IM Q6-12hr
- Contraindicated in organic mercury poisoning as can paradoxically increase mercury levels
- DMSA (succimer) 10mg/kg TID x 5days then 10mg/kg BID x 14days
Disposition
See Also
External Links
- The biological monitoring of mercury in the Seychelles study: Methylmercury and human health http://www.ncbi.nlm.nih.gov/pubmed/8714867
- Cognitive performance of children prenatally exposed to "safe" level of methylmercury http://www.ncbi.nlm.nih.gov/pubmed/9600810
References
- Haddad and Winchester's Clinical Management of Poisoning and Overdose
- Goldfrank's Toxicology
- http://en.wikipedia.org/wiki/Mercury(I)_chloride
- http://en.wikipedia.org/wiki/Minamata_disease
- http://en.wikipedia.org/wiki/1971_Iraq_poison_grain_disaster