EMmedonline

• Mercury occurs in both inorganic and organic forms.

• Inorganic mercury exist as elemental mercury(quick silver) and mercurous salt (mercurous chloride or calomel) and mercuric salt (cinnabar or mercuric sulfide).

• Organic mercury exist as short chain and long chained alkyl and aryl compounds.

• Short chained alkyls such as methyl and ethyl mercuric are more toxic to human and must lethal been dimethyl mercury.

Pharmacology

Elemental mercury

• Elemental mercury is absorbed primarily by inhalation of its vapor.

• Vacuuming elemental mercury as from broken thermometer, increases volatility.

• Absorption by GI tract is highly negligible and doesn't produce any adverse effects unless the tract is damaged.

• IV injection of mercury produces pulmonary and systemic emboli. They can also cross BBB where it is ionized and trapped in the CNS.

• IM injection can induce abcess and granuloma formation. Slow absorption and delayed toxicity has been reported.

Inorganic mercury salts

• They are absorbed primarily through GI tract, may be absorbed from intact skin.

• They are deposited in the ionised form primarily in the kidney, followed by liver and spleen.

• Mercury salts do not enter CNS nor cross placenta.

Organic mercury

• They absorbed primarily by GI tract .

• They can cross membranes and accumulates in RBC, CNS, liver kidney and fetus.

• Inorganic and aryl organic mercurials are eliminated in the urine and feces . Short chained alkyl compounds are excreted primarily in bile, where they undergo significant enterohepatic circulation.

Pathophysiology

• Mercruy binds with sulfhydryl groups, affecting a diverse number of enzyme and protein systems.

• Methyl mercury also inhibits choline acetyl transferase, which catalyses the final step in the production of acetylcholine and may produce symptoms of acetylcholine deficiency.

Clinical Features

• Elemental mercury

  • Shortness of breath, fever, chills, cough, nausea, vomiting, diarrhea, metallic taste, headache, weakness and blurring vision.

  • Severe cases patients can develop acute lung injury and severe respiratory distress.

• Inorganic mercury

  • Mercuric salts are caustic and an acute ingestion can produce severe hemorrhagic gastroenteritis with abdominal pain .

  • Graying of oral mucosa and metallic taste, excessive salivation, burning sensation in the mouth.

  • Shock and CVS collapse may ensue rapidly.

  • ARF results from both direct toxicity of the mercury ions and from decreased renal perfusion due to shock.

• Chronic neurological toxicity includes tremors, neuroasthenia and erethism.

• Neurasthenia is characterised by fatigue, depression, headaches and difficulty concentrating.

• Erethism refers to easy blushing and extreme shyness; other symptoms include emotional liability, irritability, insomnia and delirium.

• Acrodynia, also known as “pink disease” is an immune mediated reaction characterised by a generalized rash; edema and erythema of the palms, soles and face; excessive sweating, fever irritability , splenomegaly and generalised hypotonia.

Organic mercury

• After a latent period of weeks to months, orofacial parasthesia develop.

• Patients may develop headache, tremor and fatigue. Severe cases ataxia, muscle rigidity and spasticity, blindness, hearing deficits and dementia.

Diagnosis

• For all forms of mercury poisoning except short chained alkyl 24 hr urinary measurement of mercury should be performed after a 5 days of seafood free diet.

• A level 20>mcg/L indicates meaningful exposure.

• Whole blood mercury levels are measured as these compounds concentrate in erythrocytes.

• Blood mercury levels normally <5mcg/ml.

• Short chained alkyl mercury compounds are excreted by bile and measuring urine mercury is invalid.

Treatment

• For elemental mercury severe respiratory failure following inhalation or aspiration of volatilized elemental mercury may require positive pressure ventilation.

• For ingestion of inorganic mercuric salt treat with aggressive IV hydration and GI decontamination, including gastric lavage and consider activated charcoal.

• For organic mercury toxicity institute gastric decontamination. Neostigmine may improve motor function in methyl mercury poisoned patients by improving acteylcholine levels at NMJ.

• Chelation

• It is indicated only if there is history of significant mercury poisoning, elevated blood or urine mercury levels , signs and symptoms consistent with mercury poisoning.

• Dimercarpol is contraindicated in methyl mercury poisoning as it can worsen neurological symptoms.

• Adverse reaction includes nausea, vomiting,headache, paresthesia,diaphoresis. Fever in childrens.

Updated on 30/4/14

Reference

• Tintinalli