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Monday, May 2, 2011


The major source of mercury is the natural degassing of the earth's crust.
Sources of additional production by man include burning of fossil fuels, production of steel, cement and phosphate, and the melting of metals from their sulphide ores. Food is the main route of entry in non-occupational exposures, since methyl mercury compounds accumulate in fish, to high levels in contaminated waters. Outbreaks of chronic mercury poisoning in the general population occurred in the villages round Minimata Bay, and also the Niigata river, in japan. In both circumstances mercury compounds from local industry had contaminated the water and fish. Over a thousand cases of chronic mercury poisoning were identified. Other epidemics have occurred due to ethyl or methyl mercury fungicides on wheat intended for planning but actually used for making bread. The largest of these was in Iraq, When over 6000 people were admitted in hospital.
Clinical features
The most common signs and symptoms of chronic mercury poisoning are paraesthesia, constriction of the visual fields, impairment of hearing and ataxia. Classical symptoms of severe poisoning include erethism (irritability, excitability, loss of memory, insomnia, excessive sweating and flushing), intention tremor and gingivitis. Renal damage may occur. The clinical effects may not reverse much even after exposure ceases. Acute mercury poisoning of any mercurial compound leads to bleeding from, and necrosis of , the gut; vomiting, circulatory collapse and renal failure. Acute pulmonary oedema may result from the inhalation of mercury vapour.
Chronic inorganic mercury poisoning
This is treated with dimercaprol for high exposures or symptomatic patients, or pencillamine for lower exposures or asymptomatic patients. Haemodialysis may be required for renal failure in occasional cases.
Acute poisoning
This may require respiratory support to fluid and electrolyte balance, gastric lavage, oral charcoal and a magnesium cathartic. Treatment of organic mercury poisoning is less effective. Penicillamine and an oral non-absorbable thiol resin can reduce blood concentrations of mercury, though this may not be associated with much clinical benefit. Dimercaprol is contraindicated, since it increases the mercury concentrations in the brain.

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