MERCURY

TRACE ELEMENTS FACT SHEET

Introduction

Atomic mass 201. Mercury sulphide is the principal component of mercury ores. Mercury and its organic and inorganic compounds have been used in medicine for centuries as cathartics, desiccants, antiseptics, vermicides and diuretics. Phenyl mercuric compounds are used as fungicides. Mercury is a component of some materials used in dentistry. Mercury in the natural environment arises from out-gassing of mercury vapour from the earth's surface and burning of fossil fuels. Microorganisms that live in marine and freshwater sediments methylate mercury. Methyl mercury is concentrated up the food chain and can be present in high concentrations in top predators. Elevated concentrations of mercury have been found in freshwater fish species living in areas subject to acid rain.

Exposure

Occupational exposures occur during the mining and processing of mercury ores, the manufacture, use and disposal of scientific instruments, batteries and fungicides. The number of people potentially exposed to mercury may not be related to the mass of metal in use – for example, dentistry. It appears likely that the major component of human exposure to inorganic mercury may be from dental amalgams. The major component of exposure to organic mercurials is seafood. Overexposures to mercury containing medications are potentially lethal and may occur due to misunderstandings over the use of the compounds, for example the use of desiccants on open wounds.

Absorption

Metallic mercury is readily absorbed by inhalation whereas little is absorbed after ingestion. Inorganic mercury compounds are also poorly absorbed from the gut. Organic mercury compounds are very well absorbed from either the lungs or the gut. Phenyl mercuric compounds may be absorbed through the skin.

Distribution

Inorganic mercury compounds are lipid soluble. Once the compounds are absorbed, the divalent oxidation state is favored and the compounds concentrate in the central nervous system (except the brain) and the kidney. Inorganic mercury compounds are able to cross the placenta. Phenyl mercuric compounds behave in a similar fashion to inorganic mercurials. Methyl mercury is the predominant compound involved in organo mercurial exposures. Methyl mercury is almost completely absorbed from the gut and is probably well absorbed through the lungs and skin. After absorption methyl mercury binds to hemoglobin, circulates systemically and is distributed to all organs (notably including the brain). Methyl mercury is directly incorporated into growing hair from the blood.

Excretion

Inorganic mercury is excreted in the urine. Methyl mercury is secreted into the bile and mostly reabsorbed from the gut. Microbes demethylate a small proportion of the recirculating methyl mercury and the resulting inorganic mercury is excreted in the faeces.

Pathology

Mercury toxicity is related to the method of exposure and the type of mercurial involved. Elemental mercury that is ingested is essentially non-toxic. Elemental mercury that is inhaled is a pulmonary toxin. As the metal enters systemic circulation it rapidly produces headache, blurred vision and encephalopathy. Acute exposure to inorganic mercurials produces inflammation of the mouth, oesophagus and lower gut. If the dose is sufficient, renal failure and death may occur. Chronic exposure to elemental mercury vapour, inorganic mercurials and phenyl mercurials produce dermatitis, gingivitis, salivation, stomatitis and neuropsychiatric symptoms. Exposure to methyl mercury produces neurotoxicity after a latent period of weeks to several months dependent on the extent of the exposure, with high doses associated with shortened latent periods.

Monitoring

As the various mercury species partition differently, it is important to either, screen generally if mercury toxicity is suspected, or to ensure that the mercurial involved is identified and the appropriate matrix chosen for monitoring. Exposure to elemental or inorganic mercury will only produce modest changes in the blood while urine excretion will be elevated. Methyl mercury is excreted to the bile and so that exposure will not produce increased urinary mercury concentrations. Blood levels will, however, increase, as will the mercury content of growing hair.

Treatment

Intramuscular BAL has been used to treat inorganic mercury poisoning. Its use is contraindicated in methyl mercury poisoning. Dimercaptosuccinic acid is a new drug that shows promise for the treatment of mercury exposures of all types.

Analysis

Mercury is determined by cold vapour atomic absorption spectrometry following various wet digestions or extractions of the starting matrix.

For further information please contact Graham Hams, PaLMS Trace Elements on (02) 9926 7682.
Last updated: Nov 98