Module 3: Toxicology - Section 12: Heavy Metals

OHM12.X: Mercury - Part 2

C. Metabolism:

1. Absorption:Approximately 80% of inhaled mercury vapor is absorbed by the alveoli; this is the most important route of exposure to metallic mercury. Although elemental mercury may also be absorbed through the skin this is not often a significant route of exposure. Metallic mercury is not appreciably absorbed through the gastrointestinal tract although there is a theoretical risk of colonic anaerobic bacteria methylating ingested elemental mercury hence cathartics are still in order. Inorganic mercury salts absorbed both by inhalation (as aerosols) and by ingestion. Organic mercury compounds are readily absorbed by inhalation, ingestion, and skin contact.
2. Distribution and excretion: After inhalation of mercury vapor, mercury is rapidly distributed to the rest of the body and is carried equally by the plasma and the red blood cells. The half life for elimination from the blood is two to three days. It accumulates preferentially in the kidneys and in the case of organic mercurials, via the biliary tract. The half time for excretion from the body is 60 days. The half life for excretion from the brain is on the order of years.

Inorganic mercury compounds are also rapidly distributed to the rest of the body and are carried by the plasma and red blood cells. They are accumulated preferentially by the kidneys, but in contrast to metallic mercury, not by the brain. They are excreted mainly via the urine and to a lesser extent the biliary tract.

After exposure to either mercury vapor or inorganic mercury salts, small amounts are excreted through the salivary, lacrimal, and sweat glands. Excretion in sweat may significant during periods of heavy perspiration. Mercury may also be detected in the expired air for a few hours after exposure to mercury vapor, but this is not a significant route of excretion. Mercury has been shown to cross the placenta in monkeys.

Organic mercury compounds are rapidly distributed by the blood, and are preferentially carried by the red blood cells (90%) rather than the plasma (10%). The short chain alkyl compounds (e.g. methylmercury) are chemically stable, whereas the aryl and alkoxyalkyl compounds are transformed in vivo to liberate inorganic mercury. These latter compounds are eliminated in the urine and feces in the same manner as other sources of inorganic mercury. Methylmercury is eliminated in the feces but not appreciably in the urine.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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