Mercury is mined predominantly as HgS in cinnabar ore and is then converted commercially to a variety of chemical forms. Key industrial and commercial applications of mercury are found in the electrolytic production of chlorine and caustic soda; the manufacture of electrical equipment, thermometers, and other instruments; fluorescent lamps; and dental amalgam. The widespread use of elemental mercury in artisanal gold production is a growing problem in many developing countries. Mercury use in pharmaceuticals and in biocides has declined substantially in recent years, but occasional use in antiseptics, folk medicines, and cosmetic skin-lightening creams is still encountered. Thimerosal, an organomercurial preservative that is metabolized in part to ethylmercury, has been removed from almost all the vaccines in which it was formerly present. Environmental releases of mercury from the burning of fossil fuels, which contributes to the bioaccumulation of methylmercury in fish, remains a concern in some regions of the world. Low-level exposure to mercury released from dental amalgam fillings occurs, but systemic toxicity from this source has not been established.
The United States banned the export of elemental mercury in 2013. Once fully implemented, the international Minamata Convention on Mercury, signed by 128 countries since 2013, will result in a worldwide phase-out by 2020 of mercury in numerous products including batteries, switches and relays, fluorescent lamps, pesticides, biocides and antiseptics, measuring instruments (eg, thermometers, sphygmomanometers), and manufacturing processes such as chloralkali production (by 2025)
The absorption of mercury varies considerably depending on the chemical form of the metal. Elemental mercury is quite volatile and can be absorbed from the lungs (Table 57–1). It is poorly absorbed from the intact gastrointestinal tract. Inhaled mercury is the primary source of occupational exposure. Organic short-chain alkylmercury compounds are volatile and potentially harmful by inhalation as well as by ingestion. Percutaneous absorption of metallic mercury and inorganic mercury can be of clinical concern following massive acute or long-term chronic exposure. Alkylmercury compounds appear to be well absorbed through the skin, and acute contact with a few drops of dimethylmercury has resulted in severe, delayed toxicity. After absorption, mercury is distributed to the tissues within a few hours, with the highest concentration occurring in the kidney. Inorganic mercury is excreted through the urine and feces. Excretion of inorganic mercury follows a multi-compartment model: most is excreted within weeks to months, but a fraction may be retained in the kidneys and brain for years. After inhalation of elemental mercury vapor, urinary mercury levels decline with a half-life of approximately 1–3 months. Urine mercury concentration is <3 mcg/L in most individuals without occupational exposure, and the median general population urine mercury concentration in the 2011–2012 NHANES was 0.324 mcg/L. Methylmercury, which has a blood and whole-body half-life of approximately 50 days, undergoes biliary excretion and enterohepatic circulation, with more than two thirds eventually excreted in the feces. The geometric mean total blood mercury concentration in the US population in the 2011–2012 NHANES was 0.703 mcg/L; the 95th percentile was 4.40 mcg/L (~90% present as methylmercury). Mercury binds to sulfhydryl groups in keratinized tissue, and as with lead and arsenic, traces appear in the hair and nails. Mercury in hair has served as a valid biomarker of methylmercury exposure over an interval of weeks to months in epidemiologic studies.