"Mercury is the hottest, the coldest, a true healer, a wicked murderer, a precious medicine and a deadly poison, a friend that can flatter and lie." – Woodall from The Surgeon’s Mate, London, 1639
Mercury is a chemical element with symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum. Wikipedia
Melting point: -37.89°F (-38.83°C)
Electron Configuration: [Xe] 4f14 5d10 6s2
Atomic number: 80
Boiling point: 674.1°F (356.7°C)
Discovered: 2000 BC
Atomic mass: 200.59 ± 0.02 u
The greatest source of mercury in the biosphere is currently of human origin. Mercury is number three on the Agency for Toxic Substances & Disease Registry (ATSDR) 2011 Substance Priority List. Although mercury is a naturally occurring element, most of it is sequestered in subterranean rock formations and coal beds. Two-thirds of the mercury entering the biosphere comes from man-made sources, including industrial plants, coal burning and incinerators; the additional one-third is emitted from natural sources. Many former chlor-alkali facilities (for producing chlorine and sodium hydroxide) are major point sources of mercury to aquatic ecosystems and are currently designated Superfund sites. Mercury is released into the air or directly into water bodies and makes its way into lakes and estuaries, where some of it settles to the bottom. Bacteria living in the mud of lake, river and estuary bottoms helps transform mercury into methylmercury (see below).
But mercury is considered a global pollutant, as it's capable of spreading far beyond its source area. The arctic, for example, has no known sources of mercury, but it harbors mercury-contaminated fish, and recent studies indicate that whales feeding in the arctic have high levels of mercury in their tissue.
What is Methylmercury? Methylmercury is an extremely toxic form of mercury that biomagnifies in aquatic food chains. It is a potent neurotoxin and the easiest form for animals to store in their tissue. It harms the brain, affecting memory, understanding and movement. Studies have shown that mercury exposure in humans can result in developmental delays in children, motor impairment, cardiovascular effects and, in acute cases, death. Its effects have been studied in fish, whales, seals and seabirds. Methylmercury binds to proteins and easily crosses cell membranes, including the blood-brain barrier and the placenta. Affected wildlife, such as loons, develop behaviors that ultimately reduce their chances for survival and reproduction. Studies conducted on human populations have estimated that between 200,000 and 400,000 children in the United States alone are born each year with pre-natal exposure to methylmercury sufficient to put them at risk of neurologic impairment.
Inorganic mercury is the term used to refer to mercuric ion (HgII). Inorganic mercury is highly toxic but not very mobile. Inorganic mercury in sediments, soils and food sources does not pass easily into biological tissues. However, once inside of the tissue, inorganic mercury is very difficult to remove. Inorganic mercury accumulates in tissues when a more mobile form of mercury such as elemental mercury vapor, methylmercury or ethylmercury enters the tissue and breaks down into inorganic mercury. In biological tissues, most organic forms of mercury will eventually break down into inorganic mercury.
Like methylmercury, ethylmercury is an organic form of mercury. Ethylmercury can be present in sediments or petroleum hydrocarbons. Ethylmercury is also used as a component in vaccine preservatives (thimerosal). Vaccination is the most common exposure route for this organic form of mercury. Like methylmercury, ethylmercury can move easily into biological tissues. However, ethylmercury tends to break down into inorganic mercury more rapidly than methylmercury.