Mercury is
an element that is found in air, water and soil. It has several forms. Metallic
mercury is a shiny, silver-white, odorless liquid. If heated, it is a
colorless, odorless gas. It also combines with other elements to form powders
or crystals. Mercury is in many products. Metallic mercury is used in glass
thermometers, silver dental fillings, and button batteries. Mercury salts may
be used in skin creams and ointments. It's also used in many industries.
Mercury in
the air settles into water. It can pass through the food chain and build up in
fish, shellfish, and animals that eat fish. The nervous system is sensitive to
all forms of mercury. Exposure to high levels can damage the brain and kidneys.
Pregnant women can pass the mercury in their bodies to their babies.
Mercury was
known to ancient Chinese and Hindus before 2000 BC and was found in tubes in
Egyptian tombs dated from 1500 BC. It was used to forma amalgams of other
metals around 500 BC. The Greeks used mercury in ointments and the Romans used
it, unfortunately for those using it, in cosmetics. Mercury is one of the
elements which has an alchemical symbol, (alchemy is an ancient pursuit
concerned with, for instance, the transformation of other metals into gold). Named
after the planet "Mercury" (the origin of the symbol Hg is the Latin
word "hydrargyrum" meaning "liquid silver").
Mercury can
be used to make thermometers, barometers and other scientific instruments.
Mercury conducts electricity and is used to make silent, position dependent
switches. Mercury vapor is used in streetlights, fluorescent lamps and
advertising signs.
Mercury
easily forms alloys with other metals, such as gold, silver, zinc and cadmium.
These alloys are called amalgams. Amalgams are used to help extract gold from
its ores, create dental fillings (in the case of silver) and help extend the
life of dry cell batteries (in the case of zinc and cadmium). Mercury forms
useful compounds with other elements. Mercuric chloride (HgCl2) is a very
poisonous salt and was once used to disinfect wounds. Mercurous chloride
(Hg2Cl2), also called calomel, is an antiseptic used to kill bacteria. Mercuric
sulfide (HgS) is used to make a red paint pigment called vermilion. Mercuric
oxide (HgO) is used to make mercury batteries.
Mercury is
poisonous and can enter the body through the respiratory tract, the digestive
tract or directly through the skin. It accumulates in the body, eventually
causing severe illness or death. Mercury in the elemental (gaseous) form
targets the brain, kidney, and lung. Divalent mercury forms in the kidney and
methyl mercury targets the brain, and the fetal brain.
Most people
are not exposed to inorganic mercury but rather absorb methylmercury through
the consumption of fish and shellfish. Methylmercury is easily absorbed in the
digestive tract, where it forms a complex with the amino acid cysteine. This
new complex resembles a large neutral amino acid found in the body, methionine,
and can more easily gain entry into cells. As with inorganic mercury, once in
the bloodstream, methylmercury will accumulate in the brain and cause damage to
the central nervous system. Methylmercury is naturally removed from the body
over time. Eventually, this methylmercury-cysteine complex is transported to
the liver where it is secreted into bile, after which enzymes break the complex
down into its amino acid and methylmercury parts. Some of this methylmercury
then comes in contact with the bacteria in the intestine and is broken down
into inorganic mercury and carbon. The inorganic mercury is poorly absorbed in
the digestive tract and 90 percent is excreted in the feces. The rest of the
methylmercury that does not interact with bacteria is reabsorbed by the body
and goes through the process again. It takes about 30 to 40 hours for
methylmercury to be distributed to the tissues of the body (Clarkson &
Magos, 2006). This cycle is the reason it takes so long to rid the body of
mercury and how it can accumulate in the blood. It can take up to a year for
mercury levels to drop significantly
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