Introduction of mercury
The properties of elemental mercury can be explained in physical and chemical properties.
For physical properties, mercury has an atomic weight of 200.59 g/mole. It has a freezing point
of -38.8°C and a boiling point of 356.7°C. Mercury is a heavy, silvery-white liquid metal. For
chemical properties, mercury does not react with most acids, such as dilute sulfuric acid.
Mercury dissolves many other metals such as gold and silver to form amalgams. Mercury
readily combines with aluminum to form a mercury-aluminum amalgam when the two pure
metals come into contact. This is because mercury can react with metal.
Nowadays, mercury have a lot of uses in this world. For example, mercury is used in medical
and scientific products like thermometers, barometers and manometers. The type of mercury
that have in the thermometer is elemental mercury. It means that the mercury is not expose to
the surroundings. Besides, it has a large thermal expansion which is constant over a large
temperature range although it is being phased out in favour of safer liquids. Moreover, mercury
also used as a component for dental amalgams for making fillings for teeth and mercury also
used for treatment in the past where it is used to treat syphilis, which is the most deadly disease
in the 15 century. At that time antibiotics was not invented, so mercury was use to cure syphilis.
Mercury is a naturally occurring element that is found in air, water and soil. Mercury can be
found in various forms including elemental mercury, inorganic mercury compounds, and
organic mercury compounds such as methyl mercury. Elemental or metallic mercury is a shiny,
silver-white metal and is liquid at room temperature. It is used in thermometers, fluorescent
light bulbs and some electrical switches. At room temperature, exposed elemental mercury can
evaporate to become an invisible, odourless toxic vapour. People can be exposed to elemental
mercury vapour when products that contain mercury break and expose mercury to the air,
particularly in poorly-ventilated spaces. Meanwhie, inorganic mercury compounds take the
form of mercury salts and are generally white powder or crystals, with the exception of
mercuric sulphide which is red. Inorganic mercury compounds have been included in products
such as fungicides, antiseptics or disinfectants. Some skin lightening and freckle creams, as
well as some traditional medicines, can contain mercury compounds. The others one is organic
mercury compounds such as methylmercury, are formed when mercury combines with carbon.
Microscopic organisms convert inorganic mercury into methylmercury, which is the most
common organic mercury compound found in the environment. Methylmercury accumulates
up the food chain.
In this world, there is a lot of sources mercury. The most common forms of mercury that
occur naturally in the environment are metallic mercury, the inorganic salts, mercuric sulfide
and mercuric chloride; and methylmercury. Microorganisms and various natural processes can
change these forms of mercury, from one form to the other. Methylmercury is the most
common form created by these natural processes. This compound is of particular concern
because it can bioaccumulate through the food chain. That is, small organisms and plants take
up methylmercury as they feed, animals higher up the food chain eat these plants and
organisms, and the process continues with methylmercury levels increasing up the food chain.
Of particular concern is seafood, such as fish and shellfish which had bioaccumulated mercury.
This is so as there may be harmful effects on humans when they consume seafood containing
mercury. Thus, human being are easily expose to mercury. But how we are expose to mercury
? Mercury in the air eventually settles into water or onto land where it can be washed into
water. Once deposited, certain microorganisms can change it into methylmercury, a highly
toxic form that builds up in fish, shellfish and animals that eat fish. Fish and shellfish are the
main sources of methylmercury exposure to humans. Methylmercury builds up more in some
types of fish and shellfish than others. The levels of methylmercury in fish and shellfish depend
on what they eat, how long they live and how high they are in the food chain. Therefore,
seafood is difficult for human to consume it since it could have mercury. Another less common
exposure to mercury that can be a concern is breathing mercury vapour. These exposures can
occur when elemental mercury or products that contain elemental mercury break and release
mercury to the air, particularly in warm or poorly-ventilated indoor spaces.
Nowadays, there are some methods that can be used to detect the presence of mercury and
monitoring also. Mercury can be detected and monitored by a few methods. They are Atomic
Absorption Spectrophotometry(AAS).
The components that we have in AAS are,
• Hollow cathode lamp : A light source which emits a stable and intense light of a particular
wave length which will be absorb by the sample (253.7nm for mercury lamp).
• A burning unit.
• Monochromator : A prism to disperse and isolate emission line.
• A photodetector which is fixed together with an appropriate amplifier.
Basic working for AAS is each element can readily absorb a specific wavelength. Therefore
the decrease in intensity of the light source can be use to determine the concentration of the
element present in the sample. The graph of the absorbance against the concentration could be
plot out with standard solution, thus the reading of the machine can be converted to a result.
