Mercury is the only naturally-occurring metallic element that is liquid at room temperature. It is also known to be toxic to living organisms. This silver liquid metal is characterized by its high density and high surface tension, and therefore is often found in the form of a tiny perfect sphere in pores of rocks. Mercury is represented by the chemical symbol “Hg”, and has the following properties:
|Atomic Number :80|
|Atomic Weight ：200.59|
|Metallic Bonding Radius :1.50A|
|Melting Point ：-38.9°C／234.3K|
|Boiling Point ：357°C／630K|
|Electrical Conductivity ：0.0106/m・Ohm|
|Thermal Conductivity ：7.8W/m・K|
|Heat of vaporization ：58.1 kJ／mol|
|Heat of Fusion ：2.33 kJ／mol|
Zerovalent is the most stable form of mercury and is barely soluble in water. If spilt, metallic mercury vaporizes at room temperature, thus presenting a health hazard as this vaporized mercury can be inhaled and absorbed into the blood. Metallic mercury can also be absorbed by blood by penetrating the skin.
Organic mercury compounds, e.g. methyl mercury and dimethyl mercury, are the most toxic. These compounds can be synthesized industrially, and in nature are produced by bacteria from other mercury compounds (e.g. methyl mercury). Chemically synthesized organic mercury compounds have been used as fungicides. Some organic mercury compounds are water-soluble and so they bio-accumulate in the aquatic food chain. They can also readily enter the human body through all three ways!! the lungs, skin and stomach.
Inorganic mercury compounds contain ionizable mercury, which usually forms a salt (e.g. mercury chloride) by bonding with chlorine. Many inorganic mercury compounds have been banned from use by local governments, particularly in consumer products and agriculture, because of its toxicity. However, inorganic mercury compounds have been used as disinfectants and pesticides throughout the world. If inhaled, the compounds are absorbed through the lungs and excreted through the skin. If swallowed, however, the compounds can be absorbed through the stomach. Many inorganic mercury compounds cause inflammation or sores to the skin, eyes, and even the mucus membranes of the nose.
Where is mercury found
Mercury is a naturally occurring element which can be found in the environment mainly in the form of cinnabar ore (HgS). Mercury is also found in fossil fuels in significant amounts, and even in minerals and rocks, although in trace amounts. Although mercury is naturally occurring, two thirds or more of the mercury present in the atmosphere now comes from man-made products and energy production sources. Mercury can be released into the atmosphere through a variety of means such as evaporation / vaporization from water and soil, but primarily through coal-fired boiler utilities and waste (medical & municipal) combustor emissions. Mercury gets into the soil through the natural breakdown of mercury containing rocks, disposal of mercury in landfills, and atmospheric depositions. It enters the water table through runoff, atmospheric depositions and by people pouring mercury containing products down drains. Once mercury enters the water cycle, it can be transformed into methyl mercury by microorganisms. Methyl mercury, which is fat-soluble, bio-accumulates in the tissues of fish and other aquatic animals, and magnifies up the food chain.
What can we do to help prevent mercury pollution
As we already know, two thirds of the mercury present in the atmosphere comes from human pollution. And once mercury vapors are released into the atmosphere, they are very difficult to remove. So the best practice is to prevent mercury from entering the environment, whenever feasible. Mercury is being phased out of many retail products such as thermometers. However, as a consumer, we need to educate ourselves so as not to buy anything containing mercury if substitutes are available. Disposal of mercury-containing products can also promote mercury pollution. Therefore, separating household waste containing mercury (for example fluorescent lamps and bulbs, thermometers, etc.) and disposing of them as hazardous waste material separately from domestic wastes are advantageous for municipal incineration. Recycle and reuse as many products as possible to decrease the amount of waste that needs to be incinerated. Of the two-thirds of mercury pollution generated by humans, 80% comes from energy generation by coal, oil, and gas (that naturally contain mercury) burning utilities. Therefore, if we conserve electricity, these electric generating stations will burn less coal, oil and gas, and thus reduce the level of mercury emission into the environment.
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