Mercury, which occurs naturally in the environment, is a heavy metal like lead or cadmium which exists in different chemical forms. Most common among the forms of mercury which exist in the environment are metallic mercury, mercuric sulphide, mercuric chloride, and methylmercury.
Why should I be aware of this?
Mercury being one of the basic chemical elements out of which all things are made, it cannot be broken down or degraded into something else. Once released into the biosphere through natural events or human activities, mercury readily moves into the environment and remains there. Soil, water bodies and the sediments underneath them are believed to be the places where mercury comes to rest and we constantly run the risk of exposure.
Impact on health
Mercury has major impact on our health and on wildlife. It impacts us primarily from consumption of mercury-contaminated fish. The impact can permanently affect fetal and child development and can damage the brain, kidneys and lungs. Whereas mercury released into the environment is primarily inorganic or elemental by nature, when in the environment, it is converted by bacteria to a methylated or organic form, which is the most toxic and bioaccumulative form of mercury. Once formed, methyl mercury can be readily passed through the food chain.
How does this affect me?
Mercury has for centuries been used commercially and medicall. In the past it was a common constituent of many medications. It is still used in hospitals in thermometers and blood-pressure cuffs and commercially in batteries, switches, and fluorescent light bulbs. Large quantities of metallic mercury are employed as electrodes in the electrolytic production of chlorine and sodium hydroxide from saline.
Exposure to general population
Today the general population is exposed to mercury from three major sources: * fish consumption,
- dental amalgams,
- and vaccines.
Dental amalgams emit mercury vapor that is inhaled and absorbed into the bloodstream. Dentists and anyone with an amalgam filling are exposed to this form of mercury. Liquid metallic mercury still finds its way into homes, causing a risk of poisoning from the vapor and creating major cleanup costs.
Humans are also exposed to two distinct but related organic forms, methyl mercury (CH3Hg+) and ethyl mercury (CH3CH2Hg+). Fish are the main if not the only source of methyl mercury, since it is no longer used as a fungicide.
In many countries, babies are exposed to ethyl mercury through vaccination, since this form is the active ingredient of the preservative thimerosal used in vaccines. Whereas removal of certain forms of mercury, such as that in blood-pressure cuffs, will not cause increased health risks, removal of each of the three major sources described in this article entails health risks and thus poses a dilemma to the health professional.
All about mercury
Mercury (Hg) is the only metal that is liquid at room temperature and has a melting point of -40 C, and a boiling point of 357 C. This silvery liquid metal is very dense, yet has a high surface tension that causes is to form tiny little perfect spheres in the pores of the rocks it is found in.
Types of mercury
There are three types of mercury:
- Elemental or metallic mercury
This is mercury in a shiny, silver-white metallic form which is liquid at room temperature. This form of mercury is rarely found in nature. If not sealed off, mercury slowly evaporates into the air, forming a vapour. The quantity of vapour formed increases as temperatures rise. Elemental mercury is traditionally used in thermometers and some electrical switches.
- Inorganic mercury
Inorganic mercury compounds or mercury salts, include mercuric sulphide (HgS), mercuric oxide (HgO) and mercuric chloride (HgCl2)which are mostly found in nature. Most of these are white powders or crystals, except for mercuric sulphide which is red and turns black after exposure to light. Some mercury salts, such as mercury chloride, also form vapour, but they stay in the air for a shorter time than elemental mercury because they are more soluble in water and more reactive.
- Organic mercury
This is formed when mercury combines with carbon and other elements. Examples of organic mercury compounds are dimethylmercury, phenylmercuric acetate and methylmercuric chloride. The form most commonly found in the environment is methylmercury.
There is a common belief that the amount of mercury in our environment, and in the fish we eat, is increasing dangerously.
However, research has found considerable evidence that the amount of mercury in fish has remained the same (or even decreased) during the past 100 yeas. Researchers from Duke University and the Los Angeles County Natural History Museum compared 21 specimens of Atlantic Ocean blue hake preserved during the 1880s with 66 similar fish caught in the 1970s. No change in the concentration of mercury was found.
In another study, Princeton scientists compared samples of yellowfin tuna from 1971 with samples caught in 1998. They expected to find a mercury increase of between 9 and 26 percent, but they found a small decline instead. 
- U.S. Geological Survey
- Blood and Hair Mercury Levels in Young Children and Women of Childbearing Age—United States, 1999
- Long-term use of nicotine chewing gum and mercury exposure from dental amalgam fillings