Mercury was one of the first metals known and its compounds have been used throughout history. Archaeologists found mercury in an Egyptian
tomb dating from 1500 BC. It has been known for some time that high concentrations of mercury can be toxic to humans; the first account of
mercury poisoning was recorded as early as 50 B.C. Today, we recognize that mercury is a neurotoxin and that high levels of exposure can lead
to serious illness and, in extreme cases, death. The Mad Hatter, made famous in Lewis Carroll's Alice in Wonderland, was "mad" as
a result of mercury poisoning. Mercury nitrate was used to preserve the beaver felt hats that were popular in 19th century fashion.
The workers in the beaver felt factories of the time would, in fact, go mad as a result of breathing the toxic mercury fumes, some effects
of which are irreversible. Irritability is one of the early symptoms of mercury poisoning and this may also account for the description of
"mad" hatters. Since the 1950s and 1960s, a growing body of scientific evidence has suggested that mercury emissions from human
activities, called anthropogenic emissions, are having widespread impacts on environmental and human health.
Mercury is characterized by several unique properties that people have found both novel and useful through the ages. For example, it is the
only metal that is a liquid at room temperature and it evaporates, or vaporizes, relatively easily. Mercury can also combine with other metals
to make "amalgams", or solutions of metals, and has been used in the extraction of gold because of this property. One of the first
metals to be mined, it was found in Egyptian tombs dating back to 1500 B.C. Mercury has been a part of the occult arts and human folklore
and has been used in medicine, science and technology for millennia. Today, there are still many commercial and industrial applications in
which mercury is used. Mercury can be found in thermometers, dental fillings and fluorescent light bulbs, and is released from a range of
industrial processes such as the generation of electricity, base metal smelting and waste incineration.
Since industrialization, the amount of mercury found in the environment has increased by a factor of 2 to 4, largely because of human activities.
Mercury has always been emitted from natural sources such as volcanic eruptions, the weathering of soils and rocks
and vaporization from the oceans; however, scientists believe that more than half of the mercury in the environment today is from anthropogenic
sources. U.S. anthropogenic emissions of mercury to the atmosphere in 1995 are estimated to have been approximately 120 tons, while global
emissions were approximately 2,200 tons.
When released, tiny molecules of the metallic form of mercury can drift and be transported in the atmosphere for one to one and a half years,
traveling on wind currents from the primary source of emission, before settling on the soil or in bodies of water. This deposition of mercury
molecules occurs as dry deposition by simply settling out of the air, or as a result of absorption into rainfall or snowflakes and falling
to the earth with precipitation, which is known as wet deposition.
Mercury in the Environment
In the environment, mercury can migrate between various media, such as air, soil and water. Conceptually, movements of mercury between these
different environmental "compartments" are commonly known as "fluxes", and the quantities of mercury in the various compartments
are often referred to as "pools". These fluxes and pools are studied in order to help assess the global mercury budget. Quantifying
human versus natural mercury fluxes can be challenging because mercury deposited from anthropogenic releases can be re-emitted from land and
water, undergo long-range transport in the atmosphere, be re-deposited elsewhere, and so on. This process of emission and re-emission is the
reason why animals and peoples in remote areas with no local mercury releases, such as in the Arctic, may have elevated mercury levels.
Mercury in Fish, Wildlife and Humans
Mercury exists as a gas and in a range of organic (carbon containing) and inorganic (not containing carbon) forms that vary in toxicity and
persistence in living organisms. In the environment, mercury is transformed through complex biogeochemical interactions that affect environmental
and biological forms and concentrations. Some mercury compounds are more easily absorbed by living organisms than elemental mercury itself.
When atmospheric mercury falls to earth, it may be altered by bacterial or chemical action into an organic form known as methylmercury.
Methylmercury is much more toxic than the original metal molecules that drifted in the air, and has the ability to migrate through cell membranes
and "bioaccumulate" in living tissue. Bioaccumulation is the process by which a substance
builds up in a living organism from the surrounding air or water, or through the consumption of contaminated food. Bioaccumulation will vary
for different species and will depend on emission sources as well as local factors like water chemistry and temperature.
The bioaccumulation of methylmercury in natural ecosystems is an environmental concern because it inflicts
increasing levels of harm on species higher up the food chain. This occurs through a process known as "biomagnification", whereby
persistent substances like methylmercury will increase in concentration from microorganisms, to fish, to fish eating predators like otters
and loons, and to humans. Elevated methylmercury levels may lead to the decline of affected wildlife populations and may affect human health
when people consume significant quantities of fish or other contaminated foods. The most infamous case of this impact occured in Minimata,
Japan, where local residents consumed fish with toxic levels of methylmercury originating from an industrial sewer discharge, leading to the
deaths of more than 1000 people. This type of exposure has now come to be known as Minamata disease.
The challenge is to ensure that the levels of mercury in the environment do not exceed the concentrations which we would expect from natural
processes. As the dangers of mercury and its compounds become more apparent, governments are working with concerned citizens, industries and
environmental organizations to examine a range of mercury management tools, including laws, policies, regulations, initiatives and agreements
aimed at reducing anthropogenic sources. Educational programs are being created to inform people of appropriate reduction measures that can
be used in the home, cars, schools and the workplace.
In addition to providing information on the topics outlined above, this website provides a selection of resources for visitors, including
publications, links, fish
consumption advisories, steps for cleaning
up small mercury spills and proper disposal of products that contain mercury.