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History
Mercury is the Roman name for the Greek god Hermes, the protector
of travelers, thieves and merchants. On the periodic table of elements,
the chemical symbol for mercury is Hg, from the Latin word -
Hydrargyrum - meaning liquid silver. For quite some time, we have
known 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. 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. In the modern
world, there are many cultural, commercial and industrial uses for the metal
still in practice.
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 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. In the following figure, the concept of accumulated
methylmercury is illustrated by the red dots, however the dots are not to
scale.
 d
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.
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. Canadian anthropogenic
emissions of mercury to the atmosphere in 2000 are estimated to have been
approximately 8 tonnes, while the U.S.A. and global emissions were
approximately 120 and 2200 tonnes respectively during 1995. In addition to industrial releases, mercury can be found in thermometers, dental fillings, fluorescent light bulbs, and other consumer products.
The challenge for governments 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. In Canada, mercury is managed by federal legislation and guidelines, various programs and research groups, and through participation in international initiatives. Provincial and territorial governments have also established tools for reducing the impact of mercury pollution. Several Canada-wide standards have been endorsed by Environment Ministers from provinces, territories, and the federal government to ensure that efforts are consistent across the country.
Educational programs are being created to answer the question,
"what can I do?" in order 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 an extensive list of
links,
fish consumption advisories, steps for
cleaning up small mercury spills, information about mercury disposal, and a
glossary of terms related to mercury.
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