Mercury exists in various
forms: elemental (or metallic) and inorganic (to which people may be exposed
through their occupation); and organic (e.g., methylmercury, to which people may
be exposed through their diet). These forms of mercury differ in their degree of
toxicity and in their effects on the nervous, digestive and immune systems, and
on lungs, kidneys, skin and eyes.
Mercury occurs naturally in the earth's crust. It is released into the
environment from volcanic activity, weathering of rocks and as a result of human
activity. Human activity is the main cause of mercury releases, particularly
coal-fired power stations, residential coal burning for heating and cooking,
industrial processes, waste incinerators and as a result of mining for mercury,
gold and other metals.
Once in the environment, mercury can be transformed by bacteria into
methylmercury. Methylmercury then bioaccumulates (bioaccumulation occurs when an
organism contains higher concentrations of the substance than do the
surroundings) in fish and shellfish. Methylmercury also biomagnifies. For
example, large predatory fish are more likely to have high levels of mercury as
a result of eating many smaller fish that have acquired mercury through
ingestion of plankton.
All humans are exposed to some level of mercury. Most people are exposed to low
levels of mercury, often through chronic exposure (continuous or intermittent
long term contact). However, some people are exposed to high levels of mercury,
including acute exposure (exposure occurring over a short period of time, often
less than a day). An example of acute exposure would be mercury exposure due to
an industrial accident.
Factors that determine whether health effects occur and their severity include:
the type of mercury concerned;
the dose;
the age or developmental stage of the person exposed (the foetus is most
susceptible);
the duration of exposure;
the route of exposure (inhalation, ingestion or dermal contact).
Generally, two groups are more sensitive to the effects of mercury. Foetuses are
most susceptible to developmental effects due to mercury. Methylmercury exposure
in the womb can result from a mother's consumption of fish and shellfish. It can
adversely affect a baby's growing brain and nervous system. The primary health
effect of methylmercury is impaired neurological development. Therefore,
cognitive thinking, memory, attention, language, and fine motor and visual
spatial skills may be affected in children who were exposed to methylmercury as
foetuses.
Elemental and methylmercury are toxic to the central and peripheral nervous
systems. The inhalation of mercury vapour can produce harmful effects on the
nervous, digestive and immune systems, lungs and kidneys, and may be fatal. The
inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal
tract, and may induce kidney toxicity if ingested.
Neurological and behavioural disorders may be observed after inhalation,
ingestion or dermal exposure of different mercury compounds. Symptoms include
tremors, insomnia, memory loss, neuromuscular effects, headaches and cognitive
and motor dysfunction. Mild, subclinical signs of central nervous system
toxicity can be seen in workers exposed to an elemental mercury level in the air
of 20 μg/m3 or more for several years. Kidney effects have been reported,
ranging from increased protein in the urine to kidney failure.
There are several ways to prevent adverse health effects, including promoting
clean energy, stopping the use of mercury in gold mining, eliminating the mining
of mercury and phasing out non-essential mercury-containing products.
Promote the use of clean energy sources that do not burn coal.
Burning coal for power and heat is a major source of mercury. Coal contains
mercury and other hazardous air pollutants that are emitted when the coal is
burned incoal-fired power plants, industrial boilers and household stoves.
Eliminate mercury mining, and use of mercury in gold extraction and other
industrial processes.
Mercury is an element that cannot be destroyed; therefore, mercury already in
use can be recycled for other essential uses, with no further need for mercury
mining. Mercury use in artisanal and small-scale gold mining is particularly
hazardous, and health effects on vulnerable populations are significant.
Non-mercury (non-cyanide) gold-extraction techniques need to be promoted and
implemented, and where mercury is still used safer work practices need to be
employed to prevent exposure.
Phase out use of non-essential mercury-containing products and implement safe
handling, use and disposal of remaining mercury-containing products.
Mercury is contained in many products, including:
batteries
measuring devices, such as thermometers and barometers
electric switches and relays in equipment
lamps (including some types of light bulbs)
dental amalgam (for dental fillings)
skin-lightening products and other cosmetics
pharmaceuticals.