Context - Mercury is a heavy metal of which some forms are known to be highly toxic. Though mercury occurs naturally in the environment it is now mainly released by human activities.
Are these releases being controlled? Are humans and the environment at risk?
This Digest is a faithful summary of the leading scientific consensus report produced in 2002 by the United Nations Environment Programme (UNEP): "Executive Summary of the Global Mercury Assessment" Learn more...
- Source document:UNEP (2002)
- Summary & Details: GreenFacts
1. What is mercury?
Mercury is a heavy metal,
sometimes known as quicksilver, that occurs naturally in the environment
in different chemical forms. The pure form,
elemental mercury, is liquid at
room temperature and slowly forms a vapour in the air. Forms more
commonly found in nature are
inorganic mercury and
Natural events (e.g. volcanic activity, weathering of rocks) and human
activities (e.g. mining, fuel use, products and processes) can cause
mercury releases into the environment. Once released, it can move easily
between air, water and land: natural processes can even change mercury
from one form to another.
Mercury can have adverse effects on living organisms and the
environment, though these depend on its form as well as
2. What are the impacts of mercury on human health?
Mercury and its compounds are highly
toxic substances for humans.
elemental mercury are of the
highest concern. They are poisonous to the nervous system. There is
at present that methylmercury can cause
cancer in humans, but it is far
from conclusive. However, there is no evidence at present that elemental
mercury causes cancer in humans. Moreover,
exposure to methylmercury during
pregnancy may affect the unborn baby.
Humans are mainly exposed to
methylmercury through their diet
(particularly fish), and to
elemental mercury vapours from
tooth fillings and at certain workplaces.
Governmental bodies have set daily mercury
intake levels that are considered
safe, but some people take in more than these levels.
Risks vary from one place to
another. The risk from diet mainly
depends on how much contaminated fish is eaten: moderate consumption of
fish with low levels of mercury is not a cause for concern.
3. What are the impacts of mercury on the environment?
Methylmercury can accumulate along the food chain © Aurileide Alves
Mercury can be particularly harmful for the environment because it can
accumulate in organisms. The levels
of methylmercury increase along the
food chain and with age.
Mercury may harm bird reproduction
and behaviour. Some seals and whales in the Arctic and some predatory
marine mammals in warm waters may be at
Some ecosystems, such as forest
soils, may be affected by mercury.
4. Where is mercury found?
Mercury is released into the environment through both natural
processes (e.g. volcanic activity, weathering of rocks) and human
activities (e.g. mining, fuel use, products and processes). Once
released, mercury enters air, water and soil, and moves from one to
another until it comes to rest in sediments or landfills.
Mercury deposited from the atmosphere at any particular place comes
from both local and global sources.
Human activity is now the main source of mercury being released into
the environment. Much is released unintentionally from processes where
mercury is an unwanted impurity. Emissions into the air, mainly from
fossil fuel power plants and waste
incinerators, are expected to increase unless other energy sources are
used or emissions better controlled. However, mercury mining is
decreasing and therefore releases from mining and mercury use may be in
Weathering and evaporation from mercury-rich rocks and soils lead to
natural mercury release, as do forest fires and volcanic activity.
Although natural emissions are difficult to determine, current estimates
suggest that less than 50% of total mercury releases come from natural
5. Where do the world's supplies of mercury come from?
Mercury placed on the world market comes mainly from
cinnabar mines in Spain, China,
Kyrgyzstan and Algeria. It can also be recycled from industrial
Large amounts of recycled mercury will be available over the next
decade and beyond and steps are being taken to manage the way it is
used. Increased recycling will reduce the movement of new mercury onto
the market and into the environment.
Because of its unique properties, mercury has been used for extracting
gold and silver from ores, in
chlor-alkali chemical manufacture,
in thermometers and manometers, in lights and switches, and in
dental amalgam fillings, among
others. However, use of mercury and mercury compounds has been reduced
for health and environmental reasons.
6. What can be done to reduce mercury releases?
Mercury releases from current human activity may be limited by either
preventive measures or control measures.
Preventive measures include reducing the use of mercury-containing
products and raw materials, and replacing products and processes that
contain or use mercury with ones that do not.
Control measures include
end-of-pipe techniques and
effective waste management.
A suitable approach for reducing mercury emissions should involve both
preventive and control measures.
There have been many national initiatives to manage the use and
release of mercury. These include the setting of mercury emission
limits, environmental standards and restrictions on use.
International initiatives include legally binding agreements,
non-binding initiatives and voluntary private-sector initiatives.
7. What further research and information is needed?
Most countries need more information in order to manage mercury
effectively. Some lack basic information about their own uses and
releases of mercury, as well as levels in their local environment, while
others want more advanced data in order to assess and manage the
Mercury is one of the best-studied environmental
toxicants, but there are still some
gaps in understanding a number of global issues. However, the
information available is sufficient to address, without delay, the
global adverse effects of mercury.
There should be international action to reduce the
risks to human health and the
environment arising from mercury release into the environment.
While more data will help, the
adverse impacts of mercury need to
be addressed at the global, regional, national and local levels. Various
options for doing this have been identified, and areas for immediate
action have been proposed.