Global Mercury Assessment
SHOULD WE BE CONCERNED AND CAN INTERVENTION RESULT IN CHANGE?
is Present throughout the Environment
mercury levels have increased considerably since the on-set of the
industrial age. Mercury is now present in various environmental media and
food (especially fish) all over the globe at levels that adversely affect
humans and wildlife. Widespread exposures are occurring due to
human-generated sources, and past practices have left a legacy of mercury
in landfills, mine tailings, contaminated industrial sites, soils and
sediments. Even regions with no significant mercury releases, such as the
Arctic, are adversely affected due to the transcontinental and global
transport of mercury.
is Persistent and Cycles Globally
significant releases of mercury pollution are emissions to air, but
mercury is also released from various sources directly to water and land.
Once released, mercury persists in the environment where it circulates
between air, water, sediments, soil and biota in various forms. Current
emissions add to the global pool– mercury that is continuously mobilised,
deposited on land and water, and re-mobilised.
of mercury released varies depending on source type and other factors. The
majority of air emissions are in the form of gaseous elemental mercury,
which is transported globally to regions far from the emissions source.
The remaining emissions are in the form of gaseous inorganic ionic
mercury forms (such as mercuric chloride) or bound to emitted particles.
These forms have a shorter atmospheric lifetime and will deposit to land
or waterbodies within roughly 100 to 1000 kilometres of their source.
Elemental mercury in the atmosphere can undergo transformation into ionic
mercury, providing a significant pathway for deposition of emitted
deposited, the mercury form can change (primarily by microbial metabolism)
to methylmercury, which has the capacity to collect in
organisms (bioaccumulate) and to concentrate up food chains (biomagnify),
especially in the aquatic food chain (fish and marine mammals).
Methylmercury is therefore the form of greatest concern. Nearly all
of the mercury in fish is methylmercury.
Exposure Has Serious Effects
has caused a variety of documented, significant adverse impacts on human
health and the environment throughout the world. Mercury and its compounds
are highly toxic, especially to the developing nervous system. The
toxicity to humans and other organisms depends on the chemical form, the
amount, the pathway of exposure and the vulnerability of the person
exposed. Human exposure to mercury can result from a variety of
pathways, including, but not limited to, consumption of fish, occupational
and household uses, dental amalgams and mercury-containing vaccines.
is adversely affecting both humans and wildlife. This compound readily
passes the placental barrier and the blood-brain barrier, and is a
neurotoxicant, which may in particular cause adverse effects on the
developing brain. Studies have shown that methylmercury in pregnant
women’s diets can have subtle, persistent adverse effects on
children’s development as observed at about the start of school age.
Moreover, some studies suggest small increases in methylmercury
exposure may cause adverse effects on the cardiovascular system. Many
people (and wildlife) are currently exposed at levels that pose risks of
these, and possibly other adverse effects.
populations are especially susceptible to mercury exposure, most notably
the fetus, the newborn, and young children because of the sensitivity of
the developing nervous system. Thus, parents, pregnant women, and women
who might become pregnant, should be particularly aware of the potential
harm of methylmercury. Moderate
consumption of fish (with low mercury levels) is not likely to result in
exposures of concern. However,
indigenous populations and others who consume higher amounts of
contaminated fish or marine mammals, as well as workers who are exposed to
mercury, such as in small-scale gold and silver mining, may be highly
exposed to mercury and are therefore at risk.
their importance to many native cultures, fish are an extremely valuable
component of the human diet in many parts of the world, providing
nutrients that are often not available in alternative food sources.
Mercury is a major threat to this food supply. Likewise, contaminated fish
can bring serious economic problems to communities and regions dependent
on fisheries for their economic survival.
also particularly vulnerable ecosystems and wildlife populations. These
include top predators in aquatic food webs (such as fish-eating birds and
mammals), Arctic ecosystems, wetlands, tropical ecosystems and soil
Can be Successful
pollution has significant impacts at local, national, regional and global
levels. These impacts can be addressed through a range of actions at each
of these levels, targeting reductions in uses, releases and exposures.
Numerous actions implemented in Europe, North America and elsewhere have
successfully reduced uses and releases of mercury. However, inventories
are still incomplete in these regions, and some releases are still
significant. The extent of decreases in environmental levels and ecosystem
improvements in response to decreased releases of mercury will vary
considerably depending on local ecosystem characteristics and other
factors, and in some cases may take several decades. However, an
evaluation of mercury levels in Swedish lakes indicates that, by reducing
releases, environmental levels of mercury, such as in freshwater fish, may
be reduced significantly in specific locations within one to two decades.
IS LOCAL/REGIONAL ACTION, BY ITSELF, NOT SUFFICIENT?
Cycling of Mercury Increases the Problem
described above, the origins of atmospheric mercury deposition are local
and regional as well as hemispherical or global. Besides local sources of
mercury releases (such as waste incineration and coal combustion
facilities), the general global background concentrations (global pool)
contribute significantly to the mercury burden at most locations.
Similarly, virtually any local source contributes to the global pool.
Also, rivers and ocean currents are media for long-range mercury
some nations, local and regional mercury depositions have gradually
increased contamination levels to the point that countermeasures have been
enacted in recent decades to reduce emissions. However, due to long-range
transport, even nations with minimal mercury releases, and other areas
remote from industrial activity, may be adversely affected. For example,
high mercury levels are observed in the Arctic, far from the sources of
any significant releases.
Has an Impact on Global Fishing
Many fish species in international waters migrate to remote and diverse
locations. Moreover, after harvest, commercial fish are commonly exported
to various nations throughout the world, to locations far removed from
place of origin. Therefore, mercury contamination of lakes, rivers, and
especially oceans is truly a global issue, affecting fishing industries
and fish consumers around the world.
May Be More Problematic to Less-Developed Regions
awareness of mercury's adverse impacts has increased, the uses of mercury
have been reduced significantly in many industrialised countries.
Alternatives are commercially and competitively available for most uses.
However, these reductions in use have
had the effect of lowering demand relative to the supply of mercury, which
has kept mercury prices low and encouraged ongoing (and in some
cases, increased) use of mercury and outdated mercury technologies in
less-developed regions or nations. As
mercury regulations and restrictions are less comprehensive or less
well enforced in many less-developed regions, these trends have
contributed to the concentration, in these areas, of a disproportionate
burden of some of the health and environmental risks that accompany
is Subject to Significant International Use and Commerce
improved awareness of risks, mercury
continues to be used in a variety of products and processes all over the
mercury metal is used in small-scale mining
of gold and silver; chlor-alkali production; manometers for measurement
and control; thermometers; electrical switches; fluorescent lamps; and
dental amalgam fillings. Mercury compounds are used in batteries;
biocides in the paper industry, pharmaceuticals; paints and on seed grain;
and as laboratory reagents and industrial catalysts.
is significant ongoing trade in mercury and mercury-containing products,
some of which is illegal, uncontrolled and/or unregulated. The most significant global movement of mercury that remains poorly
understood is the flow of mercury through international commerce. While
overall quantities of mercury traded (and mined) have diminished in recent
years, significant amounts are still transported. The unabated demand in
many developing nations is a particular concern. Mercury
available on the world market is supplied from a number of sources,
including, among others:
Mining of mercury (extracted from ores within the earth’s crust) either
as the main product or as a by-product of mining and refining other
metals (gold, zinc) or minerals;
Private and government stocks (mercury in chlor-alkali plants, government
Recycled mercury recovered from spent products and industrial wastes.
under current regulations and restrictions, many of the uses and movements
of mercury and mercury containing products are likely to eventually result
in the release of mercury to the global environment. Meanwhile, large
amounts of mercury that remain in mine tailings, landfills and sediments,
as well as stockpiles, continue to present a threat of future release.
Hence, actions to reduce, manage and address uses, stocks and trade may be
useful at local, regional, national and international levels to prevent or
minimize future releases.
DOES MERCURY GET INTO HUMANS AND WILDLIFE?
local conditions may affect mercury exposure in
certain populations, most people are primarily exposed to methylmercury
through the diet (especially fish) and to elemental mercury vapours
due to dental amalgams and occupational activities. The toxicity of
methylmercury is described above. Elemental mercury vapour is also toxic
to the nervous system and other organs. While methylmercury is of greatest
concern for general populations, elevated exposures to elemental mercury
are also of concern.
methylmercury levels have been measured in numerous freshwater and marine
fish species throughout the world. The highest levels are found in large
predatory fish and fish-consuming mammals.
Exposure studies from diverse geographic areas indicate that a
significant portion of humans and wildlife throughout the world are
exposed to methylmercury at levels of concern, primarily due to
consumption of contaminated fish.
on local mercury pollution load, substantial additional contributions to
the intake of total mercury can occur through air and water. Also,
personal use of skin lightening creams and soaps, mercury use for
religious, cultural and ritualistic purposes, use in some traditional
medicines and mercury in the home and working environment can result in
substantial elevations of human exposure. Exposures also occur through the
use of vaccines and some other pharmaceuticals containing mercury
preservatives (such as Thimerosal/Thiomersal).
elemental mercury levels in the working environment have been reported in chlor-alkali plants, mercury mines, thermometer factories,
refineries, dental clinics, and in mining and manufacturing of gold and
silver extracted with mercury. The relative impacts from local pollution
(such as former mining sites), occupational exposure and local traditions
may vary considerably between nations and are known to be significant in
wildlife species that rely on fish as a large part of their diet can have
elevated mercury levels that raise the risk of adverse effects. Animals
with the highest mercury levels include otter, mink, raptors, osprey, and eagles,
which are top predators in the aquatic food chain. For example, eggs
of certain Canadian bird species have mercury levels that are a threat to
reproduction. Moreover, mercury levels in Arctic ringed seals and beluga
whales have increased by 2 to 4 times over the last 25 years in some areas
of the Canadian Arctic and Greenland. In warmer waters, some predatory
marine mammals are also at risk. In addition, recent evidence indicates
that soils are adversely affected over large parts of Europe and
potentially in many other locations. However, in some environments, even
fairly heavy mercury loads have very little effect on organisms as either
mercury is not efficiently bioaccumulated throughout the local food chain
or the mercury is not easily methylated. In addition, the effects of
watershed management practises in certain locations on methylmercury
levels may be more significant than the effects of direct or diffuse
ARE THE PRIMARY SOURCES OF MERCURY RELEASES?
The releases of mercury can be grouped in four
sources - releases due to natural mobilisation of naturally
occurring mercury from the Earth's crust, such as volcanic activity
and weathering of rocks;
anthropogenic (associated with human activity) releases from the mobilisation
of mercury impurities in raw materials such as fossil fuels –
particularly coal, and to a lesser extent gas and oil – and other
extracted, treated and recycled minerals;
anthropogenic releases resulting from mercury used intentionally in
products and processes, due to releases during manufacturing,
leaks, disposal or incineration of spent products or other releases;
of historic anthropogenic mercury releases previously deposited
in soils, sediments, water bodies, landfills and waste/tailings piles.
large portion of the mercury present in the atmosphere today is the result
of many years of anthropogenic emissions. The natural component of the
total atmospheric burden is difficult to estimate, although
available data suggest anthropogenic activities have increased levels of
mercury in the atmosphere by roughly a factor of 3, average deposition
rates by a factor of 1.5 to 3 and deposition near industrial areas by a
factor of 2 to 10.
contaminated industrial sites and abandoned mining operations continue to
release mercury. Also, land, water and resource management activities such
as forestry and agricultural practices and flooding can make mercury more
bioavailable. Methylation and bioaccumulation are influenced by high
levels of nutrients and organic matter in water bodies. In addition,
frequent extreme weather events can contribute to release of mercury
through flooding and soil erosion.
ARE THE ANTHROPOGENIC SOURCES?
regard to anthropogenic releases, the relative importance of releases
associated with intentional uses versus mobilisation of mercury impurities
vary between nations and regions, particularly depending on: extent of
substitution of intentional uses (products and processes); reliance on
fossil fuels, particularly coal, for energy; extent of mining and mineral
extraction industry; waste disposal practices; and state of implementation
of pollution control technologies. In nations where there is mercury
mining or use of mercury for small-scale gold or silver mining, these
sources can be quite significant.
of the more important anthropogenic processes that mobilise mercury
impurities include: coal-fired power and heat generation; cement
production; and mining and other metallurgic activities involving
the extraction and processing of mineral materials, such as production of
iron and steel, zinc and gold. Some
important sources of anthropogenic releases that occur from the
intentional extraction and use of mercury include: mercury mining;
small-scale gold and silver mining; chlor-alkali production; (breakage
during) use of fluorescent lamps, auto headlamps, manometers, thermostats,
thermometers, and other instruments; dental amalgam fillings;
manufacturing of products containing mercury; waste treatment and
incineration of products containing mercury; landfills; and cremation.
CAN RELEASES BE REDUCED?
or eliminating anthropogenic mercury releases will require controlling
releases from mercury-contaminated raw materials and feedstocks as well as
reducing or eliminating the use of mercury in products and processes. The
specific methods for controlling these mercury releases vary widely,
depending upon local circumstances, but fall generally under four
mercury mining and consumption of raw materials and products that
of products and processes containing or using mercury;
mercury releases through end-of-pipe controls; and
first two of these are “preventive” measures – preventing some uses
or releases of mercury from occurring at all. The latter two are
“control” measures, which reduce (or delay) some releases. Preventive
measures for reducing consumption of raw materials and products that
generate mercury releases are generally cost-effective, and among the most
viable means of eliminating mercury releases. Also, substitution of
products and processes without mercury is an important preventive action.
mercury releases through end-of-pipe techniques, such as exhaust gas
filtering, may be especially appropriate to processes using raw materials
with trace mercury contamination - fossil-fueled power plants, cement
production, extraction and processing of primary raw materials such as
zinc, gold and other metals, and processing of secondary raw materials
such as steel scrap. Existing control
technologies that reduce sulphur dioxide (SO2), nitrogen oxides
(NOx) and particulate matter (PM) for coal-fired boilers and
incinerators, while not widely used in many countries, also yield some
level of mercury control. Technology for additional mercury control is
under development and demonstration, but is not yet commercially deployed.
In the long run, integrated multi-pollutant (SO2, NOx,
PM, and mercury) control technologies may be a cost-effective approach.
However, end-of-pipe control technologies, while mitigating the problem of
atmospheric mercury pollution, still result in mercury wastes that are
potential sources of future emissions and should be disposed of or reused
in an environmentally acceptable manner.
waste management has become more complex as more mercury is collected from
a variety of sources, including gas filtering products, sludges from the
chlor-alkali industry, ashes, and mineral residues, as well as used
fluorescent tubes, batteries and other products that are often not
recycled. The cost of acceptable disposal of mercury waste in some
countries is such that many producers now investigate whether alternative
non-mercury products exist. Proper management of mercury wastes is
important to reduce releases to the environment, including those that
occur due to spills (such as broken thermometers) or releases that occur
over time due to leakage from certain uses (such as auto switches and
dental amalgams) or releases through waste incineration and cremation. A
well thought-out combination of prevention and control measures is
necessary to optimize reductions in mercury releases.
nations have implemented actions to limit and prevent uses, releases and
exposures, such as:
and regulations that control mercury releases into the environment;
control actions and regulations for mercury-containing products;
quality standards, specifying a maximum acceptable mercury
concentration for different media such as drinking water, surface
waters, air, soil and foodstuffs such as fish;
standards, actions and programmes, such as regulations on mercury
exposures in the workplace, reporting requirements, fish consumption
advisories and consumer safety measures.
legislation is a key component of most national initiatives, other efforts
exist to reduce mercury use such as developing and introducing safer
alternatives and cleaner technology, the use of subsidies and incentives
to encourage substitution efforts, voluntary agreements with industry, and
of mercury’s long-range cycling and persistence in the environment, a
number of countries have already initiated measures at regional,
sub-regional and international levels to identify common reduction goals
and ensure coordinated implementation among countries.
WOULD IMPROVE OUR UNDERSTANDING AND INTERNATIONAL COORDINATION?
data gaps, sufficient understanding has been developed of mercury
(including knowledge of its fate and transport, health and environmental
impacts, and the role of human activity), based on extensive research over
half a century, that international actions to address the global mercury
problem should not be delayed. Nonetheless, further research and other
activities would be useful to improve our understanding and coordination
in a number of areas, including:
of national uses, consumption and environmental releases;
on transport, transformation, cycling, and fate of mercury in various
and monitoring of mercury levels in various media (such as air and air
deposition) and biota (such as fish), and associated impacts on humans
and wildlife, including impacts from cumulative exposures to different
forms of mercury;
and evaluation tools for human and ecological risk assessments;
measures to prevent and reduce releases from various sources;
among nations dealing with the spectrum of scientific and technical
issues, including mercury waste management and remediation; and
on the global commerce and trade of mercury and mercury-containing