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Global Mercury Assessment 

 

Key findings

 

WHY SHOULD WE BE CONCERNED AND CAN INTERVENTION RESULT IN CHANGE?

Mercury is Present throughout the Environment

1.      Environmental 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.

Mercury is Persistent and Cycles Globally

2.      The most 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.

3.      The form 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 elemental mercury. 

4.      Once 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.

Mercury Exposure Has Serious Effects

5.      Mercury 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.

6.      Methylmercury 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.  

7.      Some 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.

8.      Besides 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.

9.      There are 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 microbial communities.

Intervention Can be Successful

10.      Mercury 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.

WHY IS LOCAL/REGIONAL ACTION, BY ITSELF, NOT SUFFICIENT? 

Global Cycling of Mercury Increases the Problem

11.      As 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 transport.

12.      In 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.

Mercury Has an Impact on Global Fishing

13.      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.

Mercury May Be More Problematic to Less-Developed Regions

14.      As 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 mercury.

Mercury is Subject to Significant International Use and Commerce

15.      Despite improved awareness of risks, mercury continues to be used in a variety of products and processes all over the world.  Elemental 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.

16.      There 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 reserves);

  • Recycled mercury recovered from spent products and industrial wastes.

17.      Even 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.

HOW DOES MERCURY GET INTO HUMANS AND WILDLIFE?

18.      Although 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.

19.      Elevated 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.

20.      Depending 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).

21.      Elevated 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 some areas.

22.      Numerous 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 mercury inputs.

WHAT ARE THE PRIMARY SOURCES OF MERCURY RELEASES?

23.      The releases of mercury can be grouped in four categories:

  • Natural sources - releases due to natural mobilisation of naturally occurring mercury from the Earth's crust, such as volcanic activity and weathering of rocks;

  • Current 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;

  • Current 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;

  • Re-mobilisation of historic anthropogenic mercury releases previously deposited in soils, sediments, water bodies, landfills and waste/tailings piles.

24.      A 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.

25.      Highly 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.

WHAT ARE THE ANTHROPOGENIC SOURCES?

26.      With 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.

27.      Some 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.

HOW CAN RELEASES BE REDUCED? 

28.      Reducing 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 groups: 

  • Reducing mercury mining and consumption of raw materials and products that generate releases;

  • Substitution of products and processes containing or using mercury; 

  • Controlling mercury releases through end-of-pipe controls; and

  • Mercury waste management.

29.      The 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. 

30.      Controlling 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.

31.      Mercury 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.

32.      Many nations have implemented actions to limit and prevent uses, releases and exposures, such as:

  • Actions and regulations that control mercury releases into the environment;

  • Product control actions and regulations for mercury-containing products;

  • Environmental quality standards, specifying a maximum acceptable mercury concentration for different media such as drinking water, surface waters, air, soil and foodstuffs such as fish;

  • Other standards, actions and programmes, such as regulations on mercury exposures in the workplace, reporting requirements, fish consumption advisories and consumer safety measures.

33.      Although 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 awareness raising.

34.      Because 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.

WHAT WOULD IMPROVE OUR UNDERSTANDING AND INTERNATIONAL COORDINATION? 

35.      Despite 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:

  • Inventories of national uses, consumption and environmental releases;

  • Information on transport, transformation, cycling, and fate of mercury in various compartments;

  • Assessment 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;

  • Data and evaluation tools for human and ecological risk assessments;

  • Additional measures to prevent and reduce releases from various sources;

  • Collaboration among nations dealing with the spectrum of scientific and technical issues, including mercury waste management and remediation; and

  • Information on the global commerce and trade of mercury and mercury-containing materials.