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UNEP Chemicals

Global Mercury Assessment


25 April 2002

UNEP Chemicals

Global Mercury Assessment


25 April 2002

Report no. 54790-01

Issue no. 01

Date of issue 25 April

Prepared JAM, FSL/COWI, PAM/Concorde, AT/UNEP Chemicals

Checked CR/COWI (COWI’s internal QA)

Table of Contents

Summary 5

1 Introduction 6

1.1 Background and mandate 6

1.2 Submission of information for this report 7

1.3 Sources of information for this report 9

1.4 Scope and coverage in this report 9

1.5 Purpose of this report 10

2 Chemistry 11

2.1 Overview 11

2.2 Transformation and methylation processes 12

3 Toxicology 16

3.1 Overview 16

3.2 Methylmercury 16

3.3 Elemental and inorganic mercury 23

3.4 Interactions - protective effects of certain nutrients 28

4 Current exposure and impacts on human health 31

4.1 Overview 31

4.2 Evaluations of exposure levels causing risks 31

4.3 Routes of mercury exposure – a general overview 36

4.4 Exposure through diets of fish and marine mammals 40

4.5 Submitted data on mercury concentrations in fish 45

5 Impacts of mercury on the environment 51

5.1 Overview 51

5.2 Eco-toxicological effect levels 52

5.3 Ecosystems at risk and vulnerable species 56

5.4 Mercury concentrations in environmental media 63

6 Sources of mercury to the global environment 65

6.1 Overview 65

6.2 Natural sources of mercury 68

6.3 Anthropogenic sources of mercury 70

6.4 Pathways of mercury to – and in – the environment 82

7 Current production and use of mercury 92

7.1 Overview 92

7.2 Global production 94

7.3 Current use patterns 97

7.4 Particulars on chlor-alkali production and gold extraction 104

8 Prevention and control technologies and practices 109

8.1 Overview 109

8.2 Substitution 115

8.3 Reducing mercury emissions 121

8.4 Waste management practices 133

8.5 Mercury control costs and effectiveness 136

9 Initiatives for controlling releases and limiting use and exposure 144

9.1 Overview 144

9.2 National initiatives 145

9.3 International agreements and instruments 169

9.4 International organizations and programmes 180

9.5 Sub-regional and regional initiatives 187

10 Data gaps 194

11 Glossary, acronyms and abbreviations 195

References 199


COMMENT TO WORKING GROUP MEMBERS - This section will only be drafted in time for the meeting of the Working group, tentatively scheduled to take place in September 2002.

It is expected that the summary will be around 10-15 pages, and the text of the summary will reflect the information in the overview found at the beginning of each individual section.


1.1Background and mandate

  1. This report responds to the request of the Governing Council of the United Nations Environment Programme (UNEP), through GC decision 21/5, that UNEP undertake a global assessment of mercury and mercury compounds, in cooperation with other members of the Inter-Organization Programme for the Sound Management of Chemicals (IOMC), to be presented to the Governing Council at its session in 2003. The assessment would include contributions from Governments, intergovernmental and non-governmental organizations and the private sector, and cover the following elements:

(a) To summarize existing information including recent authoritative reviews of the chemistry, including transformation and methylation processes, toxicology, and impacts of mercury on human health and the environment;

(b) To compile and summarize existing information concerning the global natural and anthropogenic sources of mercury;

(c) To consolidate and analyse information regarding relevant environmental long-range transport and the origin, pathways, deposition and transformation of these substances on a global scale;

(d) To examine and describe the sources of release of mercury to the environment, and the current production and use patterns of mercury as a global commodity;

(e) To compile and summarize information about prevention and control technologies and practices, and their associated costs and effectiveness, that could reduce and/or eliminate releases of mercury, including the use of suitable substitutes, where applicable;

(f) To describe ongoing actions and compile information about future plans at the national, sub-regional or regional levels for controlling releases, and limiting use and exposures, including waste management practices; and

(g) To provide, for elements (a) through (f), a summary description of scientific and technical information needs and data gaps;

  1. The Governing Council also requested an outline of options for consideration at its 22nd session addressing any significant global adverse impacts of mercury, inter alia, by reducing and or eliminating the use, emissions, discharges and losses of mercury and its compounds; improving international cooperation; and ways to enhance risk communication. This outline of options is contained in a document separate from this report.

  2. In this assessment report, the specific elements listed by the UNEP Governing Council are covered as follows:

  • Element (a) is covered in sections 2 to 5;

  • Element (b) is covered in section 6.2 and 6.3;

  • Element (c) is covered in section 6.4;

  • Elements (d), (e), (f) and (g) are covered by sections 7, 8, 9 and 10, respectively.

1.2Submission of information for this report

  1. UNEP, in April 2001, as a follow-up to the request from the Governing Council, invited Governments, intergovernmental and non-governmental organizations and the private sector to submit information relevant to mercury and mercury compounds. As information was received, it was as far as possible posted on the Global Mercury Assessment web site, specially established for the purpose of allowing insight into the information collected. For submitted reports and articles protected by copyright laws, respective copyright rules were observed. The address of the Global Mercury Assessment (GMA) website is http://www.chem.unep.ch/mercury/.

  2. As of 25 April 2002, 65 Governments, 10 intergovernmental and 10 non-governmental organizations had submitted information. A list of submissions is available in a document separate from this report. The distribution of submissions from Governments between different UN regions is shown in Figure 1.1**.

Figure 1.1 Overview of submissions to the Global Mercury Assessment, by UN region

  1. Figure 1.2 ** illustrates the global coverage of the information submitted from Governments. Further details on the specific countries within each region and the intergovernmental and non-governmental organizations that have submitted information is available in the list of submissions mentioned above or on the GMA web site.

  2. Although a relatively large number of Governments submitted information for the report, it should be noted that there were substantial differences in the amount of information available from each Government. Some Governments, especially those of OECD-countries, have comprehensive inventories that document mercury production, use and releases over a number of years, while others, although they are aware of mercury use in their country, have very limited documented data.

Figure 1.2 Submissions from Governments to the Global Mercury Assessment – global coverage.

1.3Sources of information for this report

  1. The sources of information used to develop this report are:

  • Submissions from Governments, intergovernmental and non-governmental organizations and the private sector, received as of 2 April 2002;

  • Additional publications, articles and reports of relevance to mercury identified through a literature search in scientific literature; and

  • Additional information, publications and reports publicly available on websites of various Governments, intergovernmental and non-governmental organizations.

  1. References for the information used to develop this report are given as far as possible in the text. If no specific reference is provided, it has been found in the submission provided by the specific Government or organization.

  2. Because of the large volume of reports, articles, abstracts, etc. relating to mercury that were submitted/collected, it was not possible to review all the information in detail in the time available. The information was screened and a prioritisation was made. Focus was given to country-specific information that might add to the global understanding of the use and regulation of mercury, especially from non-OECD countries, and information that might add to the general knowledge of the various issues linked to mercury, based on the recently published authoritative reviews on such issues.

  3. Because this report should provide a global overview of the issues related to mercury, there are substantial amounts of detailed information dealing with various aspects that have not been included, e.g. detailed national mercury consumption and use data. This information might, however, be a basis for further, more detailed review and analysis later should a decision on further work be taken.

1.4Scope and coverage in this report

  1. Although this report is entitled “Global Mercury Assessment”, it does not assess mercury in the true meaning of the word – to judge or decide the amount, value, quality or importance of (Cambridge International Dictionary of English, 1995). It is not a scientific analysis of the toxicology of mercury and mercury compounds, its effects on human health or the environment and environmental long-range transport and pathways, nor a global assessment of the risks related to use and emissions of mercury.

  2. Rather, it attempts, for each element identified by the Governing Council, to compile and provide, as far as possible, a global overview of evaluations and assessments already made and conclusions already drawn by the scientific community, national Governments, organizations, etc on the various issues related to mercury. The report draws mainly on recently published authoritative reviews on the various topics relevant to mercury, supplemented by national information. As a large part of the previously published reviews focus on OECD-countries, where much of the current research is ongoing and some reduction measures implemented, an attempt has been made to identify and include relevant information from non-OECD countries.

  3. The Governing Council also requested an outline of options for addressing any significant global adverse impacts of mercury. This report does not contain such an outline – a draft will be circulated in advance of the Global Mercury Assessment Working Group meeting, for consideration once this report has been reviewed and finalized by the Working Group. However, this report, especially sections 9 and 10 on prevention and control technologies and practises and initiatives for controlling releases and limiting use and exposure, respectively, will form an important basis for considering such options.

  4. As this report attempts to provide a global overview of the issues related to mercury on a limited number of pages, all the information submitted by each individual country or organization cannot be reflected. However, certain compilations have been developed that contain comprehensive national information on certain specific issues, e.g. regulatory actions. If they are found useful, these might be kept updated in future.

  5. To facilitate reading, in each section an overview of the main points in the section is given at the very beginning of the section. In addition, section 1 constitutes a 10-page summary of the main conclusions from each section. When reading the full report, readers might notice that there is some overlap in the information in some of the sections. However, this was deemed necessary, as it is assumed that in the future many of the sections might be read separately by a reader interested in a specific topic.

  6. The report was originally drafted by COWI in Denmark and Concorde East/West in Belgium, with COWI as the project manager. The main contributor in each company was Mr. Jakob Maag and Mr. Peter Maxson, respectively. Both have extensive experience and have previously been involved in a number of publications relevant to mercury, both at national and international level. Ms. Aase Tuxen of UNEP Chemicals coordinated the work and contributed to the drafting and editing of the report.

1.5Purpose of this report

  1. The draft report will be reviewed and revised by members of the Global Mercury Assessment Working Group and national information supplemented by input from the respective national members of the Working Group, first through a comment round by mail, then through a meeting, tentatively scheduled for 16-20 September 2002. The final report will be submitted to the UNEP Governing Council in February 2003 for consideration, together with an outline of options for addressing any significant global adverse impacts of mercury.

  2. By having initiated the development of this report, the Governing Council will have a better basis for considering whether any concerted international action on mercury is called for, thus promoting the environmentally sound management of mercury and its compounds. The assessment report will contribute to increased awareness and understanding among decision makers of the major issues related to mercury and its compounds, thereby facilitating the debate on the issue at the next session of the Governing Council.



  1. Mercury occurs naturally in the environment and exists in several forms. These forms can be organised under three headings: metallic mercury (also known as elemental mercury), inorganic mercury, and organic mercury. Metallic mercury is a shiny, silver-white metal that is a liquid at room temperature. Metallic mercury is the elemental or pure form of mercury (i.e., it is not combined with other elements). Metallic mercury metal is the familiar liquid metal traditionally used in thermometers and some electrical switches. At room temperature, some of the metallic mercury will evaporate and form mercury vapours. Mercury vapours are colorless and odorless. The higher the temperature, the more vapours will be released from liquid metallic mercury. Some people who have breathed mercury vapours report a metallic taste in their mouths.

  2. Inorganic mercury compounds occur when mercury combines with elements such as chlorine, sulfur or oxygen. These mercury compounds are also called mercury salts. Most inorganic mercury compounds are white powders or crystals, except for mercuric sulfide (also known as cinnabar), which is red and turns black after exposure to light.

  3. When mercury combines with carbon, the compounds formed are called "organic" mercury compounds or organomercurials. There is a potentially large number of organic mercury compounds; however, by far the most common organic mercury compound in the environment is methylmercury (also known as monomethylmercury). In the past, an organic mercury compound called phenylmercury was used in some commercial products. Another organic mercury compound called dimethylmercury is also used in small amounts as a reference standard for some chemical tests. Like the inorganic mercury compounds, both methylmercury and phenylmercury exist as "salts" (for example, methylmercuric chloride or phenylmercuric acetate). When pure, most forms of methylmercury and phenylmercury are white crystalline solids. Dimethylmercury, however, is a colorless liquid.

  4. Several forms of mercury occur naturally in the environment. The most common natural forms of mercury found in the environment are metallic mercury, mercuric sulfide (cinnabar ore), mercuric chloride, and methylmercury. Some microorganisms (bacteria and fungi) and natural processes can change the mercury in the environment from one form to another. The most common organic mercury compound that microorganisms and natural processes generate from other forms is methylmercury. Methylmercury is of particular concern because it can build up in certain edible freshwater and saltwater fish and marine mammals to levels that are many times greater than levels in the surrounding water.

  5. Mercury is mined as cinnabar ore, which contains mercuric sulfide. The metallic form is refined from mercuric sulfide ore by heating the ore to temperatures above 1,000 degrees Fahrenheit (540ºC). This vaporises the mercury in the ore, and the vapours are then captured and cooled to form the liquid metal mercury.

  6. Methylmercury is produced primarily by microorganisms (bacteria and fungi) in the environment, rather than by human activity.

  7. Mercury is an element and therefore cannot be broken down or degraded into harmless substances. As described, mercury may change between different states and species in its cycle, but its simplest form is elemental mercury, which it self is harmful to humans and the environment. Once mercury has been brought into circulation in the biosphere by human activity it does therefore not “disappear” again in time spans comparable to human lifetime.

  8. The above was extracted from the general presentation of mercury in US ATSDR (1999). Unless otherwise mentioned, the rest of the chapter is mainly based on the submission from the Nordic Council of Ministers.

2.2Transformation and methylation processes

  1. The different forms mercury exists in are commonly designated “species”. For instance elemental mercury vapour, methylmercury and mercuric chloride are examples of different mercury species. As mentioned above, the main groups of mercury species are elemental mercury, inorganic mercury species and organic mercury species. The phenomenon that mercury exists in various forms or species is designated “speciation”.

  2. The speciation plays an important part in the toxicity and exposure of mercury to living organisms. Among other things, the species influence:

  • The physical availability for exposure - if mercury is tightly bound to in-absorbable material, it cannot enter the organism;

  • The internal transport inside the organism to the tissue on which it has toxic effects - for instance the crossing of the intestinal membrane or the blood/brain barrier;

  • Its accumulation, bio-modification, detoxification in – and excretion from – the tissues.

  1. Additionally, speciation influences the transport of mercury within and between compartments in the environment: Atmospheric transport and transport in the oceans, among others.

  2. Mercury exists in the following main states under natural conditions:

  • As metallic vapour (elemental mercury);

  • Bound in mercury containing minerals (solid);

  • As ions in solution or bound in ionic compounds (inorganic salts etc.);

  • As soluble ion complexes ;

  • As gaseous or dissolved non-ionic organic compounds;

  • Bound to inorganic or organic particles/matter by ionic, electrophilic or lipophilic adsorption.

2.2.1Mercury species and transformation in the atmosphere

Galperin et al (1996) gives a review of the 1995-state-of-the-art of the perception of atmospheric mercury speciation, as used in the modelling of atmospheric mercury transport. In the atmosphere mercury is mainly present in metallic form (elemental form, Hg(0)) and in the two-valency form Hg(II) incorporated in chemical compounds. In both cases it may be in the form of gas (vapour), in aerosols (water droplets), or adsorbed on particle surfaces moving with the air masses. Some of the possible species are elemental mercury (Hg), mercury-dichloride (HgCl2), mercury-oxide (HgO), mercury-sulphite (HgSO3) and dimethylmercury. The interaction between different species is dynamic. Figure 2.1** from Galperin et al (1996) shows a model of interactions between mercury species in the atmosphere.

igure 2.1 Model of interactions between mercury species in the atmosphere (Galperin et al, 1996). Legend: Hg0 = elemental mercury, Hg2+ = divalent mercury, DD = dry deposition, WD = wet deposition.

  1. Axenfeld et al. (1991, as quoted by Pirrone et al., 2001) concluded that as much as 60 % of the anthropogenic emissions in Europe were in gaseous elemental form, 30 % as gaseous bivalent mercury and 10 % as elemental mercury on particles.

  2. Most of the emissions from combustion of fuels (an important source of emissions) occur in the gaseous phase. In the combustion zone, mercury present in coal and other fossil fuels evaporates in the elemental form. While in the flue gases, some of it is oxidised. The oxidised form can be retained in modern flue gas cleaning systems. The emission generation process for mercury during incineration of wastes is similar, except that more mercury in the oxidised form is expected from incinerators, due to the higher content of chlorine in waste matter than in fossil fuels (AMAP, 1998).

  3. In table 2.1** an overview of the speciation of emissions from a number of major anthropogenic source types is given. The table was prepared by Pirrone et al. (2001).

Table 2.2 Emission profiles (fraction of the total) of mercury from anthropogenic sources, 1995 (table from Pirrone et al., 2001).


Coal Combustion
Power Plants

Coal Combustion Residential Heat

Oil Combustion

Cement Production

Non-Ferrous Metals

Pig & Iron

Caustic Soda

Waste Incineration


Average of all sources

Information Source

Hg0 (gas)











Pacyna et al., 2000












Modified by Pacyna, 1998












2.2.2Mercury species and transformation in aquatic environments

  1. AMAP (1998) gives the following overview of mercury speciation in aquatic environments:

“Mercury exists in natural waters in three oxidation states: Hg(0), Hg(I) and Hg(II). The numbers in brackets indicate the number of electrons missing in the mercury atom in the actual compounds/species as compared to the metallic state Hg(0). Hg (II) forms complexes with water molecules even at low pH values. These complexes predominate among inorganic forms of mercury under natural conditions (acidity, pH> 6), even in the presence of considerable concentrations of chloride ions. Mercury can also form stable complexes with many organic ligands (ions), especially those containing sulphur (amino acids, oxycarbonic acids etc.) and higher molecular natural compounds like fulvic and humic acids (from degraded plants material etc.). In natural waters, mercury compounds are strongly bound to particulate matter. Bound to particles, mercury is readily transported in rivers (and other water currents) and accumulated in bottom sediments. In addition to hydrophobic organic complexes, Hg(II) can form water and lipid-soluble organo-mercury compounds with linear hydrocarbons (alkyl derivates), primarily methylmercury. Methylmercury compounds can be formed in two main ways: Microbiological and chemical. The latter mechanism usually involves natural organic substances (mostly fulvic acids).”

  1. Methylmercury is the predominant mercury species in fish. The US EPA states in an updated mercury overview paper that in most adult fish, 90 to 100% of mercury content is methylmercury (US EPA, 2001). As a consequence, the US EPA recommends that the cheaper total mercury chemical analysis be used for (state) evaluation of risk from local fish, and that results should be used as if mercury was present as 100% methylmercury in order to be most protective of human health.

  2. Mason and Fitzgerald (1996) have reviewed aspects of the cycle of mercury in oceans and other waters: From open ocean studies, it is apparent that elemental mercury, dimethylmercury and, to a lesser extent, methylmercury are common constituents of the dissolved mercury pool in deep ocean waters. In open ocean surface waters dimethylmercury is lacking, maybe as a result of decomposition in the presence of light and an additional potential loss via evaporation from the water surface. Recent results suggest that low oxygen conditions are not necessary for the formation of dimethylmercury in the open oceans.

  3. This contrasts with temperate lakes where methylmercury is the predominant species, and dimethylmercury is rarely detected. Studies in freshwater and estuarine environments have shown that methylation of mercury is primarily taking place under low oxygen conditions and mainly by sulphate-reducing bacteria. Here methylmercury is the product of methylation of ionic mercury. Figure 2.2** shows a diagram of the principal mercury reactions in the ocean.

igure 2.2 Dynamic interactions between the various mercury species in ocean waters (based on Mason and Fitzgerald, 1996). Hg(0) = elemental mercury, DMHg = dimethylmercury, MMHg = (mono)methylmercury.

2.2.3Mercury species and transformation in soil

  1. Soil conditions are typically favourable for the formation of inorganic compounds, such as HgCl, Hg(OH) and inorganic Hg(II) compounds, which form complexes with organic anions. This complexing behaviour greatly limits the mobility of mercury in soil. Much of the mercury in soil is bound to bulk organic matter and is susceptible to elution in runoff only by being attached to suspended soil or humus.

  2. For these reasons mercury has a long retention time in soil and as a result, the mercury accumulated in soil may continue to be released to surface waters and other media for long periods of time, possibly hundreds years (Pirrone et al., 2001).

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