GLOBALMERCURYASSESSMENT2018GLOBAL MERCURY ASSESSMENT 2018
Copyright © United Nations Environment
Programme, 2019
Citation: UN Environment, 2019.
Global Mercury Assessment 2018. UN
Environment Programme, Chemicals and
Health Branch Geneva, Switzerland
ISBN: 978-92-807-3744-8
Disclaimer
The designations employed and thepresentation of the material in thispublication do not imply the expression of
any opinion whatsoever on the part of theUnited Nations Environment Programme
concerning the legal status of any country,
territory, city or area or of its authorities,
or concerning delimitation of its frontiers
or boundaries. Moreover, the views
expressed do not necessarily represent thedecision or the stated policy of the United
Nations Environment Programme, nordoes citing of trade names or commercial
processes constitute endorsement.
Reproduction
This publication may be produced inwhole or in part and in any form foreducational or non-profit purposes
without special permission fromthe copyright holder, provided
acknowledgement of the source is made.
Material in this report can be freely quoted
or reprinted. UN Environment Programme
would appreciate receiving a copy of
any publication that uses this reportas a source.
No use of this publication may be madefor resale or for any other commercial
purpose whatsoever without priorpermission in writing from the United
Nations Environment Programme.
Funding
The work has been funded by theGovernments of Canada, Denmark,Sweden, Norway, the Nordic Council of
Ministers and the EU.

Produced by
UN Environment Programme
Economy Division
Chemicals and Health BranchInternational Environment House
1 11-13, Chemin des Anémones
CH -1219 Châtelaine, Geneva
Switzerland
Tel: +41 (0) 22 917 12 34
Fax: +41 (0) 22 797 34 60
Email: metals.chemicals@unep.org
Website: https://www.unenvironment.org/
explore-topics/chemicals-waste
The report can be found athttps://www.unenvironment.org/exploretopics/chemicals-waste
UN Environment Programme promotes
environmentally sound practices globallyand in its own activities. This publication
is printed on paper from environmentallymanaged forests, using vegetable-based
inks and other eco-friendly practices.
Our distribution policy aims to
reduce UN Environment Programme’s
carbon footprint.
Layout and technical production
Burnthebook Design, Derby DE24 8HR,
United Kingdom (burnthebook.co.uk)
Printing
Narayana Press, Gylling, DK-8300 Odder,
Denmark (www.narayanapress.dk) a swanlabelled printing company, 541 562

‐ BACKGROUND AND MANDATE P4‐ DEVELOPING THE 2018 REPORT P5‐ SCOPE AND COVERAGE P5

2 UNDERSTANDING THE GLOBAL MERCURY CYCLE P6‐ CURRENT UNDERSTANDING AND QUESTIONS P7‐ REVISED GLOBAL AND OCEANIC TOTAL MERCURY BUDGETS P8

3 MERCURY EMISSIONS TO AIR P10‐ METHODS FOR COMPILING AN INVENTORY OF MERCURY EMISSIONS P10‐ 2015 GLOBAL ANTHROPOGENIC MERCURY EMISSIONS TO AIR P11‐ SUMMARY OF RESULTS BY REGION P12‐ BREAKDOWN OF GLOBAL RESULTS BY SECTOR P14‐ COMPARING THE 2010 AND 2015 GLOBAL INVENTORY ESTIMATES P16‐ WHERE THE EMISSIONS OCCUR P18‐ BOX: COMPARING GMA GLOBAL INVENTORY ESTIMATES WITH NATIONAL INVENTORIES P19

4 LEVELS OF MERCURY IN AIR P20‐ SPATIAL VARIABILITY IN THE SOUTHERN AND NORTHERN HEMISPHERES P21‐ REGIONAL VARIABILITY IN ATMOSPHERIC MERCURY P22‐ VERTICAL PROFILES OF MERCURY IN THE ATMOSPHERE AND THE DISTRIBUTION OF MERCURY PLUMES P23

5 ATMOSPHERIC PATHWAYS, TRANSPORT, AND FATE OF MERCURY P24‐ EMISSIONS AND DIFFERENT TYPES OF MERCURY P24‐ RESULTS FROM MERCURY MODELLING P25‐ ATMOSPHERIC CHEMISTRY P28‐ REMOVAL PROCESSES P28‐ HISTORICAL TRENDS AND FUTURE SCENARIOS P29

6 ANTHROPOGENIC RELEASES OF MERCURY TO WATER P30‐ METHODS FOR ESTIMATING GLOBAL ANTHROPOGENIC MERCURY RELEASES P31‐ GLOBAL ANTHROPOGENIC MERCURY RELEASES IN 2015 P32‐ BOX: ARTISANAL AND SMALL-SCALE GOLD MINING P32‐ SUMMARY OF RELEASES BY REGION P33‐ RELEASES FROM SELECTED SECTORS P34‐ BOX: POTENTIAL SECONDARY SOURCES OF MERCURY RELEASES P35

7 MONITORING MERCURY CONCENTRATIONS IN BIOTA P36‐ METHYLMERCURY IN BIOTA P36‐ BIOMONITORING PROGRAMS P37‐ BIOINDICATORS FOR HUMAN HEALTH P38‐ BIOINDICATORS FOR ECOLOGICAL HEALTH P39

8 UNDERSTANDING TRENDS IN MERCURY IN AQUATIC BIOTA P44‐ RECENT ADVANCES IN UNDERSTANDING MERCURY METHYLATION AND DEMETHYLATION P44‐ THE RESPONSE OF MERCURY LEVELS IN AQUATIC BIOTA TO CHANGES IN ATMOSPHERIC MERCURY CONCENTRATIONS P44‐ MERCURY IN FISH AND BIRDS IN LAKES AND COASTAL WATERS OF NORTH AMERICA P45‐ MERCURY IN FRESHWATER FISH IN FENNOSCANDIA P46‐ MERCURY IN FISH IN RESERVOIRS IN NORTH AMERICA AND EUROPE VERSUS ASIA P47‐ MERCURY IN ARCTIC ANIMALS P48‐ CAUSES OF THE MISMATCH BETWEEN ATMOSPHERIC AND AQUATIC MERCURY TRENDS P49‐ THE IMPLICATIONS OF MERCURY EMISSION REGULATIONS ON MERCURY LEVELS IN BIOTA P50

9 MERCURY LEVELS AND TRENDS IN HUMAN POPULATIONS WORLDWIDE P52‐ MERCURY AND HUMAN HEALTH P53‐ MERCURY EXPOSURE ASSESSMENT USING BIOMARKERS P54‐ MERCURY LEVELS IN HUMANS P54‐ PROSPECTS FOR ACTION P57

PHOTOGRAPHS P59

GLOBAL MERCURY ASSESSMENT 2018
CONTENTSKEY POLICY-RELEVANT FINDINGS P2
1 INTRODUCTION P4

KEY POLICYRELEVANT FINDINGSThe Global Mercury Assessment 2018 is the fourth such assessment undertaken by The United Nations
Environment Programme (UN Environment), following earlier reports in 2002, 2008, and 2013. It is
the second assessment produced by UN Environment in collaboration with the Arctic Monitoring andAssessment Programme (AMAP). The assessment is supported by a technical background document, thechapters of which have been prepared by teams of experts and peer-reviewed for scientific quality. Thissummary document presents the main findings of the technical document in plain language. Recognizing
the relevance of the results of the Global Mercury Assessment 2018 for policy makers, this section presents
key findings of highest policy relevance.

A new global inventory of mercury emissions to air fromanthropogenic sources in 2015 quantifies global emissions
from 17 key sectors at about 2220 tonnes. There are also smaller
anthropogenic sources that are not yet possible to quantify in the detailed
global inventory. Emissions from these additional sources are evaluatedto total on the order of tens to hundreds of tonnes per year. They would
therefore not significantly change the total global emissions inventory
but may be of local or regional significance.

1

2

3

4

Emissions patterns in 2015 are very similar to those in 2010.
The majority of the 2015 emissions occur in Asia (49%; primarily
East and South-east Asia) followed by South America (18%) and
Sub-Saharan Africa (16%). Emissions associated with artisanal and smallscale gold mining account for almost 38% of the global total and are themajor contributor to the emissions from South America and Sub-SaharanAfrica. In other regions, emissions associated with energy production
and industrial emissions predominate.

2

Estimated global anthropogenic emissions of mercury to
the atmosphere for 2015 are approximately 20% higher thanthey were in updated estimates for 2010. Continuing action to
reduce emissions has resulted in modest decreases in emissions in North
America and the European Union. Increased economic activity, notably
in Asia, and the use and disposal of mercury-added products appears tohave more than offset any efforts to reduce mercury emissions.

Stationary combustion of fossil fuels and biomass is responsible
for about 24% of the estimated global emissions, primarily fromcoal burning (21%). Main industrial sectors remain non-ferrous
metal production (15% of the global inventory), cement production (11%)
and ferrous metal production (2%). Emissions from waste that includes
mercury-added products comprise about 7% of the 2015 global inventory.

Human activities have increased total atmospheric mercury
concentrations by about 450% above natural levels. This
increase includes the eff ects of mercury emitted from humansources in the past which is still circulating in the biosphere, known aslegacy mercury. Historical emissions up to the end of the 19th century,
mainly from gold and silver mining in the Americas, and mercury(cinnabar) mining and refining contributed more to the present-day
anthropogenic mercury in soils and the oceans than all 20 th century
industrial sources combined. The presence of legacy mercury and thepotential for climate change to influence its remobilization complicates
our ability to assess potential future changes.

56Natural production of methylmercury in the oceans and in somelakes is often not limited by the input of inorganic mercury.
Other factors such as climate change and changes in terrestrial andaquatic ecosystem processes are playing increasingly important roles in
the mercury cycle, affecting the distribution, chemical interactions andbiological uptake of mercury in the environment.

7

8

9

10

Mercury loads in some aquatic foodwebs are at levels ofconcern for ecological and human health. Anthropogenic
mercury emissions and releases, current and legacy, are the major
contributors to increased mercury levels and exposure.

The Global Mercury Assessment 2018is based on improved informationfor estimating emissions and releases
and improved understanding of themercury cycle in the environment. In
addition, the 2018 report provides
new information about mercury
exposure in animals and humans. These
improvements are the result of mercury
research and monitoring around theworld. They provide a strong base ofknowledge to support actions to reduce
mercury emissions and releases and to
reduce ecosystem and human exposure.

Artisanal and small-scale gold mining introduced about
1220 tonnes of mercury into the terrestrial and freshwater
environments in 2015, but this amount cannot be reliably
separated between discharges to soils and releases to water.
Global releases of anthropogenic mercury from other sources to aquatic
environments totalled about 580 tonnes in 2015. The major sectors
contributing to these 580 tonnes are waste treatment (43%), ore mining
and processing (40%), and energy (17%).

Reductions in mercury emissions and resulting declines inatmospheric concentrations may take time to show up as
reductions of mercury concentrations in biota. For some time
to come, methylmercury will continue to be produced from the legacy
mercury previously deposited into soils, sediments, and aquatic systems.

All people are exposed to some amount of mercury.
For many communities worldwide, dietary consumption offish, shellfish, marine mammals, and other foods is the mostimportant source of methylmercury exposure. Exposures to elemental
and inorganic mercury mainly occur in occupational settings (including
artisanal and small-scale gold mining) or via contact with products
containing mercury. There remains high concern for vulnerable groups
including some indigenous populations and other populations with highdietary or occupational exposure to mercury.

Further improvements in our
understanding of mercury can further
reﬁne the ability to identify eﬃcientactions to reduce mercury pollution andits eﬀects. Such improvements include
basic research on aspects of the mercury
cycle as well as systematic monitoring
methods to expand the geographic
coverage of measurements of mercury
pollution. As a chemical element,
mercury cannot be destroyed. Mercury
removed from fuels and raw materials
in order to reduce emissions will result
in mercury-contaminated waste, which
in turn can be a source of releases.

Mercury removed from emissions andfrom releases must still be managed
responsibly to avoid it becoming a waste
management problem or a secondary
source. Understanding how mercury
removed from current uses and sources
is currently managed and how it canbe safely managed and stored in the
future will help account for the fulllife-cycle of mercury that is mobilized
through human activity, safeguarding
the environment and humans when
it is removed.

3

1 INTRODUCTION
4

Background and mandate
Global inventories for mercury emissions to air from humansources have been produced at approximately five-year
intervals since 1990 by scientific groups. The United Nations
Environment Programme (UN Environment) produced its first
Global Mercury Assessment in 2002 and subsequent reports
in 2008 and 2013. These reports have provided the scientificbasis for the negotiations that resulted in the Minamata
Convention on Mercury, which was adopted in October 2013
and entered into force in August 2017.
This report constitutes the Global Mercury Assessment 2018
(GMA 2018). Its findings are supported by the TechnicalBackground Report to the GMA. The GMA 2018 has been
prepared in response to a request from the Governing Councilof UN Environment (now the UN Environment Assembly)
in 2013 to update the Global Mercury Assessment 2013
(GMA 2013) for delivery no later than 2019.

Cyril Villemain/UN Environment

Developing the 2018 Report

Scope and coverage

As in 2008 and 2013, the Technical Background Reportto the GMA forms the basis for the statements madein this report and is fully referenced according tostandard scientiﬁc practice. As such, it is the single
reference for this GMA 2018 Report. It has again been
prepared in co-operation with the Arctic Monitoringand Assessment Programme (AMAP). The chapterson emissions to air and releases to water use bothnational and independently compiled global data on
activity levels to derive estimates of emissions andreleases using a standardized methodology. As such theresulting estimates are not oﬃcial national estimates.
Contributions have also been incorporated from the UN
Environment’s Global Mercury Partnership, in particular
its partnership areas on mercury in artisanal and smallscale gold mining, and mercury air transport and fate;
the AMAP mercury expert group; the UN Economic
Commission for Europe Convention on Long-range
Transboundary Air Pollution groups; industry; and nongovernmental organizations. Each chapter was preparedby a team of experts and then reviewed to ensure its
scientiﬁc accuracy. The evaluation of information on
mercury levels in humans is a new component of GMA
2018 and beneﬁts from contributions from experts fromthe World Health Organization (WHO).

This update to GMA 2013 provides the most recent information
available for the worldwide emissions to air, releases towater, and transport of mercury in atmospheric and aquatic
environments. In this report, “mercury” refers to the chemicalelement in all forms, in contrast to the Minamata Convention,
which distinguishes “mercury” from “mercury compounds.” To
the extent possible, the information comes from the publishedscientiﬁc literature, supplemented where necessary by othersources. Since the GMA 2018 is intended as a basis for decision
making, emphasis is given to anthropogenic emissions (mercury
going into the atmosphere) and releases (to water), that is, those
associated with human activities.
The report reﬂects progress made by the scientiﬁc community,
national authorities and organisations in better understanding
mercury cycling (Chapter 2), atmospheric mercury emissions(Chapter 3), mercury levels in air (Chapter 4), atmospherictransport and fate (Chapter 5), releases to water (Chapter 6),
and the cycling and methylation of mercury in the aquatic
environment (Chapter 8). In addition to updating GMA 2013,
new sections are included on observed levels of mercury inbiota (Chapter 7) and observed levels and trends of mercury inhumans (Chapter 9).
Technical Background Report chapters prepared by teams ofexperts were subject to peer and national review to ensure theirscientiﬁc validity. This GMA 2018 Report is based on the content
of the Technical Background Report and has been reviewed
by the authors of the Technical Background Report. It was also
circulated for national review.

5

UNDERSTANDING
THE GLOBAL MERCURY CYCLE

Mercury is emitted to the atmosphere and released towaters and land as a result of anthropogenic or humanactivities, and from natural sources and processes such as
volcanoes and rock weathering. Mercury in the air can be
carried around the world, eventually being deposited onto
soils, waters, or plants. From there, mercury can re-volatilize
into the air, or be transported further by water, or be taken
into the food web. Over the course of centuries or longer,
mercury is removed from this global cycle through burial
in deep ocean sediments, lake sediments, and subsurface
soils. Only a minute fraction of the mercury present in theenvironment is methylmercury, a toxin of high concern thatbiomagnifies in the food web. Methylmercury is produced
from inorganic mercury, mainly in aquatic ecosystems
through microbial action. An improved understanding of
the global mercury cycle is important for predicting how
efforts to reduce mercury emissions to air and releases towater and land will affect mercury concentrations in theenvironment, including biota and humans.

Volcanically active areas
are natural sources of
mercury emissions.

Rui Serra Maia/Shutterstock.com

6

Current understanding and questions

Since The GMA 2013 wascompleted, new studies of New
World mining emissions fromthe 16th century onwards, andre-examination of mercury
proﬁles in lake sediments andpeat bogs, have shown thathuman inﬂuence on the global
mercury cycle began well before
the start of the Industrial Age.
Previous assessments often
used 1850 as the starting point
for gauging human eﬀects on
mercury levels worldwide.
There is not yet agreement on
the earlier time that should
be used instead, but it is clearthat current atmosphericconcentrations of mercury
are several times higher than“natural” levels.
In the terrestrial system,
soils globally are likely tocontain more anthropogenic
mercury than was estimatedMartin Fortier/ArcticNet

The GMA 2013 estimatedthat anthropogenic activities
cumulatively had increased
atmospheric mercury
concentrations by 300-500%
over the past century. Mercury
in surface ocean waters lessthan 200 metres deep had
approximately tripled in thesame period. Deeper waters
exhibited smaller increases
because anthropogenic inputs
take longer to reach the isolated
water masses of the deep ocean.
Substantial amounts of mercury
were already naturally present insoils worldwide, so the additionof anthropogenic mercury
has also made only a modest
diﬀerence there in terms of total
storage. Mercury from historicalhuman activities now in soils
and oceans acts as a reservoir bybeing available for re-emissions
to air, maintaining atmosphericmercury concentrations at
higher levels than would be thecase only from current emissions.
previously. For the oceans, newmodels diﬀer signiﬁcantly intheir conclusions. Becausemuch of the risk of mercury
contamination for humans andwildlife comes via marine foodwebs, it is important to improvethe understanding of the role ofanthropogenic mercury in thesea. The models diﬀer primarily
in their estimates of themercury delivered to the ocean
as a result of New World silver
and gold mining between the
16th and late 19th centuries, andin their estimates of how muchnatural mercury was alreadypresent in the oceans.
The total amount of mercury
currently in the environment
reﬂects a mixture of sources:
historical anthropogenic
releases to air, land and oceans;historical natural inputs; andcurrent anthropogenic andnatural releases. The inﬂuenceof historical silver mining on
the oceanic mercury budget isparticularly important in thisregard. How much was emitted
to air or released to water is the
crucial question. Recently, a
new historical study examined
mercury importation andconsumption during colonial
silver mining in what are now
Mexico, Peru, and Bolivia.
Lake sediment proﬁles near
the mining operations show
substantial increases in mercury
during the mining era. Outside
this region, however, the global
record in lake sediments, peatbogs, and glacier ice shows anegligible impact from colonial
mining, suggesting a far moremodest role for anthropogenic
contamination in that period
than was assumed in previous
emissions inventories
and models.

Loss of sea ice in the
Arctic due to climatechange allows greater
exchange of mercury
between the oceans andthe atmosphere.

7

Revised global and oceanic total mercury budgets
Removal of anthropogenic
mercury from the world’s
oceans will take many
decades to centuries, varying
substantially between
diﬀerent ocean basins. In
the shorter term, mercury
in seawater and marine foodwebs is likely to increase
even at current levels ofanthropogenic emissions
and releases, simply becausesome of the legacy mercury
from soils will continue tobe carried by rivers to thesea and to be re-volatilized
into the air. Regardless of thetimeline, however, emissions
reductions are required toreverse the trend in oceanic
anthropogenic mercury backtowards natural levels.

system. Most of the changes
from the GMA 2013 are
relatively small, though theemissions from soils andvegetation are notably lower
than the previous average.
Based on this revised global
budget, the mercury budget
in the world’s oceans was
updated as well.

With these new ﬁndings
in mind, recent modellingindicates that mining sincethe 16th century accounts
for about two-thirds of allanthropogenic mercury
currently in the oceans. Thismercury entered the oceans
prior to 1920. The remaining
third of anthropogenic
mercury inputs to oceans
have come since then, mainly
from coal combustion andother industrial activities.
The results of this model
are consistent with otherestimates of the amountof anthropogenic mercury
in the world’s oceans. The
new information has beenused to create a revised total
mercury budget for the GMA
2018, showing the storesand movement of mercury
in the global environmental

The uncertain role ofhistorical mining on global
anthropogenic mercury
levels, combined withlimited understanding ofsome basic oceanographic
processes, makes it diﬃcult
to assess how quickly
mercury levels in the ocean
will respond to emission
reductions. All the models
predict that the marine
response will be much slower
than that of the atmosphere.

Atmosphere:
4400 (450%)

500

600

1000

The updated global mercury
budget shows the impact ofhuman activities on the mercury
cycle and the resulting increase
in mercury accumulated in soils
and oceans.

Net evasion (gaseous
elemental mercury)2500(2000-3000)

Deposition
to land/freshwater

Deposition
to oceans

3600

3800

3400
(2900-4000)(250%)

Biomassburning

Geogenic

Soil andvegetation
Anthropogenic

310%
600

Best estimates of mercury stored and cycling through the global environment

810Anthropogenic mercury emissions and releases (tonnes per year)

10

Natural mercury emissions and releases (tonnes per year)

10

Re-emission/re-mobilization (natural and legacy mercury, tonnes per year)

100

Amount of mercury stored, tonnes(%)

Percentage increase in mass due to human activities

300 (130

Surface ocean: 2600 (230%)%)

Intermediate waters:
120 000 (25%)
Deep waters:
190 000 (12%)

100
Geogenic

Particle removal

Mineral soils: 800 000

RiversNet vertical transport

Organic soils: 150 000 (15%)

The Stephen Low Company

Hydrothermal vents on thesea floor release mercury to
deep ocean waters.
The amount of mercury
removed by burial in deep ocean
sediments is small compared tothe amounts currently depositedat the surface of the ocean. This
leads to a build up of mercury inocean waters.

ATMOSPHERE

800 + 3600 tonnes

Rivers

740

90
210

100

Transfer (tonnes per year), mercury fromnatural sources

100

Transfer (tonnes per year), mercury fromanthropogenic sources

2700
730

3100

SURFACE OCEAN

340

780 + 1800 tonnes
230

760

PARTICULATEORGANIC MATTER

80

60

280

INTERMEDIATE& DEEP OCEAN

90

257000 + 53000 tonnes

210

620

140

Coastal sediments

PARTICULATEORGANICMATTER

180

420

100
Hydrothermal
Deep ocean sediments

9MERCURY
EMISSIONS TO AIR

Industrial activities to produce power
and other commodities, together witha range of intentional uses of mercury
in processes and products, result inanthropogenic emissions of mercury to
the atmosphere. Stationary combustionof fossil fuels, especially coal, andhigh temperature processes involved
in industrial activities such as metalsmelting and cement production giverise to emissions as a by-product. The
use of mercury-added products such as
lamps, batteries, and dental fillings also
result in mercury emissions to air (andreleases to water), largely during waste
disposal. Mercury is also used in industrial
processes such as chlor-alkali production.
The predominant intentional use of
mercury is in artisanal and small-scale
gold mining where mercury is used to
extract gold from gold-bearing sediments

and rocks. Of these sources, stationary
combustion of coal and artisanal gold
mining are estimated to be responsible foralmost 60% of emissions to air in 2015.

Methods for compilingan inventory of
mercury emissions

The method employed to produce the 2015
global inventory of anthropogenic emissions
to air is essentially the same as that used in
the 2010 inventory reported in GMA 2013.
The method applies a mass-balance approachto derive emissions estimates that considers:As part of the work to prepare GMA 2018,a new global inventory of anthropogenic
mercury emissions to air has been produced,
for the target year 2015. This inventory
addresses emissions from identiﬁed sectors
and activities. The inventory includes threesectors not previously quantiﬁed: biomass
combustion (for energy production),secondary steel production, and mercury
emitted during production of vinyl chloride
monomer, a raw material for PVC-plastics.
Additional, though smaller, sectors have been
identiﬁed that are not yet possible to fully
quantify in global emission inventory work.

10

Mercury emissions to air have changed
over time. Historically gold and silvermining have been major sources of
mercury emissions and releases. With
the advent of the industrial revolution(ca. 1850s) and the subsequent rise offossil fuel economies, mercury emissions
increased. Emissions remain high,estimated at around 2000-2500 tonnes
per year so far in the 21st century. Theseemissions give rise to global pollution,
including long-range transport to remoteregions, with associated concerns
for impact on health of wildlife andhuman populations.

• the amounts of fuels and raw materials used,or commodities produced (activity data);• the associated mercury content of fuels
and raw materials and the types of process
involved (reﬂected in ‘unabated’ emissions
factors); and• technology applied to reduce (abate)emissions to air (through technology proﬁlesthat reﬂect the degree of applicationand the degree of eﬀectiveness of air
pollution controls).

In addition to the improvements inemission inventory methodology,
improved information on nationalemissions have been made available fromnational research and inventory eﬀorts
in many countries.

Methodological improvements applied in the GMA 2018
SectorChange(s) in methods or data

Coal burning

Updated technology proﬁles
Separation of coal burning by industry sector

Biomass burning

Quantiﬁed for the ﬁrst time

Cement production

Separation of emissions from diﬀerent steps incement production

Primary iron and steel
productionMore details on the individual steps in production
Separation of coal burning from other steps

Secondary steel production

Quantiﬁed for the ﬁrst time

Copper, lead, and zincproduction

Better data on mercury levels and emission rates
Separation of coal burning from other steps

Aluminum production

Better data including new emission factors

Large-scale gold production

Better data on emission reductions in some countries

Oil refning

Minor adjustments to mercury content in oilfrom diﬀerent countries

Vinyl-chloride monomer
production

Quantiﬁed for the ﬁrst time

Waste disposal andincineration

Mercury assumed to be released continuallyMore detailed assessment of emissions and technology

Crematoria emissions

Updated data on dental ﬁllings and cremation rates

Artisanal and small-scale
gold mining

Improved information globally, especially fromSouth America
Revised methodology on emission rates associatedwith diﬀerent practices

2015 global anthropogenic
mercury emissions to air
The global inventory of mercury emissions to the atmospherefrom anthropogenic sources in 2015 is estimated to be 2220
tonnes. Such emissions account for about 30% of mercury
emitted annually to the atmosphere. A further 60% of current
global mercury emissions to air result from environmental
processes, much of which involves recycling of anthropogenic
mercury previously deposited to soils and water. The
remaining 10% comes from present-day natural sources suchas volcanoes. This global inventory total for 2015 does notinclude sectors that cannot yet be reliably quantiﬁed. These
unquantiﬁed sectors may add tens to a few hundred tonnes of
mercury to the actual emission inventory total.
The 2015 inventory is consistent with the GMA 2013 statementthat global emissions to air in the ﬁrst part of the 21st century
from principal anthropogenic sectors are of the order of

2000-2500 tonnes per year. Uncertainties associated with the2015 inventory estimate of 2220 tonnes give an approximate
range to this estimate of anthropogenic emissions of 20002820 tonnes. The emissions total for 2015 is higher than it wasfor 2010, when the same methods are applied in both cases.
The increase has several explanations. Some are associated withimproved information. Others, such as increased emissions
from some industrial sectors, appear to be largely due toincreased economic activity in some regions, notably East
Asia. Emission increases have to some extent been oﬀset bydecreases in coal use and installation of sulphur dioxide andmercury control technologies in China. Updated estimatesof emissions for 2010 also incorporated ﬁnal activity data for2010 from key sources including the International Energy
Agency. The resulting updated total inventory of 1815 tonnes
for 2010 is somewhat lower than the 1880 tonne estimate
presented in GMA 2013.

11

savva_25/Shutterstock.com

The artisanal and small-scale gold mining
and mercury-added product sectors
employ variations on this approach. A
variety of improvements have been madein the way this method has been applied,generally reﬂecting improvements
in available information. The method
used to spatially distribute the global
inventory to point and distributed
sources across the globe has also been
upgraded as part of GMA 2018. These newdevelopments allow national estimates
to be mapped at a ﬁner geographicalresolution for use in modelling work.

Summary of results by region
Regional (i.e., sub-continental)
contributions to the global inventory
in 2015 are very similar to thoseof 2010. The majority of emissions
occurred in Asia (49%, of which
39% in East and South-east Asia),
followed by South America (18%)
and Sub-Saharan Africa (16%).
The consistency in the regional
distribution of emissions
indicates that these patterns arerobust and not inﬂuenced to
any undue extent by changes inmethodology or the addition of
more sectors since GMA 2013.
It is noteworthy that artisanaland small-scale gold mining(ASGM) accounts for about 70%
and up to 80% of the emissions fromSouth America and Sub-SaharanAfrica, respectively.

Regional breakdown of global
emissions of mercury to air fromanthropogenic sources in 2015.

East and Southeast Asia
South America
Sub-Saharan Africa
South Asia
CIS & other European
countries
EU28
Middle Eastern States
Central America
and the Caribbean
North America
North Africa
Australia, New
Zealand & Oceania

If emissions associated with artisanaland small-scale gold mining are set aside,
the East and South-east Asian region
remains responsible for the largest shareof emissions (47% of the remaining total),with South Asia responsible for a further
16%. Sub-Saharan Africa and the former
Soviet Union (CIS) and other European
countries outside the European Union,
between them, contribute a further
16% of emissions, with the non-ferrous
metals industry as the main source. In
the remaining regions of the world, coal

combustion still accounts for the majorpart of the emissions in North America(almost 60%), the European Union (EU)(over 50%) and Australia, New Zealandand Oceania (37%). In the Middle EasternStates and North Africa, the cement
industry is the principle source ofemissions (43% and 52% of the regional
totals, respectively). Sources associatedwith wastes from mercury-added products

account for approximately 10-20% ofemissions in most regions, somewhat
higher in North Africa (27%) and lower
in the EU, East and South-east Asia, SouthAmerica, and Sub-Saharan Africa regions.

Sector group (emissions, tonnes)

Regional total(range),tonnes% of global
total

Quantities of mercury emitted to air
from anthropogenic sources in 2015,
by different sectors in different regions.

All percentage contributions need
to be considered in relation to thetotal (absolute) amounts of mercury
emitted in each sub-region.

Intentional-use
Artisanal and small(including
scale gold mining
product waste)

Fuelcombustion

Industry
sectors

Australia, New Zealand & Oceania

3.57

4.07

1.15

0.0

8.79 (6.93-13.7)

0.4

Central America and the Caribbean

5.69

19.1

6.71

14.3

45.8 (37.2-61.4)

2.1

CIS & other European countries

26.4

64.7

20.7

12.7

124 (105-170)

5.6

East and Southeast Asia

229

307

109

214

859 (685-1430)

38.6

EU28

46.5

22.0

8.64

0.0

77.2 (67.2-107)

3.5

Middle Eastern States

11.4

29.0

12.1

0.225

52.8 (40.7-93.8)

2.4

North Africa

1.36

12.6

6.89

0.0

20.9 (13.5-45.8)

0.9

North America

27.0

7.63

5.77

0.0

40.4 (33.8-59.6)

1.8

South America

8.25

47.3

13.5

340

409 (308-522)

18.4

South Asia

125

59.1

37.2

4.50

225 (190-296)

10.1

Sub-Saharan Africa

48.9

41.9

17.1

252

360 (276-445)

16.2

Global inventory

533

614

239

838

2220 (2000-2820)

100.0

12

Comparison of regional results

Australia, New Zealand& Oceania

North Africa
Stationary Combustion

Central America andthe Caribbean

North America

Industry
Intentional Use
ASGM

CIS & other
European countries

East andSoutheast Asia

South America

South Asia

Sub-Saharan Africa
EU28

Middle Eastern States

Larry C. Price

The relative pattern of regional
contributions from the major sector
categories to the global mercury
inventory is heavily influenced byemissions from artisanal andsmall-scale gold mining.

13

Nyani Quarmyne/Panos Pictures/Felix Features

TFoxFoto/Shutterstock.com

indu

al d

in g

om

est

do

me

s ti

min
old
le g
sca
all -

ic

s tr y

sca

el
s te
ar y nin g ldi
nc o ion e fee
S e du c t O il r d s t
o
n
r
a
p
n
ry
ir o
rcu
Pig
Me

old

lants

n
Non-ferrous metal produc tio

La

en t

r ge

C em

14

sm
is a
Ar t

c

le g

p ower p

co

rn

er

ry coalc o al

ry

bu

oth

S tationa

nar y

na

ss

te
Was

S tatiot io

as r yt
dg
an t u so il an in dr y pl g
na e r int io ow urn
S t a in g p s s b
rn abu Biom

S ta

ma

an d

ss
Bio

nal

Cremation
Was te incinerationcell)
Chlor-alkali (Hgomerride monVinyl chloma

Proportions of global
emissions of mercury to air fromdifferent anthropogenic source
sectors in 2015.

Bio

As with the regional breakdown,
the breakdown of 2015
anthropogenic mercury
emissions by sectors is very
similar to that of 2010. The
predominant source sector is
artisanal and small-scale gold
mining (about 38%) followed bystationary combustion of coal(about 21%). These are followedby emissions from non-ferrous
metal production (about 15%)and cement production (about11%). Emissions associatedwith disposal of mercuryadded product waste (7%),
stationary combustion of otherfuels including biomass (3%),
ferrous-metal production (2%),
and other sources (2%) makeup the rest.

in g

Breakdown of global
results by sector

r.classen/Shutterstock.com

Kemal Jufri/Panos Pictures/Felix Features

Quantities of mercury emitted to air from anthropogenic sources in 2015, by different sectors.

Mercury emission(range), tonnes

Sector

Sector %of total

Artisanal and small-scale gold mining (ASGM)

838 (675-1000)

37.7

Biomass burning (domestic, industrial and power plant) *51.9 (44.3-62.1)

2.33

Cement production (raw materials and fuel, excluding coal)

233 (117-782)

10.5

Cremation emissions

3.77 (3.51-4.02)

0.17

Chlor-alkali production (mercury process)15.1 (12.2-18.3)

0.68

Non-ferrous metal production (primary Al, Cu, Pb, Zn)

228 (154-338)

10.3

Large-scale gold production

84.5 (72.3-97.4)

3.8

Mercury production

13.8 (7.9-19.7)

0.62

Oil reﬁning

14.4 (11.5-17.2)

0.65

Pig iron and steel production (primary)

29.8 (19.1-76.0)

1.34

Stationary combustion of coal (domestic/residential, transportation) 55.8 (36.7-69.4)

2.51

Stationary combustion of gas (domestic/residential, transportation)

0.165 (0.13-0.22)

0.01

Stationary combustion of oil (domestic/residential, transportation)

2.70 (2.33-3.21)

0.12

Stationary combustion of coal (industrial)

126 (106-146)

5.67

Stationary combustion of gas (industrial)

0.123 (0.10-0.15)

0.01

Stationary combustion of oil (industrial)

1.40 (1.18-1.69)

0.06

Stationary combustion of coal (power plants)

292 (255-346)

13.1

Stationary combustion of gas (power plants)

0.349 (0.285-0.435)

0.02

Stationary combustion of oil (power plants)

2.45 (2.17-2.84)

0.11

Secondary steel production *10.1 (7.65-18.1)

0.46

Vinyl-chloride monomer (mercury catalyst) *58.2 (28.0-88.8)

2.6

Waste (other waste)

147 (120-223)

6.6

Waste incineration (controlled burning)

15.0 (8.9-32.3)

0.67

Total

2220 (2000-2820)

100

Colour coding indicates main sector groups(Stationary combustion, dark blue; Industry, light blue; Sectors associated with Intentional use,
dark orange; ASGM, light orange).
* Sectors included for the first time in the 2015 inventory.

15

Comparing the 2010 and 2015 global inventory estimateshigher than they were in 2010. Continuing
action to reduce emissions has resulted
in modest decreases in emissions in someregions and some sectors, but increasing
emissions are seen in most other regions.
Increased economic activity, as reﬂected in
activity data, seems to be a major factor in
driving up emissions associated with certain
industrial sectors in a number of regions. In
this respect, diﬀerences between 2010 and2015 may also reﬂect recovery following
the ﬁnancial crisis in 2008 that may haveinﬂuenced global emissions in 2010. These
factors appear to have more than oﬀset any(technological) eﬀorts to reduce mercury
emissions in most regions.

As a ﬁrst step in trying to gain a reliableinsight into whether apparent changes
in emissions patterns between 2010 and2015 represent real changes in emissions,an updated 2010 inventory was preparedusing the same emission factors, abatement
technology, and sources of data on activity
levels as were used for the 2015 inventory, as
well as inclusion of a retrospective emission
estimate for most of the sectors newly
introduced in the 2015 inventory. For somecountries, activity data for 2010 were also
updated with respect to those applied in theoriginal 2010 inventory presented in the
GMA 2013. Changes in inventory methods
from one assessment to the next complicatecomparisons between inventories produced
at diﬀerent times, and make it impossible tocompare the 2010 and 2015 inventories withthose prepared for earlier years.

Changes inemissions from 2010
to 2015 (tonnes)
from different
sectors (columns) indifferent regions(rows). Increases areshown in orange anddecreases in blue.
Size of coloured bars
indicate thepercentage change.

Mercury emissions to air have decreased
between 2010 and 2015 in two of the elevenworld regions: North America and the EU.
In the case of North America in particular,
shifts in fuel use (from coal to oil/gas) in theenergy sector, combined with introductionof control measures that have high eﬃciency

Estimated global emissions of mercury
to the atmosphere from anthropogenic
source in 2015 are approximately 20%

Ar

tis

an
al

an

ds
go malld l-smi canin le
g

Bio
ma
s

Ce
sb
ur
nin
g

Cr
em
me
ati
nt
on
pr
em
od
iss
uc
ion
tio
n
s

Ch

lor
(m alka
erc li p
ur rodyp u
roc ctio
es n
s)

No
n-f
err
pr ousod m
uc eta
tio l
n

Pr
im
ar
y

Me
rge
rcu
-s
ry
pr caleprood g
duuc old
cti
tio
on
n

La

Oil
re

fin
ing

Do
me
iro
co stic
al /rena
co sid
pr nd
mb e
od s
uc teeus ntia
tio l
tio l
n
n

0

0.004

0.063

-0.0190-0.0160.029

0-0.005-0.005-0.009

2.22

0.128

0.247

-0.119

0

-1.75

3.64

1.92

0.001

0.023

0.027

0.675

0.077

1.58

0.055

-0.221

1.55

5.61-0.635

0.018

0.155

-0.668-30.2-0.63131.8-0.486

0

83.0

-2.82

0.338

0.681

1.77

3.25

0

0.256

-1.36

-0.582

-2.98

-1.34

0.172

0

-0.0360.090-0.6080.225-0.0902.78-0.002

0

0.092

0.362

0

0.017

0.109

-0.5740-0.0060.499-0.0005

0-0.6690.602-0.034-0.025-0.02400-0.0380.607-0.034-0.91-0.029

0.076

0

0.064

0.017

-0.181

163

0.224

1.00

-0.195

0.106

-1.14

1.24

0

-0.006-0.157

0.009

3.38

1.12

6.31

0.241

-1.88

2.00

-0.035

0

0.537

1.12

-0.809

19.9

1.35

3.03

-0.0026

0

-3.88

2.54

0

-0.008-0.041

0.906

159

2.39

46.5

-1.14

-5.89

77.8

11.4

1.59

1.24

3.06

1.34

Australia, New Zealand & Oceania
Central America and the Caribbean
CIS & other European countries
East and Southeast Asia
EU28
Middle Eastern States
North Africa
North America
South America
South Asia
Sub-Saharan Africa
Total

16

to reduce mercury emissions at major
point sources appears to be a major factor.
In all other regions, however, mercury
emissions increased.

Emission, tonnes
2500

Higher global emissions in 2015 thanin 2010 were estimated for some large
source sectors: cement production, coal
combustion in power plants, non-ferrous
metal production, primary iron and steel
production, and waste associated withmercury-added products. The chlor-alkaliindustry is the only sector for whichemissions are estimated to have decreased
signiﬁcantly between 2010 and 2015.
The 6 tonne reduction in chlor-alkali
emissions, however, is dwarfed by the
200 tonne increase from other sectors, notcounting artisanal and small-scale gold
mining. In that latter sector, estimatedemissions for 2015 are 158 tonnes higher
than in 2010, largely due to improved
information about the use of mercury inthat sector, especially in South America.

ial
ial
nt
nt
n
n
ide
ide n
t io
s
s
t io
us
us
/re tion/re stio
b
b
c
c
i
i
m
s t uss t buom t r y
co tr yme mb
me oms c usal us
G a in d
D o il c o
D o as c
C o in dinoing
0.00010.00550.012

0.0001

Changes in global
emissions of mercury to air
from anthropogenic sourcesin 2015 in relation to 2010 indifferent regions.

2000

1500

Sub-Saharan Africa
1000

South Asia
South America
North America
North Africa
Middle Eastern States

500

EU28
East and Southeast Asia
CIS & other European countries
Central America and the Caribbean
Australia, New Zealand & Oceania

0

on
s ti
bu r ymt
c o usO il in d
in

n
t io
us n t sbalm
co r p
al we
C o poin-0.007-0.3622015

2010(updated)

l
n
on
tee
t io
s t i an t s
us an t s
ys
r
u
b
l
l
a
mb p
om r pnd ionc o wers c weco c tS e r o du
Ga p oO il p oininp0.00050.001-0.004)al t eno s waspt iosradi c ten
ts e roduia p
in c e d )r w r ys t e t r o ll
he rcu
a
t
O e
W on
(m
(c
0.246

0.086

% change
Increaset
ToalOver 50

0.021

10 – 500-0.0006

0.613

0.0003-0.067-0.7540.0008-0.013

0.042

1.00

0.005

7.16

1 – 10-0.0023-0.011-0.882-0.0002-0.021-0.651-0.0035-0.040

0.139

4.37

0.071

11.5

0.5 – 10.0067

0.036

-4.22

0.0048

-1.30

19.2

0.012

-0.085-0.306

3.88

1.11

163

0.1 – 0.5
-0.0076-0.038-0.136-0.0009-0.059-1.12-0.012-0.095-0.121-2.26-0.770-11.0<0.1
0.00320.075-0.2930.0035

0.005

0.334

0.011

0.010

0.265

3.30

0.063

6.69

0.0009-0.0004-0.0007-0.0003-0.033

0.282

0.002

0.044

-0.009

2.21

0.007

2.85

Decrease-<0.1
0.0008-0.022-0.5590.0022-0.085

-6.25

0.017

-0.009

0.125

-2.92

-1.11

-11.2

-0.1 – -0.5
0.0005

0.009

0.123

-0.0008-0.069

1.08

0.003

0.032

0.003

0.164

0.0009165-0.5 – -1
0.0005

0.009

8.37

-0.0015-0.01816.9-0.002

0.009

0.335

11.4

0.036

49.2

-1 – -10
0

0.013

0.206

0.0007

0

-4.59

0.001

0.008

-0.011

10.5

0.044

29.9

-10 – -50
0.0029

0.077

3.24

0.0079

-1.65

24.1

0.030

-0.136

0.458

32.0

-0.451

413

Over 5017

Where the emissions occur
The regional breakdown of emissions shownon previous pages is a ﬁrst step in analyzing
global patterns of mercury emissions. But
the regions are large, and the precise locationof the actual emissions may have large
implications for transport and fate of themercury. For example, mountain ranges andweather patterns can aﬀect air movement,
and so the same amount of mercury
emitted in one place may be transported ina diﬀerent direction from mercury emitted

a relatively short distance away. Finerscale distribution of mercury emissions isnecessary for modeling mercury distribution
and deposition around the world. As
can be seen in the map below, mercury
emissions vary greatly from place to place
within each region. Data of this kind help
explain diﬀerences in atmospheric mercury
measurements at diﬀerent monitoring
stations, as well as patterns in mercury
deposition around the world.

Spatially distributed
emissions in 2015.

Total mercury, g per km2
0.001 0.005 0.01 0.05

0.1

0.5

1

5

10

100

500

1000 5000 10000

aapsky/Shutterstock.com

018

Comparing GMA global inventory estimateswith national inventories
The target for the GMA 2018 air emissions inventory
activity remains the production of a robust global
inventory for the target year of 2015, for a deﬁned set of
sectors for which reliable global estimates can be produced.
Although it presents emission estimates broken down
by sector for each of some 200 countries, the applied
methodology is directed at a global/regional- rather thannational-level application.
A major new development since GMA 2013 is that morethan 150 countries are engaged in preparing new national
inventories or national emission/release estimates, manyof these associated with the Minamata Initial Assessments(MIAs) or Minamata National Action Plans. Many countries
have started developing national action plans on artisanaland small-scale gold mining, including establishing baseline
data for this sector. The preparation of national inventories
and estimates allows increased possibilities for comparing
the global and nationally derived emissions estimates.
In general, the GMA inventory estimates of nationalemission totals agree fairly well with available nationallyreported values prepared in response to reporting
obligations for the UN ECE Convention on Long-range
Transboundary Air Pollution or the Minamata Convention,
but there can be signiﬁcant diﬀerences on the sector level.
These diﬀerences are often associated with the way sectors
are deﬁned and emissions attributed to diﬀerent sector
categories and activities.
They may also be due to methodological diﬀerences in
the approach employed to estimate emissions, or use of
diﬀerent years of (activity) data. Preliminary comparisonswith the few MIAs that were available at the time of
preparing the GMA 2018 identiﬁed diﬀerences that canalso be due to errors in national data collection for the
MIAs; or, regarding the GMA 2018 estimates, applicationof default emission factors and technology proﬁles not
representative for that speciﬁc country, and a variety ofother reasons.
Some national inventories include additional emissions
that are not yet quantiﬁed in the GMA 2018 inventory,
such as other chemical manufacturing processes, othermineral products (e.g., lime manufacturing), secondary
non-ferrous metal production, oil and gas extraction, pulp
and paper industry, and food industry, etc. These emission
sources are currently diﬃcult to quantify at the global
scale, largely due to lack of comprehensive activity data as
well as lack of emission factors for highly variable process
technologies. However, for the few (generally developed)
countries reporting emissions from ‘other’ sources thecontribution is approximately 5-20% of the national
inventory totals, which extrapolated globally could amountto additional emissions of the order of tens to hundreds oftonnes. Emissions estimates associated with many of these
additional sources have a high level of uncertainty.

Emission, tonnes
0Austria
Azerbaijan
Belgium

5

10

15

LRTAP
GMA
LRTAP
LRTAP
GMA
APEI

Canada LRTAP
GMA

Croatia

LRTAP
GMA

Cyprus

LRTAP
GMA
LRTAP

Czech Republic

GMA

Denmark

LRTAP
GMA

Estonia

LRTAP
GMA

FinlandLRTAP
GMA

France LRTAP
GMA
Georgia

LRTAP
GMA

Germany

LRTAP

Hungary
Iceland
IrelandItaly
LatviaLithuania
Luxembourg

GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA

Malta

LRTAP

Moldova

LRTAP

Netherlands
NorwayPolandPortugal

GMA
GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA
LRTAP
GMA

Romania LRTAPGMA

Slovakia

LRTAP

Spain

LRTAP

SwedenLRTAPSwitzerland
Turkey

GMA
GMA
GMA
LRTAP
GMA
LRTAP
GMA

Ukraine LRTAP
GMA

United Kingdom

LRTAP
GMA

Stationary combustion - power plants
Stationary combustion - domestic/residential
Stationary combustion - industry

Industry
Waste
Other

Comparison of GMA emission estimates for 2015 with emissions
reported for some countries under the UN ECE Convention on Long-range
Transboundary Air Pollution.

19

Pure EarthLEVELS OF
MERCURY IN AIR

There are several major global and regional mercury
monitoring networks around the world. Although there
are monitoring sites in both the northern and southernhemispheres, there are still large regions that lackany sites and hence any data, such as Africa, Latin
America and the Caribbean, and Russia. Nonetheless,much can be said about mercury levels in the world’s
atmosphere. Globally, mercury levels are higher in thenorthern hemisphere, due to the presence of more
emission sources. Regionally, mercury levels in theatmosphere reflect the presence of local sources aswell as transport pathways that can carry mercury
plumes for thousands of kilometres.

20

Spatial variability in theSouthern and Northern
Hemispheres

Alert

Zeppelin
PallasLittle Fox Lake
Mace Head

Saturna

There is a clear gradient of mercury
concentrations between the Northernand Southern hemispheres, conﬁrmingthat the gradient observed is mostly
driven by local and regional sources,
which can be anthropogenic, natural,or a combination of both. Seasonalvariations of gaseous elemental mercury
concentrations have also been observedat all European sites in the Northern
Hemisphere, with most of them showing
higher concentrations during the winterand spring and lower concentrations
in summer and autumn seasons.
Measurements of gaseous elemental
mercury show a downward trend overtime from the 13 northern sites, which
continued to have signiﬁcantly higher
median concentrations than thoserecorded at the southern sites. Long
term monitoring data exist from someof these sites. A downward temporal
trend was observed at Mace Head,
Ireland, from 1996 to 2015, while datafrom Cape Point, South Africa, show aslight increase from 2007 to 2014.

Råö

Listvyanka
Col Margherita

EgbertMt. WalinguanLongobucco

Minamata
Cape Hedo

Ev-K2
Mt. Ailao

Sisal
CalhauNieuw Nickerie

Mt. Changbai

KodaicanalManausCape Point

Bariloche

Amsterdam Island

Long-term air monitoringsites (>10-year time-series)

Dumont d'Urville
Concordia

0

0.5

1.0

2013
GEM, ng/m3
1.5
2.0

2.5

3.0

3.5

0

0.5

1.0

2014
GEM, ng/m3
1.5
2.0

2.5

3.0

3.5

90
85

Villum Research Station , Greenland Alert, Canada
Zeppelin, Svalbard

80
75
70

Polar

Pallas, Finland

65
60

45
40
35
30

Northern Hemisphere

55
50

25
20

Calhau, Cape Verde

15
10

Kodaicanal, India

5

Nieuw Nickerie, Suriname

0

Manaus, Brazil

-5
-10
-15
-20
-25
-30
-35
-40
-45
-50

Southern Hemisphere

LatitudeLittle Fox Lake, CanadaRåö, Sweden
Mace Head, Ireland
Listvyanka, Russia
Saturna, Canada
Col Margherita, Italy
Egbert, Canada
Mt. Changbai, China
Longobucco, Italy
Mt. Walinguan, China
Minamata, Japan
Ev-K2, Nepal
Cape Hedo, Japan
Mt. Ailao, China
Sisal, Mexico

Tropics

Seasonal trend analysis of total mercury
in precipitation showed increasing
concentrations and deposition during
the spring and summer months. The
dominant factor in determining the
mercury wet deposition at all European
sites was the amount of precipitation,with highest precipitation resulting
in highest deposition. Mercury
deposition measurements are scarcein tropical latitudes, though high wet
mercury deposition measured at Sisal
Station, Mexico, suggests that othertropical areas may be hotspots for
mercury deposition as well. In remoteareas particularly in the Southern
Hemisphere, far from any local sources,
atmospheric deposition has beenrecognized as the main source of
mercury to the ocean.

VillumCape Point, South Africa
Amsterdam Island, French Southern and Antarctic Lands
Bariloche, Argentina

-55
-60
-65

Dumont d'Urville, Antarctica

-70
-75

Concordia Station, Antarctica

Polar

Latitudinal trends in gaseous elemental
mercury at air monitoring stations shown on the
map above in 2013 and 2014, also showing sites
with long-term (>10 years) monitoring.

21

Regional variability in atmospheric mercury
Total mercury concentration, 2015

Total mercury wet deposition, 2015

0 2

Mercury, µg/m2
8
10
14

≥18

Total mercury concentrations and wet deposition in the USA in 2010 and 2015.

Although mercury is transported aroundthe world in the atmosphere, there are
distinct regional patterns in mercury
concentrations and deposition. A few
studies shed light on the extent of suchvariation, which has implications forhow much mercury will be available toecosystems and humans.
In North America, signiﬁcant wet
deposition of mercury is found along
the U.S. Gulf Coast, and somewhat
inland. Wet mercury deposition inthese areas strongly correlates withhigher precipitation. By contrast, thehighest concentrations are found in
the western areas where precipitation
is lowest and dominated by wintersnow. Data through the mid-2000s
showed general decreases in eastern
U.S. concentrations, with signiﬁcantdecreases at about half of these sites.
Fewer signiﬁcant trends were seen in

Spatial and temporal trends ofatmospheric mercury have been
investigated for many measurementsites across Canada for over 20 years.
Linear trends were estimated for all
available data from each site. In all but
2 sites in western Canada, the data show
a decrease in mercury concentrations.

Pure Earth22

the Southeast, but the general tendency
was for decreasing concentrations. Twosites in the West (Colorado, Washington)
showed the same decreases. No
signiﬁcant concentration increases werenoted, with little change in the Upper
Midwest concentration or deposition.
Regional trend analyses revealed
signiﬁcant positive trends in mercury
concentration in the Rocky Mountains,
Plains, and Upper Midwest regions forthe more recent time periods.

Atmospheric mercury concentrations
recorded at remote Chinese sites
are elevated compared with thoseobserved in remote areas in Europe
and North America and at othersites in the Northern Hemisphere.
In Chinese urban areas, the highly
elevated concentrations were mainly
derived from local anthropogenic
mercury emissions, whereas regional
anthropogenic emissions and longrange transport are the primary causesof the elevated mercury concentrationsat remote sites. Wet deposition ﬂuxesof mercury at urban sites in China werehigher compared with those in North
America and Europe, but wet deposition
ﬂuxes of mercury at remote sites werein the lower range of those observedin North America and Europe. In the
Republic of Korea, local coal combustion
was a main cause of enhancing mercury
concentrations in urban areas, whereas
the concentrations of diﬀerent airborne
mercury species in rural areas were also
aﬀected by chemical reactions occurringin the atmosphere.
Atmospheric mercury levels in central
Europe are elevated, as expected due
to inﬂuence from anthropogenic
sources like coal combustion. Coastal
Arctic sites in Norway have slightly
higher levels than those observedat Greenland and farther inland in
Finland and Sweden, which might bedue to summertime evasion from theocean or due to the fact that the High
Arctic archipelago of Svalbard receives
several direct transport episodes fromthe continent, especially in winter andspring. Inter-annual variability is large
among European sites, but a signiﬁcantreduction has occurred since the early
1990s, attributed to declines in primary
anthropogenic source emissions.

Mercury in precipitation, ng/L
35

Mercury in air, ng/m3
3
Rörvik/RåöZingstPallas (Matorova)
Mace Head
Zeppelin Mountain(Ny-Ålesund)

Pallas (Matorova)
De Zilk
Westerland
Rörvik/RåöZingst

30

25

2
20

15
1
10

5

0
1990

1995

2000

2005

2010

2015

0
1990

1995

2000

2005

Vertical profiles of mercury in the atmosphereand the distribution of mercury plumes

On several research ﬂights in
the U.S., plumes from large
mercury point sources were
sampled, mainly coal-ﬁred
power plants in the Southeast

U.S. For some of the largest
mercury emitters in the U.S.,
the observations suggest
substantially higher mercury
emissions than are estimatedin emission inventories. Flights
over the highly industrialized
area of Chicago-Gary (USA)suggest that there may be
many smaller emission sources
not accounted for in existing
emission inventories, or thatthe re-emission of mercury isunderestimated in that region.

2015

Trends in mercury in airand precipitation at selected
stations in Europe.

Contrary to previously
measured vertical proﬁles,
inside the boundary layer
the gaseous elemental
mercury backgroundconcentration was foundto be 10 to 30% higher thanin free tropospheric air at
higher elevations. Insideeach layer of the atmosphere,
gaseous elemental mercury isevenly distributed.

NSF/NCAR

Recent research has provided
new insights into mercury
patterns in the atmosphere.
Large-scale pollution plumes
in the upper troposphere, as
measured from commercial
aircraft, show how mercury is
carried from sources to distantregions. Plumes thousands ofkilometres in size have beenmeasured over Africa, SouthAmerica, and Asia. The sourcesof the Asian plumes were largely
industrial and urban, whereas
those from Africa and SouthAmerica were primarily frombiomass burning. Forest ﬁresin Siberia and in the Southeast
U.S. have also produced large
mercury plumes indicating
the inﬂuence of this source(not included in emission
inventories) for atmosphericmercury cycling.

2010

23

ATMOSPHERIC PATHWAYS,
TRANSPORT, AND FATE OF MERCURY
24

Mercury has a long environmental lifetime and cycles between the atmosphere,
ocean, and land. Mercury released to the atmosphere can travel globally: it undergoes
atmospheric reactions, deposits to the Earth’s surface, and can continue to cycle between
surface and atmosphere for decades to centuries and longer. Using a combination ofmodels and measurement, work since GMA 2013 has addressed aspects of mercury’stransport and fate, including emissions, atmospheric chemistry, removal processes,
modelling, and historical trends. In addition, several other studies have provided
additional insights into regional and local mercury cycling.

Emissions and different types of mercury
Accurate emission inventories and anunderstanding of their uncertainty areimportant for implementation of the
Minamata Convention. The observed
decrease in atmospheric mercury in the
United States is consistent with signiﬁcantregional decreases in emissions upwind of
measurements sites shown in global as well
as U.S. and Canadian national inventories.
Additionally, the observed increase inmercury concentrations measured in
the Southern Hemisphere at Cape Point
over the last decade is consistent with theestimated increase in mercury emissions
from artisanal and small-scale gold mining
in the Southern Hemisphere over thesame period. Some studies suggest that
there has been a 20% decrease in global
anthropogenic mercury emissions between
1990 and 2010. However, changes in theway emissions inventories have been
produced and the quality and completenessof information on which they are based
makes it diﬃcult to reliably compare global
estimates produced at diﬀerent times.

Since GMA 2013, the discussion of emission
speciation—the chemical and physicalforms in which mercury is emitted—has
also continued. While mercury emissions
from anthropogenic sources have been
quantiﬁed and updated with a reasonableconsistency, estimates of natural mercury
emission from the Earth’s surfaces,
including re-emission from previously
deposited mercury, remain very uncertain.
The range of error is comparable to thetotal anthropogenic emission of mercury.
This limits our understanding of global
and regional mercury cycling budgets. The
primary challenge in quantifying mercury
release from natural surfaces is the lack ofunderstanding of fundamental processes
driving the releases from diﬀerent surfaces.

Results from mercury modelling

Modelled Hg0 in air, ng/m3
0

1.1

1.2

1.3

1.4

1.5

1.8

2.4

Observed values using the same color scales

Recent model development has advanced our ability tosimulate mercury transport in the atmosphere between
diﬀerent geographical regions and account for multi-media
cycling of mercury, including the importance of legacy
mercury. New modelling results based on the updated global
mercury emissions inventory for 2015 provided up-to-dateestimates of mercury dispersion on a global scale, source
apportionment of mercury deposition to various terrestrial
and aquatic regions, and the contributions of diﬀerent
emission sectors to mercury atmospheric loads.
Re-emissions of mercury and natural sources are the main
contributors for mercury deposition over all regions except
East Asia. Deposition over East Asia is dominated by direct
anthropogenic emissions. Transpaciﬁc transport of East
Asian emissions is the major foreign source of mercury
deposition in North America. Europe, Southeast Asia, and theIndian subcontinent also make signiﬁcant contributions tomercury deposition in some receptor regions.

0

1

2

3

5

8

12

25

Modelled gaseous elemental mercury concentration insurface air and wet deposition in 2015 compared withobserved values (circles).

Wet deposition is relatively equally distributed between
the Northern and Southern Hemispheres and reﬂects theinﬂuence of multiple factors including anthropogenic
emissions, oxidation chemistry, and precipitation patterns.
Wet deposition is higher in areas inside and downwind of
the industrial regions of Asia, North America, and Europe aswell as over the high precipitation zones in the Tropics. The
lowest wet deposition levels are in arid areas of Greenland,
Northern Africa, and Antarctica. The simulations reproduce
measured levels of wet deposition in North America, Europe,and Australia reasonably well.

ESA/ATG Medialab

Modelled Hg wet deposition, g/km2/y

The current state of mercury dispersion in the atmosphereand deposition to various terrestrial and aquatic regions wasstudied by an ensemble of chemical transport models using
the new inventory of anthropogenic mercury emissions in2015 prepared for this assessment. The global distributionof gaseous elemental mercury concentration in the surface
air in 2015 simulated by the model ensemble shows alatitudinal gradient from the temperate latitudes of theNorthern Hemisphere to the high latitudes of the Southern
Hemisphere. These results are generally consistent withobservations from monitoring sites and other studies.

25

The regional pattern of deposition comparedwith atmospheric concentrations of gaseous
elemental mercury shows relatively low wet
and dry deposition in the Middle East andformer Soviet Union countries and elevateddeposition in Africa and South America. Over
most of the regions average dry depositionis higher than wet deposition by 20-120%. In
contrast to terrestrial regions, wet deposition
to the ocean is higher than dry deposition.

Modelled total (wet and dry)mercury deposition in 2015.

Hg deposition, g/km2/y
0

1

2

4

7

Terrestrial receptor regions
Northwest
Atlantic

CIS countries

Northeast
Atlantic

North America

Western
Central Atlantic

Central America

Eastern
Central Atlantic

South America

Southwest
Atlantic

AfricaSoutheast
Atlantic

Middle East

Mediterranean& Black

South Asia

Northwest
Pacific

East Asia

Northeast
Pacific

Southeast Asia

Western
Central Pacific

Australia and
New Zealand

Eastern
Central PacificArcticSouthwest
Pacific

Antarctica

Southeast
Pacific
0%

20%

40%

60%

80%

South Asia
East Asia
Southeast Asia
Australia and
New Zealand
ArcticAquatic receptor regions

Europe100%60

Source apportionment of
mercury deposition fromanthropogenic emissions to various
terrestrial (left) and aquatic regions(right) in 2015. Colors depict source
regions, indicated in map above:
hatching shows the deposition ina particular region that originatesfrom the region itself.

Western
Indian Ocean
Eastern
Indian Ocean
Southern
Ocean
0%

26

25

Deposition from direct
anthropogenic emissions
represents the mixture ofdomestic emissions andatmospherically transported
mercury from sources locatedin other regions (foreign
emissions). The share of foreignsources varies from 100% in
Antarctic to 23% in East Asia.
The largest foreign contributors
are characterized by large
anthropogenic emissions aswell as active artisanal andsmall-scale gold mining.

Source region
EuropeCIS countries
North America
Central America
South America
AfricaMiddle East

13

20%

40%

60%

80%

100%

The domestic shares inanthropogenic deposition
show an increase since 2010
in East Asia (from 76% to77%) and South Asia (58%
to 66%), which is explainedby the increase in Asiananthropogenic emissions
since 2010. Domestic andforeign anthropogenic
sources contribute almost
equally to the total
anthropogenic mercury
deposition in Europe. In North
America, the share of domestic
sources shows a reduction
from 23% to 15%, consistent
with the reduction in North
American anthropogenic
emissions since year 2010.
Remote regions including
the Arctic and Antarctic are
predominantly inﬂuenced
by the long-range transportof atmospheric mercury
from East Asia and Africa.

East Asia and Africa remain
the largest contributors to
the global ocean reservoirs,
owing to their large
anthropogenic emissions.
To assess the relative roles ofdiﬀerent emission sectors, allsources were aggregated into
four general groups: (i) power
generation, (ii) industrial
sources, (iii) intentional use
and product waste, and (iv)
artisanal and small-scale gold
mining. Mercury deposition
from the power generationgroup is largely restricted
to a number of industrial
regions in East and SouthAsia, Europe, North America,and South Africa, where themajority of large stationary
combustion sources arelocated. Emissions from theindustrial sectors group are
more widely distributed

over the world. Therefore,
signiﬁcant deposition fromindustrial sources covers
wide areas in Asia, Europe,
North and South America,and Africa. The impact of theintentional use and productwaste group of sectors is
also mostly related to majorindustrial regions but its
contribution is considerably
lower. The majority ofartisanal and small-scale gold
mining emission sources arelocated in low latitudes of theboth Hemispheres. Mercury
emissions from this sector aretransported globally, but themost signiﬁcant deposition
occurs closer to emission
sources and thus largely
impacts South America,
equatorial Africa, and Eastand Southeast Asia.
Modelled mercury deposition in2015 from major emission sectors.

Power generation

Industrial sources

Intentional use and product waste

Artisanal and small-scale gold mining

0

0.3

0.7

1.4

2.5

5

10

20

Hg deposition, g/km2/y27

Pavel Rumlena/Shutterstock.com

Atmospheric chemistry

Removal processes

New information has improved ourknowledge about mercury oxidation
reactions, including the importance ofbromine chemistry in mercury oxidation.
Models including these reactions
have shorter mercury lifetimes in theatmosphere and can better reproduce
some free tropospheric observations.
Recent model intercomparisons haveshown that there remain challenges in
reproducing observed concentrations
and patterns.

Mercury removal from the atmosphereoccurs via wet and dry deposition.
Wet deposition measurement-modelcomparisons, in particular in convective
storms, have provided insight into thevertical distribution of mercury inthe troposphere as well as oxidation
processes. Dry deposition remains morepoorly quantiﬁed than wet deposition,and there remains disagreement amongmodels on its global magnitude.

The major obstacle to understanding
the processes by which mercury reacts
in the atmosphere and interacts withatmospheric particles is that the natureof oxidised mercury compounds inthe atmosphere remains uncertain.
Furthermore, bromine distribution in
the atmosphere is not well documented,
adding further uncertainty to any
conclusions that may be drawn about
its role in atmospheric mercury
reactions. Uncertainties in measurement
techniques challenge our ability tofurther advance model-measurementcomparison of mercury species.

28

The type of storm aﬀects how
much mercury will be deposited by
precipitation and also where in theatmosphere the mercury will come from.
Convective storms, ones that typically
produce thunder and lightning, havedeposition rates more than one and halftimes those of horizontal rainclouds.
Convective storms can scavenge mercury
from as high as 10 kilometres in theatmosphere. Thunderstorms in the
Northeast U.S. have less wet deposition
than thunderstorms in the Southeast,
due to diﬀerences in cloud dynamics
between the two regions.

Mercury is taken up by leaves ingrowing plants. Deciduous trees area mercury sink during the growing
season, which may explain some
atmospheric mercury depletion eventsin forest areas. When the leaves fall,they carry mercury down to the surface,creating another form of deposition
to soils. Dry deposition of mercury has
been found to be important in inland
Arctic tundra, where it may accountfor 70% of the deposited mercury. This
result, however, appears to contradict
other studies showing that terrestrial
surfaces are a net source of gaseous
elemental mercury.

Historical trends and future scenarios
Europe and North America and an increase(up to 50 %) in South and East Asia. According
to the “New Policy” scenario, in which policies
that have been proposed are adopted, adecrease in mercury deposition (20-30%) was
predicted in all regions except for South Asia.
Model predictions based on the “Maximum
Feasible Reduction” scenario demonstrated
consistent mercury deposition reduction
on a global scale. It should be noted that thegeogenic and legacy sources were assumed to
be unchanged in this study.

Recently, declines have been observed in both
atmospheric mercury and wet depositionin Europe and North America, on the orderof 1-2% per year, that diﬀer by region.
Some modelling studies have reproduced
these trends, attributing some regionalvariations to declines in emissions. Observed
trends, however, are small compared withuncertainties in surface-atmosphere ﬂuxes,
anthropogenic sources, and attributablefraction. Future changes under policy
scenarios could reduce mercury deposition in
the future; however, the inﬂuence of climatechange and legacy mercury complicates
our ability to assess these potential futurechanges in models.

Even if anthropogenic emissions stayunchanged, mercury deposition will continue
to increase due to eﬀect of the legacy ofanthropogenic production emissions
accumulated in the ocean. Generally,
the atmosphere responds quickly to thetermination of future emissions, but longterm changes are sensitive to a numberof factors, including historical changes inanthropogenic emissions, air-sea exchange,
and mercury burial in deep ocean andcoastal sediments.

Recently, several modelling studies haveinvestigated changes of atmospheric mercury
concentration and deposition through 2035
due to changes in anthropogenic emissions,land use and land cover as well as climatechange. The “Current Policy” scenario, in
which no policy changes are made, predicteda decrease (20-30%) of mercury deposition in

East Asia

South Asia

Source apportionment of
mercury deposition in various
geographical regions fromanthropogenic sources in 2013
with projections for 2035 under
three scenarios (current policy,
new policy, and maximum feasible
reduction), based on results fromtwo models. Re-emissions of
mercury deposited in earlier years
from anthropogenic sources are
not included.

Hg deposition flux, g/km2/y

Hg deposition flux, g/km2/y

North America
Hg deposition flux, g/km2/y

15

25

5

20

4

15

3

10

2

5

1

10

5

0

0

0
2013

CP

NP

MFR

2013

Europe

CP

NP

MFR

2013

CP

NP

MFR

ArcticHg deposition flux, g/km2/y

Hg deposition flux, g/km2/y

102
Source region

8

Australia and New Zealand
ArcticMiddle East
North America
Central America
South Asia

6
1
4
2
0

CP
NP
MFR

0
2013

CP

NP

MFR

2013

CP

NP

South America
Southeast Asia
AfricaEast Asia
CIS countries
EuropeCurrent Policy
New Policy
Maximum Feasible Reduction

MFR

29

W. Eugene Smith/Magnum Photos

ANTHROPOGENIC RELEASES OF
MERCURY TO WATER

As with mercury emissions to air, releases of mercury towater come from a variety of sectors of human activity inaddition to natural sources. Mercury that is not emitted to air
in these processes may be released to water instead, either
directly or through washing of waste materials or throughweathering of waste deposits. Globally, releases of mercury
directly to water may be the largest contributor to freshwater
mercury levels. Artisanal and small-scale gold mining is thelargest single activity causing mercury releases worldwide.
In the following discussions, it is considered separately,as estimates for this sector include releases to both waterand land. Together, these are believed to account for about
1220 tonnes of mercury releases worldwide. Other sources
included in the 2015 estimate account for about 580 tonnesof mercury releases to water.

30

The GMA 2018 produced a new
global inventory of primary
anthropogenic mercury releases
to aquatic systems. This newinventory has the target yearof 2015, though such recent
information is not available for all
sectors and countries or regions.
As a result, the actual data used
come from the 2000-2015 period.
The selection of the sectors andactivities to be included in theaquatic inventory was driven by
previously established knowledge
and assumptions about their relative
importance. The categorization of
diﬀerent sectors was, to the extent
possible, kept comparable with thatused for the air emission sectors. The
estimates in the release inventory
include the following sectors:• Production of non-ferrous
metals (primary productionof aluminium, copper, leadand zinc)• Production of mercury metal• Production of gold fromlarge-scale mining• Mercury releases fromoil reﬁning• Production of gold fromartisanal and small-scale
gold mining• Mercury releases fromchlor-alkali industry(mercury cell technology)• Mercury releases from mercuryadded products (batteries,
measuring devices, lamps,
electrical and electronic devices,
dental applications, and otheruses) use and waste disposal• Mercury releases withmunicipal waste-water• Mercury releases fromcoal-ﬁred power plants• Mercury releases fromcoal washing
Additional sectors andanthropogenic activities, not taken
into account in this inventory,might be responsible for the
release of additional mercury to
local aquatic systems. Considering
the relatively low expected
importance of these sectors, andthe lack of data to support a global
estimate, these sectors were notincluded in the 2015 inventory.
Other possible sources of mercury
releases to aquatic systems also notassessed here are vinyl-chloride
monomer production, aluminium
ﬂuoride production, celluloseproduction, and titanium dioxide
production. In addition, evenamong the sectors included in theinventory, some processes leading
to mercury release may not havebeen considered, again due to lackof information.
Various methods were employed toestimate releases of mercury at theplant or facility, national, regional,
and global level. In general, they fallunder one of the three main groups:
Group 1 includes the chlor-alkaliindustry, oil reﬁning, and largescale gold and non-ferrous metal
production. The UN Environment’s
Toolkit provides a means ofestimating mercury releases towater and land in relation to
mercury emissions to air. These
factors were used together withthe most recent mercury emission
inventory (Chapter 3) to calculate
the releases to water.
Group 2 is made up of sectors
for which estimates were derived
based on measured mercury
concentrations and associatedvolumes of wastewater released
and/or other relevant activity
data. The sectors included aremunicipal wastewater, wastewaterfrom coal-ﬁred power plants, andcoal washing.
Group 3 covers releases fromwastes associated with the use of
mercury-added products: batteries,
measuring devices, lamps,
electrical and electronic devices,
dental applications, and other

W. Eugene Smith/Magnum Photos

Methods for estimating global anthropogenic mercury releases

uses. Releases are estimated fromregional patterns of consumptionof mercury and mercurycontaining products, considering
also the speciﬁc pathways by which
diﬀerent products will releasemercury to water.
Initially, estimates of mercury
releases for all sectors weremade on the country level, as the
majority of input data are country
speciﬁc. Based on the countrylevel information, mercury release
estimates were then summarised
according to the same subcontinental regions used in the
air emission inventory.
Given the global scope of thisassessment, there are several
limitations of this work. The
estimates presented here arejust that–estimates. The useof alternative approaches andassumptions might result insigniﬁcantly diﬀerent values.
An additional limitation is thepossible double counting on
one hand and the potential forunderestimation of releases on
the other. The current inventoryof global anthropogenic
mercury releases to aquatic
systems is nonetheless animportant step towards ﬁllinga major gap in inventories ofanthropogenic mercury releases
to the environment.

31

Global anthropogenic mercury releases in 2015
The total estimated inventory of anthropogenic
mercury releases from sources for which there
was enough information to provide quantitative
estimates is about 580 tonnes, not including
artisanal and small-scale gold mining (see Box).

Minzayar Oo/Panos Pictures/Felix Features

Apart from releases to water and land resulting
from artisanal and small-scale gold mining, themajority of global anthropogenic releases of
mercury to aquatic systems are associated withthe broad categories of waste treatment (42%),ore mining and processing (42%), and the energy
sector (16%). Overall, the inventory is dominatedby releases from non-ferrous metal production
and two sectors within the waste treatment
category, which are the use and disposal of
mercury added products and the disposal ofmunicipal wastewater.

Artisanal and small-scale gold mining
Releases associated with artisanal and small-scale gold
mining remain a “special” sector in the inventory, due
to large uncertainties in how mercury is released andwhether those releases are to land or water. In addition
to the direct losses occurring during ore amalgamation,
large quantities of mercury are accumulating in soils andsediments surrounding artisanal and small-scale gold
mining sites over time. This accumulated mercury has
potential to be remobilised and enter aquatic systems.
It is estimated that combined mercury releases fromthis sector to water and land in 2015 were about 1220
tonnes, more than twice the estimated releases to water

32

from other sectors included in the inventory. The vast
majority of releases from artisanal and small-scale gold
mining occur in South America (53%), East and Southeast
Asia (36%), and Sub-Saharan Africa (8%). Other regions
where artisanal and small-scale gold mining activities
are undertaken — Central America and the Caribbean,
CIS and other European countries, South Asia, and the
Middle East — contribute a minor share of the total.

Summary of releases by region
East and Southeast Asia contribute the most to the global
mercury release inventory. This is driven by large population
and associated large industrial and other activities. As thisregion is a dominant source of mercury releases from all
sectors, the distribution of releases among sectors reﬂects
the global pattern. Elsewhere, the relative contributions of
mercury releases from diﬀerent sectors varies widely, reﬂecting
diﬀerences in technological and socio-economic status.

Sub-Saharan Africa

South Asia

South America

North America

North Africa

Middle Eastern States

EU28

East andSoutheast Asia

Sub-Saharan Africa

EU28South Asia

East and Southeast Asia

South America

CIS and other European countries

North America

Central America and the Caribbean

North Africa

Australia and New ZealandMiddle Eastern states

Contribution to global mercury releases to water (excluding releases from artisinaland small-scale gold mining) in 2015 from different regions.

CIS & other
European countries

Central America andthe Caribbean

Australia, New Zealand& Oceania

Regional pattern of global anthropogenic mercury releases to water in the 2015
inventory from different sector groups (centre column), and contributions fromartisinal and small-scale gold mining to releases to both water and land (rightcolumn); releases to water alone from artisinal and small-scale gold mining
activities cannot yet be distinguished.

Non-ferrous metal production (Al, Cu, Pb, Zn)
Large scale gold
Mercury production
Oil refining
Coal-fired power plants

Coal washing
Municipal waste water
Mercury-added products
Chlor-alkali (Hg cell)
ASGM (release to water and land)33

Chlor-alkali (Hg cell)
Mercury-added
products

Non-ferrous
metal production(Al, Cu, Pb, Zn)

Largescale gold

Municipal
waste water

Mercury production
Oil refining
Coal washing

Coal-fired
power plants

Contribution to global mercury releases to water in 2015 from different anthropogenic source
sectors, excluding artisinal and small-scale gold mining.

Releases from selected sectors
The 2015 global inventory of releases to water excludes releases fromartisanal and small-scale gold mining, which are treated separately.
Mercury releases from copper, lead, zinc, aluminium, mercury, andlarge-scale gold production were estimated to be about 240 tonnes
or 40% of the inventory. About a quarter comes from large-scale
gold production.

The 2015 inventory shows that mercury-added products are also amajor source of mercury releases. The use of mercury in products,
such as batteries, lamps, dental applications, and others, is in
decline and so are resulting mercury releases, especially indeveloped countries.
The 2015 inventory considers mercury releases in wastewaterfrom coal-ﬁred power plants and those resulting from coal washing.
Together both releases are estimated to contribute about 15% of
the global inventory. In addition, tens of tonnes of mercury per
year accumulate in slurry ponds at coal washing sites globally,
creating a hazard for local aquatic systems.

34

People Image Studio/Shutterstock.com

Municipal sewage contributes about a further quarter of the
global mercury release total. The phase-out under the Minamata
Convention of many products that contain mercury is expected
to decrease mercury releases in municipal sewage. Anticipatedimprovements in municipal wastewater treatment around theworld are also expected to decrease mercury releases.

Pure Earth

Potential secondary sourcesof mercury releases
In addition to direct releases
to water, some of the sectors
discussed here contributemercury to land, generalwaste and sector-speciﬁcstorage, which can be equally
if not more important to theglobal mercury cycle. For
example, zinc production is
responsible for an estimated4200 tonnes of mercury
per year. Large-scale gold
mining is estimated to put
2700 tonnes of mercury
into soils each year, 45 times
more than it releases directly

to water. A further 940 or
so tonnes of mercury from
mercury-added products
enters the solid waste stream,of which only 6% is estimatedto be stored safely. A roughestimate of anthropogenic
mercury input to soils is
7000-8000 tonnes. All of thismercury becomes a potential
secondary source of releases
to water as well as emissions
to air. A great deal remains
unknown about this pathway
of mercury pollution.

35

MONITORING MERCURY
CONCENTRATIONS IN BIOTA

Areas with high mercury deposition do not necessarily have high methylmercury
levels and consequent uptake into the food web. Areas with low mercury deposition
may still have high levels of methylmercury in predatory fish and animals. Suchcircumstances need to be recognized and understood because methylmercury
is a potent neurotoxin that can cause physiological, neurologic, behavioural,
reproductive, and survival harm to fish and wildlife. It readily biomagnifies, increasingin concentration as it moves up the food web. As a result, top predators in a food web
may have concentrations of methylmercury in their tissues ten million times higher
or more than the concentrations found in the area’s water. Organisms with elevatedmethylmercury levels and those posing risks for human exposure are often used as
bioindicators of mercury contamination in an ecosystem.

Methylmercury in biota
The availability of methylmercury to hightrophic level organisms varies widelyaround the world. As an example, some of
the lowest air mercury wet deposition levels
measured in the United States and southern
Canada are in Kejimkujik National Park in
Nova Scotia, Canada, yet methylmercury
exposure of ﬁsh and birds is some of thehighest in North America, often exceeding

Ricardo Funari/BrazilPhotos/Alamy Stock Photo36

health thresholds for these species. Mostlakes in this area are sensitive to mercury
input and have high methylation rates.
Ultimately, the identiﬁcation of suchbiological mercury hotspots can be madethrough the collection of existing biotic
data and modelling ecosystem sensitivity
at regional or global scales.

Biomonitoring programs
An analysis of the geographicalcoverage of mercury biomonitoring
networks reveals a general lack ofnational initiatives around the world.
No such activities are being undertaken
in Africa and Australia. Most Asian
countries are minimally involved, with
the notable exceptions of Japan and theRepublic of Korea. In North America,
Canada’s Northern Contaminants
Program focuses on the measurementof contaminants, including mercury,in ﬁsh and wildlife that are traditional
foods of northern Indigenous peoples.
One of the strengths of that program is
the interdisciplinary approach taken
to assess and monitor mercury risks toecological and human health throughthe participation of Indigenousorganizations, environmental scientists,and human health professionals.

In addition to national programs,
hundreds of local studies provide acomprehensive and geographicallymore balanced global data platform
about existing biotic mercury
concentrations. Unfortunately, someof the countries with the highest ﬁshconsumption are poorly covered bybiomonitoring eﬀorts, including muchof Latin America, Western and Central
Africa, many parts of Asia including
the Indo-Paciﬁc, and most of the small
island developing states around theworld. Local scientiﬁc studies can makea signiﬁcant and welcome contribution
toward better identifying where, when,and on what to conduct biomonitoring.
Mercury concentrations measured
in biota at various locations aroundthe world.

Rich Carey/Shutterstock.com

Total mercury concentrations

High

Moderate

Low

37

Bioindicators for human health
Patterns of dietary methylmercury
uptake in humans can be shown byﬁsh species and by ocean basin. Many
freshwater lakes and rivers haveelevated mercury concentrations inﬁsh, especially in the tropics and intemperate regions such as Scandinavia,
Russia’s Kola Peninsula, and Canada
and the northern U.S. In the Arctic,
ﬁsh, birds, and marine mammals
are regularly taken by Indigenous
communities as important sourcesof protein, vital nutrients, minerals,
and fatty acids, and are important for
cultural and overall well-being.

In the Arctic, mercury levels haveincreased by a factor of ten over the
past 150 years, but the trend has
become inconsistent in the past three
decades. Nonetheless, the importanceof ﬁsh and wildlife to Arctic residents

and the extensive monitoring record
make the region an important area forfurther study. The rapid rate of climatechange in the Arctic ampliﬁes its
signiﬁcance for global understandingof mercury trends. The major river
basins of South America, including the
Magdalena, Orinoco, Amazon and La
Plata, support a large freshwater ﬁshery,
providing livelihoods for small-scaleartisanal ﬁshermen as well as majorcommercial enterprises. Diets highin ﬁsh in this region are linked tohigh human exposure. Of particularconcern are areas aﬀected by artisanaland small-scale gold mining. Future
biomonitoring would produce valuable
information in areas with those andother mercury point sources withintropical ecosystems that appear to besensitive to elevated methylation rates.

W. Eugene Smith/Magnum Photos

These and other considerations suggest
a number of strong candidates forbiomonitoring in relation to humanhealth. Tuna are one of the mostimportant global sources of marineﬁsh, with commercial harvests ofnearly 3.5 million tonnes per year.

Mercury concentrations vary widely
by species and ocean and tuna are amajor source of human exposure tomercury worldwide. Swordﬁsh haveimportant commercial value and area substantial income source for many
Small Island Developing States (SIDS).
They also tend to have high mercury
concentrations, which poses a risk forhuman health and can limit the abilityof the ﬁshing nations to export theircatch. Switching to other ﬁsh species
may be diﬃcult due to overﬁshing.
Thus, swordﬁsh monitoring can beimportant for human health and for
economic reasons.

38

Bioindicators for ecological healthlevels or are otherwise important for understanding mercury
in the environment. Many sharks, skates, and rays have muscle
mercury concentrations that are well above the humanhealth advisory levels set by the World Health Organization(WHO). They are of particular concern because they have highconservation status and they are often used for food.

Many species of ﬁsh and wildlife are at risk to the adverse
impacts of mercury. The selection of a particular organismor suite of bioindicators depends on the objective, such as
ecosystem health, detection of spatial or temporal trends,
human health, particular eﬀects, or sampling techniques.
As with bioindicators of human health, those for ecologicalhealth include several species groups that have high mercury

0

500

1000

Estimated harvest in 2013, thousands of tonnes
1500
2000
2500

3000

Harvest <5000 t

Blackfin tuna

3500
Tuna

Harvest 10 - 15,000 t

Atlantic bluefin tuna

Mercury concentrations in muscle
tissue of nine tuna species andcommercial harvest levels of thesame species worldwide.

Bigeye tuna
Pacific bluefin tuna Harvest 10 - 15,000 t
Longtail tuna
Albacore

Mercury in muscle
Commercial harvest

Southern bluefin tuna
Yellowfin tuna
Skipjack tuna
0

0.2

0.4
US EPAadvisory level

0.6
0.8
Total Hg in muscle, mg/kg ww

1.0

1.2

1.4

Mercury concentrations in dorsal
muscle tissue of swordfish fromdifferent ocean basins.

Swordfish

North PacificNorth Atlantic
South PacificIndianSouth Atlantic
Mediterranean
0

0.5

1.0
Total Hg in dorsal muscle, mg/kg ww

1.5

2.0

Sharks and allies

Great white shark
Largetooth sand tigers
Narrowtail cat sharks
Gray sharks
Lemon sharks
Spotted cat sharks
Winghead shark
Makos
Sawtail cat sharks
Bonnethead andHammerhead sharks
Blue shark
Tiger sharks
Thresher sharks
Sharpnose sharks
Smooth hound sharks
0

0.5

1.0

1.5

2.0

2.5

Total Hg in muscle, mg/kg ww

3.0

3.5

4.0
Mercury risk category

High

Moderate

Low

Mercury concentrations in muscle tissue of various shark species.

39

Ondrej Prosicky/Shutterstock.com
Daniel Poleschook

Loons have been used as bioindicators of
methylmercury availability in both theirbreeding and wintering areas for several
decades. In Canada, the Common Loon andits prey are being used to evaluate the successof national regulatory standards to reduce
mercury emissions. New ﬁndings on elevatedmercury exposure and migration behavior
in songbirds suggest the potential for
substantial adverse health eﬀects, especiallyfor long-distance migrants.

Most seabirds are situated high in foodwebs, and thus can be highly exposed tomethylmercury. The study of a group of
seabirds with contrasting ecologies fromthe same region allows determination of
methylmercury availability for multiple
marine zones and therefore a more
complete view of the ecosystem. Variation
in mercury contamination in seabirds
can reveal diﬀerences in the degree ofcontamination between major ocean
basins, as well as latitudinal gradients ofcontamination within basins, and trends at
a series of both spatial and temporal scales.

Mercury concentrations inthree tissues of seabird families.

Birds

Albatrosses

Storm petrels

Fulmars, Petrels,
and Shearwaters

Body feathers (fw)
Blood (ww)Eggs (ww)Diving petrels
0

40

5

10

15
20
Total Hg in tissue, mg/kg

25

30

35

Mercury risk category

High

Moderate

LowAMatveev/Shutterstock.com

Giedriius/Shutterstock.com

Toothed whales and some seals are the marine
mammals of greatest concern for humanand ecological health purposes. Mercury
concentrations associated with subclinicalneurochemical eﬀects are found regularly inbrain tissues from these species. Many subsistence
communities, mostly in the Arctic, depend on
the harvest of narwhal, beluga, pilot whales,
ringed seals, and other marine mammals. Toothed
whales appear to be one of the most vulnerable
groups of marine mammals to the dietary uptakeof methylmercury.

Mercury concentrations inmuscle tissue of various speciesof toothed whales.

False killer whale
Striped dolphin
Risso's dolphin
Melon-headed whale
Bottlenose dolphin
Rough-toothed dolphin
Pilot whales
Pantropical spotted dolphin
Beaked whales
Killer whale
Sperm whale
Atlantic spotted dolphin
BelugaCommon dolphin
Spinner dolphin
Harbour porpoise
Dall's porpoise

Marine mammals

Indo-pacific humpback dolphin
Pygmy sperm whale
Indo-pacific bottlenose dolphin
Dwarf sperm whale
NarwhalGray dolphin
Long-beaked common dolphin
Heaviside's dolphin
Dusky dolphin
White-beaked dolphin
Franciscana
0
Mercury risk category

High

Moderate

Low

2

4

6

8

10
12
14
16
18
Total Hg in muscle, mg/kg

20

22

24

26

41

Sea Turtles

Mercury risk category
Low

Dan Exton/Shutterstock.com

Moderate

42

43

Recent advances in
The response of mercury
understanding mercury
levels in aquatic biota tomethylation and demethylation changes in atmosphericmercury concentrations
Mercury is methylated by bacterial processes
in sediments and the water column of large
water bodies, such as the ocean and large
lakes. The concentration of methylmercury
in any given aquatic environment is the
net result of many competing processes offormation, transport, and demethylation. In
biota, the fraction or methylmercury increases
as it moves up the food web, reaching over 95%
in certain tissues of top predators.
In the last few years, a number of studies
have challenged the idea that methylation
occurs primarily in sediments. Furthermore,demethylation appears to play a larger rolein controlling methylmercury levels than
was previously realized. Understandingof the role of nutrients in methylation issimilarly evolving, as is the role of oxygen
levels in water and sediments. Together, theseand similar ﬁndings show how variable theprocesses and outcomes can be in diﬀerent
areas, in diﬀerent seasons, and over time.
In both coastal seas and open oceans aswell as deep lakes and reservoirs, there isincreasing evidence for active mercury
methylation in the oxygenated water columnof open oceans. This most likely occurs inside
decaying organic particles, where oxygenfree conditions provide ideal conditions
for methylation. In addition, mercury
methylation may also occur within sea ice.

44

In addition to methylation and demethylation
processes, many other processes and factors
aﬀect the uptake of mercury by aquatic biota.
The complexity of these processes, along withthe large inventories of legacy anthropogenic
and natural mercury stored in the terrestrial
and aquatic systems, dictate that biotic
mercury trends may or may not follow thesame short-term trends as atmosphericmercury. Even if they do follow similar
trends, there could be a signiﬁcant time lag
between them. Four case studies illustrate thevariation that can be expected, from North
America, Europe, Asia, and the Arctic. These
are the locations where parallel long-term
data are available for mercury in biota andthe atmosphere.

AlexLinck/Shutterstock.com

ANDING TRENDS
8 INUNDERSTMERCURY IN AQUATIC BIOTA

Mercury emitted to the atmosphere is almost entirely in an inorganic form. When it
is deposited to land or water, it is still in an inorganic form. Mercury released directly
to water is also almost entirely inorganic. Once in the water and sediments, however,inorganic mercury can be transformed into methylmercury. This organic form of
mercury is far more toxic than the inorganic forms and can also bioaccumulate andbiomagnify as it moves through the food web. Because methylation of mercury occurs
primarily in aquatic systems, aquatic animals are generally more exposed to, andhave higher tissue concentrations of, mercury than land animals. The consumptionof fish and marine mammals is thus the most common pathway of human exposure
to mercury. The factors controlling the rates of methylmercury formation anddecomposition are diverse, as are the factors controlling methylmercury accumulationin biota. It is clear, however, that reductions in emissions and releases of inorganic
mercury will ultimately reduce methylmercury concentrations in biota in the long-term,
although short-term trends may reflect local environmental conditions instead.

Mercury in fish andbirds in lakes andcoastal waters ofNorth America
A large number of studies havereported inconsistent, diverging,or mixed mercury trends inaquatic biota throughout North
America since the 1970s. The
early declines in mercury levels inbiota were most likely due to thedecrease in atmospheric mercury
concentrations and deposition
rates. The subsequent reversal or
stasis may be due to increasing
local emissions, food webchanges, climate change, sulfur
deposition, or other factors.
Mercury trends in ﬁsh fromhundreds of small lakes in
Ontario, Canada, varied bylake and by species of ﬁsh,demonstrating the complexityof ecosystem responses tochanges in atmospheric mercury
deposition. Results from coastal
waters in eastern Canada showed
relatively constant mercury levels
in biota in recent years despite
decreases in airborne mercury.
It is possible that changes in
feeding behavior played arole in the inconsistent biotic
mercury response to declining
atmospheric mercury.

Hg in egg, L n concentration ȝg/g ww

Herring gull, Hg in egg, L n concentration ȝg/g ww
Granite Island
0

0

-0.5

-0.5

-1.0

-1.0

-1.5

-1.5

-2.0

-2.0

-2.5

-2.5

-3.0

-3.0

Hg in muscle, L n concentration ȝg/g ww

Lake trout, Hg in muscle, L n concentration ȝg/g ww
Whitefish Bay
0

0
-0.5

-0.5

-1.0

-1.0

-1.5

-1.5

-2.0

-2.0

-2.5

-2.5

-3.0

-3.0

-3.5
1970

1980

1990

Herring gull,
Agawa Rocks

2000

-3.5
2020 1970

2010

1980

1990

Lake trout,
Pie Island

2000

2010

2020

Pie Island
Lake Superior
Agawa Rocks
Whitefish Bay

Granite Island

Mercury trends in
herring gulls and lake trout
in Lake Superior andbluefish on the northeast
coast of the USA from 1972
to 2011.

Mercury in adult bluefish muscle, ȝg/g
0.8

0.6

0.4

0.2

0
1965

1975

1985

1995

2005

2015

45

Mercury in freshwater
fish in Fennoscandia
Mercury levels in various species of freshwater ﬁsh
across Sweden, Finland, Norway, and the Kola Peninsula
in Russia were aﬀected in some cases by historical,
local releases directly to water, and in other cases
by deposition of atmospheric mercury transported
from distant sources. As expected, lakes thatwere aﬀected by local pollution sources
had higher mean observed mercury
concentrations in ﬁsh than lakes thatwere predominantly aﬀected byatmospherically deposited
mercury. The levels in ﬁshshowed a consistent andsigniﬁcant decreasing
trend, matchingwell with the generaldeclining atmosphericmercury trend over
Northern Europe.

Total Hg in muscle, mg/kg ww
0.03 - 0.25
0.26 - 0.50
0.51 - 0.75
0.76 - 1.00
1.01 - 3.57

Kletr/Shutterstock.com

Mercury in fish (1 kg pike equivalent), mg/kg ww
2.0

1.0
0.9
0.8
0.7
0.6
0.5

1960

1970

1980

1990

2000

2010

2020

Average mercury concentrations in five freshwater fish species across Fennoscandia, showing geographic distribution and trends from 1965 to 2015.

46

steven690/Shutterstock.com
tanakornsar/Shutterstock.com

luchunyu/Shutterstock.com

Mercury in fish in reservoirs in North America and Europe versus Asia
Some of the longest time series of aquatic mercury data exist
for man-made reservoirs due to concerns about the eﬀects
they have on mercury methylation rates and thus on ﬁshmercury levels. In North America and Europe, new dams ﬂood
vegetation and organic matter in submerged soil, stimulating
microbial mercury methylation. Fish methylmercury
concentrations peaked on average three years after the dam
was built, declined rapidly for about a decade, and thencontinued a slow decline for many decades afterwards.

Reservoirs in Asia, however, present a diﬀerent story. There,
most reservoirs support aquaculture for human consumption.
The ﬁsh mercury concentrations from these reservoirs are
typically low due to biodilution, as there are more ﬁsh in whichto accumulate the available mercury. In the drainage of the
Wujiang River, a large tributary of the Changjiang (Yangtze
River), a series of reservoirs were built between 1960 and 2008.
In contrast to the rapid increase in ﬁsh mercury levels seen in
North American and European reservoirs immediately after
they were ﬁlled, ﬁsh mercury is found at low levels in all thereservoirs studied in this region.

Total mercury in size-standardized fish, mg/kg ww
0.5

0.4

0.3

0.2

0.1

0

0

20

40

60

80

100

120

140
160
Reservoir age, years

Mercury trends by age of reservoir in fish tissues from reservoirs across western North America.

47

Mercury in Arctic animals

Frits Steenhuisen

In the Arctic, increasing trends inmercury have been found in somemarine species such as ringed seals
in Arctic North America and polar
bears in west Greenland. In east
Greenland and European Arctic,
mercury levels have generally
decreased. Diﬀerent trends inemissions in Asia, North America,
and Europe could play a role, as
could changing bioavailability of
mercury or ecosystem functioning
due to climate change. Mercury
levels in polar bears in Svalbard
have decreased, due to lower
environmental levels of mercury.
In the southern Beaufort Sea,
however, declining mercury levels
in male polar bears are most likely
a result of changing foraging
patterns rather than changes inatmospheric mercury deposition.
Eggs from thick-billed murres
also show diﬀerent patterns in
diﬀerent parts of the Canadian
Arctic, indicating changes in feeding
patterns in some cases and changes
in environmental conditions or
climate change in others.

Lancaster Sound

Svalbard

Great Slave Lake

Mercury in eggs, L n concentration μg/g dw
0.6
Seabirds, Lancaster Sound

Mercury in teeth, ng/g dw
10

Polar bear, Svalbard

0.4
8

0.2
0.0

6

-0.2
-0.4

4

-0.6

Northern fulmar
Thick-billed murreBlack-legged kittiwake

-0.8
-1.0
1975
1980
Hg in muscle, μg/g ww
0.4

1985

1990

2

1995

2000

2005

2010

2015

Burbot, West Basin, Great Slave Lake1970
Hg in muscle, μg/g ww
0.4

0.3

0.3

0.2

0.2

0.1

0.1

0
1992

1996

2000

2004

Mercury trends in various aquatic animals across the Arctic.

48

2008

2012

0
1992

1996

1980

1990

2000

Burbot, East Arm, Great Slave Lake

2000

2004

2008

2012

Frits Steenhuisen

Causes of the mismatch between atmospheric and aquatic mercury trends
In contrast to the recent decadal datasets
described above, the available centuryscale mercury trends in biota generally
matched remote glacial ice core archivesof atmospheric mercury concentrations
and deposition. Starting in the mid- tolate-19th century, mercury concentrationsin the atmosphere and in aquatic biota
increased steadily up to about the
1970s-80s. As atmospheric and biologicalmonitoring has become more widespreadand frequent over the last two to three
decades, a mismatch between the aquatic
biotic and atmospheric mercury trends
has become apparent. This mismatch may
be due primarily to large inventories of
mercury in soil and the ocean that are
subject to diﬀerent geochemical, climate,and ecosystem processes. Whereas thelevels of methylmercury in biota used
to be determined by the availability of

mercury, now there is suﬃcient mercury
in the environment that mercury levels
in biota may instead be limited by therates of methylation and demethylation
as well as other factors inﬂuencing
bioaccumulation, creating highly variable
outcomes from place to place.
In soil and terrestrial environments notincluding wetlands, there is relatively
little mercury methylation. Soils
nonetheless release inorganic mercury
into aquatic systems and emit it into
the air. Soils also aﬀect aquatic organiccarbon levels that inﬂuence methylation
rates in oceans, lakes, and reservoirs.
Atmospheric mercury trends may
thus have little short-term inﬂuenceon biotic mercury trends in manyaquatic ecosystems, as noted in the casestudies above. Aquaculture, overﬁshing,and invasive species are among thechanges that can have large eﬀects on
methylmercury levels.
Globally, the broad eﬀects of climatechange are believed to be among the mostimportant contributors to the mismatch
between environmental mercury andmercury levels in biota. In the Arctic, therapid decline in sea ice has inﬂuenced
mercury distribution and transport,
altered mercury methylation anddemethylation rates, promoted changes
in primary productivity, and shifted foodweb structures. The impact of climatechange on mercury in biota has also been
observed in lower latitude regions.

49

Ricardo Funari/BrazilPhotos/Alamy Stock Photo

The implications of mercury emission regulations on mercury levels in biota
The fact that short-term trends in mercury in biota
do not always follow trends in atmospheric mercury
should not discourage actions taken to reduce mercury
emissions and releases. Instead, implementation of the
Minamata Convention and related actions are necessary
to achieve long-term results and to cause declines inmercury as soon as possible.
Prior to anthropogenic inﬂuences, inputs of mercury
to aquatic systems were generally low, and so were
biotic concentrations. Around the mid-19th century, as
anthropogenic mercury emissions increased sharply,
aquatic mercury concentrations responded rapidly due
to increasing mercury deposition and methylmercury
formation. Once an aquatic ecosystem had
accumulated suﬃcient mercury, however, additional
increases became secondary to the amount alreadystored in the system. In these cases, methylation andbioaccumulation were controlled primarily by internal
processes rather than new mercury inputs.

50

As mercury emissions and releases in future arecontrolled by the Minamata Convention, a new phase
may emerge. Anthropogenic mercury emissions
and releases will decrease, leading to decreased
atmospheric concentrations. Legacy mercury in oceans
and soils, however, will remain a major source of
inorganic mercury to be turned into methylmercury
and accumulate in the food web. The decline inmercury in aquatic biota will thus take much
longer than the decrease in mercury emissions andatmospheric concentrations, and in some cases may
even increase in the short term. Further attention
is needed on the fate and eﬀect of legacy mercury
that is already stored in the environment, on thefactors and processes that aﬀect the recovery timeof mercury in biota, and on eﬀective remediation
and adaptation strategies for communities facing
mercury contamination.

Air Hg

Concentrations in air

NaturalIncreasing

Stabilizing

Decreasing

Stabilized

Concentrations in biota

Emission driven

Processes driven

With emissions control

Biotic Hg

Naturalbackground

Range of possible outcomes~1850

Time, not to scale

Minzayar Oo/Unearth-NRGI/Panos /Felix Features

A schematic representation of the response of mercury concentrations in biota to changes in mercury concentrations in air, as the limiting factors in bioaccumulation change.

51

Great Lakes Region
Fish consumption advisories(Knobeloch et al., 2011)

MERCURY LEVELS AND TRENDS
IN HUMAN POPULATIONS WORLDWIDE
52

Arctic Indigenous Peoples
Marine mammals and seafood drive
dietary MeHg exposures (AMAP 2015)

Dental Professionals and Patients
Amalgams drive Hg0 exposure(Goodrich et al., 2016)

Selected studies
across the world
depicting strong andrepresentative evidenceof mercury sourceexposure relationships.

Amazonian Tapajós River
Fish and mining drive exposures(Berzas Nevado et al., 2010)

Mercury has three major chemical forms relevant to human exposures: elemental
mercury, inorganic mercury compounds, and organic mercury compounds.
The most important form of organic mercury is methylmercury. The source,
environmental fate, exposure, and toxicity of these different mercury forms varies.
Human exposures to elemental and inorganic mercury may occur in occupationalsettings and via contact with products containing mercury. Dietary exposure tomethylmercury is primarily through fish, shellfish, and marine mammals. Groups
with high consumptions of these foods are likely to have higher exposure, butthese foods also provide numerous health benefits, posing a dilemma for overall
well-being. Fetuses and infants are also vulnerable to effects from mercury, so
pregnant women and recent mothers are also a concern for mercury exposure.

Faroese Cohort
Pilot whale consumption(AMAP 2015)

Mediterranean Region
Fish drive dietary MeHg exposures(Višnjevec et al., 2014)

European Exposures
Diverse Hg source-exposures(Višnjevec et al., 2014; Castaño et al., 2015)

MeHg sources
H0 and HgII sources
Mixed Hg sources

Japan 10 district study
Tuna drives dietary MeHg exposure(Yasutake et al., 2004)

Contaminated Sites
Contaminated rice in mining sites(Rothenberg et al., 2014)

Ghana ASGM
Environmental and occupational factors(Basu et al., 2014)

Seychelles Cohort
Seafood consumption(Shamlaye et al., 1995)

Mercury and human health
Seafood is the main source of protein for about one billion
people worldwide. For many communities, therefore, dietaryconsumption of ﬁsh, shellﬁsh, and marine mammals that arecontaminated with methylmercury is the most importantsource of exposure. Rice grown in sites heavily contaminatedwith mercury may also be a source of mercury exposure forsome communities.
Mercury is a pollutant of global concern principally due to its
adverse eﬀects on human health. Everyone in the world is likely
exposed to some amount of mercury. All forms of mercury are
toxic but the principal eﬀects diﬀer. Exposures to elemental

mercury may aﬀect the nervous system. Exposures to inorganic
mercury compounds may aﬀect the kidneys. Exposures tomethylmercury are associated with adverse eﬀects on brain
development, especially in fetuses. The latter has received
the most attention largely due to notorious methylmercury
poisoning events in Japan and Iraq following high exposures.
Studies on the toxicity of methylmercury carried out over recent
decades have provided a growing body of evidence that chronic,
relatively low-level methylmercury exposures can be associatedwith a range of other adverse health outcomes as well, aﬀecting
for example the cardiovascular and immune systems.

53

Human exposure to mercury is
estimated by the measurement of
mercury in human tissue and othersamples. The most commonly usedbiomarkers are the concentrationsof mercury in hair, urine, blood, andumbilical cord blood.
Most of the mercury in hair ismethylmercury. Mercury taken up
in hair remains there, providing
an integrated measure of exposurethat can be tracked over time as hair
grows. Hair is also easy to collect andtransport, though care must be taken
to distinguish mercury within thehair from mercury that has fallen
on the hair during activities suchas artisanal and small-scale gold
mining. Urine analysis primarily
provides information about exposure
to inorganic and elemental mercury,although methylmercury may also
contribute to the burden of urinary
mercury, particularly among avid
seafood consumers. Like hair,urine is a relatively easy and noninvasive sample to collect. Mercury
measured in whole blood provides
information about exposures toboth methylmercury and inorganic
mercury within the past month or
two. The measurement of mercury
in umbilical cord blood provides
information about developmental
exposure. Blood collection,
storage, and transport pose certain
logistical, ethical, and ﬁnancial
barriers, however.
When multiple biomarker measures
are taken from a given individual,
and also combined with surveys
about diet and behaviour, a deeper
exposure assessment of mercury
exposure is possible. In general,
careful measurement of mercury
content in hair and urine oﬀers themost convenient and cost-eﬀective
way to monitor mercury, particularly
in resource-limited settings.

54

Kemal Jufri/Panos Pictures/Felix Features

Mercury exposure
assessment using
biomarkers

Mercury levels in humans
outcome relationships. They tend toprovide high quality exposure data forvulnerable groups and can be used to
explore trends in space and time and to
examine connections between mercury
sources and biomarkers of exposure.
Cross-sectional studies on vulnerable
populations can be used to increase
understanding of mercury exposuresin diﬀerent population groups. Here,

This initial global assessment of
human exposure to mercury focuseson three study population categories.
National human biomonitoring programs
are usually sponsored or run byoﬃcial government agencies andtend to provide high quality data.
Longitudinal birth cohort studies areusually well designed and most
pertinent for establishing exposure-

Total Hg in blood, μg/L
0
0.5

1.0

1.5

2.0

2.5

3.0

3.5

Republicof Korea
FranceBelgium
Slovenia

SwedenUSA
Germany
Czech
Republic
Canada

Adult
Child

Comparison of mercury
concentrations in blood of adults andchildren in national biomonitoring
programs of different countries,
from the years 2003 to 2014.

Pregnancy
Outcome?
Birth 0–18 yrs
Hg exposure
Background (lowest)
Background (low)Elevated
Moderately highHigh
Adverse outcome
measured

the focus is on four groups: the general backgroundpopulation, with no particular or signiﬁcant
exposure to mercury; those who are vulnerable
because of exposure to point sources of elemental
or inorganic mercury such as artisanal and smallscale gold mining or mercury-contaminatedsites; people exposed to relatively high levels of
methylmercury through their diet; and populations
vulnerable through fetal exposure.
National human biomonitoring data were available
from Belgium, Canada, the Czech Republic,
France, Germany, the Republic of Korea,
Slovenia, Sweden, and the U.S. The total sample
population was 121,413 people, from whomthere were 192,651 biomarker measurements ofmercury exposure. Across the national programs,
the majority of participants had blood mercury
levels that fell below 5 micrograms per litre. In
adults, blood mercury levels were just over twice
as high as in children. Urine mercury levels wereconsistent across the countries from which data
were obtained, with a majority of the values
falling below 3 micrograms per litre. Like blood,urine mercury levels were higher in adults
than in children.
Changes in mercury exposure over time were
evaluated by reviewing national datasets inwhich there were two or more comparable
sampling periods. For blood mercury, datasetsfrom four countries were reviewed and ingeneral they showed declining exposures.

For urinary mercury, similar decreases canbe observed, particularly in the U.S. dataset
where the most recent mercury levels areapproximately half of what they were a decade
earlier. Urinary mercury values now in the U.S.
are similar to those in Canada.

Locations of mercury birthcohort studies showing
mercury exposure levels anddetection of mercuryassociated adverse outcomes.

Thirty-two birth cohort studies from 17 countries
included at least one mercury exposure
measurement during pregnancy or birth, aswell as a follow-up time period in which an
outcome measurement was taken. The total
sample population of these birth cohort studies
was 23,374 mother-child pairs from which
47,699 biomarker measurements were taken.
In general, these birth cohort studies focusedon methylmercury exposures. There are somenoteworthy observations. Groups consuming
large amounts of ﬁsh and seafood or marine
mammals have the highest mercury exposures,with umbilical cord blood mercury levels often
exceeding 10 micrograms per litre. On the other
hand, people in the Faroe Islands and the Seychelle
Islands have seen dramatic decreases frompreviously very high levels of mercury. Elsewhere,
Mediterranean populations tended to have higher
levels than people in Asia, whose levels in turnwere generally higher than those in North America
and Europe. A range of mercury-exposure-related
health outcomes were measured in newborns,
infants, toddlers, or children. These span a range of
exposures so are not limited to groups or regionswith high overall exposure to mercury.

55

From the cross-sectional studies information was taken from265 scientiﬁc articles, which together include184,510
mercury biomarker measurements taken from 167,830
individuals from 73 countries. The results in general
correspond well with those from national biomonitoringstudies. The cross-sectional data also highlight geographic
diﬀerences in exposure. For example, hair mercury levels
from the Western Paciﬁc, Eastern Mediterranean, andSoutheast Asia were higher than those in the Americas,
Europe, and Africa. These results can help establish
background mercury levels for the general population inareas with no signiﬁcant exposure to mercury sources.

Hg in blood and urine, μg/L
10

Hg in hair, μg/g
10Population group
Background
Dietary exposure to MeHg
Point source exposure to
inorganic and elemental Hg

8

8

6

6

4

4

2

2

0

0
Blood

Urine

Hair

Median blood, urine and hair mercury levels across different population groups
following a systematic review of 265 relevant cross-sectional studies from 73 countries.

Hg in urine, μg/L
4

3

2

1

0
0

0.5
AfricaEurope1.0
1.5
Hg in hair, μg/g
AmericasEastern MediterraneanSouth-East Asia
Western Pacific2.0

Bubble plot of hair and urine Hg levels from cross-sectional studies on backgroundpopulations according to WHO geographic regions. The size of the bubble reflects the
sample size. The asterisk indicate that urinary Hg levels from background populations in
Africa and South-East Asia were not available, and thus urinary Hg levels from all
populations within these regions was used.

56

Among vulnerable groups, methylmercurycontaminated seafood poses a particularrisk-beneﬁt dilemma. Seafood provides many
valuable nutrients and associated health beneﬁts,
but some seafood also contains high levels of
methylmercury. The median blood mercury
concentration among groups is about fourtimes higher than in the general backgroundpopulation. Indigenous Peoples in many areasof the world, especially Inuit in the Arctic andgroups in the Amazon region, generally experiencehigh exposure to mercury, most likely throughtheir reliance on traditional foods such as ﬁshand marine mammals for sustenance. Per capita
seafood consumption in these communities is
15 times higher than in non-Indigenous groups.
In addition, such traditional foods also form astrong basis for the culture, spirituality, recreation,

Ian Berry/Magnum Photos

and economy of many of these communities andso contamination of food by mercury presents
an issue of environmental justice.
Another vulnerable group includes those working
and living in artisanal and small-scale gold mining
areas. This practice continues to grow rapidly, withupwards of 15 million miners involved worldwide
and potentially 100 million people living in theircommunities. There are a number of public healthconcerns in artisanal and small-scale gold mining
communities as well as a growing number of humanbiomonitoring studies. Mercury levels among suchminers tend to be high on average, nearly three times
that of the general population, with some individuals
at extremely high levels of exposure.

Prospects for action
All populations are exposed to some amount of mercury,and there is great variability in exposures around theworld. Population groups at high risk are Arctic peoples
who consume ﬁsh and marine mammals; tropical riverine
communities (especially in the Amazon Basin) who consume
ﬁsh and in some cases may be exposed to mining; coastal
or small-island communities who substantially depend on
seafood; and individuals who either work or reside among
artisanal and small-scale gold mining sites. However,despite a relatively large database of mercury biomarker
measurements compiled here, data are completely lacking ina number of countries and geographic regions. More, goodquality, nationally representative data would allow changes
in human exposure over time and space to be gauged.
Programs to harmonize mercury biomonitoring activities
across regions will contribute to better quality data.

57

Brian Skerry/Getty Images

Many studies focus on developmental exposures during
pregnancy and childhood though there are also concerns
about mercury susceptibility during other lifestages. Much
remains to be learned about the range of physiologicalsystems aﬀected by mercury, about interactions between
mercury and other chemicals and environmental factors
including climate change, and concerning the role of genetic
diﬀerences in mediating exposure biomarker levels or
exposure-outcome relationships. While mercury exposures
may diﬀer between men and women because of diﬀerencesin diet, occupation, behaviour and physiology, this has notbeen systematically studied and warrants further attention.

Total mercury, ȝg/L

There are also success stories to be noted. Many steps to limit
mercury exposures may be eﬀective. The approximately
two-fold decline in urinary mercury levels in the U.S. over the
past decade is likely due to improvements in dental materials
and practices that reduce contamination from ﬁllings inteeth. Similar trends have been observed in German children
and among U.S. dental professionals. Across the Arctic,
mercury exposures remain elevated but have dropped overthe past two decades, probably as a result of local dietaryadvisories and changing consumption patterns. In otherplaces, mercury exposures have decreased as a result of
dietary consumption advisories, as has been seen in both
the Faroe Islands and the Seychelles. Within the artisanaland small-scale gold mining sector, urinary mercury levels
are signiﬁcantly lower in workers from licensed sites versus
unlicensed ones in Ghana. It can be expected that further
eﬀorts will continue to yield beneﬁcial results.

Total mercury, ȝg/L
2.0

58

Blood

5

4

3

USA
CanadaCzech Republic
Republic of Korea

2

1

0

Urine

1.6

1.2

0.8

0.4

0

2000

2002

2004

2006

2008

2010

Trends in mercury concentrations in blood and urineof adults from national biomonitoring studies.

2012

2014

2016

GLOBAL MERCURY ASSESSMENT 2018
PHOTOGRAPHS

Cover Splitting the catch: Audun Rikardsen, Norway
5 UN Environment Assembly, Closing Plenary, Dec 4 to 6, 2017, Nairobi, Kenya, 6, December 2017:
Cyril Villemain/UN Environment
6 Colorful landscape views of Norris geyser basin in Yellowstone National Park, USA: Rui Serra Maia
7 Loss of sea ice in the Arctic due to climate change allows greater exchange of mercury between theoceans and the atmosphere: Martin Fortier
9 Film still from “Volcanoes of the Deep Sea,” 2003, A Stephen Low Film
10/11 Smoke, air emissions from an industrial pipe on a blue sky background: savva_25
13 A woman tends fires of burning coal at a village outside Djaria, India: Larry C. Price
14 Steel and pipe work of a smoke pollution scrubber that is being dismantled after the plantshut down: TFoxFoto
14 Abdul Aziz (right), 13 years old and in Grade five, working in an informal gold processing facility
where ore from illegal ‘galamsey’ mines is brought: Nyani Quarmyne
14 A man burns an amalgam to release the gold particles the mixture contains, along with poisonous
mercury used to help extract gold: Kemal Jufri
14 Lignite Power Plant ot sunset with cloudy sky in Neurath, Germany: RV. Classen
18 Urban landscape smoked polluted atmosphere from emissions of plants and factories, view of pipes
with smoke and residential apartment buildings: aapsky
20 Man taking air samples at the Agbogbloshie e-waste site in Ghana: Pure Earth
22 The villagers of Dong Mai, Vietnam have turned to battery recycling and small-scale lead smelting
to earn their living: Pure Earth
23 NSF/NCAR C-130 research aircraft, essentially a flying laboratory, to conduct research flights in the
Northeast Metropolitan Corridor, the Ohio River Valley, and the Southeast regions
24/25 ESA/ATG Medialab
28 Car covered with pollen and fine dust in the spring: Pavel Rumlena
30 Minamata Bay, Japan. Toxic chemicals, containing mercury, flowing from the Chisso Chemical Plant
into the bay, which is used by local fishermen: W. Eugene Smith
31 Industrial waste from the Chisso Chemical Plant being dumped into Minamata Bay, Japan: W. Eugene Smith
32 A man panning for gold on a makeshift bamboo raft in the Irrawaddy River: Minzayar Oo
34/35 Water Treatment Plant at sunset: People Image Studio
36 Sign, warning of the dangers of eating fish from this small northern Wisconsin McGrath Lake, near
Hazelhurst, Wisconsin: Drake Fleege
38 Minamata Bay, Japan: W. Eugene Smith
40 Black-browed albatross, Thalassarche melanophris, with waves in the Atlantic ocean, on the Falkland
Islands: Ondrej Prosicky
40 Loon: Daniel Poleschook
40 White-tailed sea Eagle (Haliaeetus albicilla), catching a fish, Norway: Giedriius
41 Shark with open toothy mouth swimming in deep blue sea near reef; AMatveev
42/43 Green turtle (Chelonia mydas) with a yellow remora (Echeneidae) swimming over a coral reef.
Taken in the Wakatobi, Indonesia: Dan Exton
44 Ocean water: AlexLinck
46 Underwater photo of a big Northern Pike (Esox Lucius): Kletr
47 Yuankou Reservoir Dam, Yongzhou, Hunan, China: steven690
47 Aquaculture in Fujian, China: Luchunyu
47 Floating cage Aquaculture farm of Tilapia in reservoir Thailand, economic fish industry concept:
Tanakornsar
48 Polar bear: Frits Steenhuisen
49 Seabird colony: Frits Steenhuisen
50 Part of the hydraulic gold mining process known as “chupadeira system”: Ricardo Funari
51 Women, including the mine owner Daw Bauk Ja and her daughter Bauk Mai, pan gold from the
muddy sediments that the miners collected during the day: Minzayar Oo
54 A student from Bandung Institute of Technology, majoring in environmental engineering, collects
water and soil samples to check for mercury contamination: Kemal Jufri
56/57 Miners burn mercury off the gold amalgam in the open air close to their dwellings at the
Margaret Ikee Conventional Open Cast Mine: Ian Berry
58 Fishermen haul in a bluefin tuna caught in the old Mattanza method. Brian SkerryUnited Nations Environment Programme
P.O. Box 30552 Nairobi, Kenya
Tel: ++254-(0)20-762 1234
Fax: ++254-(0)20-762 3927
E-mail: uneppub@unep.org
www.unenvironment.org
Job number: DTI/2229/GE