Tag Archives: science

The Mercury Legacy: Defining “Natural” versus “Anthropogenic” Mercury

by Helen Amos

Written by Helen Amos from Harvard University, this is the first of our Guest Scientist Blogs. Helen is a fourth year PhD candidate in the Earth and Planetary Sciences Department at Harvard. Her research focuses on understanding the biogeochemical cycling and environmental fate of mercury and other toxics. She is currently using state-of-the-science models to get a handle on the impact of past historical releases of anthropogenic mercury on present-day and future levels of mercury in the environment. Email: amos@fas.harvard.edu      Website: http://people.fas.harvard.edu/~amos

When you go out and measure mercury in the environment today, how much of that mercury occurs naturally and how much is the result of anthropogenic (i.e., man-made) releases? This is a critical question with an uncertain answer. Much of the uncertainty stems from not considering the impact of anthropogenic mercury released in the past.

Human activities (e.g., mining) have been releasing mercury to the environment since antiquity (Nriagu, 1994; Cooke et al., 2009; Streets et al., 2011). The result of several millennia of anthropogenic mercury releases is mercury enrichment in the atmosphere, ocean, and soil.

Mercury continuously cycles between the atmosphere, ocean, and soil. Mercury emitted to the atmosphere (e.g., from a coal fired power plant) is eventually deposited to ocean or soil where it may be sequestered or may be re-emitted back to the atmosphere. This creates a “legacy” of mercury in the environment such that much of the mercury today originates from historical anthropogenic releases in the past.

It is all too common that mercury emitted from the ocean and soil is simply referred to as “natural mercury emissions”. However, not all of the mercury currently being emitted from the ocean and soil is truly “natural”. Rather, some fraction is naturally occurring and the remainder is anthropogenic mercury that was once deposited and is now being re-released to the atmosphere.

New work (Amos et al., 2013) suggests that a large fraction of mercury present in the environment today is a legacy of historical anthropogenic mercury emissions. Globally, more than half of the mercury in the ocean today is of anthropogenic origin (Amos et al., 2013). And more than half of the mercury emitted to the atmospheric today is legacy anthropogenic mercury (Amos et al., 2013).

How we define “natural” versus “anthropogenic” mercury has direct relevance to the UNEP mercury treaty. If policymakers want to regulate mercury or set targets for reductions, we need to know what the natural background levels of mercury in the environment actually are. If mercury emissions are incorrectly labeled as natural emissions, the impact of anthropogenic releases is underestimated and our ability to reduce or stabilize mercury concentrations in the environment is overestimated. Decision-makers need to keep this science in mind as they prepare a global mercury policy.



Amos, H. M. et al. (2013), Legacy impacts of all-time anthropogenic emissions on the global             mercury cycle, Glob. Biogeochem. Cycles, in review.

Cooke, C. A., et al. (2009), Over three millennia of mercury pollution in the Peruvian Andes,             Proc. Natl. Acad. Sci. U. S. A., 106(22), 8830-8834.

Nriagu, J. O. (1994), Mercury pollution from the past mining of gold and silver in the Americas,             Sci. Total Environ., 149(3), 167-181.

Streets, D. G., et al. (2011), All-time releases of mercury to the atmosphere from human             activities, Environ. Sci. Technol., 45(24), 10485-10491.

Where in the World is Mercury? Part 1: The Atmosphere

by Noelle Selin

Mercury is a slippery little element. One of the reasons that it’s the topic of global discussions is that it’s present everywhere on earth. Mostly, this is a result of human activities, both past and present. Mercury concentrations, though, can be higher in some places than others. Identifying where the problem is, and tracking it through time, will be important scientific tasks as implementation of an eventual treaty moves forward. Here’s a quick summary of what we know about mercury concentrations worldwide, beginning with mercury in the atmosphere.

Mercury in air, which exists primarily as elemental mercury, is present throughout the globe. Since mercury remains in the atmosphere for 6 months to a year after it is emitted, it has plenty of time to circle the globe. Typical concentrations of mercury in surface air are about 1.6 ng/m3, but can be substantially higher near sources. Atmospheric measurements can be used, along with models, to monitor changes in mercury atmospheric loadings and help validate emissions estimates. Much activity in this area has been prompted by the UNEP Mercury Air Transport and Fate Research partnership area (for more on the UNEP mercury partnerships, see our earlier post).

Concentrations of mercury in the air are measured at the ground (at land-based stations and on ocean cruises), on mountaintops, and from airplanes. A key project in this area is the Global Mercury Observation System, which aims to establish a worldwide monitoring system for mercury in air and precipitation. A figure of the distribution of stations is below.

GMOS ground-based monitoring sites

GMOS ground-based monitoring sites

Additional measurements are available from the Canadian Atmospheric Mercury Measurement Network (CAMNet) and the U.S. Atmospheric Mercury Network (AMNet), as well as from individual scientific studies. Measurements of mercury in precipitation are conducted in the US by the National Atmospheric Deposition Program’s Mercury Deposition Network and in Europe by EMEP.

A recent example of mercury measurements from a ship cruise is the global circumnavigation of the Galathea 3 [pdf]. From aircraft, mercury is routinely measured as part of the CARIBIC experiment, in which air pollution monitors are included on Lufthansa commercial planes. In addition, research aircrafts studying pollution also measure mercury. The ARCTAS aircraft campaign in 2007-2008 focusing on Arctic pollution included mercury in its measurements, and in the summer of 2013, the North American Airborne Mercury Experiment (NAAMEX) campaign will fly as part of a larger campaign on the NSF C-130 aircraft (picture below). I will be providing modeling support for the NAAMEX campaign, along with MIT students Amanda Giang and Shaojie Song, in collaboration with the University of Washington.


MIT Mercury group presents poster at INC5


We will be presenting a poster at the MIT Joint Program on the Science and Policy of Global Change display booth at INC5, starting tomorrow and running until the end of the negotiating session. Our poster summarizes recent scientific findings of relevance to the mercury negotiations. If you’re at the INC, please stop by to see us!

Download a copy here: MIT Mercury poster at INC5


Issue Overview: Mercury Emissions and Releases

by Leah Stokes and Rebecca Saari

Each year, humans mobilize around 2000 tonnes of mercury, with about 90% emitted to the air and 10% released to land and water. Since releasing mercury leads to environmental and human health impacts, addressing emissions and releases needs to be a central part of the global mercury treaty.

The draft text of the treaty, developed during the INC4 in Uruguay, distinguishes between emissions to the atmosphere and releases to land and water. However, the extent of controls on anthropogenic emissions remains to be seen, and it is possible that releases will be excluded altogether.


UNEP’s 2013 estimation of  2010 emissions from each global region. These estimations significantly changed since the 2008 reports, where East and Southeast Asia was estimated to contribute two-thirds of global emissions. These changes likely reflect a reduction in the estimation of mercury from coal power plants in Asia and an increase in the estimation of mercury from ASGM in Sub-Saharan Africa and South America.

Currently, almost 40% of mercury emissions come from East and Southeast Asia. Many developed countries have significant regulations on emissions, and the treaty is in part an effort to have all countries adopt standards. Yet most historic emissions came from the developed world. As is the case with climate change negotiations, this dynamic raises equity issues – mainly, who should pay: past emitters or current emitters?

Unlike carbon dioxide, however, mercury is toxic with acute health and environmental impacts, and its release is not tightly coupled with countries’ GDP. For this reason, all countries should be interested in reducing their mercury emissions and releases.

UNEP's 2013 report, "Time to Act" recently updated the proportion of emissions from each source. ASGM is now the largest estimated source of emissions, with coal plants in second place.

UNEP’s 2013 report, “Time to Act” recently updated the proportion of emissions from each source in 2010. ASGM is now the largest estimated source of emissions, with coal plants in second place.

About one-quarter of all global mercury emissions to air come from coal-fired combustion, including power plants and industrial boilers. This suggests an important aim for the treaty is reducing mercury emissions from coal-fired power and heating. There are many ways to achieve this, including pre-treatment of coal and various post-combustion technologies. These options also reduce co-emissions of other harmful air pollutants, and conventional post-combustion treatment can be enhanced to remove 80-90% of mercury emissions. Mercury-specific post-combustion control, which can achieve 90% mercury removal, is also available.

With a variety of emissions control options available, and significant variation in the mercury content of coal, the Chair and delegates are challenged to set appropriate goals and measures. When asked, most countries that currently regulate mercury responded that they employ emissions limits, or limits to the amount of mercury exiting a stack (flue gas concentrations).

Thus far, proposed flue gas limits range from 0.01 to 0.2 mg/m3. For reference, 0.05 mg/mg3 is one of the highest values measured at a series of US plants with limited pollution control through a fabric filter and a low-NOx boiler. In other words, a standard set as high as 0.2 mg/m3 could imply almost no control technology at all (See document: UNEP(DTIE)/Hg/INC.5/4 for more details). Ultimately, the level of control technology required will dramatically affect the treaty’s effectiveness.

While coal-related emissions present a clear priority, other mercury emissions are challenging to address, since they comes from a wide variety of sources, including: gold, cement and metal production, the chlor-alkali industry, waste incineration and dental amalgams. The Chair’s most recent updates also highlighted mining tailings, and sewage and wastewater treatment plants as potential sources. Over one-third of all emissions are from artisanal and small-scale gold mining (ASGM), which is addressed in a separate part of the treaty. Decisions on ASGM will dramatically affect global emissions, given that the UNEP 2013 report recently named it the largest source of emissions.

This week, countries have many decisions to make on mercury emissions and releases. Which sources should be controlled—existing or new plants, and from which industries? For examples, it is currently unclear whether the oil and gas sector will be included as a source.

Should small sources be exempted from requirements to inventory and reduce their emissions, and if so, what would the threshold be for a “small” source? Potential thresholds for required controls are listed in the Chair’s documents. For example, coal-fired power plants smaller than 50 MW could be exempted from mercury control technology. For context, 20% of all US coal units are 50 MW or smaller, meaning that this threshold could exempt a significant proportion of plants.

What should the goal be – should the treaty set reduction goals, emission limits, or require best available techniques? As the discussion about flue gas concentrations implies, these standards will have significant consequences. And finally, how flexible should the requirements be—should countries have to commit to specific standards, or can they develop flexible national plans and report at a later date?

The draft text reflects many of these debates. Article 10, which addresses atmospheric emissions, has two options: one, which would require goals, best available techniques or emissions limits; the other, which would require national plans. These issues and many more will need to be decided in the coming week. Decisions on atmospheric emissions and releases to land and water are essential to shaping the treaty’s ultimate environmental and health impacts.