Daniel J. Jacob, Harvard University

MERCURY IN THE GLOBAL ENVIRONMENT:Where does it come from, where does it go?

Hg

HgHg

A brief human history of mercury poisoning

Qin Shi Huang,1st emperor of China

Mad hatters

Minimata disaster

Karen Wetterhahn,Dartmouth professor

Iraq grain disaster

200 BC

19th-20th century

1950s

1971

1997

The perilsof eating too much fish

Jeremy Piven, actor Richard Gelfond IMAX CEO

Both hospitalized for extended time due to mercury poisoning from daily fish consumption over many years

Mercury from fish consumption: a global environmental issue

Children IQ deficits (fetal exposure)Well-established

Adult cardiovascular effectsSuspected

EPA reference dose (RfD): 0.1 μg kg-1 d-1 (about 2 fish meals per week)

Hg

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Mercury biomagnification factor

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Most US states have freshwater fish advisories…but our exposure is mainly rom ocean fish caught worldwide

Why are atmospheric chemists interested in mercury?

Mass number = 80: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2

• Filling of subshells makes elemental Hg(0) liquid, volatile• Mercury can also shed its two outer electrons (6s2) and be present as Hg2+ , also called Hg(II)

6s2

Mercury is present in the atmosphere as an elemental gas

XeKrNe

ArHe

Hg Rn

…a property that it shares only with the noble gases!

But unlike noble gases, mercury has a biogeochemical cycle driven by:

Hg(0) Hg(II)oxidation

reductionelemental mercury

mercuriccompounds

Natural biogeochemical cycle of mercury

Hg(0) Hg(II)

particulate

Hg

burial

SEDIMENTS

uplift

volcanoeserosion

oxidation

Hg(0) Hg(II)reduction biological

uptake

HUMAN PERTURBATION:fuel combustion

mining

ATMOSPHERE

OCEAN/SOIL

VOLATILE WATER-SOLUBLE

deposition

re-emission

Rising mercury in the environment

Dietz et al. [2009]

Mercury in Wyoming ice core Mercury in Arctic wildlife

Human perturbation started in Antiquity; present-day mercury levels in global environment are about ten-fold higher than natural

Global transport of mercury through the atmosphere

Circle around mid-latitudes: 1 month

Transport to southern hemisphere:1 year

Implies global-scale transport of anthropogenic emissions

Mercury emitted anywheredeposits to oceans worldwide

Human emission of mercury to atmosphere

Atmospheric concentrations

UNEP [2013]; Soerensen et al. [2010]

Mercury wet deposition is controlled by global transport

EPA deposition data (circles), model (background)

Global Hg(II) pool

scavenging

Florida T-storm

Highest mercury deposition in US is along the Gulf Coast, where thunderstorms scavenge globally transported mercury from high altitudes

Selin and Jacob [2008]

UNEP Minimata Convention on MercuryFirst major global environmental treaty in over a decade

• Requires best available control technology for coal-fired power plants• Mercury mining to be banned in 15 years• Many mercury-containing commercial

products to be banned

Opened for signatures in October 2013; already signed by 128 countries

Convention requires ratification by 50 countries to go into effect; nine (including the US) have ratified so far

But mercury pollution is in large part a legacy problem

The dominance of Asian emissions is a recent development

Streets et al. , 2011

Global emissions from coal combustion, mining, and industry

Grasshopper effect keeps mercury in environment for decades

Amos et al. [2013, 2014] – ex UW!

Res

ervo

ir f

ract

ion

Fate of an atmospheric pulse in the Harvard global biogeochemical model for mercury:

AtmosphereSurface soils Deep soils

Surface/subsurface ocean Coastal sediments

Deep sediments

Deep ocean

Hg

deep oceanrivers

SEDIMENTS

Land Ocean

0

Global source contributions to Hg in present-day surface ocean

Amos et al. [2013]

EuropeAsia

N America

S America

former USSR

Rest of world

pre-1850natural

by time of initial emission:

by source continent:

Half of human-derived mercury presently in the ocean

was emitted before 1950

Atmospheric mercury has been decreasing from 1990 to 2010; why?

Circles = observations Background = model

Decreasing trend is inconsistent with standard emission inventories

Yanxu Zhang (ex UW!)

Long-term stations for atmospheric mercury Long-term wet deposition flux data

Disposal of mercury in commercial products:a previously missing component of the biogeochemical cycle

Global production of commercial mercury peaked in 1970

Horowitz et al., 2014

• Commercial Hg enters environment upon use or disposal; much larger source than inadvertent emission• Use of commercial mercury has decreased since the 1970s due to

environmental concern; could this explain the observed atmospheric decrease?

Global Hg production Global inadvertent Hg emission[Streets et al., 2011]

Many commercial products contain mercury

Wiring Devices &Industrial Measuring Devices

Medical Devices

Pharmaceuticals & Personal Care Products

Pesticides and Fertilizer Explosives/Weapons

Dyes/Vermilion

Many commercial products contain mercury

Global historical use of mercury in commercial products

Horowitz et al. [2014]

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r

Year AD

Artisanal gold mining

Tracking the environmental fate of commercial mercury

Global mercury mined per decade

Commercial use by country

Disposal

Air Land Water

Landfill

Horowitz et al., 2014

Additional releases from commercial Hg in the context of atmospheric emissions

Historical release of commercial mercury to the environment

Horowitz et al., 2014; Yanxu Zhang, in prep.

Decreasing disposal of commercial mercury can explain atmospheric mercury trend

“Inadvertent” mercury (coal combustion, silver/gold mining)

Air

Soil

WaterLandfills

Co

mm

erci

al m

ercu

ry

What can we hope from the Minimata Convention?

Effect of zeroing all human emissions

by 2015

Zeroing human emissions right now would decrease ocean mercury by 50% by 2100, while keeping emissions constant would increase it by 40%

Amos et al. [2013, 2014]

The wild card of climate change:potential mobilization of the large soil mercury pool

Global soils: 270,000 tons mercury Oceans: 330,000 tons

Atmosphere: 5,000 tons

Increasing soil respirationdue to warmer temperature

Climate change may be as important as emission controls for the future of environmental mercury in the century ahead.