Daniel J. Jacob, Harvard University MERCURY IN THE GLOBAL ENVIRONMENT: Where does it come from, where does it go? Hg Hg Hg
Dec 21, 2015
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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Sea
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Sab
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Mercury biomagnification factor
Sal
mo
n
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]
Co
nsu
mp
tio
n,
Mg
per
yea
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.