DETERMINATION OF METHYLMERCURY FLUX FROM ONONDAGA LAKE

SEDIMENTS USING FLOW-THROUGH REACTORS

GREGORY ALBERT E. GALICINAODEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

MICHIGAN TECHNOLOGICAL UNIVERSITY

STUDY SITE: ONONDAGA LAKE

-surface area: 11.7 km2

-mean depth : 12.0 m

-maximum depth: 20.5 m

-short retention time: flushes 2.5 to 4.0 times each year

-distinguished by two depositional basins, with a saddle region between them

-littoral zone occupies only a small area of the lake relative to the profundal sediments

-eutrophic and dimictic

-during summer and winter, the thermally- layered Onondaga Lake also has a sulfidic (>10 mg S·L-1) and anoxic hypolimnion

OTHER WATER QUALITY PROBLEMS

•ammonia, nitrate and phosphorus

•presence of pathogenic microorganisms

•high levels of PCBs, calcium chloride, mercury and other trace metals

•minimum dissolved oxygen concentration standard (4 mg·L–1) is frequently violated

•Mercury.......

Onondaga Lake (sign not to scale)

Testimony to the U.S. Senate has described Onondaga Lake as one of the most polluted in the country – perhaps the most polluted.

Hennigan, R.D., 1990. America's Dirtiest Lake. Clearwaters 19: 8-13.

METHYLATION AND METHYLMERCURY

*picture courtesy of Dr. Betsy Henry, Exponents

-conversion of Hg to methylmercury (MeHg) when a methyl group transfers from an organic compound to a mercury ion

-net methylation is optimal in the absence of oxygen

• elemental mercury

• Ionic mercury

• Organic mercury

-Mercury: a toxic substancefound naturally or as a contaminant introduced to the environment

MERCURY & METHYLMERCURY

*picture courtesy of Betsy Henry, Exponents

-MeHg Bioconcentration Factor: 104 to 107

-methylmercury: microbially-mediated reactions convert Hg to MeHg, a highly toxic form

HISTORY OF MERCURY POLLUTION

-Industrial waste generated and discharged to the lake by two chlor-alkali facilities

-75,000 kg from 1946-1970 -Allied Signal was ordered to reduce external loadings from 10 kg·day-1 to 0.5 kg·day-1 in 1970

-Chlor-alkali production operations halted in 1988

-Largest sources of Hg to the lake are: Ninemile Creek (7.1 kg.year-1), the METRO wastewater treatment plant (3.8 kg.year-1) and Onondaga Creek (1.8 kg.year-1) and unquantified amount from upland sources & resuspended sediments

+ anode

Hg cathode

carbonelectrode

Cl2

26% NaCl

24% NaCl

sodium amalgam, NaHg

H2

HgH2O

50% NaOH

THE CHLOR-ALKALI PROCESS

*picture courtesy of Dr. Martin T. Auer

MERCURY IN ONONDAGA LAKE TODAY

-mercury concentrations in the lake remain high

• water :• sediment :• fish :

-It still contains very high levels of HgT at 2-25 ng·L-1 Hg and 0.3-0.7 ng·L-1 of methyl mercury (MeHg)

-Hg concentration measured in lake fish also exceeded federal food limits set by the US Food and Drug Administration of 1 μg.g-1

-catch & release policy

*pictures courtesy from Dr. Betsy Henry

MERCURY IN ONONDAGA LAKE TODAY

....All roads lead to SEDIMENT as the possible culprit

*pictures courtesy from Dr. Betsy Henry

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Dept

h (m

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MeHg (ng·L-1)

LAKE RESTORATION EFFORTS:

-Closure of the Allied Signal chlor-alkali plants

-Bottom sediments and adjacent sites were assigned to the Federal Superfund National Priorities List

-Clean-up of upland sites has been completed wherein 8,500 tons of soil were treated

-Wetland Restoration was completed in 2007

-Groundwater Collection System/Barrier Wall—barrier wall construction has begun and groundwater treatment is in progress

Innovative Soil Washing Technology

*pictures courtesy from Dr. Betsy Henry and http://www.cnylink.com/news_images/lrg/onondagaoutletweb.jpg

THE NEXT STEPS•Dredging and Capping of Contaminated Lake Sediments-dredge 2.65 million cubic yards (SMU 1-7)-20% of the bottom area will be covered with clean sediment-isolation cap over 425 acres

•Monitored Natural Recovery-sequestration and burial will ultimately isolate contaminant from the lake water and reduce Hg concentrations, exposure, and mobility -Probable Effects Level (PEL) is set in Onondaga Lake to be attained

*picture courtesy of Betsy Henry, Exponent

Sediment Management Units (SMU) in Onondaga Lake

Long Term Recovery

What do we do while the lake approachesits new equilibrium?

*pictures courtesy of Dr. Martin T. Auer

Protect the ecosystemFrom MeHg flux

•Electron Acceptor Amendment-chemical-augmentation by adding oxygen and nitrate

INTERIM MANAGEMENTOF CONTAMINATED LAKE SEDIMENTS: ELECTRON ACCEPTOR AMENDMENT

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Fate of mercury in the sediments:Advection in Sediments > Diffusion

Engineered solution: Chemical Augmentation

SULFATE REDUCTION & METHYLATION

•Electron-donor (carbon)

•Electron acceptor (sulfate)

•Bioavailable species of inorganic Hg (HgS0)

C

O

S

N

HgmgS

2-L-1

ngMeHgL

-1

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22 4 2 2 2( )C H O SO H S CO H O

THE ROLE OF in METHYLATION

-Sulfate-Reducing Bacteria-principal methylators of mercury

SRB utilize sulfate as an electron acceptor in metabolizing organic carbon

-Hg2+ forms a neutrally-charged complex, HgS0

-Uncharged Hg-S complexes have fair lipid solubility and are relatively nonpolar.

-Sulfate-concentration:100-200 µM

-High levels of sulfate yield high concentrations of sulfide which has an inhibitory effect on methylation

C(H2O) SO4

NO3

O2

INTERIM MANAGEMENTOF CONTAMINATED LAKE SEDIMENTS: ELECTRON ACCEPTOR AMENDMENT

SINK PROCESSES:

SORPTIONDEMETHYLATION

It is the sink processes that exert a major control on the flux of methylmercurytransported to the overlying water

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THE ROLE OF ELECTRON ACCEPTORS in METHYLATION

2006

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Apr May Jun Jul Aug Sep

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gen

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L∙-1)

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MeH

g (n

gNL∙-1)

18 m

18 m

12-19 m

C(H2O)

O2

SO4

NO3

As the sequestered mercury is buried, it passes through a sediment layer (sulfate reduction) favorable for methylmercury production with subsequent diffusion to the overlying water

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sulfideMeHg

Dep

th (

mm

)

mg S·L-1 and ng MeHg·L-1

*pictures courtesy of Dr. Martin T. Auer

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GAUGING ELECTRON ACCEPTOR AMENDMENT EFFICIENCY:USE OF FLOW-THROUGH INCUBATION CHAMBERS

OBJECTIVE: to demonstrate that addition of electron acceptors can inhibit MeHg flux from the sediments

FeedStock

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EXPERIMENTAL SET-UP

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THEORY AND OPERATION: MASS BALANCE

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EXPERIMENTAL SET-UP

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A BASELINE FOR EVALUATING THE RESPONSE TO ELECTRON ACCEPTOR AMENDMENTS

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1a 2a 2c 4a 4b 4c 5c 5d 6c 6d

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+ Hi

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Low

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+ N

O3

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A BASELINE FOR EVALUATING THE RESPONSE TO ELECTRON ACCEPTOR AMENDMENTS

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“How much is the flux coming out of the lake sediments? How big is the ‘monster’? ”

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Hypolimnetic Accumulation Rates

Porewater Calculations

Flow-through No/No

ng.m

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ELECTRON ACCEPTOR AMENDMENT

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Hi O2 + Hi NO3

Low O2 + NO3

No/No O2 NO3

ng.m

-2.d

-1

DECREASING TREND IN MeHg RELEASE

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Recent 2008 data translates to a ∽85% decrease in MeHg flux over a four-year period

*Data provided by Upstate Freshwater Institute

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2005 2006 2007 2008

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ELECTRON ACCEPTOR AUGMENTATION IN A LARGER CONTEXT

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Sediments serve as a repository of the “sins of the past”-Dr. Martin T. Auer

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Net demethylation

Sulfate Reduction and Methylmercury Production

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Less organic matter means less “fuel” topower the sulfate-reduction engine (and consequently methlyation of mercury)

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1989 1991 1993 1995 1997 1999 2001 2003 2005 2007

aerobic metabolism

denitrification

sulfate reduction

methanogenesis

ELECTRON ACCEPTOR BUDGET OF ONONDAGA LAKE

•At the onset of 2004, there was a decrease in sulfate-reduction

•Advanced Nitrification program of METRO

* Data provided by Upstate Freshwater Institute

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CONCLUSION

•Chemical-augmentation as an interim management procedure effectively inhibited the release of MeHg to the water column of Onondaga Lake

•Percent reduction of MeHg release after addition of oxygen and nitrate is between 65-97%

FUTURE WORK•Further experimental work with nitrate additions is needed

•More research to characterize and identify which, between sorption or demethylation, is the controlling MeHg sink process

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ACKNOWLEDGMENT

I want to thank the following people for making this project possible:

•Dr. Hand, Dr. Urban and Dr. Bagley for agreeing to be part of my committee

•Upstate Freshwater Institute , Syracuse University and Cornell University for collaborating with us in this research project

•Honeywell Inc.

•Jesse Nordeng, Rob Fritz and Dave Perram

•Denise Heiniken and the MTU Writing Center

•To my friends here at MTU

•To our Research Group: Brandon Ellefson and Phil Depetro and the undergraduate students, Justen Stutz, Adam Di Pietro & Ken Windsand

•To my family and friends

•To my great adviser, Dr. Martin T. Auer

•To God

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QUESTIONS?