Case History
Sediment Redox Processes and Mercury Management
in Onondaga Lake, New York
C O
S
N
Hg
ENVE5504 – Surface Water Quality Modeling
Hennigan, R.D., 1990. America's Dirtiest Lake. Clearwaters 19: 8-13.
Testimony to the U.S. Senate has described Onondaga Lake as one of the most polluted in the country – perhaps the most polluted.
Syracuse, New York: The Salt City• 1615 – first European visitor, Samuel Champlain• 1654 – salt springs discovered, Father Simon Lemoyne• 1794 – salt industry in place, James Geddes• 1820 – local brine springs failing• 1838 – wells dug around Onondaga Lake fail to locate source• 1862 – salt industry reaches its peak
The Solvay Process
http://pubs.acs.org/subscribe/journals/tcaw/11/i02/html/02chemchron.html
In 1865, a Belgian chemist, Ernest Solvay, developed a process to produce soda ash from calcium carbonate (limestone) and sodium chloride (salt). Soda ash is used in softening water and in the manufacture of glass, soap and paper:
3 2 3 22CaCO NaCl N Ca O ClC a
Ernest Solvay
1943: wastebeds collapse flooding region with soda ash waste
Solvay Process Allied Chemical Allied Signal Honeywell
1884 soda ash production begins on west shore using locallyproduced salt brine and limestone from nearby Dewitt
1880s salt production moved to Tully Valley
1912 limestone quarries moved to Jamesville
1986 industry closes
The Chlor-Alkali Process
The mercury cell chlor-alkali process was used to produce chlorine gas and sodium hydroxide through electrolysis of a salt brine solution.
( ) 2 ( ) ( ) 2( ) 2( )2 2 2aq l aq g gNaCl H O NaOH Cl H
+ anode
Hg cathode
carbonelectrode
Cl2
26% NaCl
24% NaCl
sodium amalgum, NaHg
H2
HgH2O
50% NaOH
The Chlor-Alkali Process
There is loss of mercury through leakage and dumping as the cells are cleaned or replaced. Approximately 75,000 kg of mercury were discharged to Onondaga Lake over the period 1946-1970.
0
75m
g∙kg
DW
-1
Adapted from Atlantic States Legal Foundationhttp://www.aslf.org/ONONDAGALAKE/gallery1.html
Hg(0) – mercury can be present as elemental or metallic mercury, a form that is subject to volatilization and release to the atmosphere;
Hg(II) – mercury can be present in ionic form, associated with salts and existing in equilibrium with Hg(0);
MeHg, (Me)2Hg – mercury may be present in the mono- and dimethyl forms, readily available for biotic uptake and produced from ionic mercury by sulfate-reducing bacteria.
(0) ( )Hg Hg II MeHg
Source: Global Mercury Assessment, United Nations Environment Programmehttp://www.chem.unep.ch/mercury/Report/GMA-report-TOC.htm
Adapted from Atlantic States Legal Foundationhttp://www.aslf.org/ONONDAGALAKE/gallery1.html
0
75
mg∙kgDW-1
Superfund
Dredge and Cap: the plan includes dredging of 2.65 million cubic yards of contaminated sediment with capping of 579 acres (20%) of the lake bottom.
MSNBC, 16 October 2006
Superfund
-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
Sediment Remediation Plan: dredge and cap, 20%
Sediment Remediation Plan: the other 80%
EPA does not consider monitored natural recovery to be a ‘no-action’ alternative, but rather an alternative means of achieving remediation objectives (U.S. EPA 1999). Selection of this approach implies that contaminant degradation and/or sequestration will eventually lead to remediation of the sediment environment (U.S. EPA 2005) and restoration of lost beneficial uses.
Monitored Natural Recovery
The Mercury Cycle
Hg(0) me-Hg
Hg(II) Hgp
SRB
SRB
complexation - sequestration
Monitored Natural Recovery
• fully protective of human health and the environment
• objectives achieved in a reasonable time
Enhanced Natural Recovery
• where MNR guidelines are not met, consider in situ approaches to reduce risk as sediments proceed toward a new SS following source controls.
Chemical Augmentation • oxygen• nitrate
Mercury Sulfur Interactions
Methylmercury production is associated with the activities of sulfate reducing bacteria.
22 4 2 2 2( )C H O SO H S CO H O
Source: Matilainen, T. 1995. Involvement of bacteria in methylmercury formation in anaerobic lake waters. J WAS, Vol. 80.Data from Dave Matthews, Upstate Freshwater Institute (S) and Svetoslava Todorova, Syracuse University (Hg)
J A S O
mgS
2-L
-1ngM
eHgL
-1
0
5
10
15
20
0
2
4
6
8
C(H2O)
Sulfur and the Ecological Redox Series
O2
SO4
NO3
2 2CO H O
C(H2O)
Sulfur and the Ecological Redox Series
O2
SO4
NO32 2 3 2N CO HCO H O
C(H2O)
Sulfur and the Ecological Redox Series
SO4
NO3
2 2 2H S CO H O
O2
0
2
4
6
0.0
0.5
1.0
1.5
2.0
0
5
10
15
Oxygen
Nitrate
HydrogenSulfide
mgS
2-L
-1m
gN-
L-1m
gO2
L-1
A M J J A S
Redox Manifestations in Onondaga Lake
The depletion of alternate electron acceptors (oxygen and nitrate) and the accumulation of an end-product of sulfate reduction (hydrogen sulfide) in the hypolimnion of Onondaga Lake tracks the ecological redox series.
Data from Dave Matthews, Upstate Freshwater Institute
Oxygenation and Nitrate Augmentation
0
2
4
6
0.0
0.5
1.0
1.5
2.0
0
5
10
15
Oxygen
Nitrate
HydrogenSulfide
mgS
2-L
-1m
gN-
L-1m
gO2
L-1
A M J J A S
Nitrate augmentation is one means of blocking sulfate reduction and the attendant production of methylmercury.
Data from Dave Matthews, Upstate Freshwater Institute
22 2 2( )C OH O CO H O
3 232 2 2( )C H O N CO HCO H ONO
2 24 2
2( )C H O Mn COMn H O
2 23 2
2( )C H O Fe COFe H O
22 2 2 24( )C H O H S CO H OSO
42 2( ) C OC HH O C
electrondonor
electronacceptor CO2+ reduced species
end product+
various various
Mapping Diagenesis
-2
8
18
28
38
48
58
0 2 4 6 8 10
-2
8
18
28
38
48
58
0 2 4 6 8 10
Sediment Profiles
Measuring Methylmercury Flux
1. Determine the MeHg flux from the sediments with the nitrate concentration in the hypolimnion maintained at 2 mg/L.
2. Describe setup and conditions for the laboratory measurements.
3. Write the equation that will yield the desired flux and identify the source of the input terms to that equation.
J
FeedStock
Q C∙ in Q C∙
EXPERIMENTAL SET-UP
J
Measuring Methylmercury Flux
FeedStock
Q C∙ in Q C∙
EXPERIMENTAL SET-UP
J
indCV Q C Q C J Adt
0.0
0.2
0.4
0.6
0.8
1.0
0 2 4 6
Flow
(m
Lm
in∙
-1)
Days
0
1
2
3
1 2 3 4 5 6
Nitr
ate
(mgN
L∙-1 )
Days
0
2
4
6
8
10
12
1 2 3 4 5 6
Oxy
gen
(mg
O2.L
-1)
Days
Q
0.0
0.1
0.2
0.3
0.4
0 2 4 6
MeH
g (n
g.L
-1 )
Days
ssQJ CA
Css
Results
Results
0
30
60
90
120
150
Hypolimnetic Accumulation Rates
Porewater Calculations
Flow-through No/No
ng.m
-2.d
-1
Results
0
40
80
120
160
200
Hi O2 + Hi NO3
Low O2 + NO3
No/No O2 NO3
ng.m
-2.d
-1
0102030405060708090
100
0 3 6 9 12 15
Net demethylation
Sulfate Reduction and Methylmercury Production
Application