Effect of Oxygenation on Speciation, Behavior, and Fate of Chromium in
Estuarine Sediments
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Amar R. Wadhawan and Edward J. Bouwer
Department of Geography and Environmental EngineeringJohns Hopkins University
Sustainability: Reducing Toxic PollutantsEnvironmental Management for Enclosed Coastal Seas (EMECS9), 8/29/11
Contaminated Sediments in the Baltimore Harbor
“The problem of contaminated marine sediments has emerged as an environmental issue of national importance” – NRC report -1989
Status of chemical contaminant effects on living resources in the Chesapeake Bay’s tidal rivers
Chromium Processing Plant
• Chromium ore processing from 1845 – 1985
• Chromium Ore Processing Residue (COPR) used as fill material throughout the harbor and its surrounding area
• CrVI leaching from COPR material into the harbor
Cr Species and Their Behavior
CrIII CrVI
Oxidation
Reduction
• Less soluble
• Inert – (hydr)oxides
• Nutritional supplement
• Less toxic
• Soluble
• Readily bioavailable
• Carcinogen
Project Motivation
Toxicity in the Baltimore Harbor Sediments Cr speciation and biogeochemistry in anoxic estuarine sediments
Experimental Approach
Batch reaction experiments and HPLC-ICP-MS technique
Influence of Sediment Oxygenation
Loss in sediment reductive capacity and oxidation of CrIII
CrIII Oxidizing Potential of Sediments
Correlating rates of CrIII oxidation with measurements of bulk sedimentcharacteristics
Lag time behavior
CrVI Reoccurrence in Sediments
Effect of sediment loading and CrIII aging
Summary
Talk Overview
Toxicity in the Baltimore Harbor
McGee et al 1999. Environ. Toxicol. & Chem., 18, (10), 2151-2160.
48
dmt
CC
IH
BC
33
Site
AVS
(umoles/g
dry wt)
CrT
(mg/kg dry
wt)
FeT (g/kg
dry wt)
MnT
(mg/kg dry
wt)
AVS/SEM
DMT 0.3 – 25 65 - 1270 10 - 30 110 - 800 0.01 – 0.2
BSM 68 70 - 80 350 - 360 44 375 – 530 0.1- 0.7
BSM 54 10 - 50 80 - 130 83 440 - 520 0.1 - 0.6
BSM 45 110- 250 140 - 280 75 - 80 410 - 700 0.2 - 0.4
BSM 33 175 - 580 525 - 820 73 140 - 490 0.4 - 0.7
BC 307 600 87.0 611 0.47
IH 147 294 40.8 483 NM
BSM 38 132 239 42.9 559 0.93
Research Objective
Determine biogeochemical changes in the sediments that will favor CrIII oxidation to CrVI
O2
CrIII
CrVI
NOM
NOM
Reduced Fe
Reduced sulfur
Microbes
NOM
MnII
MnHS+
MnS
MnII
MnIII,IV(hydr)oxides
CrVI
Precipitated CrIIIAnaerobic sediment
Redox-active zone
Aerobic water column
AVS
Adapted from Masscheleyn et al 1992. Environ. Sci. & Technol., 26, 1217-1226.
Experimental Design
ICP-MSHPLC
Magnetic Stir Plate
Data Acquisition System
Crd
Batch Reactors
1 - 10 g/L N2-sparged sediment sediment suspension
10 mM NaCl + 10 mM (DEPP pH 4, MES pH 5 & 6, MOPS pH 7,
EPPS pH 8, CHES pH 9, CAPS, pH 10 & 11)
FiltrationCrIIIaq or CrVI
aq
spike
5 ml sample
5 mM
Phosphate
extraction
pH 7
Filtration
CrT
Aeration instantaneous
on CrIIIaq spike
Aeration once all spiked
CrVIaq reduced to CrIII
Analytical Evidence
Cr(III)
Cr(VI)
t1
t2
t3
t4
t5t1
t2
t3
t4
t5, t6
t6
Direct chromatographic evidence of CrIII oxidation
0
50
100
150
200
250
0 300 600 900 1200 1500 1800
Time (mins)
[dis
slo
ved
Fe]
(m
g/L
)
0
10
20
30
40
50
60
70
80
0 300 600 900 1200 1500 1800
Time (mins)
[dis
slo
ved
Mn
] (m
g/L
)
• 20 g/L Inner Harbor (IH) sediment suspension aerated under continuous stirring
• Samples collected and analyzed for AVS over several hours
• An aliquot of each sample collected was filtered, acidified, and analyzed for
dissolved Fe and Mn by ICP-MS
0
20
40
60
80
100
120
140
160
180
0 300 600 900 1200 1500 1800
Time (mins)
[AV
S]
(m
M/g
) d
ry w
t)
kAVS = 0.0085 min-1 Half life = ~82 mins
Influence of Sediment Oxygenation
Influence of Sediment Oxygenation (continued)
100 µM CrIIIaqspike
5 g/L dmt-207 suspension
10 mM NaCl + 10 mM MOPS, pH 7
No CrIII oxidation under anaerobic conditions and in sediment / CrIII
controls
CrIII Oxidizing Potential of Sediments
10 g/L suspension *2.75 g/L
100 µM CrIIIaq spike
10 mM NaCl + 10 mM MOPS
pH 7
~ 0.1 – 1%
oxidation at pH 7
in most samples
~ 25% oxidation at
pH 7 in dmt-109
sample
5 g/L suspension
100 µM CrIIIaq spike
10 mM NaCl + 10 mM EPPS
pH 8
~ 0.5 – 3%
oxidation at pH 8
in most samples
~ 70% oxidation at
pH 8 in dmt-109
sample
Predicting CrIII Oxidation
Sites showing CrIII oxidation potential
Correlation with Sediment Parameters
CrVI Reoccurrence upon Sediment Aeration
5 g/L sediment suspension,
10 µM CrVIaqspike
10 mM NaCl + 10 mM EPPS, pH 8
CrVI reduced to CrIII ( Cr(OH)3(s) , CrxFe1-x(OH)3(s) ) anaerobically within 4 hrs for all sites except DMT-207 and DMT-109, which took ~ 5 days
Sediment aerated after all CrVI reduced to CrIII
1 – 15% CrIII oxidation
CrVI Reoccurrence: Effect of Sediment Loading
N2-sparged 68-909 suspension
20 µM CrVIaq spike
Aeration - 55 hours after CrVIaq spike
for 1.6 g/L and 25 hours for the rest
10 mM NaCl + 10 mM EPPS, pH 8
N2-sparged 68-909 suspension
4 µM CrVIaq spike / 1 g sediment
Aeration 25 hours after CrVIaq spike
10 mM NaCl + 10 mM EPPS, pH 8
CrVI Reoccurrence: CrIII Aging Effects
5 g/L dmt-909 suspension
10 µM CrVIaqspike
10 mM NaCl + 10 mM EPPS, pH 8
O2
CrIII
CrVI
NOM
NOM
Reduced Fe
Reduced sulfur
Microbes
NOM
MnII
MnHS+
MnS
MnII
MnIII,IV(hydr)oxides
CrVI
Precipitated CrIIIAnaerobic sediment
Redox-active zone
Aerobic water column
AVS
Summary
Acknowledgements
Prof. Edward Bouwer
Prof. Alan Stone
Bouwer research group
Funding Sources
supported by Honeywell International Inc.
National Science Foundation
Questions!
Correlation with Sediment Parameters
Effect of Sediment Loading: CrIII Oxidation
Sediment suspension
100 µM CrIIIaq spike
10 mM NaCl + 10 mM EPPS, pH 8
Effect of pH: CrIII Oxidation
Cr3+
CrOH2+
Cr(OH)2
+
Cr(OH)3
0
Cr(OH)4
-
Calculation performed using HYDRAQL
Equilibrium data from Ball W.B. and D. K. Nordstorm 1998.
J. Chem. Eng. Data, 43, 895-918
5 g/L dmt-207 suspension
100 µM CrIIIaqspike
10 mM NaCl + 10 mM pH buffer
No CrVI formation at pH 3, 5 and 6
Effect of pH: CrIII Oxidation (continued)
5 g/L 68-909 sediment suspension
100 µM CrIIIaqspike
10 mM NaCl + 10 mM pH buffer
Effect of pH: CrIII Oxidation and CrVI
Reoccurrence
CrVI Reoccurrence
5 g/L 68-909 suspension
37.5 µM CrVIaqspike
Aeration 1 day post CrVIaqspike
10 mM NaCl + 10 mM pH buffer
CrIII Oxidation
5 g/L 68-909 sediment suspension
100 µM CrIIIaqspike
10 mM NaCl + 10 mM pH buffer
Effect of MnII Addition: CrIII Oxidation
5 g/L sediment suspension
100 µM CrIIIaq spike
10 mM NaCl + 10 mM EPPS, pH 8
Effect of MnII Addition: CrVI Reoccurence
5 g/L N2-sparged sediment suspension
10 µM CrVIaq spike,
Aeration 4.5 hrs post CrVIaq spike
10 mM NaCl + 10 mM EPPS, pH 8
Effect of Dissolved Mn: CrIII Oxidation
5 g/L sediment suspension
10 µM CrVIaq spike
Aeration 4.5 hrs post CrVIaq spike
10 mM NaCl + 10 mM EPPS, pH 8
MnIII,IV(hydr)oxide formation: Abiotic vs Microbial Mn oxidation
5 g/L dmt-207 sediment suspension
100 µM CrIIIaqspike
10 mM NaCl + 10 mM MOPS, pH 7
CrIII Oxidation: Influence of Sediment Oxygenation
Oxygenation of bulk sediments followed
by CrVI extraction (EPA method 3060A)
and HPLC-ICP-MS analysis
Mn Characterization in Sediments
Total reducible Mn determined by
extracting the sediments with 1.5 M
NH2OH.HCl and 0.1 M HNO3
Easily reducible Mn determined by
extracting the sediments with 0.02 M
hydroquinone and 1 M CaCl2
Methods adapted from:
Bartlett, R., and B. James. 1979. J. Environ Health
Persp. 92, 17-24.
Negra et al. 2005. Soil Sci. Soc. Am. J., 69, 87-95.
SEM Mn determined by extracting the
sediments with 1 N HCl during AVS
analysis under N2 sparging
0
2
4
6
8
10
12
14
16
DMT 68 54 45 33 69 bear creek
inner harbor
Mn
co
nc
(µm
ole
s/g
dry
wt
basis
)
Sampling stations
Total reducible Mn
Easily reducible Mn
Dissolved Mn
0
1
2
3
4
5
6
7
8
9
10
Colgate Creek DMT BSM 45 BSM 54
Mn
co
nc (
µm
ole
s/g
dry
wt
basis
)
Sampling stations
total reducible Mn
easily reducible Mn
SEM Mn
Influence of pH on Mn Speciation and Solubility in a Sulfidic Environment
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3 5 7 9 11
To
tal D
isso
lve
d [
i] (
mM
)
pH
HS-
Mn2+
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3 5 7 9 11
[i]
(mM
)
pH
HS-
Mn2+
H2S
Mn(OH)4
Mn2(OH)3MnHS
MnOH
s2
MnS(grn)
MnS(pnk)
Calculations performed using Visual MINTEQ
Conclusions• CrVI formation occurs under aerobic conditions but not under anaerobic conditions. The CrVI formation
correlates negatively with the AVS concentration in the sediments and positively with porewater-Mn /AVS ratio.
• The rate of CrIII oxidation increases with increase in sediment loading for dmt-207 site which is low in AVSbut decrease with increase in sediment loading for 68-909 site which is high in AVS. This suggests that CrVI
formation is a function of the sediment oxidizing capacity but its persistence is a function of the sedimentreducing capacity.
• Once all CrVI is reduced to CrIII under anaerobic conditions, we observe CrVI reoccurrence upon sedimentoxygenation. This CrVI reoccurrence is a function of the aging time.
• No CrVI formation is observed below pH 7. The rate of CrVI formation increases with increase in pH abovepH 7. This CrVI formation is coupled with loss of dissolved Mn above pH 7.
• CrVI formation increases with increase in MnII addition. This coupled with the observations of initial lagtime, the loss of dissolved Mn upon aeration at pH ≥ 7, and no effect of microbial activity suggest that CrIII
oxidation in Baltimore Harbor sediments is controlled by heterogeneous autocatalytic oxidation ofdissolved Mn by O2 that results in the formation of MnIII,IV(hydr)oxides responsible for oxidizing CrIII insediments.
Conclusion• Oxygenation of anoxic estuarine sediment facilitates CrIII oxidation and CrVI
persistence in these sediments at pH ≥ 7.
• CrIII oxidizing potential of sediments, the lag time, and the variation in CrVI
formation rates among different sediment sites appear to correlate negatively with
[AVS] and positively with [PW-Mn]/[AVS].
• Loss of dissolved Mn from solution due to autocatalytic oxidation by O2 at pH ≥ 7
should result in the formation of reactive MnIII,IV(hydr)oxides responsible for
oxidizing CrIII in sediments upon oxygenation. However, CrVI persistence in
sediments depends on [AVS].
• CrVI reoccurrence is observed upon oxygenation of anoxic CrVI spiked sediments at
pH ≥ 7. The rate of CrVI reoccurrence decreases with increase in CrIII aging and
increase with increase in pH at pH ≥ 7.
Summary: CrIII Oxidation in SedimentsSpatial and temporal variation
Lag time and rates of CrVI formation among different sites correlate negatively with [AVS] and positively
with [PW-Mn]/[AVS]
Effect of [CrIII]0
Rates of CrIII increase with increase in [CrIII]0 upto 150 µM. At higher concentration surface Cr(OH)3 ,
CrxFe1-x(OH)3 precipitates seem to inhibit the reaction
Effect of sediment loading
Rates increase with increase in sediment loading for low AVS sites but decrease with increase in
sediment loading for high AVS sites. CrIII oxidation appears to be a function of dissolved [Mn] whereas
CrVI persistence appears to be a function of [AVS]
Effect of pH
CrVI formation observed at pH 7 and above and it correlates with loss of dissolved Mn suggesting that
autocatalytic Mn oxidation is potentially responsible for CrIII oxidation in sediments
Effect of MnII addition
Increase in [MnII] spike increases the reaction rate
CrVI reoccurrence is observed upon oxygenation of anoxic CrVI spiked sediments at pH ≥ 7. The rate of
CrVI decreases with increase in CrIII aging and increase with increase in pH at pH ≥ 7.