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.