Defining the Availability of Defining the Availability of Contaminants in SedimentsContaminants in Sediments

Danny D. Reible, PhD, PE, DEE, NAE University of Texas

Acknowledgements: Nate Johnson, XiaoXia Lu, Dave Lampert, Brian Drake, Alison Skwarski

Linking Sediment Exposure and Linking Sediment Exposure and RiskRisk

Relevance of bulk sediment concentrationErosive sediments if complete desorption possibleSurficial sediments if complete desorption possible or if organisms can access all of contaminant

Relevance of pore water concentrationMobile fraction of buried stable sedimentsIndicator of bioavailability of surficial or erodible sediments ?

A Tale of Two ContaminantsA Tale of Two Contaminants

Hydrophobic Organic ContaminantsPAHsPCBs

Mercury

Hydrophobic Organic Hydrophobic Organic CompoundsCompounds

Does pore water concentration define exposure and risk?

Bulk Sediment Concentration Bulk Sediment Concentration Correlates only Weakly with PAH Correlates only Weakly with PAH Toxic EndpointsToxic Endpoints

0

20

40

60

80

100

1 10 100 1000 10000

Su

rviv

al (

%)

Sediment Total PAH16 Conc. (mg/kg)

H. azteca 28-day chronic toxicity test

PEC22.8 ppm

TEC1.6 ppm

Dave Nakles, RETEC

Porewater Concentration Better Porewater Concentration Better Correlates with SurvivalCorrelates with Survival

Dave Nakles, RETEC

Su

rviv

al (

%)

0

20

40

60

80

100

0.001 0.01 0.1 1 10 100 1000

EPA H. azteca 28-day test

Sediment Porewater PAH34 Conc. (Toxic Units)

Bioavailability StudiesBioavailability Studies

Test organismDeposit-feeding freshwater tubificide oligochaeteIlyodrilus templetoni

Ease to cultureHigh tolerance to contaminants and handling stressIntense sediment processing environment (overcome MT resistances?)

Measure of bioavailability= steady state BSAF

WhereCt is contaminant concentration accumulated in organisms’ tissue (g/g ) flip is organisms’ lipid content (g lipid/g dry worm) Cs is the sediment concentration (g/g dry sediment) foc is total organic carbon content of the sediment (g TOC/g dry sediment).

/

/t lip

s oc

C fBSAF

C f

Normalized Accumulation as Normalized Accumulation as Indicator of BioavailabilityIndicator of Bioavailability

BSAF of O(1) for reversibly sorbed non-metabolizing contaminants in directly exposed organisms at steady state ( e.g. benthic deposit feeders)If accumulation indicated (not necessarily caused) by porewater concentration

,

,

lipid porewater observedpredicted

oc porewater reversible

K CBSAF

K C

Does it predict uptake of PAHs ?Does it predict uptake of PAHs ?

Uptake of benzo[Uptake of benzo[aa]pyrene from water]pyrene from water

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3000.0

3500.0

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4500.0

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Time(hours)

Tiss

ue c

once

ntra

tion

of B

aP(d

pm/m

g dr

y w

orm

)

Predicted uptake from pore w ater

Observed total uptake from sediment

Contribution of ingestion to the Contribution of ingestion to the uptake of benzo[uptake of benzo[aa]pyrene]pyrene

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Time(hours)

Tis

sue c

oncentr

atio

n o

f B

aP

(dpm

/mg d

ry w

orm

)

observed total uptake from sediment

predicted uptake via sediment ingestion

Measurement of Porewater Measurement of Porewater ConcentrationsConcentrations

ProblemsLow porewater concentrations limits the measurement of more hydrophobic compounds like PCBs Solvent extraction overestimates the freely dissolved pore-water concentration due to the absorption by DOCErrors due to the measurement of DOC and uncertainties in determination of KDOC

Solution – solid phase microextraction SPMEPotential extremely low detection limits due to high fiber-water partition coefficients Decouple sampling from water-DOC matrix effectsHigh spatial resolution, rapid dynamicsEmployed ex-situ by National Grid/RETEC (Nakles)

Other Porewater Measurement Other Porewater Measurement ApproachesApproaches

Ex-situ SPMEProving to be valid approachMaintenance of profiles?Maintenance of sample integrity?

Semi-permeable membrane devicesDynamics?Spatial resolution?

Passive Polyethylene Samplers Currently under development (P. Gschwend)

Objectives of ESTCP effortObjectives of ESTCP effort

Demonstrate solid-phase micro extraction (SPME) for the in-situ assessment of bioavailability Demonstrate viable deployment approachDemonstrate relationship’ to sediment pore water concentrationsDemonstrate relationship to benthic organism body burdens

Overall Project planOverall Project planLaboratory

Optimization of Deployment ConditionsCorrelation with uptake in benthic organisms under controlled conditions

FieldDemonstration of relationship between measured pore water and organism uptakeComparison to conventional measurements

Commercial LaboratoryDemonstrate potential for routine availability

Laboratory effortsLaboratory effortsEvaluate key implementation characteristics

Fiber-water partition coefficientDynamics of uptake Reproducibility Accuracy

Confirm relationship to availability PCBs/ PAHsFreshwater/ Marine OrganismEndpoint- AccumulationMethods

“Raw” Sediment exposure Sequential dilution exposure

Field effortsField efforts

Freshwater and Marine Sites Opportunistic organisms and controlled (caged) organism studies PAHs/PCBsAdherence to DoD QA/QC guidelinesCooperative efforts where possible

Anacostia Active Capping Demonstration (Reible) Hunters Point Demonstration (Luthy) PET development (Gschwend) Survival endpoint (Nackles)

Solid Phase MicroExtractionSolid Phase MicroExtractionSorbent PolymerSorbent Polymer

PDMS (poly-dimethylsiloxane) Thickness of glass core: 114-108 µm Thickness of PDMS coating: 30-31 µmVolume of coating: 13.55 (±0.02) µL PDMS per meter of fibre

x

Using SPME to Measure Porewater Using SPME to Measure Porewater ConcentrationConcentration

Matrix-SPME ---A nondepletive, equilibrium extraction

“nondepletive” refers to an extraction that is limited to a minor part of the analyte and which does not deplete the analyte concentration “equilibrium” refers to extraction times are sufficiently long to bring the sampling phase into its thermodynamic equilibrium with the surrounding matrix.

At equilibrium,

Cfiber=mass of contaminant absorbed by fiber/fiber volume (volume of PDMS)

Kfiber-water is fiber-water partition coefficient

waterfiberfiberporewater KCC /

Expected detection limit PDMS fiberExpected detection limit PDMS fiber

Compounds Log KPDMS,

water

Method detection limit

Cdet,water

(1 cm fiber) Cdet,water (5cm fiber)

Phenanthrene 3.71 1.14 μg/L 164.6 32.9 ng/L pyrene 4.25 3.44 143.3 28.7 chrysene 4.66 0.79 12.8 2.56 B[b]F 5.0 0.32 2.37 0.47 B[k]F 4.77 0.15 1.89 0.38 Benzo[a]pyrene 4.87 0.17 1.70 0.34 PCB 28 5.06 0.5 3.22 0.645 PCB 52 5.38 0.5 1.54 0.31 PCB 153 6.15 0.2 0.11 0.021 PCB 138 6.20 0.2 0.0935 0.019 PCB 180 6.40 0.2 0.059 0.012

Uptake of PAHs in PDMS fiber Uptake of PAHs in PDMS fiber (Sediment)(Sediment)

0

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600

800

1000

1200

0 5 10 15 20 25 30 35

Time (d)

Fib

er c

once

ntra

tion

(ug/

L)

phenanthrene chrysene B[b]F B[k]F B[a]P

Uptake of PCBs in PDMS fiber Uptake of PCBs in PDMS fiber (Sediment)(Sediment)

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600

0 10 20 30 40 50 60

Time d

Fibe

r con

cent

ratio

n (u

g/L)

PCB28 PCB52 PCB153 PCB138 PCB180

• Conduct whole-sediment exposures to simultaneously measure bioaccumulation and fiber uptake.

Benthic Bioaccumulation Experiments

Exposure designMass of exposure organism per replicate approximately 50 mgRatio OC to biomass > 50:121-day exposure durationNo feedingGentle aerationOverlying water exchanged 2x weekly

benthic invertebrates

SPME

SPME Deployment in SedimentSPME Deployment in Sediment

Conder and La Point (2004): Env. Tox. Chem. 23:141

Teflon disk

Experimental Species

Leptocheirus plumulosusNeanthes arenaceodentata

Lumbriculus variegatus Tubifex tubifex

Field Deployment SystemField Deployment System

Porewater Concentration ProfilesPorewater Concentration Profiles

SPME Measured Porewater Profile

Depth cm

0 5 10 15 20 25 30

Con

cent

ratio

n n

g/L

0

100

200

300

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500

600

Surface mean

Pore water ConcentrationSurface mean

Anacostia Sediment Porewater Anacostia Sediment Porewater ConcentrationConcentration

PAH Measured

SPME

Measured

by LLE

If

Reversibly

Sorbed

Phenanthrene 210 370 1810

pyrene 610 730 990

chrysene 7.1 7.8 83

B[b]F 2.1 5.3 70

B[k]F 1.8 2 55

B[a]P 1.9 2 68

PAHs correlated with:PAHs correlated with:

R2 = 0.49

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0.00E+00 5.00E+09 1.00E+10 1.50E+10 2.00E+10 2.50E+10 3.00E+10 3.50E+10

Koc*Csed/foc

Ct/

flip

Bulk Sediment

PAHs correlated with:PAHs correlated with:

R2 = 0.82

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12000

0.00E+00 1.00E+03 2.00E+03 3.00E+03 4.00E+03 5.00E+03 6.00E+03

Koc*Cpw

Ct/

flip

Pore water

PCBs correlated with:PCBs correlated with:

R2 = 0.38

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3500

0.0E+00 2.0E+02 4.0E+02 6.0E+02 8.0E+02 1.0E+03 1.2E+03 1.4E+03 1.6E+03 1.8E+03

Koc*Cpw

Ct/

flip

R2 = 0.03

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3500

0.0E+00 5.0E+09 1.0E+10 1.5E+10 2.0E+10 2.5E+10 3.0E+10

Koc*Csed/focC

t/fl

ip

Pore water Bulk Sediment

Transition to the fieldOptimization of the field implementation approach

SPME Fiber

Outer slotted tube

Inner rod – SPME support

TECHNICAL PROGRESSTECHNICAL PROGRESS

Field Deployment System

Biota-sediment accumulation factors of Biota-sediment accumulation factors of PAHs and PCBs(Measured vs predicted)PAHs and PCBs(Measured vs predicted)

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0.05

0.1

0.15

0.2

0.25

0.3

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Predicted BSAF

Mea

sure

d B

SA

F

PAHs

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0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3

Predicted BSAF

Mea

sure

d B

SA

F

PCBs

Preliminary ConclusionsPreliminary Conclusions

Good correlation of porewater concentration with uptake for all compoundsSPME provides excellent indication of porewater concentration and uptake (within a factor of two in this preliminary assessment)Measured BSAF for both PAHs and PCBs were greater than predictedIndicates Klipid/Koc > 1

PAH - Klipid/Koc~ 1.25 - 2PCB - Klipid/Koc ~ 1-3PAHs – BSAF<<1 indicates desorption resistance in complex field-contaminated sediment

MercuryMercury

Do soluble species define exposure and risk?

Benoit et al.

Mercury Containment by a CapMercury Containment by a Cap

Methylmercury Containment by a Methylmercury Containment by a CapCap

Methylmercury ProductionMethylmercury Production

MotivationMotivation

• Nutrient Cycling in

Sediments

• Nutrient gradients governed

by bacterial activity.

• Mercury methylation mediated

by Sulfate Reducing Bacteria.

• Mercury Methylation tied to

Sulfate Reduction

Experimental Set-upExperimental Set-up

Bulk sediment samples placed in

experimental microcosms and

allowed to equillibrate

Aluminum support and

micromanipulator used

to hold electrodes in

place

Voltammetric MicroelectrodesVoltammetric Microelectrodes

• Theory

• Apply sweeping electric potential to electrode

• Electroactive species in porewater are oxidized/reduced at characteristic potentials

• Capabilities

• Gold-Mercury amalgam microelectrode (ideally <1mm) measures O2, Fe2+, Mn2+, HS-, and FeS(aq), all environmentally important for redox cycling in sediments

Oxygen: -0.3; -1.3V Sulfide: -0.7V

Fe2+: -1.4V

Mn2+: -1.55V

Preliminary FindingsPreliminary Findings

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

0 50 100 150 200 250 300 350

Concentration [uM]

Dep

th [

mm

]

O2 [uM] Mn2+ [uM]

• Preliminary Profiles

• Oxygen disappears in first 2-3 mm in sediment

• Increasing amounts of Mn2+ (>200 uM) and Fe2+ observed

• No sulfide observed, but evidence of FeS(aq)

complex

• Probing dynamics

• Size of electrode used for profiling important

• Should be <1mm for reasonable time to equilibrium

Future PlansFuture Plans

• Capping Simulation

• Install electrodes at depths in and above sediment

• Monitor to observe steady behavior

• Place 1-2cm cap and monitor dynamics of changes in O2, Mn2+, Fe2+ due to cap placement.

• Mercury Implications

• Before and after capping simulation, core column and measure total and methyl mercury.

• Geochemical Modeling

• Calibrate geochemical model with results of experimental observations

• Link mercury methylation to sulfate reduction in model

ConclusionsConclusionsHydrophobic organic uptake controlled by pore water concentrationSPME promising method for determining pore water concentrations in-situMercury risk controlled by methyl mercury formation which is a strong function of sediment biogeochemistry and soluble species in pore waterCapping appears to reduce methylation and effectively contains all mercury speciesVoltametry promising characterization method