dynamic pcb partitioning in ashtabula harbor, ohio … stable sediments at depth show...
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US Army Corps of EngineersBUILDING STRONG®
Dynamic PCB Partitioning in Ashtabula Harbor, Ohio Sediments
Andrew Lenox
Environmental Engineer
US Army Corps of Engineers, Buffalo District
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IntroductionAshtabula Harbor, Ohio►Federally (USACE) maintained deep-draft
harbor►USEPA Great Lakes Area of Concern (AOC)
• Restriction on dredging beneficial use impairment (BUI)
• Contaminants of Concern (COC) listed as mercury, chromium, lead, zinc, chlorinated organic compounds, polychlorinated biphenyls (PCBs), and low level radionuclides
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BackgroundPCBs are main COC with respect to dredged material management►Evaluation based on tiered assessment of
bioaccumulation in benthic organisms (Great Lakes Dredged Material Testing and Evaluation Manual )
• Use sediment chemistry data to model bioaccumulation
• Measure uptake into tissue in lab
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Theoretical Bioaccumulation Potential (TBP) Model
►Equilibrium partitioning theory-based algorithm for bioaccumulation of sediment associated non-polar organic contaminants in benthic organisms
►BSAF – Biota-Sediment Accumulation Factor, a measure of bioavailability that relates TOC normalized contaminant concentration in sediment to lipid-normalized contaminant concentration in organisms
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Biota-Sediment Accumulation Factor
TOCCsLipidCtBSAF =
Site-specific BSAF values encompass unique bioavailability influencing parameters including contaminant and sediment sorption properties, resulting in variability
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BSAF Variability Within Ashtabula Harbor
Bioaccumulation testing show BSAFs within the harbor differ significantly -ranging from 0.25 to 2.43Lower BSAFs►Outer Harbor and Lower River ChannelHigher BSAFs►Upper limits of Federal Channel
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Outer HarborBSAFs range from 0.25 to 0.51
Lower RiverBSAFs range from 0.54 to 0.91
Upper RiverBSAFs range from 1.20 to 2.43
Lake Erie
N
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Factors Affecting Bioavailability
Physical►Contaminant resuspension►Concentration gradient
Chemical►Contaminant sorption/desorption
Biological►Organism lipid content, size, growth rate,
gender, diet, metabolism
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Black Carbon
Coal dock and stockpiles are located at the head of the Ashtabula River►Condensed, aromatic carbonaceous material
show strong and nonlinear sorption, leading to lower bioaccumulation than assumed for natural organic matter
►PCBs partition onto black carbon over time
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Strong BC Influence
Outer Harbor provides an accumulation area for black carbon affected sediments, leading to increased contact time between PCBs and sediment
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Moderate BC Influence
Lower River sediments reflect differing degrees of contact time between PCBs and sediment ►Riverine and lacustrine current-based coal
soot deposition►More stable sediments at depth show
bioavailability similar to the Outer Harbor
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Negligible BC Influence
Upper River sediments receive less lacustrine current-based coal soot depositionBSAFs of 1.2 to 2.43 are more reflective of PCB bioavailability associated with a predominance of natural TOC in sediments
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BSAF Compared to BC Content
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
40.00%
45.00%
50.00%
0.00
0.50
1.00
1.50
2.00
2.50
3.00
1 2 3 4 5 6 7 8 9
BSAF Black Carbon (%TOC)
Moving Upstream from Outer Harbor
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Potential Factors Influencing BSAF Variability Throughout the Harbor
BSAFVariability
Organic MatterCharacteristics
Equilibrium Time with Sediment
Sediment Resuspension/
Mixing
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PCB Sediment Quality Criterion (SQC) needed to model future dredging restrictions►Should emphasize a bioaccumulation
endpoint►Should be spatially variable (due to spatial
changes in PCB bioavailability)
Incorporating Variability into Dredged Material Management
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Incorporating Variability into Dredged Material Management
Develop SQG based on TBP model and site-specific BSAFs Use Lake reference area tissue dataSQG predicts bioaccumulation from harbor sediment similar to that expected in the open-lake
BSAFLipidCtTOCCs =
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Ashtabula Harbor Total PCB Sediment Quality Guidelines (ug/kg)
300
200
70
Outer Harbor Lower River Upper River
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Dredged Material Management Considerations
PCB bioavailability is key driver in the characterization and management of Ashtabula Harbor dredged material ►Variability results in different conclusions
throughout the harbor►Bioavailability rather than bulk sediment
concentrations dictates suitability determinations
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ConclusionsPCB contamination in harbors can be assessed based on bioavailabilityBioavailability can be variable; use of default BSAFs may be overly conservative or inaccurate in estimating bioavailability TBP model with site specific, empirical BSAFs can be utilized in dredged material testing and evaluation
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