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Tittabawassee River Aquatic Ecological Risk Assessment – Results. Hector Galbraith Galbraith Environmental Sciences Newfane, Vermont October 2003. Background. Contamination of Tittabawassee River sediments by dioxins and furans known since 1980s

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Tittabawassee river aquatic ecological risk assessment results l.jpg

Tittabawassee River Aquatic Ecological Risk Assessment – Results

Hector Galbraith

Galbraith Environmental Sciences

Newfane, Vermont

October 2003


Background l.jpg
Background Results

  • Contamination of Tittabawassee River sediments by dioxins and furans known since 1980s

  • Between 2000 and 2003 intensive sampling efforts by MDEQ and USFWS characterized magnitude and spatial distribution of contaminants

  • Based on these data ERA determined to be necessary.


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Tittabawassee River Aquatic Ecological Risk Assessment (ERA) - Objectives

Overall objectives of ERA:

  • To evaluate extent to which dioxins and furans in sediments of Tittabawassee River and downriver areas pose risks to ecological receptors

  • To characterize spatial variability of risk and to determine whether risk “hotspots” exist


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Tittabawassee River Ecological Risk Assessment - Objectives - Objectives

Objectives of presentation:

  • Provide overview of approaches used

  • Describe how models and parameters were selected

  • Evaluate magnitude and distribution of risk to receptors

  • Discuss implications for risk management


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Tittabawassee River Ecological Risk Assessment – Presentation Structure

  • Overview of toxicity, environmental behavior of dioxins and furans and their presence in study area

  • Overall ERA approach

    • TCDD-EQ approach

    • USEPA ERA Framework

    • ERA model parameter identification

  • Evaluation of risk

  • Spatial distribution of risk


  • Tittabawassee river ecological risk assessment l.jpg
    Tittabawassee River Ecological Risk Assessment Presentation Structure

    Dioxin/furan toxicity – overview

    • Intrinsic toxicity - thresholds in biological tissues can be in low ppt (e.g., <10 pg/g, wet weight in chicken eggs – embryo mortality)

    • Environmentally persistent

    • Lipophilic, bioaccumulate and biomagnify in food chains

    • Pose risks to top predators (especially early life-stages)


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    Tittabawassee River Ecological Risk Assessment Presentation Structure

    Dioxin/furan toxicity – complications:

    • Structures highly variable and large numbers of isomers (congeners) possible:

      dioxins – 75 (dioxins)

      furans – 135 (furans)

    • Congeners differ in intrinsic toxicity (across 4 orders of magnitude) and environmental behavior

    • Environmental media typically contain complex mixtures of congeners – ERA should focus at level of congeners


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    Tittabawassee River Ecological Risk Assessment Presentation Structure

    Contaminants in Tittabawassee River:

    • Dioxins, furans, and PCBs all present in sediments

    • Other contaminants may also be present but have not been evaluated

    • Most of potential toxicity driven by dioxins and furans

    • Relatively little potential toxicity due to PCBs

    • This ERA focuses on dioxins and furans


    Tittabawassee river ecological risk assessment9 l.jpg
    Tittabawassee River Ecological Risk Assessment Presentation Structure

    Toxicity Equivalence (TEQ) approach:

    • Dioxins/furans exist in study area as complex mixtures

    • Because of intrinsic differences in toxicity, complex mixtures complicate assessment of toxicity

    • Toxicity of each congener relative to 2,3,7,8-TCDD can be expressed using a Toxicity Equivalence Factor (TEF)

    • A number of TEF categorizations exist – most recent (and most widely accepted for ERA) is WHO

    • By multiplying environmental concentration of each congener by TEF, then adding products, we get estimation of toxicity of mix relative to 2,3,7,8-TCDD - TCDD-EQ

    • Approach has limitations, is best method available with relatively wide acceptance


    Tittabawassee river ecological risk assessment10 l.jpg

    Selected WHO TEFs: Presentation Structure

    Birds Fish Mammals

    2,3,4,7,8-PeCDF 1 0.5 0.5

    2,3,7,8-TCDF 1 0.05 0.1

    1,2,3,4,7,8-HxCDF 0.1 0.1 0.1

    1,2,3,7,8-PeCDF 0.1 0.05 0.05

    Differences across taxa

    Differences within taxa

    Tittabawassee River Ecological Risk Assessment


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    Tittabawassee River Ecological Risk Assessment Presentation Structure

    Congener Environmental Behavior:

    Congeners differ also in:

    • Abilities of organisms to metabolize and excrete them

    • Efficiencies of biological uptake

    • Propensities to bioaccumulate

      Knowing intrinsic toxicity is not enough – also have to estimate congener-specific exposure


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    Tittabawassee River Ecological Risk Assessment – USEPA 1998 Framework

    • 1. Problem Formulation:

    • Conceptual model

    • Assessment endpoints

    • Analysis plan

    • 2. Analysis:

    • Exposure characterization

    • Effects characterization

    Communication

    to Risk Managers

    • 3. Risk Characterization:

    • Risk estimation

    • Risk distribution

    • Risk description


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    Tittabawassee River Ecological Risk Assessment 1998 Framework

    Overall approach:

    • Use data from site and parameters from scientific literature to evaluate exposure to piscivorous (fish-eating) wildlife

    • Use data from scientific literature to evaluate sensitivity of receptors

    • Combine above in risk characterization

    • Use sediment toxicity thresholds (STCs) to map distribution of risk


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    Tittabawassee River Ecological Risk Assessment 1998 Framework

    IN

    OUT

    • Environmental data

    • From site:

    • Sediment PCH conc.

    • Degree of Risk:

    • How Much?

    • Biological data

    • from site

    • PCHs in fish tissues

    • PCHs in bird eggs

    Ecological Risk

    Assessment Model

    • Spatial Extent of Risk:

    • Where?

    Literature Values


    Tittabawassee river ecological risk assessment exposure model l.jpg
    Tittabawassee River Ecological Risk Assessment – Exposure Model

    Toxicity Reference

    Values (TRVs)

    • Piscivorous

    • Wildlife

    • Mink

    • Birds

    Biomagnification

    Factors

    (BMFs)

    Biomagnification

    Factors

    (BMFs)

    • Bottom-feeding

    • Fish

    Benthos

    Water Column

    Fish

    Plankton

    Sediment

    PCDDs

    PCDFs

    Floodplain

    Water

    column


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    Tittabawassee River Ecological Risk Assessment Model

    Definition of terms:

    • Biomagnification Factor (BMF): ratio between contaminant concentration in prey and in tissues of predators.

    • Toxicity Reference Values (TRVs): Greatest TCDD-EQ in diet or eggs protective of organism viability (e.g., embryo survival)

      Functions are to translate media contaminant concentrations into exposures and risks to ecological receptors. Need to be congener-specific


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    Steps In Aquatic ERA Model

    Estimate of risk

    to avian embryos

    Estimate of risk

    to mink and otter

    Compare with

    Egg TRVs

    Compare with

    Dietary TRVs

    Estimate bird egg

    TCDD-EQ

    BMFs

    TCDD-EQ Concentrations

    in prey of mink

    and otter

    Fish Tissue

    TCDD-EQ

    Concentrations


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    Tittabawassee River Ecological Risk Assessment – Bird Egg TRVs

    TRVs for bird embryo survival exist for:

    Wood duck Mallard

    Great blue heron Eastern bluebird

    Forster’s tern Black-headed gull

    Common tern Chicken

    Double-crested cormorant Rock dove

    Pheasant Herring gull

    Turkey Domestic goose

    Bobwhite

    American kestrel



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    Bird Egg TCDD-EQ TRVs TRVs

    Most sensitive species: 5-50 pg/g, ww

    Less sensitive species: 50-100 pg/g, ww

    Least sensitive species: >100 pg/g, ww



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    Mammalian Piscivore TRVs TRVs

    *LOAEC – lowest observed adverse effects concentration

    *NOAEC – No observed adverse effects concentration


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    Mammalian Piscivore TRVs TRVs

    • 1 pg/g TCDD-EQ in diet assumed to be mink TRV

    • Very similar to values used in previous Great Lakes ERA

    • 1 pg/g TCDD-EQ also assumed to be TRV for river otter


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    TCDD-EQ TRV - Summary TRVs

    Birds:

    5 pg/g, ww in egg

    50 pg/g, ww in egg

    100 pg/g, ww in egg

    Mink and River Otter:

    1 pg/g, ww in diet


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    Steps In Aquatic ERA TRVs

    Estimate of risk

    to avian embryos

    Estimate of risk

    to mink and otter

    Compare with

    Egg TRVs

    Compare with

    Dietary TRVs

    Estimate bird egg

    TCDD-EQ

    BMFs

    TCDD-EQ Concentrations

    in prey of mink

    and otter

    Fish Tissue

    TCDD-EQ

    Concentrations






    Avian and mammalian trvs l.jpg
    Avian and Mammalian TRVs TRVs

    USEPA 1993 Sediment thresholds:






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    Mink HIs Areas


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    Mink HIs Areas



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    Mink and Saginaw Bay Carp Areas

    • Saginaw Bay carp fed to captive mink

    • TCDD-EQ in carp – 78 pg/g, ww (WHO mammalian TEFs)

    • Majority of TCDD-EQ from dioxins and furans

    • 10% carp in diet resulted in reproductive impairments

    • Tittabawassee River carp have 128 pg/g, ww TCDD-EQ

      Giesy et al. (1994); Heaton et al. (1995); Tillitt et al. (1996)




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    Sediment Threshold Concentrations (STCs) Areas

    • STCs are estimated TCDD-EQ concentrations in sediment that would result in HIs equal to or less than 1

    • STCs calculated using existing sediment TCDD-EQ data, and estimated bird egg and mammalian HIs


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    Sediment Threshold Concentrations (STCs) Areas

    5 pg/g egg TRV:

    HI of 206 results from sediment mean

    TCDD-EQ conc. of 2,109 pg/g

    HI of 1 would result from sediment mean TCDD-EQ conc. of 2,109/206 = 10 pg/g









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    Sediment Threshold Concentration Exceedences Areas

    • No sample sites except those upriver and immediately downriver of Midland had HI <1

    • At spatial scale of sampling and emphasis on depositional areas, risk not clumped into “hotspots” but is pervasive


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    Saginaw River and Saginaw Bay Sediments Areas

    * STC corresponds to least protective TRV (100 pg/g ww in egg)


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    Risk Summary Areas

    • Furans and dioxins in sediments of Tittabawassee River pose risks to reproduction and early life stages of piscivorous birds and mammals

    • Risks to wildlife pervasively distributed throughout the 22 miles of the Tittabawassee River below Midland

    • Furans and dioxins in sediments of Saginaw River and Bay pose risks to reproduction and early life stages of piscivorous birds and mammals

    • Experimental (mink feeding) and observational data (fish and bird egg contaminant data) confirm that dioxins and furans are bioaccumulated and pose risks to wildlife


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    Uncertainty Areas

    • All predictive scientific studies include uncertainty

    • Uncertainty in ERA can result from (for example):

      site contaminant characterization

      parameter selection

      food chain specifics

      toxicity relationships


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    Uncertainty Areas

    • The job of an ecological risk assessor is to provide results that if used in remediation will be protective of environment

    • Precautionary principle means that it is important that we guard against false negatives

    • It is also important not to overstate risks (for financial and public perception reasons)

    • In face of unresolvable uncertainty, “Ideal” ERA will shade slightly toward caution


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    Uncertainties in ERA Areas

    • Diets of piscivorous birds and mammals

    • Avian TRVs

    • Mammalian TRVs

    • Fish – Bird egg BMFs


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    Uncertainty and Robustness of Results of ERA Areas

    • Even if <100% fish diet assumed HIs still exceed acceptable level for mammals and birds

    • Even if less protective parameters used HIs still exceed acceptable level:

      - Avian and mammalian TRVs

      - Bioaccumulation of TCDF


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    ERA “Taxonomy AreasSpectrum”

    Preliminary/Screening

    Few site-specific data

    Can we confidently ignore the possibility

    of unacceptable risk?

    Outcome - more study, clean-up

    +

    Uncertainty

    Final/Definitive/Comprehensive

    Site-specific data

    What is magnitude of risk?

    Which organisms at risk?

    What is distribution of risk?

    Outcome - risk management decisions

    -


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    Utility of ERA Areas

    • Would further correctly collected site-specific data reduce uncertainty still further? YES

    • Notwithstanding, do we know enough to make management decisions YES

    • Can we identify important remediation sites YES

    • Does this also address terrestrial environment? NO


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