Application of RESRAD-BIOTA for a Site-specific Ecological Risk Assessment and the Development of Ra...
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Application of RESRAD-BIOTA for a Site-specific Ecological Risk Assessment and the Development of Radiological Tissue Guidelines for Aquatic Organisms. Jing-Jy Cheng, Charley Yu, Ihor Hlohowskyj, Allen Tsao, and Mary Picel Environmental Science Division Argonne National Laboratory

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Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

Application of RESRAD-BIOTA for a Site-specific Ecological Risk Assessment and the Development of Radiological Tissue Guidelines for Aquatic Organisms

Jing-Jy Cheng, Charley Yu, Ihor Hlohowskyj, Allen Tsao, and Mary Picel

Environmental Science Division

Argonne National Laboratory

Argonne, IL 60439, U.S.A.


Presentation outline

Presentation Outline

  • RESRAD-BIOTA and its applications

  • Site-specific ecological risk assessment

    • Source of contamination and environmental setting

    • Risk Assessment approach

    • Conceptual model

    • Dose modeling

    • Risk characterization

    • RESRAD-BIOTA results

  • Development of screening tissue guidelines for aquatic organisms

    • Approach

    • Selection of bioaccumulation factors

    • RESRAD-BIOTA results


Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

RESRAD-BIOTA

  • A computer code that implements the U.S. Department of Energy’s (DOE’s) graded approach methodology for evaluating radiation doses to biota resulting from environmental contamination of radioactive materials

  • Can be applied to

    • Demonstrate compliance with biota protection requirements

    • Derive remediation goals for contaminated environmental media to meet the protection requirements

    • Evaluate radiological impacts to biota and ecosystems resulting from

      • Decontamination and decommissioning

      • Facility construction and operation

      • Waste management

  • Can be used to conduct both screening analyses and site-specific detailed analyses


Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

RESRAD-BIOTA Levels

  • Correspond to the graded approach guidance from U.S. DOE

  • Is equipped with kinetic/allometric modeling tool and new organism wizard for site-specific and species-specific analysis


Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

Site-specific Ecological Risk Assessment

  • Soils were contaminated with depleted uranium (DU) because of past operations in two areas (G and K areas)

  • Distribution of DU in soils was characterized by a number of environmental investigations

    • Soil contamination is very heterogeneously distributed

      • Limited to the top 30 cm

      • Spotted with high DU concentrations, which decreased exponentially to very low level over short distances

      • DU concentrations for most of the area are at background levels

Measurement of total uranium conc. in mg/g


Environmental settings

Environmental Settings

  • Desert environment

    • Annual temp range: 0-118oF; Annual rainfall: 3-6 inches

    • Area geography: flat, dry lakebeds, dry washes, and alluvial fans

    • Soils: sandy deposits with fine-grained clays

    • Typical desert vegetation: sparse, includes creosote, hopsage, and shadscale

    • No surface waters


Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

Risk Assessment Approach

  • A site-specific analysis was conducted following a simple screening analysis

  • Focused on evaluating potential risks to ecological resources that are known or expected to occur at the site

  • Calculated radiation doses to individual receptor species with

    RESRAD-BIOTA

  • Because of the distribution of DU

    • 90th percentile soil concentration was selected for estimating reasonable maximum risk

    • 50th percentile soil concentration was selected for estimating center tendency risk


Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

Exposure Point Concentrations


Conceptual site model

Conceptual Site Model

1o/2o Arthropoda

Consumer + Scavenger

Source

1o Producer

1o Consumer

2o Consumer

3o Consumer

Carnivorous

Mammals

Herbivorous

Mammals

Food

Ingestion

Insectivorous

Mammals

Depleted Uranium

Herbivorous

Birds

Carnivorous

Birds

Macroinverts

(insects)

Plant

Soil

Omnivorous

Mammals

Herbivorous

Reptiles

Carnivorous

Reptiles

Air

External Radiation

Inhalation


Receptors of concern

Receptors of Concern

  • Surrogate species were selected to represent each trophic level and receptor category


Receptors of concern cont

Receptors of Concern (Cont.)

  • Criteria for selecting surrogate receptors included

    • known to occur or is likely to occur at the site

    • is representative of an important taxonomic group, and/or trophic level

    • ecological information is readily available, and

    • known or considered to be radiosensitive

  • Species-specific exposure factors were used to model radiation exposures

    • obtained from literature sources

    • derived using allometric equations, or

    • taken from a closely related species, as appropriate


Exposure factors

Exposure Factors


Dose modeling

Dose Modeling

  • Both external and internal radiation were considered

  • External dose was adjusted for time spent on and within soil

  • Internal dose was calculated with tissue concentration

    • For vegetation: root uptake

    • For animal species: ingestion of different food sources and inhalation

  • Insect tissue concentrations were assumed the same as soil concentrations (dry weight basis)

  • Short-lived decay products were assumed in secular equilibrium with parent radionuclide (i.e. with the same concentration)

  • Consider time fraction spent in the contaminated area and contamination fractions of food sources

    • Home range/area of contamination

  • Calculate maximum tissue concentration within life time

    • Radiological decay and biological decay


Risk characterization

Risk Characterization

  • Screening analysis

    • HQ = Soil Conc. / BCG

    • BCG (biota concentration guide) is the radionuclide-specific soil concentration limit, included in RESRAD-BIOTA

  • Site-specific analysis

    • HQ = Dosetotal / dose limit

    • Dose limits

      • 0.01 Gy/d (1 rad/d) for terrestrial plants

      • 0.001 Gy/d (0.1 rad/d) for terrestrial animals

  • HI = HQU-234 + HQU-235 + HQU-238

    • HI < 1, no unacceptable risks

    • HI > 1, potential for unacceptable risks


Jing jy cheng charley yu ihor hlohowskyj allen tsao and mary picel

Results of Screening Analysis

  • G Area - No unacceptable risks indicated from the G Area

  • K Area

    • HI > 1 (only slightly) with 90% concentrations

    • HI < 1 with 50% concentrations (no unacceptable risks)


Results of site specific analysis

Results of Site-specific Analysis

  • Only for the K Area

    • With 90% soil concentration

      • The maximum HI was 0.65 for the Kangaroo Rat

      • No unacceptable risks


Results of site specific analysis cont

Results of Site-specific Analysis (Cont.)

  • Only for the K Area

    • With 50% soil concentration

      • The maximum HI was 0.01 for the Kangaroo Rat

      • No unacceptable risks


Conclusions

Conclusions

  • Potential radiation exposures of biota under current conditions (and conservative exposure assumptions) at the K Area and G Area are well below levels that could result in potentially unacceptable risks, and therefore, do not warrant either further evaluation or remediation

  • Any removal of hot spots can be expected to decrease ecological exposures and potential risks to even lower levels than those identified in this risk assessment


Development of tissue guidelines for aquatic organisms

Development of Tissue Guidelines for Aquatic Organisms

Are they at risk?

  • Conventional approach

    • Human protection

      • Evaluate tissue concentrations through the perspective of human health risks resulting from consuming the organisms

    • Radiation exposures of organisms are not considered

Are they at risk ?

Are they at risk ?

Are they at risk ?


Approach

Approach

  • Develop tissue guidelines by considering radiation exposure of organisms

  • Based on a dose limit of 0.01 Gy/d (1 rad/d)

  • Consider different types of organisms with different sizes

    • Fish, crustaceans, and mollusks

      • 0.001 – 100 kg for fish

      • 0.001 – 10 kg for crustaceans and mollusks

  • Consider both external and internal exposure

    • External exposure from contaminated water and sediment

  • Among the results for different organisms and geometric sizes, choose the most conservative values as tissue guidelines for screening purposes


Approach cont

BAFs from literature

BAFs from literature

Kds from NUREG/CR-6697

Kds from NUREG/CR-6697

Unit tissue

concentration

(1 pCi/g)

Unit tissue

concentration

(1 pCi/g)

Water

concentration

(pCi/g)

Water

concentration

(pCi/g)

Sediment

concentration

(pCi/g)

Sediment

concentration

(pCi/g)

Internal dose coefficient (rad/yr)/(pCi/g) from

RESRAD-BIOTA

Internal dose coefficient (rad/yr)/(pCi/g) from

RESRAD-BIOTA

External dose coefficient (rad/d)/(pCi/g) from

RESRAD-BIOTA

External dose coefficient (rad/d)/(pCi/g) from

RESRAD-BIOTA

External dose

(rad/d)

External dose

(rad/d)

External dose

(rad/d)

External dose

(rad/d)

Internal dose

(rad/d)

Internal dose

(rad/d)

Dose limit

(1 rad/d)

Dose limit

(1 rad/d)

Preliminary

tissue

guideline

(pCi/g)

Preliminary

tissue

guideline

(pCi/g)

Total dose

(rad/d)

Total dose

(rad/d)

Screening

tissue guideline

(Bq/kg)

Screening

tissue guideline

(Bq/kg)

Approach (Cont.)

For each geometric size and organism

BAFs from literature

Kds from NUREG/CR-6697

Unit tissue

concentration

(1 pCi/g)

Water

concentration

(pCi/g)

Sediment

concentration

(pCi/g)

Unit tissue

concentration

(1 pCi/g)

External dose coefficient

Internal dose coefficient

External dose

(rad/d)

External dose

(rad/d)

Internal dose

(rad/d)

Dose limit

(1 rad/d)

Preliminary

tissue

guideline

(pCi/g)

Total dose

(rad/d)

Screening

tissue

guideline

(Bq/kg)


Bioaccumulation factors and kds

Bioaccumulation Factors and Kds

  • Smallest bioaccumulation factors among different sources were used to get higher water concentrations

  • Kds suggested in NUREG/CR-6697 for generic soils were used to get sediment concentrations


Resrad biota results dose per unit tissue concentration

RESRAD-BIOTA Results – Dose per Unit Tissue Concentration

  • Geometric size has small effect on dose results

  • Depending on radionuclides, internal radiation dose can be smaller or greater than external radiation dose


Comparison of tissue guidelines

Comparison of Tissue Guidelines

Notes: (1) Unit for tissue guidelines is Bq/kg.

(2) The tissue guidelines based on 4 mrem/yr were derived assuming a consumption rate of 220 kg/yr

by fishermen.

(3) FDA DIL values were taken from U.S. Food and Drug Administration, 1998, Accidental Radioactive

Contamination of Human Foods and Animal Feeds: Recommendations for State and Local

Agencies, Washington, D.C., August 13.


Summary and conclusions

Summary and Conclusions

  • An approach was proposed to evaluate aquatic organism tissue concentrations from the perspective of biota exposures than human exposures.

  • The biota tissue guidelines derived based on the biota protection criterion are, in general, two to three orders of magnitude greater than those derived based on the human protection criterion.

  • The derived tissue screening guidelines can be used for comparison with tissue sampling data to determine whether further, more detailed analysis is necessary.


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