Application of RESRADBIOTA for a Sitespecific Ecological Risk Assessment and the Development of Radi

1
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.

2
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

3
RESRAD-BIOTA

• A computer code that implements the U.S.
  Department of Energys (DOEs) 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

4
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

5
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
6
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

7
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

8
Exposure Point Concentrations
9
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
10
Receptors of Concern

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

11
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

12
Exposure Factors
13
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

14
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 lt 1, no unacceptable risks
• HI gt 1, potential for unacceptable risks

15
Results of Screening Analysis

• G Area - No unacceptable risks indicated from the
  G Area
• K Area
• HI gt 1 (only slightly) with 90 concentrations
• HI lt 1 with 50 concentrations (no unacceptable
  risks)

16
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

17
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

18
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

19
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 ?
20
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

21
Approach (Cont.)
For each geometric size and organism
BAFs from literature
Kds from NUREG/CR-6697
Unit tissue concentration (1 pCi/g)
Sediment concentration (pCi/g)
Water 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)
22
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

23
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

24
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.
25
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.