Background Objective - to demonstrate Radioecological Risk Assessment

Application of ERICA outputs and AQUARISK to evaluate radioecological risk

of effluents from a nuclear site

J. Twining & J. Ferris

• BackgroundObjective - to demonstrate Radioecological Risk Assessment

• Dose Assessment software - EXPOSURE

• FASSET Radiation Effects Database - RESPONSE

• Ecological Risk Assessment (AQUARISK)

• Case Study in Radioecological Risk Assessment

• Results

• Conclusions

Outline of talk

Quantitative, probabilistic, radioecological risk assessment

• Radiological Impact Analysis for Coastal Aquatic Ecosystems V1.15 and Freshwater Ecosystems V1.15

• Converts measured or modelled radioactivity concentrations in water (Bq L-1) into dose rates (Gy hr-1)

• For a range of radiologically significant nuclides, biota and habitats

• Each organism is represented as an ellipsoid for LET calculations

• Assessment of dose to each organism is determined using concentration factors (internal dose) and positioning relative to soil/sediment or water (external dose).

Radiological Dose - EXPOSURE


• FRED is a database of published information on the effects of acute and chronic exposure to ionising radiation on different biota (EC 5th Framework FASSET initiative)

• Groups data by:

• wildlife “group” (e.g. amphibians, reptiles, mammals etc.)

• umbrella endpoint: mutation, morbidity, reproduction, mortality

• Provides information on dose (rate) response

Radiological Effect - RESPONSE(FASSET Radiation Effects Database, FRED)


• A 3-tiered approachTier-1: Comparison with regulatory limits or guidelines

Tier-2: Desk-top study involving available and relevant literature data

Tier-3: Site-specific data and modelling

• The 2nd & 3rd Tiers use probability density functions to derive site &/or species specific acceptability criteria

Pro

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)

Exposurecurve

Responsecurve

(Log) Dose-rate(µGy hr-1)

% of specieslikely to beaffected

reduction in dose-rate required to achieve a tolerable level of harm

• Convolution of the Exposure and Response PDFsdetermines the likely degree of ecological impact andthe extent ofremediation required

Ecological Risk Assessment (AQUARISK)

• Effluent releases from ANSTO at the LHSTC in Sydney, Australia

(1) Routine releases into the marine environment at Potter Point via the sewage system and tertiary treatment at Cronulla STP (assumes 735x dilution as realistic for the site, chronic exposure)

(2) Possible accidental release into the Woronora River after failure of the main holding tank (assumes no loss of activity overland, no dilution, acute exposure)

Case Study - Scenarios


Scenarios

(2) Woronora R

(1) Potter Point

• Monitoring data for 3H, 60Co, 131I & 137Cs over Jan 2002-Jun 2003 based on monthly averages• Activity concentrations were converted to dose rates using either Coastal or Freshwater RIA software (using updated CFs and default weighting factors)

• Once converted to dose-rate no differentiation was made for radionuclide

• Only used output for organisms that corresponded to data available in the FASSET Radiation Effects Database (FRED)

AQUARISK Input data - EXPOSURE


• Dose-rate from averaged radionuclide concentrations- Scenario #1

EXPOSURE Estimation

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• Dose from averaged radionuclide concentrations- Scenario # 2

EXPOSURE Estimation

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• FASSET Radiation Effects Database (FRED) (using categories and information in the FRED to select data for use in Radioecological Risk Assessment)

• HNEDRs and LOEDRs only, and excluding ‘Background’ data (retains ~10% of available data)

• no distinction based on radionuclide• no discrimination based on effect measured (all adverse effects assumed to be ecologically relevant)

• all units converted to Gy hr-1 or Gy (using conservative assumptions)

AQUARISK Input data - RESPONSE


• Dose-response cumulative probability (data from FRED)

RESPONSE Estimation

• Scenarios (1) and (2) both pass a Tier-1 assessment against international recommendations

Maximum estimated dose rates for all spp.(Gy hr-1, n = 162)

(1) Routine release into a marine ecosystem 0.3 [(2) Accidental release to a freshwater system 8.7]

Gy hr-1 NCRP IAEA CanadaFreshwater organisms 400 400Benthic invertebrates 100Fish 50

Results: Tier-1 assessment


Garnier LaPlace et. al. 2006 – Freshwater ecosystems 10Gy hr-1

Results: Tier-2 AQUARISK-derived criteria (using data selected from the FRED)

• Criteria for 90-95% protection (using Acute &/or Chronic data selected from the FRED) cover the range of international dose-rate recommendations (i.e. 10 – 400 uGy.hr-1)

• Criteria based exclusively on chronic RESPONSE data are substantially lower• Max. est. acute dose in Scenario (2) is 0.006 Gy

Marine Freshwater Acute &

Chronic Chronic

only Acute &

Chronic Acute only

n 425 85 52 32

Units µGy hr-1 µGy hr-1 µGy hr-1 Gy

90 % 740 2.2 230 0.9 Species protection

level 95 % 13 0.3 33 0.3


• Probability of criteria exceedence

Chronic Marine

A & C FW

Acute FW (Gy)

Criteria IAEA, NCRP

Canada 90%

95%

90%

95%

90%

95%

Value (Gy.hr-1or Gy) 400 100 50 4.5 0.3 250 40 0.9 0.4

Probability of exceedence (%)

0

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Results: Tier-2 Assessment



Results: Tier-2 Assessment (cont.)

estimated proportion of affected species

Convolution of the EXPOSURE and RESPONSE probability density functions indicates the % of species potentially affected

• Scenario (1) - Marine = 1.5 to 2.5% (depends on selection

of ‘Acute & Chronic’ or ‘Chronic only’ RESPONSE data)• Scenario (2) - Freshwater = 0.2 to 0.3% (depends on selection of ‘Acute & Chronic’ dose-rate data or ‘Acute only’ dose

data)

• Scenarios (1) and (2) pass the Tier-1 RRA and hence can be considered of low risk to the organisms in the receiving environments

• Tier 2 assessments using AQUARISK indicate lower dose rate criteria may be applied for chronic, routine releases under Scenario (1)

- Operational efforts should focus on Co-60

• However, low species impacts are predicted for either scenario even when all conservative assumptions have been applied in line with the Precautionary Principle.

• Biomonitoring under scenario (1) has not shown any adverse effects at Potter Point

Conclusions - Case study


• Available software can be conservatively and successfully applied to RRA

• Calculated exposure criteria (90-95% spp protection) are comparable to published recommendations, BUT chronic exposure criteria are substantially lower

• Straightforward technique was used here

- Scenario selections could be more realistic (mixing-zone dilutions and bioavailability) and can be refined to suit other site-specific applications

- Improved selectivity of RESPONSE data will help (more site-relevant data recovery from the FRED)


Conclusions - general

• Bioavailability (particulate adsorption)

• Co-60 dominant in the marine environment

• Categories within FRED(ERICA)


Some Lessons

Thank you.

Documents

Background Objective - to demonstrate Radioecological Risk Assessment