Presentation on theme: "Application of ERICA outputs and AQUARISK to evaluate radioecological risk of effluents from a nuclear site J. Twining & J. Ferris Objectives of this study."— Presentation transcript:
1 Application of ERICA outputs and AQUARISK to evaluate radioecological risk of effluents from a nuclear siteJ. Twining & J. FerrisObjectives of this studyTo apply quantitative, probabilistic radioecological risk assessment to routine and accidental release scenarios for liquid effluent from a working research reactorTo link currently available software & dataTo assess the applicability and suitability of the methodology to the task at hand.
2 Outline of talkBackground Objective - to demonstrate Radioecological Risk AssessmentDose Assessment software - EXPOSUREFASSET Radiation Effects Database - RESPONSEEcological Risk Assessment (AQUARISK)Case Study in Radioecological Risk AssessmentResultsConclusionsExposure- What the receiving environment is exposed to. For any environmental assessment this is derived from measurement or modelling (or a combination thereof) of the contaminant concentrations in the specific site.Response - Recorded measures of contaminant concentrations (in the literature or as a result of site & species specific studies) at or beyond which adverse impacts on biota are expected.Quantitative, probabilistic, radioecological risk assessment
3 Radiological Dose - EXPOSURE Radiological Impact Analysis for Coastal Aquatic Ecosystems V1.15 and Freshwater Ecosystems V1.15Converts 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 habitatsEach organism is represented as an ellipsoid for LET calculationsAssessment of dose to each organism is determined using concentration factors (internal dose) and positioning relative to soil/sediment or water (external dose).JF COMMENT - suggest listing of radionuclides covered by software (Those used are identified later - refer slide 9)The ‘Radiological impact assessment for coastal aquatic ecosystems’ software (Version 1.15; Copplestone et al. 2001) uses concentration factors (CFs) to calculate both external and internal dose to a series of ellipsoidal reference organisms – weighting factors for habitat and the primary radiation types are incorporated.Quantitative, probabilistic, radioecological risk assessment
4 Radiological Effect - RESPONSE Radiological Effect - RESPONSE (FASSET Radiation Effects Database, FRED)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, mortalityProvides information on dose (rate) responseNote that the filtering of the database to provide input to AQUARISK is covered on slide 10Quantitative, probabilistic, radioecological risk assessment
5 Ecological Risk Assessment (AQUARISK) A 3-tiered approachTier-1: Comparison with regulatory limits or guidelinesTier-2: Desk-top study involving available and relevant literature dataTier-3: Site-specific data and modellingThe 2nd & 3rd Tiers use probability density functions to derive site &/or species specific acceptability criteriaConvolution of the Exposure and Response PDFsdetermines the likely degree of ecological impact andthe extent ofremediationrequired(derived from frequency of observations)Probability densityExposurecurveResponse(Log) Dose-rate(µGy hr-1)% of specieslikely to beaffectedreduction in dose-rate requiredto achieve a tolerable level of harm* Three-tiered approach comparing measured/modelled environmental concentrations (in this case dose rates) with adverse effect criteria* Draws on two separate streams of information 1) site specific data on potential EXPOSURE (ie based on an exposure scenario and data on concentrations of given radionuclides in liquid effluent to calculate likely dose to various ecosystem components) and 2) Either regulatory/guideline values or Literature data on dose-RESPONSE by a range of different organisms with varying exposure periods and to different sources of radiationAQUARISK (Twining et al. 2002) fits probability distributions, separately, to both exposure and response data and uses a convolution algorithm to evaluate the overlap between the two. Probabilistic estimates of exposure criteria (dose or dose-rate) are derived from the distribution fitted to the response data selected from the FRED. These derived criteria can be set at stakeholder agreed values (eg 95% species protection (can range from 50-99%) and can also include an uncertainty factor (eg the 67% lower uncertainty bound of the 95% protection level). Uncertainty generally increases as the number of data decreases and hence leads to lower criteria values.AQUARISK uses a similar approach to that used to generate the Australian Water Quality Guidelines for concentrations of non-radiological materials in aquatic ecosystems (ANZECC/ARMCANZ, 2000) and similar approaches are applied internationally.
6 Case Study - ScenariosEffluent 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)Scenario (1) the 735x dilution represents directly sampled and measured data for dilution of known H-3 releases at Potter Point – achieved through periodic offshore water samplingScenario (2) effectively imprisons the freshwater ecosystem into the large release tank at ANSTO.Quantitative, probabilistic, radioecological risk assessment
7 Scenarios (1) Potter Point (2) Woronora R Potter Pt has a cliff-based outfall for tertiary-treated sewage
8 AQUARISK Input data - EXPOSURE Monitoring data for 3H, 60Co, 131I & 137Cs over Jan 2002-Jun 2003 based on monthly averagesActivity 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 radionuclideOnly used output for organisms that corresponded to data available in the FASSET Radiation Effects Database (FRED)All isotopes detected regularly were included in the analysis. When any of those isotopes were not detected in any month they were assigned a value of half the LLD for the purposes of dose-estimation.JF - In the course of analysing data from the environmental monitoring, I do not bother with stats for radionuclides where the amounts are not detected for more than 50% of the available data. The same approach has been applied in retaining the four nuclides used.Quantitative, probabilistic, radioecological risk assessment
9 EXPOSURE EstimationDose-rate from averaged radionuclide concentrations- Scenario #1All isotopes detected regularly were included in the analysis. When any of those isotopes were not detected in any month they were assigned a value of half the LLD for the purposes of dose-estimation.JF - In the course of analysing data from the environmental monitoring, I do not bother with stats for radionuclides where the amounts are not detected for more than 50% of the available data. The same approach has been applied in retaining the four nuclides used.
10 EXPOSURE Estimation Dose from averaged radionuclide concentrations - Scenario # 2All isotopes detected regularly were included in the analysis. When any of those isotopes were not detected in any month they were assigned a value of half the LLD for the purposes of dose-estimation.JF - In the course of analysing data from the environmental monitoring, I do not bother with stats for radionuclides where the amounts are not detected for more than 50% of the available data. The same approach has been applied in retaining the four nuclides used.
11 AQUARISK Input data - RESPONSE 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 radionuclideno 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)A simple data filtration, based on classificatory information provided within the FRED, was applied to exclude data with doses/dose-rates identified as ‘background’ and where both the standardized dose and dose-rate equalled zero. Data that were not either Lowest Observed Effect Dose-rates (LOEDR) or Highest No Effect Dose-rates (HNEDR) were then excluded, leaving a total of CHECK this value 554 HNEDR and LOEDR response entries from some Ditto 123 references. Of these, some 83% were for fish. It should be noted that identification of LOEDR and HNEDR in the FRED is only based on references specifying these values. As a result, other relevant references will have been excluded.Quantitative, probabilistic, radioecological risk assessment
12 RESPONSE EstimationDose-response cumulative probability (data from FRED)EXPLAIN1) Axes and units (ie Ln toxicity is actually dose-rate)2) Two Probability Density Functions fit (Log and Burr III) - Burr III fits the data best3) Vertical lines indicate ‘Guidelines’ and probabilistic ‘Criteria’ derived from the PDFs by AQUARISK but based solely on the data available from FRED
13 Results: Tier-1 assessment Scenarios (1) and (2) both pass a Tier-1 assessment against international recommendationsGarnier LaPlace et. al – Freshwater ecosystems 10Gy hr-1Maximum 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]Tier 1 - comparison of measured/modelled activity concentrations with recommended levelsThe marine dose rate is less than the freshwater dose rate because the activity was diluted by 25. The ratio is not exactly 25 because the dose estimates for FW organisms use different dose-conversion factorsQuantitative, probabilistic, radioecological risk assessment
14 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 lowerMax. est. acute dose in Scenario (2) is GyJF COMMENTs - suggest using explanation of uncertainty (in inverted commas below) only if there is time, or use it earlier (jrt-slide 6) in the general explanation of what AQUARISK does ‘Use of lower confidence limits based on uncertainty reduces the criteria even further, especially as the n decreases’Suggest that the role of AQUARISK-derived criteria needs explanation here - ie AQUARISK Tier-2 involves effectively using whatever input dose-response data it’s given to assign its own ‘guidelines’ and then compares the exposure PDF against the ‘Response’ PDF (criteria) to estimate probability of exceedence and % of species likely to be affected.Also Suggest that some caveat as to the conservative data selection used here should accompany the comment on criteria derived from exclusively ‘chronic’ response dataQuantitative, probabilistic, radioecological risk assessment
15 Results: Tier-2 Assessment Probability of criteria exceedenceNote that in most of the comparisons, ie either with international recommendation or with AQUARISK-derived values, the scenario has NO significant probability of exceeding the criterion used.The chronic marine scenario (1) is the only one where exceedence is likely.Even given that likelihood, the proportion of species that will be effected is very small (~5% at worst).The reason for the high likelihood of exceedence despite the low spp impact is due to the fact that the response data from FASSET has a long tail at the low dose rate end of the distribution. Hence, the exposure distribution is likely to overlap the response distribution but the area under the curve for the region of overlap is very smallQuantitative, probabilistic, radioecological risk assessment
16 Results: Tier-2 Assessment (cont.) estimated proportion of affected speciesConvolution of the EXPOSURE and RESPONSE probability density functions indicates the % of species potentially affectedScenario (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)Note that in most of the comparisons, ie either with international recommendation or with AQUARISK-derived values, the scenario has NO significant probability of exceeding the criterion used.The chronic marine scenario (1) is the only one where exceedence is likely.Even given that likelihood, the proportion of species that will be effected is very small (~5% at worst).The reason for the high likelihood of exceedence despite the low spp impact is due to the fact that the response data from FASSET has a long tail at the low dose rate end of the distribution. Hence, the exposure distribution is likely to overlap the response distribution but the area under the curve for the region of overlap is very smallQuantitative, probabilistic, radioecological risk assessment
17 Conclusions - Case study Scenarios (1) and (2) pass the Tier-1 RRA and hence can be considered of low risk to the organisms in the receiving environmentsTier 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-60However, 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 PointNOTE - Conservative assumptions were applied, in line with the Precautionary PrincipleThe FRED does have some impacts noted at very low dose rates (lowest is for fish uGy/hr LOEDR to produce abnormalities in Plaice larvae)spp impact did not consider any dilution within a mixing zone at the end of the pipe. Given that this is an ocean outfall the real dilution would be considerable. It also ignores biological responses both adaptive (to chronic exposures) and behavioural (eg avoidance) to acute high levels.There is no dilution implied apart from the 25 times (see notes for Case Study slide) - this underestimates likely dilution but aligns with ANSTO’s trade-waste agreement. There is going to be more dilution between the CSTP inter-stage and the outfall, even before it hits the sea. These are quite conservative scenarios, perhaps not ‘worst case’ but effectively quite close. This aligns with a tiered approach but it may arguably be better to set up and maintain as realistic as possible a scenario and apply a single, known factor at the very end. A next obvious step, in the event of the 5.5% effect being considered any sort of problem, is to bring in some sort of dispersion modelling to look at declining effect with distance from source, running a select few scenarios at various times or distances from the source. This is a more complex ask up front, but may be better than the current process of creeping towards the true situation by incremental refinements of the exposure scenario.Quantitative, probabilistic, radioecological risk assessment
18 Conclusions - generalAvailable software can be conservatively and successfully applied to RRACalculated exposure criteria (90-95% spp protection) are comparable to published recommendations, BUT chronic exposure criteria are substantially lowerStraightforward technique was used here- Scenario selections could be more realistic (mixing-zone dilutions and bioavailability) and can be refined to suit other site-specific applicationsImproved selectivity of RESPONSE data will help (more site-relevant data recovery from the FRED)Just want to underscore that 1) We succeeded in doing a basic RRA using three bits of software strung together. The ease with which this was accomplished points to the approach being generically robust and broadly applicable. Whilst not covered in the talk we have investigated sufficiently to suggest that further selectivity of the data is unwarranted, partly because the declining n increases the uncertainty 2) The AQUARISK-derived criteria are low for purely chronic exposure data - this deserves more study, 3) We were pretty conservative at various stages of the process and a we could be less so by considering dispersion modelling (but to what end in the case study considered). Also, similar questions regarding biological response (eg bioavailability, adaptation and avoidance) apply here as in non-radiological ERA, and 4) that we think there’s more useful data in the FRED than our conservative KISS approach recovered and that ERICA could/should look at ways to enhance the ability to select RRA-relevant data from FRED updated.Quantitative, probabilistic, radioecological risk assessment
19 Some Lessons Bioavailability (particulate adsorption) Co-60 dominant in the marine environmentCategories within FRED(ERICA)adsorption, rather than chemical bioavailabilitywithin the few nuclides considered‘aquatic generic’ dominates?Quantitative, probabilistic, radioecological risk assessment
20 Thank you. Objectives of this study To apply quantitative, probabilistic radioecological risk assessment to routine and accidental release scenarios for liquid effluent from a working research reactorTo link currently available software & dataTo assess the applicability and suitability of the methodology to the task at hand.