Risk Analyses and the Development of Radiological Benchmarks

1. Risk Analyses and the Development of Radiological Benchmarks Tom Hinton (IRSN)

2. OBJECTIVES What is a benchmark? Why are benchmarks needed? How are benchmarks derived? How are benchmarks used?

3. INTRODUCTION The need for benchmarks... ... a retrospective screening model example www.ceh.ac.uk/PROTECT

4. A Tier-1 screening model of risk to fish living in a radioactively contaminated stream during the 1960s Fundamental to this approach is the necessity for the dose estimate to be conservative This assures the modeler that the PREDICTED DOSES areLARGERthan the REAL DOSES www.ceh.ac.uk/PROTECT

5. 5000 4000 1) SOURCE TERM: used 1964 3000 maximum release as a mean Total 137-Cs Released (GBq) 2000 for calculations 1000 2) EXPOSURE: assumed fish 0 were living at point of discharge 54 59 64 69 74 79 84 Year 3) ABSORPTION: assumed all fish were 30 cm in diameter which maximized absorbed dose 4) IRRADIATION: behavior of fish ignored, assumed they spent 100% of time on bottom sediments where > 90% of radionuclides are located CONTAMINATED SEDIMENTS Conservative Assumptions for Screening Calculations www.ceh.ac.uk/PROTECT

6. Resulting Dose Rates (mGy y-1) www.ceh.ac.uk/PROTECT

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10. We need a point of reference; a known value to which we can compare… …a BENCHMARK value

11. Definition of Benchmarks Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach. Benchmarks values are concentrations, doses, or dose rates that are assumed to be safe based on exposure – response information. They represent « safe levels » for the ecosystem. • The derivation of benchmarks needs to be through transparent, scientific reasoning • Benchmarks correspond to screening values when they are used in screening tiers www.ceh.ac.uk/PROTECT

12. Knowledge of ionising radiation’s effect on wildlife is the basis for the derivation of radiological risk benchmarks www.ceh.ac.uk/PROTECT

13. Whatisknown about effectsfromionising radiation? www.ceh.ac.uk/PROTECT

14. Henri Becquerel (1852-1908) Becquerel plate, 1896 Discoverer of radioactivity, 1903 Nobel Prize in Physics Wilhelm Rontgen (1845—1923) First roentgenogram, 1895 Marie Curie (1867-1934) First Nobel Prize in Physics, 1901 www.ceh.ac.uk/PROTECT

15. DNA is the primary target for the induction of biological effects from radiation in ALL living organisms Broad similarities in radiation responses for different organisms……and yet, wide differences in radiation sensitivity www.ceh.ac.uk/PROTECT (Whicker and Schultz, 1982)

16. Different kinds of DNA damage induced by γ-radiation per 0.01 Gy base loss base change H O OH single stand break H double stand break interstrand crosslinks www.ceh.ac.uk/PROTECT Feinendegen, Pollycove. J. Nucl. Medicine. 2001. V.42. p. 17N-27N

17. Free Radicals (unstable molecule that loses one of its electrons) www.ceh.ac.uk/PROTECT

18. DNA damage and repair www.ceh.ac.uk/PROTECT

19. Cell Death Cancer Fate of Mutations Germ Cells Somatic Cells Decrease in number and quality of gametes Alteration to offspring Increased embryo lethality www.ceh.ac.uk/PROTECT

20. Confer a selective advantage Spread in the population Cell Remove from the population Deleterious mutations Mutation Persist over many generations Neutral mutations Fate of mutations in non-human biota • For humans, risk of hereditary effects in offspring of exposed individuals is about 10% of the cancer risk to the exposed parents(UNSCEAR, 2001) • For non-human biota the risk of hereditary effects is unknown www.ceh.ac.uk/PROTECT

21. Knowledge on Effects of Radiation Exposure on Wildlife www.ceh.ac.uk/PROTECT

22. wealth of data about the biological effects of radiation on plants and animals • early data came from… • laboratory exposures • accidents (Kyshtym, 1957) • areas of naturally high background • nuclear weapons fallout • large-scale field irradiators www.ceh.ac.uk/PROTECT

23. Factors Influencing the Sensitivity of Plants to Radiation (Sparrow, 1961) www.ceh.ac.uk/PROTECT

24. Radiation Effects on Non-Human Biota Early Mortality premature death of organism These categories of radiation effects are similar to the endpoints that are often used for risk assessments of other environmental stressors, and are relevant to the needs of nature conservation and other forms of environmental protection Morbidity reduced physical well being including effects on growth and behavior Reproduction is thought to be a more sensitive effect than mortality Reproductive Success reduced fertility and fecundity www.ceh.ac.uk/PROTECT

25. for chronic, low level exposure to radiation, alone, or mixed with other contaminants population, community, ecosystem > mortality, < fecundity, sublethal effects Fundamental Differences In Human and Ecological Risk Analyses TypeUnit of ObservationEndpoint Dose-Response Human individual lifetime cancer relationships risk established Ecological varies varies not established www.ceh.ac.uk/PROTECT

26. Predicting radiological effects to wildlife is complicated because: Populations are resilient Compensating mechanisms exist Indirect effectsoften occur that are unpredictable Blaylock (1969) studies at Oak Ridge DIRECT EFFECT: Increased mortality of fish embryos exposed to 4 mGy / d INDIRECT EFFECT: Fish produced larger brood sizes NET RESULT: No effect to population www.ceh.ac.uk/PROTECT

27. With the removal of humans, wildlife around Chernobyl are flourishing 48 endangered species listed in the international Red Book of protected animals and plants are now thriving in the Chernobyl Exclusion Zone Russian Boar Wolves Prejevalsky Horses www.ceh.ac.uk/PROTECT

28. Data Base of Knowledge on Effects of Radiation Exposure on Biota FREDERICA (www.frederica-online.org) • An online database of literature data to help summarise dose-effect relationships • FREDERICA can be used on its own; or in conjunction with the ERICA assessment tool (for conducting risk assessments of wildlife exposed to ionising radiation) (> 1500 references; 26 000 data entries) www.ceh.ac.uk/PROTECT

29. FREDERICA Database Chronic - external Acute-internal Chronic - internal Acute-external Chronic-internal Chronic-external Acute-external Acute-internal 73% of all data effects data; per ecosystem per exposure pathway (external or internal irradiation) per duration (acute or chronic) www.ceh.ac.uk/PROTECT

30. Data on radiation effects for non-human species Chronic effects and γ external irradiation Reproductive capacity Morbidity Mortality Mutation Amphibians Aquatic invertebrates Aquatic plants Bacteria Birds Crustaceans Fish Fungi Insects Mammals Molluscs Moss/Lichens Plants Reptiles Soil fauna Zooplankton To few to draw conclusions No data Some data www.ceh.ac.uk/PROTECT

31. Approaches to derive protection criteria www.ceh.ac.uk/PROTECT

32. Exposure-response relationship from ecotoxicity tests Effect (%) 100 % Observed data Regression model 50 % LOEC: Lowest observed effect concentration NOEC: No observed effect concentration 10 % Contaminant Concentration How to derive « safelevels » methods recommended by European Commission for estimating predicted-no-effects-concentrations for chemicals …based on available ecotoxicity data; (i.e. Effect Concentrations; EC) typically EC50 for acute exposure conditions and EC10 for chronic exposures EC10 EC50 www.ceh.ac.uk/PROTECT

33. How to derive « safelevels » ....adapted for radiological conditions.... Exposure-response relationship from ecotoxicity tests (specific to stressor, species, and endpoint) Effect (%) 100 % Observed data Regression model 50 % LOEC: Lowest observed effect concentration NOEC: No observed effect concentration 10 % EC50 ED50 EDR50 Concentration (Bq/L or kg) Dose (Gy) Dose Rate (µGy/h) EC10 ED10 EDR10

34. Deriving benchmarks for radioecological risk assessments i.e. screening values thought to be protective of the structure and function of generic freshwater, marine and terrestrial ecosystems. • Two methods have been developed • Fixed Assessment (Safety) Factors Approach • Species Sensitivity Distribution Approach www.ceh.ac.uk/PROTECT

35. Fixed Assessment Factor Method PNEV = minimal Effect Concentration / Safety Factor The safety factor method is highly conservative as it implies the multiplication of several worst cases www.ceh.ac.uk/PROTECT

36. The approach used to derive no-effects values www.ceh.ac.uk/PROTECT

37. The predicted no-effect dose rate (PNEDR) evaluation www.ceh.ac.uk/PROTECT

38. SSD for generic ecosystem at chronic external γ-radiation (ERICA) • The 5% percentile of the SSD defines HDR5 (hazardous dose rate giving 10% effect to 5% of species) • HDR5 = 82 μGy/h • PNEDR used as the screening value at the ERA should be highly conservative • SF = 5 • PNEDR ≈ 10 μGy/h PNEDR = HDR 5% / SF www.ceh.ac.uk/PROTECT

39. Percentage of Affected Fraction 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 5% 0% 0.1 1 10 100 1000 10000 100000 1000000 10000000 Dose rate (µGy/h) HDR5 = 17 µGy/h [2-211] Best-Estimate Centile 5% Centile 95% Vertebrates Plants Invertebrates SSD for generic ecosystem at chronic external γ-radiation (PROTECT) Generic ecosystem and chronic g exposure EDR10 and 95%CI: Minimum value per species PNEDR=10 µGy/h (SF of 2) www.ceh.ac.uk/PROTECT

40. We need a point of reference; a known value to which we can compare… …a BENCHMARK value 10 μGy/h * 24 h / d = 240 μGy/d = 0.2 mGy /d www.ceh.ac.uk/PROTECT

41. Reminders… • The PNEDR is a basic generic ecosystem screening value to benchmark where additional work is needed • The derived PNEDR equal to 10 μGy/h can be applied to a number of situations for which environmental and human risk assessment are carried out • The risk assessor needs to be aware of the following rules while using the ERICA tool: • the PNEDR does not apply for any other ecological object to be protected besides the generic ecosystem • the PNEDR was derived for use only in the first two tiers of the ERICA Integrated Approach • the PNEDR is the benchmark value for screening against incremental dose rates, and not the total dose rates including background www.ceh.ac.uk/PROTECT

42. IAEA (1992) and UNSCEAR (1996) suggested the following no-effect values for populations of non-human biota: • for aquatic animals and terrestrial plants- 400 μGy/h • for terrestrial animals- 40 μGy/h • Derived using a SSD approach, the PNEDR of 10 μGy/h is consistent with these previously recommended values • The hazardous dose rate definition means that 95% of species would be protected. However, there may be keystone species among the 5% that are unprotected. www.ceh.ac.uk/PROTECT

43. Background radiation exposure for wildlife (UNSCEAR, 1996; 2000) Derived screening dose rate (10 μGy/h) is more than 10 times these background values www.ceh.ac.uk/PROTECT

44. ‘Concentration limits’ Both ERICA Tool & RESRAD-BIOTA use ‘tiered assessments’ with initial assessment (Tier-1) being very simple (minimal input---conservative output) YOUR media concentrations compared to the MODEL’s pre-defined concentrations (i.e. media concentrations that result in a PNEDR) • ERICA: ‘environmental media concentration limits’ EMCLs • RESRAD-BIOTA: ‘biota concentration guidelines’ BCGs www.ceh.ac.uk/PROTECT

45. ERICA Tool – EMCLs Environmental Media Concentration Limits Estimated assuming: • Habitat characteristics that maximise exposure • Probability distributions associated with the default CR and Kd databases were used to determine 5th percentile EMCL • No conservatism applied to dosimetry • For aquatic ecosystems EMCL for water includes consideration of external dose from sediment and that for sediment includes external dose from water and biota-water transfer www.ceh.ac.uk/PROTECT

46. RESRAD-BIOTA - BCGs Estimated assuming: • Infinitely large (internal) and small (external) geometries for dose calculations • Daughter T1/2’s up to 100 y included • All terrestrial organisms 100% in soil; aquatic 100% water-sediment interface • ‘Maximum’ CR values or 95th percentile CR values predicted using a kinetic-allometric approach www.ceh.ac.uk/PROTECT

47. Answers What is a benchmark? How are benchmarks derived? Safety Factor Method stringentmethod as the PNEC value isobtained by dividing the lowestcritical data by an appropriate SF rangingfrom 10 to 1000. Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach. Is the new benchmark of 10 µGy/h final? SpeciesSensitivity Distribution based on a statistical extrapolation model to address variation betweenspecies in theirsensitivity to a stressor. www.ceh.ac.uk/PROTECT