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Update of UNSCEAR 1996

PROTECT Protection of the Environment from Ionizing Radiation in a Regulatory Context. 28 Years of Environmental Excellence. SENES Consultants Limited. Update of UNSCEAR 1996. Presented To: Workshop on Numerical Benchmarks for Protecting Biota Against Radiation in the Environment:

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Update of UNSCEAR 1996

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  1. PROTECT Protection of the Environment from Ionizing Radiation in a Regulatory Context 28 Years of Environmental Excellence SENES Consultants Limited Update of UNSCEAR 1996 Presented To: Workshop on Numerical Benchmarks for Protecting Biota Against Radiation in the Environment: Proposed Levels and Underlying Reasoning Aix-en-Provence, May 14, 2008 Presented By: Dr. Douglas B. Chambers

  2. Outline • Background • Estimating Doses to Non-Human Biota • UNSCEAR 1996 Summary • Chernobyl Dose Effects Summary • Effects of Radiation on Non-Human Biota (General Literature) • Conclusions

  3. Background (1) • In the past non-human biota have been considered as part of pathway to humans • Over past decades prevailing view on effects of ionizing radiation on non-human biota was: • If humans adequately protected, “then other living things are also likely to be sufficiently protected” (ICRP 1977) or “other species not put at risk” (ICRP 1991) • UNSCEAR first considered effects of ionizing radiation on biota in its 1996 report

  4. Background (2) • Increased worldwide concern over sustainability of environment (e.g., UNEP) has resulted in various efforts to assess effects to non-human biota • Due to increased interest in many countries, UNSCEAR decided to revisit its 1996 assessment of the dose rates below which effects on populations of non-human biota are unlikely

  5. UNSCEAR • Established by UN General Assembly resolution in 1955 • Scientists from 21 UN Member States • Other States & organizations provide relevant data • Holds annual sessions • Assess as scientific information on levels and effects of ionizing radiation • Disseminates findings to UN Assembly, UN agencies, scientific community & public

  6. General Assembly, public & scientific community • ICRP • Protection • Philosophy • Principles & units Effects Risks Findings • UNSCEAR • - Levels, effects, risks • Scientific independence Recommendations • FAO, IAEA, ILO, • WHO, UNEP • Protection • Standards Levels Data Scientific Literature, UN Member States, organizations & NGOs Development Implementation MemberStates

  7. UNSCEAR 1996 Update • Draft to be reviewed by Committee in July 2008 • (Hopefully) approved and published by year end • Key observations from review draft follow

  8. Outline • Background • Estimating Doses to Non-Human Biota • UNSCEAR 1996 Summary • Chernobyl Dose Effects Summary • Effects of Radiation on Non-Human Biota (General Literature) • Conclusions

  9. Estimating Doses to Non-Human Biota • Key Issues Include: • Transfer from Environment to Organism • Internal and External Radiation Exposure • Fraction of Radiation Absorbed by Organism • Relative Biological Effectiveness (RBE)

  10. Major Environmental Transfer Routes

  11. Fraction of Radiation Absorbed by Organism (1) • Radiation absorption is determined by: • Activity concentration in organism • Size of organism • Type of Radiation • Energy of Radiation • Key quantity for estimating doses is absorbed fraction [(E)]: • Fraction of energy emitted by radiation source that is absorbed within the target tissue, organ or organism • Internal and External dose conversion coefficients (DCC) for monoenergetic radiation have been calculated • In simplest case organism assumed to be in infinite homogenous medium, have uniformly distributed activity throughout body and densities of medium and organism’s body identical

  12. DCC for Reference Organisms Living on Soil

  13. DCC for Earthworm at Various Depths in Soil

  14. Relative Biological Effectiveness (Alpha) • Number of authors have reported nominal values for alpha RBE ranging from 5 to 40 • As noted by FASSET, difficult to develop a generally valid radiation weighting factor for use in environmental risk assessment • Updated UNSCEAR document recommends a nominal (generic) RBE of 10 for internally deposited alpha radiation

  15. Relative Biological Effectiveness (Beta) • Number of studies suggest that low-energy beta radiation with energies below 10 keV have higher biological effectiveness than beta radiation with energies above 10 keV (depends on reference radiation) • Updated UNSCEAR document continues to recommend a nominal (generic) RBE value of 1 for beta radiation but acknowledges the most appropriate RBE for low energy (<10 keV) beta radiation remains “open question”

  16. Outline • Background • Estimating Doses to Non-Human Biota • UNSCEAR 1996 Summary • Chernobyl Dose Effects Summary • Effects of Radiation on Non-Human Biota (General Literature) • Conclusions

  17. UNSCEAR 1996 Summary (1) • Unlikely that radiation exposures causing minor effects in most exposed individual would have significant effects on population • Individual responses to radiation exposure likely to be significant to population level: • Reproduction Endpoints • Mortality • Reproductive changes more sensitive indicator of radiation effects than mortality

  18. UNSCEAR 1996 Summary (2) • Mammals most sensitive animal organism • Dose rates that are unlikely to result in significant effects on population: • Chronic dose rates of less than 100 uGy/h to most exposed individual in terrestrial animal population • Maximum dose rates of 400 uGy/h to small proportion of individuals in aquatic populations • Notional range of 1 to 10 Gy acute exposure unlikely to result in effects on populations of non-human biota

  19. Outline • Background • Estimating Doses to Non-Human Biota • UNSCEAR 1996 Summary • Chernobyl Dose Effects Summary • Effects of Radiation on Non-Human Biota (General Literature) • Conclusions

  20. Chernobyl Dose EffectsSummary (1) • Chernobyl Forum important consolidation of data • Chernobyl Forum identifies 3 Distinct Exposure Phases:

  21. Chernobyl Dose EffectsSummary (2) • Phase 1: First 20 days, acute exposures due to large quantities of short-lived radionuclides • Gamma irradiation up to ~20 Gy/d deposited onto plant & ground surfaces • Additional  dose rate from deposited radionuclides to surface tissues and small biological targets (e.g., mature needles) • High doses to thyroids of vertebrate animals

  22. Chernobyl Dose EffectsSummary (3) • Phase 2: Summer and Autumn of 1986, short-lived radionuclides decayed and longer-lived radionuclides transported to different environmental components • Dose rates at soil surface declined to <10% of initial values • ~80% of total radiation accumulated on plants and animals was received within first 3 months and 95% of this was from beta radiation

  23. Chernobyl Dose EffectsSummary (4) • Phase 3: Continuing Phase, decay of short-lived radionuclides and migration of remaining Cs-137 into soil • Chronic dose rates less than 1% of initial values • Migration of Cs-137 has led to total radiation exposure from beta and gamma radiation more comparable

  24. Chernobyl Dose EffectsSummary (5) • Main Observations from Chernobyl Forum : • Numerous acute adverse effects in biota located in areas of higher exposure • No adverse radiation-induced effects reported in plants and animals to doses <0.3 Gy in first month after accident (i.e., <10 mGy/d) • By next growing season, population viability of plants and animals substantially recovered

  25. Population Effects Around Chernobyl(Geras’kin et al. 2008) Summarized effects data for: • Scots pine • Spruce • Herbaceous plants • Soil fauna • Amphibians • Hydrobiants • Small mammals • cattle

  26. Population Effects Around Chernobyl (Geras’kin et al. 2008)

  27. Outline • Background • Estimating Doses to Non-Human Biota • UNSCEAR 1996 Summary • Chernobyl Dose Effects Summary • Effects of Radiation on Non-Human Biota (General Literature) • Conclusions

  28. Previous Generic Reference Dose Rates

  29. Canada ENEVs • Environment Canada and Health Canada’s approach used in ecological risk assessment is using Estimated No Effect Values (ENEVs) • Application (safety) factor of 1 was used to estimate ENEVs for radiation • ENEVs based on detailed evaluations of literature

  30. ENEVs Used For Assessment Near Canadian Nuclear Facilities

  31. Summary for Chronic Effects Data Based on FRED

  32. Dose Rates Proposed Basedon ERICA Data

  33. ERICA SSD (1) • Species Sensitivity Distribution (SSD) developed for chronic and acute exposures to derive Predicted No Effect Dose Rate (PNEDR) • Chronic • SSD approximated the dose rates where 95% of species in aquatic/terrestrial ecosystem protected • HDR5 which results in 10% effect to 5% species • No statistical justification to derive ecosystem specific screening dose rates • HDR5 was 81.8 uGy/h • Derivation of PNEDR used safety factor of 5 • Screening dose rate of 10 uGy/h

  34. ERICA SSD(2) • Acute • Same SSD method applied for acute exposure • Statistical difference between marine ecosystems compared to terrestrial and freshwater ecosystems • Varied from about 1 to 5.5 Gy, according to ecosystem type • To derive PNED, safety factor of 5 was applied • PNEDs of 900 mGy for marine ecosystem and 300 mGy for terrestrial and freshwater ecosystems

  35. PROTECT Protection of the Environment from Ionizing Radiation in a Regulatory Context 28 Years of Environmental Excellence SENES Consultants Limited Conclusion • Overall conclusion is that population level effects on non-human biota are unlikely to be observed at chronic dose rates below (about) 100Gy/h, unchanged from 1996 • Recommend further work on mechanisms

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