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1 PROTECT: Numerical Benchmarks Workshop, May 2008 Update of UNSCEAR 1996 Presented To: Workshop on Numerical Benchmarks for Protecting Biota Against Radiation.

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Presentation on theme: "1 PROTECT: Numerical Benchmarks Workshop, May 2008 Update of UNSCEAR 1996 Presented To: Workshop on Numerical Benchmarks for Protecting Biota Against Radiation."— Presentation transcript:

1 1 PROTECT: Numerical Benchmarks Workshop, May 2008 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 SENES Consultants Limited 28 Years of Environmental Excellence PROTECT Protection of the Environment from Ionizing Radiation in a Regulatory Context

2 2 PROTECT: Numerical Benchmarks Workshop, May 2008 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 3 PROTECT: Numerical Benchmarks Workshop, May 2008 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 4 PROTECT: Numerical Benchmarks Workshop, May 2008 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 5 PROTECT: Numerical Benchmarks Workshop, May 2008 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 6 PROTECT: Numerical Benchmarks Workshop, May 2008 Data Scientific Literature, UN Member States, organizations & NGOs General Assembly, public & scientific community Findings Levels Member States DevelopmentImplementation UNSCEAR - Levels, effects, risks - Scientific independence ICRP - Protection - Philosophy - Principles & units Effects Risks FAO, IAEA, ILO, WHO, UNEP - Protection - Standards Recommendations

7 7 PROTECT: Numerical Benchmarks Workshop, May 2008 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 8 PROTECT: Numerical Benchmarks Workshop, May 2008 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 9 PROTECT: Numerical Benchmarks Workshop, May 2008 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 10 PROTECT: Numerical Benchmarks Workshop, May 2008 Major Environmental Transfer Routes

11 11 PROTECT: Numerical Benchmarks Workshop, May 2008 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 organisms body identical

12 12 PROTECT: Numerical Benchmarks Workshop, May 2008 DCC for Reference Organisms Living on Soil

13 13 PROTECT: Numerical Benchmarks Workshop, May 2008 DCC for Earthworm at Various Depths in Soil

14 14 PROTECT: Numerical Benchmarks Workshop, May 2008 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 15 PROTECT: Numerical Benchmarks Workshop, May 2008 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 16 PROTECT: Numerical Benchmarks Workshop, May 2008 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 17 PROTECT: Numerical Benchmarks Workshop, May 2008 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 18 PROTECT: Numerical Benchmarks Workshop, May 2008 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 19 PROTECT: Numerical Benchmarks Workshop, May 2008 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 20 PROTECT: Numerical Benchmarks Workshop, May 2008 Chernobyl Dose Effects Summary (1) Chernobyl Forum important consolidation of data Chernobyl Forum identifies 3 Distinct Exposure Phases:

21 21 PROTECT: Numerical Benchmarks Workshop, May 2008 Chernobyl Dose Effects Summary (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 22 PROTECT: Numerical Benchmarks Workshop, May 2008 Chernobyl Dose Effects Summary (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 23 PROTECT: Numerical Benchmarks Workshop, May 2008 Chernobyl Dose Effects Summary (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 24 PROTECT: Numerical Benchmarks Workshop, May 2008 Chernobyl Dose Effects Summary (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 25 PROTECT: Numerical Benchmarks Workshop, May 2008 Population Effects Around Chernobyl (Geraskin et al. 2008) Summarized effects data for: Scots pine Spruce Herbaceous plants Soil fauna Amphibians Hydrobiants Small mammals cattle

26 26 PROTECT: Numerical Benchmarks Workshop, May 2008 Population Effects Around Chernobyl (Geraskin et al. 2008) Species effect Estimated minimum doses (or dose rate) at which effect was observed Estimated maximum doses at which effect was not observed Scots pine. Death of weakened trees8–12 Gy5 Gy Mass death of young cones and anthers10–12 Gy5 Gy Mass yellowing of needles, Scots pine 35–40 years old8–12 Gy5 Gy Inhibition of reproductive capacity (reduced number of seeds per cone and increased fraction of hollow seeds) 1–5 Gy0.5 Gy Morphological disturbances one year after the accident0.1–1.0 Gy0.05 Gy Significant increase in cytogenetic effects in seedlings and needles0.5 Gy0.05 Gy Frequency of mutations of enzyme loci in seed endosperm0.07 Gy0.01 Gy Spruce, 10–15 years old. Death of trees4–5 Gy1 Gy Spruce, 25 years old. Dying-off of young sprouts. Mortality of much of the trees within 2–3 years 8–10 Gy5 Gy Spruce, 40 years old. Noticeable reduction in sprout mass2.5–3 Gy1 Gy ETC

27 27 PROTECT: Numerical Benchmarks Workshop, May 2008 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 28 PROTECT: Numerical Benchmarks Workshop, May 2008 Previous Generic Reference Dose Rates BiotaIAEA 332NCRP 109UNSCEAR 1996 Terrestrial Plants10 mGy/d (4 Gy/a) -10 mGy/d (4 Gy/a) Terrestrial Animals - Mortality - Reproductive 1 mGy/d (0.4 Gy/a) mGy/d (4 Gy/a) 1 mGy/d (0.4 Gy/a) Aquatic Organisms -10 mGy/d (4 Gy/a) 10 mGy/d (4 Gy/a)

29 29 PROTECT: Numerical Benchmarks Workshop, May 2008 Canada ENEVs Environment Canada and Health Canadas 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 30 PROTECT: Numerical Benchmarks Workshop, May 2008 ENEVs Used For Assessment Near Canadian Nuclear Facilities TaxaENEV (Gy a -1 ) Fish0.2 (0.5 mGy/d) Benthic invertebrates2 (5 mGy/d) Algae1 (3 mGy/d) Macrophytes1 (3 mGy/d) Mammals1 (3 mGy/d) Terrestrial plants1 (3 mGy/d) Terrestrial invertebrates2 (5 mGy/d)

31 31 PROTECT: Numerical Benchmarks Workshop, May 2008 Summary for Chronic Effects Data Based on FRED Wildlife group MorbidityMortality Reproductive capacity Mutation Plant Plant growth begins to be affected at >100 μGy h -1. Continued exposure at 21 μGy h -1 for 8 years increases the sensitivity in pines 50% mortality at 8 years at ~10 3 μGy h -1 in pines A field study indicated a decrease in seed weight of a herb at 5.5 μGy h -1 The mutation rate in microsatellite DNA increased at ~40 μGy h -1 Fish One experiment, but not another, indicates effects on immune system at 8.3 μGy h - 1 Too few data to draw conclusions One study showing effects on gametogenesis at 230 μGy h -1. Otherwise effects at >10 3 μGy h -1 Radiation exposure increases the mutation rate Mammals Rat growth not affected at 16 μGy h -1 but affected at >3 x 10 3 μGy h -1 Some blood parameters affected at 180–850 μGy h -1. No effect on thyroid function at 8 x 10 3 μGy h 1 No effect on mouse lifespan at 460 μGy h - 1, but significant reductions above ~10 3 μGy h -1 in the mouse, goat and dog Threshold for effects at ~100 μGy h -1, with clear effects at >10 3 μGy h -1 Too few data to draw conclusions. One of nine references gives an LOEDR of 420 μGy h -1 for mice.

32 32 PROTECT: Numerical Benchmarks Workshop, May 2008 Dose Rates Proposed Based on ERICA Data Targeted protected level as described in the source Method/justification of the value Dose rate (µGy h 1 ) Reference Terrestrial ecosystems Generic ecosystemsSSD-95% species protected plus SF of 5 SSD giving an HDR5 of 81.8 Gy h 1 divided by an SF of 5 and rounded down 10[E9] Generic ecosystemsSF method: SF of 10 applied to the lowest critical radiotoxicity value EDR [E9] PlantsBackground0.02–0.7[U3] PlantsReview, SF on the lowest critical radiotoxicity value 110[B31, E5] PlantsReview based on NCRP 1991; IAEA 1992; UNSCEAR [O1, U16] ETC Aquatic and terrestrial flora and fauna Review concluded that few indications for readily observable effects at chronic dose rates below <100[F5]

33 33 PROTECT: Numerical Benchmarks Workshop, May 2008 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 HDR 5 which results in 10% effect to 5% species No statistical justification to derive ecosystem specific screening dose rates HDR 5 was 81.8 uGy/h Derivation of PNEDR used safety factor of 5 Screening dose rate of 10 uGy/h

34 34 PROTECT: Numerical Benchmarks Workshop, May 2008 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 35 PROTECT: Numerical Benchmarks Workshop, May 2008 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 SENES Consultants Limited 28 Years of Environmental Excellence PROTECT Protection of the Environment from Ionizing Radiation in a Regulatory Context


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