update of unscear 1996

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PROTECT: Numerical Benchmarks Workshop, May 2008

Update of UNSCEAR 1996

Presented To:

Workshop onNumerical 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 Limited28 Years of Environmental Excellence

PROTECTProtection of the Environment from IonizingRadiation in a Regulatory Context

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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

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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

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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

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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

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Data

Scientific Literature,UN Member States,

organizations & NGOs

General Assembly, public & scientific community

Findings

Levels

Member States

Development Implementation

UNSCEAR- Levels, effects, risks- Scientific independence

ICRP- Protection- Philosophy - Principles & units

EffectsRisks

FAO, IAEA, ILO, WHO, UNEP- Protection- Standards

Recommendations

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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

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Outline



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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)

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Major Environmental Transfer Routes

Activity in air and rain Activity in water/sediment

Plants Soil/Sediment

Biota

Radiation exposure of biota

Internalexposure

Externalexposure

Externalexposure

Activity in air and rain Activity in water/sediment

Plants Soil/Sediment

Biota

Radiation exposure of biota

Internalexposure

Externalexposure

Externalexposure

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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

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DCC for Reference Organisms Living on Soil

Photon source energy (MeV)

0.01 0.1 1 10

DC

C (

Gy

per

phot

on/m

2 )

10-17

10-16

10-15

10-14

cattle roe deer wolf rabbit mole mouse

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DCC for Earthworm at Various Depths in Soil

0.01 0.1 1 1010-15

10-14

10-13

10-12

depth= 0,00 m depth= 0,05 m depth= 0,25 m depth= 0,50 m

DC

C (

Gy

per

phot

on/k

g)

Photon source energy (MeV)

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PROTECT: Numerical Benchmarks Workshop, May 2008Relative 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

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PROTECT: Numerical Benchmarks Workshop, May 2008Relative 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”

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Outline



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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

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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

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Outline



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Chernobyl Dose EffectsSummary (1)

Chernobyl Forum important consolidation of data

Chernobyl Forum identifies 3 Distinct Exposure Phases:

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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

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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

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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

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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

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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

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

Species effectEstimated minimum doses

(or dose rate) at which effect was observed

Estimated maximum doses at which effect

was not observed

Scots pine. Death of weakened trees 8–12 Gy 5 Gy

Mass death of young cones and anthers 10–12 Gy 5 Gy

Mass yellowing of needles, Scots pine 35–40 years old 8–12 Gy 5 Gy

Inhibition of reproductive capacity (reduced number of seeds per cone and increased fraction of hollow seeds)

1–5 Gy 0.5 Gy

Morphological disturbances one year after the accident 0.1–1.0 Gy 0.05 Gy

Significant increase in cytogenetic effects in seedlings and needles 0.5 Gy 0.05 Gy

Frequency of mutations of enzyme loci in seed endosperm 0.07 Gy 0.01 Gy

Spruce, 10–15 years old. Death of trees 4–5 Gy 1 Gy

Spruce, 25 years old. Dying-off of young sprouts. Mortality of much of the trees within 2–3 years

8–10 Gy 5 Gy

Spruce, 40 years old. Noticeable reduction in sprout mass 2.5–3 Gy 1 Gy

ETC

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Outline



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Previous Generic Reference Dose Rates

Biota IAEA 332 NCRP 109 UNSCEAR 1996

Terrestrial Plants

10 mGy/d

(4 Gy/a)

- 10 mGy/d

(4 Gy/a)

Terrestrial Animals

-Mortality-Reproductive

1 mGy/d

(0.4 Gy/a)

-

-

-

-

-

-

10 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)

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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

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ENEVs Used For Assessment Near Canadian Nuclear Facilities

Taxa ENEV (Gy a-1)

Fish 0.2 (0.5 mGy/d)

Benthic invertebrates 2 (5 mGy/d)

Algae 1 (3 mGy/d)

Macrophytes 1 (3 mGy/d)

Mammals 1 (3 mGy/d)

Terrestrial plants 1 (3 mGy/d)

Terrestrial invertebrates 2 (5 mGy/d)

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Summary for Chronic Effects Data Based on FRED

Wildlifegroup

Morbidity MortalityReproductive

capacityMutation

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 ~103 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 >103 μGy h-1

Radiation exposure increases the mutation rate

Mammals

Rat growth not affected at 16 μGy h-1 but affected at>3 x 103 μGy h-1

Some blood parameters affected at 180–850 μGy h-1. No effect on thyroid function at 8 x 103 μGy h‑1

No effect on mouse lifespan at 460 μGy h-

1, but significant reductions above ~103 μGy h-1 in the mouse, goat and dog

Threshold for effects at ~100 μGy h-1, with clear effects at >103 μGy h-1

Too few data to draw conclusions.One of nine references gives an LOEDR of 420 μGy h-1 for mice.

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Dose Rates Proposed Basedon ERICA Data

Targeted protected level as described in the

sourceMethod/justification of the value

Dose rate (µGy h‑1)

Reference

Terrestrial ecosystems

Generic ecosystems SSD-95% species protected plus SF of 5SSD giving an HDR5 of 81.8 Gy h‑1 divided by an SF of 5 and rounded down

10 [E9]

Generic ecosystems SF method: SF of 10 applied to the lowest critical radiotoxicity value EDR10

0.6 [E9]

Plants Background 0.02–0.7 [U3]

Plants Review, SF on the lowest critical radiotoxicity value

110 [B31, E5]

Plants Review based on NCRP 1991; IAEA 1992; UNSCEAR 1996

400 [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]

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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

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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

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Conclusion

Overall conclusion is that population level effects on non-human biota are unlikely to be observed at chronic dose rates below (about) 100Gy/h, unchanged from 1996

Recommend further work on mechanisms

SENES Consultants Limited28 Years of Environmental Excellence

PROTECTProtection of the Environment from IonizingRadiation in a Regulatory Context

update of unscear 1996

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