protectfp6-036425 derivation of environmental radiological protection benchmarks an overview...

FP6-036425FP6-036425PROTECT PROTECT

Derivation of Environmental Radiological Protection

Benchmarks

an overview

[email protected]


Definition of benchmarksNumerical values used to guide risk assessors These values need to be based on scientific reasoning & be transparent. They correspond to screening values when they are used in screening tiers.

Concentration (Bq per unit volume or mass), dose (Gy) or dose rate (Gy per unit time) assumed to be ‘safe’ for the object of protection Based on exposure –response information (e.g. ecotoxicity test endpoints). Referred to as PNEDR (Predicted No-Effects Dose Rate for ecosystems) in ERICA, as ENEV (a set

of Estimated no-effects values wildlife group-specific) in Env.Canada/CNSC…


How are they used to characterize the risk?

The risk index is expressed as the ratio Predicted environmental dose rate:PNEDR

PNEDR

0

PEDRDeterministic method

pdf1 Uncertainty is introduced only in the exposure

estimate. The risk index is expressed as a probability that the exposure estimate exceeds the PNEDR

Semi-probabilistic method

A statistical distribution is also assigned to PNEDR (e.g. a species sensitivity distribution). This allows calculation of the probability of the risk.0

1pdf

Probabilistic method


For chemicals, all existing approaches are based on available critical ecotoxicity data, typically EC50 for acute exposure conditions (short-term) and EC10 (preferred to NOEC) for chronic exposure conditions (long-term).

How to derive those « safe levels »?

Effect (%)

Regression model

100 %

50 %

10 %

ED10

EDR10

Dose (Gy)Dose Rate (µGy/h)

ED50

EDR50

Observed data

NOEDR: No observed effect dose rate

LOEDR: Lowest observed effect dose rate

Exposure-response relationship from ecotoxicity tests(stressor, species, endpoint) -> transpose to radioactive substances


SF

LowestEDRPNEDR 10

2 methods recommended by EC for chemicals (Technical Guidance Document (2003) – easily adaptable to radioactive substances when ED50 or EDR10 are available

The Safety Factor Method

Available ecotoxicity data SF to obtain

chronic PNEDR

At least one short-term ED50 from each of

three trophic levels (plant, invertebrate, vertebrate)

1000

One long-term EDR10 (either vertebrate or invertebrate)

100

Two long-term EDR10 from species representing two trophic levels among (plant, invertebrate, vertebrate)

50

Long-term EDR10 from at least three species (Plant, invertebrate, vertebrate) representing three trophic levels

10



Safe levels can be calculated with statistical extrapolation models to address variation between species in their sensitivity to a stressor.

The species for which results are known are representative, in terms of sensitivity, of the totality of the species in the ecosystem.

The endpoints measured in laboratory tests are indicative of effects on populations in the field.

The Species Sensitivity Distribution (SSD) Method

0

20

40

60

80

100

1 10 100 1000 10000

Dose (Gy) or Dose Rate (µGy/h)

PAF (%)


5%

HDR5%

Calculation of a dose rate that is assumed to protect a given % of species

In the Technical Guidance Document (2003): the agreed concentration is the hazardous concentration affecting 5 % of species with 50% confidence. When its remains other extrapolation issues, the TGD recommends to apply an additionnal SF (1-5)->until now, only used for ERICA screening value

SF

HDRPNEDR 5


Analysis of the effects data from FREDERICA by ERICA

More than 25,000 data entries - couples (dose, effect) along with info on their acquisition - « raw » data series from experiments – lab or field) - dose-effect relationship not mathematically structured

Acute data (80% - external irradiation) : chronic data (20% - external irradiation)

Mainly γ radiation types some: alpha, beta, neutron, X-ray

Four endpoints: mortality, morbidity, reproductive capacity, mutation

more on reproduction for acute; more on morbidity for chronic, followed by reproduction; too few data on mutation whatever the exposure regime

Only data devoted to effects induced by external irradiation pathway were quantitatively adequate to be mathematically structured in terms of dose-effect relationships.

Meta-analysis of effect data to reconstruct dose-effect relationships and to estimate comparable critical ecotoxicity endpoints ie ED50 for acute exposure and EDR10 from chronic exposure


Sp = weighted; TW: none

0%

20%

40%

60%

80%

100%

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07

Dose Rate (µGy/h)

Best-Estimate Centile 5% Centile 95%

Vertebrates Plants Invertebrates

R² = 0.9513

KSpvalue = 0.500wm.lg = 3.71wsd.lg = 1.09

Log Normal – Generic Ecosystem (SW+FW+TER)

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HDR5 = 81.8 µGy/h

CI95% = [23.8-336] µGy/h

Number of data = 24Number of species = 18

Sp = weighted; TW: none

0%

20%

40%

60%

80%

100%

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07

Dose Rate (µGy/h)

Best-Estimate Centile 5% Centile 95%

Vertebrates Plants Invertebrates

R² = 0.9513

KSpvalue = 0.500wm.lg = 3.71wsd.lg = 1.09

Log Normal – Generic Ecosystem (SW+FW+TER)

Cum

ula

tive

we

ight

ed

pro

bab

ility

HDR5 = 81.8 µGy/h

CI95% = [23.8-336] µGy/h

Number of data = 24Number of species = 18

Data set adequate to apply SSD-based method to derive the PNEDRThe application of the SF method came out with more stringent value.ERICA adopted SSD-based methodology to derive its screening value.

HDR5=81.8

SF = 5rounded downand keeping 1 digit

PNEDR 10 µGy/h

Chronic external exposure conditions: SSD

SSD-based PNEDR


How to use properly the ERICA PNEDR?

PNEDR does not apply for any other ecological object to be protected (than generic ecosystem)

PNEDR was derived to be used in the first tiers of the ERICA tiered approach

PNEDR is the benchmark value to screen against incremental dose rates and not to total dose rates including background (similar to the added risk method (Struijs et al., 1997).

■ Implicit assumption is that the BG has resulted in the biodiversity of ecosystems. No deleterious potential effect originating from the

background


Existing values: a brief review

Environment Canada Review, SF on the lowest Critical radioToxicity Value Terrestrial Plants 110 Terrestrial Invertebrates 220 Small mammals 110 Aquatic algae/macrophytes 110 Amphibians/Reptiles 110 Benthic invertebrates 220 Fish 20 USDoE Review based on NCRP 1991; IAEA 1992; UNSCEAR 1996 Terrestrial Plants or Aquatic animals 400 Terrestrial Animals 40 Environment Agency (UK) Critical review for screening purpose from IAEA 1992 Terrestrial Plants 400 Terrestrial Animals 40 Freshwater and coastal marine organisms 400 Marine mammals 40 Deep ocean organisms 1000 5 % of guideline values from AIEA at initial screening tier fSu Review Contaminated environments Vertebrates and cytogenetic effects 4 – 20 Vertebrates and effects on morbidity 20 – 80 Vertebrates and effects on reproduction 80 – 200

Method used and derived values (in µGy/h)


Objectives within PROTECT WP3 “To derive an extended set of numerical target values and their

associated derivation methods, designed to assure compliance to environmental protection goals that resonate with protective goals set up for releases of hazardous substances in general, and to assess the implications for society at large.”

On the basis of the target for protection (& the level of protection) [WP1-WP2], explore the possibility for the application of advanced statistical methods (classical or Bayesian) that:

(1) allow to make the best use of the available knowledge when this is represented by small data sets,

(2) allow to quantify the associated uncertainty,

(3) easily allow to revise the outcoming values when new knowledge becomes available


News from UNSCEARUNSCEAR literature review (1996) is currently under

revision

Some of the key components of the « effects » sections:New knowledge on effects since 1996 presented, starting with a

review on effects mechanisms from subcell to higher organisational level

Review of existing approaches (methods used to assess the radiological impact or the risk to ecological objects & their associated benchmarks).

Case studies for illustration purpose

Too early to say whether this would result in a major revision of the former well- known statement

protectfp6-036425 derivation of environmental radiological protection benchmarks an overview...

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