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Derivation of Environmental Radiological Protection Benchmarks a n overview

Derivation of Environmental Radiological Protection Benchmarks a n overview. jacqueline.garnier-laplace@irsn.fr. Definition of benchmarks. These values need to be based on scientific reasoning & be transparent. They correspond to screening values when they are used in screening tiers.

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Derivation of Environmental Radiological Protection Benchmarks a n overview

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  1. Derivation of Environmental Radiological Protection Benchmarksan overview jacqueline.garnier-laplace@irsn.fr

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

  3. Semi-probabilistic method pdf Uncertainty is introduced only in the exposure estimate. The risk index is expressed as a probability that the exposure estimate exceeds the PNEDR 1 • Probabilistic method pdf 1 A statistical distribution is also assigned to PNEDR (e.g. a species sensitivity distribution). This allows calculation of the probability of the risk. 0 How are they used to characterize the risk? • Deterministic method PNEDR PEDR The risk index is expressed as the ratio Predicted environmental dose rate:PNEDR 0

  4. Exposure-response relationship from ecotoxicity tests (stressor, species, endpoint) -> transpose to radioactive substances Effect (%) 100 % Observed data Regression model 50 % LOEDR: Lowest observed effect dose rate NOEDR: No observed effect dose rate 10 % ED50 EDR50 Dose (Gy) Dose Rate (µGy/h) ED10 EDR10 How to derive those « safe levels  »? • 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).

  5. How to derive those « safe levels  »? • 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

  6. 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 5% HDR5% How to derive those « safe levels  »? • The Species Sensitivity Distribution (SSD) Method • 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. PAF (%) 100 80 60 40 Dose (Gy) or Dose Rate (µGy/h) 20 0 1 10 100 1000 10000

  7. 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 • Only data devoted to effects induced by external irradiation pathway were quantitatively adequate to be mathematically structured in terms of dose-effect relationships. 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 • Mainly γ radiation types some: alpha, beta, neutron, X-ray • Acute data (80% - g external irradiation) : chronic data (20% - g external irradiation) • 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

  8. Chronic g external exposure conditions: SSD • Data set adequate to apply SSD-based method to derive the PNEDR • The application of the SF method came out with more stringent value. • ERICA adopted SSD-based methodology to derive its screening value. SSD-based PNEDR HDR5=81.8 SF = 5 rounded down and keeping 1 digit PNEDR 10 µGy/h

  9. 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

  10. Existing values: a brief review Method used and derived values (in µGy/h)

  11. 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

  12. News from UNSCEAR • UNSCEAR 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

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