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David Copplestone Centre for Ecology & Hydrology - Lancaster October 2011.

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Presentation on theme: "David Copplestone Centre for Ecology & Hydrology - Lancaster October 2011."— Presentation transcript:

1 David Copplestone Centre for Ecology & Hydrology - Lancaster October 2011

2 What is a benchmark? Why are benchmarks needed? How are benchmarks derived? How are benchmarks used?

3 The need for benchmarks a retrospective screening model example

4 Fundamental to this approach is the necessity for the dose estimate to be conservative A Tier-1 screening model of risk to fish living in a radioactively contaminated stream during the 1960s This assures the modeler that the PREDICTED DOSES are LARGER than the REAL DOSES

5 Conservative Assumptions for Screening Calculations

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10 …a BENCHMARK value We need a point of reference; a known value to which we can compare…

11 Benchmarks values are concentrations, doses, or dose rates that are assumed to be safe based on exposure – response information. They represent « safe levels » for the ecosystem Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach The derivation of benchmarks needs to be through transparent, scientific reasoning Benchmarks correspond to screening values when they are used in screening tiers

12 No data To few to draw conclusions Some data

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15  From literature reviews  Earlier numbers derived by expert judgement (different levels of transparency)  Later numbers, more quantitative/mathematical  Levels of conservatism?  Often “maximally exposed individual” not population...  NCRP 1991 states use with caution if large number of individuals in a population may be affected

16  Used to derive the ERICA and PROTECT values  Consistent with EC approach for other chemicals

17 Effect (%) Regression model 100 % 50 % 10 % Contaminant Concentration Observed data NOEC: No observed effect concentration LOEC: Lowest observed effect concentration Exposure-response relationship from ecotoxicity tests …based on available ecotoxicity data; (i.e. Effect Concentrations; EC) typically EC 50 for acute exposure conditions and EC 10 for chronic exposures Methods recommended by European Commission for estimating predicted-no-effects-concentrations for chemicals EC 10 EC 50

18 Effect (%) Regression model 100 % 50 % 10 % EC 10 ED 10 EDR 10 Concentration (Bq/L or kg) Dose (Gy) Dose Rate (µGy/h) EC 50 ED 50 EDR 50 Observed data NOEC: No observed effect concentration LOEC: Lowest observed effect concentration Exposure-response relationship from ecotoxicity tests (specific to stressor, species, and endpoint)....adapted for radiological conditions....

19 i.e. screening values thought to be protective of the structure and function of generic freshwater, marine and terrestrial ecosystems. Two methods have been developed Fixed Assessment (Safety) Factors Approach Species Sensitivity Distribution Approach

20 Main underlying assumptionsIn the frame of this approach, extrapolations are made from: The ecosystem response depends on the most sensitive species Protecting ecosystem structure protects community function Acute to chronic One life stage to the whole life cycle Individual effects to effects at the population level One species to many species One exposure route to another Direct to indirect effects One ecosystem to another Different time and spatial scales PNEV = minimal Effect Concentration / Safety Factor

21 Main underlying assumptionsIn the frame of this approach, extrapolations are made from: The ecosystem response depends on the most sensitive species Protecting ecosystem structure protects community function Acute to chronic One life stage to the whole life cycle Individual effects to effects at the population level One species to many species One exposure route to another Direct to indirect effects One ecosystem to another Different time and spatial scales PNEV = minimal Effect Concentration / Safety Factor The safety factor method is highly conservative as it implies the multiplication of several worst cases

22 STEP 1 – quality assessed data are extracted from the FREDERICA database STEP 2 – A systematic mathematical treatment is applied to reconstruct dose-effect relationships and derive critical toxicity endpoints. For chronic exposure, the critical toxicity data are the EDR10

23 STEP 3 – The hazardous dose rate (HDR5) giving 10% effect to 5% of species is estimated The final PNEDR is then obtained by applying an additional safety factor (typically from 1 to 5) to take into account remaining extrapolation uncertainties

24 The 5% percentile of the SSD defines HDR 5 (hazardous dose rate giving 10% effect to 5% of species) HDR 5 = 82 μGy/h PNEDR used as the screening value at the ERA should be highly conservative SF = 5 PNEDR ≈ 10 μGy/h PNEDR = HDR 5% / SF

25 Best-EstimateCentile 5%Centile 95% VertebratesPlantsInvertebrates 5% HDR 5 = 17 µGy/h [2-211] PNEDR=10 µGy/h (SF of 2) EDR 10 and 95%CI: Minimum value per species

26 …a BENCHMARK value We need a point of reference; a known value to which we can compare… 10 μGy/h * 24 h / d = 240 μGy/d = 0.2 mGy /d

27  The PNEDR:  is a basic generic ecosystem screening value  Can be applied to a number of situations requiring environmental and human risk assessment  Be aware of:  PNEDR was derived for use only in Tiers 1 and 2 of the ERICA Integrated Approach  Use for incremental dose rates and not total dose rates which include background

28 Marine organisms – μGy/h (Hosseini et al., 2010) Freshwater organisms – 0.4 – 0.5 μGy/h (Hosseini et al., 2010) Terrestrial animals and plants – μGy/h (Beresford et al., 2008)

29 Marine organisms – μGy/h (Hosseini et al., 2010) Freshwater organisms – 0.4 – 0.5 μGy/h (Hosseini et al., 2010) Terrestrial animals and plants – μGy/h (Beresford et al., 2008) Derived screening dose rate (10 μGy/h) is more than 10 times these background values

30  The hazardous dose rate definition means that 95% of species would be protected at a 90% effect However, there may be keystone species among that are unprotected at the 10% level and the effect on the 5% may be > 10%  Some keystone species will be more radiosensitive than others

31  ERICA (default) and R&D128 assume a single (generic) screening dose rate (i.e. application of predicted no effect dose rate) applicable across all species and ecosystems  Advantage = simple  PROTECT objective to consider scientifically robust determination of (generic) screening dose rate(s)  What are limiting organisms for the 63 radionuclides considered in ERICA?

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35  Application of generic screening dose rate:  Identifies the most exposed organism group  Does not (necessarily) identify the most ‘at risk’ (relative radiosensitivity not taken into account)  What does this mean for the assessment  Likely to be conservative  May be overly so  Propose wildlife group specific benchmark dose rates

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37  As part of ICRP 108, effects considered  No dose ‘limits’ but still need something to compare to  …background  …derived consideration reference levels

38  Derived Consideration Reference Levels  “A band of dose rate within which there is likely to be some chance of deleterious effects of ionising radiation occurring to individuals of that type of RAP (derived from a knowledge of expected biological effects for that type of organism) that, when considered together with other relevant information, can be used as a point of reference to optimise the level of effort expended on environmental protection, dependent upon the overall management objectives and the relevant exposure situation.”

39 DeerRatDuck FrogTroutFlatfish BeeCrab Earthworm Pine tree GrassSeaweed mGy/d Background level

40  Provision of advice on how to use the RAP framework  Likely to use ‘representative organism’ concept

41 Reference Animals and Plants ‘Derived consideration reference levels’ for environmental protection REPRESENTATIVE ORGANISMS Radionuclide intake and external exposure Planned, emergency and existing exposure situations

42 Integration  Integrating the ICRP systems of protection for humans and non-human species  Consider ethics and values  Consider how principles of justification, optimisation etc apply to both humans and non- human species  Consider the principles used in chemical risk assessment/protection

43 In radiation protection, usually applied as the incremental dose ABOVE background Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach

44  Quantitative approach eg chemicals  Safety factor, SSD  ICRP – will use DCRL values  Are they benchmarks?  Currently summarise where biological effects are likely to occur  C5 is working on how the DCRLs can be incorporated into the wider ICRP system of radiological protection

45  Range of methods for deriving benchmarks  Range of benchmarks proposed  Be careful with the wording around the benchmark  What does it reflect?  Look for clear, well documented benchmark values  Watch this space for further developments!

46  Adapted text in the older documents from NCRP (1991), IAEA (1992) and UNSCEAR (1996) is given below:  NCRP Aquatic organisms: it appears that a chronic dose rate of no greater than 0.4 mGy h −1 to the maximally exposed individual in a population of aquatic organisms would ensure protection for the population. If modelling and/or dosimetric measurements indicate a level of 0.1 mGy h −1, then a more detailed evaluation of the potential ecological consequences to the endemic population should be conducted  IAEA Terrestrial organisms: irradiation at chronic dose rates of 10 mGy d −1 and 1 mGy d −1 or less does not appear likely to cause observable changes in terrestrial plant and animal populations respectively. Aquatic organisms: it appears that limitation of the dose rate to the maximally exposed individuals in the population to <10 mGy d −1 would provide adequate protection for the populations  UNSCEAR Terrestrial plants: chronic dose rates less than 400 μGy h −1 (10 mGy d −1 ) would have effects, although slight, in sensitive plants but would be unlikely to have significant deleterious effects in the wider range of plants present in natural plant communities. Terrestrial animals: for the most sensitive animal species, mammals, there is little indication that dose rates of 400 μGy h −1 to the most exposed individual would seriously affect mortality in the population. For dose rates up to an order of magnitude less (40–100 μGy h −1 ), the same statement could be made with respect to reproductive effects. Aquatic organisms: for aquatic organisms, the general conclusion was that maximum dose rates of 400 μGy h −1 to a small proportion of the individuals and, therefore, a lower average dose rate to the remaining organisms would not have any detrimental effects at the population level


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