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The derivation of benchmarks

The derivation of benchmarks. CEH Lancaster 1 st – 3 rd April 2014. OBJECTIVES. What is a benchmark?. Why are benchmarks needed?. How are benchmarks derived?. How are benchmarks used?. INTRODUCTION. The need for benchmarks... ... a retrospective screening model example.

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The derivation of benchmarks

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  1. The derivation of benchmarks CEH Lancaster 1st– 3rdApril 2014

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

  3. INTRODUCTION The need for benchmarks... ... a retrospective screening model example www.radioecology-exchange.org

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

  5. 5000 4000 1) SOURCE TERM: used 1964 3000 maximum release as a mean Total 137-Cs Released (GBq) 2000 for calculations 1000 2) EXPOSURE: assumed fish 0 were living at point of discharge 54 59 64 69 74 79 84 Year 3) ABSORPTION: assumed all fish were 30 cm in diameter which maximized absorbed dose 4) IRRADIATION: behavior of fish ignored, assumed they spent 100% of time on bottom sediments where > 90% of radionuclides are located CONTAMINATED SEDIMENTS Conservative Assumptions for Screening Calculations www.radioecology-exchange.org

  6. Resulting Dose Rates (mGy y-1) www.ceh.ac.uk/PROTECT

  7. www.radioecology-exchange.org

  8. www.radioecology-exchange.org

  9. www.radioecology-exchange.org

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

  11. Definition of benchmarks Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach 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 The derivation of benchmarks needs to be through transparent, scientific reasoning Benchmarks correspond to screening values when they are used in screening tiers www.radioecology-exchange.org

  12. Data on radiation effects for non-human species To few to draw conclusions No data Some data www.radioecology-exchange.org

  13. Approaches to derive protection criteria www.radioecology-exchange.org

  14. www.radioecology-exchange.org

  15. Historic reviews • 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. UNSCEAR 2011 conclusions • As in its 1996 recommendations, UNSCEAR considers that chronic dose rates of • less than 100 μGy h‑1 to the most highly exposed individuals would be unlikely to have significant effects on most terrestrial communities; and • that maximum dose rates of 400 μGy h‑1 to any individual in aquatic populations of organisms would be unlikely to have any detrimental effect at the population level www.radioecology-exchange.org

  17. UNSCEAR 2011 Overall summary of (illustrative) chronic effects data for plants, fish and mammals www.radioecology-exchange.org

  18. A Quantitative approach • Used to derive the ERICA and PROTECT values • Consistent with EC approach for other chemicals

  19. Exposure-responserelationshipfromecotoxicity tests Effect (%) 100 % Observed data Regression model 50 % LOEC: Lowest observed effect concentration NOEC: No observed effect concentration 10 % Contaminant Concentration How to derive « safelevels » Methods recommended by European Commission for estimating predicted-no-effects-concentrations for chemicals …based on available ecotoxicity data; (i.e. Effect Concentrations; EC) typically EC50 for acute exposure conditions and EC10 for chronic exposures EC10 EC50 www.radioecology-exchange.org

  20. How to derive « safelevels » ....adapted for radiological conditions.... Exposure-responserelationshipfrom ecotoxicity tests (specific to stressor, species, and endpoint) Effect (%) 100 % Observed data Regression model 50 % LOEC: Lowest observed effect concentration NOEC: No observedeffect concentration 10 % EC50 ED50 EDR50 Concentration (Bq/L or kg) Dose (Gy) Dose Rate (µGy/h) EC10 ED10 EDR10

  21. Deriving benchmarks for radioecological risk assessments 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 www.radioecology-exchange.org

  22. Fixed assessment factor method PNEV = minimal Effect Concentration / Safety Factor www.radioecology-exchange.org

  23. Fixed assessment factor method PNEV = minimal Effect Concentration / Safety Factor The safety factor method is highly conservative as it implies the multiplication of several worst cases www.radioecology-exchange.org

  24. The approach used to derive no-effects values www.ceh.ac.uk/PROTECT

  25. The predicted no-effect dose rate (PNEDR) evaluation www.ceh.ac.uk/PROTECT

  26. SSD for generic ecosystem at chronic external γ-radiation (ERICA) • The 5% percentile of the SSD defines HDR5 (hazardous dose rate giving 10% effect to 5% of species) • HDR5 = 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 www.radioecology-exchange.org

  27. Generic ecosystem SSD for chronic external γ-radiation (PROTECT) Percentage of Affected Fraction 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 5% 0% 0.1 1 10 100 1000 10000 100000 1000000 10000000 Dose rate (µGy/h) HDR5 = 17 µGy/h [2-211] Best-Estimate Centile 5% Centile 95% Vertebrates Plants Invertebrates EDR10 and 95%CI: Minimum value per species PNEDR=10 µGy/h (SF of 2) www.ceh.ac.uk/PROTECT

  28. We need a point of reference; a known value to which we can compare… …a BENCHMARK value 10 μGy/h * 24 h / d = 240 μGy/d = 0.2 mGy /d www.ceh.ac.uk/PROTECT

  29. Reminders… • 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

  30. Background radiation exposure for ICRP RAPs (weighted dose rates) www.radioecology-exchange.org

  31. Background radiation exposure for ICRP RAPs Derived screening dose rate (10 μGy/h) is more than 10 times these background values www.ceh.ac.uk/PROTECT

  32. Furthermore... • 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

  33. Generic screening dose rate • 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?

  34. Limiting organisms Marine ecosystem ERICA Tool – generic screening dose rate

  35. Limiting organisms Freshwater ecosystem ERICA Tool – generic screening dose rate

  36. Limiting organisms Terrestrial ecosystem ERICA Tool – generic screening dose rate

  37. Generic screening dose rate • 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

  38. ICRP Approach

  39. Effects • As part of ICRP 108, effects considered • No dose ‘limits’ but still need something to compare to • …background • …derived consideration reference levels www.radioecology-exchange.org

  40. DCRLs • 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.”

  41. DCRLs Earthworm Bee Crab mGy/d Deer Rat Duck Pine tree Frog Trout Flatfish Grass Seaweed Backgroundlevel

  42. Application • Provision of advice on how to use the RAP framework • Likely to use ‘representative organism’ concept

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

  44. 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

  45. What is a benchmark? Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach In radiation protection, usually applied as the incremental dose ABOVE background www.radioecology-exchange.org

  46. How are benchmarks derived? • 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

  47. Summary • 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! www.radioecology-exchange.org

  48. Combining chemical and radioactive risk assessments www.radioecology-exchange.org

  49. Dealing with mixtures • Adding apples and pears together… • Garnier-Laplace et al 2009 • Outlined a possible method for combined risk assessment in freshwater ecosystems • Uses an assumption of zero interactions between substances when in mixture • Uses the outputs of SSDs • Hazardous concentration … • Hazardous dose rate … • …affecting 50% of species www.radioecology-exchange.org

  50. Dealing with mixtures • Adding apples and pears together… • Potentially affected fraction (PAF) (50%) • Back calculate concentration in media for each chemical and radionuclide • Can then use these data to rank (essentially RQ) each contaminant in terms of potentially impact • But… www.radioecology-exchange.org

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