Risk Analyses and the Development of Radiological Benchmarks Tom Hinton (IRSN)

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

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

Conservative Assumptions for Screening Calculations

Resulting Dose Rates (mGy y -1 )

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

Definition of Benchmarks 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

Knowledge of ionising radiation’s effect on wildlife is the basis for the derivation of radiological risk benchmarks

What is known about effects from ionising radiation?

Wilhelm Rontgen (1845—1923) First roentgenogram, 1895 Henri Becquerel ( ) Becquerel plate, 1896 Discoverer of radioactivity, 1903 Nobel Prize in Physics First Nobel Prize in Physics, 1901 Marie Curie ( )

DNA is the primary target for the induction of biological effects from radiation in ALL living organisms Broad similarities in radiation responses for different organisms ……and yet, wide differences in radiation sensitivity (Whicker and Schultz, 1982)

base loss base change single stand break double stand break interstrand crosslinks OOH H H Feinendegen, Pollycove. J. Nucl. Medicine V.42. p. 17N-27N Different kinds of DNA damage induced by γ-radiation per 0.01 Gy

Free Radicals (unstable molecule that loses one of its electrons)

DNA damage and repair

Fate of Mutations Somatic Cells Somatic Cells Germ Cells Germ Cells Decrease in number and quality of gametes Increased embryo lethality Alteration to offspring Cell Death Cell Death Cancer

 For humans, risk of hereditary effects in offspring of exposed individuals is about 10% of the cancer risk to the exposed parents (UNSCEAR, 2001)  For non-human biota the risk of hereditary effects is unknown Fate of mutations in non-human biota Mutation Cell Confer a selective advantage Deleterious mutations Neutral mutations Spread in the population Remove from the population Persist over many generations

Knowledge on Effects of Radiation Exposure on Wildlife

early data came from… laboratory exposures accidents (Kyshtym, 1957) areas of naturally high background nuclear weapons fallout large-scale field irradiators early data came from… laboratory exposures accidents (Kyshtym, 1957) areas of naturally high background nuclear weapons fallout large-scale field irradiators wealth of data about the biological effects of radiation on plants and animals

Increasing SensitivityDecreasing Sensitivity Large nucleusSmall nucleus Large chromosomesSmall chromosomes Acrocentric chromosomesMetacentric chromosomes Low chromosome numberHigh chromosome number Diploid or haploidHigh polypolid Sexual reproductionAsexual reproduction Long intermitotic timeShort intermitotic time Long dormant periodShort or no dormant period Factors Influencing the Sensitivity of Plants to Radiation (Sparrow, 1961)

Radiation Effects on Non- Human Biota Early Mortality premature death of organism Early Mortality premature death of organism Morbidity reduced physical well being including effects on growth and behavior Morbidity reduced physical well being including effects on growth and behavior Reproductive Success reduced fertility and fecundity Reproductive Success reduced fertility and fecundity These categories of radiation effects are similar to the endpoints that are often used for risk assessments of other environmental stressors, and are relevant to the needs of nature conservation and other forms of environmental protection Reproduction is thought to be a more sensitive effect than mortality

Fundamental Differences In Human and Ecological Risk Analyses Type Unit of Observation Endpoint Dose-Response Type Unit of Observation Endpoint Dose-Response Human individual lifetime cancer relationships risk established Ecological varies varies not established population, community, ecosystem > mortality, < fecundity, sublethal effects for chronic, low level exposure to radiation, alone, or mixed with other contaminants

Populations are resilient Indirect effects often occur that are unpredictable Blaylock (1969) studies at Oak Ridge DIRECT EFFECT: Increased mortality of fish embryos exposed to 4 mGy / d INDIRECT EFFECT: Fish produced larger brood sizes NET RESULT: No effect to population Compensating mechanisms exist Predicting radiological effects to wildlife is complicated because:

Prejevalsky Horses Russian Boar Wolves With the removal of humans, wildlife around Chernobyl are flourishing 48 endangered species listed in the international Red Book of protected animals and plants are now thriving in the Chernobyl Exclusion Zone

Data Base of Knowledge on Effects of Radiation Exposure on Biota FREDERICA (  An online database of literature data to help summarise dose-effect relationships  FREDERICA can be used on its own; or in conjunction with the ERICA assessment tool (for conducting risk assessments of wildlife exposed to ionising radiation) (> 1500 references; data entries)

effects data; per ecosystem per exposure pathway (external or internal irradiation) per duration (acute or chronic) Acute-external Acute-internal Chronic-external Chronic-internal Acute-external Acute-internal Chronic - external Chronic - internal 73% of all data FREDERICA Database

Aquatic invertebrates To few to draw conclusions Some data Data on radiation effects for non-human species Morbidity Mortality Reproductive capacity Mutation Amphibians Aquatic plants Bacteria Birds Crustaceans Fish Fungi Insects Mammals Molluscs Moss/Lichens Plants Reptiles Soil fauna Zooplankton No data Chronic effects and γ external irradiation

Approaches to derive protection criteria

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 How to derive « safe levels » EC 10 EC 50

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) How to derive « safe levels »....adapted for radiological conditions....

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

Fixed Assessment Factor Method The safety factor method is highly conservative as it implies the multiplication of several worst cases PNEV = minimal Effect Concentration / Safety Factor

The approach used to derive no-effects values 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

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. The predicted no-effect dose rate (PNEDR) evaluation

The 5% percentile of the SSD defines HDR 5 (hazardous dose rate giving 10% effect to 5% of species) HDR 5 = 82 μGy/h SSD for generic ecosystem at chronic external γ-radiation (ERICA) PNEDR used as the screening value at the ERA should be highly conservative SF = 5 PNEDR ≈ 10 μGy/h PNEDR = HDR 5% / SF

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 Generic ecosystem and chronic  exposure SSD for generic ecosystem at chronic external γ-radiation (PROTECT)

…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

Reminders…  The PNEDR is a basic generic ecosystem screening value to benchmark where additional work is needed  The derived PNEDR equal to 10 μGy/h can be applied to a number of situations for which environmental and human risk assessment are carried out  The risk assessor needs to be aware of the following rules while using the ERICA tool:  the PNEDR does not apply for any other ecological object to be protected besides the generic ecosystem  the PNEDR was derived for use only in the first two tiers of the ERICA Integrated Approach  the PNEDR is the benchmark value for screening against incremental dose rates, and not the total dose rates including background

IAEA (1992) and UNSCEAR (1996) suggested the following no-effect values for populations of non-human biota: for aquatic animals and terrestrial plants μ Gy/h for terrestrial animals - 40 μ Gy/h Derived using a SSD approach, the PNEDR of 10 μ Gy/h is consistent with these previously recommended values The hazardous dose rate definition means that 95% of species would be protected. However, there may be keystone species among the 5% that are unprotected.

Background radiation exposure for wildlife (UNSCEAR, 1996; 2000) terrestrial and aquatic plants – μ Gy/h; terrestrial animals (mammals) μ Gy/h freshwater organisms – μ Gy/h terrestrial animals and plants μ Gy/h (Beresford et al., 2008) Derived screening dose rate (10 μ Gy/h) is more than 10 times these background values

Both ERICA Tool & RESRAD-BIOTA use ‘tiered assessments’ with initial assessment (Tier-1) being very simple (minimal input---conservative output) YOUR media concentrations compared to the MODEL’s pre-defined concentrations (i.e. media concentrations that result in a PNEDR)  ERICA: ‘environmental media concentration limits’ EMCLs  RESRAD-BIOTA: ‘biota concentration guidelines’ BCGs

Estimated assuming:  Habitat characteristics that maximise exposure  Probability distributions associated with the default CR and K d databases were used to determine 5th percentile EMCL  No conservatism applied to dosimetry  For aquatic ecosystems EMCL for water includes consideration of external dose from sediment and that for sediment includes external dose from water and biota-water transfer Environmental Media Concentration Limits

Estimated assuming:  Infinitely large (internal) and small (external) geometries for dose calculations  Daughter T 1/2 ’s up to 100 y included  All terrestrial organisms 100% in soil; aquatic 100% water-sediment interface  ‘Maximum’ CR values or 95th percentile CR values predicted using a kinetic-allometric approach

Is the new benchmark of 10 µGy/h final? How are benchmarks derived? Safety Factor Method stringent method as the PNEC value is obtained by dividing the lowest critical data by an appropriate SF ranging from 10 to Species Sensitivity Distribution based on a statistical extrapolation model to address variation between species in their sensitivity to a stressor. What is a benchmark? Benchmarks are numerical values used to guide risk assessors at various decision points in a tiered approach.