EMRAS Biota Working Group –EMRAS Biota Working Group –Main findingsMain findings

IAEA EMRAS Biota Working IAEA EMRAS Biota Working GroupGroup

Regular participants:

Belgium - SCK·CEN; Canada – AECL; France – IRSN; Japan – NIRS; Lithuania – IoP; Netherlands – NRG; Norway – NRPA; Russia – Spa-Typhoon; UK – CEH, EA, Westlakes; Ukraine – IRL; USA - ANL

ActivitiesActivities

• Two exercises to compare (i) dosimetry and (ii) transfer components of models.

• Two case study scenarios (predictions v’s data): Perch Lake (Canada) and terrestrial ecosystems within Chernobyl 30 km exclusion zone.

Models and approaches participatingModels and approaches participating• RESRAD-BIOTA (USA) [all]• Environment Agency ‘R&D 128’ (UK) [all] • ERICA (& FASSET) (European) [all]• Atomic Energy Canada Limited approach [all]• LIETDOS-BIO (Lithuania) [all]• DosDimEco (SCK·CEN approach) (Belgium) [1,2, Ch]• Dmax (UK) [PL,Ch]• EDEN-CENTEAUR (France) [1,2,PL]• LAKE(ECO) (Netherlands) [PL]• ECOMOD (Russia) [1,2,PL]• EPIC-DOSES3D (European) [all]• SÚJB approach (Czech Republic) [1,2]

Exercise 1 - dosimetry comparisonExercise 1 - dosimetry comparison• Assume 1 Bq per unit media or organism •Estimate unweighted internal and external dose rates for Cs-137, Am-241, Co-60, U-238, C-14, Sr-90, H-3 • Organisms selected from list of proposed ICRP Reference Animals & Plants• Equates to comparison of dose conversion coefficients (DCCs) used within models where:

)()/(

)/(

mediaororganismbodywholekgBqionconcentratActivity

hGyratedoseabsorbedunweightedDCC

Internal dose ratesInternal dose rates

• Internal dose estimates generally all within 20 % of mean (of predictions)– exception being for U-238: two approaches

including U-234 as daughter (resulting in 2x higher DCC)

External dose ratesExternal dose rates• Considerably more variable between models –

especially for β- emitters

e.g. Duck on soil surface e.g. Duck on soil surface predictions for Sr-90predictions for Sr-90

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

AECL EA EDEN ERICA LIETDOS RESRAD SCK SUJB

DCC

External dose ratesExternal dose rates• More variable between models – especially for β-

emitters– Especially H-3 & C-14 (e.g. external DCC for duck on

soil for H-3 ranged 0 to 5E-11)

• Media assumptions (density and distribution of contamination) can be seen to result in some variation

• Differences in approaches that do not matter:– use of specific geometries v’s nearest default– number of emissions assumed

Exercise 2 – transfer comparisonExercise 2 – transfer comparison• Assume 1 Bq per unit media to estimate wholebody

activity concentration of range of radionuclides (241Am,14C,60Co,137Cs,131I,210Po,239Pu,226Ra, 90Sr,99Tc,232Th & 238U) in 19 terrestrial & freshwater organisms

Terrestrial organisms Freshwater organisms

Grass/Herb Phytoplankton Pelagic fish

Shrub Zooplankton Benthic fish

Earthworm Macrophyte Fish egg

Herbivorous mammal Benthic mollusc Amphibian

Carnivorous mammal Benthic crustacean Duck

Bird egg

ApproachesApproaches• Many use concentration ratios (CR):

• But others using foodchain models, most often incorporating allometric relationships for dietary intake and radionuclide biological half-lives– Y=a∙(liveweight)b

• Some have ‘guidance’ derived values in the absence of defaults

)dry weight kg (Bq soilin ion concentratActivity

ht)fresh weig kg (Bqbody wholebiotain ion concentratActivity CR

1-

-1

Predicted activity concentrationsPredicted activity concentrations• Considerable variation between predictions (3-

orders of magnitude being common)

Pu-239

Predicted activity concentrationsPredicted activity concentrations• Some variation can be understood, e.g.:

– Missing value guidance approach often give comparatively high estimates (often for little studied organisms)

– Site specific (and national) data– Some approaches include reindeer data in derivation

of CRs leading to high predictions for mammals (especially Po-210)

• Tc-99 predictions had least variation– Very few data and all using similar approach

Perch Lake Case StudyPerch Lake Case Study

• H-3, Cs-137, Co-60, Sr-90 data for wide range of freshwater biota

PerchLake

Built-up Area

Chalk River Laboratories

Waste Management Area

Legend

Lake / River

Road

CRL Boundary

Stream0 1 2

kilometres

Sudbury

Ottawa

TorontoLake Ontario

Lake Erie

Lake Huron

CRL

Data presentationData presentation

• For each species/organism type mean prediction for each model normalised to mean measurement

Cesium-137 in Aquatic MacrophytesCesium-137 in Aquatic MacrophytesFreshwater Primary Producers

Model

AECL

ERICA (CEH)

EA R&D128

CASTEAURDmax

ECOMOD

LakeCo

RESRAD-BIOTA (UK)M

od

eled

-to

-Mea

sure

d 1

37C

s C

on

cen

trat

ion

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

10

100

Emergent MacrophytesFree-floating MacrophytesFloat-leafed MacrophytesSubmergent MacrophytesMinimum Measured (free-floating)Maximum Measured (free-floating)Minimum Measured (floating-leafed)Maximum Measured (free-floating)

Minimum Measured (submergent)Maximum Measured (submergent)

Strontium-90 in Freshwater FishesStrontium-90 in Freshwater FishesFreshwater Fishes

Model

AECL

ERICA (CEH)

EA R&D128

ERICA (NRPA)

Dmax

ECOMOD

LakeCo

RESRAD-BIOTA (UK)

RESRAD-BIOTA (NRPA)M

od

eled

-to

-Mea

sure

d 90

Sr

Co

nce

ntr

atio

n

0.001

0.01

0.1

1

10

Brown BullheadCyprinidsPumpkinseedsMinimum Measured (bullhead)Maximum Measured (bullhead)Minimum Measured (cyprinids)Maximum Measured (cyprinids)

Minimum Measured (pumpkinseed)Maximum Measured (pumpkinseed)

Cobalt-60 in Freshwater MammalsCobalt-60 in Freshwater Mammals

Chernobyl Case StudyChernobyl Case Study

•Available data for Cs-137, Sr-90 Am-241, Pu-isotopes data - bias towards mammals (some birds, amphibians, invertebrate, plant, reptile). •TLD measurements for small mammals at 4 sites.

Species Common name Number of predictions

(English) 90Sr 137Cs Pu 241Am Dose rates TLD

Aegithalos caudatus Long-tailed tit - - 1 - 1 -

Apodemus flavicollis Yellow necked mouse 5 5 1 - 2 2

Apodemus sylvaticus Wood mouse 1 1 - - 1 -

Canis lupus Wolf 2 2 - - 1 -

Capreolus capreolus Roe deer 7 7 - - 1 -

Clethrionomys glareolus Bank vole 7 6 2 1 2 2

Erithacus rubecula Robin 2 2 - - 1 -

Hirundo rustica Barn swallow 1 1 - - 1 -

Lactera agilis Sand Lizard 1 1 - - 1 -

Microtus arvalis Common vole 2 2 - - 1 -

Microtus oeconomus Root vole 2 3 - - 1 1

Microtus spp. Vole species 1 1 1 - 1 1

Parus major Great tit 2 2 1 - 1 -

Perdix perdix Partridge - 2 - - 1 -

Rana esculenta Edible frog - 2 - - 1 -

Rana terrestris Brown frog 2 4 - - 1 -

Sicista betulina Northern birch mouse 1 1 - - 1 -

Sorex araneus Common shrew 5 5 - - 1 -

Sturnus vulgaris Starling 1 1 - - 1 -

Sus scofa Wild boar 9 9 - - 1 -

Beetles 1 1 - - 1 -

Grassy vegetation 4 4 - - 1 -

Data presentationData presentation

• Each prediction normalised to the data mean for a given site

• Normalised predictions averaged by organism group for each model

TLD reading prediction TLD reading prediction (= external Cs-137 prediction)(= external Cs-137 prediction)

Total unweighted dose ratesTotal unweighted dose rates

• Presented as normalised to the mean prediction for each site

SummarySummary

• Estimation of dose rate (DCC) adds little to variability in exposure estimates

• Efforts should concentrate on transfer component– Support IAEA TRS 364 for biota

• Can begin to understand some variability between predictions & improve the participating models

Comparison of Exercise 2 Cs-137 predictions by DoseDimEco

SummarySummary

• … But we have only completed two model-data comparisons – and overall considered a fairly limited range of

radionuclides

• Recommendations will contain a justification for continuing activities of BWG into EMRAS II