Radioecological sensitivity Brenda Howard Outline Background - - PDF document

Radioecological sensitivity

Brenda Howard

Outline

• Background
• Exposure pathways
• Quantification of radioecological sensitivity

– Four quantities

• Examples
• Application

Background

• Prior use of critical group approach

– critical pathways

• Post-Chernobyl focus on certain key

exposure routes and their spatial attribution

• application of GIS allows spatial analysis

Why?

Considerable variability in radiation doses Generalizations can mask high individual exposure Factors leading to high exposure need identification, quantification and locating Enabling improved preparedness and response

Criteria

• pathways

– high transfer capacity – need to identify “sensitive” parts of pathways – habits effects (occupancy, self- sufficiency, diet)

• regions

– proximity to nuclear sites – presence of “sensitive” features

• social

– Economic and social costs

Vulnerable (or sensitive) ecosystems

• vulnerability to radioactive

contamination can be considered in terms

• f the extent of radiation dose to man or

biota

• regions, pathways or communities can all

be considered to be vulnerable to radioactive contamination if they give rise to, or receive relatively high radiation doses

Comparison of indigenous peoples in the Arctic

AMAP -Norway AMAP - Russia

Berries Mushrooms Fish Reindeer and wild Meat Meat (other) Fruit and vegetables Potatoes Cereals and Flour Milk and Cheese

Comparison of 137Cs Dose in Lovozero

0% 84% 5% 3% 0% 8%

Milk Reindeer meat Mushrooms Berries Potatoes Freshwater fish

1% 64% 8% 9% 0% 18%

Reindeer herders Locals

Sources of 137Cs for rural people in Chernobyl affected areas

R2 = 0.994 0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 500 1000 1500

Dietary radiocaesium from fungi and milk combined (Bq d-1) Total dietary radiocaesium (Bq d-1)

Vulnerability

• quantification

l SPECIFIC

• specific activity

(Bq/kg) in a product – predicted using deposition, transfer coefficients and effective ecological half-lives

lFLUX

• total Bq output in

a product (Bq) – needs estimates of production or rates of harvesting

Vulnerability

• Spatial analysis
• compiling variation in food production and

harvesting rates

• mapping the distribution of food products,

especially wild foods

• quantification of transfer, relevant to soil

type and species

• incorporating changes with time in

contamination of important foodstuffs

Vulnerable areas or groups

• proximity to potential sources
• high precipitation rate
• high milk production rate dominance of

“small” animals

• presence of semi-natural ecosystems

– organic soils, forests

• special groups, with high consumption rates of

contaminated products

– mushroom foragers, game consumers

Vulnerability

Generalizations can mask high individual exposure Consideration of vulnerability at a small spatial scale can improve estimates of:

lcollective dose lindividual dose lprovide guidance on uncertainities

Vulnerability

• emergency response
• prior studies of vulnerability and its spatial and

temporal variation can identify areas, and types of foods which would be contaminated above intervention limits

• Identification of vulnerable areas, combined with

contamination maps can guide monitoring and implementation of countermeasures

Radioecological sensitivity

• Radionuclide specific
• Spatially variable
• Time dependent

Time dependency

• speciation effects
• ecological half-lives
• acute vs mid-long term

– surface effects – seasonality

1 10 100 1000 10000 1986 1990 1994 1998

Date

137Cs activity concentration

Fish, UK Bq/kg Fish, Norway Bq/kg Vegetation Bq/kg Water mBq/l

Aggregated transfer coefficient (m2 kg-1) Action loads (Bq m-2) Flux (Bq y-1)

Biota exposure Production / harvesting Intervention limit (Bq kg-1)

Individual exposure of humans (mSv Bq-1 m2)

Food distribution

Contamination

Quantification

Dose coefficients Diet and social habits Environmental transfer

Radionuclide transfer

• Environmentally mobile

radionuclides – Cs, Sr, I

• Radionuclide with high

accumulation factors – Tc and lobsters – Ru/Tc and seaweed

Radiocaesium contamination

• f Arctic foodstuffs

Reindeer / Caribou Fresh water fish Mushrooms Lamb Brown Cheese Other meat Moose Ptarmigan Vegetables Berries Normal cheese Cow milk

*

Hare Whale Marine fish Seal Potatoes Shrimp Molluscs 0.1 1 10 100 1000

Site studies – Faroe Islands

5 10 15 20 25

Bøur Velbastað Hvalvík Skáli Norðoyri Sandur Hvalba Sumba

Cs-137 transfer to lamb meat, 1990-2000

Tag value 137cs 10-3 m2/kg ww

86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 200 400 600 800 1000 1200 W inter Summer Kemin Sompio Paistunturi Ivalo

137Cs Bq7kg (w.w)

Reindeer- Finland

137Cs Bq/kg fw

Fluxes

• Activity concentrations and production rates
• Fluxes

– The total amount of radioactivity transferred to Man or leading to exposure of biota

• Dependent on

– transfer rates – production

• Intensive, extensive
• quantities
• 1
• 1
• 1

2

• 2

y Bq y kg kg m m Bq : Flux ⇒ ∗ ∗

Critical load concept

The highest pollution load for which there are no negative effects on the environment

Considers deposition, transport and retention Comparison with standard values characterising impact (or upper acceptable limits)

• uses “significant harmful effects” concept
• emphasis on

ecosystem functioning /population interactions

100 Deposition (load) or concentration (level) Effect % Critical load/level

Intervention limits in the EC

Radionuclides Maximum Permissible activity levels in foodstuffs (Bq kg-1) Baby Food Dairy Products Other Products Liquid food Caesium 400 1000 1250 1000 Iodine 150 500 2000 500 Strontium 75 125 750 125 Plutonium 1 20 80 20

Action or Critical loads

• The amount of radionuclide deposition

necessary to produce radionuclide concentrations in food products exceeding intervention limits for areas used in the production or harvesting of foodstuffs

• Action load– short term (surface)
• Critical load – mid-long term

Critical Load

• radioecological perspective

The deposition level of a specific radionuclide which results in an activity concentration in a foodstuff equal to the intervention level

dependent on:

• soil type
• pathway considered
• agricultural practice

Action loads – Agroland predictions

1.00E +03 1.00E +04 1.00E +05 1.00E +06

0.1 0.2 0.4 0.6 0.8 1

Biomass (kg m-2)

I-131 14 days Cs-137 14 days Cs-137 180 days

Variation in radiocaesium Tag with soil category

• 5
• 10

15 10 5 log Tag (m²/kg) Frequency

Clay

• 5
• 10

15 10 5 log Tag (m²/kg) Frequency

Loam

• 5
• 10

15 10 5 log Tag (m²/kg) Frequency

Sand

• 5
• 10

15 10 5 log Tag (m²/kg) Frequency

Organic

Critical load for mid-term

137Cs transfer to milk

Additional critical loads for 137Cs in arctic systems

40 80 120 160 25 50 75 100 Global fallout

137Cs deposition (kBq m

• 2)

Cs-137 Critical additional load (kBq m

• 2)

Additional critical loads

40 80 120 160 25 50 75 100 Global fallout

137Cs deposition (kBq m

• 2)

Cs-137 Critical additional load (kBq m

• 2)

Reindeer Cow milk Moose

Action or Critical loads

• Potential method of addressing issues of

vulnerability to radionuclide contamination

• Can be defined as the amount of

radionuclide deposition necessary to produce radionuclide concentrations in food products exceeding intervention limits for areas used in the production or harvesting of foodstuffs

Application

• Policy and planning

– Prior identification of “sensitive” pathways, areas, communities and individuals – Environmental impact assessment for location

• f nuclear facilities
• Targeted routine sampling
• Improved, better focused emergency

response

• Identify data requirements

WG 8 ?

• Critical and/or action loads?
• Doses to biota (co-op with Theme 2)