CHAPTER 5 – INTERCOMPARISON OF MODELS
5.4. APPLYING THE MODELS
5.4.1. GENERIC ASPECTS OF MODEL PARAMETERISATION
All three models have default organisms (Table 5.2) with pre-defined parameters which can be used to undertake generic assessments or used as a basis for modelling site-specific organisms. These default organisms are referred to as reference organisms in both the ERICA Tool and R&D128/SP1a. To model a site-specific organism it is necessary to assign parameters that define the organism geometry, the transfer of radionuclides to the organism and the behaviour of the organism within the environment. For the plants, lichen and fungi, the most appropriate default organism within each model was used to define these parameters (Table 5.3). The data used to guide the parameterisation of the animals
(organism dimensions, mass and ecology) were standardised across the three models. Although the mass and dimensions of the organisms sampled from the dunes were
recorded, field sampling was undertaken specifically to provide activity concentration data with which to compare model predictions. Direct measurements of the dimensions and masses of site-specific organisms are often not available to an assessor. Therefore, in order to simulate the informed user application, these data were sourced from literature and web- based resources (Table 5.4).
Most literature sources only provide length measurements for individual organisms so images of the organisms were used to determine the proportional relationship between length and the other two axes (nominally width and height) of the organism as suggested in
the ERICA Tool „help‟ file. These three measurement axes are referred to as x, y and z
within Table 5.4.
Multiple literature sources had to be used to compile the underpinning data sets for defining some organisms. As a result there are instances where mass data and dimension data do not
reflect expected relationships. For example, B. bufo has body dimensions that are
approximately twice those of B. calamita but the available references suggested the two
species have similar masses. Whilst there is no reason to assume the density of B. calamita
is significantly higher than that of B. bufo, the decision was taken to proceed using the
available data for each species.
To calculate the radionuclide activity concentrations in an organism, the three models use transfer parameters; numerical multipliers that relate the activity concentration of a particular radionuclide in the environmental medium to the whole-body activity
concentration of that radionuclide in the organism. These transfer parameters are referred to as concentration ratios (CRs) in the ERICA Tool, concentration factors (CFs) in
R&D128/SP1a and bioaccumulation factors (Bivs) in RESRAD-BIOTA. For the
Table 5.2. Default organisms for terrestrial assessments in the three models used within this intercomparison exercise (the ERICA Tool, R&D128/SP1a and RESRAD-BIOTA)
The ERICA Tool R&D128/SP1a RESRAD-BIOTA
Amphibian Ant Terrestrial Animal
Bird Bacteria Terrestrial Plant
Bird egg Bee
Detritivorous invertebrate Bird
Flying insect Bird egg
Gastropod Carnivorous mammal
Grasses and herbs Caterpillar
Lichen and bryophytes Earthworm
Mammal Fungi
Reptile Herb
Shrub Herbivorous mammal
Soil invertebrate Lichen
Tree Reptile Rodent Seed Shrub Tree Woodlouse
Table 5.3. Default organisms used to define the transfer, dosimetry and occupancy parameters for the sand dune plants, lichen and fungi within the ERICA Tool, R&D128/SP1a and RESRAD-BIOTA
Organism R&D128/SP1a The ERICA Tool RESRAD
A. arenaria Herba, b Grasses & herbs Terrestrial plant
F. rubra Herba, b Grasses & herbs Terrestrial plant
C. vulgaris Shruba Shruba, c, d Terrestrial plant
E. cinerea Shruba Shruba, c, d Terrestrial plant
E. tetralix Shruba Shruba, c, d Terrestrial plant
U. europaeus Shruba Shruba, c, d Terrestrial plant
C. portentosa Lichena, b, c Lichen & bryophytea, c, d Terrestrial plant
R. canescens Lichena, b, c Lichen & bryophytea, c, d Terrestrial plant
Hygrophorous sp Fungia, c, d Lichen & bryophytea, c, d Terrestrial plant
Lepiota sp Fungia, c, d Lichen & bryophytea, c, d Terrestrial plant
Lycoperdon sp Fungia, c, d Lichen & bryophytea, c, d Terrestrial plant
Marasmius sp Fungia, c, d Lichen & bryophytea, c, d Terrestrial plant
Rhodophyllus sp Fungia, c, d Lichen & bryophytea, c, d Terrestrial plant
Russula sp Fungia, c, d Lichen & bryophytea, c, d Terrestrial plant
Transfer parameters for aTc, bSr, cAm and dPu were derived using guidance given within the
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Table 5.4. Parameters used to define the sand dune animals within the ERICA Tool, R&D128/SP1a and RESRAD-BIOTA Organism Dimension (mm) Mass (kg) R&D128/SP1a &
ERICA Tool OFs
R&D128/SP1a reference organisms for ERICA Tool
reference organism
for CRs
RESRAD-BIOTA
DPUCs CFs Geometry number Generic organism BIVs AF GF (soil)
x y z In soil At soil
surface In air
Arctiidae spp 65 a 8 a 8 a 1.00E-03 b 0 0 1 c Earthworm Caterpillar v, w, x, y, z Gastropod v 2 Terrestrial animal 1 0.5
Gastropoda 80 d 13 d 10 d 6.43E-04 e 0 0.25 0.75 c Fungi Caterpillar v, w, x, y, z Gastropod v 3 Terrestrial animal 1 0.5
L. terrestris 80 d 6 d 6 d 8.78E-04 e 1 0 0 Caterpillar Earthworm v, w Soil invertebrate (worm) v 2 Terrestrial animal 1 1
B. bufo 150 f 85 f 75 f 4.45E-02 g 0.25 0.75 0 Reptile Reptile v, w, x, y, z Amphibian x, y 4 Terrestrial animal 1 0.625
B. calamita 80 f 40 f 30 f 5.07E-02 h 0.6 0.4 0 Reptile Reptile v, w, x, y, z Amphibian x, y 4 Terrestrial animal 1 0.8
R. temporaria 110 f 55 f 45 f 2.30E-02 i 0.25 0.75 0 Reptile Reptile v, w, x, y, z Amphibian x, y 4 Terrestrial animal 1 0.625
T. cristatus 150 f 19 f 14 f 7.00E-03 j 0 1 0 Rodent Reptile v, w, x, y, z Amphibian x, y 3 Terrestrial animal 1 0.5
T. helveticus 95 f 9 f 8 f 7.00E-03 k 0 1 0 Bee Reptile v, w, x, y, z Amphibian x, y 2 Terrestrial animal 1 0.5
T. vulgaris 110 f 13 f 10 f 7.00E-03 k 0 1 0 Fungi Reptile v, w, x, y, z Amphibian x, y 3 Terrestrial animal 1 0.5
A. fragilis 500 f 12 f 12 f 4.50E-02 l 0.4 0.6 0 Fungi Reptile v, w, x, y, z Reptile v,x, y 2 Terrestrial animal 1 0.7
L. vivipara 140 f 10 f 7 f 6.00E-03 m 0.4 0.6 0 Fungi Reptile v, w, x, y, z Reptile v,x, y 2 Terrestrial animal 1 0.7
V. berus 650 f 20 f 20 f 1.00E-01 n 0.75 0.25 0 Rodent Reptile v, w, x, y, z Reptile v,x, y 3 Terrestrial animal 1 0.875
A. crecca 360 o 175 o 160 o 3.64E-01 p 0 0.25 0.25 q Carnivorous mammal Bird v, w, x, y Bird x, y 5 Terrestrial animal 0.5 0.5
A. platyrhynchos 580 r 250 r 200 r 1.08E+00 s 0 0.3 0.25 q Carnivorous mammal Bird v, w, x, y Bird x, y 5 Terrestrial animal 0.55 0.5
A. sylvaticus 110 t 40 t 40 t 2.90E-02 u 0.5 0.5 0 Reptile Rodent v Mammal (rat) v 4 Terrestrial animal 1 0.75
M. agrestis 90 t 35 t 35 t 4.00E-02 u 0.2 0.8 0 Reptile Rodent v Mammal (rat) v 4 Terrestrial animal 1 0.6
S. araneus 85 t 30 t 30 t 1.20E-02 u 0.7 0.3 0 Bird egg Rodent v Mammal (rat) v 3 Terrestrial animal 1 0.85
T. europaea 140 u 60 u 50 u 9.50E-02 u 0.95 0.05 0 Reptile Rodent v Mammal (rat) v 4 Terrestrial animal 1 0.975
a http://ukmoths.org.uk/show.php?id=2069; b assumed same as L. terrestris; c the ERICA Tool can only model organisms „in air‟ when organism mass >0.035kg so for the
ERICA Tool assessment assumed 100% time at soil surface (OF at soil surface =1); d Catt, 1998; e Bradford et al., 2002; f Arnold, 2004; g Hoglund & Saterberg, 1989;
h
Miaud & Sanuy, 2005; i http://animaldiversity.ummz.umich.edu/site/accounts/information/Rana_temporaria.html; j Jehle & Arntzen, 2000; k assumed same mass as T. cristatus; l Gent & Gibson, 1998 & Platenberg & Griffiths, 1999; m Herczeg et al., 2008;
n http://animaldiversity.ummz.umich.edu/site/accounts/information/Vipera_berus.html.; o http://blx1.bto.org/birdfacts/results/bob1840.htm;
p http://animaldiversity.ummz.umich.edu/site/accounts/information/Anas_crecca.html; q height above ground set to 10m within ERICA Tool assessment; r
http://blx1.bto.org/birdfacts/results/bob1860.htm; s http://animaldiversity.ummz.umich.edu/site/accounts/information/Anas_platyrhynchos.html; t Hofmann, 1995;
It should be noted that the authors had to assume that the RESRAD-BIOTA Bivs were derived using the same fresh weight organism:dry weight soil relationship used to define the CRs and CFs because the RESRAD-BIOTA software and accompanying guidance documentation did not specify whether the units used within the model were dry weight or fresh weight. Subsequent discussions with RESRAD-BIOTA developers (Jing-Jy Cheng, Argonne National Laboratory, pers. comm.) have confirmed this assumption to be correct.
The ERICA Tool and RESRAD-BIOTA have additional functionality in relation to
transfer. The ERICA Tool allows the use of a probability distribution function (instead of a single numeric value) to define radionuclide transfer for a particular radionuclide-organism
combination and reports results based on the mean, 5th and 95th percentiles by default.
RESRAD-BIOTA can also implement a kinetic-allometric approach to predict transfer using biological scaling relationships based on organism body mass (Higley et al., 2003), providing an alternative to the use of equilibrium transfer parameters and a method for predicting radionuclide transfer in the absence of measured transfer parameters for particular radionuclide-organism combinations.
The three models require organism geometries to be defined for the dosimetry component of the modelling process. Numerical multipliers that relate activity concentrations in soil and whole-body activity concentrations in biota to external and internal unweighted
absorbed dose rates for each radionuclide-geometry combination are defined on the basis of these geometries (ellipsoids for most organisms). This parameter is referred to as a dose conversion coefficient (DCC) in the ERICA Tool, a dose per unit concentration factor (DPUC) in R&D128/SP1a and dose conversion factor (DCF) in RESRAD-BIOTA.
Calculated whole-body activity concentrations and absorbed dose rates are adjusted within the modelling process to account for differences in organism ecology (mainly habitat utilisation). Corrections are made to define the fraction of time an organism spends at a site
under assessment and the organism‟s location within that site. For example, A.
platyrhynchos is not permanently resident at the Drigg dunes whereas L. terrestris is. L. terrestris is located within the soil whereas A. platyrhynchos spends time on the soil surface and in the air above the site. The factors applied to correct for these differences are referred to as occupancy factors (OFs) in R&D128/SP1a and ERICA. These two models use three OFs for each organism, defining the fraction of time the organism spends in the soil, at the soil surface and in the air. If the OFs sum to less than 1, this implies that an organism is not permanently resident at the site and hence not permanently exposed to radionuclide
using an area factor (AF) to describe the fraction of time the organism spends at the site and a geometry factor (GF) to define the geometric relationship between the organism and the radionuclide source. The radionuclide source at a terrestrial site is assumed to be the soil so a GF of 0.5 implies a 2π geometry (organism on the soil surface) and a GF of 1 describes a 4π geometry (organism in the soil).
The following sections (5.4.2 to 5.4.4) describe the models and documentation used for this intercomparison exercise and the specific methods implemented for the parameterisation of each model.