CHAPTER 5 – INTERCOMPARISON OF MODELS
5.4. APPLYING THE MODELS
5.4.3. RESRAD-BIOTA
RESRAD-BIOTA is the computer code that implements the USDoE‟s „Graded Approach‟ (USDoE, 2002). The assessment used „Level 3‟ of the RESRAD-BIOTA 1.22 Beta Tool and was applied with reference to the User Guide (USDoE, 2004), the technical guidance documentation (USDoE, 2002) and the database of bioaccumulation factors (available at http://homer.ornl.gov/nuclearsafety/nsea/oepa/bdac/database.html).
When modelling site-specific organisms in RESRAD-BIOTA the assessor must select one of the eight default organism geometries to provide the organism DCFs. The model lists example organisms to help the assessor select the appropriate geometry but the examples are often for organisms specific to the United States. Therefore, the method used for selecting the reference organism geometries in R&D128/SP1a (using the surface
area:volume ratio of the ellipsoids) was applied and the nearest default RESRAD-BIOTA geometry selected (Table 5.4). This concept is less confusing within RESRAD-BIOTA because the geometries are identified by a numerical code (1 – 8) rather than being referred to by reference organism names.
The AFs and GFs used for the plants, lichen and fungi were those for the default „terrestrial plant‟ (Table 5.3). For the animals, literature-derived information on the ecology of the organisms was used to define organism-specific AFs and GFs (Table 5.4). To ensure consistency in the approach used to parameterise the three models, the animal AFs were the
sum of the OFs used for each organism in R&D128/SP1a and ERICA (e.g. A.
platyrhynchos has OFs of 0 in the soil, 0.3 at the soil surface and 0.25 in air so the AF used
for modelling A. platyrhynchos in RESRAD-BIOTA was 0.55). The GFs were also
determined to be consistent with the parameterisation of the other models; the GF being calculated for this study as the fraction of time that an organism is exposed to a 2π (GF of
spends in the soil is 0.25 and the fraction of time it spends at the soil surface is 0.75 so the
GF assigned to B. bufo was calculated as (0.25 x 1) + (0.75 x 0.5) = 0.625. This approach
was adopted by the assessor because the RESRAD-BIOTA guidance does not describe fully the use of the GF.
RESRAD-BIOTA was run using the default Bivs for „terrestrial animal‟ and „terrestrial
plant‟. However, these are generic Bivs for the two organism groups and are intended to be
used for simplistic conservative assessments. Therefore, the assessment was repeated for a selection of the animals (birds, mammals and reptiles) using RESRAD-BIOTA‟s kinetic- allometric function in an attempt to make more realistic, species-specific predictions. The allometric equations in RESRAD-BIOTA calculate radionuclide biological half-life, food intake rate, soil ingestion rate, maximum lifespan and inhalation rate. Organism mass is used in calculating the intake rates and maximum lifespan. The user can override the allometric calculations and change any of the parameters. However, this requires additional species-specific data and these data were rarely available. For this study, the parameters for which appropriate data were identified were organism mass (Table 5.4), maximum lifespan and diet (Table 5.5). Species-specific data on soil ingestion and inhalation rates could not be identified so the default allometric equations were used to derive values for these two parameters based on the organism mass.
Table 5.5. Parameters for allometric assessment in RESRAD-BIOTA 2, 3 & 4
Organism Maximum lifespan (yr) Fresh matter intake rate (FMI, g d-1)a Dietary component (fraction of diet)
Anas crecca 3b 120 Invertebrate (0.5), Plant (0.5)c
Anas platyrhynchos 3d 254 Invertebrate (0.5), Plant (0.5)e
Anguis fragilis 15f 1.21 Invertebrate (1)f
Apodemus sylvaticus 2g 20.3 Plant (0.75), Invertebrate (0.25)h
Lacerta vivipara 12f 0.19 Invertebrate (1)i,j
Microtus agrestis 2g 23.6 Plant (1)h
Sorex araneus 1.25g 10.9 Invertebrate (1)h
Talpa europaea 3g 46.7 Invertebrate (1)g,h
Vipera berus 10f 1.37 M. agrestis (0.4), A. sylvaticus (0.4),
L. vivipara (0.2)f a Nagy, 2001; b http://blx1.bto.org/birdfacts/results/bob1840.htm; c http://animaldiversity.ummz.umich.edu/site/accounts/information/Anas_crecca.html; d http://blx1.bto.org/birdfacts/results/bob1860.htm; e http://animaldiversity.ummz.umich.edu/site/accounts/information/Anas_platyrhynchos.html; f
Arnold, 2004; g Burton, 1976; h Hofmann, 1995;
i http://www.arkive.org/species/ARK/reptiles/Lacerta_vivipara/more_info.html?section=biology; j http://www.uksafari.com/commonlizard.htm
To quantify radionuclide transfer for a site-specific organism using RESRAD-BIOTA‟s allometric functionality, the assessor must define dietary components for that organism,
both in terms of the percentage composition of the diet (Table 5.5) and the Bivs for each
dietary component. RESRAD-BIOTA then uses allometry to calculate the site-specific organism‟s fresh matter intake rate (FMI) based on the body mass of the organism. For the
invertebrate and plant dietary components, the default Bivs for „terrestrial animal‟ and
„terrestrial plant‟ were used. The Bivs for other dietary components were calculated using
repeat allometric runs of RESRAD-BIOTA, following the approach described in (Beresford et al., 2008a) to model trophic transfer up the food chain. For example, RESRAD-BIOTA
was run allometrically using the default Bivs for „terrestrial animal‟ and „terrestrial plant‟ to
define the dietary components when calculating activity concentrations in A. sylvaticus, L.
vivipara and M. agrestis. The calculated activity concentrations were then used to
calculate the corresponding Bivs for these three organisms and these Bivs were entered into
the allometric calculations to predict the activity concentrations in V. berus.
The use of calculated FMIs and generic Bivs may result in highly conservative predictions.
To investigate this, the allometric assessment was repeated using FMIs calculated from measured field metabolic rates in free-living animals (Nagy, 2001) that were representative of the organisms being modelled (Table 5.5) and more organism-specific literature-derived
Bivs (Table 5.6), the most comprehensive source available being the terrestrial transfer
database from ERICA (Beresford et al., 2008d). In total, four assessments were undertaken using RESRAD-BIOTA to predict activity concentrations and dose rates for:
1. All site-specific organisms using RESRAD-BIOTA default Bivs (hereafter this
assessment is referred to as RESRAD-BIOTA 1);
And for sub-set of site-specific organisms (birds, mammals and reptiles) using:
2. RESRAD-BIOTA‟s allometric function to calculate FMIs and using default Bivs
for the invertebrate and plant dietary components (hereafter this assessment is referred to as RESRAD-BIOTA 2);
3. FMIs from Nagy (2001) and default Bivs for the invertebrate and plant dietary
components (hereafter this assessment is referred to as RESRAD-BIOTA 3); and
4. FMIs from Nagy (2001) and ERICA CRs for the invertebrate and plant dietary
Table 5.6. Transfer parameters used to define transfer to dietary components for RESRAD- BIOTA allometric assessment
Radionuclide Plant Invertebrate
BIVa ERICA Tool CRb, c
BIVa ERICA Tool CRb
Diet 1d Diet 2e Diet 3f
241Am 7.64E-03 4.96E-03 4.00E-03 1.33E-01 1.01E-01 9.99E-02 137Cs 9.50E+00 6.93E-01 1.10E+02 8.87E-02 1.34E-01 8.94E-02 238
Pu 1.00E-02 1.44E-02 3.25E-03 5.99E-02 3.88E-02 2.90E-02
239Pu 1.47E-02 1.44E-02 3.00E-03 5.99E-02 3.88E-02 2.90E-02 90Sr 3.84E+00 2.07E-01 7.58E+01 1.69E-01 4.07E-01 8.97E-03 99Tc 8.00E+00 2.00E+01 3.48E+00 3.70E-01 3.70E-01 3.70E-01
a
used in RESRAD-BIOTA 2 & 3; b used in RESRAD-BIOTA 4; c CR for „grasses and herbs‟; d mean of the ERICA Tool CRs for „gastropod‟, 'soil invertebrate' and 'detritivorous invertebrate' to be representative of invertebrate dietary component for A. crecca, A. fragilis, A. platyrhynchos, A. sylvaticus and S. araneus; e ERICA Tool CR for 'detritivorous invertebrate' to represent dietary intake of L. vivipara; f ERICA Tool CR for 'soil invertebrate' to represent dietary intake of T. europaea.