A number of models have recently been, or are currently being, developed to enable the assessment of radiation doses from ionising radiation to non-human species. A key component of these models is the ability to predict whole-organism activity concentrations in a wide range of wildlife. In this paper, we compare the whole-organism activity concentrations predicted by eight models participating within the IAEA Environmental Modelling for Radiation Safety programme for a range of radionuclides to terrestrial and freshwater organisms. In many instances, there was considerable variation, ranging over orders of magnitude, between the predictions of the different models. Reasons for this variability (including methodology, data source and data availability) are identified and discussed. The active participation of groups responsible for the development of key models within this exercise is a useful step forward in providing the transparency in methodology and data provenance required for models which are either currently being used for regulatory purposes or which may be used in the future. The work reported in this paper, and supported by other findings, demonstrates that the largest contribution to variability between model predictions is the parameterisation of their transfer components. There is a clear need to focus efforts and provide authoritative compilations of those data which are available.
The disposal of large quantities of radioactive wastes in
Arctic Seas by the former Soviet Union has prompted interest
in the behavior of long-lived radionuclides in polar
waters. Previous studies on the interactions of radionuclides
prominent in radioactive wastes have focused on
temperate waters; the extent to which the bioconcentration
factors and sediment partitioning from these earlier
studies could be applied to risk assessment analyses
involving high latitude systems is unknown. Here we present
concentrations in seawater and calculated in situ
bioconcentration factors for 90Sr, 137Cs, and 239+240Pu (the
three most important radionuclides in Arctic risk assessment
models) in macroalgae, crustaceans, bivalve molluscs,
sea birds, and marine mammals as well as sediment K
d
values for 13 radionuclides and other elements in samples
taken from the Kara and Barents Seas. Our data analysis
shows that, typically, values for polar and temperate
waters are comparable, but exceptions include 10-fold
higher concentration factors for 239+240Pu in Arctic brown
macroalgae, 10-fold lower K
d values for 90Sr in Kara
Sea sediment than in “typical” temperate coastal sediment,
and 100-fold greater Ru K
d values in Kara Sea sediment.
For most elements application of temperate water
bioconcentration factors and K
d values to Arctic marine
systems appears to be valid.
A number of approaches have been proposed to estimate the exposure of non-human biota to ionizing radiation. This paper reports an inter-comparison of the unweighted absorbed dose rates for the whole organism (compared as dose conversion coefficients, or DCCs) for both internal and external exposure, estimated by 11 of these approaches for selected organisms from the Reference Animals and Plants geometries as proposed by the International Commission on Radiological Protection. Inter-comparison results indicate that DCCs for internal exposure compare well between the different approaches, whereas variation is greater for external exposure DCCs. Where variation among internal DCCs is greatest, it is generally due to different daughter products being included in the DCC of the parent. In the case of external exposures, particularly to low-energy beta-emitters, variations are most likely to be due to different media densities being assumed. On a radionuclide-by-radionuclide basis, the different approaches tend to compare least favourably for (3)H, (14)C and the alpha-emitters. This is consistent with models with different source/target geometry assumptions showing maximum variability in output for the types of radiation having the lowest range across matter. The intercomparison demonstrated that all participating approaches to biota dose calculation are reasonably comparable, despite a range of different assumptions being made.
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