IAEA-TECDOC-1950

This publication describes the work undertaken by Working Group 4 (WG4) of the IAEA’s MODARIA programme on the prioritization of radionuclides contributing to total dose rates to wildlife and on the revision of goat and cow milk transfer parameters. Three IAEA Technical Reports Series publications (TRS 422, 472, 479) provide datasets of transfer parameter values that may be used in assessments to estimate the effective doses to humans and wildlife. MODARIA WG4 has further explored the development of approaches to evaluate the potential importance of radionuclides in radiological environmental impact assessments for wildlife and methods to prioritize these based on radionuclide contribution to dose rates for different reference organisms and wildlife groups. A collation of data to improve the quality of parameter values for the transfer of radionuclides to cow and goat milk has also been undertaken. The work of WG4 related to the improvement of distribution coefficient (Kd) datasets for soils and freshwater sediments will be reported as part of a separate report that covers the work undertaken under both the MODARIA I and MODARIA II programmes. Different approaches were developed to rank the potential importance of anthropogenic and naturally occurring radionuclides in contributing to the total dose rates to wildlife. The prioritization analysis for anthropogenic radionuclides released during planned exposure situations showed that the ranking of radionuclides, in terms of their importance in contributing to dose rates to wildlife, differed substantially if the amounts of each radionuclide released were considered, rather than assuming all the radionuclides were released in equal quantities. In a prioritization exercise for naturally occurring radionuclides, the use of parameter values from IAEA Technical Reports Series No. 479, when applied to a specific uranium mining site, was shown, for some radionuclides, to under- or overestimate dose rates to wildlife due mostly (but not always) to differences in the whole organism concentration ratios (CRwo-media) and tissue conversion factors measured at the site. The consideration of both radioecological data and tissue conversion rates in evaluating gaps in the available data is, therefore, important. A substantial revision of the goat and cow milk transfer parameter dataset published in IAEA Technical Reports Series No. 472 has improved information on both the provenance of the data used and transparency of data selection or rejection. The revised dataset includes a wider range of radionuclides, especially for concentration ratio (CR) values between concentrations in animal feed and concentrations in milk. Overall, there were only minor differences in values for both the CR and the equilibrium transfer coefficient, Fm, reported in the revised dataset compared with the previous dataset published by the IAEA. Comparison of gut absorption values with the transfer parameter values indicates that, in the absence of available data, published gut absorption values for humans can be used to estimate order of magnitude transfer parameter values to milk for different radionuclides