Exploring methods to prioritise concentration ratios when estimating weighted absorbed dose rates to terrestrial Reference Animals and Plants

The ICRP and IAEA have recently reported Concentration Ratio values (CRwo-media e equilibrium radionuclide
activity concentration in whole organism divided by that in media) for Reference Animals and
Plants (RAPs) and a wide range of organism groups, respectively, based on a common online database.
Given the large number of data gaps in both publications, there is a need to develop methods for
identifying the relative importance of improving currently available CRwo-media values. A simple, transparent
approach involving the derivation and comparison of predicted internal and external weighted
absorbed dose rates for radionuclides considered by ICRP (2009) for terrestrial RAPs is presented. Using
the approach of applying a reference value of CRwo-soil ¼ 1 or using the maximum reported values where
CRwo-soil >1, we provisionally identify terrestrial radionuclide RAP combinations which could be
considered low priority, notably: Ca, Cr and Ni consistently; Mn for all RAPs except Deer and Pine Tree;
and Tc for all RAPs but Wild Grass. Equally, we can systematically identify high priority elements and
radioisotopes, which largely, but not exclusively, consist of alpha-emitters (especially isotopes of Ra and
Th, but also consistently Am, Cf, Cm, Np, Pa, Po, Pu, U). The analysis highlights the importance of the
radiation weighting factor default assumption of 10 for alpha-emitters in the ERICA Tool when
comparing the magnitude of the internal dose and trying to identify high priority RAP-isotope combinations.
If the unweighted Dose Conversion Coefficient (DCC) values are considered, those for alphaemitters
are often one order of magnitude higher than those due to some beta-gamma emitters for
terrestrial RAPs, whereas with the radiation weighting factor applied they are two orders of magnitude
higher.