Characterisation of background dose-rates for marine environments

Norwegian Radiation Protection Authority, PO Box 55, 1332 Østerås, Norway

Abstract

Environmental risk assessment methodologies often require background dose-rates for wild flora and fauna to be derived in a robust and transparent way. To facilitate this task, information can be organised around reference organisms (ROs), entities that can be used as representatives of the broader ecosystem. In this study, generic datasets have been collated on levels of naturally occurring radionuclides in sediments, seawater and ROs for marine ecosystems. In some cases, data gap filling methods have been required owing to a paucity of information. Once full datasets have been acquired, dose conversion coefficients (DCCs) can be applied and dose-rate calculations can be performed probabilistically allowing the variability in the underlying datasets to be accounted for. Unweighted absorbed dose-rates for marine reference organisms lie between 0.02–1.2 µGy h^-1, whereas weighted dose-rates fall in the range 0.08 µGy h^-1 to 8.8 µGy h^-1. Except for the special case of sea anemones/corals, the most important nuclides for the total dose-rates are ²¹⁰Po and ²²⁶Ra for heterotrophic ROs (i.e. all vertebrate and invertebrate animals), whereas ²²⁶Ra and ²²⁸Th contribute most for autotrophic ROs (i.e. macroalgae, phytoplankton and aquatic plants). In addition, ⁴⁰K has a considerable impact on unweighted dose-rates for all ROs. Non-parametric statistical tests have been applied to show whether there are differences between activity concentrations data for ROs and ICRP-defined Reference Animals and Plants (RAPs).