Models and approaches available to estimate the exposure of non-human biota: an international comparison of predictions

Over the last decade, there have been a number of models and approaches proposed to estimate the exposure of non-human biota to ionising radiations. Some countries are now using these within their national regulatory frameworks for nuclear and other sites which may be releasing radioactivity to the environment. To date validation of these approaches has been limited and there has been little attempt to compare the outputs of the different models being applied. To address this gap, a new Biota Working Group (BWG) has been formed by the IAEA as part of the EMRAS (Environmental Modelling for Radiation Safety) programme. The primary objective of the EMRAS BWG, as set by its participants, is: ‘to compare and validate models being used and developed by Member States for biota dose assessment (that may be used) as part of regulatory process of licensing and compliance monitoring of authorised releases of radionuclides in order to improve Member State’s capabilities for protection of the environment’. Initial exercises are directed at the comparison and validation of screening level models. In this paper, we will report on a recently conducted comparison of predicted activity concentrations in a range of non-human biota assuming a simple scenario. Unweighted internal and external dose conversion coefficients will also be compared for a selection of reference organism geometries, as currently being proposed by the ICRP, in environmentally relevant media. The models and approaches used encompass those being developed and applied in the USA, Canada, France, Belgium and the UK, as well as the outputs from international collaborative programmes. The results of this work will be discussed in the context of the longer term objectives of the EMRAS Biota Working Group.