IAEA

International Atomic Energy Agency (IAEA)

Biota Working Group

The Biota Working Group http://www-ns.iaea.org/projects/emras/emras-biota-wg.htm (BWG)was formed in 2004 by the IAEA as part of the Environmental Modelling for Radiation Safety (EMRAS)programme to address the gap of little validation and comparison of the different models and approaches being used and developed to estimate the radiation exposure on wildlife. The primary objective of the BWG, was: to improve Member State's capabilities for protection of the environment by comparing and validating models being used, or developed, for biota dose assessment (that may be used) as part of regulatory process of licensing and compliance monitoring of authorised releases of radionuclides.

In total, 15 models and approaches have been applied to one or more of the exercises conducted by the BWG. The models/approaches applied encompass those being developed, and in some instances, used in a regulatory context, in Belgium, Canada, France, Lithuania, Russia, the UK and the USA, as well as the outputs of recent EC EURATOM programmes. The participating models included those available to any interested user (RESRAD-BIOTA, the ERICA Tool, England and Wales Environment Agency R&D 128 and FASSET) and in-house models being used/developed by various BWG participants (see IAEA [2] for a description of all participating models). Group members included modellers, regulators, industry and researchers.

The BWG conducted four intercomparison exercises to enable an evaluation of the basic components of the models:

• Dose conversion coefficients (DCCs) – participants were asked to estimate the unweighted absorbed dose rates for both internal and external exposure assuming an activity concentration of 1 Bq kg⁻¹in the organism or surrounding media, respectively. A selection of freshwater and terrestrial geometries proposed by the ICRP [4] for their [Reference Animal and Plants] (RAPs) were used for the exercises. Estimates were made for seven radionuclides (³H, ¹⁴C, ⁶⁰Co, ⁹⁰Sr, ¹³⁷Cs, ²³⁸U and ²⁴¹Am) chosen to cover a range of energies and radiation types. The results of this exercise are described fully by
  [Vives i Batlle et al (2007)].

• Transfer – participants were required to estimate the whole-body activity concentration, of eighteen radionuclides, in seven terrestrial organisms (grass/herb, shrub, earthworm, herbivorous mammal, carnivorous mammal, rodent, bird egg) and twelve freshwater organisms (phytoplankton,zooplankton, macrophyte, benthic mollusc, small benthic crustacean, large benthic crustacean, pelagic fish, benthic fish, fish egg, amphibian, duck and mammal) assuming an activity concentration of 1 Bq per unit (kg, L or m3) of media (soil, water or air, respectively). The results of this exercise
  are evaluated in Beresford et al. (2008).