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 for a description of all participating models). Group members included modellers, regulators, industry and researchers.

The BWG conducted two intercomparison exercises to enable an evaluation of the basic components of the models and subsequently two model-data comparisons:

• 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^−1{^}in 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 (^3{^}H, ^14{^}C, ^60{^}Co, ^90{^}Sr, ^137{^}Cs, ^238{^}U and ^241{^}Am) 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)|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).

Perch Lake - located on the AECL Chalk River Laboratories site (Ontario), Perch Lake has received
chronic, low-level inputs of a number of radionuclides since the 1950s. Participants were supplied
with 90Sr, 3H, 60Co and 137Cs activity concentrations in water and sediments for selected years
to allow the comparison of predictions of whole-body activity concentrations in a range of biota,
including different fish species, aquatic mammals, plants, aquatic reptiles, amphibians and a range of
invertebrate species. Unweighted internal and external absorbed dose rates were also estimated.
• Chernobyl exclusion zone - participants were provided with soil activity concentrations (90Sr, 137Cs,
241Am and Pu-isotopes) and requested to make predictions of whole-body activity concentrations,
and internal and external unweighted absorbed dose rates. Results were compared to available data
for a range of biota types including: graminaceous vegetation; invertebrates; birds; a wide range of
mammal species (from small rodents to deer and carnivorous species) and amphibians. Results from
thermoluminescent dosimeters attached to small mammals were also available allowing a comparison
with predicted external gamma dose rates.

RECOMMENDATIONS
The need for a system to protect the environment from ionising radiation is now generally recognised
and environmental protection is referred to in the draft revision of IAEA Basic Safety Standards and
new recommendations of the ICRP 1. However, many aspects including the discussion of protection
goals, agreement of benchmark values and parameterisation of models applied in the work described
here are still under development.
An aim of the BWG was to improve the models used byMembers States. The collaborative exercises
led to the sharing of parameters and re-parameterisation by some of the participating models. However,
the model-model inter-comparisons and the scenario applications only compared a limited number of
radionuclides. Additionally, whilst the scenarios considered sites for which extensive databases were
available, these may not, especially Chernobyl, be typical of situations needing to be assessed within
regulatory frameworks.
In the near future, there are a number of international developments which will have an impact on
the field of radiological protection: The ICRP will deliver its framework for assessing environmental
protection; (ii) The UNSCEAR will report on its review of effects data; (iii) The EC EURATOM
project PROTECT will make recommendations on protection goals and numeric benchmark values
(see http://www.ceh.ac.uk/protect).
These developments are all likely to impact upon any future activities of the BWG, which will
continue, in some form, within the follow-up programme to EMRAS. Bearing these developments in
mind, and to aid the IAEA in the development of future guidance on the radiological assessment of
biota, a suggested future direction for the activities of the BWG is outlined below.
4.1 Transfer parameters
The work of the BWG has clearly demonstrated that the largest contribution to variability between
model predictions, and comparison with available data, is the parameterisation of the models transfer
components. Other studies are in agreement with this conclusion 7, 8. There is a clear need to better
share knowledge on the transfer of radionuclides to biota and to provide authoritative collations of those
data which are available. It is suggested that a document for biota which is equivalent to the IAEA
handbook on transfer parameters for human food chains 9 should be produced.
4.2 ICRP framework
Outputs of the ICRP should clearly be considered by the BWG and if possible the ICRP outputs should
be evaluated in any future scenario applications and model intercomparisons.
4.3 Future scenarios
Future scenarios should focus on situations which regulators/industry are having to consider (e.g. waste
repositories, assessments for new power stations, sites contaminated by TeNORM). Such scenarios
would enable the comparison of the available approaches within a regulatory context, and evaluation
of the various tiers of assessment (from screening level through to detailed assessment) which the more
comprehensive approaches contain. Consideration should also be given to involving more 'informed
users' within the BWG rather than a predominance of model developers.
4.4 Radiation effects data
The models used by the BWG predict dose rates to biota, but there is also a need to define benchmark
dose rates for use within assessments and be able to determine the potential consequences of predicted
dose rates. A large amount of data on the effects of ionising radiation on biota has recently been
collated into the FREDERICA database (see www.frederica-online.org). This compilation can be used to
aid decision-making on the potential impact of predicted exposures to ionising radiation. However, the
effects data available in the FREDERICA database cover only a proportion of the available scientific
570 RADIOPROTECTION
literature. Furthermore, to be of most use to decision-makers there is a need to better evaluate the quality
of much of these data to ensure that they are applicable. It is suggested that this could be best achieved
through a subgroup of the BWG.
Whilst approaches from chemical assessments (such as species sensitivity distributions) are being
adopted in trying to define dose rate benchmarks for biota, these do not really inform us of the actual
potential impact on a given species or ecosystem. It is suggested that the BWG should consider how
population modelling techniques (from other fields) might be applied to aid setting thresholds against
which the degree of environmental protection can be determined.