77 Ecological Risk Assessment for Radionuclides: Current Status and Critical Knowledge Gaps J. Garnier-Laplace * C. Adam * O. Simon * R. Gilbin * K. Beaugelin ** JC. Gariel *** * Laboratory of Radioecology and Ecotoxicology, Institute of Radioprotection and Nuclear Safety, Cadarache, Bldg 186, BP 1, 13108 St Paul lez Durance cedex, France Name ** Laboratory of Environmental Modelling, bld 159, same address. ***Division of Studies of Radionuclides Behaviour in Ecosystems, same address. ABSTRACT: The debate on the need for a system of radiological protection of the environment drives regulators to urge scientists on conceptualisation of methods demonstrating explicitly that the environment is protected against radioactive contaminants. As regards the FASSET database on radiation effects to non-human biota, one of the major difficulties in the implementation of ecological risk assessment for radioactive pollutants is the lack of data for chronic low level exposure. A general way to deal with situations for which there are no relevant data as regards the actual situation where the risk is to be estimated is to use safety factors. The highest are their values, the highest is the uncertainty on the risk estimate, but, on the other hand, any safety factor could be reduced as more data become available. Going back to radionuclides for which data are sparse, both concerning fate and effects in ecosystems, derivation of ecologically relevant and scientifically defensible benchmarks become a critical issue in ERA. The scope of this paper is to illustrate the relevance of the development of a greater depth of understanding of radionuclide fate and biological effects at several hierarchical levels to support quantitative risk assessments with defined and acceptable uncertainty bounds. 1 CONTEXT AND GLOBAL SCOPE At the present time, international debate on the need for a system of radiological protection of the environment [1,2] drives regulators to urge scientists on a rapid conceptualisation and implementation of methods demonstrating explicitly that the environment is protected against radioactive contaminants. This debate is obviously brought together with the preservation of resources, habitats and genetic and biological diversity; these major issues do not point out any perticular stressors but pollution in general. The recent FASSET project funded by the European Commission, has provided a framework for the assessment of environmental impact of this category of pollutants, with, among others, an extensive database on radiation effects to non-human biota [3]. For chemicals, Ecological Risk Assessment approach constitutes the traditional methodology to help the demonstration of the providence of an appropriate level of protection for ecosystems [4]. ERA is a process that evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure