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Protection of human and non-human biota for situations of chronic exposure to radionuclides. Towards the improvement of risk assessment linked to internal contamination.

J. Garnier-Laplce and F. Paquet IUR Newsletter n°39 - February 2002, p.16

Summary

In the framework of environmental chronic exposure to radionuclides, characterized by very low levels of contamination, there still exists a lack of knowledge concerning the resulted consequences for-both the biological components of ecosystems and the members of the public. Indeed, in ecotoxicology as well as in radioecology, the available knowledge mainly corresponds to short term exposure and high "doses" of isolated pollutant. However, these situations of chronic exposure at low levels are likely to cause toxic responses distinct from those observed after acute exposure at high doses, because of the bioaccumulation phenomena. In tissues and cells, these highly localised accumulations of radionuclides, coupling radiological and chemical toxicities, may give rise to particular biological responses of a cell group, capable of causing functional or structural abnormalities. The assessment of these bioaccumulation phenomena is primordial with regard to internal exposure to radionuclides since they increase locally both the radionuclide concentration and the biological effect of the delivered dose. More especially with regard to man, it becomes therefore necessary to precise the validity field of the conceptuel system of dosimetry used in radioprotection, which is based on a homogeneous radionuclide distribution pattern. For the environment, taking into account these processes and the resulting biological effects will improve and complete the impact assessment, and should be integrated in models for which the ionising radiation effects on biota are still ignored. (1) to characterize chronic accumulation phenomena in terms of biokinetics; to compare them with available data for acute exposure conditions; to evidence and quantify bioaccumulation processes (radionuclide microlocalisation at the subcellular level); (2) to analyse biological effects induced by bioaccumulation on behaviour, growth and reproductive capability of individuals, focusing systematically the research on deterministic effects on immune system, central nervous system and reproductive system; (3) to analyse the consequences of bioaccumulation with regard to dosimetry and environmental models i.e. to reassess radiation doses delivered to organs and organism taking into account bioaccumulation and/or biokinetic alterations; to link the observed effects at individuel scale with the population dynamics; (4) to study the mechanisms of bioaccumulation phenomena.

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