Chronic radionuclide low dose exposure for non-human biota: challenges in establishing links between speciation in the exposure sources, bioaccumulation and biological effects. Uranium in aquatic ecosystems : a case-study.

J Garnier-Laplace, C Fortin, C Adam, O Simon, F H Denison*
Actes de la conférence "3rd International Symposium on the Protection of the Environment from Ionising Radiation -22/26 juillet 2002 -Darwin (Australia)." p.15-24
* étudiant en contrat de thèse au laboratoire.

In the field of environmental radioprotection, the knowledge gaps concern situations leading to chronic exposure at the lower doses typical of the living conditions of organisms influenced by radioactive releases. For any radionuclide and ecosystem, the specificities of these situations are as followed : (i) various chemical forms occur in the environment as a function of the physico-chemical conditions of the medium; (ii) each transfer from one component to another can lead to a modification of these forms with a “chemical form-specific” mobility and bioavailability; (iii) different categories of non-radioactive toxicants are simultaneously present. In this multipollution context, the biological effects of ionising radiation may be exacerbated or reduced with the potential for action or interaction of all the pollutants present simultaneously. These situations of chronic exposure at low levels are likely to cause toxic responses distinct from those observed after acute exposure at high doses since long-term accumulation mechanisms in cells and tissues may lead to microlocalised accumulation in some target cells or subcellular components. The assessment of these mechanisms is primordial with regard to internal exposure to radionuclides since they increase locally both the radionuclide concentration and the delivered dose, coupling radiological and chemical toxicity. This is the main purpose of the ENVIRHOM research programme, recently launched at IRSN. After a global overview of the experimental strategy and of the first results obtained for phytoplankton and uranium, this paper scans the state of art for uranium within freshwaters and underlines inconsistency encountered when one wants to carry out an Ecological Risk Assessment (ERA) on the chemical or on the radiological standpoint. This example argues for future research needs in order to establish well-defined relationship between chemo-toxicity and radiotoxicity for internal contamination. The operational aim is to bring adequacy between ecological and human health risk assessment for radioactive or “conventionnal” substances.