A unified Ecological Risk Assessment on freshwaters for chemical and radiological ecotoxicity: The uranium case

¹ Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Laboratoire de Modélisation Environnementale, Bât. 159, Centre de Cadarache, BP. 3, 13115 St. Paul-les-Durance, France
² IRSN, Service d'Étude du Comportement des Radionucléides dans les Écosystèmes, same address
³ IRSN, Laboratoire de Radioécologie et d'Écotoxicologie, Bât. 186, same address

Abstract

The classic ERA method is today recognised as relevant for both chemicals and radionuclides. As uranium presents the double ecotoxicity, a unique method may then now be applied to evaluate in tandem the associated ecological risks, following the classic four steps methodology (problem formulation, effect and exposure analysis, risk characterisation [1]). The approach is developed for freshwater ecosystems receiving ore mining releases, exposed to uranium as a chemical element and as the radioactive families of its isotopes 234, 235 and 238. The structure and the function of the ecosystem are described by a conceptual model on which both the exposure and the effect analysis are based. Species Sensitivity Distributions are applied (1) to the chemotoxicity data, to estimate a Predicted-No-Effect-Concentration for uranium in water (in µg/L); (2) to radiotoxicity effect data, to estimate a Predicted No-Effect-Dose-Rate (in µGy/h). The risk is assessed at first through the risk quotient approach, a screening method involving for the radiological aspect back calculation of the water limiting concentration from the PNEDR for each isotope taken into account. When significant, the assessment is refined applying probabilistic techniques. The whole approach applicability was tested on a real case-study related to a former uranium mining site.