Uranium Chemical and Radiological RiskAssessment for Freshwater Ecosystems ReceivingOre Mining Releases: Principles, Equations andParameters

摘要

Uranium is an element that has the solely characteristic to behave as significant hazardboth from a chemical and radiological point of view. Exclusively of natural occurrence, itsdistribution into the environment may be influenced by human activities, such as nuclear fuelcycle, military use of depleted uranium, or coal and phosphate fertilizer use, which finally mayimpact freshwater ecosystems. Until now, the associated environmental impact and riskassessments were conducted separately. We propose here to apply the same methodology toevaluate the ecological risk due to potential chemotoxicity and radiotoxicity of uranium. Thismethodology is articulated into the classical four steps (EC, 2003: problem formulation, effect andexposure analysis, risk characterisation). The problem formulation dealt both with uranium viewedas a chemical element and as the three isotopes 234, 235 and 238 of uranium and their maindaughters. Then, the exposure analysis of non-human species was led on the basis of a commonconceptual model of the fluxes occurring in freshwater ecosystems. No-effect values for theecosystem were derived using the same effect data treatment in parallel. A Species SensitivityDistribution was fitted : (1) to the ecotoxicity data sets illustrating uranium chemotoxicity andallowing the estimation of a Predicted-No-Effect-Concentration for uranium in water expressed inμg/L; (2) to radiotoxicity effect data as it was done within the ERICA project, allowing theestimation of a Predicted No-Effect-Dose-Rate (in μGy.h~(-1)).Two methods were then applied tocharacterize the risk to the ecosystem: a screening method using the risk quotient approach,involving for the radiological aspect back calculation of the water limiting concentration from thePNEDR for each isotope taken into account and a probabilistic risk assessment. A former uraniumore mining case-study will help in demonstrating the application of the whole methodology.