Bioavailability in ecological risk assessment for radionuclides

Garnier-Laplace J, Denison F, Gilbin R, Della-Vedova C, Adam C, Simon O, Beaugelin K. Bioavailability in ecological risk assessment for radionuclides. ECORAD 2004 - Scientific trends in radiological protection of the environment, Editions TEC&DOC, Lavoisier: 41-57

The guidance for performing Ecological Risk Assessments (ERA) in Europe has been
published in 2003 in the EC’s Technical Guidance Document. This document constitutes the official reference in which current water quality standards and risk assessment approach for metals/metalloids are still mainly based on total or dissolved concentrations. However, it has been recognized that accurate assessment of the bioavailable metal fraction is crucial, even if the way to incorporate bioavailability into these procedures is still under discussion. The speciation of a pollutant in the exposure medium is the first factor that regulates its bioavailability and consequently its bioaccumulation and the induced biological effects. Therefore, within any ecological risk assessment, bioavailability has obvious implications: firstly in exposure analysis which aim is to determine Predicted Exposure Concentration (PEC); secondly in effect analysis while deriving the so-called Predicted No-Effect Concentrations (PNEC) as toxicity is often linked to the amount of the contaminant incorporated into the tissues of biota. Similarities between metals/metalloids and radionuclides are limited to the biogeochemical behaviour of the element considered and to the need to use bioavailability models. In addition, for radionuclides, emitted ionising radiations (type and energy) need to be taken into account for both exposure and effect analyses whilst performing dosimetric calculations appropriate to the exposure scenarios. A methodology for properly implementing bioavailability models is explained and illustrated for aqueous U(VI), starting from a comprehensive review of the thermodynamic data relevant to environmentally-realistic physico-chemical conditions. Then, the use of thermodynamic equilibrium modelling as a tool for interpreting the bioavailability of U(VI) is presented. Using a systematic approach, different bioavailability models of increasing complexity were tested to model U biouptake, on the basis of well-defined experiments under controlled conditions. Finally, the implication of bioavailability in risk characterisation is illustrated for radionuclides for which there are a lack of internal exposure and effect data. The use of the Species Sensitivity Distribution technique is proposed to derive an appropriate Predicted No-effect Dose Rate value to be used in the calculation of the risk index combining both exposure and no-effect dose-rates. A number of numerical applications are given as examples for pelagic invertebrates under chronic exposure conditions, demonstrating the sensitivity of this risk formulation to bioavailability.


Summary of the book "ECORAD 2004 - Scientific trends in radiological protection of the environment " :

This volume brings together some of the most outstanding guest contributions at the 2 ° ECORAD International Conference held in Aix en Provence, France, on 6-10 September 2004. Traditionally dealing with Radioecology, this Conference event has focused on the scientific basis for environmental protection against ionising radiation . The aim is to consider the current challenges faced by this scientific discipline in an emerging general context that places environmental protection issues on a par with human-related concerns. This is not just a trend or the latest conveniently-milked fashion, but the natural and credible consequence of the intensity of human activity, which is now encroaching in many different ways on both human and environmental health. The contributions included herein provide an advanced, updated and focused understanding that will help to ensure that environmental regulations currently at the centre of international debate are pertinent and adequate, and contribute to an increasingly efficient system of environmental intervention and crisis management. The Institute for Radiological Protection and Nuclear Safety (IRSN) is a public organization conducting research and appraisal activities in the field of nuclear safety and radiological protection. It acts as an expert to the public authorities and also performs the public service activities defined in the regulations. In particular, these include radiological monitoring of French territory and of workers, managing emergency situations, and keeping the public informed. IRSN expertise is available to partners and customers both in France and abroad.