Current studies within the field of Environmental Risk Assessments associated with the presence of radionuclides in ecosystems tend to implement the usual approach developed for chemicals, that includes four steps: (1) pollutant inventory in the sources of exposure, (2) effect analysis, (3) exposure analysis and (4) risk calculation. In the case of ionising radiation, the third stage involves radiological dose calculation. For humans, this kind of calculation is internationally codified by the ICRP, that provides both models and associated dose coefficients. For non-human biota, this task is a new field of investigations and no international consensus exists at the present time. We thus propose a computer tool to evaluate the dose rate at which the energy produced by ionising radiations is deposited in representative organisms of non-human biota. This energy depends on several parameters, describing the geometry of the relative position of the ionising source and the target, in association with the main properties of the latter. Concerning the source, the radiation type (alpha, beta or gamma) should be taken into account as well as the energy emissions of the concerned nuclides. The target-organism is described by its geometry (assimilated to an ellipsoid characterised by its three axes), its chemical composition and its lifestyle (exposure pathways, dietary habits, behaviour). E.D.E.N. (Elementary Dose Evaluation for Natural environment) is the operational code that we are developing to evaluate the Dose Per Unit of Concentration (expressed in Gy.time-1 / Bq.mass-1 or Bq.volume-1) due to internal and external exposures of any non-human organism to any radionuclide. A user-friendly interface is provided to build the exposure scenario of interest, characterising the target and the sources involved. Several cases are presented to illustrate the possibilities of E.D.E.N.