Quantifying exposure of plants and animals to radiation: a new methodology

The IAEA is updating its simple methodology for calculation of doses to people from radioactive discharges. The update will provide a harmonised dose assessment methodology for both humans and flora and fauna. The approach is intended for the assessment of planned releases from facilities and estimates radiation exposure during the 100th year of discharge (expected life-time of a nuclear facility). The environmental protection elements of the methodology will, as far as practicable, utilise relevant aspects of the ICRP’s framework for environmental protection. Here we describe the new IAEA methodology for calculating the radiation exposure of terrestrial wildlife focussing on differences with existing methodologies and demonstrating the potential impact of these differences. The application of whole body concentration ratios, CRwo-soils, is often aimed to be conservative. However, it has been suggested that the application of CRwo-soils in situations of prolonged atmospheric discharges will result in an underestimation of the exposure of plants and some animals. This is because radionuclides deposited onto plant surfaces are predicted to contribute a significant component of the total plant activity. Ignoring externally deposited radionuclides from the assessment is also inconsistent with models used to assess human exposure. Consequently, the new methodology adopted by the IAEA incorporates an explicit consideration of this exposure pathway, including consideration of herbivorous animals feeding on plants with external deposition. Other differences in the new approach compared to existing environmental assessment tools are the correction of CRwo-soils for radionuclide physical half-life and the approach used to consider the scenario-specific contribution of radioactive progeny to parent radionuclide dose. The paper will compare results using the existing and new methodologies