Study on comparison of model for estimation of concentration of tritium in wheat from long-term atmospheric releases of tritium

Normally, when the plant has higher water content, the specific activity model is used to calculate concentration of tritium in the plant tissue water to assess ingestion dose from long-term atmospheric releases of tritium. But grains have much lower water content and much higher organism, the calculation must take account of organically bound tritium. Taking the wheat as an example, in this paper various methods for estimating tritium concentration in plant and the assumptions behind them are described. Tritium concentration in wheat and resulting ingestion doses are compared for the various methods. The results showed the specific activity model overestimate the concentration of tritium in wheat and underestimate doses received from ingestion of wheat since they do not take specific account of organically bound tritium. The estimation of the concentration of tritium in plant should simultaneously take into account the contribution from the tritium in air moisture and soil moisture. HTO and OBT must be treated separately in the estimation of ingestion doses in grains because the dose conversion factor (DCF) for OBT is higher than the DCF for HTO by a factor of about 2, so that the estimated concentrations and ingestion doses can properly reflect the actual situation. (authors)