The enhanced Craig-Gordon deuterium model as a tool for estimating free and organically bound tritium in plants

For the past 4 decades, researchers have relied on the Craig-Gordon model to estimate and simulate the deuterium and oxygen-18 isotopic fractionation effects of hydrologic processes on surface waters, soils and vegetation. In parallel, researchers focussed on the relationship between tissue free water and organically bound tritium in plants have used deuterium as an anolog for tritium in sensitive laboratory settings. In this proof-of concept investigation, plant process applications of the enhanced Craig-Gordon model are parameterized for tritium to assess the influence of a range of controls on organically bound tritium formation in plants. Simulation results identify the interplay of humidity, soil porewater tritium and tritium in air on free water and organically bound tritium formation in plant tissues. Regulatory transfer factor model simulations are compared with the enhanced Craig-Gordon simulation results, showing agreement between the two only under specific conditions. The proof-of-concept results presented here are promising in that they identify the mechanisms that can results in OBT concentrations exceeding regulatory model predictions. Although promising as a proof-of-concept, laboratory and field testing of the approach is required for verification.