Uptake of Tritium in the Organically Bound Form into the Biomass of the Soil

Laboratory experiments and field observations have shown that elemental tritium HT is completely converted into tritiated water ( HTO ) by the activity of soil microorganisms. No organically bound tritium ( OBT ) is formed initially, but some tritium is taken up into soil biomass by general biosynthesis. Only a small fraction of tritium is directly incorporated from HTO into OBT with the non-exchangable portion becoming the dominant source of tritium in OBT. In practice a small fraction of non-exchangeable OBT must be separated by vacuum distillation from a large amount of soil water containing HTO. The method has been tested by labelling the soil water with HTO and H₂¹⁸O, respectively. Several steps are necessary to obtain a complete yield. During the incubation experiments a continuous loss of HTO by an exchange between soil water and air water vapour must be taken into account. Uptake of tritium into biomass of about 0.1 % per week was observed. The biological synthesis and consequently the uptake of tritium from HTO into OBT can be stimulated by the addition of energy sources such as glucose.