The derivation of tritium transfer parameters for farm animals on the basis of a metabolic understanding

In contrast to many radionuclides (which often have no biological function) 3H has a stable analogue which is an elemental component of major nutrients, animal tissues and drinking water. Therefore concepts used to predict the transfer of other radionuclides are not valid for 3H. In this paper we present an approach for the derivation of tritium transfer parameters which is based on the metabolism of hydrogen in animals. The derived transfer parameters separately account for transfer, to and from, free (i.e. water) and organically bound tritium. A novel aspect of the approach is that tritium transfer can be predicted to any animal product for which the required metabolic input parameters are available. Predicted equilibrium transfer coefficients are compared to available independent data. Agreement is good (R2=0.97) with the exception of the transfer from tritiated water to organically bound 3H in ruminants. This may be attributable to characteristics of ruminant digestion. Tritium transfer coefficients will vary in response to the metabolic status of an animal and the use of a single transfer coefficient from diet to animal product is inappropriate. However, we demonstrate that concentration ratios are less subject to metabolic variation and are a more useful parameter than transfer coefficients