Logistic analysis of OBT dynamics.

Formation and depuration of non-exchangeable organically bound tritium (OBT) is measured in mussel dry tissue on expanding time scales. The OBT course of time is analyzed by means of the Verhulst logistic growth function. Two separate routes are found as well for OBT formation as depuration, i.e., restoration of organically bound hydrogen (OBH). Routes which arrive at saturation earlier than sampling started are assigned to respiration. Other routes which start with one-day delay are attributed to metabolc pathways. The metabolic route of OBT formation includes, in addition to the logistic growth function, one rapid mechanism with <or=0.01 d half-time. This rapid OBT formation comprises about 75% of the metabolic OBT formation yield. About the same yield as the sum of both metabolic OBT formations is re-found in the OBH turnover of metabolic depuration. The protein rich tissue guides, in context of well-known dynamics of protein formation, the suggestion of reaction mechanisms. The major part of traditionally determined OBT which is considered in tritium dose assessment to be tritium bound to carbon is traced back to exchangeable tritium in the living state. This may lead to overestimation of the risk of HTO- and OBT-incorporation.