Dynamics of Tritiated Water and Organically Bound Tritium After an Acute Tritiated Water Intake in Humans

Tritiated water^o (HTO) represents the mosl important occupational and environmental exposures to tritium, as far as radiation protection is concerned We have studied the dynamics of HTO and organically bound tritium^* (OBT) in urine, feces and blood from male workers at 100–300 d following an acute intake of HTO. Blood and cumulative 24 h urine and fecal samples were collected and analyzed for HTO and OBT. The activity concentrations oi HTO in urine and HTO in feces were in equilibrium and were representative of HTO in the body water (HTO in blood). The ratio of bound tritium per gram hydrogen (Bq·H⁻¹) in organic matter in feces (OBT_feces) to urine (OBT_urine) was 1.0 ± 0.1. Similarly, the ratios of OBT_blood to OBT_urine and OBT_blood to OBT_feces were 0.9 ± 0.2 and 1.1 ± 0.2, respectively. These results suggest that, providing an equilibrium condition exists, a measurement of the tritium activity per unit mass of organic matter in urine or feces can provide an assessment of the specific activity of tritium in the organic fraction ol the soft tissue. The activity concentrations of HTO and OBT in urine samples, from a few days up to 300 d post-exposure, were examined for the clearance kinetics of HTO in urine and OBT in urine. The early presence of OBT in urine indicated that a portion of tritium from the ingested HTO is rapidly fixed into organic constituents of the body. The half-life for the longer-term component of OBT in urine is comparable to the half-life for the longer-term component of HTO in urine. This close relationship between the longer-term excretion of HTO in urine and OBT in urine suggests that most of the HTO produced in its longer-term component is a by-product of metabolized OBT. This work has demonstrated that OBT is excreted in urine in all examinations, up to 300 d post-exposure to HTO, and that a fraction of the metabolized OBT is also excreted in feces.