Urinary and Fecal Excretion Functions

DOE-HDBK-1184-2004

Of the HTO that is absorbed into the bloodstream, 3% is converted to organically

bound tritium (OBT) that is retained in the body with a 40-day half-life and the

remaining 97% remains as HTO and is retained with a 10-day half-life. All of the

OBT is excreted into the urinary bladder and ultimately the urine. HTO is excreted

from the systemic compartment in the following ratios:

1.4/3 fraction to the urinary bladder and ultimately the urine;

0.1/3 fraction to ULI and ultimately the feces; and

1.5/3 fraction to other systemic excreta (e.g., "insensible losses" and sweat).

These ratios are derived from the ICRP 23 (ICRP 1975) Reference Man water

balance.

5.1.2

Urinary and Fecal Excretion Functions

Urinary and fecal excretion are expressed as 24-hour incremental quantities. For

example, the 24-hour incremental urinary excretion ∆Eu(t) of tritium (not accounting

for radioactive decay) at t days after intake is given by

∆E u (t ) = Qu (t ) - Qu (t - 1)

(Eq. 5-1)

where Qu(t) is the content of the urine compartment at time t and Qu(t-1) is the

content of the urine compartment one day earlier. The 24-hour incremental urinary

excretion of tritium that does not account for radioactive decay is adjusted for

radioactive decay to give the incremental excretion of tritium ∆eu(t)

∆eu(t) = ∆Eu(t)e-?t

(Eq. 5-2)

Urinary excretion of tritium following an intake of HTO is typically expressed as the

concentration of radioactivity per unit volume of urine such as Ci/L, based on the

assumption that the concentration of HTO is the same in all body fluids. The

presence of the OBT compartment in the ICRP 78 model precludes this approach

and warrants the use of 24-hour incremental urinary excretion functions.

Incremental fecal excretion is calculated in an analogous fashion. A detailed

example of how to calculate urinary and fecal excretion is given in Appendix B.

5.1.3

The Respiratory Tract Biokinetic Model

The ICRP respiratory tract model is rather complex and is discussed in great detail

in ICRP Publication 66. A brief overview is provided here as an introduction to the

model. The respiratory tract model is composed of five major components:

anatomical model;

deposition model;

particle mechanical clearance model;