Ease of Uptake

DOE-HDBK-1184-2004

2.3.1

Ease of Uptake

Ease of uptake refers to the rate at which radioactive material can be taken into the

bloodstream. For STCs this process includes both uptake of tritium that has

dissociated from a host or carrier material and uptake of an entire STC molecule.

The International Commission on Radiological Protection (ICRP) (ICRP 1994)

categorizes most radioactive materials in terms of the rate of absorption from the

respiratory tract to the bloodstream. Materials absorbed on the order days are

classified as Type F (fast), those absorbed on the order of weeks are classified as

Type M (moderate) and those absorbed on the order of years are classified as Type

S (slow). (In addition to the three absorption classes, ICRP (ICRP 1998b)

categorizes certain vaporous substances that are very rapidly absorbed by the body

as Type V.) For purposes of understanding some of the radiation protection

elements expounded in this handbook, Type S and M materials can be considered

insoluble and Type F material can be considered soluble. Note that the ICRP

classification forms the basis of the dosimetric calculations contained in Chapter 5.

NOTE: In the Mound Technical Basis Document (Mound 2000), the document

from which much of the material in this handbook is derived, the term

stable is used instead of insoluble to describe particles from which the

tritium dissociates slowly, and the term unstable is used instead of soluble

to describe particles from which the tritium dissociates more rapidly. The

terms soluble and insoluble are selected for this hand book in order to

apply the same terminology to describe ease of tritium uptake by the body

for all STCs.

Particles or particulates can be formed from all types of STCs. To explain the

uptake of these particles, the ICRP in publication 71 (ICRP 1995) assumes that the

tritium dissociates from the rest of the particle and is then taken up by the body.

The tritium that is not dissociated from the particle irradiates those tissues it comes

in contact with while it remains in the body. Tritiated particles from which the tritium

dissociates slowly may be considered insoluble. Tritiated particles from which the

tritium dissociates rapidly may be considered soluble. In this handbook the

operational distinction between soluble and insoluble particles is that insoluble

particles do not readily release the bound tritium to either aqueous solutions or air

during the interval between sample collection and analysis.

Another class of STCs is organically bound tritium (OBT) compounds. For these

types of STCs, the tritium is not readily released from the carbon-tritium bonds to air

or aqueous solution (Hill, 1993), therefore, the classification as either soluble or

insoluble is based on the ease by which the entire molecule is taken up by the

body.

Soluble OBT is rapidly taken up by the body while insoluble OBT is more slowly

taken up by the body.

2.3.2

Physical Form

The manner in which in the body takes up STCs, and hence the radiological

controls for STCs, is determined by the physical form of the STC. In this handbook,