Insoluble OBT

DOE-HDBK-1184-2004

Solvents such as octane, cyclohexane, or acetone have been used in pump

cleaning and material dispersion processes. They can become tritium-labeled from

extended exposure to tritiated materials. Since these solvents are volatile, they are

considered soluble. Individual intake of tritiated solvents can occur through

inhalation, ingestion, or by diffusion through the skin. Evaluation of solvent OBT

intakes should be performed via urine bioassay.

The potential hazard of the skin absorption pathway should be assessed using

known or analyzed activity of the liquid. Volatile OBT also produces vapors that

can become dispersed in air, resulting in a second potential intake pathway of

vapor inhalation and skin absorption. Therefore, an air concentration value (ACV)

will be derived in the next section to relate volatile OBT air concentration to the

annual CEDE. Volatile OBT vapors are readily detected by the tritium gas air

monitoring method (e.g. ion chamber).

If a solid particle OBT that has been determined to be soluble in lung fluids is

discovered, urine bioassay should be used to determine internal dose.

4.4.2

Insoluble OBT

For insoluble OBT, absorption through the skin is not an intake pathway. Following

ingestion (or inhalation), some fraction of insoluble OBT will likely be digested in the

stomach and converted to HTO or soluble OBT. Since HTO and soluble OBT are

rapidly assimilated physiologically, these dose components are readily assessed

via urine bioassay. In addition however, following inhalation, insoluble OBT may

reside in the lung for a period of time, delivering dose to the lung. This material is

largely formed by incidental contamination of environmental dust and is found in

many tritium contamination areas. Solid particulate OBT is considered primarily

insoluble, and intake by skin absorption is not expected, but inhalation is a possible

intake mechanism. Inhalation of this material, including determination of intake

through air monitoring, assignment of doses, and use of DCFs and ACVs, should

be treated the same as inhalation of ITPs. Because monitoring and intake/dose

assessments are the same for solid particulate OBT and for general ITP, these two

materials do not need to be distinguished during workplace characterizations when

the dose conversion assumptions are applied.

4.4.3

OBT Oils

Trivedi (1995) has shown that tritiated oils can be absorbed by mammalian skin. In

this section skin absorption and inhalation are both discussed as valid intake

pathways for various components of tritiated oils. Tritiated oils can be found in

pumps and compressors located in tritium areas. Tritiated pump oils are

considered to be a mixture of three components: insoluble large molecule OBT

(original molecules of oil labeled by tritium), soluble small molecule OBT (created

by radiolytic and degradation processes and labeled by tritium), and HTO. As a

reasonable hypothesis, the tritium in OBT oils should be expected to partition into

the above three components in approximately an 80:10:10 ratio, respectively. This

is consistent with a ~70:20:10 ratio of tritium components removable from oily

surfaces (Johnson, 1988), where all three components were observed. The small

molecule OBT is expected to be more concentrated on surfaces than in bulk oil due

to absorption of small polar molecules created from degradation processes. Data