Other Tritiated Gases

Tritium Primer

DOE-HDBK-1079-94

BIOLOGICAL PROPERTIES

Next to pump oils, the next most common group is tritiated solvents. All solvents can be

absorbed through the skin and are relatively volatile and toxic. The overall toxicity of tritiated

solvents is usually dominated by the chemical nature of the solvent.

Other Tritiated Gases

If tritium is released in a nitrogen- or air-filled glovebox, other tritiated gases may be formed,

such as ammonia and methane. The conversion of tritium to tritiated ammonia is small unless

the tritium concentration is very high. The toxicity of these gases is not believed to be greater

than that of tritium oxide.

Biological Half-Life of HTO

Studies of biological elimination rates of body water in humans date back to 1934 when the body

water turnover rate was measured using HDO. Since that time, several additional studies have

been conducted with HDO and HTO. A simple average of the data suggests a value of 9.5 days

for the measured biological half-life of water in the body with a deviation of 50%.

Calculations based on total fluid intake indicate a similar value. This is reasonable because the

turnover rate of HTO should be identical to that of body water. In other words, the biological

half-life of tritium is a function of the average daily throughput of water.

The biological half-life of HTO has been studied when outdoor temperatures varied at the time

of tritium uptake. The data suggest that biological half-lives are shorter in warmer months. For

example, the 7.5-day half-life measured in southern Nigeria is not surprising because the mean

outdoor temperature there averages 27 C. In contrast, an average 9.5-day half-life was

measured in North America, where the mean outdoor temperature averages 17 C. Such findings

are consistent with metabolic pathways involving sensible and insensible perspiration. As such,

the skin absorption and perspiration pathways can become an important part of body water

exchange routes. It is important to note that personnel who are perspiring will have a greater

absorption of tritium from contact with tritiated surfaces. For planning purposes, it is customary

to use an average half-life of 10 days. However, it is not used to calculate doses from actual

exposures.

Prolonged exposures can be expected to affect the biological half-life. Tritium's interaction with

organic hydrogen can result in additional half-life components ranging from 21 to 30 days and

250 to 550 days. The shorter duration indicates that organic molecules in the body retain tritium

relatively briefly. The longer duration indicates long-term retention by other compounds in the

body that do not readily exchange hydrogen or that metabolize more slowly. However, the

overall contribution from organically bound tritium is relatively small, that is, less than about

5% for acute exposures and about 10% for chronic exposures. Methods used to compute the

annual limits on intake of air and water specify only the body water component and include the

assumption of a 10-day biological half-life, as mentioned above.

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Tritium