Biological Properties of Tritium

Tritium Primer

DOE-HDBK-1079-94

BIOLOGICAL PROPERTIES

BIOLOGICAL PROPERTIES OF TRITIUM

At most tritium facilities, the most commonly encountered forms of tritium are tritium gas (HT)

and tritium oxide (HTO). Other forms of tritium may be present, such as metal tritides, tritiated

pump oil, and tritiated gases such as methane and ammonia. As noted earlier, deuterated and

tritiated compounds generally have the same chemical properties as their protium counterparts,

although some minor isotopic differences in reaction rates exist. These various tritiated

compounds have a wide range of metabolic properties in humans under similar exposure

conditions. For example, inhaled tritium gas is only slightly incorporated into the body during

exposure, and the remainder is rapidly removed (by exhalation) following the exposure. On the

other hand, tritiated water vapor is readily taken up and retained in the body water. In this

Primer, we will address only those compounds likely to be found at DOE laboratories: gaseous

tritium, tritiated water, other tritiated species, metallic getters, and other tritiated liquids and

gases.

Metabolism of Gaseous Tritium

During a brief exposure to tritium gas, the gas is inhaled and a small amount is dissolved in the

bloodstream. The dissolved gas circulates in the bloodstream before being exhaled along with

the gaseous waste products (carbon dioxide) and normal water vapor. If the exposure persists,

the gas will reach other body fluids. A small percentage of the gaseous tritium is converted to

the oxide (HTO), most likely by oxidation in the gastrointestinal tract. Early experiments

involving human exposure to a concentration of 9 Ci/mL resulted in an increase in the HTO

concentration in urine of 7.7 10-3 Ci/mL per hour of exposure. Although independent of

the breathing rate, this conversion can be expressed as the ratio of the HTO buildup to the

tritium inhaled as HT at a nominal breathing rate (20 L/min). In this context, the conversion

is 0.003% of the total gaseous tritium inhaled. More recent experiments with six volunteers

resulted in a conversion of 0.005%. For gaseous tritium exposures, there are two doses: (a)

a lung dose from the tritium in the air inside the lung and (b) a whole body dose from the

tritium gas that has been converted to HTO. The tritiated water converted from the gas in the

body behaves as an exposure to tritiated water.

Intake of gaseous tritium through the skin has been found to be negligible compared with that

from inhalation. Small amounts of tritium can enter the skin through unprotected contact with

contaminated metal surfaces, which results in organically bound tritium in skin and in urine.

Ordinarily this is not a serious problem because surfaces highly contaminated with tritium gas

are inaccessible to skin contact. Also, most tritium exposed to air will be converted to the oxide

form (water vapor) before the internal surfaces of equipment are handled during maintenance

or repair operations.

Metabolism of Tritiated Water

The biological incorporation (uptake) of airborne HTO can be extremely efficient: up to 99%

of inhaled HTO is taken into the body by the circulating blood. Ingested liquid HTO is also

Rev. 0

Page 15

Tritium