Ingestion - doe-std-1136-20040035

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

2.3.2.2 Ingestion

Appropriate uranium contamination controls should prevent ingestion of uranium. Nevertheless, the

potential exits for accidental ingestion of uranium. Particles inhaled through the mouth and temporarily

deposited there are removed from the respiratory system to the esophagus. Deposition and removal of

ingested uranium are approximated using the Gastrointestinal (GI) Tract Model adapted from Eve (Eve

1966). This model calculates material transferred from the GI tract to the blood based on solubility classes

(ICRP 1979 and IAEA 1994) or based on a single value for all compounds, as described in ICRP

Publication 69 (ICRP 1995).

Distribution of uranium transferred into the bloodstream is calculated using a once-through

metabolic model. ICRP Publication 30 also provides values for this distribution and excretion to calculate

committed doses and long-term tissue retention. Recent models (Wrenn et al. 1994 and ICRP 1995) have

been developed to include recycling of uranium back into the blood.

2.4. CHEMICAL TOXICITY

The chemical toxicity of uranium is a primary concern in establishing control limits. A heavy

metal, uranium is chemically toxic to kidneys and exposure to soluble (transportable) compounds can

result in renal injury. The factors to be considered in determining whether the chemical or radiological

hazard is controlling are the enrichment, mode of entry, and the solubility/transportability of the material.

Chemical toxicity is a higher risk with soluble material of 10% or less enrichment.

A concentration of 3 g of uranium per gram (g U/g) of kidney tissue has traditionally been used as

the guideline for controlling the chemical toxicity of uranium. Reference man has a kidney mass of 310 g,

so this concentration translates to a total kidney burden of 1 mg. A review of the literature by Leggett

(Leggett 1989) suggests that worker exposure to 2 to 6 g U/g kidney might be tolerated with no serious

effects. However, he emphasizes that this range is not necessarily the same as the level causing no

detectable damage. He concludes that a lower limit would be prudent until more of the physiological

mechanisms of response to uranium in the kidney are better understood. Other studies (McGuire 1991)

report that detectable effects from an intake of soluble uranium of 10 mg or less is unlikely and that an

intake of 40 mg and perhaps as high as 100 mg is unlikely to cause permanent damage. Other evaluations of

toxicity to the kidney concluded that a limit of 1.0 g U/g kidney is consistent with results in the recent

literature.

An airborne concentration limit of 0.2 mg/m3 was adopted by the Nuclear Regulatory Commission

(NRC) and the American Conference of Governmental Industrial Hygienists (ACGIH) for occupational

exposures, based on the 3 g/gm of tissue value. The Occupational Safety and Health Administration

(OSHA) has adopted a limit of 0.05 mg/ m3 for soluble uranium and 0.25 mg/m3 for insoluble uranium. In

most DOE facilities, the most conservative of the two standards (OSHA or ACGIH) should be used unless

enrichment and solubility dictate more stringent controls based on radiological concerns. Table 2-8 lists

airborne concentration limits for transportable uranium that have been published by various organizations.

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