Uranium oral exposure

There are no reports of human deaths from oral exposure to uranium compounds. However, data from animal studies demonstrate that soluble uranium compounds, at very high intake levels, can be lethal to animals through the oral route for all durations of exposure. Uranium compounds at these concentrations are not palatable to animals and require sweetening. 

No human studies were located regarding respiratory, endocrine, dermal, ocular, body weight, or other systemic effects in humans following acute-, intermediate-, or chronic-duration oral exposure to uranium compounds. 

Figure 2-3. Levels of Significant Exposure to Uranium - Oral (cont.)... 

Respiratory Effects. Respiratory effects from oral exposure to uranium are unlikely. In an acute-duration animal study, no adverse effects on the respiratory system were reported in rats given single oral doses of 118 mg uranium per kilogram body weight per day (U/kg/day) as uranyl acetate dihydrate (Domingo et al. 1987). 

Oral exposure to uranium compounds has caused body weight effects in animals, but these effects are not necessarily the result of systemic toxicity. The initial loss of body weight observed in animals exposed... 

No information was located regarding the effects of uranium on the immune system in humans following oral exposure for any duration. 

No studies were located for humans regarding neurological effects following oral exposure to uranium compounds. 

No studies were located that reported developmental effects in humans following oral exposure to uranium for any duration. Animal studies indicate that oral exposure to uranium can cause developmental effects, but only at relatively high doses. 

No evidence linking oral exposure to uranium to human cancer has been found. Although natural, depleted, or enriched uranium and uranium compounds have not been evaluated in rodent cancer bioassays by any route by the NTP (BEIR 1980, 1988, 1990 Hahn 1989 Sanders 1986 UNSCEAR 1982,1986,1988), there is potential for the carcinogenicity of uranium, since it emits primarily alpha radiation. Nevertheless, no evidence has been found to associate human exposure to uranium compounds and carcinogenesis. The National Academy of Sciences has determined that bone sarcoma is the most likely cancer from oral exposure to uranium however, their report noted that this cancer has not been observed in exposed humans and concluded that exposure to natural uranium may have no measurable effect (BEIR IV). 

The ICRP (1994, 1996) developed a Human Respiratory Tract Model for Radiological Protection which contains respiratory tract deposition and clearance compartmental models for inhalation exposure that may be applied to uranium. The ICRP (1995) also developed a biokinetic model for human oral exposure that applies to uranium. Two other compartmental models (Fisher et al. 1991 Sontag et al. 1986) are also described below. The National Council on Radiation Protection and Measurement (NCRP) has also developed a respiratory tract model for inhaled radionuclides (NCRP 1997). At this time, the NCRP recommends the use of the ICRP model for calculating exposures for radiation workers and the general public. Readers interested in this topic are referred to NCRP Report No. 125 Deposition, Retention and Dosimetry of Inhaled Radioactive Substances (NCRP 1997). In the appendix to the report, NCRP provides the animal testing clearance data and equations fitting the data which supported the development of the human model. 

Minimal Risk Levels (MRLs) have been derived for the effects from inhalation and oral exposure to uranium, and those values are identified in this section and their bases are detailed in Appendix A. MRLs for radiological exposure were not calculated because ... 

An MRL of 2x10 mg/kg/day has been derived for intermediate-duration oral exposure (15-364 days) to soluble compounds of uranium. 

Musculoskeletal Effects. No studies have reported effects of uranium on the musculoskeletal system in humans following inhalation, oral, or dermal exposure for any duration. Laboratory animal studies support a lack of toxicological effects on the musculoskeletal system after oral exposures (Gilman et al. 1998a, 1998b, 1998c). 

ATSDR has derived an MRL of 2.0x10 mg/kg/day has been derived for intermediate-duration oral exposure (and is protective for chronic-duration oral exposure) to soluble compounds of uranium based on a LOAEL of 0.05 mg U/kg/day d for renal effects in rabbits (Gilman et al. 1998b). 

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