Uranium inhalation exposure

Other Systemic Effects. Several general effects have been attributed to uranium inhalation exposure. In animal studies, dogs exposed to 13 mg U/m as uranium hexafluoride for 30 days exhibited decreased water intake (Spiegl 1949). Reduced food intake was also observed in a 4-week study of rats and mice exposed to 16 mg U/m as uranium trioxide (Rothstein 1949c) and in a 5-week study of rats and mice exposed to 15 mg U/m as sodium diuranate for 6 hours per day, 5V2 days per week (Rothstein 1949d). 

After inhalation exposure, the primary route of excretion is in the feces following ciliary clearance from the lungs to the gastrointestinal tract (Wrenn et al. 1981). Fecal excretion may account for as much as 97% of total excretion (Fisher et al. 1983). Higher levels of thorium-230 were excreted in the feces by active crushermen (uranium mill workers exposed to uranium ore dust in the crusher building) compared to retired workers or controls (Fisher et al. 1983). Levels of thorium-230 in the urine were comparable to those of retired workers, and the levels in both were significantly greater than controls. 

The lethal effects of inhalation exposure to uranium have been investigated in humans in epidemiological studies and in animal studies under controlled conditions. Epidemiological studies indicate that routine exposure of humans (in the worlq)lace and the environment at large) to airborne uranium is not associated with increased mortality. Brief accidental exposures to very high concentrations of uranium hexafluoride have caused fatalities in humans. Laboratory studies in animals indicate that inhalation exposure to certain uranium compounds can be fatal. These deaths are believed to result from renal failure caused by absorbed uranium. The low specific activity of uranium precludes the possibility of absorbing enough uranium to deliver a lethal dose of radiation. 

In several other inhalation-exposure animal studies, no deaths were observed when either soluble or insoluble uranium compounds were administered. In one of these animal studies, no mortality was... 

No animal studies were located regarding the endocrine, metabolic, dermal, or ocular effects of uranium in animals following acute-duration inhalation exposures to uranium. Nor were any studies located regarding the metabolic, dermal, ocular, or other systemic effects in animals following intermediate-duration inhalation exposure to uranium. There are animal data for acute-, intermediate-, and chronic-duration inhalation exposures to uranium for respiratory, hematological, cardiovascular, gastrointestinal, renal, or body weight effects. However, animal data on hepatic effects are limited to acute- and chronic-duration inhalation exposures to uranium. 

Figure 2-1. Levels of Significant Exposure to Uranium - Inhalation (cont.)... 

Because particles containing insoluble uranium compounds can reside in the lung for years, it is likely that radiotoxicity as well as chemical toxicity can result from inhalation exposure to highly enriched uranium compounds. Radiation effects on tissues from the alveolar regions of the lungs were examined in Albino HMT (Fischer 344) male rats exposed, nose-only, for 100 minutes to an aerosol of to 92.8% U-enriched uranium dioxide with a concentration of 2,273 nCi/m (84.1 kBq/m ) to 5,458 nCi/m ... 

Cardiovascular Effects. No cardiovascular effects have been reported in humans after inhalation exposure to uranium. No effect on blood pressure or pulse rate was observed in a man accidentally exposed to powdered uranium tetrafluoride for 5 minutes (Zhao and Zhao 1990). Air concentration and mean particle size of the powder were not determined. Electrocardiograms and chest X-rays were normal shortly after the accident and over a 7.5-year follow-up period. 

In other intermediate-duration exposure studies, inhalation exposures to uranium dioxide dusts containing 1 mg U/m for 30 weeks and 2 mg U/m for 26 weeks in rabbits and guinea pigs, respectively (Stokinger et al. 1953), 19.4 mg U/m for 5 weeks in mice, and 9.2 mg U/m for 5 weeks in dogs and rats had no adverse effects on hematological parameters (Rothstein 1949b). Similarly, exposures to... 

Musculoskeletal Effects. No studies were located regarding the chemical or radiation effects of uranium on the musculoskeletal system in humans or animals following inhalation exposure for any duration. 

Renal effects can be produced in animals after acute-duration inhalation exposures to uranium. A 10-minute exposure to 637 mg U/m as uranium hexafluoride produced severe degeneration of the cortical tubules 5-8 days later in rats (Spiegl, 1949). These same effects were observed in dogs 1-3 days after a 1-hour exposure to 250 mg U/m as uranyl fluoride (Morrow et al. 1982). Proteinuria and glucosuria were also observed in rats after 2-10-minute exposures to uranium hexafluoride (Leach et al. 1984). 

Although no studies were located that specifically tested immunological effects in humans following inhalation exposure to uranium, all epidemiologic studies of workers in uranium mines and fuel fabrication plants showed no increased incidence of death due to diseases of the immune system (Brown and Bloom 1987 Checkoway et al. 1988 Keane and Polednak 1983 Polednak and Frome 1981). 

Human studies that assessed damage to cellular immune components following inhalation exposure to uranium found no clear evidence of an immunotoxic potential for uranium. No association was found between the uranium exposure and the development of abnormal leukocytes in workers employed for 12-18 years at a nuclear fuels production facility (Cragle et al. 1988). Increases in the number of fatal malignant disease of the lymphatic and hematopoietic tissue reported among uranium mill workers may have been caused by other carcinogens in the work environment such as °Th. The authors of this report estimated that the workers were exposed to 8-5,100 mg/m (median 110 mg/m ) uranium mill dust, which contains °Th as a natural component (Archer et al. 1973b). 

There is some evidence from animal studies that exposure to 90% enriched uranium may affect the immune system. Increased macrophage activity, associated with localized alpha tracks in all 5 lobes of the lungs, was seen in Fischer 344 rats exposed to 6,825.5 nCi/m (252 kBq/m ) through inhalation exposure to enriched uranium dioxide for 100 minutes. The increased activity was evident from days 1-7, 180, 360, 540, and 720 with increases in percent activity of 0.44, 2.15, 19.70, 6.54, and 37.84, respectively. The number and size of macrophage clusters in the lung increased with time postexposure. The radioactive material concentration of the mixture was estimated as 1.91 kBq/mg (51.6 nCi/mg) (Morris et al. 1992). The degree of enrichment was calculated based on this specific activity. 

It is unlikely that inhalation of uranium produces a significant effect on reproductive health. Studies of one human population group (miners) were located which identified a reproductive effect associated with the inhalation exposure of mine air, but the association with uranium compounds was unclear, and the other miner studies observed no reproductive effects. Also, no adverse animal studies were found. 

Three studies of one mining population were located that equivocally associated reproductive effects in humans following inhalation exposure to uranium. The studies reported that male uranium miners were found to have more first-born female children than expected, suggesting that uranium s alpha radiation damaged the y-chromosomes of the miners (Muller et al. 1967 Waxweiler et al. 1981b Wiese 1981). In addition, it is not certain if the effect described is from exposure to uranium because the workers were also exposed to Rn, chlorine, hydrofluoric acid, lead sulfate, nickel, nitric acid and nitrogen oxides, silicon dioxide, and sulfuric acid (Dupree et al. 1987). 

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