Occupational uranium exposure. Thun and colleagues (1985) compared kidney function in uranium mill workers (39 subjects) and a control group consisting of cement plant workers (36 subjects matched for sex, race, and age). In 115 of 535 (21 percent) of urinary uranium assays, mill workers had levels >30 μg/L (<1 μg U/g kidney weight). Uranium workers excreted more beta 2-microglobulin and five amino acids than the control group. The amount of proteinuria was small. The clearance of beta2-microglobulin, relative to that of creatinine, increased with increasing length of time that the uranium workers had spent in the yellowcake drying and packaging area, the work area with the highest exposures to soluble uranium. The age of the workers did not account for this relationship. Serum beta2-microglobulin was significantly higher in the uranium workers, an effect that was not due to reduced glomerular function, since glomerular function (serum creatinine and creatinine clearance) was the same in uranium workers and controls. The aminoaciduria was due to increased excretion of dicarboxylic amino acids and methionine by the uranium workers. The data suggest a reduction in renal proximal tubular reabsorption of amino acids and low-molecular-weight proteins, which is consistent with uranium nephrotoxicity.

The U.S. Uranium Registry reevaluated the intake and deposition of uranium in three men 38 years after they had been accidentally exposed to soluble uranium compounds in an explosion in 1944 (Kathren and Moore, 1986). The initial deposition of uranium in the lungs was approximately 40–50 mg, based on incomplete urinary excretion data that were obtained shortly after the accident (Eisenbud and Quigley, 1956). Two of the workers had extensive medical and health physics examinations 38 years after the accident. There was no detectable uranium, and the workers had no physical findings or renal function abnormalities that could be attributed to uranium exposure.

Lu and Zhao (1990) reported on renal function in a male worker 64 days after a 5-minute accidental exposure to uranium tetrafluoride powder (an estimated radioactivity of 6,905 Bq/m3). The worker showed a significant increase in urinary protein, nonprotein nitrogen, amino acid nitrogen and creatinine, and phenolsulfonphthalein. These abnormal levels were present up to 3 years later but gradually returned to normal values.

Boback (1975) describes uranium excretion and clinical urinalysis in accidental exposures to an estimated 100–200 μg/kg of soluble forms of uranium. Despite an initial urine uranium excretion of 7–14 mg per day, there was no renal injury as measured by urinary protein, sugar, pH, specific gravity, or excretion of formed elements such as red blood cells or tubular casts.

Drinking water exposure. Zamora and colleagues (1998) compared the effects of uranium on kidney function in two communities, one of which had private wells supplied by underground water with a uranium content higher than the Canadian drinking water guideline. The authors divided the subjects into two groups: a low-exposure group (n = 20), whose drinking water contained <1 μg U/L, and a high-exposure group (n = 30), whose drinking water contained uranium levels from 2 to 781 μg U/L. In the low-exposure group, time of residence

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