Answer to Question #1906 Submitted to "Ask the Experts"

Q

What effects does uranium have as a chemical poison and as a radioactive agent on the kidney? How vulnerable is the kidney to chemical and radiological toxins?

A

Uranium, being a naturally occurring heavy metal, is chemically toxic, as are other heavy metals such as lead. Uranium poisoning or effects are rare in humans and hence most of our knowledge of uranium toxicity has come from studies with animals, largely rats and mice. These studies, as well as a very limited amount of human data from uranium miners and workers with accidental exposures, indicate that uranium affects the proximal tubules of the kidney; at very high acute doses, tubular degeneration and necrosis (that is, death of tissue) may occur a few days after the intake of uranium. Depending on the dose, regeneration of tissue is likely. At lower doses, minor and transitory effects may occur, including the presence of certain so-called biomarkers in the urine, such as presence of protein and elevated levels of certain biochemicals such as beta-2-microglobulin. These are nonspecific and may or may not be indicative of uranium effects. At lower doses there is generally no diminution in kidney function. The radioactivity of uranium found in nature is weak, and the chemical toxicity effects on the kidney from ingestion of natural uranium are vastly greater than the radiological effects—so much so that the radiological effects can be ignored as they are trivial in comparison to the potential chemical effects. Radiation effects on the kidney have typically not been observed in either animals or humans from exposure to uranium.

The second part of your question relates to the vulnerability of the kidney with respect to uranium effects. The kidney is apparently relatively resistant to the potential toxic effects of uranium, and relatively high intakes are required before any signs of chemical toxicity occur. Indeed, before the discovery and availability of insulin, uranium was used therapeutically for the treatment of diabetes; relatively high doses were administered by mouth to patients, but there were no reports of kidney toxicity.

Finally, it bears mention that uranium is only poorly absorbed from the gut, so even if a large dose is swallowed, only about 1% or so will be absorbed—sort of a natural protective mechanism against potential toxic effects on the kidney.

Ronald L. Kathren, CHP
Professor Emeritus of Pharmaceutical Science
Washington State University