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