Historical Document
This document is provided by the National Center for Environmental Health ONLY as an historical reference for the public health community. It is no longer being maintained and the data it contains may no longer be current and/or accurate.
For current information about cancer clusters, please visit
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What is uranium?
Uranium is a common, naturally occurring element, present in low amounts in rocks, soil, air, surface water and groundwater. Uranium is naturally radioactive, like many other naturally occurring radioactive elements in nature. Natural uranium exists as a mixture of three types, or isotopes, called U-234 (234U), U-235 (235U), and U-238 (238U).
All three types of uranium behave the same chemically, but they have different radioactive properties. U-238 is the most common type of uranium on earth and is the least radioactive. More than 99% of naturally occurring uranium is U-238. U-234 is the most radioactive type of uranium. U-235 is used as a fuel in power plants and weapons.
Radioactive elements are unstable and they become stable by giving off energy, a process called radioactive decay. All three uranium isotopes go through radioactive decay primarily by giving off what is called an alpha particle. These particles have very low penetrating ability and cannot pass through solid objects such as a piece of paper or human skin. There are also some weak gamma rays that are given off by uranium and these gamma rays can penetrate the body in the same way that x-rays do.
Uranium was present when the earth was formed. It is already naturally present throughout the environment (rocks, soil, water) and will remain as part of our natural world for billions of years. Although it is present in small amounts everywhere, higher concentrations of uranium ores have been found and mined in some places such as the southwestern United States.
How can people be exposed to uranium?
- Everyone is exposed to low amounts of radiation and radioactivity in our environment, including that from uranium.
- From radioactivity that is present outside the body, like natural uranium in soil in our backyards, people receive what is called "external" exposure.
- From radioactivity that is present in our body, people receive what is called "internal" exposure.
- We have small amounts of uranium inside our body because of the water we drink, food we eat, and any airborne dust we inhale.
- If there are increased levels of uranium in the environment, people’s exposure to uranium may increase.
Can increased exposure to uranium make people sick?
Exposure to a large amount of uranium can injure the kidneys. This damage results from the chemical properties of uranium as a heavy metal, not from its radioactive properties. Damage to the body as a result of radiation from low levels of natural uranium has not been detected.
Can uranium cause any type of cancer, including leukemia?
Excessive exposure to radiation or excessive amounts of radioactive elements in the body can cause cancer, including leukemia. In order for uranium outside the body to cause such injury, the levels of uranium in the environment have to be very high as to be easily detected by instrumentation or lab analysis. Again, in order for uranium inside the body to cause cancer, the levels of uranium have to be so large that they are easily detected by laboratory analysis and almost certainly will cause severe kidney damage before any sign of cancer is detected.
The more radioactive an element is, the more likely it is to cause cancer. Your chance of getting cancer from uranium is greater if you are exposed to enriched uranium. Enrichment is the process by which the amount of uranium isotopes U-234 and U-235 are increased in naturally occurring uranium (U-238). No cancer of any type has been linked with human exposure to natural (non-enriched) uranium.
Studies have reported lung cancer and other cancers in uranium miners, but some of the miners also smoked and were exposed to other substances that are known to cause cancer, such as radon and silica dust.
Can uranium cause reproductive or developmental problems?
We do not know whether exposure to uranium causes problems with the reproductive system or with the development of the human fetus.
What were the results of uranium testing in urine in Churchill County?
The median urine concentration of uranium for the people tested in Churchill County was 0.02 μg/L compared with 0.006 μg/L for people reported in the Second National Exposure Report.
The U.S. Nuclear Regulatory Commission’s action level to protect people exposed to uranium at work is a urine uranium level of 15 μg/L.
In one study of people who drank well water with high natural uranium concentrations, the median urinary concentration was 78 μg/L without effects on their kidney function.
We are not aware of any studies that reported health problems in people with urine levels of uranium in the range found in people in Churchill County.
