CAS ID #: 7440-61-1
Affected Organ Systems: Renal (Urinary System or Kidneys)
Cancer Effects: None
Chemical Classification: Inorganic substances, Radionuclides (radioactive materials)
Uranium is a common naturally occurring and radioactive substance. It is a normal part of rocks, soil, air, and water, and it occurs in nature in the form of minerals – but never as a metal. Uranium metal is silver-colored with a gray surface and is nearly as strong as steel. Natural uranium is a mixture of three types or isotopes called U-234/234U, U-235/235U and U-238/238U. All three are the same chemical, but they have different radioactive properties.
Typical concentrations in soil are a few parts per million ppm. Some rocks contain high enough mineral concentrations of uranium to be mined. The rocks are taken to a chemical plant where the uranium is taken out and made into uranium chemicals or metal. The remaining sand is called mill tailings. Tailings are rich in the chemicals and radioactive materials that were not removed, such as radium and thorium.
One of the radioactive properties of uranium is half-life, or the time it takes for half of the isotope to give off its radiation and change into another substance. The half-lives are very long around 200,000 years for 234U, 700 million years for 235U, and 5 billion years for 238U. This is why uranium still exists in nature and has not all decayed away.
The isotope 235U is useful as a fuel in powerplants and weapons. To make fuel, natural uranium is separated into two portions. The fuel portion has more 235U than normal and is called enriched uranium. The leftover portion with less 235U than normal is called depleted uranium, or DU. Natural, depleted, and enriched uranium are chemically identical. Du is the least radioactive and enriched uranium the most.
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The Oak Ridge Reservation is a US Department of Energy (DOE) facility that was established in Oak Ridge, Tennessee in 1942 as part of the Manhattan Project, the federal government's World War II effort to build the atomic bomb. There are three major installations at the Oak Ridge site: the Y- 12 weapons plant; the X-10 complex, now known as the Oak Ridge National Laboratory; and the gaseous diffusion plant, K-25, now known as the East Tennessee Technology Park.
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The MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse, non-cancer health effects over a specified duration of exposure. The information in this MRL serves as a screening tool to help public health professionals decide where to look more closely to evaluate possible risk of adverse health effects from human exposure.
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- Page last reviewed: March 3, 2011
- Page last updated: March 3, 2011
- Content source: Agency for Toxic Substances and Disease Registry