What Is Uranium?

The EPA says uranium is present naturally in virtually all soil, rock and water, and that as rocks break down into soil that is moved by water and wind, uranium is carried into streams, lakes and surface water. ATSDR says natural uranium is a naturally occurring chemical substance that is mildly radioactive, that everyone is exposed to low amounts of uranium through food, water and air, and that exposure to high levels of natural or depleted uranium can cause kidney disease.

Federal drinking water regulations at 40 CFR 141.66 set the maximum contaminant level for uranium at 30 micrograms per liter. A 2021 USGS study done in cooperation with the Connecticut Department of Public Health projects that 4.7% of private wells in Connecticut have uranium concentrations higher than EPA standards, and that approximately 3.9% have arsenic above the EPA maximum contaminant level for public drinking water supplies.

Mining left a lasting legacy in some places. The EPA says that from 1944 to 1986, nearly 30 million tons of uranium ore were extracted from Navajo lands under leases with the Navajo Nation, that many Navajo people worked the mines, often living near the mines and mills, and that a legacy of uranium contamination remains, including over 500 abandoned uranium mines as well as homes and water sources with elevated levels of radiation.

The Nuclear Regulatory Commission defines depleted uranium as uranium with a lower percentage of uranium-235 than the 0.7 percent by mass contained in natural uranium, and says it is the byproduct of the uranium enrichment process. ATSDR describes depleted uranium as an adjusted mixture of natural uranium isotopes that is less radioactive. The NRC says that commercially, uranium-235 is enriched to 3 to 5 percent, from its natural level of 0.7 percent, and then further processed to create nuclear fuel.