![]() There are three basic categories of uranium isotope mixtures (based on the mass percentage of 235U relative to that of the earth’s crust): natural uranium, enriched uranium, and depleted uranium. The radionuclides in these transformation series (such as isotopes of radium and radon), emit alpha or beta particles, as well as gamma and x-rays, with energies and intensities that are unique to the individual radionuclide. The process continues through a series of radionuclides until reaching a stable, non-radioactive isotope of lead (or bismuth in the case of 233U). When an atom of any of these five isotopes decays, it emits an alpha particle (the nucleus of a helium atom) and transforms into a radioactive isotope of another element. The most toxicologically important of the 22 currently recognized uranium isotopes are anthropogenic uranium-232 ( 232U) and uranium-233 ( 233U) and naturally occurring uranium-234 ( 234U), uranium-235 ( 235U), and uranium-238 ( 238U). It exists in a number of isotopic forms ( NNDC 2011), all of which are radioactive. ![]() Uranium is naturally occurring or has been produced in nuclear reactors and in high energy physics experiments. The process continues until a stable (nonradioactive) state is reached (see Appendix D for more information). This transformation or decay results in the formation of different elements, some of which may themselves be radioactive, in which case they will also decay. Radioactive elements are those that undergo spontaneous transformation (decay), in which energy is released (emitted) either in the form of particles, such as alpha or beta particles, or electromagnetic radiation with energies sufficient to cause ionization, such as gamma rays or x-rays. Uranium is a naturally occurring radioactive element and a member of the actinide series. ![]() Also, whenever the term “ radiation” is used, it applies to ionizing radiation and not to non-ionizing radiation.Īlthough natural and depleted uranium are primarily chemical hazards, the next several paragraphs describe the radiological nature of the toxicologically-important uranium isotopes, because individual isotopes are addressed in some of the health effects studies. This profile is primarily concerned with the effects of exposure to natural and depleted uranium, but does include limited discussion regarding enriched uranium, which is considered to be more of a radiological than a chemical hazard. The health effects associated with oral or dermal exposure to natural and depleted uranium appear to be primarily chemical in nature and not radiological, while those from inhalation exposure may also include a slight radiological component, especially if the exposure involves prolonged exposure to insoluble uranium compounds. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.Ī glossary and list of acronyms, abbreviations, and symbols can be found at the end of this profile. The primary purpose of this chapter is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of uranium.
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