Uranium – 238
Uranium is alpha and weak gamma emitter with very long half-life: 4.5 billion years. All uranium isotopes are radioactive. It has a long series of decay products, raising health concerns. It is extremely dense and heavy metal. Uranium occurs naturally in the +2, +3, +4, +5 and +6 valence states, but it is most commonly found in the hexavalent form. Naturally occurring uranium (natU) is a mixture of three radionuclides (234U, 235U and 238U), all of which decay by both alpha and gamma emissions.
Natural uranium consists almost entirely of the 238U isotope, with the 235U and 234U isotopes respectively comprising about 0.72% and 0.0054%. Uranium is widespread in nature, occurring in granites and various other mineral deposits.
Uranium is used mainly as fuel in nuclear power stations, although some uranium compounds are also used as catalysts and staining pigments.
Uranium is present in the environment as a result of leaching from natural deposits, release in mill tailings, emissions from the nuclear industry, the combustion of coal and other fuels and the use of phosphate fertilizers that contain uranium.
Uranium is chemically as well as radioactively toxic. Greatest health risk is from toxic damage to kidneys. It can accumulate in bones. In humans, the body excretes more than 99%. If inhaled, can cause lung cancer. EPA maximum level for drinking water is 30 µg/L (micrograms/liter).