Uranium A naturally occurring radioactive element with atomic number 92 (number of protons). It was named after the planet Uranus. Its principal natural isotopes are uranium-235 (0.72% of natural uranium), which is fissile in nuclear reactors, uranium-238 (99.3% of natural uranium) and uranium-234 (0.0056% of natural uranium), which is a daughter product of the radioactive decay of uranium-238. All uranium isotopes are radioactive. Natural uranium is mostly in the form of isotope U-238, which has a half-life of 4.5 billion years. It is a toxic heavy metal of silver gray color that is more dense than lead. As it loses atomic particles, it decays and ends up, after millions of years, as lead. It can be used to date very old rock layers. Uranium comprises 0.0004% of the earth's crust. It is the basic fuel of a nuclear reactor and used to make nuclear energy in nuclear power plants. It is mined in many countries.

The atoms in any radioactive material are constantly disintegrating and emitting particles and electromagnetic waves that can cause damage to whatever they hit. Radiation is harmful because it can 'ionise' living matter, making permanent changes in its atomic structure. Cancer, damage to developing cells in the fetus and growing children, and mutations of chromosomes are among the chronic effects of exposure to ionising radiation. When uranium decays in the environment transform to radioactive mineral radium, which via oral exposure, is known to cause lung, bone, brain, and nasal passage tumors in humans, and radon, via inhalation exposure, causes lung cancer in humans. Uranium may cause lung cancer and tumors of the lymphatic and hematopoietic tissues.

A high amount of Uranium is found in drinking water of Bangladesh. This has been assigned a provisional guideline value of 2 B5g L '1 (For uranium: 1 B5g = 0.72 pCi.) by WHO. Concentrations in excess of this were found in the worst arsenic affected areas of Bangladesh. Uranium gets into water from rocks in aquifers and from tailings of uranium mines and mills. Aeration of water to promote the release of radon is very effective and one of the more affordable water treatment technologies available. [Sanzida Murshed]