Basis
for protection standard for uranium
Uranium,
a terrestrial radionuclide, is naturally present in the environment – in soil,
rocks, in sea water, ground water, in food in the human body itself. The mass
concentration of uranium varies from place to place depending on the
environmental conditions. Natural uranium consists of three isotopes of
uranium-238U, 235U and 234U with different
half-lives. The longest-lived 238U has a half-life of 4.5 billion
years. Typically, the soil concentration is about 3 parts per million (ppm).
In
addition to its radioactive nature, it is, as water soluble uranium compounds, is
chemically toxic. Uranium gets deposited in the kidneys due to its
physicochemical properties. The US EPA (2001) and WHO (2011) standard for
uranium in drinking water is 30 micrograms per liter which is equivalent to
0.75 Bq/liter. The threshold limit value (TLV) (ACGIH, 1994) in air in work
environment for insoluble uranium is 0.2 mg/m3.
The
protection standards for uranium (soluble) is limited by the chemical toxicity,
while for insoluble compounds, the protection standards are based on
radiological considerations.
