35
Radium [Ra, 88]
35.1 INTRODUCTION
Radium (Ra) is an almost pure white alkaline metal of group 2 in the periodic table
of elements, but may be oxidized readily and become black. It is the heaviest of all
the alkaline earth metals. It exists mainly as a divalent radioactive cation, composed
of several isotopes, which are highly radioactive. They are common products of the
U and Th decay chain. The most stable and relatively frequent radionuclide in the
biosphere is 226 Ra, which has a half-life of 1601 years and decays into radon gas. Its
chemical properties are similar to those of Ba, Sr, and Ca. It is a lithophilic element
and is associated with minerals of zeolite group. Its typical mineral is radiobarite,
(Ba,Ra)SO 4 .
The average content of 226 Ra in the Earth’s crust is 0.9 ng/kg (range 0.1–1.1 ng/kg)
and may be concentrated in coal. It forms several compounds, such as RaOH + ,
RaCl + , RaCO 3 , and RaSO 4 . It is a natural component of the environment, but is
mainly of the anthropogenic origin. Its main sources are U mining and processing,
P and K fertilizers, radioactive and luminizing wastes, coal combustion, and cement
factories. The mean concentration of 226 Ra in coal is on the order of 1 pCi/g, and in
soils surrounding coal-fired power plants, its level may be up to 8 pCi/g (ATSDR
2002b). Also residues from oil and gas industries often contain Ra and its daughters.
Water from oil well, when discharged into the sea and mixed with seawater, may
affect the precipitation of Ra and its accumulation in bottom sediments.
Radium is not necessary for living organisms, and its adverse health effects are
likely, when it is incorporated into biochemical processes, because of its radioactivity and chemical reactivity. It was formerly used in self-luminous paints for watches,
nuclear panels, aircraft switches, clocks, and instrument dials. It has also been used
in silk, leather, and wood industries for stains and dyes.
Radium (usually in the compound RaCl + ) is used to produce radon gas, which has
been used for cancer treatment. Currently 223 Ra is still under investigation for use in
the treatment of bone cancer.
35.2 SOILS
Radiation of Ra in soils range broadly from 4.4 to about 150 Bq/kg in Canada and
Turkey, respectively. Increased 226 Ra levels are in soils around some mining and
industrial plants, especially of U and P processing. Also some P fertilizers may contain its higher levels at about 75 Bq/kg. The estimated annual deposition of 226 Ra and
228 Ra in agricultural soils is 4.5 and 0.5 Bq/m 2 , respectively.
Radium sorption in soils highly varies and the lowest is in sandy soils (Smith and
Amonette vide Kabata-Pendias 2011). The influence of soil biota on its mobility is
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