34
Polonium [Po, 84]
34.1 INTRODUCTION
Polonium (Po) is a highly radioactive element of group 16 in the periodic table of
elements, chemically similar to Bi and Te, and may follow the biochemical pathway
of Se and Te. Based on its properties and behavior, it is sometimes classified as a
metalloid. Its abundance in the Earth’s crust is estimated to be 1 fg/kg (10 −16 %) or
2 pg/kg (10 −13 %). It may be accumulated in some coals and in phosphate rocks. Its
highest concentrations are in uranium (U-pitchblende) ores, up to about 0.1  μg/kg,
and it has been its source for quite a time. Nowadays, Po is obtained by irradiating Bi,
with high-energy neutrons or protons. There are 25 known Po isotopes, with atomic
masses from 194 to 218, of which 7 isotopes occur naturally. The only one occurring
to any extend is 210 Po, with the half-life of 138.4 days.
Applications of Po are few and include heaters in space probes, antistatic
devices, and sources of neutrons and alpha particles. It is highly dangerous and
has no biological role. The main hazard is its intense radioactivity (as α-radiation
emitter), when it is ingested, inhaled, or absorbed, and it is very difficult to handle
it safely.
Uses of 210 Po include nuclear batteries, neutron sources, and film cleaners. It is
a  lightweight nuclear heat source for thermoelectric power in space satellites.
However, Po needs to be replaced in these devices nearly every year, because of its
short half-life. Due to its dangerous properties, it has been replaced by other sources
of beta particles.
Alexander Litvinenko, a Russian dissident, was probably the first person who
died of the acute α-radiation effects of 210 Po. It has also been suggested that Irène
Joliot-Curie died from leukemia, which resulted from the exposure to 210 Po.
34.2 SOILS
The natural abundance of 210 Po in soils range from 10 to 220 Bq/kg. This is the result
of 222 Rn decay, in the top layer of soils, as well as the fall down of 210 Po suspended
in the air. This radionuclide is strongly, almost irreversibly fixed by soil particles,
mainly by metal hydroxides and/or sulfides. It is also likely to be bound by soluble
organic matter (SOM), and a close correlation between levels of 210 Po and SOM
contents was observed (Korenkov et al. vide Kabata-Pendias 2011). It is not very
mobile in soils. There are suggestions that it may be methylated, similar to Hg,
Se, and Te.
Soils around U ore deposits in India contain 210 Po, on average, 125  Bq/kg
(Marbagniang et  al. vide Kabata-Pendias 2011). Its much higher concentrations
(15,000–22,000 Bq/kg) are in various U mine tailings. Also environments (soils, plants,
and wild animals) of phosphate rock processing are enriched in this radionuclide.
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