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Trace Elements in Abiotic and Biotic Environments
It is likely to accumulate in acidic igneous rocks, 10–23  mg/kg, and may also be
concentrated, up to 10–22 mg/kg, in some argillaceous sedimentary rocks. It occurs
in several minerals, of which the most common are thorite (ThSiO 4 ), thioranite,
(ThO 2 + UO 2 ), and monazite [(Sm,Gd,Ce,Y,Th)PO 4 ].
Data on Th production are limited, and according to Reimann and Caritat (1998),
it was 0.7 Mt in 1984. Its economically available reserves in the world are estimated to
be 1913 Mt of ThO 2 , of which 1000 Mt is present in Canada, 963 Mt in India, 440 Mt
in the United States, and 300 Mt in Australia (Cotton 1991).
Thorium is used in several electronic equipments, mainly as a component of various electrodes. It is also applied in special optic and scientific instrumentations. It is
used in aircraft equipment, nuclear reactors, nuclear weapons, and rockets to impart
high strength and resistance to elevated temperature. It is commonly used as a fuel
in nuclear power stations. It produces a radioactive 220 Rn. Thorium (as well as U) is
the only radioactive element with major commercial applications.
58.2.2 SOILS
Thorium contents of soils in the EU countries are estimated within the range of
0.2–53.2  mg/kg, and in the United States, 6.1–7.6  mg/kg (Haneklaus and Schung
vide Kabata-Pendias 2011). Elevated Th amounts are in soils around AC ore bodies
(e.g. 76–96 mg/kg in Brazil). The background Th content of soils from the wetland
in South Carolina (USA) is given as 1.3 mg/kg, whereas in contaminated sites its
content is 166 mg/kg (Hinton et al. 2005). Various Th mean contents of soils are
reported for several countries: the lowest is for Poland, 3.4 mg/kg, and the highest
for Russia, 13.4 mg/kg (Kabata-Pendias 2011).
The hydroxides of Th 4+ are dominant species in soils and are responsible for its
mobility over a broad range of pH. Especially some organic acids may increase its solubility. Its mobility may be limited due to the formation of slightly soluble compounds
(carbonates, phosphates, oxides) as well as adsorption by clays, some minerals, and
soluble organic matter (OM). The increased use of apatite, as a soil amendment,
results in the enhanced desorption of Th in soils and sediments. Nevertheless, Th
predominates in a residual fraction of both apatite and soil amended with apatite
(Kaplan and Knox 2004).
The range of Th concentration in groundwaters is 0.08–2.0 μg/L, and it is higher
in soils of areas of hot and dry climates (Kabata-Pendias and Mukherjee 2007).
58.2.3 WATERS
The worldwide average Th concentration in river water is estimated to be 0.041 μg/L,
within the range of 0.0005–1.054 μg/L (Gaillardet et al. 2003). Waters of the Baltic
Sea contain Th from 0.0005 to 0.0077  μg/L (Szefer 2002). Some bacteria strains
(Streptomyces levoris) may adsorb relatively high amounts of Th from water, at pH
3.5 (Tsuruta 2004). The levels of Th in seaweeds range from 0.02 to 0.62  mg/kg
(Szefer and Ostrowski 1980).
The median Th concentration in bottled waters of the EU countries is 0.00062 μg/L
and is slightly lower than in tap water, estimated to be 0.00077 μg/L (Birke et al. 2010).