Actinides
383
In rainwaters collected during 1999 in Sweden, the mean Th content was
0.0023 μg/L and its wet deposition was 0.08 g/ha/yr (Eriksson 2001a). Atmospheric
Th deposition in city regions of the United Kingdom is estimated to be <0.5–1 g/ha/yr
(Cawse 1987).
58.2.4 AIR
The concentration of Th in air over Antarctica is within the range of 0.02–0.08 pg/m 3 ,
whereas in air over cities of various continents its amounts vary from 1,000 to
13,000 pg/m 3 (Reimann and de Caritat 1998).
Mosses, collected during the last century, from Spitsbergen, Norway, contain
Th up to 1.14 mg/kg, and its fairly similar maximum content was in mosses from
Norway, up to 1.8 mg/kg (Steinnes et al. vide de Caritat et al. 2001).
58.2.5 PLANTS
Phytoavailability of Th from soils is variable and controlled by various factors; however, it is often accumulated in roots (Shtangeeva 2010). Thorium uptake by netted
chain fern (Woodwardia areolata) from contaminated soils was very high (329 mg/kg),
compared with plant grown in greenhouse soil (6.4 mg/kg). This plant is proposed
for the phytoremediation of Th-contaminated soils (Knox et al. 2008). Red maple
(Acer rubrum) grown in background soil contains Th at 0.03  mg/kg, whereas in
plants from contaminated soil its content is 2.6 mg/kg (Hinton et al. 2005). The addition of Th to the germination medium increased its contents from <0.02 to 0.17 mg/kg,
and from <0.02 to 2.4 mg/kg, in leaves and roots of wheat, respectively. Elevated Th
contents in wheat seedling resulted in the decrease of Ca in leaves, as well as in the
uptake of other nutrients (Shtangeeva et al. vide Kabata-Pendias 2011).
Mobile Th species in soils are easily available to plants. Its contents in pumpkin
seed oil vary, depending on its geographic origin (median value, in mg/kg): 0.04 in
Austria, 0.04 in Russia, and 0.34 in China (Bandoniene et al. 2013). Thorium amount
in sweet gum (Liquidambar styraciflua L.) from uncontaminated soil is 0.04 mg/kg,
whereas it is 5.3 mg/kg from polluted soil.
Among various native plants grown in the polluted area of the Northern Europe
(Kola Peninsula), crowberry (Empetrum nigrum) contains Th <0.02 mg/kg and moss
(Hylocomium splendens) about 0.05 mg/kg (Reimann et al. 2001).
58.2.6 HUMANS
The total Th content in the human body is 40 μg (Emsley 2011). Thorium can be
taken into the body by food, drinking water, and inhalation of Th-contaminated
dust. However, its amounts in air are so small that the uptake through air can usually
be ignored (ATSDR 1990b).
Most Th that is inhaled or ingested is excreted within a few days, with only a
small fraction being absorbed into the bloodstream, about 0.02%–0.05% of the
ingested amount. Gastrointestinal absorption from food or water is the principal
source of internally deposited Th in humans. Of the amount entering the blood,