How does thorium get into the environment?
Natural thorium is present in very small quantities in virtually all rock, soil, water, plants and animals. Where
high concentrations occur in rock, thorium may be mined and refined, producing waste products such as mill tailings. If
not properly controlled, wind and water can introduce the tailings into the wider environment.
Commercial and federal facilities that have processed thorium may also have released thorium to the air, water, or soil. Man-made thorium
isotopes are rare, and almost never enter the environment.
How does thorium change in the environment?
As thorium-232 undergoes radioactive decay, it emits an alpha particle, with accompanying gamma radiation, and
forms radium-228. This process of releasing radiation and forming a new radionuclide continues until stable lead-208
is formed. The half-life of thorium-232 is about 14 billion years.
Two other isotopes of thorium, which can be
significant in the environment, are thorium-230 and thorium-228. Both decay by alpha emission, with accompanying
gamma radiation, in 75,400 years and 1.9 years, respectively.