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Preface
Uranium (U) is the heaviest naturally occurring actinide, existing almost entirely as
the primordial isotope
238
U (99.27%, half-life of 4.5 billion years), as
235
U in minor
quantities (0.72%), and as
234
U in trace quantities (0.0055%). With an average concentration of 0.0003% (3 mgkg
–1
) in the Earth’s crust, uranium is present in all
soils; in rocks such as volcanic rocks, granites, dark shales, sedimentary rocks that
contain phosphate, and metamorphic rocks; and in seawater (3.3 ppb of U by weight
(3.3 μgkg
–1
)). Uranium concentration in the Earth’s crust may range from 1 to
4 mgkg
–1
in sedimentary rocks to tens or even hundreds of mg/kg in phosphate-rich
deposits or in U ore deposits. In surface soils and sediments and in aqueous systems,
U reacts with oxygen to form predominantly the hexavalent uranyl ion (UO 2
2+
)
which is highly stable and soluble, which determines its mobility, bioavailability,
uptake, and toxicity. Contamination of the biosphere by extensive release of uranium (or its progenies) poses serious threats to living organisms, due to chemical
and radiological toxicity. Anthropogenic U contamination by mining and milling
operations contributes to the degradation of the environment. Even before its formal
discovery by the German chemist, Martin Klaproth, in 1789, U has been used for a
wide variety of purposes for coloring glass and ceramics. Its actual use is dominated
by the nuclear power industry, but also for military purposes.
Uranium has no essential biological function in the organisms, but a wide range
of both terrestrial and aquatic organisms uptake U from the environment. For example, plants, bacteria, algae, and fungi were shown to accumulate U, and it has been
reported that the biological action of bacteria, algae, fungi, and plants can affect U
speciation and thus U bioavailability by adjusting the pH, extracellular binding, and
transformation and formation of complexes or precipitates. These organisms can
thus contribute in decreasing or increasing U entry into the food chain but could also
be used to develop bioremediation tools to decontaminate uranium-polluted surroundings. In fresh water, numerous physico-/biochemical variables may affect U
speciation, bioavailability, uptake, and toxicity, which include pH, hardness, natural
organic matter, and microbial activity. In the case of soil, migration and mobility of
radionuclide always depend on various factors including pH, texture, exchangeable
Preface
Uranium (U) is the heaviest naturally occurring actinide, existing almost entirely as
the primordial isotope
238
U (99.27%, half-life of 4.5 billion years), as
235
U in minor
quantities (0.72%), and as
234
U in trace quantities (0.0055%). With an average concentration of 0.0003% (3 mgkg
–1
) in the Earth’s crust, uranium is present in all
soils; in rocks such as volcanic rocks, granites, dark shales, sedimentary rocks that
contain phosphate, and metamorphic rocks; and in seawater (3.3 ppb of U by weight
(3.3 μgkg
–1
)). Uranium concentration in the Earth’s crust may range from 1 to
4 mgkg
–1
in sedimentary rocks to tens or even hundreds of mg/kg in phosphate-rich
deposits or in U ore deposits. In surface soils and sediments and in aqueous systems,
U reacts with oxygen to form predominantly the hexavalent uranyl ion (UO 2
2+
)
which is highly stable and soluble, which determines its mobility, bioavailability,
uptake, and toxicity. Contamination of the biosphere by extensive release of uranium (or its progenies) poses serious threats to living organisms, due to chemical
and radiological toxicity. Anthropogenic U contamination by mining and milling
operations contributes to the degradation of the environment. Even before its formal
discovery by the German chemist, Martin Klaproth, in 1789, U has been used for a
wide variety of purposes for coloring glass and ceramics. Its actual use is dominated
by the nuclear power industry, but also for military purposes.
Uranium has no essential biological function in the organisms, but a wide range
of both terrestrial and aquatic organisms uptake U from the environment. For example, plants, bacteria, algae, and fungi were shown to accumulate U, and it has been
reported that the biological action of bacteria, algae, fungi, and plants can affect U
speciation and thus U bioavailability by adjusting the pH, extracellular binding, and
transformation and formation of complexes or precipitates. These organisms can
thus contribute in decreasing or increasing U entry into the food chain but could also
be used to develop bioremediation tools to decontaminate uranium-polluted surroundings. In fresh water, numerous physico-/biochemical variables may affect U
speciation, bioavailability, uptake, and toxicity, which include pH, hardness, natural
organic matter, and microbial activity. In the case of soil, migration and mobility of
radionuclide always depend on various factors including pH, texture, exchangeable