TRANSURANIC SPECIATION IN THE ENVIRONMENT
E. A. Bondietti and F. H. Sweeton
Oak Ridge National Laboratory
ABSTRACT
The speciation of transuranium elements in the environment was discussed with
particular emphasis on Pu. The thermodynamic approach to evaluating Pu speciation was reviewed and examples presented to exemplify the complexities of Pu
chemistry in aqueous solutions. An example of the actual evaluation of Pu
oxidation states {n natural water was presented. The results, which indicated
that Pu(IIL) and/or Pu(IV) dominated the soluble Pu fraction, were compared to
a simple model involving the hydrolytic species of Pu(IV).
Literature data
were also evaluated with respect to the Pu({IV) model.
In all cases, the
soluble concentrations of Pu in natural waters were in reasonable agreement
with the model. Dissolution studies with Pu0, were reviewed and data presented
to demonstrate that oxidized Pu (Pu(V) and/or Pu(VI)) species may be responsible
for the relatively high Pu concentrations reported. The mechanism of oxidation
appeared to be related to radiolytic effects. The plant uptake of transuranium
elements was discussed and the influence of actinide oxidation state illustrated,
Plutonium in one soil-plant uptake experiment resembled Th more than U in
plant availability.
INTRODUCTION
The environmental behavior of the transuranium elements is complex because of
both source term differences and chemical differences between each element.
An understanding of the characteristic chemical states of the actinides is
important in evaluating their present behavior and in projecting their biogeochemistries.
The oxidation state chemistry of the transuranium elements is unique in that
the elements, when present in a given oxidation state, behave alike chemically,
The individual oxidation states, however, display different chemistries.
In
effect, it is oxidation state, rather than the element per se which governs
chemical behavior. While this seems obvious, it is often overlooked when
isotopes, usually with different specific activities, are compared.
Thus
differences which are noted in the behavior of isotopes may often actually be
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