PLUTONIUM-237:
AN IMPORTANT RESEARCH TOOL FOR STUDIES OF
ENVIRONMENTAL PLUTONIUM KINETICS
John R. Trabalka and L. Dean Eyman
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee
ABSTRACT
The oroduction and use of the ohoton-emitting isotone olutonium-237 in
investigations of the untake, retention, and distribution of monomeric
olutonium (IV) both in an aquatic vertebrate, the channel catfish
Ietalurus punetatus, and in a littoral aquatic micro-ecosvstem, are
presented. The rationale for use of plutonium-237 in environmental
studies is discussed.
Chelation can either enhance or reduce the uptake of ingested plutonium
relative to plutonium hydroxide (monomer) in channel catfish. The
highest observed retention (whole bodv) at 63 days was 3.8% of ingested
dose for olutonium-237 citrate, while retention of the fulvate was 0.6%.
Reduced uptake of the fulvate complex is due either to its high molecular
weight (> 10,000) or to its stability in metabolic svstems. Increased
uotake of plutonium-237 citrate is attributable to instability of the
comolex in metabolic svstems.
Tissue distribution studies revealed that relatively little (< 10%) of
intracardially injected plutonium citrate was excreted. Blood clearance
rates were similar to those found in smal] mammals, with the plutonium
being primarily associated with the plasma protein transferrin.
The
fractional bodv burdens in bone, liver, and kidney 17 days after injection
were 31%, 24%, and 9% of the injection dose, respectively.
High kidney
burdens relativy to mammals are expnected, since the kidney functions as
the major site of homopotesis in teleosts. Absence of significant excretion indicates that a short half-life component of elimination following
qut clearance in gavage studies is due to plutonium labeling of the gut.
A distribution coefficient of 9 x 104 was observed for sediment in a
year-old aquatic microcosm spiked with plutonium-237 nitrate.
A materials
batance at 90 days post-spike provided the following estimates: 0.001%
in water, 0.04% in biota, and over 99.9% in sediments. Concentrations
48S