in whole animals including fish were
5 urprisingly unff.
factorof 10, 1.2-9.9% of mean
sediment concentration) Theat
°
ated to gut loading of sediments
and/or surface contamination. The
Quite
uptake sett.
by rooted
«0.03
macrop
tonna
h ge not exposed to surfac
e contamination was
Sorpt
ion of plutonium to plant surf.
aces, on gut walls, and o
of Pu behaviow nate in Submerged
components of aquatic systems. Recv
iten
potential for teressenscusse
used
d | in terms of ecological signi
i
ficance
C and
INTRODUCTION
There are three important reasons why we have used the plutonium-237
isotope so extensively in our laboratory work involving aquatic organisms.
Firstly, plutonium-237 is predominantly a photon emitter-190 Kev-complex
x-rays accompany 45% of all decays while a-emisstons occur in only 3 out
of every 100,000 transitions (Lederer et al,,1967).
Thus, one is able
to do repeat counting of individually-tagged organisms in an uptake
experiment. Since destructive analytical techniques are not required,
one can follow uptake and elimination patterns in some organisms over
the entire lifetime. Even where destructive sampling is required (as in
tissue distribution studies, for example), analytical procedures are
both simple and inexpensive. One is also able to reduce the sample size
required for a given end point since individual variability as a function
of time is determined in uptake and elimination work.
Secondly, plutonium-237 has a high specific activity - approximately
1 x 10" Ci/g in our product.
Thus, uC concentrations of plutonium-237
contain the same concentrations of plutonium atoms as pCi levels of
plutonium-239,
Therefore, we are able to work with reasonably high
activity levels of plutonium-237 to reduce radioanalvtical error and at
the same time maintain plutonium atom concentrations which closely mimic
a "real-world" situation. This is an important requirement in terms of
the environmental chemistry of the element.
Thirdly, plutonium-237 has a relatively short physical half-life of 45.6
days; and, as noted previously, negligible a-activity.
Thus, the investi-
gator can avoid the enormous costs associated with use of double-containment facilities required for reasonable quantities of plutonium-239 or
plutonium-238, (ne has essentially the same freedom in experimental
design as if the radionuclides were Zn-65, or Cs-137, or Ce-144, for
example.
PRODUCTION AND CHARACTERISTICS
Plutonium-237 is produced by helium ion bombardment of 735U.
Trace
quantities of plutonium-236 provided the only significant contamination
of the material we received.
Table 1 illustrates the physical charac-
teristics of plutonium-237 for comparison with a-emitting isotopes
(Eyman et al,,1976). The characteristics for plutonium-246 are included
since it represents an alternative photon emitter for use in plutonium
research, Its disadvantages are its very short physical half-life and
low specific activity (as a consequence of contamination with its parent
isotope, ?""Pu}. Although we did undertake some early work involving
plutonium-246, we would not recommend it for future aquatic environmental
studies because its specific activity fs unrealistically low.
490
491