-23Three of the radioactive non-fission- product elements,
zinc, cobalt, and iron, contributed an average Of 71 per
cent of the total activity in the plankton samples.
observation is
This
in contrast to those on terrestrial samples
in which these isotopes were absent or,
trace amounts only (16).
at most,
present in
Thus, either a concentrating
Dag prieeutee.ie awk th ae
a
mechanism must function in the sea for the non-fissionproduct elements, making them available to the organisms,
or an exclusion mechanism must operate on land.
The ex-
tremely low levels at which these isotopes occur in dirt
samples near the target area suggest that concentration occurs in the sea.
In the case of these radicelements the previously discussed factors that control uptake by marine organisms,
with
the possible exception of scavenging action by calcium hydroxide or calcite, would tend to cause increased uptake.
Thus,
these elements in fallout probably occur itn the sea in
particulate form, are not subject to chemical competition by
similar elements or to appreciable isotope dilution by their
stable counterparts, nor would co-precipitation occur in the
strict sense of the word.
ménganese,
However,
negatively charged cobalt,
and zinc would tend to precipitate with iron into
eee
Saeed- < waenliplieweass..
a finely divided form, exhibiting only a limited tendency to
Sink below the thermocline and thus remain available to the
Plankton in the mixing layer.
The isotopes Mnd4, Fe29, Co57, Co58, ¢060, and zn©5 are
transition elements and have characteristies of
variable