-25-
The probability that the non-fission radioisotopes would
be present in particulate form in the sea was discussed
=
earlier.
Particles of non-fission-product material either
adsorbed onto or assimilated into the phytoplankton or exi
if
isting as free perticulate matter in the water would be avail-
able to the invertebrate filter feeders.
Thus the second
concentration stage for non-fission radioisotopes would occur
in the zooplankton through the filter feeders.
Of course
factors such as (a) average life spans of the phytoplankton
and zooplankton organisms (b) average biological half lives
of the different radioactive elements within the zooplankton,
and (c) species differences between filter feeders regarding
choice of food,
the assimilation of the different radioele-
ments and retention of the radioelements would influence the
levels of the non-fission radioactive elements
plankton.
in the zoo-
These factors are not known.
There is little probability, however,
that the above
mentioned factors or any other biological effects are re-
sponsible for the variations in ratio between Co57 and C060
found in plankton samples from the different stations.
the heavier elements at least,
For
organisms have little or no
ability to differentiate between 1sotopes of a given element.
Thus, the variation in ratio of Co-! to C960 probably reflects
the variation in level of occurrence of these two isotopes in
the fallout material in different geographical locations.