13
low amounts when present in marine plants or on the land.
None
of the radioactive transition elements or only low levels are
present in island soil, in plants growing in the soil, or in the
herbivorous
field rats.
However,
in the plankton,
invertebrate filter feeders and omnivores,
the marine
and in the fishes,
the
transition elements may contribute up to 100 per cent of the total
radioactivity.
Other observations on the biological uptake of radioisotopes
are as
follows:
Of the long-lived fission product isotopes--Sr°”,
cst3? and
cel44__onty ce 144 enters into the biological cycle in the marine
environment to a significant extent.
Cc s
1
37 are taken up but ce l44 is not,
However,
on land,
Sr
90
and
to any great extent.
Of the gamma-emitting isotopes present in ten tissues of
reef and lagoon fish the radioisotopic composition did not vary
greatly from tissue to tissue except that radiocobalt was not
found in the bone.
in fish.
Practically no fission products were found
The transition elements ranked in order of abundance
are radioiron,
zinc,
cobalt and manganese.
Oceanic fish differ
from reef and lagoon fish in that radiozinc ranks first in abundance in the former.
In comparison with fish, plankton have greater amounts of
radiocobalt and lesser amounts of radioiron.