16
The source of 60K for the tuna must be Bikini Atoll
and not worldwide fallout because we analyzed tissues
from 214 tuna,
including 75 yellowfin tuna,
taken from
the Japanese tuna fishery during 1968 and 1969, and found
no 6006
(NVO-269-7,
Annual Report).
In contrast,
the
ne concentrations in the dark muscle of the tuna from
the Japanese fishery ranged from 3.3 to 1600 pCi/g dry,
most of the values fell in the range of 101 to 500
pci/g dry.
It appears, therefore, that a major amount
of the one in the Bikini tuna is from worldwide fallout.
One of the principal sources of radionuclides at
Bikini is Bravo Crater in the reef adjacent to and
southwest of Nam I.
Figure 1 shows a gamma-ray spectrum
of sediment taken from a depth of 160 feet.
Clearly,
6000 and 20735 predominate among the gamma emitters.
In most soils,
13745 is the most abundant radionuclide.
an intermediate condition exists at the southwestern
end of Eneman I.,
where a low area is occasionally
overwashed by seawater,
and at the high tide line, where
the 137a6 is being leached from the soil.
The retention of 6060 and 207 54 by the sediments
is reflected in the fact that the bottom-feeding goat-
fish in the vicinity of the craters contain ten times
more 6006 than the herbivorous convict surgeonfish
and plankton feeding mullet.
However,
some 6060 is
being transported eastward by the bottom current in
the lagoon either in solution or associated with fine
(colloidal?)
particles,
because the difference in 6006 con-
tent between convict surgeonfish and mullet in the
vicinity of Bravo Crater and 16 miles eastward near
Bikini I.
is only by
a
factor
less
than
two.
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