betes AN a
248
atte et ts
IRON-55 IN RONGELAP PEOPLE, FISH AND SOILS
Table 3. Iron-55 content in goatfish (Mulloidichthys, sp.) and soil samplesfrom Rongelap Atoll, Number of
Jish livers contributing to single, pooled sample analyzed are in parentheses; stable Fe and ™¥Fe are expressed
per kilogram af wet tissue or per kilogram dry soil
Content
Location
Sample
Collection
date
55Fe
(uCi)*
Stable
Fe
{g)
BoE.
Fe
(#Ci)
g
Biological samples
Kabelle islet
September 1959
4.04
Liver (71)
August 1963
2.49
Liver (7)
Liver (10)
September 1961
March 1963
0.68
1.40
0.98
0.76
LAS
0.37
4.1
0.9
1.2
6.7
Soils
Kabelle islet
Kabelle islet
Rongelapislet
Rongelapislet
Soil
Soil
Soil
Soil
(0-2.5 cm)
(0-2.5 cm)
(0-2.5 em)
(0-2.5 em)
August
August
March
August
1959
1963
1959
1963
0.24
0.06
0.05
0.006
* Sample counting times were arranged to determine **Fe in biological samples to +5% at
the 95% confidence level (2c); soilsamples to +5-20°%at the 67% confidencelevel (1¢). Stable
Fe determination, +10% at the 67% confidencelevel (10). Activities are correctedto collection
date.
on the levels of Zn, 4’Cs and 9Sr observed,
55Fe body burdens were probably small."The
Rongelapese returned to the atoll in mid-July
1957. Whole body counting and urinalysis
measurements one yearlater disclosed increased
body burdens of severa)] radionuclides, the most
notable being ’Cs. It is probable that Fe
body burdens increased similarly.
The concentrationsof 55Fe in a selected species
of fish and in the calcareous soils are listed in
Table 3. Activity in the fish is based on wet
weights for comparison with previous work.
The amount of sample that was available for
analysis was small and therefore it was necessary
to combine individual samples. This prevents
an estimate of the range of 55Fe concentrations
which occur between fish, ie. the within
sample variation. The number in parenthesis
in Table 2 for the biological samples indicates
the numberof fishes which contributed to the
pooled, single sample analyzed. The 55Fe
values for soil samples collected in 1963 at both
Kabelle Islet and Rongelap Islet are averages of
samples collected at depth increments of 0-1.3
and 1.3-2.5cm. Specific activities are not
given for soils since varying amounts of pre-1954
plant detritus could significantly alter the stable
iron content but not the 55Fe activity. In this
instance, activity per unit weight of soil is a
better index of changes which occuras a result
of inputor loss than is specific activity.
The decrease in 55Fe specific activities in
Mulloidichthys, sp. (goatfish) at Rongelap between 1959-1961 corresponds to an ecological
half-life of 11 months, identical to that ob-
served by Jenninecs.24 Higherspecific activities
may have occurred at earlier times; however,
estimates based only on exponential loss would
not take into account possible retention and
cycling of 55Fe within the lagoon, or the time
lag between deposition and maximum specific
activity in the aquatic biota.
The increase in specific activity of goatfish
liver between late 1961 and mid 1963 reflects
the increased environmental concentrations of
55Fe resulting from testing nuclear devices in
1961-1962. Introduction of this radionuclide
to Rongelap Atoll can occur both by atmospheric
fallout and by water transport of radioactivity
from oceanic regimes. The westward-moving
North Equatorial Current is comprised of waters
from northern latitudes where fallout from the
oe ee
Kabelleislet
Rongelapislet
Liver (20)
tet mem
Rongelapislet