247
T. M. BEASLEY, E. E, HELD and R. M. CONARD
approximately 1/100th of the maximum
permissible body burden which has been established for non-occupationally exposed individuals considering the total body as thecritical
organ.4%) Previous measurements of ®5Fe body
burdens during a period of increasing **Fe
fallout generally showed that 5°Fe body burdens
of females were higher than those of males.@:5)
Presumably this is due to higher turnover rates
of iron in females than in males, with the result
that females are more nearlyat equilibrium with
their environment. As environmental levels of
55Fe decrease, females should, on the average,
reflect this change by exhibiting lower Fe
body burdens than those of males. Figure |
shows that more female body burdens tended
toward values <0.4 wCi, while male body
burdens were more normally distributed, about
a mean of 0.43 uCi. Regression analysis of age
on body burdens showed a significant correlation (P < 0.001); older individuals had
higher *5Fe body burdens. Table 2 shows a
tabulation of the average ®°Fe body of males
and females by age groups. The number of
samples per age group is admittedly small yet
the general increase of **Fe body burden with
age appears qualitatively consistent with earlier
data obtained by analyzing blood from Seattle,
Washington males in 1966.
Comparison of the 55Fe body burdens of
peoples of different countries) requires knowl-
edge of the turnoverrates of 9°Fe in the environ-
ment and in humans. Jennincs’?) has shown
that the 55Fe specific activities of salmon taken
Table 2. Average body burden of *°Fe in Rongelapese
residents of different ages
Males
Females
Number of
Body burden
Age
samples
(ui)
16-20
8
0.31
21-31
32-42
43-53
54-64
> 64
16-20
21-31
32-4?
43-53
54-64
> 64
4
5
2
6
3
6
12
5
7
2
2
0.33
0.52
0.58
0.53
0.48
0.23
0.34
0.33
0.66
0.57
0.66
from the northeast Pacific Ocean decreased
eightfold between 1S64-1£67. Assuming that a
first order reaction governed the removal of
*5Fe from the mixed layer of the ocean (upper
100 m) he calculated the effective half-life for
55e loss as 11 months. Measurements in cattle
and rain waters show decreases, but at lesser
rates. Tron-55 body burdens of adult males
in Richland, Washington, decreased approximately 4 fold between 1067 and 1970,
corresponding to an effective **Fe half-life of
1.5 yr. If the ®*Fe turnover rates of Richland,
Washington, residents are similar to those of
insular populations, we conclude that people
from maritime cultures would exhibit similar
and perhaps faster turnover rates of Fe
because of the short “‘ecological half-life’? of
this radionuclide in the marine environment.
The highest **Fe body burdens previously
measured were in female natives at Bethel,
Alaska, during 1966.)
The average body
burden of 18 females was 1.1 wCi. During the
same year, the average 5°Fe body burden of
females and males at Tokai-mura, Japan was
0.92 wCi and 0.63 wCi respectively.’
We
determined the ®°*Fe body burdens of 32 females and 37 males from Tokai-mura from
blood collected in October 1970; the average
values were 0.12 and 0.17 respectively. Thus,
not only do the Rongelapese havesignificantly
higher 55Fe body burdens than those of the
Tokai-mura residents, but the decrease in the
55Fe body burdens of this latter group from
1966 to 1970 appears comparable to that for
Richland, Washington, males.
As previously stated, all of the donors of the
Rongelap study were subjected to external
radiation during the accidental contamination of
Rongelap Atoll in 1954. Because of the high
levels of radioactivity at the Atoll, the Rongelap
natives were moved to Majuro Atoll where they
resided for 3.5 yr. Following exposure in 1954,
whole body counting and urinalysis disclosed
measurable quantities of internally deposited
fallout radionuclides. By 1957, however, the
only radionuclides present in the Rongelapese in
significantly measurable quantities were °°Zn,
137Cs and %Sr.49) No 5°Fe analyses were per-
formed at that time so body burdens of this
radionuclide are not known.
However, based