19
role in radiosensitivity of the optic lens, and defini-
Table 11
Estimated Bodv Burdens of Radioisotopes in Rongelap
Peopie on Day | From Radiochemical Urine Analyses
Isotope
_
Activity, wCi
8°Sr
140Ba
16 - 2.2
0.34- 2.7
141] (in thyroid gland)
5.6 -22.4
13Ru
Ca
Fissile material
0
QO
0
Rare earth group
0
-1.2
- 0.013
- 0.019
- 0.016 (zg)
those in females until the age of 50. The normal
rise in lens flecks with increasing age is similar to
that found in the mouse, in which it ts felt to represent the gradual accumulation of defective lens
fibers descended from abnormal but viable cells
residing in the germinalzoneof the lens epithelium.
The progressive increase in the nonexposed individual suggests that somefraction of these cells
has been abnormal from the timeof lens formation. In distinction to that in the (female) mouse,
the rise of lens flecks in the human appears to have
a rapid phase coinciding with adolescence in the
female, a period of life during which the ratio of
estrogen to androgen maybeelevated.
The second finding of interest is the greater
radiosensitivity (for the production of lens flecks)
in females, particularly those aged 13 to 20 years
at the time of radiation exposure. As noted above,
this is a period of rapid rise in lens flecks in the
normal, and possibly of relatively high estrogen
level. Experimental evidence pertainingto the influence ofestrogen on radiolethality in the mouse?!
suggests the possibility that gonadal hormones may
have been at least partly responsible for the difference in radiosensitivity between the sexes, and
also for the difference in incidence between adolescence and maturity in the female. Such a mecha-
nism might imply varying radiosensitivity in the
female as a function of stage in the menstrual cycle
or pregnancyatthe timeofirradiation. Little information was available as to menstrualstatus at
the timeoffallout exposure. Of three women who
had been pregnant whenthey received 175 rads,
two havefleck counts higher than would be expected
for their age, but the fleck count in the third person was below that expected. These data serve
only to suggest the possibility of a gonadal hormone
tive answers must be sought elsewhere.
Finally, it should be emphasized thatthis survey
has involved the counting of small numbers of
discrete opacities of diameters measurable in mi-
crons. These rare, minute defects, possibly involving only portionsofsingle lens fibers, are extremely
unlikely to be capable of any effect on visual function. The dense subcapsular and diffuse nuclear
changes commonly seen in persons of ages beyond
the sixth decade are far more impressive and functionally important.
THYROID FINDINGS
Estimation of Dose of Radiation
to the Thyroid Glands
The calculations of dose to the thyroid from the
absorption of radionuclides in the fallout un-
fortunately could be madeonly from radiochemical urine analyses obtained several weeks after the
accident. These calculations are summarizedbriefly
here (see BNL 50029?! for details). In addition to
131] the isotopes 133], 135], and to a lesser extent
1327 in the fallout contributed significantly to the
thyroid dose. The only direct data available on the
Rongelap people are radiochemical analyses of
pooled urine samples taken 15 days or longerafter
the fallout. At 15 days the urinestill contained
small amounts of 131]. The doseto the thyroid from
131] on thefirst day of the fallout was estimated to
be 11.2 wCi (5.6 to 22.4 wCi) assuming that 0.1%
(0.05 to 0.2%) of the maximum thyroid burden
{not corrected for physical decay) was excreted in
the urine on the 15th day. Table 11 shows estimated body burdensof various isotopes on day I.
The dose of 160 rads to the adult thyroid was
calculated from oral intake and inhalation of the
combined various iodine isotopes, considering their
fission yield, the average energy deposited in the
thyroid per disintegration, and the time of absorption. The dose to the thyroid glands of children 2
to 4 years of age was then calculated by means of
these factors with consideration of pulmonary
function andthethyroid size of the child of that
age. The main source of iodine ingestion was considered to be water, andsince it was being rationed
at the timeoffallout it was assumedthatthe children drank the same amountas adults and therefore had the same thyroid burden of radioiodines.
The small size of the children’s thyroid resulted in
a substantially larger dose. The total estimated