....
Table L Summary of cytogcnctic
ExPosure
group
(rads)
175
70
cells
scored
Subjccts
(No.)
(No,)
30
13
1500
650
43
2150
findinbs
in Marshall
Isltmders exposed to fallout radiation. Pcrcenmges appcw in parcnihcses.
Chromosome aberrations
Cells
wit h
Sub-
46
2n +
(%)
jects
as%eled
10
8
Frag-
Dicen-
ments
tncs
12
11
11(0.73)
10(1.53)
23
21 (0.93)
6(0.4)
2(0.3)
Totals for
8
“
400
9
5.5
who were exposed to fallout radiation
(9).
.
These people were accidentally exposed to radioactive fallout on Rongelap Island in 1954: the wind shifted
unpredictably after the detonation of a
high-y ield’nuclear device at Bikini, 160
km away; 64 inhabitants were exposed
to 175 rads ( estimate~ whole-body) of
gamma rays. Eighteen other Rongelap
Islanders, away fishing on a neighboring island, were exposed to 70 rads
(estimated). Exposure resulted in temporary
depression of blood cells, skin
bums from beta radiation, and internal
absorption of radionuclides,
the most
important being iodine and strontium.
It was estimated that the thyroid glands
of the adults received 150 rads—those
of the children, as much as 1,000 rads
—from absorbed radioiodine in addition to the whole-body exposure to
gamma rays. Recent development
of
pathological changes in the thyroid is
believed to have resulted from thts ex.
posure (10).
Chromosome preparations were obtained from 5 i individuals during the
annual medical review of the Marshall
kl~nders in 1964; 30 of them had been
exposed to 175 rads; 13, to 70 rads
of gamma rays. Eight Marshall Islrmders who had escaped exposure were in.
eluded for comparison. , The exposed
group comprised 20 males and 23 females, their ages ranging from embryo
irt u~ero to 67 years at the time of exposure. Twenty-one were under 20 and
22 over, with males and females about
equal in number. The comparison group
included three males and five females
ranging in age from 10 to 71 years;
Unfortunately
it was impossible to examine
more
unexposed
individuals
matched to the exposed with respect to
age and sex.
Cultures of peripheral blood lymphocytes were made by use of a modification of the meti’od of Moorhead et
al. (11 ); they were harvested at 48 and
446
5
TotaIs for
,9(2.25)
exposed
8(0.37)
unexposed
Rings
1(0.15)
Chroma-
TotN
chromoTransio-
cations
Total
tid
aberra-
some
tions
(No.)
breaks
5(0.33)
8(1.23)
22(1.46)
21(3.23)
33(2.2)
32(4.9)
58(3.8)
35(s.3)
13(0.61)
43(2.0)
65(3.02)
93(4.3 )
9(:.25)
11(2.7)
subjects
1(0.04)
subiects
72 hours (12). The slides were stained
with aceto-orcein
and examined
by
phase microscopy. Because comparison
of “the 48- and 72-hour cultures from
showed no differences
five individuals
in aberration rates, all examinations but
one were made on 50 cells of each individual from the 72-hour cultures. Al.
together 2150 cells were examined from
the 43 exposed subjects; 400 cells from
the eight unexposed.
Aberrations were scored as follows
(i) aneuploidy, including polyploid cells,
(ii) chromosome
aberrations, and (iii)’
chromatid aberrations. Karyotypes were
made in cases” where the counts were
equivocal or where chromosomes
of
questionable
morphology
were seen.
Only aberrations that were agreed on
by several observers were included in
the final tabulation. Additional karyotypes were made from eight euploid
cells, showing ‘no gross abnormalities,
from each of four subjects showing
more aberrations than most others; this
was done in an effort to detect minor
structural abnormalities such as small
deletions or inversions that could easily
escape notice under the microscope.
l%al]y, bone-marrow preparations were
made from two exposed subjects and
one control; only one preparation from
an exposed subject contained enough
suitable cells in metaphase
to warrant evacuation.
Proportionally the largest number of
aberration-positive
persons appeared in
the low-exposure group (Table 1); we
cannot explain this paradox and so
treat all the exposed subjects as one
group in comparing them with theltnexposed (Table 1).
Chromosome-type
aberrations
were
found in 23 of the 43 exposed peopie
and in five of the eight unexposed. The
high incidence of acentric fragments in
the latter group was unusual and unexpected, and we cannot account for it.
The total numbers of all types of chromosome aberrations in the two groups
9(2.25)
were 43 and 9—rates of 2.0 and T
percent, respectively. Thus superfic~
there appears to be no difference
tween the two groups, but we sh
point out that in the exposed gJ
half of alI chromosome aberrations
sisted of two-break aberrations SUC,
dicentric chromosomes,
translocat:
and a ring, the remainder being ace:
fragments. In contrast, no two-b
aberrations
were found in the L,
posed group in which all aberr:t
were acentric fragments. Only sevc
the exposed people resembled the
trois in showing single-break a/tions onl~ all others showed two-’
aberrations either alone or in coc,
tion with fragments. The clifferenc
tween the exposed
and unex,
groups in the relative incidence oi
break aberrations
and acentric
ments was significant at the 1-pi
level (P< .01).
Aberrations ranged from one t.,
per person. Sixteen of the 23 esl
and two of the five unexposed pc
had multiple aberrations. - In m~
stances no more than one aber~ ‘
was noted per cell. Aneuploidy
higher in the exposed than in the ~
posed group, but the difference
not significant; in most cells, arteu;
was due to loss of chromosomes
number of chromatid and isochrm
gaps and breaks, although som
higher in the exposed group, was
in normal limits. Polyploid ccli
ctsrred with equaI frequency in th
groups. No aberrations were fou
the karyotypes
that had been
from the 32 grossly intact cells
the four subjects showing relative[?
rates of aberration. Likewise, n.
normalities were seen in 50 cells
the bone marrow of one of the es.
subjects.
We pointed out earlier that th
portion of aberration-positive
p
in the low-exposure group wa~
that among the highly exposed. \\
SCIENCE, V{