664
clearly indicates the need for further data on
human beings.’“If leukemia does result
from pelvimetry, it may indicate that the
fetus is extremely sensitive or that in reality
there is no threshold.”?* However, no differences in the incidence of leukemia have been
found among a numberof metropolitan areas
of the United States with different cosmic
defects in man, the total of gross physical
and mental defects from all atomic weapons
tests through 1961 and all future generations
has been estimated’®® 1° as 1,000 (range
200 to 5,000) from fallout and 2,000 (range
400 to 10,000) from carbon-14. The total
number of such defects due to all causes
garding the possibility that the irradiated
be between 4,000,000 and 6,000,000. The
number of additional cases occurring in the
radiation backgrounds.’ The question re-
sample may not be representative of the
whole childhood population needs to be more
precisely answered.**
Chromosomal aberrations in peripheral
leukocytes have been reported following di-
agnostic x-irradiation doses of 4 to 12 r.75
That similar changes may occur at lower
doses is suggested by a report of the development of chromosome abnormalities after 825
mr (0.8 rad) total body exposure.”* None
were noted after 20 to 80 mrradiation.”
Current available data on human subjects
do not permit any definitive assessment of
the development of other somatic effects
from exposure to low-level irradiation. In
reference to life shortening, extrapolation
from animal to human has been attempted
but the clinical observations are inconclusive.
#7, 87, 102 Clinically significant cataract formation probably has not occurred below 600
rads, although it is generally believed that
the minimal effective dose is lower in children.*’ Studies of growth and development
in children have not been reported other
than those carried out on populations exposed to whole-body doses of 69 r or more.
58-61
Hereditary effect. There exists no body of
direct observation of human population
which permits the precise quantitative determination of the genetic effect of low-level
radiation.®* 1° The potential genetic con-
sequences of exposure to radiation have
been estimated indirectly in such terms as
“Jethal-equivalents,’’** total estimated numbers of gross physical or mental defects in
future
generations,*°1° and “gonadal
doses” or “doubling doses” of radiation TT, 103, 107
Based on radiation-induced mutation rates
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in man and on the spontaneous incidence of
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October 1965
Sutow and Conard
(hereditary and nonhereditary) in children
of persons now living has been estimated to
next generation has been estimated to be 100
{range 20 to 500) due to fallout and 10 (2
to 50) to carbon-14. The risk to the individual of the next generation (of genetic
effects manifested by gross mental or physical defect) has been calculated as 1/1,000,-
000.195
The UNSCEARrepert concludes that for
acute radiation the representative doubling
dose for gene mutation for man “is somewhat lower than 30 rad but not less than 15
rad. For chronic irradiation, the most probable value is 100 rad or possibly higher.’”*™
FALLOUT RADIATION
The voluminous data on the levels and
hazards of environmental contamination
with radioactive materials (primarily from
nuclear weaponstests) have been effectively
summarized, on an international basis, by
UNSCEAR."® 5? The published records of
hearings before the Subcommittee on Research, Development, and Radiation and be-
fore the Special Subcommittee on Radiation, both of the Joint Committee on Atomic
Energy, Congress of the United States, constitute an authoritative source for basic information on almost all aspects of fallout
radiation.1°*1° The rate and distribution
of deposition of radioactive fallout from
the testing of weapons depend on the amount
of debris, altitude and geographic location
of the explosion, meteorological conditions,
and other factors,1® 57 *% 108: 119 Radiologically important nuclides which account
for most of the external irradiation from fallout include the gamma-emitters zirconium-
95 (half-life, 9 weeks), niobium-95 (halflife, 5 weeks), and cesium-137 (half-life, 30
years). The chief internal exposure hazards