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BULLETIN OF THE TORREY BOTANICAL CLUB
{Von 91
this increase in the background dose with regard to its potential effect on
man’s health and well-being.’’
The most pessimistic estimates of the potential effects of fallout on human
populations have been based on the statistical probability that small increases in exposure to radiation may result in a shortening of the average
life-span or in the increased incidence of detrimental gene mutations, leukemia, and bone tumors. Even a small increase in the incidence of detrimental genetic or somatic effects, may involve a large numberof individuals. In
the present world population, an overall increase of one leukemia case per
million people would involve approximately (1 x 10-*) x (3 x 10*) = 3000 people; but, for obvious reasons, increases of this magnitude are extremelydiffi-
cult to detect.
Most of our knowledge of the specific biological effects of ionizing radiation have been derived from experiments in which animals (or plants) were
exposed to relatively high levels of irradiation. Most of the detrimental effects of radiation are known to occur spontaneously, and the experimenter
must rely on statistical tests to measure differences between the spontaneous
and the experimentally induced incidence of such effects. In order to obtain
statistically valid results at low levels of radiation exposure, it would be
necessary to use very large numbers of organisms. In practice it is usually
expedient to use higher levels of radiation exposure and smaller numbers of
organisms.
Most of our knowledge of the effects of ionizing radiation on people has
been derived from clinical studies in which groups of individuals who had
been exposed, occupationally, to higher than average doses of radiation were
compared to similar groups of people who had not been exposed to higher
than average doses of radiation. It has been demonstrated statistically, for
example, that. radiologists have a shorter average life-span than other physicians (Advisory Committee on Biology and Medicine 1958).
Our direct evidence of the biological effeets of fallout on human populations is meager and has been derived from studies made after accidents such
as the Windseale incident in Great Britain (Chamberlain 1958), the Lucky
Dragon incident and the contamination of the Rondelapp Islands in 1954
(Cohn et al. 1960). During the several test series at the Nevada Test Site,
there have been a few reports of superficial radiation burns on cattle, but
there have been no observations of detrimental radiation effects on native
plants (Special Subcommittee on Radiation 85th Congress 1957) or animals
(Libby 1956a).
Because of the paucity of direct evidence, most attempts to evaluate the
potential hazards of fallout to man have been based on extrapolations from
experimental and clinical evidence. In most cases this involves extrapolation
from animals to man or from highto low levels of exposure to radiation or
both.
According to the Advisory Committee on Biology and Medicine (1958),