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19641 \ARTIN ; RADIOECOLOGY AND STUDY OF ENVIRONMENTAL RADIATION
317
position) and to soil contamination (root absorption). The output expres-
sions would have to aceount for physical decay, loss of particles due to the
mechanical action of wind and rain, loss of contaminated foliage by leaf fail,
andloss of foliage to herbivorous animals. Similar input and output expressions would have to be applied to all the integral parts of the system (e.g.
atmosphere, soil, plants, animals, and decomposers), Even then a deterministic model would be no more than an approximation of its ecosystem analog;
but successively closer approximations could be obtained by the inclusion of
expressions to account for seasonal changes in ecosystem dynamics, for
species differences, and for other significant rate-determining parameters. _
To account for the variability normally encountered in nature and to
facilitate the comparison of radionuclides eycling in similar and dissimilar
ecosystems under different conditions of contamination, deterministic models
might profitably be rewritten in a stochastic (= probabilistic) form and programmed for analysis by analog or digital computers, This approach as taken
by Olson (1961), and perhaps by others unknownto the writer, seems to be
representative of the current frontiers in radioecological research concerning
the occurrence, redistribution, and cycling of radionuclides in the biosphere.
Evaluation of potential biological hazards related to fallout. The scientific literature in which various estimates of the biological cost of radioactive fallout have been presented is quite formidable both in size and diversity. It is not within the scope of this paper to review the literature dealing with the problem of fallout hazards to man, but it does seem appropriate
to conclude with a few general remarks concerning the nature of the problem
and the kinds of evidence which are available to those who are attempting
to solve it.
Plants, animals and people have always been exposed to ionizing radiation in their natural environments. Because of variations in the distribution
of cosmic radiation and the radionuclides which oceur naturally in the atmosphere, lithosphere, and hydrosphere, organisms in certain habitats, especlally at higher elevations, have normally been exposed to radiation doses
at least 3 times as high as the average for the biosphere. The average worldwide inereases in background radiation as a result of fallout has been eonsiderably less than this normal variation {Larson et al. 1962). The mereased
exposure of organisms to radiation from fission products may also be rather
small in relation to natural sourees of internal radiation. Milk, for example,
which contained 3 to 12 ppe/l of Sr-90 in 1961 also contained 800 to 1400
py e/1 of K-40. (Consumers Union 1962).
‘‘The net result of fallout,’’ according to Langham and Anderson (1958),
‘‘has been a small inerease in the radiation background to which life is exposed. The problem of evaluating the potential hazard of world-wide fallout
then beeomes one of trying to ascertain the magnitude and significance of