STOCHASTIC SIMULATION OF RADIONUCLIDE UPTAKE
801
distribution of the substance in the tissues of animals consuming these
diets.
INTRODUCTION
An important aspect of the general problem of radioactive fallout
is the time-specific relation between fallout radionuclides on vegetation and the amounts of such material assimilated by herbivores and
ultimately consumed by man. One should be able to represent such
relations by mathematical models so that, if the amount of a radionuclide in one compartment of a food chain is measured, inferences
may be drawn as to how muchis or will be present in other compartments,
Such models should take into consideration the considerable vari-
ability that occurs in natural systems, as evidenced by the British
work! in Australia in 1956 and investigations at the Laboratory of
Nuclear Medicine and Radiation Biology, University of California at
Los Angeles,’»*? during the test series of 1953 and 1955. Consumers
occupying apparently homogeneous environments and presumably exposed to similar diets show tissue burdens of radionuclides which
differ greatly. From the standpoint of health physics, it is important
to understand this variability because the high extremes are more
important than modal values. This problem has been discussed pre-
viously by Libby‘ with regard to worldwide fallout of “Sr, by Eisenbud
et al.> with reference to fallout "I in New York City, and, more generally, by Neuman® and Ellett and Brownell.’ The point has also been
recognized by the Federal Radiation Council,’ which has recommended
the arbitrary assumption that the majority of individuals in a popula-
tion does not vary from' the average by a factor greater than 3.
Although several radionuclides need to be considered in food-chain
transfers, recently there has been particular interest in environmental
problems involving "I (e.g., Pendleton,’ Reiss,!° Knapp,'! Martin,”
Turner,'*
and
the
summary
analysis
of the 1962 Congressional
Hearings"*).
In a consideration of the quantitative relations between '°!I in fall-
out and in human foods, it is possible to seek some simple empirical
relation, e.g., the ratio of ‘I per liter of milk to the gross gamma
activity on the ground.
This approach has been adopted by Knapp,'!
who indicates that, for a number of past events involving the release
of '4t to the environment, the ratio of the maximum amountof 1°41,
Inax in milk (pc/liter) to the gross gamma activity (mr/hr) on the
ground at H+ 24, rp, varied from about 18,000 to 220,000. Such an
approach certainly avoids any difficulties in attempting to evaluate
intermediate steps in this relation and may have merit in emergency
situations where no other estimates of potential hazards are available.