FOOD-CHAIN KINETICS OF RADIONUCLIDES
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tissues or organs) following environmental contamination by a single
fallout event. The results of hypothetical calculations were compared
with the Radiation Protection Guides recommended by the Federal Ra-
diation-C ouncil.
INTRODUCTION
To explain the kinetics of radionuclide transfers in a given food
chain, it is first necessary to describe the routes and rates of transfer
affecting specific food-chain compartments. The major route and some
of the minor routes of radionuclide transfer and exchange in a terrestrial ecosystem are shown in Fig. 1.
Some of the fallout particles initially deposited on soil surfaces
may be redeposited by wind or rain on plants,! but most of them are
mechanically trapped and not susceptible to redeposition.’ Material
deposited on soil may enter food chains by stem-base absorption,’ by
downward leaching in the soil profile and subsequent root uptake,*® or
by accidental ingestion, especially by burrowing animals.® Mostof the
fallout deposited directly on soil can be regarded as unavailable for
rapid entry into major food chains.
Some of the radioactivity contained in the fallout particles, mostly
<44 » in diameter,’ retained on foliage may be assimilated by foliar
absorption,®’*® but a much larger fraction is subject to fairly rapid removal by wind or
rain.'?!! While it remains on plant surfaces, this
material may be ingested by herbivores.
jo EP cee
_—— a ee ee ee
ATMOSPHERE
a
{
I
|
PLANTS
| Ho
ANIMALS
A
v
SOIL
(Yeo
Ll —- >
MAJOR
MINOR
x
DECAY ORGANISMS
INPUT OUTPUT
> C— >
———> —— =>
Fig. 1—Major and minor routes of radionuclide transfer and exchange
in a terrestrial ecosystem contaminated by radioactive fallout.