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involve either adsorption of the particle onto the organism
or ingestion of particulate material.
The latter would
include both food particles and non-living particulate
detritus.
Several other factors,
of specific radioelements.
however, also control the uptake
In the case of strontium and
cesium chemical competition plays a major role.
occurring potassium,
the competitor to cesium,
sea weter at a high level of about 380 ppm.
Naturally
is present in
In comparison
to this level of occurrence, Cs137 would be present in very
small amounts, even in an area of heavy fallout.
Because of
the limited ability of animals to differentiate between po-
tassium and cesium, uptake of the latter would be low.
Natural calcium occurs at a level of about 400 ppm in
sea water and exhibits chemical competition to strontium with
regard to uptake by marine organisms.
elements, however,
occurrence
In the case of these
the uptake is not directly proportional to
in the water;
rather strontium is discriminated
against with reference to and in the presence of naturally occurring calcium by factors of approximately 3 in calcareous
algae and foraminiferans,
2 in arthropods,
2 to 7 in molluscs,
2.5 in bryozoans (25) and 3 to 10 in marine fishes (19).
In laboratory experiments utilizing radioactive strontium
Chipman (2) observed that Artemia larvae reached a steady
state
in the level of radiostrontium about 0.7 that of sea
water and Burroughs, Townsley, and Hiatt (1) reported a value