Lake Michigan environmental survey : final report / [edited] by John C. Ayers.

phytoplankton but not in zooplankton samples. In 7 samples of fish analyzed
for their radioactivity content, cesium-137 and zinc-65 were detected at approximately the same concentration, 3x10O uCi/g wet weight. This indicates
that the food chain reconcentration of zinc-65, of which there is so very
little in the lake, is much larger than the reconcentration of cesium-137.
The present concentrations of zinc-65 and cesium-137 in water are far below
their respective public maximum permissible concentrations in water.
In 1975 the amounts of natural radionuclides in water and sediment
should be the same as those found at the present time. Similarly the radioactivity in Lake Michigan from fallout will be approximately the same in 1975
as it is now, so long as there are no further atmospheric detonations. There
will be additional fallout into the lake but this activity will be offset by
radioactive decay of that activity presently there. By the end of 1975, nine
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power reactors will have generated approximately 1.8x10 MWe-hr electric power
on the shore of Lake Michigan. If the rates of release of radioactivity to
the hydrosphere from these nine reactors are similar to those reported at the
two newest and largest pressurized water reactors, Connecticut Yankee and San
Onofre, then an additional 300 curie gross beta-gamma activity and 180,000
curie tritium will be distributed throughout Lake Michigan. These projected
releases of radioactivity will increase the radioactivity concentration of
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Lake Michigan by 0.06x10 9 uCi/ml gross beta-gamma activity above an ambient
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concentration of approximately 3x10O uCi/ml. The tritium from the reactors
will add 4x10O uCi/ml, to the present of 20x10 uCi/ml.
In conclusion, man-made radioactivity in Lake Michigan at present is
predominantly tritium, strontium-90, yttrium-90, and cesium-137. The tritium
and most of the strontium-90 and yttrium-90 are in the water environment. We
estimate that two-thirds or more of the cesium-137 is in the sediment. Zinc-65
can be detected in a few samples of fish, water, and other biological organisms,
but it is at levels which are several orders of magnitude less than the values
which might be harmful to man.

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