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

Thorium-232, U-235, U-238, Ra-226, and Rn-222 are naturally occurring
alpha particle emitters.() Risley ) in 1962 found that 97 percent of the
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gross alpha analyses of Lake Michigan water contained less than 3x10-9 uCi/ml.
Eisenbud,(5) in a summary of Ra-226 in public water supplies in the United
States, reported that Chicago public drinking water, which is drawn from Lake
Michigan, contained 2.4x10l uCi/ml of Ra-226 in 1953. In 1958, Lucas(13)
found that the same water supply contained 3x10 uCi/ml of Ra-226. Holtzman reported that the Pb-210 content of Lake Michigan was 3x101 uCi/ml.
Data for uranium and Rn-222 in Lake Michigan are not known to us. Radon-222
activity in surface waters is highly variable and often unreported. The
uranium content of fresh waters generally vary up to 10 parts per billion
(10-8 g/ml), or 3x10-9 uCi/ml.(6)
The principal reactions which produce tritium are high energy (E > 100 Mev)
proton spallation reactions, and the N-14 (n,t) C-12 and 0-16 (n,t) N-14 reac(14)
tions with secondary neutrons. 4) The natural concentration of tritium before large scale weapon testing in 1952, was 6 to 20x10 uCi/ml.(15) In 1953
Kaufman(16) reported that the H-3 concentration in Lake Michigan was 1.7 H-3
atoms per 1018 hydrogen atoms. Smith(15 gives 3.3x109 as the conversion factor from H-3 atoms per 1018 H atoms to uCi/ml, so the tritium concentration in
Lake Michigan in 1953 was 56.x10 uCi/ml.
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The natural C-14 content of carbon is reported to be 7.4 ~ 2.7x106 uCi
per gram of carbon.) Natural C-14 in Lake Michigan therefore depends on the
inorganic and organic content of the water. The concentration of inorganic
- 2- (44)
carbon (as CO2, H2C9, NC03, CO ) is 24 mg/l, this is equivalent to an
2' m -10
inorganic C-14 concentration of 1.6x10 uCi/ml. The average concentrations
of suspended and dissolved organics in Lake Michigan are 1.1 mg/l and 4.9 mg/l,
respectively.(42) If it is assumed that 50% of the organic matter is carbon,(43)
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then the organic C-14 concentration is 0.2x10 uCi/ml.
In summary, the natural radionuclides and their concentrations in the
water of Lake Michigan are C-14 (0.2x109 uCi/ml), K-40 (l.lxl0-9 uCi/ml),
Ra-226 (.03x10-9 uCi/ml), Pb-210 (.003x109l uCi/ml), H-3 (5.6x10-9 uCi/ml), and
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gross alpha activity (less than 3x10-9 uCi/ml).
Fallout from Nuclear Detonations
In this section gross beta, Sr-90, Cs-137 and H-3 activity in Lake
Michigan from fallout of nuclear detonations will be reviewed.(1722) Table A-1

A-5