B. L., LARSON AND K. E. EBNER
Comparison of Sr-90 levels in milk with other foods. There has been approximately a fourfold increase in the average world Sr-90 content of milk from 1954
to the level of 5-6 S.U. in 1958. Unfortunately, the present data on the Sr-90
content of other foods are limited, but they are yradually being collected through
the efforts of Project Sunshine and other agencies such as the U. 8. Public Health
Service. Fish have an extremely low Sr-90 level because of the low concentration
of Sr-90 in the oceans, caused by dilution. Meat and eggs (not ineluding the
shells) contain little calcium and thus little Sr-90. Vegetables contain Sr-90
and an average value in Sunshine Units for various market frozen vegetables
in 1956 was about twice that found in milk (8,77). Data on cereals also are
meager, but apparently their levels of Sr-90 in Sunshine Units average about
two and one-half times that of milk. In general, the level of Sr-90 in vegetables
and cereals consumed by humans would be expected to be lower than the levels
found in the same materials consumed by animals. Humanfoods are generally
processed and surface contamination is largely removed. Furthermore, vegetables
and, to some extent, cereals for human consumption are usually grown on wellfertilized, carefully cultivated soils; whereas, animals generally consume forage
grown on less carefully maintained soils.
The 1957 level of about 5 8.U. of Sr-90 in milk suggests that the average
level of Sr-90 in the ration of the dairy cow was about 40-50 8.U., because of
the apparent discrimination factor of 7-11 (194). The average cow producing
market milk in the United States receives supplements of rock calcium phosphates containing a lowlevel of Sr-90 and/or animal bone meal containing about
5-10 §8.U. Since this is discriminated against by a factor of 7-10 in passing to
the milk, it is apparent that the present level of Sr-90 contributed by the suceulent plants, grain, cereals, etc., consumed by the cow must be quite high. Data
on this point are limited and show wide variations. Levels of Sr-90 found in
cereals, vegetables, other plant sources, and water are shown tin Table 3. The
TABLE 3
Sr-90 content of various human and animal plant sources
Sr-90 Level
Source
Vegetables (frozen)
Vegetables (frozen)
Wheat
Oatmeal
Reference
( &)
(11)
(11)
(11)
Year
Location
1956
1957
1956
1956
U.S.
US,
UB.
€?)
Rice
(17)
1956
Bean plant (parts)
(19f)
1956-7
Riee
Flour
Bran
(11)
(11)
(11)
Japan
1956
1956
1957
(?)
U.S. CTL.)
U.S. (Mich.)
U.S. (Md.)
U.S. (I1.)
England.
England
Pea plant (parts)
Alfalfa
Grass (normal soil)
Grass (acid soil)
(19f)
(197)
(19d)
(19b)
1956-7
1955
1956
1956
Drinking water
(11)
1956-7
Hay
(19e)
1955
U.S. (Md.)
England
U.S. (N.Y.)
Range
Average
— (Sunshine units )—
1-21
7
1-29
9
9-38
23
6
81-250
4-81
150
©
19-39
3-38
23-85
113-2,180
6-53
4
6
9
45
30
18
40.
370
30
0.1°
* About 0.1 uuc. of Sr-90 per liter. Based on consumption with 1 g. of Ca in diet per day.
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