STRONTIUM-90 IN MILE
N
HA
no milk
* from
A
rt per
- These data show that there has been an increase in the Sr-90 eontent of milk
in different parts of the world. The 1956 values (Table 2) for Japan appear
low when compared to the previous values in the table, but this is probably due
to the fact that only a few samples were analyzed in 1956. The amount of Sr-90
in dried milk for Mandan, North Dakota, is high in comparison with other areas
of the United States and is apparently due to the deficient levels of calcium in
the soil of that region. As a result, the deposited Sr-90 is absorbed moreefficiently
by plants.
‘
There are few data available on the Sr-30 content of fresh milk, though a
study has been carried out in the Chicago area (197). Samples of fresh milk
were obtained monthly from several large Chicago dairies from March, 1955,
to March of 1956. The milk samples were analyzed for Sr-90 and the results are
presented (Figure 2). The curve in Figure 2 shows a maximum from June to
fF
resent
of late 1957 are also tabulated in Table 2 (11).
AWA
‘e subample,
which
w-level
d may
Sr-90 in milk obtained from Japan and the United Kingdom (primarily England). The results of these analyses until December, 1956, are presented
(Table 2) and are expressed in Sunshine Units (19e). The most recent summary
of the average Sr-90 content of dried milk from various parts of the world as
n
ts.
1 to 4 yr. These analyses were made on dried milk samples that were obtained
at local plants. In January of 1955, intermittent analyses were carried out for
SUNSHINE UNITS
of the
‘eneral
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MARCH
JUNE
SEPTEMBER DECEMBER
MARCH
1955
—————————. YEAR ———_ 1956
Fig. 2. Monthly fluctuations in Sr-90 content of fresh milk in Chicago (19j).
August in 1955, followed by a minimum and then a gradualrise to about 3 8.U.
at the end of 1956. This is in agreement with the Columbus, Wisconsin, value of
3.48.U. at the end of 1956. The peak in the curve may be attributed to the fact
that there was a heavyseries of tests at Nevada that spring and when the cows
were pastured on unplowedfields they received an increased level of Sr-90 from
surface contamination of the plants. The level of 1-2 8.U. in March and April
of 1955 was apparently due to the fact that the cows were eating stored feed
which had been grown the previous summer.
[7 }
10