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January 12, 1963)
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A RECENT evaluation of radiological data gathcred by
the U.S. Atomic Energy Commission's Health and Safety
Laboratory includes a statement that the concentration of
fission products in commercial milk is essentially independent oftotal rainfall':?. However. the precipitation values
were presented as arbitrary ranges and the landscape
units used were not strictly biological regions. The
purpose of this communication is to show that if radiological data from the same source are arranged according
to natural landscape units a relationship between phytoelimatic zones and the ecsxsium-137 content of milk is
indicated.
.
.
.
.
For our purpose, the geographical region considered is
the north-western portion of the United States where broad
areas are mappedas distinctive natural vegetation zones’.
Such broad areas are necessary to allow reasonable
assurances that milk sample stations actually derive milk
from an area representative of a particular vegetation zone.
Ten of eleven milk sampling stations in the north-west
region were grouped into one of three natural vegetation
zones (Table 1).
Portland, Oregon and Burlington.
Washington. were assigned to the Pacific north-west
coniferous forest zone. Bismarck, Bottineau, and Cando,
North Dakota;
and Mitchell, South Dakota, were
assigned to the grassland zone.
Sunnyside, Washington:
Payeite and Idaho Falls, Idaho; and Monroe, Utah, were
assigned to the sage-brush zone. Because of its proximity
to the Wasatch Mountains, which provided a diversity of
a
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407948
Relation to Phytoclimatic Zones
wae?
,
(Reprinted from Nature, Vol. 197, No. 4863, pp. 197-198.
Czsium-!37 in Dried Milk Products in
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vegetation zones within a small area. the milk sampling
station of Ogden, Utah, was excluded.
Cexsium-137 is deposited on aerially exposed plant parts
directly from the atmosphere and the amounts ingested
and assimilated by grazing animals are dominantly from
this source rather than from plant uptake via contaminated
soils‘. Total precipitation is regarded as important in
depositing cesium-137 over landscapes and the amounts
deposited are related to the amountof precipitation ; moist
regions receive more cesium-137 than regions of less
moisture®.
The cesium-137 content of milk samples in pe./g potassium from stations grouped according to vegetation zones
is presented in Table 1. Milk products from sampling
stations in the coniferous zone averaged 90 pc./g potassium
as compared with only 54 and 37 for grassland and sagebrush zones. Total precipitation from weather stations
fe