Contamination from Local Fallout
The ‘“‘Strontium-Calcium Observed Ratio” 1OR) of Comar et al (1956)
was used to denote the preferential utilzation of calcium in the following
manner.
Sr. Ca of sample
OR yampie-preeursor = eenepe
Sr Ca of precursor
The Sr®discrimmation ratio in the chain from soil (5s) to bone {bj via
plants (p) can be expressed as follows:
ORvonenoit = (OR) (OR) = (0.7) (0.25) = G18
Vhe value OR,,,, == 0.25 is an approximate valuc obtained expenmentally on
rats fed a stock laboratory dict (Comar et al, 1956). This discnrmination factor
of 4 tor calcium against strontium from dict to bone m man has becn reported
by Schulert ct al (1959a) and Brvant ct al 6395S). A more appropnate value
tor the rats in this situation might be the ORwuneaer = U-10 ubtamcd by a
stud, of wild Kangaroo rats lining in the Nevada desert ‘Alexander et al. 19561.
The bods burden iw the.
,
srt Cay, = Sr Cay OR, OR, |. |
= (54% 108)(0.7) 10.16; = 974 pye Sr¥"/g Ca
Thevaluc thus obtained 1 anproximatch twice the value of 47 to S43 auc
srg of caloum obtamed by direct radiochemical analysis of the tissues of
rats living on the iskind dumng the 2-+car penod following ds tonation, This
difference in the indirect environmental estimate of the bods burden of ds:Ca
as compared with the direct analysis may reficct either errors in the discrmination ratios or a lack of equilibrium between the Sr"/Ca in the animals with
the soil at 2 vears. Since 13 rats of the same average age analyzed at 4 vcars had
values close to those of rats collected at 2 vears, at 443 = 18] puc Srg of
calcium (Held. 1955), it must be assumed that the discrimination ratios are
not suffcientl, accurate for this estimahon.
It 1s obvious that applving the samc technique of estimating the Sr” body
burdens of the Marshallese people is also difhcult because of the uncertainty of
their dict and the discontinuous nature of their habitation on Rongclap Island.
Dunning (1957) has estimated the future Sr’ body burdens in the Marshallese from the Sr®/Ca in an “average” food supply which was about 360 ppc
Sr"/g of calcium in 1956. This figure would be reduced to a daily intake of
about 100 pyc Sr°?/g of calcium if consumption of land crabs which have a
high Sr*° content were eliminated.
These estimates of average dictary intake are very approximate since the dict
is not well known. A more extensive study made in 1958 viclded Sr® ‘Calevels
of 67.5 ype Sr°/g of calcium somewhat lower than those of Dunning’s in
1956 (table 6). This study was bascd on an analysis of the avcrage diets of
14 males on Rongelap (Held, 1958) and a radiochemical study carried out by
Harley (1959). It was assumed that half of the daily calcium (0.8 g) was from
32]