weg TEED STS
90
RADIATION STANDARDS, INCLUDING FALLOUT
soil may becomeless available to plants by a few percent per yearbecause of runoff, redistribution by wind, removal in crops, and possibly
fixation in thesoil.
.
Representative Price. Dr. Comar, Mr. Ramey has a question.
Mr. Ramey. Is there any—in that formula that you gave there—
change in that. formula or the basis of it since 1959 when we had our
last calculations?
Dr. Comar. The basic form isthe same. There is more evidence now
for the numerical values of the constants. These have been determined
in three ways.
One, by looking at the situation recently where the fallout rate has
fallen to zero so that the total amount in the milk will be entirely dependent upon the cumulative factor.
Another, by doing regression analysis over past years.
And,finally, another method by using field experiments to determinethese factors. So that the values are becoming narrowerin their
range and morereliable.
Representative Price. Dr. Comar, in this connection, doall the figures in your statement on different points of research and so forth
reflect updating since 1958?
Dr. Comar. Yes; they do, wherever possible. These have been supported in the bibliography.
Representative Price. Your bibliography will indicate to us
whether or not these are different figures than we previously considered at other hearings?
Dr. Comar. Yes. Either they are the latest. figures that I have been
able to get hold of, or if they are the same figures—as for example
in the discrimination factor—they are on a firmer basis than previously.
Representative Price. Mr. Ramey.
Mr. Ramey. In Dr. Langham’s statement he is talking about the
estimates made in 1959 by our panel and he noted that there was some
discrepancy between then and now, that they were alittle optimistic
or pessimistic. They indicated that there would be a greater deposition of strontium 90.
Hesaid that this discrepancy is readily explained. The 1959 predictions were based on the assumption that strontium 90 in the diet
at that time was totally dependent on the integral surface deposition
level. This assumption led to overprediction of the 70-year doses
by approximately factorof 2.
Do yourfigures bearthat out?
Dr. Comar. Yes: I think they do. There is general acceptance
now—and I think Dr. Langham has taken this into account—that
certainly in the early phases a considerable amount of the activity in
the milk and in thetotal diet got there by the rate dependent. process.
I think that is pretty firm. We didn’t have good values on that 2 or
3 years ago.
Representative Price. Will you proceed, Doctor?
Dr. Comar. [ would like to say a word now about cesium 137.
Cesium 137, much like Sr®°, can enter plants both from surface contamination, a rate-dependent, process, and fromthe soil, a cumulativedependent, process. Absorption of cesium 137 from soil, however, 1s
inefficient, it being estimated that soil absorption of Cs? is only onetenth to one twenty-fifth that of Sr°°.
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