778
MARTIN
If the concentration of N; on pasture plants is not known, estimates
of doses to human tissue can be based on concentrations in milk (M, =
pe N,;/ml). If the time of fallout is known and M, is given for a specified time of milking, Eq. 9 can be simplified, as shown in Eq. 12, to
obtain an integration constant, I), that can then be substituted for the
expression P,K,f,, in Eqs. 10 and 11 to obtain estimates of concentrations in, H,, and doses to, D,, the humantissue or organ of reference:
Appt — ed mt
M, = 1,———_——
(12)
Am — Ap
James*® recently used a similar method to estimate human thyroid
doses resulting from a single fallout event, but many of his parameter
values (i.e., f, = 0.25, K,= 1.0 x 10, T, = 5.0 days, and T,, = 1.9 days)
were not as pessimistic as those given in Table 5. James concluded
from his investigation that a maximum concentration of 2800 pc of '34]
per liter of milk resulting from a single fallout event would, if a milk
consumption of 1 liter/day were assumed, result in a total dose of 0.5
rad to a 2.0-g thyroid. Our results (Table 6) indicate that a maximum
concentration of only 1850 pc of !°4I per liter of milk would be required
for a potential dose of 0.5 rem to a 2.0-g humanthyroid. (N.B. In this
case 1 rem = 1 rad x RBE, and RBE = 1.0; therefore 1 rem = 1 rad.)
Pendelton et al.*” based their estimates of thyroid doses on esti-
mates of total ‘I intake, I,, by people consuming 1 liter of milk per
day in various parts of Utah during the summer of 1962. According to
our hypothesis, the value of I, would be given by
(13)
I, = IpV,,
’
where I, is an integration constant obtained from.Eq, 12 and V,, is the
volume of milk in milliliters consumed per person per day.
With the use of I, from Eq. 13, the total thyroid dose would be
given, where W, is the thyroid weight (fresh) in grams, by
_ I, K, fh
Di= ALWy,
(14)
The Radiation Protection Guides (RPG’s) recommended by the
Federal Radiation Council (FRC)* are said to represent “...a rea-
sonable balance between biological risk and benefit to be derived from
useful applications of radiation and atomic energy.” The RPG’s for
human bone and thyroid are based on average rates of radiostrontium
and radioiodine intakes which, in the opinion of the FRC, should result
in doses no greater than 1.5 rem/year to “... individuals in the gen-