DIETARY INTAKE OF RADIONUCLIDES
891
mating "Sr dietary levels of representative samples of the population.
It may be necessary to derive adjusted values for certain population
groups that differ in consumption characteristics from the average
levels, but such adjustment factors could be experimentally determined to provide estimating capabilities for most ofthe population.
Other results of the study indicated no Statistically significant
differences of OR yrine/giere LevelS among individuals or within the same
individuals over the time period of the study. This would indicate a
capability for bulking samples among individuals over a given time
span to obtain estimates of dietary “Sr levels. This procedure has
already been used to estimate dietary Sr levels in Poland!® during a
five-month period in 1962. Urinary samples were collected at random
from persons undergoing periodic medical examinations, Diet estimates were based on the preliminary ORyine/gier Values obtained in the
work of Comar and Georgi'* and Shulert.'? Diet levels of 20 to 30 pc
%Sr per gram of calcium were estimated on this basis, whereas ob-
served dietary levels in surrounding countries were closer to a range
of 10 to 20 pe “Sr per gram of calcium during that period. Use of
more recently derived ORgine/aiee values from this study and those of
Samachson!® would have placed the estimate within a range of 14 to
17 pe Sr per gram of calcium.
Analyses of the urinary subSamples revealed that statistically
Significant differences were observed between the ORurine/dier Of first
morning urine specimens and total daily specimens (first morning
averaged 1.62, compared to 1.13 for the daily average). This indicates
that urinary samples should be representative of the total day’s excretion for more accurate estimations of dietary Sr levels.
Another study has been conducted to determine the feasibility of
using the urinary '"Cs/"Sr ratio as an effective estimator of “Sr
levels. The ease of measuring a gamma emitter such as }"Cs in
comparison to the time-consuming radiochemical procedures required
for Sr makesthis approach mostattractive. The experiment was set
up so that 24 young rats received radiocesium and radiostrontium in
the drinking water for a period of 67 days. After this period the rats
were
changed to
nonradioactive
water. Urinary
collections
were
maintained throughout both phases, During the first 20 days, the
urinary cesium/strontium ratio climbed rapidly to an equilibration
ratio that was then maintained until the shift to nonradioactive water
was made at 67 days (see Fig, 10). After the shift to nonradioactive
water, the urinary cesium/strontium ratio climbed rapidly for four
days to a value three times greater than the equilibrium value. It then
began a steep decline that persisted during the next 45 days of observation, Interpreting these results for the human population indi-
cates the possibility of using the '*’Cs content of the urine as an
estimator of “Sr during periods of rather stable environmentallevels