These three groups were grazed 176, 433, and 637 days, respectively. Cow
number 2 was grazed in the inner compound within the inner fence enclosing the
area around ground zero (Figure 4).
The remaining six cattle were grazed in
the outer compound between the inner and outer fences, except for one week in
May, 1974, when they inadvertently grazed the inner compound area. The data
for cow 2 are plotted separately from the other cattle data to compare tissue
concentrations resulting from grazing the two compounds.
The weighted
average 733py concentration in surface soil in the inner and outer compounds
is roughly 0.55 and 0.07 nCi/g dry, respectively. The weighted averages for
the vegetation are roughly 0.06 and 0.009 nCi/g dry, respectively. The data
identified by footnote symbols d and e in Figure 3 refer to groups {3, 8} and
symbol e refers to group {l1, 4, 6}. Data for group {3, 8} were used when data
for {1, 4, 6} were not available. Concentrations for cow 5 (grazed 637 aays)
are not shown in Figure 3 but are larger than for group {1, 4, 6} (grazed 433
days) by a factor of 3 for kidney, 1.1 for muscle, 1.1 for lymph node, and 1.3
for femur.
Comparisons Between Soil, Vegetation, Small Vertebrates,and Beef Cattle
It is clear from Figure 3 that average soil and vegetation 239Pu concentrations
decrease with distance from ground zero (GZ)
(this is shown more forcefully,
perhaps, by the 3-dimensional plot of the soil data in Figure 15 of Gilbert
et al., 1975). The vegetation samples were taken in close proximity of the
soil samples (usually within 5 to 10 feet).
The relationship between Pu
concentrations in surface (0-5 ecm) soil and vegetation is summarized and
discussed inRomney et al. (1975, 1976) by the computation of average vegetation,
x, to soil, y, concentration ratios computed as x/y.
They note that these
average ratios tend to decrease with increasing soil concentrations in surface
soil, due presumably to a differential particle size distribution occurring
within the fallout pattern of Area 13.
Gilbert et al.
(1975, Figures 29-32)
have plotted the vegetation-soil data pairs for selected strata to illustrate
the poor correlations often observed between vegetation and soil even when
collected at adjacent locations.
Concerning the relationship between concentrations in soil and small vertebrates,
Bradley and Moor (1975) point out the lack of an obvious correlation (based on
limited data) between 739Pu concentrations in pelt, GI tract, and carcass with
increasing concentrations in soil. They suggest that the mobility of rodents
results in exposure to a wide range of Pu concentrations in soil due to normal
traversing of several activity strata.
Indeed, from the amount of variability
encountered in soil concentrations even within each stratum (indicated by the
ranges for soil plotted in Figure 3), it is not surprising to see large variation
in rodent pelt and tissue concentrations.
Also, the rodent data given in
Figure 3 apply to rodents whose centers of activity fall in strata 1 through 4
(Figure 4).
The analysis of tissues from animals whose centers of activity
are nearer ground zero (strata 5 and 6) would be helpful in understanding the
relation between soil and rodent concentrations.
*Each stratum average concentration was weighted by the approximate propor-
tional area of the stratum within the compound.
244