Table 2—STRONTIUM-90 IN SOIL, GRASS, AND SHEEP BONE
Soil (HCl extraction)
Station
pH
Al
A2
A3
B
Cc
4.3
4.5
4.9
5.4
6.2
0.14
0.17
1.1
1.8
2.7
D
5.6
5.8
E
F
3.6
7.5
0.37
4.7
G
H
6.8
6.0
I
6.6
J
7.1
K
8.0
Grass
gCa/kg puc/m? puc/gCa
Bone
pyc/m?> puc/kg puc/gCa
uyc/g Ca
4900
5706
9600
6600
3300
800
760
130
59
14
60
90
15
145
2550
2500
230
1000
2100
1400
116
123
160
10000
28
50
2100
125
53
5000
2900
220
5.2
64
20
790
450
625
64
71
13
14.6
1.6
3400
2600
2.6
19
15
a 24
250
150
41
68
3.0
2500
8.0
39
1900
0.66
156
2200
0.15
b1.3
68
48
a 24
b 2,3
alé
100
89
100
33
26
32
b 2,5
a 27
b 4.8
72
190
210
26
33
28
41
24
8.7
This agreement shows that Sr*® remains substantially in the top soil and available to HCl
extraction for periods of the order of years. This lack of penetration has previously been re-
ported from the U.S. (Libby, 1956), and is shown also in the results from the 4 to 8 in. and 8 to
12 in. horizons from stations H to K, given in Appendix 1 and previously reported (Bookeretal.,
1957).
The soil results are also expressed as the specific activity of Sr*° with respect to Ca (S.U.)
in the extractant. The S.U. content of the soil is a function of the extractant used as well as the
soil, especially for calcareous soils. On acid soils different methods of extraction appear to
give approximately the same S.U. results (Fig. 3 and Bryant et al., 1956).
A more serious objection to the S.U. as a unit of Sr*® in soil is that it takes no account of
the vertical distribution of Sr®? which may be very nonuniform even within the top 4 in. This is
shown in the results from the two stations (D and E) where there was a sufficiently discrete
layer of matt between vegetation and soil for a separate sample to be taken. The matt was
found to contain about half the total activity in micromicrocurie per square meter, and the S.U.
ratio in it was 41/ times that of the soil beneath. Equally sharp variation with depth may occur
on other soils.
4.2 Sr® in Grass
The detailed results from the sheep stations are given in Appendix 2.1, and from the other
stations in Appendices 2.2 to 2.6. A summary is given in Table 2, in which the figures quoted
for stations A3 and H to K are the averages of the results on the sequential samples taken between May and September, 1956. At Stations H to K samples of accumulated growth and of new
growth were taken separately, and the results on the two types are given in the rows labelled
(a) and (b) respectively for each station.
The results are expressed in activity per square meter of ground, per kilogram dry weight
and per gram Ca in the vegetation. The Sr*° in micromicrocurie per square meter in vegetation
may be compared with the corresponding figure for soil in the fourth column of Table 2, and the
vegetation activity expressed as a percentage of that in the soil. This percentage varies from
2.2 at station B to 0.05 at station H (new growth).
The Sr*° expressed in micromicrocurie per square meter in the new growth samples at
stations H to K was only about one-sixth of that in the nearby samples of accumulated growth.
This was largely due to the difference in the weight of vegetation. Per unit dry weight the ac-
cumulated growth had 17 per cent more Sr®® than the new growth and per gram calcium 28 per
cent more. Only the latter difference is significant on a test, and both are much smaller than
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