UPTAKE OF RADIOACTIVE NUCLIDES
LL
m
of the strontiu
ren the percentages
90 to calcium in
atio of strontium
ure; in contrast,
-y of this proced
ntium
for about 3.5 years or for a short period; the quantities of strontium 90
displaced from different soils decreased with time, by 1.2 to 3.4 per cent.
Morgan (60) concluded that strontium 90 which had been accumulated in
soil from world-wide fallout over several years did not differ appreciably
in availability from that of recently added strontium 89.
These results provide convincing evidence that the conversion of
strontium 90 into sparingly soluble formsis unlikely to reduce its availability
to plants to a significant extent over a period of several years. Some small
“fixation” may occur but its magnitude is unlikely to be sufficiently great
to modify appreciably the rate at which strontium 90 passes through food
chains. Suggestions that strontium 90 may, to a large extent, be held in
ratios of stro
ecur between the
th 1 N ammonium
extracts made wi
traction with am
ex
16) found that
in an extens*
asis for comparison
preciable
actant removed ap
this extr
from
rfaces as well
-alcium from su
;
90
m
iu
nt
ro
st
of
ble as the ratio
50!
of that in the
bout 80 per cent
’
forms which are inaccessible to plants appear to rest on inadequate data.
Thus, for example, it has been suggested that the strontium 90 displaced
arth eee nag att
om
of strontium 90 fr
n the absorption
s,
ion
uct
red
e
bl
ecia
tigations (2). Appr
owH
m.
1
iu
lc
ca
i
in
w
3. occur in soi1 ls jo
uen
m the addition ne
evels of calciu
.
an
soil solution
sf calcium in the
from soil by relatively mild extraction procedures was alone available to
plants because the amount of strontium 90 absorbed by plants from different
soils was more closely correlated to this fraction than to the total strontium
90 in the soil (61). The findings of Schulz e¢ al. (62) show the danger of
characterizing the strontium 90 in soils into available and unavailable frac-
Fredriksson @ a
ore not depressed.
when 50 per cent 0
if little importance
have
with calcium.
soil is saturated
ave
y
ll
ntent usua
n their calcium co
tions on the basis of such treatments. These workers investigated 26
California soils to which radioactive strontium had been added. More than
30 per cent frequently remained in the soils after a single extraction with
1 N ammonium acetate but, with repeated extraction, progressively more
was removed and the results were in close agreement with a theoretical
extraction curve based on Vanslow’s exchange equation; thus it appeared
that essentially all the radioactive strontium was retained in exchangeable
or water soluble forms. The assumption that the availability of strontium 90
t us
m and calcium;
of both strontiu
ver
we
ho
,
are
e
Ther
is little changed.
m
ro
r
cu
oc
n
ca
m
ntiu
ysorption of stro
on
nic matter has
when much orga
of the two font an
ion
but
rrasting distri
ae
ions where stron
Under field condit
tm
ea
tr
al
ri
, manu
upper soil layers
has been reduced solely because less may be absorbed as the growing season
advances (63) rests on a still more tenuousbasis.
In practice the most important factor whichis likely to cause change with
time in the entry of strontium 90 into plants is its penetration down thesoil
profile. This is a slow process. In undisturbed soil 50 or more per cent of
ly affect uptake.
be
90 to plants may
lity of strontium
nee
ived much
» soil has also rece
e
l increase we n
wil
nt
te
ex
rly so, its
ue
ic
wh
in
s
nt
me
-e saturated. Experi
“
ars thus PO
ye
l
era
sev
for
ed
di
at
h
tent to whic
38) compared the ex
which had been
the strontium 90
e
treatment with c
d
‘ed by prolonge
proce
E
rooted crops such as ryegrass by a factor approaching 3 (50).
In the United Kingdom and in Sweden, field experiments have been
IEM AOE PT
carried out to provide quantitative information on the contamination of
crops (49, 50, 64). In the United Kingdom strontium 89 was sprayed onto
the surface of the soil which was then cultivated to varying depths. In this
way the distribution in the soil expected shortly after deposition could be
simulated as well as that which would occur after cultivation for many
years. The results of experiments carried out at sites in different parts of
England and Wales, which span the range of calcium content commonly
found in agricultural land, led to the conclusion that the presence of 1 mc
wy
TS Ee
% ,
Caetanivipeti
extraction
(59) used similar
tributed through 15 to 25 cm of soil may lower the absorption of shallow
«BRR cab RRS
d be displa
ich strontium coul
per cent during ns
10
at soils by 3 to
" we
tent of fixation
‘restimate the ex
‘| ‘
e
th
ut
ho
throug
ained equilibrium
py
e
id
ov
pr
r,
ve
howe
e of fixation was,
t
en
es
pr
the added strontium may be in the upper 5 cm several years after its deposi-
tion on the soil surface. Cultivation treatment which causes it to be dis-
cal
ai eienbrat
ie he
ium 90 from a ser
m 89 and stront
.
ter
lat
e
th
d
an
week
present for one
ca
ced by
TE
285
on parallel batches of soil in which strontium 90 had been present either
eg am
rr meme sor meeconte
gts aren eee
ath
iotawere
pe ay